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.
This paper documents the magnitude of energy savings achievable in the field by retrofitting existingpackaged rooftop air conditioner and heat pump units (RTUs) with advanced control strategies not ordinarilyused for RTUs. A total of 66 RTUs on 8 different buildings were retrofitted with a commerciallyavailable advanced controller for improving operational efficiency. The controller features enhancedair-side economizer control, multi-speed fan control, and demand-controlled ventilation. Of the 66RTUs, 18 are packaged heat pumps and the rest are packaged air conditioners with gas heat. The eightbuildings cover four building types and four climate conditions. Based on the performance data collectedfor approximately 1 year, the normalized annual energy consumption savings ranged between 22% and90%, with an average of 57% for all RTUs. The average fractional savings uncertainty was 12% at 95% confidencelevel. Normalized annual electricity savings were in the range between 0.47 kW h/h (kW h perhour of RTU operation) and 7.21 kW h/h, with an average of 2.39 kW h/h. RTUs greater than 53 kWand runtime greater than 14 h per day had payback periods less than 3 years even at electricity priceof $0.05/kW h.
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