Improving the energy efficiency of thermal machines is a key point which ensures a strong advancement in solving problems related to energy consumption and environmental protection. Our study concerns an energy characterization and optimization of geothermal heat pumps heat exchangers for industrial and residential applications. As part of this study, experimental analysis of the boiling of the R134a is carried out in a smooth horizontal tube external diameter 7.94 mm and 1m of length. The refrigerant Reynolds number ranges from 4200 to 9820. This paper presents a detailed description of the experimental device, instrumentation of the test section and analysis of results. The influence of refrigerant inlet Reynolds number on the dry-out phenomenon is determined, and flow map is presented. Based on the experimental data, correlations are proposed to predict the heat transfer coefficient and frictional pressure drop.