Ideal heat pump performance models containing one adjustable parameter and intensive thermodynamic variables were developed by transformation of the energetic functions of Rankine heat pump. Two unknown groups in the formulated model, labeled AKR and AKF, were found to curve fit to two intensive variables as linear functions. The parameters of the linear fits were obtained using the least square method; consequently, AKR and AKF were expressed as temperature-lift variables. Maximum errors of about 5% were encountered at conditions below reduced temperature of 0.8. Better accuracy was obtained in the range of practical temperature lift (i.e., 10-80 degrees C). Only one fit parameter value is required by these models where similar correlations require three or more. Furthermore, unlike some of the available models where different equations are required for each working fluid, these equations are not working fluid specific and do not require thermodynamic properties' tables or charts. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 1905-1911, 2011