OptiRef: Heat Pump with Two Heat Sources at Different Temperature Levels

Aim of this project is the development of a new hea t pump system with economizing that is able to impr ove the heating performance using two or more heat sources at different temperature levels. These heat sources are incorporated into the system with minimal loss of e xergy by adding the heat at different pressure leve ls. Practical applications for such systems are for example build ings with a heat pump and a solar thermal collector or buildings with waste heat recovery. While solar the rmal systems can be used for heating and domestic h ot water in summer, they fail to produce sufficient temperat ures for direct use in fall, spring and winter. By connecting the solar collectors to the here described heat pum p system, they are able to improve the heat pump ef ficiency significantly. Furthermore, the lower temperatures of the collectors help to improve their effectivene ss and raise the usable solar gains. While existing systems usin g two heat sources are either very costly, ineffici ent or need large amounts of waste heat, the proposed cycle can use varying amounts of waste heat and increases th e heat pump efficiency by up to 30% over a wide range of operating conditions. The paper presents an introduction to the topic and various heat pump system designs using two heat so urces. All of them incorporate the OptiRef. Simulation results and experimental analysis show that depending on t he amount of waste heat and the temperature level of t he heat pump cycle, efficiency and heating capacity improvements of 20-30% could be shown in a laboratory prototype. Oil management and control of the sys tem are the main challenges when implementing it in the laboratory or field. Altogether, the functionality of the system could be proven, but there is still room for improvement with respect to the control concept an d in order to reduce cost.