The theme of this thesis are thermal processes with a heat pump. The thesis explains the most important of the heat pump itself through chapters. In the introductory part of thesis is described the problem and the purpose of research and hypotheses and research objectives. Then it is described the historical development of heat pumps followed by generalities about them. Further, there are described the four principles of work for heat pump and their basic parts and potential heat sources: the sun, soil, water and air. Each heat source is explained in greater detail which is followed by a chapter about refrigerants of heat pumps. Through two examples is shown the economic analysis of the application of heat pumps compared to conventional energy sources. At the end, it is shown the state of the market of heat pumps in Europe, and how Europe is encouraging the use of renewable energy sources. It was also mentioned the development of Croatia and its attitude towards renewable energy sources and the use of heat pumps. The aim of this thesis is to encourage positive thinking about the use of heat pumps and increase the use of renewable sources.