Comparative Studies of Scroll and Rotary Compressors for US Market Heat Pumps and Air Conditioners
Comparative, experiment, test
Rotary compressors have long been developed and adopted for heating, ventilation, and air-conditioning (HVAC) applications across Asia, primarily due to their simpler mechanism and fewer parts as compared to their counterparts such as scroll compressors. However, rotary compressors in heat pumps (HPs) and air conditioners (ACs) in the US have limited market share and are often confined to systems smaller than 3.0 tons (10.6 kW). This paper consists of two parts; the first is on rotary compressor technology and its advantages and disadvantages from both technical and market standpoints. The review consists of a survey of the literature, as well as a survey from field experts through anonymous interviews. Conventionally, rotary compressors are regarded as having lower efficiency in systems larger than 3.0 tons (10.6 kW), which limits their current application to small packaged systems and automotive ACs. The second part includes an experimental investigation of compressor and system efficiencies using scroll and rotary compressors. The compressors compared were drop-in replaced in typical 2.5 (8.8-kW) and 5.0-ton (17.6-kW) R410A split HP systems. Experimental tests, both in cooling and heating modes, were conducted under AHRI 210/240 Standard operating conditions. The test units were extensively instrumented on both the refrigerant and air-side to measure temperature, humidity, pressure, flow rate, and power consumption, according to ASHRAE Standard 41.2. Indoor and outdoor units were placed in a wind tunnel and in an environmental chamber, respectively. The results showed the 2.5-ton (8.8-kW) unit rotary compressor’s isentropic efficiency was 2.6% and 14% higher than the scroll compressor in cooling and heating, respectively. At 5.0 tons (17.6 kW), the isentropic efficiency of the rotary compressor was 5.4% lower in cooling and 6.3% higher in heating. In terms of volumetric efficiency, at 2.5 tons (8.8 kW) the rotary compressor was 1.7% lower in cooling than scroll compressor, and comparable to the scroll compressor at two of three heating mode test points. At 5.0 tons (17.6 kW), the rotary compressor volumetric efficiency was 0.7% and 2.8% higher than the scroll compressor in cooling and heating mode, respectively. The overall system with the rotary compressor had 5.7% higher seasonal energy efficiency ratio (SEER) and 3.0% higher heating seasonal performance factor (HSPF) than the scroll compressor at 2.5 tons (8.8 kW). At 5.0 tons (17.6 kW), the system with the rotary compressor was 2.6% higher in SEER and 0.6% higher in HSPF compared to the system with the scroll compressor.