DOE/ORNL heat pump design model, overview and application to R-22 alternatives

Abstract

This computer program is a public-domain system design tool for application to air-to-air heat pumps. The main aspects of the program are reviewed with emphasis on the newest features of the current fifth-generation version (Mark V) and an upcoming more fully HFC-capable release (Mark VI). Current model predictions are compared to test data for a leading HFC alternative to HCFC-22 in heat pumps. Examples are shown of some user interfaces that have been recently developed for the program. To demonstrate the design capabilities of the model for R-22 alternatives, a refrigerant-side optimization was conducted to find the best balance of heat transfer versus pressure drop for HCFC R-22, HFCs R-134a and R-410A, and the natural refrigerant propane. COP was maximized while refrigerant charge and tube size were minimized. Independent design parameters were fraction of total area in the outdoor coil, tube diameter and number of circuits for each heat exchanger, and condenser subcooling. Heat exchanger design tradeoffs are discussed for a heat pump relative to air conditioners and heating-only units. A design optimized for heating-only operation is presented.