
such that a sector of it that contains exhaust air passes first through the purging
chamber. The author has seen wheels turning the wrong way!
In addition, contaminants can be transferred from exhaust to supply ducts
by adsorption–desorption. This was confirmed by measurements with volatile
organic compounds (Andersson et al., 1993; Roulet et al., 2000) and perceived
air quality (Pejtersen, 1996). For example, measurements performed by the
author according to the protocol described in ‘Contaminant transport in
rotating heat exchangers’, below, gave the transfer rates illustrated in Figure
6.7. This figure shows transfer rates with and without a purging sector.
Leakage and entrained air would result in the same recirculation rate for all
chemical compounds, this rate being close to zero for the unit giving the results
of Figure 6.7. This is obviously not the case.
Outdoor air
Exhaust air
Extract air
Supply air
Figure 6.6 Schematics of the purging sector
Note: A part of the outdoor air cleans the porous structure and then is sent back to the
exhaust air.
0%
10%
20%
30%
40%
50%
60%
70%
No purging sector
With purging sector
n-Decane
1-Butanol
1-Hexanol
Phenol
1-Hexanal
Benzaldehyde
1,6-Dichlorohexane
Dipropylether
Limonene
m-Xylene
Mesitylene
Figure 6.7 Average VOC recirculation rates measured in the EPFL
laboratory unit, with and without a purging sector
Source: Roulet et al., 2000.
112 Ventilation and Airflow in Buildings
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