HYGIENIC ASPECTS OF GROUND-COUPLED AIR SYSTEMS

Numerous ground-coupled air systems have been constructed in combinati on with heat recovery units in mechanically ventilated buildings in Sw itzerland. The objective of this study was to investigate the microbia l content within these ventilation systems and to monitor the quality of the air supply. The concentrations and the types of microorganisms in the outdoor air, in the air of the pipes and in the supply air of t welve ground-coupled air systems were determined. In addition, three b uildings were examined four times a year to cover seasonal changes. In general, the concentrations of fungal spores and bacteria in the air at the end of the underground pipes were lower than in the outdoor air , but great differences were observed between ventilation systems of l arge buildings and one-family houses. Occasionally, an increase in the concentration of Penicillium, Aspergillus or Actinomycetes was noted within a piping system. The concentrations in the supply air behind th e filters were always low. Based on these investigations, the operatio n of ground-coupled air systems can be recommended as long as regular controls are undertaken and cleaning facilities are available.