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The eﬀect of airﬂow on the perceived air quality from ducts was relatively

small and is probably insigniﬁcant in normal applications. Increasing the

airﬂow rate in the duct does not, surprisingly, reduc e the odour intensity: the

additional airﬂow rate certainly dilutes the evaporated oil but the increased

air velocity also evaporates more oil.

Emissions from dust/debris accumulated in the ducts during construction

(mostly inorganic substances) seem to be less important. No simple correlation

was observed between the amount of accumulated dust and odour emissions.

However, the organic dust accumulated during the operation period may

produce more severe odour emissions. When dust has accumulated on the

inner surface of the ducts, the relative humidity of the air in the ducts has a

larger eﬀect on the odour emissions of ducts without oil residues than ducts

with oil residues.

Humidiﬁers

The main reasons for pollution from humidiﬁers are: disinfecting additions, old

water in tanks or dirty tanks, microbiological growth, stagnant water in the tank

when the humidiﬁer is oﬀ, and desaliniza tion and demineralization devices and

agents (Mu

ller et al., 2000).

Humidiﬁers only pollute the air signiﬁcantly if the humidiﬁer is not used or

maintained in the prescribed way. Investigations make it clear that periodical

cleaning of humidiﬁers and the use of fresh water are paramount for a good

air quality.

Under normal conditions, it was found for all humidiﬁers that airﬂow has no

inﬂuence on the odour intensity caused by humidiﬁers (see Figure 6.3).

A relatio n was found between perceived air quality and the concentration of

bacteria on the inside of the humidiﬁer (see Figure 6.4). The odour intensity

increases with increasing number of bacteria. This was not the case for other

locations in an HVAC system. A similar correlation could not be found for

fungi.

0 500 1000 1500 2000

Odour intensity

Airﬂow rate [m

/h]

1 on 2 on 3 on

1 off 2 off 3 off

Figure 6.3 Perceived air quality for the steam humidiﬁer

Source:Mu

ller et al., 2000.

110 Ventilation and Airﬂow in Buildings

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Sharp JX-9400 Informazioni Techniche Pagina 131