Air Source Chiller/Heat Pump in a Hybrid System for Cold Climate Heating, First Year's Experience

In the continuing search for economical and low carbon solutions to heating systems in cool climates, designers often turn to heat pumps, including air source units. Hydronic distribution has a number of advantages particularly when longer distances are encountered. Capacity does not always come cheaply, even using air source equipment, and electrical demand costs can diminish the operating cost benefit of heat pumps. Utilization of a hybrid heat pump/conventional heating system can mitigate these disadvantages while still providing benefits of a low carbon heat source. This paper describes the use of a conventional air cooled chiller/heat pump in a low temperature hydronic heating system for a public works garage/vehicle storage area, its design, commissioning, and first year's operating experience. It will describe the approaches taken to maximize the efficiency of the heat pump by minimizing required water temperatures, including radiant floor heating and high capacity fin tube and air coils. The utilization of the backup heating source to minimize installed cost, control electrical demand charges, and provide system redundancy will be described. Finally, the challenges of using fairly conventional air cooled equipment for cold climate heating will be described. Defrost cycle control and actual heating Coefficients of Performance will be examined using data from the building automation system. With the promise that this equipment holds in this application, it can be hoped that advancing technology and controls can make this a viable off the shelf solution from domestic suppliers to future low carbon heating system designs, particularly when the added cost of water source applications seems out of reach.