Centre for Research on Indoor Climate and Health
Indoor Air Quality and Energy
or
Why do we need to ventilate houses?
Chris Sanders
Glasgow Caledonian University
Centre for Research on Indoor Climate and Health
3 bedroom semi-detached house with solid walls,
no insulation and single glazing
Centre for Research on Indoor Climate and Health
Components of heat loss - Uninsulated
Uwall = 2.1
Uroof = 2.2
Ufloor = 0.6
N = 1 ach
Ti = 20C Te = 0C
Centre for Research on Indoor Climate and Health
Components of heat loss - insulated
Uwall = 2.1
Uroof = 2.2
Ufloor = 0.6
N = 1 ach
Ti = 20C Te = 0C
Uwall = 0.40
Uroof = 0.16
Ufloor = 0.25
N = 1 ach
Centre for Research on Indoor Climate and Health
X
X
X
X
X
Walls lined
Chimneys removed
Floors sealed
Secondary glazing
Ventilation rate??
Centre for Research on Indoor Climate and Health
If we reduce ventilation in houses will
there be problems?
Why do we need to ventilate houses?
X
Human respiration
X
Removing pollutants
X
Providing air for combustion appliances
Centre for Research on Indoor Climate and Health
2007 Domestic Technical Handbook
Centre for Research on Indoor Climate and Health
AD F 2006 Appendix A
Performance Criteria for Dwellings
X
X
X
X
X
No visible mould on external walls
NO2 levels should not exceed specified
values for 1 hour average or long term
average
CO levels should not exceed levels specified
for various exposure times
TVOC should not specified level averaged
over 8 hours
Bio-effluents controlled with air supply rate of
3.5 l/s/person
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Human Respiration
Air supply needed to prevent CO2 concentration rising
above 5000ppm (CIBSE Guide B2)
Resulting ventilation rate in a 280m3 house with four
occupants
Centre for Research on Indoor Climate and Health
Bio-effluents (Body odour)
X
ASHRAE recommends 3.5 l/s/person
X
With 4 people in a house with volume
280m3, this translates to a ventilation
rate of 0.18 ach
Centre for Research on Indoor Climate and Health
Nitrogen Dioxide
Given typical production rates from gas cooking and a
background ventilation rate of 0.5 ach, an extract rate of 2.2 ach
or 12 l/s in a 20m3 kitchen is required to keep below the limit
Centre for Research on Indoor Climate and Health
Carbon Monoxide
The levels of CO produced from gas cookers will be controlled
by the same ventilation as for NO2
CO produced from faulty combustion appliances should be
addressed by proper maintenance and fitting CO detectors
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Total Volatile Organic Compounds
Difficult to specify the necessary ventilation rate as
sources vary from house to house
Centre for Research on Indoor Climate and Health
Water vapour
Learning from Canada
Canada Mortgage and Housing Corporation (CMHC) and Health Canada advise
controlling humidity in the home by maintaining a relative humidity of between 40 and
60 percent to limit condensation problems to avoid mould growth.
The National Building Code requires heating-season mechanical ventilation in new
residential buildings because “airtight houses can no longer rely on natural air leakage
through the building envelope for winter ventilation” where reduced air change rates
may be insufficient to provide adequate indoor air quality and could lead to
condensation problems. They identify electrically heated houses as being at greatest
risk because, unlike fuel-fired systems, they require neither the replacement of air or
chimneys, and consequently tend to experience high humidity levels, interior surface
moulds and interstitial condensation.
Linda Sheridan 2008
Centre for Research on Indoor Climate and Health
Condensation
Centre for Research on Indoor Climate and Health
Interstitial
Condensation
Problems if structure
not correctly detailed
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Centre for Research on Indoor Climate and Health
Mould Growth
9.8%
1.4%
1996 EHCS
3.5%
Centre for Research on Indoor Climate and Health
Dust Mites commoner in mattresses
furnishing, carpets etc. when humidity higher
faecal capsules major source of allergens
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Albania
Romania
Greece
China
Russia
Switzerland
Denmark
Italy
Portugal
Estonia
Iran
Argentina
Saudi Arabia
Spain
Austria
Belgium
Sweden
Japan
Norway
France
Germany
Finland
USA
Brazil
Canada
Ireland
Australia
New Zealand
England
Isle of Man
Wales
Guernsey
Jersey
Scotland
% of children with clinical asthma
.
Centre for Research on Indoor Climate and Health
Global burden of asthma
20
18
16
14
12
10
8
6
4
2
0
Centre for Research on Indoor Climate and Health
Centre for Research on Indoor Climate and Health
Centre for Research on Indoor Climate and Health
Mould has health impacts
45
40
No Mould
With Mould
% with asthma
35
30
25
20
15
10
5
0
No Smokers
Smokers
1996 EHCS
Centre for Research on Indoor Climate and Health
Sources of water vapour in housing
Overall 10 – 15 kg/day
Aquaria, saunas, whirlpool baths, storage of
green firewood?
Centre for Research on Indoor Climate and Health
Moisture release from fuels
A 4.5 kW flueless fire used for 8 hours a day will add
5.4kg of water vapour to the atmosphere of the house
Centre for Research on Indoor Climate and Health
Flueless gas fires
‘Flueless fires are a great way to make a real
contribution towards reducing your CO²
emissions, which contribute to climate change.
And not only is this type of fire 100% efficient, it
can reduce your fuel bills.’
Centre for Research on Indoor Climate and Health
MOULD and CONDENSATION
In housing:
Metal cladding
Absorbent surfaces
Non absorbent surfaces
Mould at RH>80%
Condensation RH=100%
Health Problems
Dripping?
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Psychometric Chart
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Design to avoid mould growth constrains temperatures
Centre for Research on Indoor Climate and Health
Design to avoid mould growth constrains
vapour pressure
Centre for Research on Indoor Climate and Health
Mould starts on thermal bridges
Centre for Research on Indoor Climate and Health
Effect of Internal Insulation
Ti=20C Te = 0C
Centre for Research on Indoor Climate and Health
Ti = 20C RHi = 50% Te = 0C
Centre for Research on Indoor Climate and Health
Ventilation needed to avoid mould growth
on an acceptable thermal bridge: f = 0.75
Ti = 20C Te = 5C
100
90
Surface Relative Humidity : %
Mould Growth
80
70
60
50
5 kg/day
10 kg/day
40
15 kg/day
30
0.1
0.2
0.3
0.4
0.5
0.6
Ventilation rate : ach
0.7
0.8
0.9
1
Centre for Research on Indoor Climate and Health
Ventilation needed to avoid mould growth
on a severe thermal bridge: f = 0.50
Ti = 20C Te = 5C
100
90
Surface Relative Humidity : %
Mould Growth
80
70
60
50
5 kg/day
10 kg/day
40
15 kg/day
30
0.1
0.2
0.3
0.4
0.5
0.6
Ventilation rate : ach
0.7
0.8
0.9
1
Centre for Research on Indoor Climate and Health
Ventilation needed to avoid mould growth
on a minimal thermal bridge: f = 0.9
Ti = 20C Te = 5C
100
90
Surface Relative Humidity : %
Mould Growth
80
70
60
50
5 kg/day
10 kg/day
15 kg/day
40
30
0.1
0.2
0.3
0.4
0.5
0.6
Ventilation rate : ach
0.7
0.8
0.9
1
Centre for Research on Indoor Climate and Health
The concentration of water vapour outside is
not zero and varies significantly over the year
2.0
1.8
95 Percentile
Mean
5 Percentile
Vapour Pressure : kPa
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Turnhouse 1983 - 2002
Centre for Research on Indoor Climate and Health
Much water vapour production is
intermittent and localised
2.4
Kitchen
Bedroom
Vapour Pressure : kPa
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0
3
6
9
12
15
18
21
0
Time
3
6
9
12
15
18
21
Centre for Research on Indoor Climate and Health
Moisture in the air interacts with building fabric and
furnishings – indoor humidity variations can be
controlled by modifications to the surface properties
KU Leuven 2006
Centre for Research on Indoor Climate and Health
Conclusions
X
X
X
X
We need ventilation to remove pollutants
from housing
In a typical house the most important
pollutant is water vapour which causes
mould growth
Problems are likely at ventilation rates less
than 0.5 ach
Get the ventilation right for water vapour
and it will be adequate for everything else.