Field evaluation of advanced controls for the retrofit of packaged air conditioners and heat pumps

This paper documents the magnitude of energy savings achievable in the field by retrofitting existing packaged rooftop air conditioner and heat pump units (RTUs) with advanced control strategies not ordinarily used for RTUs. A total of 66 RTUs on 8 different buildings were retrofitted with a commercially available advanced controller for improving operational efficiency. The controller features enhanced air-side economizer control, multi-speed fan control, and demand-controlled ventilation. Of the 66 RTUs, 18 are packaged heat pumps and the rest are packaged air conditioners with gas heat. The eight buildings cover four building types and four climate conditions. Based on the performance data collected for approximately 1 year, the normalized annual energy consumption savings ranged between 22% and 90%, with an average of 57% for all RTUs. The average fractional savings uncertainty was 12% at 95% confidence level. Normalized annual electricity savings were in the range between 0.47 kW h/h (kW h per hour of RTU operation) and 7.21 kW h/h, with an average of 2.39 kW h/h. RTUs greater than 53 kW and runtime greater than 14 h per day had payback periods less than 3 years even at electricity price of $0.05/kW h.