Refrigerant charge fault, Simultaneous faults, Residential air source heat pump, Fault impacts
The effects of refrigerant charge (CH) faults have been intensively investigated over the past three decades. However, the effect of CH faults in the presence of other faults, like the presence of non-condensable gas (NC), has been seldom studied. The patterns of the effect of CH faults on a system with other faults could be different from that on a fault-free system, which could degrade the performance of fault diagnostic tools and cause improper charging by technicians during installation or service of systems in the field. To address this problem, four common installation faults -improper evaporator airflow (EA), liquid line restrictions (LL), CH, and NC faults were imposed on an 18 SEER residential heat pump with a TXV metering device both individually and simultaneously, and the system was tested in a laboratory. First, the individual impacts of undercharge (UC) and overcharge (OC) on the performance of the system were evaluated under four different operating conditions. Then, the impacts of CH faults in the presence of the other three faults, both singly and in combinations, were examined at one operating condition. Under single CH fault conditions, the cooling capacity decreased for UC faults but was almost unchanged for OC faults, while the COP decreased for both UC and OC faults. In combination with other faults, the trend for UC faults is the same as those for the fault-free system. However, the OC fault can ameliorate the impacts of other faults on capacity, particularly a severe LL fault (LL32). The effect on COP for OC faults depends on fault type and intensity. For example, the COP with an OC fault decreased in the presence of light LL fault (LL22) but increased in the presence of a more severe LL fault (LL32). The variations of indicator variables such as refrigerant temperatures under different fault conditions are also presented.