Conference Year



Load-based testing, virtual building model, thermostat installation


To better characterize the performance of variable-speed DX (Direct Expansion) equipment in a laboratory environment, a load-based psychrometric chamber testing methodology has been developed as an alternative to existing steady-state testing approaches. The methodology allows equipment to respond dynamically to a virtual building model using its integrated controls. To mimic an actual building, a virtual building model incorporates sensible and latent loads along with simple lumped capacitance building dynamics that interact with the variable-speed equipment. The rated capacity of the test equipment is used along with a specified sizing factor and target sensible heat ratio (SHR) to specify the building sensible and latent load models. In addition, heuristic approaches are used to specify and scale sensible and latent capacitances of the virtual building model. Two companion papers present the overall methodology and results for different variable-speed heat pumps using default building parameters. This paper studies the impact of the virtual building load parameters on overall performance and dynamic behavior of the equipment for load-based testing. It is shown that equipment seasonal performance can increase significantly with increasing sizing factor. In addition, performance increases with decreasing building SHR results. In addition to simple lumped capacitance models, more detailed two-node models are investigated to evaluate more realistic dynamics and their impacts on seasonal efficiency ratings. In addition, the impact of the thermostat location on equipment dynamics and performance ratings is considered.