Impact of High-Efficiency and Variable-Speed Motors on the Performance of a Residential Split-System Heat Pump

In the current marketplace, most ducted split-system heat pumps feature single-speed compressors and fans. To meet forthcoming minimum energy rating requirements, reduce operational costs, and increase environmental sustainability, the seasonal heating and cooling efficiencies of heat pump systems must be improved. Variable-speed equipment offers significant advantages for load modulation and has the ability to increase the seasonal performance greatly. Additionally, novel electrical motor technologies, such as permanent magnet (PM) motors, can reduce the power consumption of the motors by up to 25-55% compared to the widely used permanent split capacitor (PSC) motor or electronically commutated motor (ECM). In this study, a low cost ducted single-speed heat pump system with a cooling capacity of 10.55 kW was analyzed to quantify the impact of fan and compressor motor efficiency on seasonal coefficient of performance (SCOP). Furthermore, single-speed components were replaced with variable to evaluate the performance increase. The single-speed heat pump was experimentally tested, and the results were used to tune a detailed model for further performance analyses. The efficiency was evaluated in heating and cooling mode according to AHRI Standard 210/240 and with an energy savings and cost analysis, that details the SCOP and costs for different locations. The conversion of the fan motors to high efficiency PM magnet motors increased the SCOP by up to 6%. The impact was dependent on the initial motor efficiency and the operational mode. The indoor unit fan motor has a large impact on SCOP in cooling mode and a low impact in heating mode because of the motor waste heat’s impact on capacity. The conversion to a fully variablespeed system greatly increased the performance, with a 72% increase in cooling SCOP and a 19% increase in heating SCOP. The energy savings and cost analysis concluded that the fan motor conversion from single-speed to high efficiency motors is economically viable, but the financial benefit of the upgrade to variable-speed depends on the intended location of use