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Figure 6.7 shows that certain categories of volatile organic compounds

(VOCs) are easily transferred by a sorption transfer mech anism. Among the

tested VOCs, those having the highest boiling point were best transferred. The

largest transfer rate in a well-installed unit was found for phenol (30 per cent).

Leakage and pollutant transfer can be avoided or at least strongly reduced

through proper installation of the wheel, good maintenance of the gasket,

proper installation of a purging sector, and by maintenance of a positive

pressure diﬀerential from supply to exhaust duct at wheel level.

Coils

Laboratory tests (Bluyssen et al., 2003) show that heating and cooling coils

without condensing or stagnating water, are components that have small contri-

butions to the overall odour intensity of the air. On the contrary, cooling coils

with condensed water in the pans are microbial reservoirs and ampliﬁcation

sites that may be major sources of odours to the inlet air.

Measurement protocols

HVAC systems are in general low sources of measurable chemical pollutants .

When searched for, most pollutants are below the detection limits of

common analysers, and chemical analyses can be successful only in very

polluted systems. They are therefore not discussed here.

No standard procedure exists for microbiological measurements in ventila-

tion systems. The techniques used are air sampling with impactors, gluing

airborne microbes (mould, yeast, bacteria) on appropriate culture media, or

simply exposing these culture media in open Petri dishes or on ﬁlms lying or

glued on the inner walls of ducts or units. The main problem is ensuring

reproducible samples.

Only two methods are presented here: the measurement of sensory pollu-

tion and the assessmen t of contaminant transfer.

Sensory pollution

Principle of the method

Since the nose is the most sensitive instrument to detect pollutants, the

measurement protocol to assess the pollution resulting from ventilation systems

or components is mainly focused on measuring the sensor y pollution eﬀect,

evaluated by a trained panel of people (Bluyssen, 1990; Elkhuizen et al., 1995).

A panel of 12–15 subjects is selected and trained to give a value to the odour

intensity. To evaluate air quality at a given place, each panel member smells the

air – after having refreshed his or her nose in pure, fresh air – and gives a value

to the odour intensity. The ﬁnal value is the average over the panel.

Contaminants in Air Handling Units 113

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Sharp JX-9400 Technical Information Seite 134