Analysis of Zoned Residential Ventilation Systems

Trends in home heating and cooling in the US are resulting in less mixing of air within dwellings, either due to not using central forced air systems, or to reduced loads and runtimes in high performance homes. This study examined the use of zoned ventilation systems using a coupled CONTAM/EnergyPlus model of new California dwellings, including a 1-story single-family dwelling and a single apartment unit. Zoned and unzoned ventilation systems were simulated for exhaust, supply and balanced fan types. Smart controls were designed to reduce ventilation energy use and provide equivalent occupant pollutant exposures, using metrics that allow the efficacy of ventilation to be calculated on a zonal basis. The key metric was the personal exposures of the dwelling occupants to a number of contaminants of concern, including moisture, formaldehyde, CO2, particles and a generic contaminant.

Emission rates were based on previous field studies and research literature, and they include a mixture of episodic and background emissions that were scheduled to align with zone occupancy patterns and activities (e.g., cooking, bathing, sleeping). These personal exposures were compared for smart controlled and baseline reference cases to ensure equivalence, as well as between zoned and unzoned fan types. Results showed that while zonal ventilation has the capability to save energy beyond that offered by single-zone approaches, care is required in the design and evaluation of zonal controls because all control types led to increased personal exposures for at least one of the contaminants. Substantial differences were identified between fan types, in terms of their ability to deliver outside airflow to occupied zones, the resulting personal pollutant exposures, and in energy performance.