In the UK we spend some 90% of our time indoors, the levels of pollution inside buildings are therefore of concern. The Building Regulations require that houses be adequately ventilated to maintain a good indoor environment. There are several ways of complying with theses regulations, houses may be fitted with whole house mechanical ventilation, passive stack ventilation, or trickle ventilators and extract fans.
UCL was funded to investigate the effects of these different ventilation regimes on carbon monoxide concentrations in social housing. This work is part funded by the Department of the Environment, Partners in Technology Programme (now DTLR), The Jackson Environment Institute, Capteur Sensors, Titon (trickle vent manufacturers), XpelAir (fan manufacturers) and Energy Conscious Design (ECD).
Carbon Monoxide ( CO ) is a poisonous gas which at high concentrations can prove fatal. There has been much publicity and concern about deaths in the home due to high concentrations of CO from faulty heating appliances (see figure). Less well understood is the effect of long term exposure to low concentrations of CO, which may aggravate heart, lung and respiratory disease. Such low levels may be present in safe homes with well maintained heating systems and ventilation designed to meet current regulations. Another gas of interest is Nitrogen Dioxide ( NO2 ) which is produced during the use of gas cookers, long term exposure to NO2 may aggravate respiratory disease. House dust mites, which live in carpets, soft furnishings and mattress etc., are associated with asthma and rhinitis. House dust mites can only breed and survive when the indoor humidity is above a critical level, hence ventilation is important in the control of dust mites.
The last amendments to Part F of the building regulations (1995)
recommended an increased size of trickle ventilator (8000mm2 from
4000 mm2) and permitted passive stacks and whole house mechanical
ventilation. The impact that these different methods of
ventilating have on indoor levels of carbon monxoide (CO),
nitrogen dioxide (NO2) and other gases however are largely
unknown. This report summarises results of a two year study to
monitor CO, NO2, temperature, relative humidity (%RH) and dust
mites in 45 dwellings built since the change in building
regulations. All of the houses were rented from either a local
authority, housing association or trust and used gas for cooking.
These dwellings had a range of ventilation systems; extract fans
with both 4000 and 8000 mm2 trickle vents, whole house mechanical
ventilation, passive stack and cooker hoods. They were all
occupied as normal for this type of property. Despite attempting
to select properties with non smokers, 39% had at least one
smoker. Each property had CO, NO2, %RH and temperature monitored
for at least 3 weeks during the winters of 96/97 and 97/98. CO,
temperature and %RH were measured every ten seconds with an
average value stored every six minutes. Average levels of NO2
were measured for each 3 week period of monitoring and dust mites
were sampled from 2 locations (generally bedroom and living room)
once in each dwelling.
The dwellings were each pressure tested as found (ie vents not
sealed) in order to test their leakiness during .
A detailed pilot study in one dwelling identified that background
levels were dependent on external levels, and peaks above the
background were associated with cooker use. Average and peak
concentrations were always higher than those in other rooms.
Detailed monitoring at several locations within a kitchen showed
that peak CO concentrations at head height were higher than at
floor level. By examining the decay of peak CO levels the
ventilation effectiveness of each strategy could be determined.
Analysis of the monitored data from all of the dwellings showed
the following:
1. No statistically significant diffe
rence in CO (peak or mean) or NO2 levels was found between
different ventilation strategies. 2. No dwellings were found with
CO levels that exceeded World Health Organisation (WHO)
guidelines.
3. Peaks of CO (10-30 ppm) were associated with cooking compared
to typical indoor background levels of 0-3 ppm.
4. Houses with smokers had mean CO levels 56% higher than those
without.
5. Mean CO levels with trickle vents normally closed were 37%
higher than those with them normally open.
6. Mean CO levels were 32% higher in dwellings with windows
normally left open compared with those normally closed.
7. Pressure test results suggest that these modern dwellings are
considerably better sealed than those monitored in the 1992
Building Research Establishment study (BRE 1992). There appears
to be no statistically significant difference in air leakiness
between ventilation strategies.
8. Occupants perceived condensation to be a problem in many of
the dwellings with damp/mould being reported at a similar level
of occurrence to that found in the 1991 English House Condition
Survey (22%).
9. There was no correlation between pressure test results or air
pollution levels and the occupantsÕ perception of whether a
house is stuffy or draughty. There is however a weak relationship
between mean air temperature and the perception of stuffiness.
10. Analysis of dust mite data showed no clear link with any of
the measured variables.
In summary, within the limitations of this study, all of the
ventilation types allowed by the Building Regulations and studied
in this project were found to maintain concentrations of CO to
within the recommended guidelines of the World Health
Organisation.
The final report is
available electronically via email request.
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