Conference Year



High-Temperature Heat Pump, Carbon Dioxide, System Design, Sauna


Building technology recently has been affected by great innovations to reduce energy demand and to enable self-sufficient operation. To test innovations and prove practicality, EMPA has built a research building called NEST, where different demonstration projects from the building industry can be integrated and scientifically monitored. Furthermore, the sector of wellness applications shows significant potential for improving energy efficiency. Usually, spa facilities such as saunas and steam baths are based on direct electric or fossil heating which is extremely energy intensive and results in high operating costs. In order to establish a more energy efficient technology to provide heat to wellness areas, the present work proposes the usage of a high temperature heat pump with CO2 as a refrigerant. Carbon dioxide is currently favored by many heat pump applications due to the demand for low-GWP refrigerants with non-toxic and non-flammable properties. High-temperature heat pumps with CO2 as a refrigerant are already available on the market and reach supply temperatures typically up to 100 °C. Wellness applications require temperatures up to 130 °C on the supplier side, which requires new system design. On the consumption side, the heat will be used on a wide variety of temperature levels considering different saunas, showers and space heating. In this context, a stratified storage system ensures the heat output on the desired temperature level. Therefore, the heat exchanger unit as well as the operating range of the heat pump are the major challenges. In Coorporation with Scheco AG, a new CO2 refrigerant system has been designed and set up as a part of EMPA research building by means of a pilot installation including different saunas, steam bath and showers. Measurements will be performed as soon as possible to start the optimization process of the system.