Controllers for Inverter-driven Compressors

Variable refrigerant flow heat pumps are increasingly being deployed in California to support building electrification and decarbonization goals. While these systems are among the most efficient commercial heating, ventilation, and air conditioning technologies available, opportunities remain to further improve performance through advanced controls that optimize compressor operation. This field demonstration evaluated an emerging technology designed to improve the efficiency of inverter-driven compressors by dynamically adjusting operating parameters to better match system load.The study evaluated the emerging technology at three commercial facilities equipped with heat-recovery variable refrigerant flow systems. The project team installed the technology as an add-on controller, operating it in alternating Bypass and Save modes, to quantify its impact on energy consumption. The evaluation included interval energy monitoring, equipment operational data analysis, site interviews, and a review of installation experiences and market adoption considerations. The field demonstration showed that the emerging technology could meaningfully reduce energy consumption while maintaining occupant comfort. Across the three test sites, the technology improved efficiency by increasing suction pressure and reducing compressor lift, allowing compressor operation to more closely align with actual cooling loads. Analysis of operational data confirmed that these changes occurred without materially affecting indoor temperature conditions.The team developed regression models using outdoor air temperature as the primary independent variable to estimate annual energy savings. Estimated electricity savings were 14 percent of baseline consumption at Sites 1 and 2 and 24 percent at Site 3. Among other factors, the higher savings at Site 3 were likely influenced by longer equipment operating hours, as the facility operates 24/7. Across the three sites, the technology had an average simple payback of approximately 11 years.It should be noted that the analysis was limited to units operating in cooling mode because data collection was conducted only during cooling operation. Consequently, the reported savings may underestimate the total potential savings, which could be greater if heating mode performance were included.