Regarding recent developments in terms of climate protection agreements, the energy efficient provision of heat for industrial processes becomes more and more important. The application of high temperature heat pumps in the industrial sector provides a possibility to upgrade waste heat for further use in the process chain. A CO2 neutral provision of process heat can be realized if the required electrical energy is based solely on renewables and therefore the utilization of fossil fuels can be avoided. The required temperature level for thermal processes lies mainly between 100 °C and 200°°C and can be found in the pulp and paper industry (bleaching, drying), in the food industry (pasteurising) as well as in the chemical industry (distilling).
The current state of the art shows, that commercially available high temperature vapor compression heat pumps can provide heat with a temperature level up to 150 °C. Therefore the synthetic refrigerant R1336mzz(Z) and a subcritical single stage heat pump process is used. Currently available high temperature vapor compression heat pumps using natural refrigerants are limited to the application of CO2 and a temperature level of 120 °C. The CO2 heat pump process has to be trans-critical at a very high pressure (up to 150 bar) due to the thermodynamic properties of the refrigerant. The current focus of trans-critical heat pump cycles lies only on the application of CO2.
The present project deals with the investigation of an innovative approach of a trans-critical cycle with natural refrigerants different from CO2 (prospective R600) for the application in a high temperature vapor compression heat pump. The application of a trans-critical cycle extends the operating range of high temperature vapor compression heat pumps to temperatures beyond 150 °C at a moderate high pressure (approx. 50 bar for R600). The consideration of natural refrigerants therefore accounts for future legal restrictions in terms of refrigerants. The construction of a functional model for the experimental analysis requires further development of the current compressor technology for flammable refrigerants regarding temperatures up to 170 °C and pressures up to 50 bar. This development should be carried out in the course of the present project. The theoretical and experimental results of this new approach can lead to the extension of the application range of high temperature heat pumps and lays the foundation for a new class of trans-critical heat pumps.