Abstract
Available research shows that water, R-718, as a refrigerant can lead to high coefficients of performance,
especially at high condensation temperatures above 100°C and high temperature lifts. Using R-718 comes with
thermodynamic and operational challenges like the large specific volume at lower pressures, the need for
precise superheat control, danger of corrosion and challenge of oil management. To overcome these challenges,
R-718 has mainly been used in higher capacity range suitable for turbomachinery. In order to expand the range
of applications for R-718 heat pumps towards lower capacities, it is necessary to address these challenges by
innovative compressor and system designs.
In this work a Modelica based model was developed as a design-basis for a high temperature heat pump using
R-718 as refrigerant. The model consists of a piston compressor with four integrated compression stages,
intercooling system and superheat control. To fulfil the requirements of a potential implementation site, the
model is tuned to target heat source and sink temperatures of 90±5°C and 180±5°C respectively, corresponding
to a temperature lift of 90±5 K. The targeted heating duty is 35 kW. In this paper, the outline and design of the
HTHP and the belonging model are presented. Employing the one-dimensional model, a comprehensive
performance evaluation is conduced, resulting in a Carnot efficiency of 52%.