the report here.

Transcription

the report here.

- Post Occupancy Evaluation Report –
Indoor Air Quality and Ventilation Performance
of
Ventive PVHR system in a Tenant-Occupied Residential Property
Royal Borough of Greenwich
Shu-Hung Lee, Imperial College London
Tom Lipinski; Miguel Ángel Fuentes Llanos; Dimitris Makris-Makridis, Ventive Ltd
th
5 December 2014
Thames House, Swan Street, Old Isleworth,
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
Company Registration Number: 07721060
VAT Registration Number: 119033441
PVHR Post Occupancy Evaluation
Contents:
1. EXECUTIVE SUMMARY ..................................................................................................................................... 2
2. INTRODUCTION ............................................................................................................................................... 3
3. MONITORING RESULTS .................................................................................................................................... 6
3.1 VENTILATION PERFORMANCE .......................................................................................................... 6
3.2 INDOOR AIR QUALITY ....................................................................................................................... 7
3.2.1 Humidity ........................................................................................................................... 7
3.2.2 CO2 Concentrations ........................................................................................................ 10
3.3 TEMPERATURE LEVELS AND HEAT RECOVERY ............................................................................... 13
4. CONCLUSIONS ............................................................................................................................................... 17
5. APPENDICES ................................................................................................................................................... 18
5.1 VENTILATION GUIDANCE AND RELEVANT REGULATION................................................................ 18
5.1.1 Indoor Relative Humidity ............................................................................................... 18
5.1.2 Indoor CO2 concentrations ............................................................................................. 19
5.2 ASSUMPTIONS AND LIMITATIONS.................................................................................................. 20
5.2.1 Monitoring Sensors ........................................................................................................ 20
5.2.2 Graphical Data ................................................................................................................ 20
5.2.3 Ventilation Rates ............................................................................................................ 20
5.2.4 Ventilation-related heat loss without Ventive ............................................................... 21
5.2.5 Savings Table .................................................................................................................. 21
6. REFERENCES................................................................................................................................................... 22
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e |1
1. EXECUTIVE SUMMARY
This case study assesses the Indoor Air Quality and overall ventilation performance of a new Passive
Ventilation system with Heat Recovery (Ventive PVHR) installed in a two bedroom house in the Royal
Borough of Greenwich, South East London. The house is occupied by a family consisting of mother and
daughter. The study follows an eight month monitoring period of the dwelling, which is sufficient to ensure
the quality of the data.
To assess Indoor Air Quality at the dwelling the data collected included indoor and outdoor Relative
Humidity and Indoor CO2 concentrations. To assess the ventilation performance, the data collected included
ventilation flow rates, indoor and outdoor temperatures and the incoming supply air temperature.
The results of the study indicate that good Indoor Air Quality has been achieved throughout the monitored
period, with humidity and CO2 registering well within the recommended levels. The study also found a
positive correlation between ventilation rates and improved Indoor Air Quality.
Ventilation heat recovery has also been assessed as part of the study, to include heat recovery efficiency and
an indication of overall energy savings. The average Heat Recovery efficiency during the monitoring period
was 68%. Heat Recovery efficiency is lower during the warmer months and higher during the winter when
the external temperatures are lower; the average efficiency of the Heat Recovery unit was 71% during
November 2014. The total annual savings have been calculated to be 2760kWh of gas and 175kWh of
electricity, which provides an overall cost saving to the tenant of approximately £160 per annum.
Overall, the Ventive PVHR system has provided immediate and noticeable benefits to the tenant in terms of
both Indoor Air Quality, and energy & cost savings. On recent inspection of the house there were no signs of
condensation-related damp and mould and the tenant provided the following statement: “Before the works,
we lived in a house that was stuffy and my daughter had to use her inhaler 5-10 times a day and now she
only uses it once a day if at all. The house feels fresh but we don't have any cold draughts”. Considering this
had been a problem property with high levels of damp and mould prior to the installation of Ventive PVHR,
this can be seen as a very good result.
Photo 1: Roof view showing position of Ventive systems
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e |2
2. INTRODUCTION
Ventive S [and S+ variant] is a Passive Ventilation system with Heat Recovery. Ventive utilises both buoyancy
and wind pressure as its driving forces and has no mechanical components – it therefore does not require
any electricity or other energy source to operate. The heat exchanger within the system enables Ventive to
recover heat from outgoing stale air to warm up incoming fresh air, thereby reducing overall heat loss from
the dwelling.
The property monitored for this study is owned by the Royal Borough of Greenwich. Prior to the
refurbishment in March 2014 it had a history of damp and mould. As part of the refurbishment scheme, a
full house Ventive PVHR system was installed, comprising of three Ventive S and two Ventive S+ units (see
Photo 1 and Figure 1 for locations). This was combined with minor airtightness measures, new kitchen and
redecoration of the interior.
Photo 2: Front of property
The monitoring system sensors were installed in the bathroom, and in the ductwork of the Ventive S+
system ventilating the bathroom. While interviewing the tenant it was established that the bathroom doors
are closed at all times and the bathroom window remains closed most of the time, mainly due to its location
on the ground floor with no private garden. If the window is open it can be detected from the bathroom
temperature sensor (as it is accompanied by a temperature drop).The occupants also noted that they tend
to keep other windows in the house closed. Some windows may get opened in the afternoon during the
summer, and the bedroom window may sometimes be opened overnight. This behaviour provides differing
airtightness levels depending on set-up and may affect the test results measured in the bathroom.
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e |3
Figure 1: Floor Plans and Vent Locations
Ventive S+
S+
S
Living Room
S
Ventive
S
An 8-channel data logger (Figure 2&3) was installed inside the boiler cupboard, directly above the bathroom,
which relays data to an online monitoring platform provided by Energence, an independent third party who
provide monitoring services to a number of Local Authorities and Housing Associations.
Figure 2: Data Logger inputs
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e |4
Figure 3: Data Logger mounted inside the boiler cupboard
The standard operation of Ventive’s Passive
Ventilation system with Heat Recovery (PVHR) is
depicted on the left hand side (Figure 4).
As warm air rises, it escapes via the exhaust
diffuser located at the top of the room. As this
stale air leaves the building, the heat is
recovered from the outgoing air in the heat
exchanger (mounted directly under the roof
cowl).
Fresh air is channelled down through the roof
cowl and into the heat exchanger, where it is
pre-warmed. It then enters the room via a duct
and a diffuser at low level, filling the room with
fresh, pre-warmed air.
Ventive has no moving parts or electrical
components; the flow of air is mainly buoyancy
driven, with wind providing assistance primarily
during the summer months. The room diffuser is
user-adjustable.
Figure 4: How PVHR works
The evaluation of system performance of the Royal Borough of Greenwich installation measures three
factors. The first is the direct Ventilation Effectiveness of the system (air inflow and outflow). The second is
Indoor Air Quality, gauged by assessing CO2 concentrations and humidity. The third is the Effectiveness of
the Heat Recovery function, which in turn affects thermal comfort levels and heating costs of the dwelling.
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e |5
3. MONITORING RESULTS
3.1 VENTILATION PERFORMANCE
The average ventilation rate for the monitored room between June and October was 13m 3/h. When
extrapolated to include all 5 systems, this provides a whole house ventilation rate of 65m 3/h. It is worth
noting that the rate is naturally lower in the summer due to lower buoyancy - the main driver behind natural
ventilation. For the same reason the ventilation rate will be lower at midday than during the evening or at
night. As most dwellings are unoccupied during the day, the reduced daytime operation is actually beneficial
since it reduces the heat loss even further when most occupants are away.
The instantaneous ventilation rate also appears sensitive to human presence and activity – increasing when
occupants enter the room and reducing when the space is vacant. This is very interesting since the system
has no controls installed – the boost occurs purely as a result of natural forces.
An example of ‘natural boost’ can be seen below in the snapshot taken from the live monitoring portal
(Figure 5), which details the 36 hour period from late evening on the 12th of March 2014 to early morning on
the 14th. Indoor temperature is around 23 degrees with the temperature pattern showing the boiler boosting
the heating approximately once per hour. The outside temperature drops down below 10 degrees at night
but reaches 23 degrees during the day, with external humidity peaking at almost 100% at night. The
ventilation rate (in magenta) oscillates in a similar pattern to the heating, dipping to 0.3 m/s (13.2m 3/h)
during a warm day as it is mainly buoyancy driven:
th
th
Figure 5: Live monitoring 12 -14 March
Interestingly, at approximately 8 am on the 13th, there is an increase in CO2 concentration and humidity –
indicating human presence and a bathing occurrence (shower or bath). The tenant stated that for the
duration of the shower the window was opened and that this avoided even temporary steaming-up in the
bathroom. With the window open, the ventilation rate doubles giving a simple but highly effective method
of purge ventilation. This, in turn, brings the humidity and CO2 back to normal, all happening naturally.
Ventilation performance (and building performance in general) cannot be completely described in numbers
alone – since buildings are used by occupants and their behaviour impacts on the performance of every part
of the building, the views of the tenant are just as important. Interviews with the resident have identified a
number of benefits following the installation of Ventive Passive Ventilation with Heat Recovery, from feeling
of freshness, not having to open the windows overnight and quiet operation, to significant health impacts
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e |6
(almost life changing). Lisa, who lives in the property with her daughter stated: “My daughter no longer
has issues with asthma and the house feels much healthier and fresher. The damp is all gone too.”
3.2 INDOOR AIR QUALITY
3.2.1 Humidity
Moisture is considered as the most significant pollutant in dwellings; its control forms the basis of the
ventilation strategy. The key is to avoid a situation where the relative humidity exceeds 70% for a prolonged
period. [2] High levels of humidity not only cause irritation to the occupants directly, but they also produce
damp and mould with severe negative impacts on both the building fabric and the occupants health. Besides
respiratory diseases and allergies, the latest research suggests mould is also suspected of damaging the
brain. [7]
Building Regulations prescribe the maximum average levels of humidity as 85% for one day, 75% for one
week and 65% for one month. [3] The graph below (Figure 6) illustrates the measured levels of relative
humidity in the monitored dwelling (following the installation of Ventive PVHR) in comparison to the
maximum levels set by the National Building Regulations:
Figure 6: Internal Relative Humidity levels at monitored property (daily, weekly and monthly averages) March-July 2014
The observed levels of relative humidity fall below the building control limits by a significant margin and are
indicative of good internal air quality. The results also depict a well-functioning heat recovery system, as the
fresh air supplied to the dwelling has clearly been de-humidified by the heat exchanger through an increase
in temperature. Without this process of heat recovery, the fresh air supplied would be at the same relative
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e |7
humidity as outside (averaging 70%) and would not be particularly effective as a control mechanism for
indoor air humidity levels.
Figure 7: Internal Relative Humidity levels at monitored property (daily, weekly and monthly averages) July-November 2014
As can be seen in Figure 7 above, August and September have consistently higher external humidity levels
than those measured during the first half of the year. Lower temperature differences between the inside
and outside environment makes humidity control particularly challenging, as there is less scope for incoming
air to warm up (lowering its humidity). To look more closely at this high humidity period, we have selected
two weeks in September showing humidity readings within the dwelling (Figure 8).
Figure 8: Internal Relative Humidity levels at monitored property September 2014
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e |8
To ascertain the link between ventilation and humidity, the relative humidity levels were evaluated against
exhaust air velocity. The relationship appears to be closely correlated and inversely proportional: the higher
the extract ventilation rate, the lower the observed level of humidity (Figure 9). This confirms that internal
humidity is closely related to ventilation rate (and therefore the reduction in the humidity level is directly
related to the new ventilation system).
Figure 9: Correlation between Internal Humidity and Extract Velocity
While external humidity levels reach up to 100%, the internal relative humidity remains in the 40% - 60%
band for 99% of the time. At no point does the internal relative humidity reach the maximum average levels
set out in Part F of Building Regulations, remaining well within acceptable levels.
Internal humidity is the most common indicator of indoor air quality and high levels of relative humidity are
often observed in retrofitted dwellings - mostly as a result of badly designed or poorly installed ventilation
measure. In some cases as much as 44% of issues that needed resolving post-retrofit were linked to
ventilation and humidity with over 16% of retrofitted homes suffering ventilation and humidity problems
within the first year from completion of work. [10] Since humidity issues can take years to manifest, the
overall size of the problem is expected to be much higher.
It is evident from the data collected during this study that the PVHR system maintains optimum levels of
humidity within the dwelling, thereby reducing the risk of moisture related issues.
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e |9
3.2.2 CO2 Concentrations
CO2 is constantly emitted by breathing humans; therefore internal levels of CO2 are commonly used as a
proxy indicator of Indoor Air Quality within occupied dwellings. This can also be used to determine if the
property is being adequately ventilated during habitation,[1] as inadequate ventilation can lead to harmful
concentrations of CO2.
A build-up of this gas in a room leads to a feeling of stuffiness, impaired concentration and when there are
high levels of CO2 respiration rates can increase. UK Government research demonstrates that a dwelling
with functioning intermittent extract fans (IEV) (complying with Building Regulations) can result in indoor
CO2 concentrations of 5000 ppm or more.[8] Slightly deeper breathing begins to occur when the atmospheric
concentration exceeds 5000 ppm (parts per million, 0.5% by volume). This is the maximum allowable
concentration of CO2 for 8-hour exposure for healthy adults. [2]
UK Building Regulations do not specify limits for CO2 concentrations in dwellings, however, a CO2 band of
800–1000 ppm is often used as an indicator that the ventilation rate in a building is adequate. The level of
1500 ppm is set as the maximum daily average level for schools.[4]
The graphs below (Figures 10&11) illustrate the observed levels of CO2 in the monitored dwelling over a
period of eight months, with the recommended maximum CO2 concentrations from CIBSE and BB101
overlaid for comparison:
Figure 10: Internal CO2 concentration (daily and 8-hour averages) March-July 2014
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e | 10
Figure 11: Internal CO2 concentration (daily and 8-hour averages) July-November 2014
The above graphs demonstrate that the CO2 concentrations within the dwelling average just below 600 ppm,
which can be classified as good to excellent with regards to Indoor Air Quality. The highest daily average was
recorded in mid-April at 940 ppm, which is still within the guideline limits recommended by CIBSE and well
below the recommended maximum level.
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e | 11
To look more closely at the instantaneous readings of CO2 concentrations within the dwelling, as well as the
peak levels and the time to recover to average, we have chosen a two week long period for a more detailed
inspection. As with the humidity, the chart covers the last two weeks of September 2014 (Figure12)
Figure 12: Internal CO2 concentration (1-hour averages) March-July 2014
As can be seen in Figure 12 above, the highest hourly average was recorded on the 30th of September at
1100 ppm, which is significantly below the daily maximum recommended by BB101[4] and CIBSE.
The 8 month long monitoring of the control dwelling in Royal Borough of Greenwich has shown that good to
excellent Indoor Air Quality is achievable in existing and period properties, provided an appropriate
ventilation system such as Ventive is specified and installed. The type of ventilation provision specified and
installed can have a higher impact on Indoor Air Quality than the type of the dwelling, occupant behaviour,
or the occupancy density.
Another beneficial aspect of this ventilation method is the fact that the supplied air is collected at or above
the roof level. The air at this level is cleaner than the air collected through the facades (including trickle or
brick vents) as heavier pollutants are concentrated at ground level and ‘locked’ between the buildings. As
the Ventive twin-flow cowl is positioned to take advantage of wind speed, contaminants such as Particulate
Matter (PM) and NOx tend to be significantly diluted by increased winds.
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e | 12
3.3 TEMPERATURE LEVELS AND HEAT RECOVERY
Figures 13 and 14 below depict instantaneous data, including ambient temperature (in blue), indoor
temperature (dark red) and temperature of supply air (post heat recovery, as it enters the room, green) for a
5 month period, starting in June 2014. All of the readings were recorded at 10 minute intervals.
Figure 13: Temperature readings June-August 2014
Figure 14: Temperature readings September-November 2014
It can be seen that the internal temperature broadly follows the line of the external ambient temperature,
with the delay representative of expected thermal inertia of a brick building (with typical internal heat
gains). On average the incoming air is only 2-3 degrees cooler than the room temperature, a difference
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e | 13
which is undetectable at normal flow rates. We can see that when the external temperature is significantly
greater than indoors, the incoming air is warmer, and that when the external temperature drops significantly
the incoming air is up to five degrees cooler than indoors. This is representative of a functioning ventilation
system with efficient heat recovery.
To look more closely at the effects of Heat Recovery we have chosen a two week long period for a more
detailed inspection. As with the humidity and the CO2 levels, Figure 15 covers the last two weeks of
September 2014.
Figure 15: Temperature readings September 2014
From the detailed temperature and airflow data during the illustrated period in Figure 15, it can be seen that
the temperature of the incoming fresh air tracks the indoor air temperature within 2-4 degrees Celsius and,
with very few exceptions, remains above 20°C.
The ventilation rate exhibits a typical PSV (Passive Stack Ventilation) behaviour. When outside temperatures
exceed or equal indoor temperatures (mainly during a hot day) the flow rate slows down, averaging 5m3 per
hour. When the outside temperature drops the ventilation rate increases, averaging 10-15m3 per hour. This
translates to 0.3 Air Changes per Hour (ACH) midday, and between 0.5 and 1 ACH during normal hours of
occupation (mornings, evenings and overnight)
To look more closely at the heat recovery efficiency we have isolated the averaged heat recovery data. In
general, the efficiency of heat transfer depends on two factors – airflow velocity, and the temperature
difference between the airflows. The efficiency is higher when the airflow is lower, and drops as the airflow
increases. On the other hand, the higher the difference in temperatures between interior and exterior, the
higher the heat transfer efficiency.
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e | 14
The average observed heat transfer rate for the period from June to October 2014 was 66%, with the
measurement distribution illustrated on the following Figure 16.
Figure 16: Heat Recovery Efficiency
With airflow rate and the instantaneous heat transfer efficiency readings, we can calculate overall energy
saved in the dwelling with Ventive installed against the energy required to heat the equivalent air without
the provision of heat recovery (Figure 17).
Heat Loss due to ventilation without Ventive
Heat Loss due to ventilation with Ventive PVHR
Figure 17: Energy demand comparison – PVHR vs No Heat Recovery
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e | 15
Figure 17 above compares the energy required to warm the air delivered to the dwelling without heat
recovery (as measured over the monitoring period) with the actual (reduced) energy required to warm up
the air with heat being passively recovered by the Ventive heat exchanger. Please refer to Appendix, 5.2.4
Ventilation-related heat loss with and without Ventive, for calculation methodology.
An additional airflow sensor was installed at the end of May 2014 leading to a change in monitoring setup.
This resulted in some data being available for the entire duration of the monitoring period while some
(including duct temperature) was only available from June 2014.
The difference between non-Ventive ventilation and Ventive ventilation (net daily saving due to Heat
Recovery) is illustrated in green in Figure 18 below.
Total saved during monitoring: 633kWh
Energy Saved in November: 212kWh
Annual heat energy savings: 1800 kWh
Outside Temperature
Energy Saved with Ventive PVHR
Figure 18: Ventilation Energy Savings
Total heat energy savings for the 5 monitored months from June (above) are 345kWh. Based on this the
energy savings over the year are estimated to be in excess of 1,800kWh. Using a standard gas boiler as a
heat source (similar to the one fitted at the property) this translates into an annual saving of 2760kWh or
£130 (at £0.0467 per 1 kWh, npower, 11/2014). If we were to consider the running costs of continuous
extract ventilation capable of similar ventilation rates we would be adding 175kWh of electricity and £29.50
of cost (at £0.1684 per 1kWh) increasing the overall annual savings to £160, excluding maintenance.
Over the average 25 year lifespan of Ventive system this adds up to £4000 of energy cost savings and 15
tonnes of CO2 emissions saved (or 600kg of CO2 per year, calculated as 0.182kg CO2/kWh for gas and
0.568kg CO2/kWh for electricity). Please note that these savings exclude the potential savings made on
maintenance costs of alternative products, the savings in remedial works to the property to eradicate effects
of poor Indoor Air Quality, and are specific to the monitored site.
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e | 16
4. CONCLUSIONS
The results of the study indicate the provision of good Indoor Air Quality throughout the monitored period,
with humidity and CO2 registering well within the recommended levels.
While external humidity levels reached up to 100%, the internal relative humidity remained at 40% - 60%
band for 99% of the time. At no point did the relative humidity reach the maximum average levels set out in
Part F of Building Regulations, remaining well within acceptable levels.
The CO2 concentrations within the dwelling averaged just below 600 ppm which can be classified as good to
excellent with regards to Indoor Air Quality. The study also found a positive correlation between the
ventilation rate and improved Indoor Air Quality.
The heat recovery aspect of the Ventive PVHR ventilation system has also been assessed as part of the study
and the temperature of fresh air, heat recovery efficiency, and overall heat energy savings were included in
chapter 3.3. The average Heat Recovery efficiency during the monitoring period was 68% and the total
annual savings are calculated to reach 2760kWh of gas and 175kWh of electricity, providing an estimated
overall cost saving to the tenant of £160 per annum. Heat Recovery efficiency was lower during the warmer
months and higher during the autumn and winter when the temperatures are lower. The average efficiency
of the Heat Recovery was 71% during November 2014.
Over the average 25 year lifespan of each Ventive system, this adds up to £4000 of energy cost savings and
15 tonnes of CO2 emissions saved (or 600kg of CO2 per year, calculated as 0.182kg CO2/kWh for gas and
0.568kg CO2/kWh for electricity). Please note that these savings exclude any further potential savings made
on maintenance costs of alternative products, or future remedial works to the property to eradicate the
effects of poor Indoor Air Quality, and are specific to the monitored site.
Overall, the Ventive PVHR system has provided immediate and noticeable benefits to the tenant in terms of
both Indoor Air Quality, and energy & cost savings. On recent inspection of the house there were no signs of
condensation-related damp and mould. The tenant provided the following statement: “Before the works we
lived in a house that was stuffy and my daughter had to use her inhaler 5-10 times a day and now she only
uses it once a day if at all. The house feels fresh but we don't have any cold draughts”. Considering this had
been a problem property with high levels of damp and mould prior to the installation of Ventive PVHR, this
can be seen as a very good result.
Annual and lifecycle benefits of Ventive PVHR system, based on the monitored installation, can be
summarised as follows:
Benefits
Energy Savings (gas + electricity)
Improved comfort and health
Annual
£160
N/A
Lower system maintenance
£120
Lifecycle
£4,000 (at today’s energy prices)
Improved productivity, lower
healthcare costs
£3,000
Lower building maintenance
CO2 saved
Litigation and management
£1,200
600kg
£320
£30,000
15 tonnes
£8,000
Comment
Tenant benefit
Tenant benefit
Landlord benefit
(against MVHR & PIV)
Landlord benefit
Landlord benefit
Landlord benefit
The basis of the calculation of these figures is included in the appendices 5.2 Assumptions & Limitations
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e | 17
5. APPENDICES
5.1 VENTILATION GUIDANCE AND RELEVANT REGULATION
5.1.1 Indoor Relative Humidity
According to National Building Regulations: Approved Document F - Section 4 0, Introduction to the
provisions states: “The key aim of the requirements of Part F 1(1) is that a ventilation system is provided,
under normal conditions, is capable of limiting the accumulation of moisture, which could lead to mould
growth, and pollutants originating within a building which would otherwise become a hazard to the health of
the people in the building.” (Approved Document F, chapter 4.2)
The maximum humidity levels are set according to the table below (Approved Document F, Appendix A):
Table A2 Indoor air relative humidity
Moving average period
Room air relative humidity
1 month
65%
1 week
75%
1 day
85%
According to CIBSE Guide A (Environmental design) [1] “humidity levels in dwellings in the range of 40–70%
RH are generally acceptable, with lower humidity often acceptable for short periods; humidity of 30% RH or
below may be acceptable, but precautions should be taken to limit the generation of dust and airborne
irritants and to prevent static discharge from occupants (CIBSE Guide A, chapter 1.3.1.3).
House dust mites prosper in warm damp conditions, providing there is a supply of food in the form of human
skin. Mites can be controlled if their immediate microclimate can be maintained below 73% RH. Buildings in
which there are prolonged periods of high relative humidity are likely to experience problems such as
airborne fungi and house dust mites, particularly if the value of indoor relative humidity exceeds 70% RH for
long periods. Allergies and respiratory illnesses have long been associated with mould growth and moisture,
particularly for asthma and rhinitis” (CIBSE Guide A, chapter 8.3.1).
CIBSE Guide B (Heating, Ventilating, Air Conditioning and Refrigeration)[2] states that: “moisture is the most
significant pollutant; its control forms the basis of the ventilation strategy. The key is to avoid a situation
where the relative humidity exceeds 70% for a prolonged period. This can usually be achieved with a whole
house ventilation rate of 0.5 air changes per hour. Alternatively, more rapid extraction in response to
moisture release within the dwelling, actuated either by humidity sensors or manually, can be beneficial in
removing moisture before it is absorbed by furnishings and/or the fabric of the building itself.
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e | 18
In domestic situations, it is particularly important to inform occupants of the intended operation and
purpose of the selected ventilation system to ensure that it achieves its intended purpose. This will ensure
that they:
— do not tamper with the system in the belief that it is costing them money to run
— do not interfere with the performance of the system through blocking air inlets or extracts, or by altering
sensor settings.” (CIBSE Guide B, chapter 2.3.10.1).
5.1.2 Indoor CO2 concentrations
Carbon dioxide (CO2) is a colourless and odourless gas and exists in the atmosphere and its concentration
varies between 0.036% (360 ppm) and 0.039% (390 ppm) by volume, depending on the location. Besides
other house related sources such as cooking CO2 is produced during the respiration of all aerobic organisms
and is exhaled in the breath of air-breathing land animals, including humans [5].
Carbon dioxide is often measured when trying to evaluate the indoor air quality of a building as it is one of
the critical indicators of adequate provision of fresh air. If the levels of CO2 are constantly high, it is assumed
that this space may not be ventilated properly, which in turn implies the build-up of other environmental
contaminants. Moreover, CO2 levels are good predictors of odours that are considered undesirable for the
overall human comfort inside conditioned spaces.
CIBSE Guide A (Environmental design) [1] states that as a general rule, the fresh air supply rate should be at
least between 5 and 8 litres per second per occupant, although this will depend on various other factors
including the floor area per occupant, the processes carried out, the equipment used and the pattern of
occupancy. The provision of 5 litres fresh air per second per occupant most of the times ends up to an
internal concentration of 1350 ppm. But the higher ventilation rate of 8 litres fresh air per second per
occupant is recommended, giving an internal CO2 concentration of approximately 1000 ppm which is unlikely
to provide any discomfort.
CIBSE Guide B, (Heating, Ventilating, Air Conditioning and Refrigeration) [2]: “Carbon dioxide is a dense
odourless gas produced by combustion and respiration. The rate of ventilation required for the supply of
oxygen for breathing is far outweighed by any requirement for the dilution of exhaled carbon dioxide (CO2).
A build-up of this gas in a room leads to a feeling of stuffiness and can impair concentration. Elevated levels
of CO2 in the body cause an increase in the rate of respiration. Slightly deeper breathing begins to occur
when the atmospheric concentration exceeds 9 000 mg•m–3 or 5 000 ppm (0.5% by volume). This is the
maximum allowable concentration of CO2 for 8-hour exposures by healthy adults. In the USA, one half of this
limit (0.25%) has been taken as appropriate for general building environments.
Within the UK, a CO2 figure of 800–1000 ppm is often used as an indicator that the ventilation rate in a
building is adequate. One thousand parts per million would appear to equate to a ‘fresh air’ ventilation rate
of about 8 litres•s–1 per person. In Sweden, the equivalent indicator is 1000 ppm, with a desired level of
600–800 ppm. Note that as outside air itself contains carbon dioxide (approx. 350 ppm), a 50% reduction in
internal levels from 1600 ppm to 800 ppm requires a four-fold increase in ventilation rate.”
www.ventive.co.uk
TW7 6RS
Tel: 02085601314
P a g e | 19
Building Bulletin 101 [4] states: “…….the following school specific recommended performance standard
applies to teaching and learning spaces:
Ventilation should be provided to limit the concentration of carbon dioxide in all teaching and learning
spaces. When measured at seated head height, during the continuous period between the start and finish of
teaching on any day, the average concentration of carbon dioxide should not exceed 1500 ppm (parts per
million).
This is based on the need to control carbon dioxide resulting from the respiration of occupants. In teaching
and learning spaces, in the absence of any major pollutants, carbon dioxide is taken to be the key indicator
of ventilation performance for the control of indoor air quality.”
5.2 ASSUMPTIONS AND LIMITATIONS
5.2.1 Monitoring Sensors
Indoor sensors were placed in the bathroom therefore the indoor temperature, CO2 and humidity readings
are representative of that specific area. As individual Ventive PVHR systems supply fresh air to all other
rooms the overall and average conditions are expected to be similar, but individual variations which are
influenced by occupant presence or cooking will differ. Tenant feedback indicates that all rooms in the house
have a similar level of air quality.
Additional airflow sensor was installed at the end of May 2014 leading to a change in monitoring setup. This
resulted in some data being available for the entire duration of the monitoring period while some (including
duct temperature) only available from June 2014.
5.2.2 Graphical Data
All graphs represent raw data as collected from site. The data was not processed besides the visual
representation of collected values. No conversion factors were applied. For simplicity of presentation, where
values were above 100% (humidity for example) they were reduced to 100%, singular sensor errors were
omitted.
5.2.3 Ventilation Rates
To establish the ventilation rate for the whole house we used the bathroom airflow rate multiplied by the
number of installed systems and divided by the volume of the house. The airflow rate was derived from
measured velocity (m/s) multiplied by the duct area and time factor (m3/h).
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e | 20
5.2.4 Ventilation-related heat loss with and without Ventive
To establish the ventilation-related heat loss without Ventive we have used equivalent ventilation rate
without heat recovery, and calculated the amount of energy required to heat up the makeup air.
To establish the ventilation related heat loss with Ventive we have applied the same calculation to the lower
temperature difference (incoming air was warmer due to heat recovery). As the properties of humid air
under different temperature are known, the specific enthalpy can be calculated by the following equation:
h = ha + X * hw = ha + RH * XMax * hw = Cpa * Ta + RH * XMax * (Cpw * Tw + hwe)
Where:
h = specific enthalpy of moist air (kJ/kg)
ha = specific enthalpy of dry air (kJ/kg)
X = humidity ratio (kgwater/kgair)
Xmax = maximum Humidity Ratio (kgwater/kgair)
hw = specific enthalpy of water vapour (kJ/kg)
Cpa = specific heat capacity of air at constant pressure (kJ/kg°C, kWs/kgK)
Ta = air temperature (°C)
Cpw = specific heat of water vapour at constant pressure (kJ/kg°C, kWs/kgK)
Tw = water vapour temperature (°C)
hwe = evaporation heat of water at 0°C (kJ/kg)
RH = relative humidity
Then the total enthalpy can be calculated as:
H = ∑ h * 𝑉̇ * t
Where:
H = enthalpy (kJ)
𝑉̇ = volume flow rate (m3/s)
t = time (s)
The calculations of energy savings are based on a presumption that the ventilation airflow in the property
remains relatively balanced (with outflow being equal to inflow with limited infiltration). If the tenant chose
to leave windows are open for prolonged periods of time the savings would not be achieved as the
ventilation would operate in purge mode without the heat recovery.
5.2.5 Savings Table
 Lower system maintenance: PIV maintenance costs approximately £80 per annum, average MVHR
maintenance costs £160 (one annual visit to replace the filters), the figure of £120 is an overall average.
 Lower building maintenance of £1,200 is based on the average mould removal and redecorating cost of
£3,600 suffered once every three years in problem properties without adequate ventilation.
 Disrepair litigation costs can range from £8,000 (case settled before trial) to £18,000 (case lost at trial)
and the figure included in the table is derived from the lower value of damp/mould claim and divided by
the 25 year life expectancy of the PVHR product. It assumes a claim is made if adequate ventilation is not
provided. Calculations are based on Disrepair Claims - The true cost of disrepair by Andy Ballard. [11]
www.ventive.co.uk
TW7 6RS
Tel: 02085601314
P a g e | 21
6. REFERENCES
[1] CIBSE Guide A: Environmental design.
[2] CIBSE Guide B: Heating, ventilating, air conditioning and refrigeration
[3] HM Government (2010). Approved Documents Part F – Ventilation (2010 Edition), Planning Portal
[4] HM Government (2006). Building Bulletin 101: Ventilation of School Buildings
[5] Satish U., Mendell M. J., Shekhar K., Hotchi T., Sullivan D., Streufert S., Fisk W.J. (2012). "Is CO2 an Indoor
Pollutant? Direct Effects of Low-to-Moderate CO2 Concentrations on Human Decision-Making Performance".
Environmental Health Perspectives 120 (12). Retrieved 2014-08-26.
[6] Lipinski T., Lee S. H., and Childs P. (2014) Domestic passive ventilation with heat recovery (PVHR):
performance criteria, tests and operational variations Proceedings of the 15th International Heat Transfer
Conference, IHTC-15, Kyoto, Japan, IHTC15-09883.
[7] C. Harding et al. Mold inhalation, brain inflammation, and behavioral dysfunction. Society for
Neuroscience Meeting, Washington, DC, November 15, 2014
[8] HM Government (2009). Investigation of Ventilation Effectiveness BD2523. Department for Communities
and Local Government, March 2009
[9] Modifiable factors governing indoor fungal diversity and risk of asthma, R. Sharpe, C. R. Thornton and N.
J. Osborne
[10] FUTUREFIT. An insight into the retrofit challenge for social housing, Affinity Sutton
[11] Disrepair Claims - The true cost of disrepair, Andy Ballard
TW7 6RS
Tel: 02085601314
www.ventive.co.uk
P a g e | 22

the report here.

Transcription

Similar documents

important notice - Mille

Tips and tricks on how to take care of your pool table

Required Local Exhaust Ventilation for Washington State Nail Salons

User Manual

Influence of Plants on the CO2 Concentration in the

vortice deumido

Supco DVTH Brochure

PREPERATION AREAS

Adroit Brochure

Prelude 9x12 HS Cover