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Improving system efficiency for a variable-capacity/variable-blower-speed residential heat-pump system with multizone ductwork

This article describes efficiency improvements resulting from incorporating zonal airflow control into a variable-capacity/variable-fan-speed residential air-conditioning system. The results described are based on full-scale laboratory testing of prototype heat-pump equipment connected to a “typical-design” residential duct system located within a climatic chamber used to produce a range of summer climate conditions. The ductwork and air handler were located in the same space as the condenser (with exhaust venting), and compressor speeds and evaporator airflow rates were manipulated over a range of practical combinations to characterize the efficiency of the entire system. System coefficients of performance (COPs) were calculated based upon the delivery effectiveness of the duct system (cooling ultimately delivered through the grilles, divided by cooling supplied at the evaporator coil) and the efficiency of the HVAC equipment. Our results indicate that duct heat gain can be significantly reduced through an appropriately zoned airflow control mechanism. Zoned ductwork produces the highest system COP at all duct-zone temperatures, with the COP improvements being more pronounced at higher duct-zone temperatures and at lower capacities and airflow rates. Our results also validate the potential for using variable-capacity/variable-fan-speed technology combined with appropriate zonal control demand response events without compromising the efficiency of the air-conditioning system.