heat pump, economizer, high efficiency, two heat sources
Aim of the project is the development of a new heat pump system with economizing that is able to improve the heating performance using two or more different heat sources. These heat sources preferably on different temperature levels are incorporated in the system with minimal loss of exergy, by adding the heat at different pressure levels. Applications are i.e. buildings with heat pump and a solar thermal collector. While solar thermal systems can be used for heating and domestic hot water in summer, they fail to produce sufficient temperatures in fall and spring. When the solar collectors are also connected to the heat pump, they are able to supply temperatures higher than ambient at a medium temperature level. This heat at medium temperature can be used to improve the efficiency of an air source heat pump using the here proposed cycle. Existing systems using two heat sources are either inefficient or need large amounts of waste heat, while the proposed cycle can also use very small amounts of waste heat up to 40% of the total heat input. Other heat sources like process waste heat or exhaust air from a building are possible. Depending on the amount of waste heat and the temperature level of the heat pump cycle, efficiency and heating capacity improvements of 20-30% are possible. Oil management and control of the system are the main challenges when implementing it in the field. The paper will present the idea of the new cycle and its application in heat pump and refrigeration systems together with simulation results that show the effects of different parameters.