Presentation

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Why Measure & Control Outdoor Air Delivery?
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•
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Industry Updates
Air Flow Measurement Technology
Innovative ways Consulting Engineers are using
Air Flow Monitoring to Enhance Building
Designs
Follow Industry Standards, Rating Systems & Codes
ASHRAE
62.1
• Specifies outside airflow rates for
acceptable IAQ.
• Requires positive building
pressurization when dehumidifying.
ASHRAE
189.1
IAQ Related Industry
Standards, Rating
Systems & Codes
LEED
IMC
• Mandates outside airflow
measurement on VAV systems.
• Requires quarterly verification of
outside airflow rates.
rates
• Currently awards 1 point for
outside airflow
measurement.
• Strict interpretation of ASHRAE
62.1 VRP requires specified
outside airflow rates are
provided for compliance.
3
0.30
2.500
Outdoor Air Intakes typically
150 to 600 fpm velocity
1.500
219
0.20
310 fpm
0.15
Vortex
Shedding
1.000
0.10
∆
Sensor Output (Volts)
Thermal
Dispersion
Sensor Output (in.w.g.)
0.25
2.000
∆P (pitot arrays)
0.500
(velocity pressure)
0.05
0.003” w.c.
0.000
0
200
400
600
800
1000
Airflow (fpm)
1200
1400
1600
1800
0.00
2000
4
Averaging Pitot Array
Probes
Air Monitor Corporation, FAN-E
Averaging Pitot Array
Stations with Honeycomb
Pitot-static Tube
Trane, Traq Damper
Terminal Box Flow
Ring/Cross
Ruskin, IAQ-50
Combination Pitot Array &
Dampers
Combination Pitot
Array/Damper with
Honeycomb
Thermal Dispersion Technology
Velocity
Power
Q=
Bead-in-glass
thermistor probe
κΑ
B+C
d
ρvd m
(µ)
Zero-power
thermistor
Self-heated
thermistor
(TH – TA)
∆T
Innovative ways Consulting Engineers
are using Air Flow Monitoring to
Enhance Building Designs
7
Intake Flow Rate Variations
Damper Issues
Hysteresis
Binding
Deterioration
Pressure Variations
Supply Fan
Speed
Wind
Stack Effect
Damper
Issues
Hysteresis - No Wind
15% Damper Open
140%
120%
% of Minimum Setpoint
Vot Setpoint
100%
80%
From Closed
From Open
60%
Average
Average
40%
20%
0%
0
25
50
75
100
Sample Number
125
150
Wind &
Stack
Pressure
Hysteresis + 15 mph Cross Wind
15% Damper Open
160%
140%
Vot Setpoint
% of Minimum Setpoint
120%
100%
From Closed
80%
From Open
Average
60%
Average
40%
20%
0%
0
25
50
75
100
Sample Number
125
150
Wind &
Stack
Pressure
Wind &
Stack
Pressure
Wind &
Stack
Pressure
Economizer
Controller
2- 10 VDC
Proportional
Actuator
(by others)
(by others)
Economizer
Mode
Min. OA
Mode
Unoccupied
High Signal Select (HSS) = Econ. Output
2.2 VDC *
HSS = Enhancer Output
Economizer ≤ 2.0 VDC = Econ. Output
Fan Inlet Piezometer Rings
• Piezometer “piezo” fan inlet rings:
Note: k factor is dependent on:
1. Entry conditions
2. Turndown
V=k
√
2∆pgc
ρ
Note: pentry is very dependent on
entry conditions
∆p=pthroat-pentry
Note: pthroat is very dependent on
wheel position and inlet cone
geometry
Understanding ∆P TOTAL Measurement Error
Upstream Pressure
DDC system
calculates velocity
for control process
V=K
√
2∆Pgc
ρ
Application
Controller
Piezometer Pressure
Airflow
Same DP issues as
pitot array
(higher pressure)
The high level output
is converted to
binary by an ADC
in host control system
Accuracy
=
Piezometer
Uncertainty
+
Transducer
Uncertainty
+
Conversion
Error
Typical ∆P Transducer Error
% F.S. Dilemma with ∆P Devices
Full Scale Pressure of ∆P Sensor
Pressure (in.w.g.)
% F.S. ∆P
Error
Full Scale of Application
Turn-down of Application
Full Scale CFM
Uncertainty
Airflow (CFM)
Determining Piezo Ring Transducer Error
Determine the uncertainty of a 1%, 0 to 25 in.w.g. pressure transducer
and piezo ring at 3,000 CFM and 30 ⁰F change after 1 year?
1. Calculate the velocity pressure for 500 fpm:
CFM=2500
pvel= (3000/2500)2= 1.44
√p
vel
( )
V
2500
2
= pvel
2. Determine the transducer uncertainty % F.S.:
1% F.S. (out of box) + 0.033% F.S./⁰F
⁰ · 30 ⁰F
⁰ + 0.5% (1 year drift) = 2.5%
F.S.
3. Determine the transducer uncertainty in in.w.g.
2.5% · 25 = 0.625
in.w.g.
4. Calculate the velocity after biasing the nominal pressure by the pressure
uncertainty and reapplying the equation above (in this case the negative
uncertainty)
V = 2500 · sqrt(0.0156 – 0.00625) = 2256 CFM or -25%
VAV Tracking Example
System:
Sensors:
Total SA flow: 100,000 CFM
∆CFM Setpoint: 10,000 CFM
Building Pressure Desired: 0.02 in.w.g.
Pressurization Flow: 5,000 CFM
Local Exhaust: 5,000 CFM
Max Turndown: 40%
DP sensor: 0 to 25 in.w.g., 1 % F.S.
Flow probe: Piezo-ring
Fan Throat Velocities:
Max velocity: 10,000 FPM
Min velocity: 4,000 FPM
Test Conditions:
DP sensor located in mechanical room
Setup temperature: 70 ⁰F
Operating temperature: 100 ⁰F, 1 year
after startup
Component Accuracies:
DP Sensor:
Total Accuracy = Accuracy + Temp Effect + Drift
1% F.S. + 1% F.S. + ½ % F.S. = 2 ½ % F.S.
Airflow Measuring Device:
5% of reading
Piezo-ring and Transducer
Tracking Uncertainty
120000
100000
Airflow (CFM)
80000
60000
40000
20000
0
40%
-20000
50%
60%
70%
Supply Air %
80%
90%
100%
Piezo-ring and Transducer
Building Pressure
0.3
0.25
0.2
Pressure
0.15
0.1
0.05
0
-0.05
40%
-0.1
50%
60%
70%
Supply Air %
80%
90%
100%
VAV Tracking Example
System:
Sensors:
Total SA flow: 100,000 CFM
∆CFM Setpoint: 10,000 CFM
Building Pressure Desired: 0.02 in.w.g.
Pressurization Flow: 5,000 CFM
Local Exhaust: 5,000 CFM
Max Turndown: 40%
SA Duct Area: 55.5 ft2
RA Duct Area: 56.7 ft2
Thermal Dispersion System (±2% of
reading sensor accuracy)
Calculated Velocities:
Max velocity SA duct: 1,800 FPM
Min velocity SA duct: 720 FPM
Max velocity RA duct: 1,500 FPM
Min velocity RA duct: 500 FPM
Component Accuracies:
Test Conditions:
Transmitter located in mechanical room
Setup temperature: 70 ⁰F
Operating temperature: 100 ⁰F, 1 year
after startup
System:
Installed accuracy: ±3% of reading
a measureable difference!
Tracking Uncertainty
120000
100000
Airflow (CFM)
80000
60000
40000
20000
0
40%
50%
60%
70%
Supply Air %
80%
90%
100%
a measureable difference!
Building Pressure
0.3
0.25
Pressure
0.2
0.15
0.1
0.05
0
-0.05
40%
50%
60%
70%
Supply Air %
80%
90%
100%
¨
Throat
¨
Face
¨
Forward
¨
Flare
Verify
• Actual placement/installation
• Area entered in transmitter
• Field adjustment has not been made
Assess
• Use a sound method to assess
performance of airflow stations
• Signal conversion at BAS
Confirm • Airflow based on a sound
verification technique
Adjust?
• Only when you are certain
the airflow measuring device
is inaccurate
AMD
AMD
AMD
AMD
AMD
AMD
AMD
AMD
AMD
AMD
AMD
AMD
MONITOR LOW PRESSURE
CONTROL DAMPERS
MAINTAIN UNDER FLOOR PRESSURE
Use to verify pressure differentials by
determining the pressurization flow
between spaces or across the building
envelope
Assure proper airflow direction across
relief dampers (supply/return fan system)
or recirculation dampers (supply/exhaust
fan systems)
Use bleed airflow to maintain stable
pressurization with under floor systems
EBTRON optional Through-Wall kit shown.
Protect from rain or snow by providing a rain
hood or louver (by others) on exposed outdoor
walls.
Sensors can also be used to determine
airflow across many intake louver
configurations (consult EBTRON for flow rate
requirements).
33
Airflow and
Temperature Probes
And/ Or
Control Damper
34
Hot / Cold
Containment
35
36
+/+/-% of Reading Error Comparison
Pressure Transducer Drift Effect vs. Ebtron ELF
ΔP Devices
pvel=ptotal-pstatic
V= 2500 x
√p
vel
Thermal
@1,250 fpm
@750 fpm
@400 fpm
Start-Up
0%
0%
0%
3%
Year 1
2.0%
5.7%
21.9%
3%
Year 2
4.1%
11.8%
53.2%
3%
Year 4
8.4%
25.5%
Error%*
3%
Year 6
12.8%
42.2%
Error%*
3%
ΔP Assumptions:
0 error at start-up
0.5% F.S./yr pressure transducer drift
2” w.c. pressure range
k = 2,500 fpm (‘amplifying’ flow cross)
* >100% Error - Airflow cannot go negative
37
Engineers take into effect all the factors that
can contribute to leakage and specify a
differential airflow based on an estimated
leakage rate or target for which the airflow
rates are adjusted
38
Pressurization is a key factor in
controlling room airflow patterns in a
health care facility. Engineers take into
effect all the factors that can contribute
to leakage and specify a differential
airflow based on an estimated leakage
rate or target for which the airflow rates
are adjusted.
39
Outside Air Applications
Floor Volume Control
Zone Regulators
Energy Recovery Ventilation
Air Flow Solutions
2 Analog Outputs
In ERV mode, place a flow probe on each side of the
wheel (supply air and exhaust air streams)
Helps solve 2 main issues with HRV’s/ERV’s
•Setup the airflow balance on each side of
the wheel airflow balance is key to wheel
efficiency
•Helps to maintain the desired balance (or
offset) during the HRV/ERV’s life
•Detects dirty filters
•Detects clogged wheels
CO2 DCV (1,000 sq.ft. classroom)
*Assumptions: Steady-state, N=10,951, OA CO2=400ppm, no sensor error or bias
500
Corresponding
CO2 level for compliance*
1200
450
Outside Airflow (CFM)
350
800
300
250
600
200
400
150
100
200
Room CO2 Level (ppm)
1000
400
ASHRAE 62 Vbz
CO2 Level*
ASHRAE 62.1-2010 Vbz = Rp · Pz + Ra · Az
50
0
0
0
5
10
15
Number of People
20
25
Reset OA airflow setpoint to maintain space CO2 level
CO2 DCV (1,000 sq.ft. classroom)
*Assumptions: Steady-state, N=10,951, OA CO2=400ppm, no sensor error or bias
500
450
Outside Airflow (CFM)
400
Use AMD to limit max OA
350
300
250
ASHRAE 62 Vbz
200
OA CFM Provided
150
Use AMD to limit min OA
100
50
0
0
5
10
15
Number of People
20
25
Reset OA airflow setpoint to maintain space CO2 level
Discover the Advantages of Airflow Measurement in HVAC Systems
for High Performing Building Design
Join our Community of:
2014 Seminar Dates:
Owners
Contractors
March 20th to 22nd
September 11th to 13th
Engineers
Air Balance Professionals
May 15th to 17th
October 23rd to 25th
Arrive: Thursday Afternoon
Architects
Energy Managers
Depart: Saturday Evening or Sunday