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ABSTRACT

Current rating standards for residential, electric-driven vapor compression systems determine seasonal energy efficiency (e.g., SEER) using a bin method along with equipment performance data from steady-state tests at different operating conditions. These standards were originally developed for equipment with single or two-stage thermostat control but have been incrementally updated to include equipment with advanced controls and variable-speed compressors and fans. However, the controls are overridden during equipment testing and therefore the rated performance does not consider the interaction of the integrated controls, equipment, and building dynamics. As a result, the standard ratings do not fully capture the characteristics of part-load operation and do not necessarily reward equipment with superior controllers. To address these issues, a load-based testing methodology has recently been developed for estimating the seasonal performance of variable-capacity cooling and heating equipment. The load-based testing methodology emulates the response of building sensible and latent loads to the equipment controls in a psychrometric test chamber by continuously updating the room temperature and humidity based on a virtual building model. The test unit thermostat naturally responds to the dynamic temperature variation and controls the equipment capacity in response to a deviation from its setpoint. The test unit thermostat is installed in a thermostat environment emulator to provide a standardized environment to the thermostat in order to ensure realistic and reproducible conditions for the thermostat. This enables the load-based testing procedure to capture realistic control interactions and performance of a heat pump in a laboratory using psychrometric test chambers. However, to adopt the developed methodology for nextgeneration rating standards, it is crucial to assess the repeatability and reproducibility of the load-based testing approach. In this paper, the assessment of the repeatability of the load-based testing methodology for a 3-ton variable-speed heat-pump operating in cooling mode is presented. The test unit performance was measured multiple times in the same psychrometric facility based on the load-based testing approach. A comparison of the test equipment estimated seasonal performance for different sets of tests is presented along with a discussion of the causes for the differences.