Effect of a needle heat exchanger on the release of microbes into supply air

The needle heat exchanger (acts as a pre filter EU3) was installed in front of the glass fiber used as a fine filter (EU7) in the supply air chamber. Thus, the temperature of the supply air increased and the relative humidity of the fine filter next to the heating unit decreased. The aim of this study was to examine how the installation of the needle heat exchanger effects on the microbial growth and release in the fine filter. The relative humidity of the fine filter in the supply air unit fell below 70 % during different seasons. Reduced relative humidity seemed to reduce the contamination or at least the release of microbes from the fine filter. However, an interesting observation was the presence of the thermophilic microbe Aspergillus fumigatus in the material sample taken from the glass fiber filter, in air of cold supply air chamber and on surfaces of the heat exchanger and warm air chambers, but not in the supply air.