Impacts of simultaneous operating faults on cooling performance of a high efficiency residential heat pump

Air conditioning systems are known to experience operating faults, often caused by problems in their installation. To understand the impacts of these faults on system-wide performance requires laboratory tests with faults imposed, and many such experimental results have been published. However, it is likely that multiple simultaneous faults occur, but published results from testing with two simultaneous faults are very limited. This paper presents results from a laboratory study of an air-to-air heat pump system with combinations of: refrigerant charge (CH) too high or too low, evaporator airflow (EA), non-condensable gas (NC) in the refrigerant, and liquid line restrictions (LL). It provides the first published results of combinations of three and four simultaneous faults, in addition to previously untested types of double fault combinations. The impacts on cooling capacity and coefficient of performance (COP) are analyzed. COP reductions up to 34% occur within operation safety limits, meaning that such fault combinations would go unnoticed. An additional analysis examines the extent to which the superposition principle applies to combined fault impacts. The superposition principle is shown to have up to 25% error, indicating that there are synergistic effects – and sometimes cancelling effects – in the impacts from fault combinations.