NIST performed a study of the use of central forced-air heating and cooling system modifications to control IAQ in residential buildings. The objective of this effort was to provide insight into the use of multizone modeling to evaluate such modifications, the potential of these modifications to mitigate residential IAQ problems, the pollutant sources they are most likely to impact, and their potential limitations of the IAQ control strategies. Another important objective of the project was to identify issues related to the use of multizone IAQ models and to identify areas for follow-up work.
CONTAM was used to simulate pollutant concentrations due to a variety of sources in eight buildings with typical HVAC systems under different weather conditions. Baseline simulations were performed to determine contaminant levels prior to implementing IAQ controls, then three IAQ control technologies were incorporated into the house models to determine their effectiveness in controlling the modeled pollutant sources. The IAQ control technologies included electrostatic particulate filtration, heat recovery ventilation, and an outdoor air intake damper on the forced-air system return.
Simulation results indicated that the system modifications reduced pollutant concentrations in the houses for some cases. However, the heat recovery ventilator and outdoor air intake damper increased pollutant concentrations in certain situations involving a combination of weak indoor sources, high outdoor concentrations, and indoor pollutant removal mechanisms. In cases where the IAQ controls reduced pollutant concentrations, they led to larger relative reductions in the tight houses than in the houses with typical levels of air tightness, though the typical houses still had lower post-control concentrations. The controls had the largest impact on concentrations of a non-decaying pollutant from a constant source. Limited system run-time under mild weather was identified as a limitation of IAQ controls that operate in conjunction with forced-air systems.