The Carnot efficiency measures how efficiently a high-temperature heat pump approaches its theoretically maximum possible efficiency. It is defined as the ratio of a heat pump’s actual Coefficient of Performance (COP) to the ideal, theoretical COP determined by the Carnot cycle.

The Carnot COP represents the theoretical maximum efficiency of the thermodynamic cycle and depends on the absolute temperatures of the heat source (T_Q) and the heat sink (T_S).

It is calculated as follows:

In this instance, temperatures are given in Kelvin.

The Carnot efficiency (η) is then defined as:

In practice, high-temperature heat pumps typically achieve a Carnot efficiency between 40% and 60%. This means that the actual COP of a high-temperature heat pump is about 40% to 60% of the theoretically maximum possible COP.

Factors influencing Carnot efficiency:

1. Temperature lift: The difference between the heat source and heat sink temperatures significantly impacts the Carnot efficiency. A larger temperature lift generally results in a lower Carnot efficiency, as the heat pump must perform more work to achieve the desired temperature.
2. Technical losses: Compressor efficiency, friction losses, incomplete heat transfer, and other inefficiencies in the system reduce the actual COP and, consequently, the Carnot efficiency.
3. Refrigerant selection: The choice of refrigerant affects the efficiency of the heat pump. Some refrigerants enable more efficient operation at high temperatures, leading to a higher Carnot efficiency.

In summary, Carnot efficiency is a crucial parameter for assessing the efficiency of high-temperature heat pumps in industrial applications. Optimizing the temperature lift, minimizing technical losses, and selecting appropriate refrigerants can enhance Carnot efficiency, leading to more efficient process heat supply.

Sources available in German:

• https://www.ost.ch/fileadmin/dateiliste/3_forschung_dienstleistung/institute/ies/projekte/projekte_tes/91_sccer-eip/literaturstudie_hochtemperatur_waermepumpen.pdf
• https://www.ost.ch/fileadmin/dateiliste/3_forschung_dienstleistung/institute/ies/projekte/projekte_tes/91_sccer-eip/arpagaus_et_al._2019_wp-tagung_burgdorf_-_waermepumpen_fuer_die_industrie_-_eine_aktuelle_uebersicht.pdf
• https://sintef.brage.unit.no/sintef-xmlui/bitstream/handle/11250/2983225/2021_DKV%2BTagung_Schlemminger%2Bund%2BAhrens_AA%2BIV%2B-%2B19_as%2Bsent%2Bto%2BKKA.pdf