Winter 2009 - Cooling Technology Institute

Transcription

The CTI Journal
(ISSN: 0273-3250)
PUBLISHED SEMI-ANNUALLY
Copyright 2009 by The Cooling
Technology Institute, PO Box 73383,
Houston, TX 77273. Periodicals
postage paid at FORT WORTH, Texas.
MISSION STATEMENT
It is CTI’s objective to: 1) Maintain and
expand a broad base membership of
individuals and organizations
interested in Evaporative Heat
Transfer Systems (EHTS), 2) Identify
and address emerging and evolving
issues concerning EHTS, 3) Encourage and support educational
programs in various formats to
enhance the capabilities and
competence of the industry to realize
the maximum benefit of EHTS, 4)
Encourge and support cooperative
research to improve EHTS Technology
and efficiency for the long-term
benefit of the environment, 5) Assure
acceptable minimum quality levels
and performance of EHTS and their
components by establishing standard
specifications, guidelines, and
certification programs, 6) Establish
standard testing and performance
analysis systems and prcedures for
EHTS, 7) Communicate with and
influence governmental entities
regarding the environmentally
responsible technologies, benefits,
and issues associated with EHTS, and
8) Encourage and support forums and
methods for exchanging technical
information on EHTS.
Contents
Feature Articles
8
14
34
58
64
70
LETTERS/MANUSCRIPTS
Letters to the editor and manuscripts
for publication should be sent to: The
Cooling Technology Institute, PO Box
73383, Houston, TX 77273.
SUBSCRIPTIONS
The CTI Journal is published in
January and June. Complimentary
subscriptions mailed to individuals in
the USA. Library subscriptions $45/yr.
Subscriptions mailed to individuals
outside the USA are $45/yr.
CHANGE OF ADDRESS
Request must be received at
subscription office eight weeks before
effective date. Send both old and new
addresses for the change. You may
fax your change to 281.537.1721 or
email: [email protected].
PUBLICATION DISCLAIMER
CTI has compiled this publication
with care, but CTI has not Investigated, and CTI expressly disclaims
any duty to investigate, any product,
service process, procedure, design,
or the like that may be described
herein. The appearance of any
technical data, editorial material, or
advertisement in this publication
does not constitute endorsement,
warranty, or guarantee by CTI of any
product, service process, procedure,
design, or the like. CTI does not
warranty that the information in this
publication is free of errors, and CTI
does not necessarily agree with any
statement or opinion in this
publication. The entire risk of the use
of any information in this publication
is assumed by the user. Copyright
2009
by Journal,
the CTI Journal.
rights
CTI
Vol. 30,AllNo.
1
reserved.
Investigation on Fan Noise Generation and its Reduction
Carlo Gallina
A New Method to Measure Viable Legionella and Total
Heterotrophic Aeriobic Bacteria
WIilliam F. McCoy, Erin L. Downes, Teresa M. Lasko, Michael
J. Neville, Melissa F. Cains
Crossflow Cooling Tower Performance Calculations
Robert Fulkerson
A Simplified Method to Evaluate Cooling Tower and Condenser Performance Using the CTI Toolkit©
Natasha Peterson & Dr. Luc De Backer
Intermittent Feeding of Aseptrol® Tablets Redefines the
Role of Chlorine Dioxide in Small and Mid-sized Cooling
Water Systems
Keith Hirsch, John Byrne, Barry Speronello
Construction Productivity Guidelines for Field Erected
Cooling Towers
Jess Seawell, P.E., Jim Baker
Special Sections
80
82
94
CTI Licensed Testing Agencies
CTI Certified Cooling Towers
CTI ToolKit
Departments
02
04
06
06
see.......page 8
Meeting Calendar
View From the Tower
Editor’s Corner
Press Release
see.......page 58
see.......page 14
1
CTI Journal
The Official Publication of The Cooling Technology Institute
Vol. 30 No.1
Winter 2009
FUTURE MEETING DATES
Journal Committee
Paul Lindahl, Editor-in-Chief
Art Brunn, Sr. Editor
Virginia Manser, Managing Editor/Adv. Manager
Donna Jones, Administrative Assistant
Graphics by Sarita Graphics
Board of Directors
Dennis P. Shea, President
Jess Seawell, Vice President
Mark Shaw, Secretary
Randy White, Treasurer
Gary Geiger, Director
Robert (Bob) Giammaruti, Director
Richard (Rich) Harrison, Director
Chris Lazenby, Director
Frank Michell, Director
Ken Mortensen, Director
Address all communications to:
Virginia A. Manser, CTI Administrator
Cooling Technology Institute
PO Box 73383
Houston, Texas 77273
281.583.4087
281.537.1721 (Fax)
Committee
Workshop
Annual
Conference
July 12-15, 2009
Marriott Colorado Springs
5580 Tech Center Drive
Colorado Springs, CO 80919
Web: http://www.marriott.com
Phone: 719.268.4201
Fax: 719.260.6911
February 8-12, 2009
Westin Riverwalk Hotel
420 West Market Street
San Antonio, Texas 78205
Web: http://www.westin.com
Phone: 210.224.6500
Fax: 210.444.6000
July 11-15, 2010
Marriott Albuquerque Pyramid North
5151 San Francisco Road NE
Albuquerque, NM 87109
Web: http://www.marriott.com
Phone: 505.821.333
Fax: 505.822.8115
February 7-11, 2010
The Westin Galleria
5060 West Alabama
Houston, TX 77056
Web: http://www.westin.com
Phone: 713.960.8100
Fax: 713.960.6553
Internet Address: http://www.cti.org
E-mail: [email protected]
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BOX 1240 • OPELOUSAS, LA 70571-1240
800-326-4050 • 337-948-3067 • 337-948-3069 (FAX)
2
Member
CTI Journal, Vol. 30, No. 1
3
View From The Tower
The events of 2008 are now history. A major hurricane
caused severe damage and destruction along the Texas
on Gulf Coast. A worldwide economic melt down
erupted and caused major financial challenges for all
industries. The United States of America elected new
President. The future is always uncertain, however, I
believe the best approach to these worries and troubles
are in the basic management principles of Steven Covey.
“Work at those things that are within your sphere of
influence and don’t worry about those things that are
outside of our control.”
bers, for replacement of wood structural members, a
vibration standard for fans and gearboxes, a drift standard and several others. The Technical Committees
are using e-mail, teleconference and just plain individual effort to get the work done.
It is now time to look to 2009. Next year promises to
be a time of great challenge, for all industries. I look
forward to tackling these challenges with everyone.
I owe a great debt to all committee chairpersons for
their time and effort put forth in 2008 to keep CTI
moving forward. I especially want to thank the out
going Board of Directors – Mark Shaw, Rich Harrison
and Bob Giammaruti. These individuals served faithfully the past
three (3) years. All three of these Board Members sacrificed additional time over and above time they spent on technical and CTI
committees. We could not keep this organization moving forward
without your knowledge, energy and support.
Denny Shea
President
In 2008, CTI followed these principles by moving forward with the
continuous improvement of the cooling industry. We reviewed
reworked and reissued old standards and guidelines. CTI is working closely with other technical organizations in US and Europe
towards cooling tower certification across the world. We are building a new ANSI standard for “Legionellosis Related Practices for
Evaporative Cooling Water Systems.” The new standard will become a pattern for design, maintenance and treatment of cooling
towers to prevent Legionellosis from cooling towers. We continue to strive and develop new standards. Currently the technical
committees are working on standards for use of fiberglass mem-
With the distribution of the CTI News and complete information for
the CTI website, registration can begin for our Winter Technical
Meeting. The program committee has 22 excellent papers, an informative panel discussion and education program. The owner/operators will meet to discuss common problems and some educational
presentations targeted for owner/operators specifically. As always, we expect a lively “Ask the Expert”
question and answer session. We have also scheduled technical committee meeting times throughout
the conference. We are expecting a large turnout in
San Antonio. If you are struggling to justify the
expense, I guarantee that the ideas, educational opportunities and contacts that are available more than
justifies the cost of our conference including travel
expenses. I have always found one implementable
cost saving idea at every conference I have ever
attended. See you in San Antonio.
As always, I will be at conference attending papers,
panel discussions, committee meetings. I invite old
and new members to catch me at anytime. I welcome
your input on conferences and CTI in general to
serve you more effectively as your president.
Denny Shea
4
5
Editor’s Corner
The last few months have been “interesting
times”, to draw on an old Chinese curse – May
you live in interesting times. Some of us remember various periods when the economics
have been challenging, and some of our parents lived through the early ‘30s when it was
much worse. It is hard to know where our
current situation will lead, but it has always
been true that having confidence that we will
see our way through these times is one of the
keys to the solution.
behind it, but the food pantries in the entire metropolitan area have been completely overwhelmed
in the last month. Now is the best time to support
the agencies like food pantries that are trying to
cope with a suddenly difficult situation.
Paul Lindahl
Sadly, tough economic times also lead to cutting
corners and unfortunate behavior by some individuals and businesses to improve their own lot.
History also shows that as times get better, people
do remember those who took advantage of them
when things were difficult.
Editor-In-Chief
I was taught while growing up that if you keep
It is hard to judge when the current situation will
doing the best you can at your job even when
turn around, but it will sooner or later turn around. How we
it is difficult, good things will come of it over time. This is behave during these times is a measure of our worth as indione of those times that things have become difficult for viduals and as a group.
many. It is important for all of us to keep in mind that
Something to think about.
many are working very hard to get by and to have patience for short tempers and pre-occupation in those whose
lives we touch.
Respectfully,
It is also a time when some are not getting by. The temptation to cut back in charitable giving when economics are Paul Lindahl
tough is very real, but the need is becoming greater to
help others as much as you can. The area where my CTI Journal Editor
company’s office is located has much economic strength
Press Release
Contact: Chairman, CTI Multi-Agency
Testing Committee
Houston, Texas
1-January-2009
The Cooling Technology Institute announces its
annual invitation for interested thermal testing
agencies to apply for potential Licensing as CTI
Thermal Testing Agencies. CTI provides an independent third party thermal testing program to
service the industry. Interested agencies are required to declare their interest by March 2, 2009,
at the CTI address listed.
6
7
Investigation on Fan Noise Generation
and its Reduction
Carlo Gallina
COFIMCO Srl, Via Gramsci
62, Pombia, ITALY
SUMMARY
Simply speaking, noise generated by
fans takes place because of turbulence generated by blades rotation.
Being the noise generated is by fans
strictly connected to the airflow turbulence around the blades, it is imCarlo Gallina
portant to understand, mainly experimentally, how the blade shape affects the amount of turbulence
produced and, consequently, the noise. Scope of the present work
is first to make a little survey of the theoretical sources of noise
generated by fans, and second to show some results in terms of
experimental tests.
FAN NOISE GENERATION
Human ear noise perception
The human ear noise perception is an elaboration of the sound
pressure generated by vibrations or turbulence. It is therefore not a
physical noise measurement: in fact given a value of pressure level,
the “noise” perceived by the human ear is strongly dependant on
the frequency of the emitted noise.
Also the sensibility to noise changes from person to person.
Statistically speaking it is observed that the sensibility to noise is
higher in the frequency range from 2 to 5 kHz. A solution to noise
reduction to be really effective has to work mainly in this frequency
range.
Why fan generates noise
Cofimco axial fans are used in those application where a high flow
rate is required like heat exchangers to cool a fluid (water or oil) or
steam; the typical heat exchangers are Process Air Cooler, Air Cooled
Condenser, Cooling Tower.
Figure 1 : airflow around a blade section
The flowlines are generated by smoke pulses, and the pulses were
released all at the same time. From this picture it is possible to
observe that the speed of the air on the top of the airfoil is higher
than the speed to the bottom. In fact the distance between the
smoke spots is higher on the top of the airfoil.
The difference in speed from top to bottom results, according to
Bernoulli principle, in different static pressure from top to bottom
and consequently in an aerodynamic force having a big component in the transverse to flow direction. The result of this flow
behavior around a profile is also the shearing of the two layers of
air at the trailing edge, and hence a vortex. This vortex is a direct
unavoidable consequence of the lift generation. This mechanism is
shown also in the Figure 2.
We can therefore say that axial fans produce noise because they
produce an aerodynamic axial load.
The vortex generated to produce lift is not the only responsible of
noise produced by fans.
The aim of a fan is to generate an airflow through the obstacles
present in the heat exchangers, i.e. fin tubes, grids, and so on. In
order to win the resistance given by the obstacles the fan has to
produce a static pressure, and that means, from an aerodynamic
point of view, that a lift has to be produced, exactly like the airplane
wing. In the same way of the wings, the blades of axial fans produce
vortexes as well, which is a necessary condition to have a lift in air.
Looking a little bit more in detail at the airflow around a blade section, it appears like in the following picture:
Figure 2 : flow behavior and pressure
distribution around a profile
8
9
Where is noise mainly generated
How to reduce noise – general considerations
Noise is created because of turbulence, and turbulence is created
when:
From the noise calculation formula, it appears that given a fan diameter and given the assigned values of required flow rate and static
pressure (which are design data for the selection of an axial fan),
the noise can be reduced by reducing the tip speed. Lower tip
speed can be obtained, giving the same performance, by using a
blade of bigger dimensions.
1)
There are two layers of air sliding one over the other at
different velocities (trailing edge).
2) There are two solid surfaces “sliding” one close to the
other (blade tip to fan ring).
3) The airflow has to pass through some obstacles like grids
or air fins.
4) The airflow on a blade is disturbed by the trail of another
blade.
The various sources of turbulence affect the frequency of the generated noise.
For example noise generated at the blade tip is typically a high
frequency noise, because of the high difference in speed between
the tip of the blade and the fan ring (up to 60 m/s) and the low
distance between blade tip and fan ring (typically from 0,0025% to
0,005% of the fan diameter).
This approach is the most immediate to be used, but has the drawback of producing blades of higher cost and weight, and therefore
it is not always the preferred solution. For a same duty point, the
noise reduction with this approach ranges from 5 dB(A) up to 10
dB(A).
The fan performance can be obtained even by changing the pitch
angle, and therefore a possible solution is to increase the pitch
setting and reducing the fan rpm. This system works, even if the
fan efficiency is lower because of the high pitch setting required.
This solution enables a general PWL reduction of 1-2 dB(A).
Once the regions where noise is generated are identified it is possible to think about possible solutions to reduce the noise level.
According to the fan laws the PWL generated by fans can be expressed by the following formula:
PWL = const + 10 ⋅ log( Ps ⋅ V ⋅ ρ ) + 30 ⋅ log(VTip ) − 5 ⋅ log(φ )
(1)
From this expression it appears that the higher is the power generated by the fan, the higher is the noise, the higher is the tip speed,
the higher is the noise, the bigger is the fan diameter, the lower is
the noise. The value of the constant is dependant on the blade
shape and profile.
Here is represented a typical noise spectrum generated by an axial
fan (SPL measured at 1 m below the fan); fan diameter was 10 ft and
the rotational speed was 230 rpm.
Figure 4 : SPL comparison for a with
standard or enlarged tip gap
How to reduce noise generated by tip vortex
Blade tip vortex are generated because of the pressure difference
from blade pressure side to suction side. These tip vortex reduces
the fan efficiency and generate noise. An efficient and quick way to
face with this problem is the use of the special tip cap, where a
deflector contrast the swirl generation. This solution enables a
general PWL reduction of 1-2 dB(A).
How to reduce noise generated at the blade tip –
fan ring
Figure 3: Typical fan noise spectrum (A weighted)
The reported SPL values are already A-weighted. Even if the highest values are present at low frequency, not negligible values are
present in the range 2-5 kHz, where the human ear is more sensible.
It can be stated in advance that the highest frequencies are due to
small structured vortex, and these vortex are generated mainly at
the blade tip because of the low distance between blade tip and fan
ring.
10
Noise generated because of the “sliding” of the blade tip against
the fan ring can be reduced only increasing the gap between the
blades and the fan ring. The “noise quality” coming from an increase of the tip gap changes significantly, as it’s frequency content is different, being the higher frequencies in the noise spectrum
removed.
The following picture shows the result of the tip gap increase on a
10 ft fan. The gap has been doubled, from the original 15 mm up to
30 mm; as result of this modification the SPL is slightly reduced (75
dB(A) vs 75,6 dB(A)), but the real quality of the noise is very
different, as it has been observed a reduction of the component at
4000 Hz of 0,7 dB(A) and at 8000 Hz of 2,1 dB(A). As previously
mentioned the highest frequencies of the perceivable noise are the
most irritating.
11
An increase in the tip clearance has however the drawback of reducing the fan efficiency, and therefore this solution is rarely adopted.
Sometimes the blade is made shorter and just a “sealing” is left at
the tip of the blade, i.e. the removed part of blade at the tip is
substituted by means of a flat foil. The result of this solution is not
satisfactory, as a flat foil hasn’t the same performance of the removed piece of blade.
How to reduce noise generated by leading and
trailing edge
An important - and not immediate to understand - effect on the
noise generated by fans is given by the shape of the leading and
trailing edge. In fact it can be observed that a curvature in the
rotation direction of the blade leading and trailing edge results in a
noise reduction. The apparent reason of this result seems to be due
to the generation of vortex in counter-phase because of the spatial
shift given by the trailing edge shape, i.e. the vortex created on a
given point is cancelled by the vortex created on another point, as
sketched in the following picture.
Figure 7: Cofimco CX
An example of the noise characteristics of this type of blade for a
three blade 14 ft fan are summarised in the following graphs, where
it can be observed that the PWL is sensibly lower than the standard blade profile.
Figure 5: principle of vortex cancellation
How new fans introduce the above mentioned
concepts – Cofimco CX, 60F and 50F
Based on the noise reduction considerations discussed till now,
Cofimco has developed a range of low noise profiles, some based
on the standard and well known Cofimco technology and some
based on new concepts of production.
It is therefore possible to find low noise profiles like the 60F and
50F, whose main strength is the big chord dimension (1700 mm for
the 60F and 1300 mm for the 50F) enabling big lifting surfaces and
hence low rpm, or it is possible to find ultra low noise profile like the
Cofimco CX whose blade shape and big surface join two of the
most important points in the noise reduction, the blade surface and
the curvature of the leading and trailing edge in the rotation direction.
Figure 8: PWL of CX fans at 14° pitch angle and 158,5 rpm at
different flow rate values
Figure 6: low noise profiles 60F
12
Conclusions
The theoretical and practical analysis of fan noise generation leads to the conclusion that the most important
factor in noise generation is the fan speed.
Based on that the main effect in noise reduction is obtained by introducing blades of big lifting surface
(Cofimco 60F and Cofimco 50F). A further evolution of
noise reduction is obtained by studying more deeply the
shape of the leading and trailing edge, as done in the
Cofimco CX.
Figure 9: PWL of CX fans at 14° pitch angle and 197 rpm at
different flow rate values
13
A New Method to Measure Viable
Legionella and Total Heterotrophic
Aeriobic Bacteria
Benefits of the PVT
WILLIAM F. McCOY, ERIN L. DOWNES,
TERESA M. LASKO, MICHAEL J. NEVILLE,
MELISSA F. CAIN
PHIGENICS, LLC
Compared to the Standard Methods for total bacteria and
for Legionella, the PVT is:
• More accurate because variations due to changes
in water samples during shipment are entirely elimiABSTRACT
nated
A new field method to measure viable Legionella and
•
Faster because transit time is not wasted and
William F.
total heterotrophic aerobic bacteria was evaluated in the
microcolonies are enumerated directly on the PVT
McCoy
laboratory, in split-sample blinded comparisons and in
field samplers; typical turnaround time from field
actual operating field conditions. The method was proven reliable
sampling to results report is 48 - 72hrs
for determining viable cell concentrations of Legionella
• More convenient because results for total bacteria AND
pneumophila serogroup 1, serogroups 2-14 and Legionella speLegionella bacteria are obtained from the same sample with
cies. Total heterotrophic aerobic bacteria results are obtained from
one protocol and results are archived by the Phigenics Anathe same sample. The new method was shown to be more accurate,
lytical Services Laboratory (PASL) in a standardized format
faster and more convenient compared to standard methods. Comfor future reference
parisons to other methods are given. Guidance is provided for use
of the new method within the context of hazard analysis and control to prevent legionellosis.
THE STANDARD METHOD AND OTHER
METHODS
INTRODUCTION
The Standard Method
The patents pending Phigenics Validation Test® (PVT) is a “dipslide
format” field sampler that has on its surfaces the standard growth
media required for Legionella enumeration. Both viable Legionella
and total heterotrophic aerobic bacteria counts can be obtained
from the same test.
For quantitative enumeration of viable Legionella in water samples,
inoculation onto growth medium, confirmation of growth on the
medium and confirmation of Legionella colonies are required. There
are two critical limitations in the Standard Method:
Laboratory experiments, split sample comparisons and case histories of field use under actual operating conditions were used to
evaluate the PVT.
Features of the PVT
The PVT field sampler consists of a sterile plastic screw-capped
container within which is held a paddle containing on one side
buffered charcoal yeast extract agar enriched with α-ketoglutarate
(BCYEα) and on the other side of the paddle, BCYEα agar plus the
selective supplements glycine, vancomycin, polymyxin B, and cycloheximide (GVPC). Figure 1 shows the PVT field sampler.
The PVT is a field sampling protocol to obtain viable cell concentrations (as CFU/ml) for the
following from the same sample:
- total heterotrophic aerobic bacteria
- Legionella pneumophila (serogroup 1)
- Legionella pneumophila (serogroup 2-14)
- non-pneumophila Legionella species
Data is obtained for the exact moment when the PVT field sampler
contacts the water sample:
- shipment of water samples to the laboratory is not required
- time required to obtain results is reduced 75-80% compared
to the Standard Method for Legionella
14
1.
the method requires transit of water samples to an analytical laboratory and
2. turnaround time for results is very long. Typically, at least 2
days in transit and set-up time is required before the 7-10
day test even begins; significant and unpredictable changes
in the sample often occur in-transit. Even water samples
that are processed a few hours after they have been taken
from the system should be regarded as suspect because
microbial and chemical factors in water samples are highly
dynamic.
All versions of the “Standard Method” relate back to Procedures
for the Recovery of Legionella from the Environment developed
by the Centers for Disease Control and Prevention1. The International Standard Organization (ISO) has published ISO 11731 Water
quality – Detection and Enumeration of Legionella which is generally regarded as the international Standard Method2.
Molecular Methods
Molecular methods include nucleic acid detection (PCR; polymerase
chain reaction or FISH; fluorescence in situ hybridization) and serologic methods by antigen/antibody reactions using immuno-specific assays or with differential fluorescent antibody (DFA) direct
cell counting. Molecular methods are useful for confirmation of
Legionella colonies. For the PVT, an immunospecific method is
used to confirm Legionella colonies on the surface of field samplers. Molecular methods to measure Legionella in water samples
15
are subject to two critical limitations:
1)
inability to differentiate viable from non-viable
Legionella and
2)
not quantitative
For water samples in the field, molecular methods are generally not
used because of these limitations. A field method based on FISH
requires use of epifluorescence microscopy or an expensive slide
scanner and requires a redefinition of “viable” which is inconsistent with how the term is used in the Standard Method.
Even more limited for field use, a recently introduced lateral flow
immuno-specific chromatographic device detects only antigens from
L. pneumophila serogroup1. This limitation is unacceptable because there are many other serogroups and other species of
Legionella which are potentially hazardous and because presence
of any of them indicates conditions in the water system that could
be dangerous. A product sensitive only to L. pneumophila SG1 was
commercially introduced for water analysis during the 1990’s but
was removed from the marketplace because results were regarded
as potentially misleading.
Occasionally, a limit of detection for immuno-specific methods is
given in viability units (e.g., 100 CFU/ml). This is incorrect and
misleading since immuno-specific assays cannot distinguish living
from dead Legionella.
The Phigenics Validation Test (PVT)
The PVT is the only field method available that gives results for
both Legionella and total bacterial counts from the same sample
and without a requirement to ship water samples back to an analytical lab. Limitations of the PVT are:
1.
field samplers must be stored between 40 °F and 75 °F,
protected from freezing and handled with care to avoid
breakage
2. the quantitative limit of detection is 10 CFU/ml
Table 1 provides a comparison of Legionella methods.
THE PVT FIELD PROTOCOL
The field protocol is fast and simple: 1) label 2 PVT samplers, 2)
collect water sample, 3) perform the 1st 3s dip, 4) add vial of pH
adjust, wait 5min, 5) perform the 2nd 3s dip" (s=second), 6) pack
PVT, 7) insert in-transit incubators and 8) ship to the Phigenics
Analytical Services Laboratory. Results and summary reports are
received by email.
Table 2 provides an itemized PVT protocol with instructions. Details of the protocol steps have been published elsewhere3.
COMPARISONS OF THE PVT TO STANDARD
METHODS
Effect of Water Sample Transit Time
To enumerate viable Legionella using the Standard Method, water
samples must be transported to an analytical microbiology laboratory. Unpredictable changes in the microbial and chemical characteristics of water samples often occurs in-transit. This uncertainty
is entirely eliminated if the water sample is processed in the field
immediately after sampling.
Water sample transit time can ruin the sample. For instance in one
published example, potable water samples had dangerously high
counts of coliform indicator bacteria on the day the samples were
16
taken (Day 1); however, after 24h storage at 5 °C and 22 °C the
levels of viable indicator organisms had declined as a result of
holding time to such an extent that these same samples met the safe
drinking water standard. Therefore, analytical results were dangerously misleading when samples were not processed immediately.
This was true even when the samples were stored cold. In those
same water samples, total heterotrophic plate counts increased 0.5
and 2.5 orders of magnitude after 30h and 48h, respectively4.
In a publication from the World Health Organization5, the history
and use of the heterotrophic plate count for water analysis is described. Early in the 20th century it was observed that there “is first
a slight reduction in the number present, lasting perhaps for six
hours, followed by the great increase noted by earlier observers. It
is probable that there is a constant increase of the typical water
bacilli, overbalanced at first by a reduction in other forms, for which
this is an unsuitable environment.” These early observations made
it obvious that samples must be examined shortly after collection.
Even in 1904, the recommendation was that the interval between
sampling and examination should not exceed 12 hours for relatively
pure water, not more than 6 hour in the case of relatively impure
water and less than 1 hour for sewage samples (see WHO, Chapter
3, pg. 31-32)5.
In a study to compare several methods for enumerating waterborne
Escherichia coli, a well-controlled statistical analysis showed that
if water samples were stored at colder than 10 °C (50 °F), then 38%
(5 of 13 samples), 29% (2 of 7 samples) and 25% (1 of 4 samples)
showed significantly different results during a 48h holding time
period. In the first phase of the study, holding times at 20 °C were
tested; E. coli counts were significantly different in 100% of samples
after 48h. After just 24h holding time at 20 °C (68 °F), half of the
samples were significantly changed. At 35 °C, some of the samples
changed after just 8h. The concentration of E. coli unpredictably
increased in some samples and decreased in others7.
In a study with another waterborne pathogen Vibrio cholerae, the
causative agent for pandemic cholera, the effects of sample holding time were shown to cause the concentration of the pathogen to
significantly increase after 20h holding time; in this study the total
counts did not increase during the 20h sample holding period 8.
Table 3 provides examples of holding time effects on water samples.
The total heterotrophic aerobic bacteria in several types of water
samples were measured on collection day (Day 1) and then again
on Day 2 and Day 3 after storage at ambient room temperature, 22
°C (Table 3).
Results indicate that bacterial counts in the sample changed significantly during the holding time period.
The effect of transit time is even more important with more complex
water samples such as those from cooling towers. The effect of
water sample holding time on Total Heterotrophic Aerobic Bacteria
(THAB) counts is shown in Figure 2. The THAB were measured
immediately after sampling (t=0) in six cooling towers at a University in the Midwestern United States. One hour later (insert graph,
Figure 2), the cooling tower water was reanalyzed; THAB declined
by at least one order of magnitude in 5 of the 6 cooling water
samples and in one of the samples there was a 3 order of magnitude
decline. After 24h holding time at ambient room temperature, THAB
counts had increased much more than one order of magnitude in all
six samples.
17
This problem is even more severe in water samples from systems
that have been treated with antimicrobials. Oxidizing antimicrobials
can be neutralized with sodium thiosulfate to eliminate the negative
effect of a sustained contact time on microorganisms; however,
this may allow the surviving microorganisms to multiply during
transit. Some antimicrobials cannot be easily neutralized and so
they are artificially provided a much longer contact time with microorganisms in the sample during transit; this can cause artificially
low results.
Results from microbiological analyses of water samples sent to an
analytical laboratory for processing could be dangerously misleading because of the unpredictable effects of water transit time.
Split Sample Comparisons of the PVT with
Standard Methods
The PVT is similar to the Standard Method in that the same growth
media and Legionella confirmation steps are used for both. However, the method of sampling is different. For the PVT, the growth
medium is dipped directly into the sample; for the Standard Method,
an aliquot of sample is removed and spread plated onto the surface
of the growth medium. From a hazard analysis perspective, a case
can be made that sampling the water with the least physical manipulation of the sample is to be preferred.
Figure 3 illustrates these two methods and shows side-by-side
comparisons of 4 examples from a1 building water system. Results
are typically very similar but not identical.
Forty-eight water samples were split in order to compare Standard
Method spread plates and PVT analyses from the same University
building water system. Figure 4 shows that most (88%) results were
not significantly different. However, PVT recovered higher counts
in some samples and the spread plate recovered higher counts in
other samples. This illustrates that the two methods are similar but
not identical.
Split Sample Comparisons of PVT with Total
Heterotrophic Aerobic Bacteria Dipslides
Results from split sample analyses with another total heterotrophic
aerobic bacteria dipslide system and with the PVT show that results were very similar over a wide range of concentrations (Figure
5). This shows that PVT field samplers are useful for estimating the
total bacterial count using order-of-magnitude comparator charts.
Precision Analysis Comparisons of the PVT with
the Standard Method
Cell suspensions of pure culture L. pneumophila SG1 (wild type
obtained from the field and confirmed by immuno-specific latex
agglutination) were made by dispersing pure culture biomass into
10ml sterile KCl (0.1M), adjusting turbidity to 35 Formazin Absorption Units (1FAU =1NTU), dilution of 1ml cell suspension into 100ml
of sterile tap water and then further dilutions to produce a range of
concentrations. Five replicate analyses of the cell suspensions by
spread plate standard method were statistically compared to 5 replicate PVT analyses of the same cell suspensions over a wide range
of cell concentrations (Figure 6). Statistical analysis of the data
was with linear regression and with t-tests for sample means with
unequal variances. Results show that the CFU count on PVT
dipslides correlated significantly (R2 = 0.9873) with CFU/ml measurements by the Standard Method. Also shown in Fig. 6 are stan18
dard deviation measurements of analytical and experimental error
(error bars) for both methods; these results indicate that precision
in the two methods is very similar and further confirms the general
reliability of PVT compared to Standard Method spread plating.
Blinded Split Sample Comparisons and
Preliminary Statistical Analysis
Blinded comparisons of 147 samples split for analysis with PVT
and with the Legionella Standard Method were processed by an
independent laboratory with no affiliation to Phigenics, LLC. Water
transit time variations were not a factor in this study because the
lab simultaneously processed both PVT and samples for the Standard Method. Most (81%) Legionella detection results were the
same. In 6 % of samples, PVT detected Legionella but the Standard
Method did not; in 12 % of samples, PVT did not detect Legionella
but the Standard Method did detect it. In 1 % of samples, Legionella
was detected by both methods but different species or different
serogroups of L. pneumophila were recovered. The data are presented in Figure 7.
Preliminary Analysis of Accuracy, Specificity, and Sensitivity.
These analyses should be considered preliminary because 1) the
PVT protocol was being developed and adjusted during the first
part of the study (the first 50 samples), 2) the Legionella confirmation method was not the same for both methods (DFA for the spread
plates and latex agglutination for the PVT) and 3) the selective
supplements used in the assays were different (CAV for spread
plates and GVPC for the PVT). Nevertheless, useful information
about split sample comparisons can be derived even from this preliminary analysis. The following binary analysis for accuracy, specificity and sensitivity was set to “True” means equivalent result to
the Standard Method.
PVT Accuracy. Accuracy is a measure of conformity to an accepted
“true” value given as reference [(True Positives + True Negatives)/
n samples]. In this study, accuracy was 81.6%.
PVT Specificity. Specificity measures the probability that the result is negative given that the reference is negative [True Neg/
(True Neg + False Pos)]. The higher the specificity, the fewer nonhazardous samples will be incorrectly labeled as hazardous. In this
study, specificity was 93%. Hazard analysis and validation methods should be set to minimize the probability of incorrectly identifying a building water sample as potentially hazardous.
PVT Sensitivity. There is always a trade-off between specificity
and sensitivity. The more sensitive one makes the method, the
more false negative results can be expected. Sensitivity measures
the probability that the result is positive given that the reference is
positive [True Pos/[True Pos + False Neg]. For this analysis “positive” was set at >100 CFU/ml since all 147 samples in this data set
were non-potable: Sensitivity was 46%.
It is important to recognize that for the purpose of these preliminary
comparative binary analyses, the Standard Method spread plate
and enumeration results were taken as “true”. However, as has
been discussed, there are distinct differences between spreading
the sample compared to dipping the growth medium into the sample.
A case can be made that the PVT protocol may be the more relevant
(“true”) sampling method for hazard analysis and validation because less physical manipulation of the sample is required.
19
RESULTS OF PVT ANALYSES OF POTABLE
AND UTILITY WATER SYSTEMS
ling them to an extent that prevents harm to people is the goal for
hazard analysis and control.11
The Data Set
Preventing Waterborne Disease Associated
Six hundred and eighty two (682) building water samples were ana- with Building Water Systems
lyzed with the PVT. Sampling was not randomized, no screening
was done and no data were omitted. The buildings were all in the
USA from the following regions: Eastern seaboard States, Southeast, Midwest, South, Southwest, Southern California, Pacific Northwest. Figures 8-11 give results which are discussed as follows.
About 51% of the sample locations were from building potable
water systems and 49% were building utility water systems (mostly
cooling tower water samples).
About two-thirds (67%) of the building potable water samples had
total heterotrophic aerobic bacteria (THAB) counts at or below 103
CFU/ml; 33% of potable water samples had THAB greater than 103
CFU/ml.
About half (51%) of the building utility water samples had THAB at
or below 104 CFU/ml; 49% of utility water samples had THAB greater
than 104 CFU/ml.
About 6% of potable water sample locations and about 10% of
utility water sample locations were positive for Legionella at 10
CFU/ml or greater. There was no direct correlation between
Legionella detections and the THAB results in potable water systems; there were more Legionella detections in utility water systems when the THAB was greater than 104 CFU/ml but no statistical analysis was done to determine the significance of the difference. These data generally confirm that total bacteria counts do
not correlate with Legionella detections. Total bacteria counts
should be used as a water quality indicator not a water safety
indicator5. When total bacteria counts in a building water system
are higher than the incoming water, it means that water quality in
the facility has been allowed to degrade. Poor water quality in building water systems could result in conditions that may become or
may already be hazardous due to pathogenic (disease-causing)
bacteria.
HOW TO USE PVT RESULTS
The PVT is useful for hazard analysis and for validation of hazard
control.
The World Health Organization has set forth guidance that every
facility should have a water safety plan based upon the principles
of hazard analysis and control 6, 9, 10.
In February 2007, the World Health Organization (WHO) published
definitive technical guidance entitled Legionella and the Prevention of Legionellosis (ISBN 92 4 156297 8) 10. This work is organized
around the Risk Management principles of hazard analysis and
control. Every chapter in the book that deals with prevention gives
technical details arranged around these principles. They apply not
only to preventing legionellosis but also, they apply to preventing
harm to people from any hazard. Hazard analysis and control risk
management is necessary in order to prevent legionellosis and other
waterborne diseases.
Validation is evidence (data) obtained under operating conditions
that hazards have been eliminated or controlled to an extent that
prevents harm to people. Eliminating biological hazards or control-
20
Prevention of disease from waterborne hazards requires facility
managers and owners to answer three site-specific questions. 9, 10, 11
• What is the hazard?
• How do we prevent the hazard from harming people?
• How do we know the hazard has been prevented from harming people?
Seven principles comprise effective hazard analysis and control:
1.
Use process flow diagrams of the water system to perform
systematic hazard analysis.
2. Identify critical control points (process steps at which the
hazard can be eliminated or prevented from harming people).
3. Establish hazard control critical limits for at each critical
control point.
4. Establish a hazard control monitoring plan for critical limits
at critical control points.
5. Establish hazard control corrective actions for each critical
limit.
6. Establish procedures to document all activities and results.
7. Establish procedures to confirm that a) the plan actually
works under operating conditions (validation), b) is being
implemented properly (verification) and c) is periodically
reassessed.
In practice, a few preliminary steps are necessary. They are:
• Assemble a cross-functional team including at least one person knowledgeable or trained in hazard analysis and control
(e.g., a trained employee, or other qualified resource).
• Identify the use and users of the water at the facility to
determine at-risk consumers.
• Develop process flow diagrams to describe how the product
is processed in the facility.
• Verify by on-site audit that process flow diagrams are accurate.
A typical outline of tasks necessary for the facility team to develop
hazard analysis and control Risk Management is:
• TASK 1: Use process flow diagrams to perform systematic
hazard analysis of the entire building water system
• TASK 2: Establish validation criteria
• TASK 3: Establish validation and verification schedules and
assign management responsibilities
• TASK 4: Using results from TASK 1-3, establish the hazard
analysis and control plan.
Validation Criteria
Validation is evidence (data) that hazards have been eliminated or
controlled to extent that prevents disease under actual operating
conditions.
There are no US laws, regulations or standards requiring any particular validation criteria for Legionella bacteria or sampling frequency or quantity for monitoring. Validation criteria must be esCTI Journal, Vol. 30, No. 1
21
tablished on a site-by-site basis. The team must consult local regulations and guidelines such as are given by OSHA (www.osha.gov/
dts/osta/otm/legionnaires/sampling.html). The following general
validation criteria guidelines should not be construed to supercede
local or regional guidance. However, based on current guidance
and our experience, the following guidelines are generally recommended by Phigenics, LLC:
Phigenics Validation Criteria Guidelines
For potable water systems, the PVT total bacterial concentration
should be <_1000 CFU/ml and the PVT Legionella bacteria concentration should be less than detectable ( 10
<_ CFU/ml). Sampling frequency should be quarterly. In healthcare facilities, take at least
two representative samples per 100 beds. For hotels and multifamily residences, take at least two representative samples per floor.
For utility water systems, the PVT total bacterial concentration
should be <_10,000 CFU/ml and the PVT Legionella concentration
should be less than detectable ( <_10 CFU/ml). All cooling towers
should be sampled quarterly.
The Rationale for Phigenics, LLC Validation
Criteria
Potable Water Systems
For an extensive review of the heterotrophic plate count method
and use of results, consult Heterotrophic Plate Counts and Drinking-water Safety: The significance of HPCs for Water Quality and
Human Health 9. Total aerobic heterotrophic bacteria are regarded
worldwide as a good water quality indicator but not a reliable water
safety indicator. The National Primary Drinking Water Standards
(NPDWS) is the federal regulation that defines acceptable microbiological quality. Municipalities are required by law to meet these
criteria. The NPDWS criterion for total heterotrophic aerobic bacteria in drinking water is that there should be less than 500 CFU/ml
(note: results from microbiological assays are generally not significant unless differences are greater than one order of magnitude;
thus, <1000 CFU/ml is not significantly different than 500 CFU/ml).
The NPDWS expectation from primary water treatment and disinfection is that there should be no detectable viable Legionella in
drinking water. That is to say, if drinking water primary treatment is
done properly, there should be less than detectable Legionella
contained in it. Phigenics agrees with those technical experts who
state that microbiological quality in building water systems should
not be allowed to degrade substantially from the NPDWS criteria.
When the municipality delivers water to the consumer, that water
becomes the property of the consumer when it cross the water
meter and enters the building. The microbiological quality of the
water may be degraded in the building as a result of processing in
the building water system. It is the responsibility of building facility management to ensure that biological hazards are prevented
from harming building occupants and visitors.
Utility Water Systems
To our knowledge, the most thorough and recent survey of US
cooling water systems indicate that about 87% of cooling towers
contain less than detectable (< 10 CFU/ml) viable Legionella13.
This indicates that the 13% of cooling towers in the US with detectable levels of Legionella should be properly treated to eliminate
the hazard, control it or prevent it from harming people. Phigenics
believes that there is no valid technical reason for any properly
22
treated cooling water system to have detectable Legionella concentrations in the recirculating water. If Legionella is detected in
cooling water, the hazard should be eliminated through properly
applied water treatment.
In regard to total heterotrophic aerobic bacteria in cooling water,
the Phigenics recommended validation criteria is derived from the
2006 position paper published by the Cooling Technology Institute (CTI) in which dipslide results >10,000 CFU/ml indicate that
better microbial control should be achieved in the system 14.
CASE HISTORIES OF PVT APPLICATIONS IN
THE FIELD
HVAC Cooling Towers at a Chicagoland
University
A major University uses a local vendor to supply their cooling
tower and condenser water treatment chemicals. The chemical vendor was measuring performance of their biocide program using
ATP testing. As part of the University’s newly implemented Water
Management Plan to manage the entire building water system, the
PVT was used to additionally validate that biological hazards were
being effectively controlled.
The first PVT results from the cooling tower were available 48h
after the field sampling. Results indicated total heterotrophic aerobic bacteria counts of 107 CFU/ml and 266 CFU/ml of Legionella
pneumophila, serogroups 2 -14. Such high viable bacteria levels
were surprising to the chemical vendor. Apparently, the ATP measurements had not been properly correlated to actual viable bacteria (as colony forming units) for that system.
A cooling water chlorine disinfection treatment was planned and
promptly implemented. The PVT was performed after the disinfection procedure was completed. Post-disinfection PVT results indicated a 99.9% reduction in heterotrophic bacteria to 104 CFU/ml
and no detectable Legionella (<10 CFU/ml). Facility management
was pleased to have documented evidence (validation) that the
cooling tower water was free of potentially harmful bacteria. Everyone observing, including the chemical water treatment vendor, was
pleased at the rapid deployment of the remediation and the prompt
PVT results confirming performance.
Subsequently, 5 other cooling towers at the University were found
to be potentially hazardous due to high total bacteria counts in
excess of 107 CFU/ml and were therefore disinfected with chlorine.
Post-disinfection PVT results indicated total counts equal to or
less than 104 CFU/ml and no detectable Legionella. These results
validated the performance of the disinfection procedure.
The facility manager is now in the process of ensuring continuance
of effective hazard control in his cooling water systems.
Disinfection of Hospital Building Water System
Facility managers for a 300 bed hospital in Los Angeles were preparing to bring a new wing of the hospital on-line. The building had
been idle for some time, which is not uncommon while trying to
meet codes and pass inspections to “go live”. Eleven days prior to
the health inspector’s arrival, management at the healthcare provider asked for an assessment of their domestic water quality. Water samples were taken and within three days, biological hazards
(high THAB and detectable Legionella species) were identified
using PVT’s at five locations within the facility. Upon receiving
23
results, the hospital facility managers worried they might not pass
the looming health inspection. Phigenics outlined an emergency
disinfection process and subsequent validation procedure that
could all take place within a five day period of time. An emergency
disinfection commenced after a process flow diagram was produced
to understand the domestic water system layout. EPA-registered
sodium hypochlorite disinfectant was added to the domestic water
system to achieve a free residual throughout the system. All water
taps were turned on to distribute the chlorine and then the system
was allowed to recirculate for 24 hours to provide adequate contact
time. The disinfection concluded with flushing all water taps until
city water chlorine levels were reached. At that time, twenty more
PVT’s were run at various sinks and showers throughout the building. Within three days, the results of the PVT’s did indeed validate
that drinking water standards had been obtained. Post-disinfection
THAB results showed that 85% of samples were below 10E3 CFU/
ml and 15% of samples at 10E3 CFU/ml; Legionella was not detectable in any post-disinfection sample. The hospital presented this
documentation to the health inspector.
The Water Management Team decided that decreases in water usage and lower flow may have been the cause of water quality degradation in the distribution system. Although Legionella was not
found in the potable water system, the Water Management Team
was concerned that heterotrophic bacteria levels exceeded the EPA
Drinking Water Treatment Technique (TT) Limit (<500 CFU/ml) by
several orders of magnitude. This indicated to the team that conditions could be favorable for Legionella growth due to indications
of biofilm. The Water Management Team took action according to
industry guidelines and began a systematic flush of the building
water system in order to elevate the level of free residual oxidant
throughout the system. Validation of this control measure with the
PVT the following month documented that total heterotrophic bacteria levels had been significantly reduced. In the wings that were
flushed (wings 4, 6, 8), July PVT results were 102 or 103 CFU/ml. One
of the building wings had not yet been flushed during the July
sampling; the counts were still very high, 106 CFU/ml. A strong
recommendation was made to flush ASAP to prevent hazards from
escalating further in that building wing.
Before any PVTs had been run in this system, water samples had
been sent to an analytical lab for standard method analyses. In the
time it took to finally receive initial test results from the standard
methods laboratory (some 12 days later), facility management had
received initial PVT results indicating potential hazards, disinfected
the system and validated that the disinfection had been effective
with receipt of results from post-disinfection PVT samples.
Prior to students returning in August, the PVT will be used again to
confirm that the hazard control strategy has been effective.
Hazard Analysis of a Cooling Tower
Facility managers at a University in the mid-Atlantic region use the
PVT to independently validate the effectiveness of the cooling
tower biocide strategy at the central chilled water plants. The water
treatment chemicals provider uses ATP tests to routinely evaluate
performance of microbiological levels in the cooling towers and
had found ATP levels to be acceptable. Monthly PVT results were
acceptable for utility water total heterotrophic bacteria (result: 103
CFU/ml, limit: 104 CFU/ml) but were positive for Legionella
pneumophila SG1 (40 CFU/ml). These results were surprising to
the university Water Management Team. They highlighted the importance of biofilm control with corresponding measurement of
Legionella and they decided that the performance goal for microbial control in cooling towers should be no detectable Legionella.
Results from the PVT provided motive for facility management to
review and upgrade the biocide program. The team agreed that
they cannot rely on heterotrophic bacteria counts and ATP levels
for determination of water safety.
PVT Highlights the Value of Controlling Total
Heterotrophic Bacteria in Potable Water
Distribution System
A University facility management team used the PVT to evaluate
the potable water system in its largest, multi-building housing facility which had been unoccupied for 4 weeks after students had
completed the Spring term. PVT results were negative for
Legionella, however results exceeded the recommended limits for
potable water total heterotrophic bacteria (results: 104 – 106 CFU/
ml, validation criteria: 103 CFU/ml). The PVT hazard analysis data
suggested that the water quality in the distribution system had
significantly degraded as indicated by increases in bacteria levels.
24
Evaporative Coolers in a Laundry
Facility managers at an industrial laundry were concerned about
the employee and visitor life safety aspect of utilizing evaporative
coolers (swamp coolers). Between twenty and thirty large evaporative coolers were used in the facility which can blow aerosols of
system water down into the plant where inhalation of micro-droplets by their employees can occur. General aerobic bacteria and
specifically Legionella were of concern to facility management.
Using the PVT, an initial Hazard Analysis showed no detectable
Legionella but total aerobic bacteria levels much higher than suggested validation criteria. The concern from facility management
then became how best to implement a control plan which could
prevent potential problems from occurring in the future. The Hazard Analysis raised awareness that both Total Heterotrophic Aerobic Bacteria and Legionella were of critical concern during the
cooling step in their water process flow. The Director of Safety and
corporate VP of facilities decided to design and implement a Water
Management Plan for this facility.
Dentist Office
A Pacific Northwest dentist expanded his surgeries from 4 to 6 and
purchased new Dental Water Line Units for the new surgeries consisting of plastic one liter supply bottles. The dentist was following
the treatment protocol outlined by the dental supply company that
represented the manufacture and was confident that his system
was free of bacteria. He wanted to perform bacterial testing to verify
his belief.
The results of the PVT test were shocking to him. The older surgeries that had the bottles cleaned once per week and were treated
with an industry recognized product on an ongoing basis had bacterial levels of 107 CFU/ml of heterotrophic bacteria at the spray
wand. Even more surprising was that the new surgeries that had
been in operation less than a month had an equally high bacteria
reading of 107 CFU/ml.
The results from testing indicated that the supply lines from the
tank reservoir to the dispensing wand were probably contaminated
25
by biofilm build-up that was not being controlled by the existing
cleaning protocol. New protocols were defined and implemented.
A Midwestern Chemical Manufacturing Plant
Validates Biological Hazard Control
The Director of Operations at a Chemical Plant wanted to validate
the success of their recently modified cooling tower biocide program. Previously, he had tested for heterotrophic bacteria, but had
not tested for the presence of Legionella. Validation testing (validation is evidence that hazards have been controlled under operating conditions) with PVT was performed at two sample locations
over 3 months. Results from PVT validation testing indicated that
the new biocide program was effective in controlling heterotrophic
microbiological growth and in controlling Legionella.
The Director of Operations was pleased with the results that validated the performance of the new biocide program. He was pleased
with the format of the results report which he has retained for documentation purposes.
Results of PVT Testing Shake Confidence of
Industrial Manufacturer in the Pacific
Northwest
Facility management at a large Pacific Northwestern manufacturing
facility allows a water treatment company to manage their utility
water systems including the cooling towers. They were confident,
based on written and verbal reports, that their cooling towers were
clean and free of any biological hazards. The PVT was used for
independent confirmation.
Eight of the twelve (66%) systems tested exceeded the recommended limits for total heterotrophic bacteria, three of them as high
as 107 CFU/ml, and three of the remaining four were at the upper
limits. All but one of the tested systems required some type of
immediate remedial action.
The water treatment company providing the outsourced services
had been cutting back products and services in an effort to control
their own costs. There was not, however, adequate validation (evidence that hazards have been eliminated or controlled under operating conditions) that after cut backs in products and services, the
program was still effective.
Conclusions: Results of PVT demonstrated to facility management
that improvements in the water treatment program were necessary
and that an overall water management plan would be helpful.
ACKNOWLEDGEMENTS
From Phigenics, LLC participating in beta testing were Ashton
McCombs, Jay Reading, Brooke Winter, Tim McMahon, Bob
Downey, Chris Bellizzi, Steve Mosher, Marty Detmer and Kristy
Maher. Whitney Haumiller contributed to the precision analysis
study. Jeff Minalga contributed to establishing the online information transfer system and in data analysis.
Legionella and other cultures were provided by Nick Cianciatto
and Jenny Dao, from Northwestern University Medical School (Chicago, IL). Kati Rossmoore, Chris Cuthbert, Gary Miners and Len
Rossmoore, at Biosan Laboratories, Inc. (Warren, MI) were helpful
in various phases of this project. Blinded split sample analyses
were performed at Environmental Safety Technologies, Inc. (Louisville, KY) by Ann Koebel, Amber Quaack, Richard Miller and Shauna
Weis.
26
REFERENCES
1.
Centers for Disease Control and Prevention (CDC). 2005.
Procedures for the recovery of Legionella from the environment. National Center for Infectious Diseases, Division
of Bacterial and Mycotic Diseases, Respiratory Diseases
Laboratory Section, Atlanta GA
http://www.cdc.gov/legionella/files/LegionellaProcedures.pdf
2. International Standards Organization (ISO). 1998. Water
Quality-Detection and Enumeration of Legionella. ISO
11731. International Organization for Standardization,
Geneva, Switzerland
3. McCoy, W.F., et al. 2007. A new method for enumerating
viable Legionella and total heterotrophic aerobic bacteria.
Associated Water Technologies. Annual Convention and
Exposition, November, 2007.
4. McDaniels, A.E., et al. 1985. Holding effects on coliform
enumeration in drinking water samples. Appl Environ
Microbiol; 50(4): 755-762
5. The World Health Organization. 2003. Heterotrophic Plate
Counts and Drinking-water Safety: The Significance of
HPCs for Water Quality and Human Health. IWA Publishing, London, UK ISBN: 92 4 156226 9
6. The World Health Organization. 2003. Heterotrophic Plate
Counts and Drinking-water Safety: The significance of
HPCs for Water Quality and Human Health. IWA Publishing, London, UK ISBN: 92 4 156226 9
7. Pope, M.L., et al. 2003. Assessment of the effects of holding time and temperature on Escherichia coli densities in
surface water samples. Appl. Environ. Microbiol.
69(10):62016207
8. Alam, M., et al. 2006. Effect of transport at ambient temperature on detection and isolation of Vibrio cholerae from
environmental samples. Appl. Environ. Microbiol.
72(3):2185-2190
9. The World Health Organization. 2006. Guidelines for Drinking-Water Quality – First Addendum to Third Edition, Volume 1 – Recommendations. WHO Press, Geneva, Switzerland ISBN: 92 4 154696 4
10. The World Health Organization (WHO). 2007. Legionella
and the Prevention of Legionellosis. WHO Press, Geneva,
Switzerland ISBN 92 4 156297 8
11. McCoy, W.F. 2005. Preventing Legionellosis. International
Water Association. IWA Publishing, London, UK. ISBN: 1
843390 94 9
12. Association of Water Technologies (AWT). 2003. Legionella
2003: An update and statement by the association of water
technologies (AWT). Association of Water Technologies,
McLean, VA http://www.awt.org/Legionella03.pdf
13. Miller, R.D and A. Koebel. 2006. Legionella prevalence in
cooling towers: Association with specific biocide treatments. ASHRAE Transactions CH-06-12-2 vol. 112, pt 1.
14. Cooling Technology Institute (CTI). 2006. Legionellosis
Guideline: Best Practices for Control of Legionella http://
www.cti.org/cgi-bin/download.pl
27
FIGURES AND TABLES
Figure 1. The PVT field sampler consists of a sterile plastic screw-capped container (A) within which is held a
α ) on one side
paddle (B) containing buffered charcoal yeast extract agar enriched with α ketoglutarate (BCYEα
α agar plus the selective supplements glycine, vancomycin, polymyxin
and on the other side of the paddle, BCYEα
B, and cycloheximide (GVPC).
Table 1. Comparison of methods to measure Legionella bacteria in water samples.
28
Table 2. Protocol steps and instructions for field use of the Phigenics Validation Test (PVT).
29
Table 3. Effect of sample holding time on total
heterotrophic aerobic bacteria (CFU/ml) in building
potable water samples at ambient temperature (22 °C).
Figure 3. Side-by-side comparisons of spread plating
(the Standard Method) and PVT in split samples from a
University building water system. Four samples (A -D)
are given as examples. Typically, results from spread
plating and PVT analyses are very similar but not
identical. See Figure 4 for a quantitative comparison
from split sample analyzes.
Figure 4. Results from a building water system in which
48 samples were split for comparison with the Standard
Method and the PVT.
Figure 2. The effect of water sample holding time on
Total Heterotrophic Aerobic Bacteria (THAB) counts. The
THAB were measured immediately after sampling (t=0)
in six cooling towers at a University in the Midwestern
United States. One hour later (insert graph), the cooling
tower water was reanalyzed; THAB declined by at least
one order of magnitude in 5 of the 6 samples and in
one of the samples there was a 3 order of magnitude
decline. After 24h holding time at ambient room
temperature, THAB counts had increased much more
than one order of magnitude in all six samples. The
types of bacterial colonies recovered at each sampling
varied unpredictably (data not shown).
30
Figure 5. PVT field samplers are useful for estimating the total bacterial count using an order of magnitude
comparator chart as demonstrated by comparisons to commercial Total Aerobic
Figure 6. The Colony Forming Unit (CFU) count of
Legionella pneumophila SG1 (wild type field isolate) on
PVT dipslide surfaces correlated significantly (R 2 =
0.9873) with CFU/ml measurements from Standard
Method (ISO 11731) spread plating. Results indicate
similar precision with both methods (error bars are Std
Dev of five replicate samples at each dilution).
Figure 7. Blinded comparisons of 147 samples split for
analysis with PVT and with the Legionella Standard
Method. Samples were processed by an independent
laboratory. Legionella detection or no detection is
indicated by + or -. “Different +” means both methods
detected Legionella but the serogroups or species
detected were different.
31
Figure 8. Six hundred and eighty two (682) building
water samples were analyzed with the PVT. Sampling
was not randomized, no screening was done and no
data were omitted. The buildings were all in the US from
the following regions: Eastern seaboard States,
Southeast, Midwest, South, Southwest, Southern
California, Pacific Northwest. Potable water samples
locations -350 (51.3%) ; Utility water (typically cooling
tower water) sample locations -332 (48.7%).
Figure 10. Heterotrophic aerobic bacterial counts in 332
utility water sample locations (mostly cooling tower
water) were compared. The 10^4 symbol in legend refers
to 104 CFU/ml of Total Heterotrophic Aerobic Bacteria
(THAB). About half (51%) of the building utility water
samples had total heterotrophic aerobic bacteria
(THAB) at or below 10 4 CFU/ml; 49% of utility water
samples had THAB greater than 10 4 CFU/ml.
Figure 9. Heterotrophic aerobic bacterial counts in 350
potable water sample locations were compared. The
10^3 symbols in the legend refers to 103 CFU/ml of Total
Heterotrophic Aerobic Bacteria (THAB). About two-thirds
(67%) of the building potable water samples had total
heterotrophic aerobic bacteria (THAB) counts at or
below 103 CFU/ml; 33% of potable water samples had
THAB greater than 103 CFU/ml.
Figure 11. About 6% of potable water sample locations
and about 10% of utility water sample locations were
positive for Legionella at 10 CFU/ml or greater. There
appeared to be no correlation between Legionella
detections and the THAB results in potable water
systems (data not shown); there were more Legionella
detections in utility water systems when the THAB was
greater than 104 CFU/ml but no statistical analysis was
done to determine significance of the difference. The
data confirmed that THAB is useful as a water quality
indicator but not a water safety indicator5
32
33
Crossflow Cooling Tower Performance
Calculations
Robert Fulkerson
Fulkerson & Associates, Inc.
INTRODUCTION
There was a period of time when the majority of cooling
towers being constructed in the United States were
crossflow towers. After the high efficiency film type fills
Robert
became popular for use in counter flow cooling towers, the
Fulkerson
percentage of the new large industrial towers, which were
crossflow, diminished. Now only about 10% of new field erected
industrial cooling towers which are sold are crossflow towers.
Crossflow cooling towers with splash bar fill may be the best design for a cooling tower where the water quality makes the use of
film type fills questionable. There are still a large number of
crossflow cooling towers in operation which are in need of repair or
upgrading. There are also splash fill manufacturers who are developing better and more efficient fill configurations to address the
need for the repair of these crossflow cooling towers.
The prediction of the thermal performance of crossflow cooling
towers requires the use of a two dimensional double integration
mathematical procedure. Sam Zivi and Bruce Brand developed
such a procedure which was published in the August 1956 issue of
Refrigerating Engineering. The original paper had an Appendix
which included an example problem with all of the calculations
required for crossflow cooling tower analysis. Unfortunately, when
the paper was reprinted, it did not include the Appendix with the
calculations. Recently, I have been asked by several people for a
copy of the paper which includes the Appendix. After contacting
ASHRAE and looking in technical libraries for a complete copy
with no success, I realized this important paper was nearing extinction.
The purpose of this paper is to re-introduce a complete copy of the
Zivi Brand paper to the cooling tower industry. I have also included an equation which can be used to convert crossflow fill
characteristic curves that were developed in a test cell to curves
which can be used for cooling towers that differ in fill dimensions
from the test cell dimensions.
DISCUSION
When power plants began to be built to provide electricity for
Thomas Edison’s inventions they needed cooling water for their
condensers. If the power plant was located close to a stream of
water or a river, a cooling tower was not needed. If the plant was
built close to a lake, then the lake could provide the condenser
cooling water. If the lake was not large enough to provide the
required cooling, then the heat dissipation could be greatly increased by returning the hot water to the lake as a spray. It was
found that a spray pond required only about 1/40 the area of a
cooling lake to provide the same amount of cooling depending on
the nozzle pressure, the height of the spray and the wind velocity.
Small heat loads could be dissipated by the use of atmospheric or
34
spray filled cooling towers where the water was sprayed
down inside a louvered box. The airflow was supposed to
be induced through the cooling tower by the downward
spray of the water. These cooling towers performed better if there was a cross wind.
Later, fans were used to move the air through the cooling towers;
and wood splash bars were introduced to slow down the falling
water and keep it broken up into small droplets. Some of the old
counterflow cooling towers had wood splash grid packing which
was installed to heights approaching 48 feet above the air inlet.
The prediction of the cooling performance of these early counterflow
cooling towers was difficult because the cooling tower manufacturers were stymied by the combination of latent heat transfer and
sensible heat transfer, both occurring at the same time.
Frederick Merkel, who was on the faculty of a college in Dresden,
Germany, had solved this problem by combining the two heat transfer processes into a single process based on enthalpy potential as
the driving force. Merkel’s paper was published in Germany in
1925, but it received little attention outside of Germany. The University of California at Berkeley had been conducting research on
cooling towers for several years. H. B. Nottage, who was a graduate student, was assigned to the cooling tower project. During a
literature search in 1938 he found several references to the work of
Frederick Merkel. After obtaining a copy of the Merkel paper
Nottage immediately recognized the importance of Merkel’s work.
For the details of the derivation of the Merkel theory, refer to “Cooling Tower Performance” by Donald Baker.¹ Joseph Lichtenstein
working with Nottage produced a series of charts where he calculated approach curves using the Merkel equation and a four point
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35
Tchebycheff numerical integration procedure. These charts were
then published in 1943 by The Foster Wheeler Corporation.² The
Foster Wheeler Black Book was the first time the Merkel theory
was presented in a usable format.
mance curves.t All of these above mentioned books were plotted
using the Merkel equation and the four point Tchebycheff numerical integration procedure. They all were also plotted using sea
level psychrometric data.
FOSTER WHEELER BLACK BOOK
Although the Merkel equation has been criticized for the several
simplifications it required, it has been used by cooling tower engineers for almost 70 years with satisfactory results. The CTI Blue
book has now been computerized and is included as a part of the
CTI Tool Kit which is available on a Compact Disk. These
counterflow curves can now be plotted at altitudes other than sea
level.
CTI BLUE BOOK
Neil Kelly and Leonard Swenson published the Pritchard Brown
Book in 1957.³ In addition to Approach curves this book contained
curves for the performance of several counterflow wood splash
decks. All of the curves plotted in the Pritchard Brown Book were
plotted on Log Log paper. This allowed the fill characteristic curves
to be plotted as a straight line. The equation of a fill characteristic
curve is of the form KaV/L=C(L/G){ n. The “Ka” is a heat transfer
coefficient, the “V” is the volume of fill in one square foot of fill
plan area and this is equal to the fill height. The L is the water
loading in pounds of water per hour falling through one square
foot of fill plan area. The “C” is a constant that must be determined
by testing. The “G” is the airflow in pounds of dry air per hour that
is flowing up through one square foot of plan area. The “n” is an
exponent that is equal to the slope of the fill characteristic line.
PRITCHARD BROWN BOOK
MERKEL EQUATION
CROSSFLOW COOLING TOWERS
When the crossflow cooling tower came into existence, it was immediately recognized that a new problem now existed. The simple
one dimensional heat transfer calculation of the counterflow cooling tower would not be adequate for a crossflow tower which is a
two dimensional problem. The air travels horizontally through the
fill, and the water falls vertically down through the fill.
In 1967 when computers became available, The Cooling Tower Institute gave a contract to Midwest Institute in Kansas City to develop a greatly expanded version of a book of approach curves.
This resulted in the publication of the CTI Blue Book of perfor36
37
Dr. Sam Zivi of Midwest Research Institute and Bruce Brand of
Havens Cooling Tower Company presented a solution to this problem in a paper which was published in the August 1956 issue of
Refrigeration Engineering. This paper describes a method of dividing a vertical, transverse section through the fill of a crossflow
cooling tower into a grid or matrix. The water temperature and
enthalpy of the air is calculated at all points throughout the grid.
This is possible because the water temperature at the top of the
grid is constant across the grid.. The air temperature down the air
inlet side of the grid is also constant and is at the wet bulb temperature. At all interior points in the grid the water temperature and air
enthalpy can be calculated using the method described in the Zivi
Brand paper. A copy of the Zivi Brand paper is included in the
Appendix of this paper.
The first mechanical draft cooling towers were predominantly
counterflow towers with splash grid fill. Crossflow cooling towers
were being built in the early 1960’s. They enjoyed several decades
when the new cooling towers being built for power plants and
chemical plants were of the crossflow design. By 1970 about 90%
of the mechanical draft cooling towers being built in the United
States were crossflow towers. This continued until the high efficiency film type fills came into use which allowed the design of
smaller counterflow cooling towers that could provide the same
cooling capacity as the larger crossflow cooling towers.
Now the pendulum has swung back again, and almost all new cooling towers being built are counterflow towers using low-clog film
type fill material.
There are still a lot of crossflow cooling towers in operation which
are now in need of repair. This repair may include the installation of
a newer and more efficient fill configuration. There is still a need for
information about crossflow fill performance and crossflow cooling tower performance expected when the newer fill splash bars
have been installed. In the past year, I have had several requests
for a copy of the Zivi Brand paper. All of my efforts to locate a good
copy which included the appendix with the calculations were futile.
I could not get a copy from ASHRAE or from technical libraries.
The only copies they had did not include the appendix. It appeared
that a valuable piece of cooling tower history was about to evaporate and be lost forever. I was eventually able to obtain a complete
copy of the Zivi Brand paper, and it is included in the appendix of
this paper. Those who desire can use it to develop their own computer program for crossflow calculations.
CONVERSION OF CROSSFLOW FILL
CHARACTERISTIC CURVES
In 1999 I presented TP99-05 “A COMPARISON OF CROSSFLOW
COOLING TOWER SPLASH_TYPE FILLS”5 at CTI which contained
fill performance characteristic curves and fill pressure drop curves
for 20 crossflow fill configurations. These curves were all drawn
for a fill height of 30 feet and an air travel through the fill of 17 feet.
In order for these curves to be used for other fill heights or air
travels they must be converted to the new cooling tower’s dimensions of fill height and air travel. This conversion is a simple and
straight forward operation.
38
As an example, let us say we have a fill characteristic curve that was
established in a test cell which had an air travel of 17 feet and a fill
height of 30 feet. The curve has a slope of -.5 and passes through
the L/G = 1 line at a KaV/L of 1.5. The equation of this curve would
then be KaV/L = 1.5*(L/G)-.5.
Now let us say we want to install this fill in a cooling tower that has
a 30 foot fill height, but we want to increase the air travel to 24 feet.
To convert this curve to a 24 foot air travel curve we must keep the
water loading per square foot of fill area unchanged. We must also
keep the airflow per square foot of fill height unchanged, and we
must keep the heat transfer coefficient “Ka” unchanged. The L/G
now has to increase by the ratio of the increase in the air travel.
Now the L/G becomes (24/17) = 1.412 at a KaV/L of 1.5. Locate this
point and draw another curve through it parallel to the original test
cell curve.
This new curve now becomes the characteristic for the fill when
installed with 24 feet of air travel and 30 feet of fill height. This
curve crosses the L/G = 1 line at a KaV/L of 1.782, so the equation
of the converted curve is KaV/L = 1.782*(L/G)-.5 .
If we want to install the fill in a tower with 17 feet of air travel but
with a fill height of 48 feet, we still have to keep the airflow per
square foot, water loading and heat transfer coefficient Ka, constant. We now have more total airflow because of the increased
height. The L/G changes because of the G now increases as the
ratio of the increase in fill height. G now becomes 48/30 = 1.6 so the
L/G becomes 1/1.6 or .625. We now locate the point where L/G =
.625 at a KaV/L of 1.5. The “V” has also changed from 30’ to 48’.
The equation of our original curve was KaV/L = 1.5*(L/G)-.5. With
the L/G set at 1 we can substitute 30 for “V”, and we can calculate
“Ka” as .05. We now multiply the Ka of .05*48 = 2.4 for the new
KaV/L at the L/G ratio of .625. We now move up the L/G =.625 line
and locate KaV/L = 2.4. We draw a curve through this point parallel
to the original test cell curve. This new curve is the fill characteristic curve for the fill when installed with 17’ of air travel and 48’ of fill
height. This curve crosses the L/G = 1 line at a KaV/L of 1.897, so
the equation of this new curve becomes KaV/L=1.897*(L/G){ ’”u .
These two calculations can be combined into one calculation, and
the intersection of the new curve and the L/G = 1 line found by
using the point slope equation of a straight line. The conversion
equation then becomes:
Conversion equation
KaV/L=(((C/(X1/X2)-n)/Y2)Y1)/(Y2/Y1)-n
Where:
C
X1
X2
Y1
Y2
n
is the KaV/L of the test cell curve at L/G = 1
is the new air travel
is the test cell air travel
is the new fill height
is the test cell fill height
is the slope of the curves
The KaV/L calculated by this equation is the new C for the new
curve.
These curves may be used in combination with the “Kelly’s Handbook of Crossflow Cooling Tower Performance” with caution. It
must be pointed out that a fills cooling performance is affected by
the hot water temperature and the air velocity through the fill. The
effect of these must be accounted for in any tower design.
Literature Cited
1.
Cooling Tower Performance. by Donald Baker, Chemical
Publishing Co. New York, N.Y. 1984
2.
Cooling Tower Performance. Bulletin CT-43-2 Foster
Wheeler Corporation 165 Broadway, New York, N.Y. 1943
3.
Counterflow Cooling Tower Performance. J. F. Pritchard &
Co. of California 4625 Roanoke Parkway, Kansas City, MO,
1957
4.
Cooling Tower Performance Curves. 1967 Cooling Tower
Institute, Houston Texas, 1976
5.
A Comparison of Crossflow Cooling Tower Splash-Type
Fills, by Robert Fulkerson, Cooling Tower Institute Paper
No. TP99-05
6.
Kelley’s Handbook of Crossflow Cooling Tower Performance. 1976 Neil W. Kelly & Associates, 525 Brush Creek
Blvd, Kansas City, MO
APPENDIX
1.
Example of fill characteristic curve converted from 17’ air
travel to 24’ air travel.
2.
Example of fill characteristic curve converted from 30’ fill
height to 48’ of fill height.
3.
Copy of Zivi Brand paper “An Analysis of The Cross-Flow
Cooling Tower”.
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
A Simplified Method to Evaluate
Cooling Tower and Condenser
Performance Using the CTI Toolkit©
Natasha Peterson & Dr. Luc De Backer
Bechtel Power Corporation
generator output, as is shown in figure 2 below. As
can be noticed from the curve in fugure 2, the generator output will typically decrease about 3 % for
Abstract
every inch increase in condenser pressure when opA simple mathematical method will be proposed to
erating above the design point. For the design point
estimate the cooling tower performance at off-design
of the cooling tower, typically a high summer ambiambient conditions. The cooling tower design data
ent wet bulb temperature is selected (for example 0.4
will be used as a starting point and the CTI toolkit will
% annual exceedance per ASHRAE), but for economibe used to calculate psychrometric properties and
cal evaluations it is important to know how the steam
the Merkel number at off-design conditions to calcugenerator output will vary with the ambient condilate the temperature of the cold water leaving the cooltions. Therefore, it is very useful to have a simplified
Dr. Luc De Backer
ing tower using the slope of the cooling tower charmethod to evaluate the performance of the mechaniacteristic curve. By applying first principles and straightforward cal draft cooling tower and its impact on the performance of the
relationships for condensers, the condenser performance at off- steam surface condenser and steam generator output.
design conditions can be predicted.
In order to predict the impact of the ambient conditions on the
Introduction
Cooling towers are widely used in power plants as the heat sink to
reject the condenser heat duty to the atmosphere. For aesthetical
and economical reasons, mechanical draft cooling towers (MDCT)
are preferred over natural draft (hyperbolic) cooling towers and it
should be noted that the application of the described method will
be limited to mechanical draft cooling towers only.
steam generator output for a given mechanical draft cooling tower
and surface condenser design selection, the performance at offdesign conditions has to be known.
Figure 2
Cooling Tower Performance prediction
Figure 1
In the most common configuration as shown in Figure 1, exhaust
steam from the low pressure steam turbine is condensed in the
steam condenser using cold water from the cooling tower. The heat
of condensation will be absorbed by the cooling water and will
result in a temperature rise in the circulating water. The hot circulating water is sent to the mechanical draft cooling tower, where it is
cooled by evaporative cooling using ambient air. The cold water
temperature (CWT) leaving the cooling tower will vary with the
ambient wet bulb temperature (WBT) and this will have an impact
on the condenser pressure which is directly related to the steam
58
The following parameters are required to design a mechanical draft
cooling tower:
• Cooling water flow rate entering the cooling tower
• Hot water temperature entering the cooling tower
• Cold water temperaturen leaving the cooling tower
• Design wet bulb temperature
• Barometric pressure or altitude
The efficiency of a cooling tower is characterized by the Merkel
number (KaV/L) which is a function of Liquid to Gas ratio (L/G).
The relationship between KaV/L and L/G is usually described with
59
an equation of the form (characteristic curve):
1
Where C is a constant and the exponent s is the slope of the characteristic curve.
The size of a cooling tower is determined by the intersection of the
demand curve with the characteristic curve, which results in design
values for KaV/L and L/G. Typically, the cooling tower supplier
provides the slope of the characteristic curve, and using the design
values for KaV/L and L/G, the constant C in the equation above can
be calculated.
The CTI Toolkit© is a powerful tool for calculating the psychrometric properties of the air along with a variety of tower performance
parameters. The Toolkit© ‘Demand Curve’ function generates demand curves with KaV/L as function of L/G for different values of
the approach, as shown in figure 3 below.
In our model, it is assumed that the circulating water flow rate is
constant and that the fan driver output power will change proportionally with the density of the air at the tower discharge.
Based on these assumptions, equation (2) can be simplified to:
3
From a heat and mass balance around a cooling tower and ignoring
the evaporated water contribution and drift loss, we know:
4
L = Circulating water mass flow rate
Cpw = Specific heat of water
R = range which is equal to the hot water temperature –
cold water temperature
G = Mass flow rate of dry air
h2 = Enthalpy of dry air leaving the tower
h 1 = Enthalpy of dry air entering the tower
Rearranging equation (4), we have a relationship between L/G and
exiting air enthalpy:
5
Calculating the cooling tower discharge air properties at off-design
conditions requires combining the heat balance equation with the
equation for L/G and iterating for a solution. This iteration procedure is described in detail in the CTI code ATC-105.
With the Toolkit© and the algebraic relationships above, the cold
water temperature can be determined at a variety of inlet wet bulb
conditions using the following methodology:
Figure 3
1.
At off design conditions, the mass flow rate of dry air (G’) will be
different from the design value (Gd); the CTI Acceptance Test Code
for Water Cooling Towers gives us the following relationship for
evaluating the off-design value for L/G:
2.
2
3.
Where
= Ratio of water mass flow rate to dry air mass flow
rate at off-design wet bulb
= Ratio of water mass flow rate to dry air mass flow
rate at design conditions
Q ' , Q d = Off-design and design circulating water flow rate,
respectively
',
d = Fan driver output power at off-design and design
W W
conditions, respectively
'
d
ρ , ρ = Off-design and design air density, respectively
υ ' ,υ d = Specific volume of air, either off-design (υ’), or
design (υd)
60
4.
Using the ‘Demand Curve’ tab of the Toolkit, input the
design parameters for the cooling tower (Range, Altitude,
and the Tower Characteristics)
Select an off-design wet bulb temperature. Utilize the
‘Psychrometrics’ tab to determine the enthalpy of the air
entering the cooling tower at this wet bulb temperature
The ‘Enthalpy @ saturated conditions’ option in the
‘Psychrometrics’ tab allows to obtain the density and specific volumes for a given discharge air enthalpy and altitude above sea level.
Using an iterative procedure and various psychrometric
properties obtained from the Toolkit©
, at off-design
conditions is calculated using equations 3 and 5.
5.
The ‘Demand Curve’ tab of the Toolkit is used to determine
the approach at off design conditions.
Steam Surface Condenser performance
prediction
The heat duty (P) that is rejected by the steam in the condenser can
be written as:
P = M′steam.(hST,out - hcond)
6
61
With the steam mass flow rate at the steam turbine exhaust and
hST,out and hcond the enthalpy of the steam at the steam turbine exhaust and enthalpy of the condensate, respectively. With a power
plant running at full constant load the heat duty does not vary a lot
and as a first approximation the condenser heat duty can be considered as a constant.
The heat duty that can be handled by the steam surface condenser
is a function of the overall heat transfer coefficient (U), the heat
exchange surface area (A) and the logarithmic mean temperature
difference (LMTD) in accordance with the following equation:
'
P = msteam
.(hST ,out − hcond )
coefficient will not vary either since the water velocity can be assumed to be constant. Consequently, it is easy to derive that for a
constant heat duty, the product of FCWT and LMTD is a constant
value. This will be the basis for the surface condenser performance
evaluation:
9
The steam temperature can be calculated as function of the offdesign value for the LMTD using the equation above:
7
10
In accordance with the HEI standard for surface condensers, the
overall heat transfer coefficient U can be written as (ref 3):
P = U . A.LMTD
8
With Uvel the uncorrected heat transfer coefficient which is mainly
a function of the circulating water velocity, FCWT the inlet water
temperature correction factor, Fmat the tube material correction factor and Fclean the cleanliness factor. A typical value for Fclean is 0.85
in accordance with industry standards.
If we combine both equations 7 and 8 above, we have:
P = Uvel.FCWT.Fmat.Fclean.A.LMTD
9
The logarithmic mean temperature difference in a surface condenser
is defined by the following equation:
With R the condenser water side temperature rise which is equal to
T2 – T1. The steam pressure in the condenser can easily be determined from the steam temperature using the steam tables for saturated steam conditions.
Model verification and example calculation
To verify the model, an example calculation was performed. A mechanical draft cooling tower and steam surface condenser was designed for a condenser pressure of 2.5 inch HgA at a wet bulb
temperature of 77 ºF using a cold water temperature at the condenser inlet of 84.8 ºF. The design conditions for the cooling tower
are summarized in the table below.
Table 1: cooling tower design data.
10
Parameter
With Tsteam the saturated steam temperature in the condenser, T1 the
cold water temperature entering the surface condenser tubes and
T2 the hot water temperature at the condenser outlet. In a steam
surface condenser it is reasonable to assume that the steam temperature is constant as shown in figure 4 below, while the water
temperature will increase from T1 to T2 when the water flows through
the condenser tubes.
Figure 4
Once the tube material and thickness is selected and the heat exchange surface area has been calculated, A and Fmat are known
constants and with all circulating water pumps running at full capacity, it is reasonable to assume that the uncorrected heat transfer
62
Value
Unit
Site elevation
473
Feet above sea level
Wet Bulb Temperature
77.0
Deg F
Cold water temperature
84.8
Deg F
Hot water temperature
102.8
Deg F
Using the method described in Section 2, the cold water temperature leaving the cooling tower was calculated for different values of
the wet bulb temperature and plotted in figure 6 below.
Figure 5
As can be seen in Figure 5, the predicted cold water temperatures
and the vendor-given values were found to be in good agreement.
In the next step, the performance of the steam surface condenser
was estimated using the method described in Section 3. Figure 6
shows the performance for a steam surface condenser (SCC) at
constant heat load and a circulating water flow rate of 100 % of the
design value.
value for economical studies of power plants that use a mechanical
draft cooling tower and steam surface condenser.
References
1.
2.
3.
CTI Test Code ATC-105, Acceptance Test Code for Water
Cooling Towers, Cooling Technology Institute, Houston,
TX, 2000
CTI Toolkit©, Version 3.00.11.00, Cooling Technology Institute, Houston, TX, 2003
HEI Standards, Standards for Steam Surface Condensers,
Ninth Edition, Heat Exchange Institute, Inc., Cleveland,
OH, 1995
Figure 6
As can be noticed from this graph, there is an
excellent agreement between the performance
curve provided by the supplier and the estimated
performance (Estimation) that was determined
using the method above. The relative difference
between the estimated performance and the one
based on the supplier performance curves was
equal or less than 1 % over the complete range of
inlet water temperatures.
Conclusion
For a given mechanical draft cooling tower and
steam surface condenser design, it is imporant
to have a simple method to calculate the off-design performance to evaluate the impact of the
ambient conditions on the generator output. The
results show that the proposed methodology is
a reliable way to calculate off-design cooling
tower and steam surfance condenser performance. Although some algebraic manipulations
are required, the CTI Toolkit© makes this a simple
and easy process. The outlined method allowed
us to predict the cooling tower cold water temperature and condenser pressure which were in
close agreement with the supplier performance
data.
The input variables required for the analysis are
few and easily obtainable, and with these values
applied to the method described above the impact on the steam generator output can be predicted easily in a straightforward manner. The
method illustrated in this paper can be of great
63
Intermittent Feeding of Aseptrol® Tablets
Redefines the Role of Chlorine Dioxide
in Small and Mid-sized Cooling Water
Systems
Keith Hirsch, John Byrne, Barry Speronello
BASF Corporation
Background
Fe+3, Mn+3), so it may be necessary to increase chlorine
dioxide dose rates in systems that contain high concentrations of those metals in dissolved form.2 Chlorine dioxide does not react with phosphates.
An initial evaluation of BASF Cooling Water Biocide
Chlorine dioxide is a powerful oxidizing biocide. Addi(BCWB), based on chlorine dioxide-generating Aseptrol®
tionally, it is a gas and is water-soluble, which enables it
tablets,
demonstrated the effectiveness of the technolto penetrate entire sections of a water treatment system.
ogy
as
a
cooling water biocide.5 Subsequent tests of
Chlorine dioxide provides several advantages over tradiKeith Hirsch
BCWB
were
carried out at two BASF manufacturing sites
tional chlorine. For example, the efficacy of chlorine dioxto
optimize
the
chlorine
dioxide dosage. One location was a relaide is independent of pH (up to 10). Chlorine dioxide also does not
tively
dusty
facility
that
manufactured
clay products and clay-based
chlorinate organics and does not produce trihalomethanes (THMs).
fluid
cracking
catalysts
in
southern
Georgia
(Attapulgus), and the
As a biocide, chlorine dioxide exhdoiibits broad-spectrum kill, showother
was
in
a
plant
with
a
much
less
dusty
environment
that manuing efficacy, for example, against Bacillus anthracis (Anthrax) and
factured
a
variety
of
inorganic
catalyst
and
pigment
products
in
Legionella pneumophelia. Furthermore, it is effective against minorthern
Ohio
(Elyria).
This
paper
summarizes
the
results
of
these
croorganisms not controlled effectively by chlorine, such as
Cryptosporidium and Giardia. Of great importance in all areas of two cooling tower trials of BCWB.
water treatment is the fact that chlorine dioxide is a very effective
Experimental
biofilm penetrant, enabling the complete removal of biofilm that
Chlorine dioxide is a powerful oxidizing biocide. Additionally, it is a
harbors microorganisms.1-3
gas and is water-soluble, which enables it to penetrate entire secAmong the oxidizing biocides, chlorine dioxide is recognized as tions of a water treatment system. Chlorine dioxide provides sevbeing the least reactive with organics and many inorganics. It is eral advantages over traditional chlorine. For example, the efficacy
widely used for bleaching wood pulp in paper manufacturing be- of chlorine dioxide is independent of pH (up to 10). Chlorine dioxcause its relative lack of reactivity with wood fibers produces the ide also does not chlorinate organics and does not produce
highest quality paper products.2 As a result, chlorine dioxide is trihalomethanes (THMs). As a biocide, chlorine dioxide exhibits
compatible with wooden components in industrial water systems. broad-spectrum kill, showing efficacy, for example, against BacilChlorine dioxide also is unreactive towards ammonia, and is the lus anthracis (Anthrax) and Legionella pneumophelia. Furtherpreferred oxidizing biocide for use in industrial water systems that more, it is effective against microorganisms not controlled effeccontain even low levels of dissolved ammonia. Chlorine dioxide is tively by chlorine, such as Cryptosporidium and Giardia. Of great
unreactive towards paraffinic hydrocarbons and only very slowly importance in all areas of water treatment is the fact that chlorine
reactive with olefins.2 It is also unreactive towards biguanide- dioxide is a very effective biofilm penetrant, enabling the complete
based biocides, such as polyhexamethylene biguanide hydrochlo- removal of biofilm that harbors microorganisms.1-3
ride (PHMB).4 Laboratory work at BASF has found that chlorine
Among the oxidizing biocides, chlorine dioxide is recognized as
dioxide is unreactive with acrylates and with all quaternary amines
being the least reactive with organics and many inorganics. It is
tested to date. It reacts slowly with aldehydes, such as glutaraldewidely used for bleaching wood pulp in paper manufacturing be4
hyde.
cause its relative lack of reactivity with wood fibers produces the
Conversely, chlorine dioxide is highly reactive with the functional highest quality paper products.2 As a result, chlorine dioxide is
groups of key classes of organic compounds. It reacts quickly to compatible with wooden components in industrial water systems.
oxidize and deodorize reduced sulfur groups including H2S and Chlorine dioxide also is unreactive towards ammonia, and is the
organo-sulfur compounds. It also oxidizes the amine group of ter- preferred oxidizing biocide for use in industrial water systems that
tiary amines, and phenolic hydroxyl groups. In those reactions, contain even low levels of dissolved ammonia. Chlorine dioxide is
however, little chlorine dioxide is consumed by unselective reac- unreactive towards paraffinic hydrocarbons and only very slowly
tions with the hydrocarbon molecular backbone. As a result, chlo- reactive with olefins.2 It is also unreactive towards biguaniderine dioxide is a highly effective deodorizer at low concentrations, based biocides, such as polyhexamethylene biguanide hydrochloas well as a powerful biocide.2
ride (PHMB).4 Laboratory work at BASF has found that chlorine
+2
Chlorine dioxide can oxidize some inorganics in solution. Fe and dioxide is unreactive with acrylates and with all quaternary amines
Mn+2 in solution can oxidize to higher valence insoluble forms (e.g., tested to date. It reacts slowly with aldehydes, such as glutaraldehyde.4
64
65
Conversely, chlorine dioxide is highly reactive with the functional
groups of key classes of organic compounds. It reacts quickly to
oxidize and deodorize reduced sulfur groups including H2S and
organo-sulfur compounds. It also oxidizes the amine group of tertiary amines, and phenolic hydroxyl groups. In those reactions,
however, little chlorine dioxide is consumed by unselective reactions with the hydrocarbon molecular backbone. As a result, chlorine dioxide is a highly effective deodorizer at low concentrations,
as well as a powerful biocide.2
Chlorine dioxide can oxidize some inorganics in solution. Fe+2 and
Mn+2 in solution can oxidize to higher valence insoluble forms (e.g.,
Fe+3, Mn+3), so it may be necessary to increase chlorine dioxide
dose rates in systems that contain high concentrations of those
metals in dissolved form.2 Chlorine dioxide does not react with
phosphates.
An initial evaluation of BASF Cooling Water Biocide (BCWB), based
on chlorine dioxide-generating Aseptrol® tablets, demonstrated the
effectiveness of the technology as a cooling water biocide.5 Subsequent tests of BCWB were carried out at two BASF manufacturing sites to optimize the chlorine dioxide dosage. One location was
a relatively dusty facility that manufactured clay products and claybased fluid cracking catalysts in southern Georgia (Attapulgus),
and the other was in a plant with a much less dusty environment
that manufactured a variety of inorganic catalyst and pigment products in northern Ohio (Elyria). This paper summarizes the results of
these two cooling tower trials of BCWB.
Results
Attapulgus, Georgia Site
5,500-Gallon Cooling Tower:
Chlorine dioxide is a powerful oxidizing biocide. Additionally, it is a
gas and is water-soluble, which enables it to penetrate entire sections of a water treatment system. Chlorine dioxide provides several advantages over traditional chlorine. For example, the efficacy
of chlorine dioxide is independent of pH (up to 10). Chlorine dioxide also does not chlorinate organics and does not produce
trihalomethanes (THMs). As a biocide, chlorine dioxide exhibits
broad-spectrum kill, showing efficacy, for example, against Bacillus anthracis (Anthrax) and Legionella pneumophelia. Furthermore, it is effective against microorganisms not controlled effectively by chlorine, such as Cryptosporidium and Giardia. Of great
importance in all areas of water treatment is the fact that chlorine
dioxide is a very effective biofilm penetrant, enabling the complete
removal of biofilm that harbors microorganisms.1-3
Among the oxidizing biocides, chlorine dioxide is recognized as
being the least reactive with organics and many inorganics. It is
widely used for bleaching wood pulp in paper manufacturing because its relative lack of reactivity with wood fibers produces the
highest quality paper products.2 As a result, chlorine dioxide is
compatible with wooden components in industrial water systems.
Chlorine dioxide also is unreactive towards ammonia, and is the
preferred oxidizing biocide for use in industrial water systems that
contain even low levels of dissolved ammonia. Chlorine dioxide is
66
unreactive towards paraffinic hydrocarbons and only very slowly
reactive with olefins.2 It is also unreactive towards biguanidebased biocides, such as polyhexamethylene biguanide hydrochloride (PHMB).4 Laboratory work at BASF has found that chlorine
dioxide is unreactive with acrylates and with all quaternary amines
tested to date. It reacts slowly with aldehydes, such as glutaraldehyde.4
Conversely, chlorine dioxide is highly reactive with the functional
groups of key classes of organic compounds. It reacts quickly to
oxidize and deodorize reduced sulfur groups including H2S and
organo-sulfur compounds. It also oxidizes the amine group of tertiary amines, and phenolic hydroxyl groups. In those reactions,
however, little chlorine dioxide is consumed by unselective reactions with the hydrocarbon molecular backbone. As a result, chlorine dioxide is a highly effective deodorizer at low concentrations,
as well as a powerful biocide.2
Chlorine dioxide can oxidize some inorganics in solution. Fe+2 and
Mn+2 in solution can oxidize to higher valence insoluble forms (e.g.,
Fe+3, Mn+3), so it may be necessary to increase chlorine dioxide
dose rates in systems that contain high concentrations of those
metals in dissolved form.2 Chlorine dioxide does not react with
phosphates.
An initial evaluation of BASF Cooling Water Biocide (BCWB), based
on chlorine dioxide-generating Aseptrol® tablets, demonstrated the
effectiveness of the technology as a cooling water biocide.5 Subsequent tests of BCWB were carried out at two BASF manufacturing sites to optimize the chlorine dioxide dosage. One location was
a relatively dusty facility that manufactured clay products and claybased fluid cracking catalysts in southern Georgia (Attapulgus),
and the other was in a plant with a much less dusty environment
that manufactured a variety of inorganic catalyst and pigment products in northern Ohio (Elyria). This paper summarizes the results of
these two cooling tower trials of BCWB.
Elyria, Ohio Site
5,500-Gallon Cooling Tower:
This test was conducted on a 5,500-gallon cooling tower at the
Elyria, Ohio plant of BASF Corporation. Two months of baseline
data were collected during which time the tower was operated with
sodium hypochlorite that was applied by the water treatment service company.6 This was followed by replacement of the chlorine
bleach with BCWB.
BCWB was added to the tower in the form of multiple 8.33-gram
tablets enclosed in a polyester fabric mesh bag. The chlorine dioxide was introduced into the unit by periodically adding a bag of
tablets to a 6.3-gallon feeder and passing water through the feeder
to the tower at a rate of 10 gallons/minute. The solution concentration of chlorine dioxide in the feeder was set to a maximum of 4,000
ppm. BCWB was added weekly for the first eight weeks, then daily
for the next three weeks, and weekly for the final three weeks.
The cooling system was run at ca. 2.5 cycles of concentration
during the baseline and trial periods. The source of the make-up
water was city water. A molybdenum-based corrosion inhibitor
67
was used at levels between 2 and 4 ppm Mo6+. The water chemistry
changed little during the trial relative to the baseline period. For
example, during the trial, conductivity was 690 mmhos vs. 740 mmhos
during the baseline period; calcium, as CaCO3, was 255 ppm vs. 305
ppm during the baseline period; total hardness, as CaCO3, was 335
ppm vs. 380 ppm during baseline period. The pH of the water was
fairly high, at 8.5 to 8.8 vs. 8.3 to 8.9 during the baseline period.
Figure 3 is a graph showing the effect of time since treatment on
microbial counts for six separate time intervals during the trial. It
shows that, as expected (with a few exceptions), counts are typically very low immediately after treatment and then rise with time
between treatments. In only one case (+ sign in Figure 3) is an
earlier count higher than a later count, and in that case both readings are relatively low. Consequently, data taken just prior to
retreatment represents a worst-case evaluation, and those are the
same data presented in Figure 4.
Figure 4 is a plot of microbial count and BCWB dose rate as a
function of time during the two periods of weekly addition. Initial
weekly dose rates were 180 grams of BCWB/1,000 gallons of water,
and microbial counts fell to zero. However, that result was later
found to be invalid due to a valve failure that caused the tower to
be flooded constantly with fresh, city water. When that was corrected, the weekly dose rate of BCWB was varied between ca. 90
and 180 grams/1,000 gallons until it was determined that acceptable
microbial counts (<104 CFU/ml) could be achieved at an average
dose rate of 155 grams/1,000 gallons/week.
Figure 5 is a graph of microbial counts and BCWB dose rate (in
grams for the entire 5,500-gallon tower) as a function of time during
the period of daily additions. It shows that dose rates may be
reduced relative to weekly addition and microbial counts can still
remain within an acceptable range (< 104 CFU/ml). Optimum control
was achieved at an average dose rate of 110 grams of BCWB/1,000
gallons/week using daily additions. This represents a 29% reduction in BCWB dosage versus the optimal weekly dosage.
Figure 6 is a graph of chlorine dioxide residual measured either 30
minutes or 60 minutes after dosing with BCWB during periods of
weekly addition. Water samples were collected at the circulation
pump discharge. The graph shows that chlorine dioxide residual
increased with BCWB dose. It is also noted that the residual after
60 minutes was consistently lower than it was after 30 minutes,
indicating loss of chlorine dioxide from the system after the 30minute interval. However, chlorine dioxide residuals were measured up to two hours after dosage, at which point readings were
no longer taken. Average chlorine dioxide residuals were slightly
below 0.1 ppm after two hours. The data in Figure 6 also show that
in this tower at the optimum weekly dose rate of ca. 130 grams/1,000
gallons, the chlorine dioxide residual after 60 minutes was in the
range of 0.1 ppm.
68
Tests were also carried out to assess the impact of chlorine dioxide
dosage on corrosion. Rates were measured using test coupons of
copper and mild steel during the period of BCWB use. Observed
corrosion rates were 0.25 mpy (90-day basis) for mild steel and 0.09
mpy (90-day basis) for copper, both excellent values. A baseline
comparison was run on two mild steel coupons after the trial when
the addition of chlorine bleach was resumed. The average corrosion rates were 0.33 mpy (180-day basis).
Conclusions
1.
BASF Cooling Water Biocide (BCWB) was able to control
planktonic microbial counts to less than or equal to the
target value of 104 CFU/ml at dose rates between 110 and
275 grams/1,000 gallons/week.
2.
A 29% reduction in the dosage of BCWB was achieved
through daily addition versus weekly addition. Based on
this observation, an automated daily feeder has been developed.
3.
Microbial control was achieved with a chlorine dioxide residual of 0.1 ppm or greater measured at the pump discharge at a time between 30 and 60 minutes from dosing.
Thus, for effective control of microbiological growth, it is
recommended that a chlorine dioxide residual of at least 0.1
ppm be achieved within 60 minutes of BCWB addition.
4.
Microbial control levels were at least equal to those achieved
using the prior commercial biocides at their recommended
dose rates.
References
1.
Gates, D. 1998 The Chlorine Dioxide Handbook. Denver:
Ammerican Water Works Association.
2.
Simpson, G. D. 2005 Practical Chlorine Dioxide , Vol. I:
Foundations. Colleyville, Texas: Greg D. Simpson & Associates.
3.
Simpson, G. D. 2005 Practical Chlorine Dioxide , Vol. II:
Applications. Colleyville, Texas: Greg D. Simpson & Associates.
4.
BASF Corporation internal data, unpublished.
5.
Puckorius, P. R., Puckorius, D. A., Speronello, B. “New Solid
Chlorine Dioxide Tablet as Cooling Water Micro-Bio Control – Case Histories / Application Data”, paper presented
at 2005 AWT Annual Conference & Exposition, Palm
Springs, CA, September 20, 2005.
6.
Service of the Elyria, OH cooling tower was provided by
Crown Solutions, Inc. of Dayton, OH.
69
Construction Productivity Guidelines for
Field Erected Cooling Towers
By
Jess Seawell, P.E.
Jim Baker
Composite Cooling Solutions, L.P.
INTRODUCTION:
The Purpose of this paper is to provide a better
understanding of labor productivity on field
erected cooling tower projects and how it affects Jess Seawell
the overall project. Within the past 20 years there has been significant research in construction labor productivity which provides an
increasing amount of empirical data as to the effects of various
factors on construction labor productivity. Most cooling tower
manufacturers have researched this subject and have their own
guidelines to follow which should fall within this information presented.
Much of the information used in this paper was taken from the
Construction Law Library and compiled by Mr. William
Schwartzkoph. Other noteworthy sources of information used came
from the Department of Labor Bulletin No. 917, the Business
Roundtable Report, the Construction Industry Institute Study, the
U.S. Army Corps of Engineers Study and Construction Productivity Studies and Data compiled by Composite Cooling Solutions.
Although there are many factors affecting a cooling tower construction project from a productivity standpoint, we will focus on
the five areas we feel are most pertinent. They are Overtime Productivity, Weather Productivity, Schedule Acceleration, Experience
Learning Curves, and Change Order Productivity.
Labor Productivity
Cooling tower construction contracts have two major types of costs:
fixed and variable.
Fixed costs are those costs which the contractor procures on a
fixed price subcontract or purchase order. The fixed costs are inherently lower in risk, because the contractor has fixed them through a
contract. Risks do exist, such as the financial failure or default of
either a vendor or subcontractor, or the installation of defective or
faulty work by a subcontractor or vendor; but the risks are much
less that the risks in variable-cost items.
Variable costs are items such as labor, supervision, equipment and
job overhead. Extensive literature has been published about delay
claims which principally are claims related to the extended duration
of the job and the resulting extended jobsite overhead costs. However, the major variable risk component on a cooling tower construction project is labor and supervision, not extended jobsite
overhead. Equipment, on many projects can be a significant cost;
however, equipment costs tend to be proportional to labor costs. It
is uncommon to have significant increase in equipment costs without significant increases in labor costs.
surprising because supervision and labor hours
frequently for many reasons stemming from the
contractor or the owner. This is an oversimplification of the problems because field cost overruns
on a project can and do result from a variety of
causes. The major areas of field labor cost increase
include Schedule Acceleration, Changes in the
Jim Baker
Work, Management Characteristics, Project Characteristics, Labor and Morale, and Project Location. Within each of
these major areas, there are significant subcategories. These subcategories are listed below:
1. Schedule Acceleration
Overcrowding
Stacking of trades
Overtime
Concurrent operations
2. Changes in work
Additional quantities of work
Learning curve changes
Delays
Engineering errors & omissions
Rework of already installed work
Changes to the plans and specifications
3. Management Characteristics
Material and tool availability
Management control
Project team
Dilution of supervision
4. Project Characteristics
Project size
Work type
Workforce size
Joint occupancy
Height of building
Fast track construction
Site access
Site conditions
5. Labor and Morale
Quality of craftsman
Quality assurance/quality control practices
Rework and errors
Absenteeism
Craft turnover
Fatigue
Morale
Wages
Incentives
On many cooling tower construction projects, the largest single
area of cost overrun is in supervision and or labor cost. This is not
70
71
6.
Project Location/External Conditions
Weather
Altitude
Area population
Commuting time
Availability of skilled labor
Economic activity in area
All of these categories, as well as other factors can and do affect
project field costs on large cooling tower projects. The existence of
a field cost overrun is not proof that an event entitling a contractor
to damages occurred, because cost overruns can occur for a variety of reasons, not all of which entitle a contractor to compensation. It is frequently difficult to link the causation in a claim to the
damages suffered.
Defining Labor Productivity
In order to understand the factors affecting construction labor productivity, it is necessary to define labor productivity. Productivity
is defined as the units of work accomplished for the units of labor
expended. In simple terms, productivity is defined in the following
formula:
Labor Productivity = Outputs
Inputs
Greater labor productivity, therefore, is greater output for the same
level of input. In the construction industry, the reciprocal is how
productivity is frequently expressed, that is, man-hours per unit of
work. When productivity is expressed in man-hours per unit, greater
productivity means a smaller number, or less man-hours expended
per unit of work.
Construction Productivity = Man-Hours
Unit of Work
Contractors are extremely interested in labor productivity and tend
to view it in narrowly-defined units of work. This is because contractors estimate work and take on fixed-price contracts based upon
estimated unit rates for productivity. Frequently the contractors
view productivity in the following way:
Labor Productivity = Labor Costs or Labor Work Hours = Unit Rate
Output-Units of Production
This formula is often referred to as the unit rate. The absolute
values of these rates are important to the contractor for estimating
purposes.
Once a project starts, a contractor’s focus changes. During the
performance of a job, it is the performance factor that contractors
frequently focus on. The performance factor is defined in the following formula:
Performance Factor = Estimated Unit Rate
`
Actual Unit Rate
On a job site, contractors often refer to productivity when they are
actually talking about the variance in performance factor, that is,
how the actual unit rates differ from the estimated unit rates.
Methods of Productivity Measurement
Many cooling tower contractors have detailed cost accounting
systems that allow them to track either productivity or surrogates
for productivity. Measuring unit cost in dollars is a surrogate measure of productivity because the dollar cost can be affected by
72
other factors, for example, overtime or wage rate variances that do
not reflect actual productivity (man-hours per unit). These cost
accounting systems, whether in unit cost or unit rates, allow on the
job tracking of the actual productivity for a project in comparison
with estimated productivity. Contractor cost accounting systems
focus on unit rates of production in either dollars or man-hours.
These systems are frequently, but not always, tied directly into the
contractor payroll systems so they are gathering data directly from
field inputs.
OVERTIME PRODUCTIVITY
Overtime is the use of labor in excess of 40 hours per man per week.
Because overtime is paid at a premium wage rate, such as time and
a half or double time, it is inherently more expensive because the
cost per hour for the overtime hours worked is greater. It is generally acknowledged that working prolonged programs of overtime
causes reduced productivity. That is, the units of work produced
(output) are less per hour. Reduced productivity is a hidden cost of
overtime.
Overtime is worked on cooling tower projects for several different
reasons. It can be worked on a sporadic or spot basis to handle
unexpected problems that arise, such as weather changes and operation changes, or to finish time critical work. Many times there is
time critical work that must be finished as soon as possible so the
project can move forward. It can also be used to produce more
work in a given number of days which could reduce the field costs
of supervision and rental. Also, it may be necessary to overcome
delays or because a project needs to be done in a less than optimum length of time for external reasons.
Overtime can also attract more workers to a project where labor is
difficult to obtain. Many large cooling tower projects are more
easily manned, whether union or non-union if a certain amount of
overtime is guaranteed. Craftsman and laborers tend to migrate to
jobs where they can make the most money in the least amount of
time.
Following are three tables reflecting the effects on productivity
with varying work schedules. We must note that the work schedules in the original tables presented by the Corps of Engineers only
reflect 5, 6, or 7 day work weeks. Many cooling tower projects are
manned with 4-day, 10-hour per day work weeks. We have added
this category to Chart 2.1. Because of the non-productive activities of a normal day, such as meetings, getting tools out and putting them away, and lunch breaks have been eliminated from the 5th
day, we have found that productivity does not decrease when working 4, 10-hour day as opposed to working 5, 8-hour days.
There is also another concept which is used when estimating
projects and that is referred to as “The Point of No Return.” Working a prolonged overtime schedule can cause less output per week
than working a normal schedule. The point of no return is reached
at that point in the overtime schedule when the cumulative work
output in a week of overtime is no greater than the work output that
would have been achieved in a normal 40-hour week.
73
TABLE 2.1
TABLE 2.3
SCHEDULED EXTENDED OVERTIME
EXTENDING THE WEEK PRODUCTIVITY
PRODUCTIVITY PROJECTIONS
(1 Week Only)
(2-10 WEEKS)
Scheduled Days
Scheduled Hours
Percent Productivity
10
8
9
10
11
12
8
9
10
11
12
8
9
10
11
12
100%
100%
95%
92%
89%
86%
97%
88%
82%
78%
75%
92%
83%
78%
75%
72%
4
5
5
5
5
5
6
6
6
6
6
7
7
7
7
7
(1) Bureau of Labor, Statistics, U.S. Department of Labor,
Bulletin No. 917.
NOTE:
1) Absenteeism increases as number of hours of work increase.
2) Injuries and the rate of incidence of injuries increase with
the number of work hours per week.
3) Scheduled overtime reduces productivity.
Scheduled Days
Scheduled Hours per Day
5
6
7
8
8
8
100%
98%
95%
2) National Electrical Contractors Association (NECA) Study; Overtime
and Productivity in Electrical Construction, 7-9 (2nd edition, 1989).
WEATHER PRODUCTIVITY
Cooling tower construction is positively impacted by good weather
and negatively impacted by adverse weather. Adverse weather is
conditions created by natural forces that are abnormal for the area
and are detrimental to the construction of the project. Because of
the nature of cooling tower construction, many times being performed in a wet environment, adverse weather conditions can actually make or break a job.
Events such as high or low temperatures, humidity, rain, snow and
high winds have effects on labor productivity. To the extent that
such events can be expected and are reasonable, they should be
considered prior to constructing a project. However changes to a
project schedule can cause work which was planned for certain
weather period and was shifted to a more severe weather period
with resulting changes in labor productivity. Remember, cold or
adverse weather affects workers not only physiologically, but also
psychologically. Different workers accept different conditions differently.
If the work is required to proceed through abnormal weather conditions or it causes added cost due to delaying the project until a
later date, a significant change in labor productivity may occur.
TABLE 2.2
Case Law
SPOT OVERTIME UNSCHEDULED
A contractor normally assumes the risk of loss for normal weather
problems. This risk of loss may be handled in two ways. The owner
may:
PRODUCTIVITY PROJECTIONS
(1 Week or Less Duration)
1)
Scheduled Days Scheduled Hours
5
5
5
5
74
8
8
8
8
Actual Hours
9
10
11
12
100%
98%
95%
92%
Grant a time extension but with no additional compensation or;
2) Require the contractor meet the completion date in spite of
adverse weather.
Some contracts allow for weather time extensions for bad weather
in excess of normal bad weather or provides for time extensions for
any lost bad weather days. If a contractor is pushed into bad weather
operation through the actions of the owner, the contractor may
have a claim for additional compensation.
75
TABLE 3.1
Construction Productivity as Function of
Temperature and Relative Humidity
Engineers states, the optimum crew size is the minimum number of
workers required to perform the task within the allocated time frame.
Relative Humidity (%)
Temperature
(ºF)
(1)
5
15
25
35
45
55
65
75
85
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10) (11)
-20
-10
0
10
20
30
40
50
60
70
80
90
100
110
120
0.28
0.44
0.59
0.71
0.81
0.90
0.96
1.00
1.00
1.00
1.00
0.95
0.81
0.58
—
0.27
0.43
0.58
0.71
0.81
0.90
0.96
1.00
1.00
1.00
1.00
0.95
0.81
0.58
0.28
0.25
0.42
0.57
0.70
0.81
0.90
0.96
1.00
1.00
1.00
1.00
0.94
0.80
0.58
0.28
0.22
0.40
0.56
0.70
0.81
0.90
0.96
1.00
1.00
1.00
1.00
0.93
0.79
0.57
0.28
0.18
0.38
0.54
0.69
0.81
0.90
0.96
1.00
1.00
1.00
0.00
0.92
0.77
0.55
0.25
0.13
0.34
0.52
0.67
0.80
0.89
0.96
1.00
1.00
1.00
0.99
0.90
0.74
0.51
0.21
0.15
0.29
0.49
0.65
0.79
0.89
0.96
1.00
1.00
1.00
0.98
0.88
0.71
0.47
0.15
—
0.21
0.44
0.62
0.77
0.89
0.96
1.00
1.00
1.00
0.96
0.85
0.67
0.41
0.07
—
0.10
0.36
0.58
0.75
0.88
0.96
1.00
1.00
1.00
0.95
0.82
0.61
0.32
—
3)
95
—
—
0.23
0.50
0.71
0.87
0.96
1.00
1.00
1.00
0.93
0.78
0.54
0.21
—
Another very real problem in our cooling tower industry that stems
from an accelerated schedule in a refinery, chemical or power plant
installation is “Trade Stacking”. Trade stacking is the term most
often applied when work areas become crowded with different
trades due to a desire to accelerate the project. This can be a
problem if different trades are attempting to work in the same area.
If the job is managed properly, productivity loss does not always
occur. A good example would be jobs where different trades can be
working in separate areas. However, a loss of productivity almost
always occurs when crowding different crews into the same work
area. The Corps of Engineers states, “Crowding occurs when more
workers are placed in a given area than can function effectively”.
Attached below are charts derived from the U.S. Army Corps of
Engineers which show the impact of Crew Over-Manning and Crew
Crowding.
Enno Koehn & Gerald Brown, Climatic Effects on Construction,
Journal of the Construction Engineering and Management, Vol.
III, No. 2 129-37 (June 1985)
SCHEDULE ACCELERATION
Acceleration of a cooling tower project occurs when the construction schedule for the project is shorter than what would be required
using normal sequences of construction on the normal agreed upon
schedule. Accelerated schedules can be agreed upon in the bid
stages and contracted as such and become the normal working
schedule. Disputes arise when the contractor is requested to complete the job in a shorter schedule than he believes was originally
agreed upon in the original contract or the contractor is asked to
maintain the original schedule after a change in scope or unforeseen conditions occur.
The requirement to accelerate the schedule can exist either because
the contractor is behind schedule due to its own actions or for the
convenience of the owner of the project who wants the project
completed earlier than the original schedule.
4) U.S. Army Corps of Engineers, Modification Impact Evaluation
Guide (July 1979)
A contractor may also be accelerated to recover lost time as a result
of delays by third parties, inadequate deliveries of materials or
equipment, permits, design changes, or other items. Acceleration
can also occur when additional work is added to the original scope
through contract changes but additional time to complete the project
is not available or not granted.
Generally, accelerated cooling tower construction work adversely
affects productivity. When construction work is accelerated, the
contractor must change schedules and methods, possibly hire additional workers, possibly work overtime, or even add shifts. It also
affects engineering, support personnel, and materials. All of these
may or may not be available. It is a combination of these changes
that affect productivity.
When the schedule is accelerated on any cooling tower project,
more than likely, additional workers will be added to the existing
crew. Cooling tower contractors must be very careful not to overman the crew. Increasing the number of workers above the optimum level on a project causes productivity losses. The Corps of
76
5) U.S. Army Corps of Engineers, Modification Impact Evaluation
Guide (July 1979)
77
EXPERIENCE LEARNING CURVES
Basic experience or learning curve theory states that each
time the number of repetitions doubles, the cumulative manhours per unit declines by a constant fixed percentage of the
previous cumulative average units. This percentage is frequently identified as the experience factor or constant. When
applying this theory to a cooling tower project, we find that
this is true to a certain extent. When constructing a 10-cell
cooling tower, we find that productivity definitely does increase due to repetition up to about 5-cells, depending on the
experience level of the crew, but productivity on the remaining 5-cells remains more constant.
Delays and Interruptions
Experience curves depend upon continuous repetitions. If repetitive actions are delayed or interrupted, there will not be
the same man-hours rate as prior due to the disruption when
the construction resumes. Thus, the result of forgetting how
the tasks were performed occurs. The degree of forgetting is
related to the length of the delay.
Additional Factors Affecting Experience Curves
The number of repetitions of an identical activity is not the
only factor which affects experience curves or project productivity.
The following factors also have a profound effect on a project
learning curve
1) Job familiarization by the workmen through repetitive
operations
2) Equipment and crew coordination
3) Job organizational planning
Number of Cells
1
2
3
4
5
6
7
8
9
10
Marginal Unit Cumulative Average
Rate-Hours
Rate-Hours
1.00
95
.90
85
.80
.775
.750
.725
.700
.675
1.00
.975
95
.925
90
.879
.861
.843
.827
.813
NOTES:
1) Cells 1-5 assumes a 95% Learning Factor
2) Cells 6-10 assumes a 97.5% Learning Factor.
3) This chart does not apply to total units if construction
is interrupted during execution of construction.
4) This chart is based on a typical 10-cell tower. Any
cooling tower greater than 5-cells should fall within
this data.
5) This chart is a conservative approach to the learning
curve productivity of cooling tower construction. Different crews may vary based on previous experience.
6) The data was derived by the methodology of Mr.
Schwartzkopf and utilizing actual Composite Cooling
Solutions construction data.
4) Engineering accuracy
CHANGE ORDER PRODUCTIVITY
5) Day-to-day supervision
Definition of Change Orders
Change order is a term frequently used in the construction
industry to label any modification or alteration of the work. A
change is a modification in the original scope of work, contract schedule, or cost of the work. A change order is a formal contract modification incorporating a change into the
contract.
6) Development of improved construction methods
7) Sufficient work space for crews
8) Efficient material supply system
9) More efficient use of tools and equipment
10) Changes to product design
11) Change in site conditions
78
TABLE 5.1
Learning Curve Productivity Factors
Changes and change orders are a normal part of the cooling
tower construction process. If a very tight specification is
initially written and enforced, change orders will be minimized,
but seldom eliminated. Typically, although by no means always, change orders increase both the amount and the cost
of the construction contract because they add to or change
the work to be performed. Changes frequently cause disputes between owners and contractors over the cost of the
change. It is generally recognized that changes made during
performance of the work are more expensive than if the same
work had been required to be performed under the original
contract.
Changes can arise from a variety of causes. These causes
include:
1) Defective plans and specifications
2) Changes in scope caused by user changes
3) Differing site conditions
4) Schedule delays
5) Value engineering
6) Substitutions
7) Incomplete design
These changes can cause the construction cost to change on
both the changed and unchanged work.
The Impact of Change Orders
Change orders can have significant impacts on cooling tower
construction projects. The changes themselves can delay the
project. As change orders increase, they can affect the unchanged work. The Construction Industry Institute (CII)
which has studied
CONCLUSION:
Properly analyzing the costs of labor productivity in field
erected cooling tower construction should aid contractors and
owners in their decision making processes on all cooling tower
projects. Understanding how labor productivity is affected
by various events should make the planning and scheduling
of cooling tower projects by both contractors and owners
more sensitive to labor productivity issues. All cooling tower
projects are different and no set method applies on every job
to accurately estimate labor productivity. The actual factors
involved in each situation must be carefully calculated. There
have been countless studies done on this subject and this paper only represents a few. Numerous labor institutions as
well as actual cooling tower manufacturers continue to accumulate data to more accurately calculate the impact of labor
productivity. We trust that the information put forth in this
paper will aid all parties in their future cooling tower projects.
construction changes and change orders states the following:
When the changes are small in scope and few in number, the
impact is real, but relatively minor. The change may or may
not affect the critical path, and even when it does, the fundamental logic of the work remains in tact. With respect to loss
of productivity, the major effect is loss of momentum, loss of
efficiency, and extended overhead associated with administration of changes and other aspects of the work.
When there are multiple changes on a project and they act in
sequence or concurrently there is a compounding effect –
this is the most damaging consequence for a project and the
most difficult to understand and manage.
The net effect of the individual changes is much greater than
a sum of the individual parts. Only may there be increase in
cost and time required that the project logic may have to be
redone.
All parties involved in a cooling tower project need to recognize the potential impact of project changes. To minimize the
impact of changes, the changes should be issued as early as
possible. The drawings and documents relating to the change
should be issued in sufficient numbers to allow them to go to
the field. Whenever possible, separate crews should be assigned to do the changed work to minimize disruption of the
ongoing unchanged work.
79
Cooling Technology Institute
Licensed Testing Agencies
For nearly thirty years, the Cooling Technology Institute has
provided a truly independent, third party, thermal performance
testing service to the cooling tower industry. In 1995, the CTI
also began providing an independent, third party, drift
performance testing service as
well. Both these services are
administered through the CTI
Multi-Agency Tower Performance Test Program and provide
comparisons of the actual operating performance of a specific
tower installation to the design
performance. By providing such
information on a specific tower
installation, the CTI MultiAgency Testing Program stands
in contrast to the CTI Cooling
Tower Certification Program
which certifies all models of a
specific manufacturer's line of cooling towers perform in
accordance with their published thermal ratings.
To be licensed as a CTI Cooling Tower Performance Test
Agency, the agency must pass a rigorous screening process and
demonstrate a high level of technical expertise. Additionally, it
must have a sufficient number of test instruments, all meeting
rigid requirements for accuracy and calibration.
Once licensed, the Test Agencies
for both thermal and drift testing
must operate in full compliance
with the provisions of the CTI
License Agreements and Testing
Manuals which were developed
by a panel of testing experts
specifically for this program. Included in these requirements are
strict guidelines regarding conflict
of interest to insure CTI Tests are
conducted in a fair, unbiased
manner.
Cooling tower owners and manufacturers are strongly encouraged
to utilize the services of the licensed CTI Cooling Tower
Performance Test Agencies. The currently licensed agencies are
listed below.
Licensed CTI Thermal Testing Agencies
License
Type*
Agency Name
Address
Contact Person
Website / Email
Telephone
Fax
A,B
Clean Air Engineering
7936 Conner Rd
Powell, TN 37849
Kenneth Hennon
www.cleanair.com
[email protected]
800.208.6162
865.938.7569
A, B
Cooling Tower Technologies Pty Ltd
PO Box N157
Bexley North, NSW 2207
AUSTRALIA
Ronald Rayner
[email protected]
61 2 9789 5900
61 2 9789 5922
A,B
Cooling Tower Test Associates, Inc.
15325 Melrose Dr.
Stanley, KS 66221-9720
Thomas E. Weast
www.cttai.com
[email protected]
913.681.0027
913.681.0039
A, B
McHale & Associates, Inc
6430 Baum Drive
Knoxville, TN 37919
Thomas Wheelock
www.mchale.org
[email protected]
865.588.2654
425.557.8377
* Type A license is for the use of mercury in glass thermometers typically used for smaller towers.
Type B license is for the use of remote data acquisition devices which can accommodate multiple measurement locations required by larger towers.
Licensed CTI Drift Testing Agencies
80
Agency Name
Address
Contact Person
Website / Email
Telephone
Fax
Clean Air Engineering
7936 Conner Rd
Powell, TN 37849
Kenneth Hennon
www.cleanair.com
[email protected]
800.208.6162
865.938.7569
McHale & Associates, Inc.
6430 Baum Drive
Knoxville, TN 37919
Thomas Wheelock
www.mchale.org
[email protected]
865.588.2654
425.557.8377
81
Cooling Towers Certified by CTI Under STD-201
As stated in its opening paragraph, CTI Standard 201... “sets forth a program whereby the Cooling Technology Institute will certify that all models
of a line of water cooling towers offered for sale by a specific Manufacturer
will perform thermally in accordance with the Manufacturer’s published ratings...” By the purchase of a “certified” model, the User has assurance that
the tower will perform as specified, provided that its circulating water is no
more than acceptably contaminated-and that its air supply is ample and
unobstructed. Either that model, or one of its close design family members,
will have been thoroughly tested by the single CTI-licensed testing agency
for Certification and found to perform as claimed by the Manufacturer.
CTI Certification under STD-201 is limited to thermal operating conditions
with entering wet bulb temperatures between 12.8°C and 32.2°C (55°F to
90°F), a maximum process fluid temperature of 51.7°C (125°F), a cooling
range of 2.2°C (4°F) or greater, and a cooling approach of 2.8°C (5°F) or
greater. The manufacturer may set more restrictive limits if desired or publish less restrictive limits if the CTI limits are clearly defined and noted in the publication.
Following is a list of cooling tower models currently certified under STD-201. They are part of product lines offered by Advance GRP
(Advance) Cooling Towers, Pvt, Ltd.; Aggreko Cooling Tower Services; Amcot Cooling Tower Corporation; AONE E&C Corporation Ltd;
Baltimore Aircoil Company, Inc.; Delta Cooling Towers, Inc.; Evapco, Inc.; Fabrica Mexicana De Torres, S.A.; HVAC/R International, Inc.;
Imeco, div of York International; Ltd; KIMCO (Kyung In Machinery Company, Ltd.); Liang Chi Industry Company, Ltd.; Mesan Cooling
Tower, Ltd; Nihon Spindle Manufacturing Company, Ltd.; Polacel b.v.; Protec Cooling Towers; RSD Cooling Towers; Ryowo (Holding)
Company, Ltd; SPX Cooling Technologies; Ta Shin F.R.P. Company, Ltd.; The Cooling Tower Company, L.C; The Trane Company; Tower
Tech, Inc; and Zhejiang Jinling Refrigeration Engineering Company who are committed to the manufacture and installation of fullperformance towers. In competition with each other, these manufacturers benefit from knowing that they each achieve their published
performance capability. They are; therefore, free to distinguish themselves through design excellence and concern for the User’s
operational safety and convenience.
Those Manufacturers who have not yet chosen to certify their product lines are invited to do so at the earliest opportunity. You can
contact Virginia A. Manser, Cooling Technology Institute, PO Box 73383, Houston, TX 77273 for further information.
82
83
Cooling Towers Certified by CTI Under STD-201
Advance GRP (Advance) Cooling Towers, Pvt., Ltd. – Advance 2020 Cooling Tower Line
CTI Certification Validation Number 07-31-01 – August 28, 2007 (Revision 0)
(51 counter-flow, induced-draft models)
CTI Model Listing: http://www.cti.org/towers/advance.pdf
Information: http://www.frpcoolingtowers.com/products.htm
Selection: http://www.frpcoolingtowers.com/aseries.htm
Aggreko Cooling Tower Services – AG Cooling Tower Line
CTI Certification Validation Number 08-34-01 – July 25, 2008 (Revision 0)
(1 counter flow, forced draft model)
CTI Model Listing: http://www.cti.org/towers/aggreko.pdf
Information: http://www.aggreko.com/NorthAmerica/products__services/
aggreko_cooling_tower_services/ACTS_AG10-1.aspx
Selection: http://www.aggreko.com/NorthAmerica/products__services/aggreko_cooling_tower_services/
CTI_Tables_in_PDF.aspx
Amcot Cooling Tower Corporation – LC Cooling Tower Line
CTI Certification Validation Number 96-20-01 – September 8, 2007 (Revision 2)
(8 cross-flow, induced-draft models)
CTI Model Listing: http://www.cti.org/towers/amcot.pdf
Information: http://www.amcot.com/temp/lc_char1.pdf
Selection: http://www.amcot.com/temp/lc_char1.pdf
AONE E&C Corporation, Ltd. – ACT-R and -RU Series Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/aone.pdf
Information (General): http://www.a-oneenc.co..kr/product_sub01.html
Information (ACT-R Models): http://www.a-oneenc.co.kr/crossflowtype01.html
Information (ACT-RU Models): http://www.a-oneenc.co.kr/crossflowtype02.html
Selection: http://a-oneenc.co.kr/bbs/data/pds/SELECTION_TABLE(1).jpg
Baltimore Aircoil Company, Inc. – ACT Series Cooling Tower Line
CTI Certification Validation Number 08-11-12 – October 14, 2008 (Revision 0)
(72 counter flow, induced draft models)
CTI Model Listing: http://www.cti.org/towers/BAC-ACT.pdf
Information: http://www.baltimoreaircoil.com/english/products/ct/act_asia/index.html
Selection: http://www.baltimoreaircoil.com/english/products/ct/act_asia/act_model.html
84
Baltimore Aircoil Company, Inc. – FXT Series Cooling Tower Line
(38 cross-flow, forced-draft models)
CTI Model Listing: http://www.cti.org/towers/BAC-FXT.pdf
Information: http://www.baltimoreaircoil.com/english/products/ct/fxt/index.html
Selection: http://www.baltimoreaircoil.com/english/info_center/pss/index.html
Baltimore Aircoil Company, Inc. – FXV Closed Circuit Cooling Tower Line
CTI Certification Validation Number 98-11-09 – April 11, 2007 (Revision 6)
(222 closed-circuit, induced-draft models)
CTI Model Listing: http://www.cti.org/towers/BAC-FXV/pdf
Information: http://www.baltimoreaircoil.com/english/products/cccs/fxv/index.html
Baltimore Aircoil Company, Inc. – PT2 Series Cooling Tower Line
CTI Certification Validation Number 07-11-11 – May 5, 2007 (Revision 0)
CTI Model Listing: http://www.cti.org/towers/BAC-PT2/pdf
Information: http://www.baltimoreaircoil.com/english/products/ct/pt2/index.html
Baltimore Aircoil Company, Inc. – Series V Closed Circuit Cooling Tower Line
(265 VF1 & 103 VFL closed-circuit, forced-draft models)
CTI Model Listing: http://www.cti.org/towers/BAC-closed.pdf
Information VF1: http://www.baltimoreaircoil.com/english/products/cccs/vccct/index.html
Information VFL: http://www.baltimoreaircoil.com/english/products/cccs/vccct/lowprofile.html
Baltimore Aircoil Company, Inc. – Series V Open Cooling Tower Line
(34 VT0 counter-flow, forced-draft models)
(81 VT1 counter-flow, forced-draft models)
(61 VTL counter-flow, forced-draft models)
CTI Model Listing: http://www.cti.org/towers/BAC-open.pdf
Information VT0 & VT1: http://www.baltimoreaircoil.com/english/products/ct/vt/index.html
Information VTL: http://www.baltimoreaircoil.com/english/products/ct/vt/lowprofile.html
85
Baltimore Aircoil Company, Inc. – Series 1500 Cooling Tower Line
CTI Certification Validation Number 98-11-08 – June 30, 2006 (Revision 6)
CTI Model Listing: http://www.cti.org/towers/BAC-1500.pdf
Information: http://www.baltimoreaircoil.com/english/products/ct/s1500/index.html
Baltimore Aircoil Company, Inc. – Series 3000A, C, & D Cooling Tower Line
CTI Certification Validation Number 92-11-06 – November 2, 2007 (Revision 8)
CTI Model Listing: http://www.cti.org/towers/BAC-3000.pdf
Information: http://www.baltimoreaircoil.com/english/products/ct/s3000/index.html
Delta Cooling Towers, Inc. – TM Series Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/delta.pdf
Information: http://www.deltacooling.com/tm.html
Selection: www.deltacooling.com/tmtable.html
Evapco, Inc. – AT Series Cooling Tower Line
(733 AT, USS/UAT, UT counter-flow, induced-draft models)
CTI Model Listing: http://www.cti.org/towers/Evapco-AT.pdf
Information - AT Models: http://www.evapco.com/atcooling.asp
Information - USS/UAT Models: http://www.evapco.com/usscooling.asp
Information - UT Models: http://www.evapco.com/utcooling.asp
Selection All Models: www.evapco.com/evapspec/welcome.asp
Evapco, Inc. – ESWA Line of Closed Circuit Coolers
CTI Model Listing: http://www.cti.org/towers/Evapco-ESWA.pdf
Information: http://www.evapco.com/esw_brochures.asp
Selection: http://www.evapco.com/evapspec/welcome.asp
Evapco, Inc. – LPT Cooling Tower Line
CTI Certification Validation Number 05-13-04 – January 3, 2005 (Revision 0)
(43 counter-flow, forced-draft models)
CTI Model Listing: http://www.cti.org/towers/Evapco-LPT.pdf
Information: http://www.evapco.com/lptcooling.asp
86
Evapco, Inc. – LSTB Cooling Tower Line
CTI Certification Validation Number 05-13-03 – January 3, 2005 (Revision 0)
(57 counter-flow, forced-draft models)
CTI Model Listing: http://www.cti.org/towers/Evapco-LSTB.pdf
Information: http://www.evapco.com/lstbcooling.asp
Fabrica Mexicana De Torres, S. A., Reymsa Cooling Towers – GHR Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/Fabrica-GHR.pdf
Information: http://www.reymsa.com/images/ghrfg.pdf
Selection: http://www.reymsa.com/images/ghrfg.pdf
Fabrica Mexicana De Torres, S. A., Reymsa Cooling Towers – HR Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/Fabrica-HR.pdf
Information: http://www.reymsa.com/images/hrfg.pdf
Selection: http://www.reymsa.com/images/hrfg.pdf
HVAC/R International, Inc. – Therflow Series Cooling Tower Line
(27 cross-flow, forced-draft models)
CTI Model Listing: http://www.cti.org/towers/HVACR.pdf
Information: http://www.hvacrinternational.com/pdf/TFW-Catalog.pdf
Selection: http://www.hvacrinternational.com/pdf/TFW-Catalog.pdf
Imeco, Div. of York International – IMC Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/Imeco.pdf
Information: http://www.johnsoncontrols.com/publish/us/en.html
Selection: http://www.johnsoncontrols.com/publish/us/en.html
KIMCO (Kyung In Machinery Company, Ltd.) – CKL Line of Closed Circuit Cooling Towers
CTI Model Listing: http://www.cti.org/towers/KIMCO-CKL.pdf
Information: http://www.kyunginct.co.kr/eng/prod1.htm
Selection: http://www.kyunginct.co.kr/eng/webcal1.htm
87
KIMCO (Kyung In Machinery Company, Ltd.) – EnduraCool Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/KIMCO-EnduraCool.pdf
Information: http://www.kyunginct.co.kr/eng/prod1.htm
Selection: http://www.kyunginct.co.kr/eng/webcal1.htm
Liang Chi Industry Company, Ltd. – LC Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/LiangChi.pdf
Information: http://www.liangchi.com.tw/Model/en/product/product_3.jsp?pi_id=PI1190774064702#a05
Selection: http://www.liangchi.com.tw/Model/en/product/product_3.jsp?pi_id=PI1190774064702#a05
Mesan Cooling Tower, Ltd. – MCR Series Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/Mesan-MCR.pdf
Information: http://www.mesanct.com/html/eng/products/cooling/mcr.htm
Selection: http://www.mesanct.com/images/eng/products/cooling/MCR -Catalogue.pdf
Mesan Cooling Tower, Ltd. – MCR-KM Series Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/Mesan-MCR-KM.pdf
Information: http://www.mesanct.com/html/eng/products/cooling/mcr-km.htm
Selection: http://www.mesanct.com/images/eng/products/cooling/MCR-KM-Catalogue.pdf
Mesan Cooling Tower, Ltd. – MXR Series Cooling Tower Line
(68 cross flow, induced draft models)
CTI Model Listing: http://www.cti.org/towers/Mesan-MXR.pdf
Information: http://www.mesanct.com/html/eng/products/cooling/mxr.htm
Selection: http://www.mesanct.com/images/eng/products/cooling/MXR-Catalogue.pdf
Mesan Cooling Tower, Ltd. – MXR-KM Series Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/Mesan-MXR-KM.pdf
Information: http://www.mesanct.com/html/eng/products/cooling/mxr-km.htm
Selection: http://www.mesanct.com/images/eng/products/cooling/MXR-KM-Catalogue.pdf
88
Nihon Spindle Manufacturing Company, Ltd. – CTA-KX Series Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/CTA-KX.pdf
Information: http://nac.eco.to/ns_de/en/cooling_tower/index.html
Selection: http://nac.eco.to/ns_de/en/cooling_tower/selection_chart1.html
Polacel, b. v. – CR Series Cooling Tower Line
(78 CMC + 180 CMDR counter-flow, induced-draft models)
CTI Model Listing: http://www.cti.org/towers/Polacel-CR.pdf
Information: http://www.polacel.com/Models.asp
Selection: http://www.polacel.com/PolaSelections/
Polacel b. v. – XR Series Cooling Tower Line
(4 XE +16 XL + 27 XT cross-flow, induced-draft models)
CTI Model Listing: http://www.cti.org/towers/Polacel-XR.pdf
Information: http://www.polacel.com/Models.asp
Selection: http://www.polacel.com/PolaSelections/
Protec Cooling Towers, Inc. – FWS Series Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/Protec-FWS.pdf
Information: www.protectowers.com/pdf/crossflow/FWSbrochure%20as%20of%206-29-06.pdf
Selection: http://www.protectowers.com/pdf/crossflow/FWSbrochure%20as%20of%206-29-06.pdf
RSD Cooling Towers – RSS Series Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/RSD-RSS.pdf
Information: http://rsd2.rsd.net/towers/RSS%20Cooling%20Tower%20Catalog.pdf
Selection: http://rsd2.rsd.net/towers/RSS%20Cooling%20Tower%20Catalog.pdf
Ryowo (Holding) Company, Ltd. – FRS Series Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/Ryowo-FRS.pdf
Information: http://www.ryowo.com/FRS.pdf
Selection: http://www.ryowo.com/english/Frsselection.php
89
Ryowo (Holding) Company, Ltd. – FWS Series Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/Ryowo-FWS.pdf
Information: http://www.ryowo.com/FWS.pdf
Selection: http://www.ryowo.com/english/Fwsselection.php
Ryowo (Holding) Company, Ltd. – FXS Series Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/Ryowo-FXS.pdf
Information: http://www.ryowo.com/FXS.pdf
Selection: http://www.ryowo.com/english/Fxsselection.php
SPX Cooling Technologies (Marley) – Aquatower Series Cooling Tower Line
CTI Certification Validation Number 01-14-05 – December 2, 2002 (Revision 1)
CTI Model Listing: http://www.cti.org/towers/SPX-Aquatower.pdf
Information: http://spxcooling.com/en/products/detail/marley-aquatower-cooling-tower/
Selection: http://qtcapps.marleyct.com/update/Login.aspx
SPX Cooling Technologies (Marley) – AV Series Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/SPX-AV.pdf
Information: http://spxcooling.com/en/products/detail/marley-av-series-cooling-tower/
SPX Cooling Technologies (Marley) – MCF Series of Closed Circuit Fluid Cooler Line
CTI Certification Validation Number 07-14-10 – February 28, 2008 (Revision 2)
(75 closed-circuit, forced draft models)
CTI Model Listing: http://www.cti.org/towers/SPX-MCF.pdf
Information: http://spxcooling.com/en/products/detail/marley-mc-fluid-cooler/
SPX Cooling Technologies (Marley) – MCW Series of Cooling Towers
(68 counter flow, forced draft models)
CTI Model Listing: http://www.cti.org/towers/SPX-MCW.pdf
Information: http://spxcooling.com/en/products/detail/marley-mcw-cooling-tower/
90
SPX Cooling Technologies (Marley) – MD Series of Cooling Towers
CTI Model Listing: http://www.cti.org/towers/SPX-MD.pdf
Information: http://spxcooling.com/en/products/detail/marley-md/
SPX Cooling Technologies (Marley) – MHF Series of Closed-Circuit Fluid Cooler Line
CTI Model Listing: http://www.cti.org/towers/SPX-MHF.pdf
Information: http://spxcooling.com/en/products/detail/marley-mh-fluid-cooler/
SPX Cooling Technologies (Marley) – NC Series Cooling Tower Line
(256 NC Class + 93 NC Fiberglass cross-flow, induced-draft models)
CTI Model Listing: http://www.cti.org/towers/SPX-NC.pdf
Information, NC Class: http://spxcooling.com/en/products/detail/marley-nc-class-cooling-tower/
Information, NC Fiberglass: http://spxcooling.com/en/products/detail/marley-nc-fiberglass-cooling-tower/
SPX Cooling Technologies (Marley) – Quadraflow Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/SPX-Quadraflow.pdf
Information: http://spxcooling.com/en/products/detail/marley-quadraflow-cooling-tower/
Ta Shin F. R. P. Company, Ltd. – TSS Series Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/tashin-TSS.pdf
Information: http://www.tower-super.com.tw/ep1.htm
Selection: http://www.tower-super.com.tw/ep4.htm
The Cooling Tower Company, L. C. – Series TCI Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/CoolingTowerCompany.pdf
Information: http://www.ctowers.com/tci.htm
Selection: http://www.ctowers.com/TCIperformance.html
91
The Trane Company – Series Quiet (TQ) Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/Trane.pdf
Information: http://www.trane.com/Commercial/DNA/View.aspx?i=985
Tower Tech, Inc. – TTXE Cooling Tower Line
(18 counter flow, forced draft models)
CTI Model Listing: http://www.cti.org/towers/TowerTechTTXL.pdf
Information: http://www.towertechinc.com/documents/TTXL_Technical_Reference_Guide_09252008.pdf
Selection: http://www.towertechinc.com/documents/TTXL_Technical_Reference_Guide_09252008.pdf
Zhejiang Jinling Refrigeration Engineering Co., Ltd. – JNT Series Cooling Tower Line
CTI Model Listing: http://www.cti.org/towers/Zhejiang.pdf
Information: www.cnjinling.com/english/product_jnt.asp
Information: www.cnjinling.com/china/product_jnt.asp
Selection: www.cnjinling.com/pdf/jnt_e/2.pdf
Selection: www.cnjinling.com/pdf/jnt/2.pdf
For the Current List of Cooling Towers certified by CTI Under STD-201
Please Check the CTI Website: http://www.cti.org/certification.shmtl
92
93
94
95
Index of Advertisers
Advance Cooling Towers .............................. 9
Aggreko Cooling Tower Service .......... 48, 49
AHR Expo ..................................................... 93
Amarillo Gear Company ............................. IBC
Amcot Cooling Tower .................................. 23
American Cooling Tower, Inc. ..................... 33
AMSA, Inc. ............................................ 37, 77
Baltimore Aircoil Company ....................... OBC
Bailsco Blades & Casting, Inc. .................... 39
Bedford Reinforced Plastics ....................... 19
Brentwood Industries .................................. 47
ChemTreat, Inc. ............................................ 51
CleanAir Engineering ..................................... 3
CTI Certified Towers .............................. 82-93
CTI License Testing Agencies ..................... 80
CTI ToolKit .............................................. 94, 95
Composite Cooling Solutions, LP ................. 71
Cooling Tower Resources ........................... 45
Dynamic Fabricators .................................... 59
Emerson Motor Technologies ...................... 53
Fibergrate Composite Structures ................ 17
Gaiennie Lumber Company ........................... 2
Glocon ................................................... 15, 74
H&F Manufacturing ...................................... 13
Howden Cooling Fans ................................... 5
Hudson Products Corporation ..................... 11
Industrial Cooling Towers .................... IFC, 63
Metrix ............................................................ 67
Midwest Towers, Inc. .................................. 65
Moore Fans .................................................. 27
Paharpur Cooling Towers Limited ............... 55
Power-Gen ................................................... 81
Rain for Rent ................................................ 57
Rexnord Industries ...................................... 21
C.E. Shepherd Company, LP ....................... 35
Spraying Services, Inc. ................................ 43
SPX Cooling Technologies ........................... 25
Strongwell ...................................................... 7
Structural Preservation System .................. 61
Swan Secure Products, Inc. ......................... 4
Tower Engineering ....................................... 73
Tower Performance, Inc. ............................. 96
96

Winter 2009 - Cooling Technology Institute

Transcription

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