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Contaminants in

Air Handling Units

The purpose of mechanic al ventilation systems is to supply appropriate

amounts of clean air and to evacuate vitiated air. However, in ﬁeld audits it

was seen that ventilation systems often host contaminant sources and are, in

the worst cases, the main source of air pollution in buildings (Fanger, 1988;

Bluyssen et al., 1995, 2000b). Compo nents in the mechanical ventilation

system may considerably pollute the passin g air. The main sources and reasons

for pollution in a ventilation system vary considerably depending on the type

of construction, use and maintenance of the system. This chapter summarizes

the results of these ﬁeld audits, and proposes methods to detect the sources of

contaminants and strategies to avoid these.

Filters

Filters are one of the main sources of sensory pollution in ventilation systems

(Bluyssen et al., 2000a). Some new ﬁlters may also inﬂuence the perceived air

quality negatively. The ﬁlter material has a signiﬁcant inﬂuence on the starting

pollution eﬀect of new ﬁlters (see Figure 6.1).

When ﬁlters get older, i.e. are in use for some time, the emission of odours

ﬁrst dec reases, but increases again later, when the ﬁlter gets loaded. The reason

for this emission after the ﬁlter is in use for some time remains unclear,

however.

Micro-organisms may not be the only pollution source on a ﬁlter, but it is

important to keep ﬁlters dry, since wet media ﬁlters are perfect supports for

microbial gr owth and microbes may also emit dangerous pollutants and bad

odours. Filters may be moistened either by snow, rain or fog entering the

outdoor air inlet, or by water droplets spread by some humidiﬁers or found

in airﬂows downstream of the cooling coils.

Environmental conditions such as airﬂow (amount or intermittent/contin-

uous) and temperature do not have a signiﬁcant inﬂuence on the pollution of

downwind air.

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Sharp JX-9400 Technical Information Seite 129