7 – Indoor Air Quality Introduction Another important objective of design for the buildings we live and work in and the transport we travel in is ensuring the indoor air quality (IAQ). Most people are aware that outdoor air pollution from traffic and smoke pollution can damage their health but may not know that indoor air pollution can also have significant effects. Studies of human exposure to air pollutants indicate that indoor air levels of many pollutants may be 2-5 times, and occasionally, more than 100 times higher than outdoor levels.
Over the past several decades, our exposure to indoor air pollutants is believed to have increased due to a variety of factors, including the construction of more tightly sealed buildings, reduced ventilation rates to save energy, the use of synthetic building materials and furnishings, and the use of chemically formulated personal hygiene products, pesticides, and household cleaners.
Impact on Humans There are 2 main objectives: a) Health - avoid risk b) Comfort - fresh and pleasant environment IAQ is not constant - it depends on several time-varying factors: building operation, occupant activity, outdoor climate.
Air Composition • Fresh air contains 21% oxygen and 0.03% carbon dioxide. • Expired air is typically 16% oxygen and 4% carbon dioxide. • Health standards are usually less strict in requirements than comfort standards, except for toxic gases that have no smell: CO2 levels > 5% (50000 ppm), acute danger to health (also if O2 < 12%) CO2 levels > 0.35% (3500 ppm), long term health implications CO2 levels > 0.1% (1000 ppm), poor comfort
Factors Affecting Indoor Air Quality It is important to understand the role that each of these factors can play in order to prevent, investigate, and resolve indoor air quality problems. a) Source: there is a source of contamination or discomfort indoors, outdoors, or within the mechanical systems of the building. b) HVAC: the HVAC system is not able to control existing air contaminants and ensure thermal comfort (temperature and humidity conditions that are comfortable for most occupants). c) Pathways: one or more pollutant pathways connect the pollutant source to the occupants and a driving force exists to move pollutants along the pathway(s). d) Occupants: building occupants are present and are affected enough to raise indoor air quality concerns.
Sources of Pollutants Indoor air contaminants can originate within the building or be drawn in from outdoors. If contaminant sources are not controlled, IAQ problems can arise, even if the ventilation system is properly designed and well-maintained.
Category Outside the Building
Source Contaminated outside air Emissions from nearby sources Soil gas
Equipment
Moisture or standing water promoting excess microbial growth HVAC system
Non-HVAC equipment Human Activities
Personal activities Housekeeping activities
Maintenance activities Building Locations that produce or components collect dust or fibres and furnishings Unsanitary conditions and water damage
Other sources
Chemicals released from building components or furnishings Accidental events
Special use areas and mixed use buildings
Examples pollen, industrial pollutants, general vehicle exhaust exhaust from local vehicles, reentrained exhaust from building radon, leakage from underground fuel tanks, landfill gas crawlspace beneath buildings
dust or dirt in ductwork or other components, improper venting of combustion products, refrigerant leakage emissions from office equipment (volatile organic compounds, ozone) smoking, cooking, body odour, cosmetic odours cleaning materials and procedures, airborne dust or dirt (e.g., circulated by sweeping and vacuuming) airborne dust or dirt, volatile organic compounds from paint textured surfaces such as carpeting, curtains, or other textiles, materials containing damaged asbestos microbiological growth in areas of surface condensation, dry traps that allow the passage of sewer gas volatile organic compounds or inorganic compounds fire damage, microbiological growth due to flooding or to leaks from roofs or piping laboratories, exercise rooms, food preparation areas
ASHRAE Fundamentals handbook: sources, possible concentrations and indoor-tooutdoor concentrations of some indoor pollutants Pollutant
Sources of indoor pollution
Possible indoor concentration
carbon monoxide
combustion equipment, engines, faulty heating systems stoves, fireplaces, cigarettes, condensation of volatiles, aerosol sprays, re-suspension, cooking combustion, solvents resin products, pesticides, aerosol sprays combustion, gas stoves, water heaters, driers, cigarettes, engines heating system combustion, resuspension, heating system matches, gas stove insulation, product binders, particleboard building materials, groundwater, soil fireproofing
100 mg/kg
IndoorOutdoor concentration ratio >>1
100 to 500 µg/m3
>>1
n/a
>1
200 to 1000 µg/m3
>>1
20 µg/m3 100 µg/m3
>1
homes, buildings
>1
n/a
>1
homes, schools, offices homes, schools, offices homes, schools, offices homes, hospitals schools, offices, public
20 µg/kg 200 µg/kg
1
respirable particles
organic vapours
nitrogen dioxide
sulphur dioxide total suspended particles without smoking sulphate formaldehyde radon and progeny asbestos mineral and synthetic fibres carbon dioxide viable organisms
ozone
Location
skating rinks, offices, homes, cars, shops homes, offices, cars, public facilities, bars, restaurants homes, restaurants, public facilities, offices, hospitals homes, skating rinks
aeroplanes offices
Outdoor air pollution Common pollution forms are as follows. a) Grit and dust: these are heavy enough to settle out of the air. b) Smoke: this consists of very fine solid or liquid particles produced by the incomplete combustion of fuels. Particle size is typically less than 1µm; the average is 0.1-0.3µm. c) Fogs: these are fine airborne droplets usually formed by condensation of vapour; mists are slightly larger droplets that are ordinarily liquid at normal temperature and pressure. d) Pollutant gases: these include sulphur dioxide, carbon dioxide, carbon monoxide and ozone. Dust usually falls close to (and downwind of) the industrial chimneys (or volcanic eruptions) which emit it, but smoke and pollutant gases mix with the air and may travel some distance unless they are washed out by rain or fog formation occurs. The effects of pollution are very wind and topography dependent. Smoke particles are deposited and adhere to building surfaces, especially where there is turbulence (e.g. near window edges, and building protrusions).
In residential areas, pollution concentration in the street is similar to that at roof height because domestic chimneys are not high enough for the smoke and gas emissions to avoid the wind turbulence at roof level. Urban pollution is worst in conditions of light winds and temperature inversion (when a layer of air warmer than that at ground level exists at a height of 100m or more). Smog, often applied to the haze caused by sunlight-induced photochemical reactions with exhaust emissions, is an air mixture of of smoke particles, mists and fog droplets that can impair visibility as well as being irritating and unhealthy.
Cigarette Smoke Environmental tobacco smoke consists of a suspension of small 0.01 to 1.0µm liquid particles that form as the superheated vapours leaving the burning tobacco condense. Also produced are numerous gaseous contaminants including carbon monoxide. Indoors, required ventilation rates are much higher in spaces in which smoking is allowed.
Volatile Organic Compounds (VOCs) • After ventilation, VOCs are usually the first concern when diagnosing an IAQ problem. • VOCs include chlorinated hydrocarbons, alcohols, benzene and esters. VOCs are emitted from a large variety of sources, some continuous (e.g. building materials), others intermittent (e.g. from carpet shampoos). Other sources are combustion products from gas stoves, paint, printers, spray cans, cosmetics, paint strippers etc. Formaldehyde, from compressed wood products, is an important VOC. • In new office buildings, the total VOC at initial occupancy can be 50 to 100 times that of the outside air; levels decrease with time (31.3 decipol
• In many well-ventilated buildings with low pollution sources, the perceived air pollution is below 1 decipol or 15% dissatisfied. • Spaces with low ventilation and high pollution sources may have a perceived air pollution above 10 decipol or 60% dissatisfied. • Air qualities around 0.1 decipol or 1% dissatisfied are hard to establish in indoor environments. • The unit of perceived air pollution can also be used in cars and aeroplanes or for quantifying outdoor pollution. • In one study of 15 offices in Copenhagen, it was found that for each occupant there were on average 6-7 olfs from other pollution sources (1-2 olfs from materials in the space, 3 from the ventilation system and 2 olfs caused by tobacco smoking), ie. only 13% of the perceived pollution was from the occupants. The ventilation rate was 25l/s per person (higher than usual rates), but due to the extensive pollutant sources, this was only equivalent to 4l/s.olf. This explains why more than 30% of occupants found air quality in the offices unacceptable. • The results were in contrast to ventilation standards throughout the world which assume that human beings are the principal polluters in offices and similar spaces. • Large variations in pollutants were found form one office to another. • Systematic removal or reduction of pollutant sources will improve air quality, decrease required ventilation rates and thereby decrease energy consumption, and diminish the risk of draught. • The development of such metrics opens the possibility of moving away from prescriptive measures to control air quality (e.g. 8l/s per person) to a performancebased criterion based on perceived pollutant levels.
Control of IAQ A) Source control • removal/replacement of source • isolation of source • local ventilation of source B) Application of general ventilation
Summary of recommended control measures and strategies for indoor pollutant control. From Air Infiltration and Ventilation Centre (AIVC) Technical Note 26 “IEA Annex IX: Minimum ventilation rates and measures for controlling indoor air quality”, 1989. Indoor
Effects
pollutant
Indoor
Control measures -
Minimum
concentration limit
source control
ventilation rate
Preferred strategy
Tobacco
annoyance,
annoyance/irritation
restriction of
50-120 m3 per
restriction or
smoke
irritation,
for healthy person:
smoking, separation
cigarette or 8-20 l/s
separation whenever
health risks
1-2 ppm CO
of smokers and non-
per person
possible, adequate
smokers
(moderate smoking
ventilation in large
in large
public rooms or
rooms/offices)
offices if smoking allowed
Particles
see above
75 µg/m3
see above
17.5l/s per person
tobacco smoke is the
(based on average
main source of
smoking habits)
particles, therefore strategy as above
Body odour
annoyance
0.10% CO2
8.0 l/s per person
ventilation variable
(0.15% CO2)
(3-4 l/s per person)
with occupancy, if occupancy predictable
Humidity
damage to
relative humidity
extract ventilation
approx. 0.5-1.0 ac/h
building
below 70% is a
in kitchen and
main sources and
fabric
necessary but not
bathroom
minimum whole house
sufficient condition Indoor
health risks
ionising
3
extract ventilation at
ventilation rate
200-400 Bq/m as
sealing to the soil,
no generally valid
radon from soil:
action level
avoiding negative
ventilation rates
sealing, avoiding
radiation
pressure gradient
negative pressure
(radon)
gradient radon from building material: balanced mechanical ventilation
Combustion
annoyance,
products
e.g.WHO guidelines
replacement of
no generally valid
replacement, local
irritation,
unvented
ventilation rates
extraction, corrective
health risks
combustion
measures for chimney
appliances, local
backdraughts (e.g.
extract ventilation
adequate outside air supply)
Selected
annoyance,
for some
restriction/interdicti
no generally valid
product control;
organic
irritation,
substances, limits
on of use of
ventilation rates
restriction/interdiction
substances
health risks
have been
carcinogens;
, limitation of
established
limitation of
emission rates
emission rates
Tutorial Questions - Air Quality
1. Which are the two main requirements with respect to the quality of indoor air? 2. What are the two main strategies for controlling indoor air quality? Give one or more examples of each. 3. Why is indoor air quality not constant? 4. For industrial environments there is a list of Threshold Limit Values (TLVs). What do these values indicate? 5. Indicate a strategy to reduce exposure to radon in the indoor air. 6. Why is it difficult to set guidelines with respect to Volatile Organic Compounds (VOCs)? Indicate some strategies to reduce VOC exposure. 7. What is an olf, and what is the unit used for? 8. What is a decipol, and what is this unit used for? 9. Assume a lecture room with a volume of air of 360m3, which is ventilated with fresh air at a rate of 1 ac/h. How much is the ventilation rate when expressed in l/s? In the room are 50 persons (in terms of pollution, assume they are on average equal to a standard person), and effectively no other pollution sources. What is the sensory pollution load expressed in olf? What is the perceived air quality when expressed in decipol? [100 l/s, 50 olf, 5 decipol].
