HVAC Systems As Emission Sources Affecting Indoor Air Quality: A Critical Review

Abstract

This study evaluates literature on heating, ventilating and air conditioning (HVAC) systems as contaminant emission sources that affect indoor air quality (IAQ). The various literature sources and methods for characterizing HVAC emission sources are reviewed. Characterization methods include in situ tests, longitudinal and cross-sectional studies, and laboratory studies. A critique of the literature reveals that few studies are well-controlled, comprehensive and quantitative. Significant gaps in the data are highlighted and procedures are suggested to improve the characterization of bioaerosol and VOC (volatile organic compound) emission sources. Several HVAC components are cited frequently as emission sources, and there is broad agreement regarding their significance. These sources include biological growth and bioaerosol generation in the presence of moisture provided by air washers and other recirculating water systems, or by poor control of humidity, badly designed humidifying systems, and inadequately maintained cooling coils and drip pans. IAQ problems appear exacerbated by dust accumulation, and by the presence of fibrous insulation. Other problems include entrainment, migration, and infiltration of indoor and outdoor contaminants that are distributed to indoor spaces by the HVAC system. The importance of good design and operation of HVAC systems, including the appropriate placement and maintenance of air intakes, building pressurization, and local exhaust in source areas, is also well accepted. More limited data implicate dust (resulting from inadequate filtration and maintenance of filters) as a secondary source for VOCs.