Evaluating the reproducibility of a load-based and climate-specific test procedure using a centrally ducted cold-climate air-source heat pump
The authors evaluated the reproducibility of a load-based rating and test procedure using a centrally ducted coldclimate air-source heat pump as part of the “3R’s” testing (Representativeness, Repeatability, Reproducibility). The procedure requires heat pumps to operate in all operating modes with native controls, such that performance results encompass steady-state and part-load cyclical operation while also taking into consideration defrost cycles and standby energy consumption. The unit under test (UUT) was a variable speed 7 kW capacity system with communicating thermostat that had previously been field and laboratory tested for evaluations of representativeness and repeatability. The UUT was installed and tested in a laboratory designed to meet the requirements of the procedure’s testing tolerances and virtual building load emulation. The objective was to produce cooling and heating seasonal coefficients of performance (SCOPC and SCOPH) from a complete series of rating tests using the same building load line and equipment installation as that used during previous testing conducted in another laboratory. The UUT achieved an overall reproducibility of “fair”, with 8.6 % mean difference in SCOPC, and 8.8 % mean difference in SCOPH between facilities. There were several factors affecting reproducibility identified during testing, including (a) differences in instrumentation measurement lag between testing facilities; (b) potential indoor chamber response lag; (c) issues in properly measuring UUT capacity during defrost operations; (d) installation differences between facilities; (e) equipment and thermostat dynamic response differences between labs, and (f) an unverifiable thermostat setup. Overall, the UUT was consistent in reproducing individual part-load and full-load behaviour under matching test conditions, which reflects favourably on the procedure’s ability to induce a consistent equipment response between testing facilities.