Integrated forced-air heating and ventilation systems: evaluation and design considerations.

Mechanical systems which use common ducts for combined heating and ventilating functions are becoming popular in the Pacific Northwest (U.S.). These systems range from simple fresh-air inlets ducted to the return side of a forced air heating s stem to more complex heat recovery ventilation systems utilizing the K eating ducts for air distribution. Typical integrated systems do not have heat recovery capability. Several approaches to integrating and controlling non-heat recovery ventilation and forced air heating systems were evaluated as part of the Residential Construction Demonstration Project (RCDP). The houses tested for this study were built under Bonneville Power Administration sponsored energy-efficiency programs. Fan pressurization tests were performed to assess the envelope leakage characteristics, and tracer gas decay tests were used to measure infiltration and mechanical ventilation rates. Large variations in envelope tightness and mechanical ventilation rates were encountered. In most cases, the amount of accidental air leakage through ducts and air handlers exceeds the amount of fresh air intentionally supplied to the system. Systems which are properly designed, installed, and operated work well, but the potential for problems is large.