An analytical investigation of a high-temperature heat pump system was developed to estimate the thermal cycle and to assess the thermal fluids for their high-temperature delivery (up to 180 degrees C) capacities without decomposition or the use of lubricant mechanisms. Then, a screw-type compressor was applied in the above conditions. Furthermore, a screw expander was also used as a replacement for the throttle valve [Taniguchi et al. J. Engng Gas Turbine and Power (ASME) 110, 628-635 (1988). In order to assess the performance of the heat pump system, leakage and friction effects had to be determined and simulated when using the screw machines. Numerical results of system tests are presented from cases where steam-water (for higher temperatures) and ammonia (for lower temperatures) were used as thermal fluids instead of normally used fluids such as halogenated chlorofluorocarbon, which has been implicated in the depletion of stratospheric ozone.