AIR AND VENTILATION 1 POLLUTION
It would be prudent to ensure that the quality of a building’s incoming air meets at least the UK Air Quality Standard Regulations 2010
environment is somewhat attenuated by the building itself, and the primary pollutants tend to decrease with height, with NO2 concentrations being lowest at roof level. Vehicle emissions increase as vehicle
speed reduces. Hence it is preferable not to site intake louvres close to road junctions or areas where traffi c is travelling slowly. Intakes facing side streets away from main traffi c would normally be preferable. However, attention must be paid to
any local loading bay or vehicle entrance, and the effects of local wind vortices on contributing sources of pollution should be considered. Air intakes located close to vehicle parking spaces or entrances are likely to entrain CO emitted from the cars. When considering mechanically
ventilated buildings, the principal concern is the position of the intake louvre. Apart from sources beyond the building curtilage and the ventilation systems themselves, local sources that can impact the quality of the air entering the louvre will include: ● Cooling towers; ● Plumbing or oil tank vents; ● Exhausts from standby generators (or combined heat and power engines);
● Vehicle loading bays; ● Roosting ledges for birds; ● Areas where leaves or other litter might collect;
● Stagnant water (eg, on fl at roofs); and ● Gardens or areas of vegetation. CIBSE TM40: Health issues in building services reports that a study of offi ce occupants has shown that air inlets located within 8m of an exhaust outlet or a rubbish container will double the reported respiratory symptoms; a similar distance from a roadway will increase the reports by 190%. TM21 includes practical guidance on
the siting of intake louvres (as in Figure 1) that requires an understanding of local meteorological conditions and the infl uences on the microclimate by the building and its surroundings. To provide a wider commentary, ASHRAE’s Indoor Air Quality Guide – Best practices for design, construction and commissioning (a version of which is freely downloadable) provides extensive background information in this area and includes specifi c guidance on the positioning of intake louvres (see Figure 2). CJ
Figure 2: Guidance on location of ventilation intakes (Source: ASHRAE Indoor Air Quality Guide)
Wind tunnel modeling, computer simulations, and computational fl uid dynamics
Rooftop AHU
5m to basin
8m to exhaust 5m
5m
Noxious Exhaust
10m
Signifi cantly Contaminated Exhaust
Cooling towers, evaporative condensors, and fl uid coolers
Laboratory fume hood and exhaust stacks
Special considerations for packaged HVAC units
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DISCOUNT ON CIBSE TM21
CIBSE TM21: Minimising pollution at air intakes is available online free to CIBSE members through the Knowledge Portal. It can also be purchased in hard copy (by both members and non-members) at a discount of 50% by using the code TM21MAR. Visit:
www.cibseknowledgeportal.co.uk
Exhaust vents Plumbing vents
Other sources of contamination
Air 5m Intake 2m
Rubbish bins
8m
Heavy Traffi c
Original source: Indoor Air Quality Guide – Best practices for design, construction and commissioning © ASHRAE 2009 Dimensioning approximately converted to SI from original IP. Used with permission
50 CIBSE Journal March 2012
www.cibsejournal.com
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