The thermal performance of a direct expansion solar assisted heat pump (DX-SAHP) is analyzed for several refrigerants using two collector configurations, namely a bare collector and a one cover collector. The REFPROP computer program, developed by the National Institute of Science and Technology, is employed to predict the refrigerant properties involved in the energy balance across the collector. The thermal performance, as characterized by the coefficient of performance (COP), is determined for a variety of pure refrigerants as well as refrigerant mixtures. The performance degradation due to switching from R-12 to pure hydrofluorocarbon (HFC) refrigerants as well as refrigerant blends is investigated. A graphical procedure is developed and illustrated for several refrigerants for sizing the solar collector area and the heat pump compressor displacement capacity for the two collector configurations considered in this study. (c) 2005 Elsevier Ltd. All rights reserved.