Experimental optimisation of the performance of a high-temperature heat pump under part load conditions

Title data

Jeßberger, Jaromir ; Briese, Lynn ; Obika, Echezona ; Heberle, Florian ; Brüggemann, Dieter:
Experimental optimisation of the performance of a high-temperature heat pump under part load conditions.
In: Applied Thermal Engineering. Vol. 302, Part 1 (2026) . - 131700.
ISSN 1359-4311
DOI: https://doi.org/10.1016/j.applthermaleng.2026.131700

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Abstract in another language

Integrating high-temperature heat pumps (HTHPs) into industrial energy systems and district heating networks offers a promising pathway towards CO2-neutral heat supply. To ensure reliable performance under fluctuating demand profiles, relevant research tasks include suitable compressor design, working fluid selection, and detailed understanding of variable operating behaviour. The present study investigates the off-design characteristics and part load optimisation of a laboratory-scale HTHP test rig equipped with an internal heat exchanger (IHX), reciprocating compressor with water-cooled cylinder heads (CHC) and a maximum thermal capacity of 37 kW. Off-design behaviour is analysed by varying the supply temperature from 75 °C to 140 °C at nominal compressor speed. The results show a linear decrease in the coefficient of performance (COP) with increasing temperature lift, ranging from a maximum COP of 4.83 at minimal lift to 1.93 at the highest supply temperature. Part load behaviour is investigated across compressor speeds from 758 rpm to 2100 rpm for multiple supply temperatures, revealing speed-dependent COP optima shifting towards higher speeds with increasing supply temperature. Optimisation measures include variation of superheat at evaporator outlet through an electronic expansion valve and the control of suction gas superheat by thermal recuperation using the IHX. At a supply temperature of 120 °C, these strategies result in COP improvements of up to 22% at minimum speed. The results demonstrate that a variable IHX heat-transfer area has the greatest influence on HTHP efficiency. Additionally, CHC further enhances performance at higher speeds by reducing discharge temperatures and enabling increased heat recuperation without exceeding thermal limits.