Authors: Benjamin Zühlsdorf; Jonas Kjær Jensen; Brian Elmegaard
Addresses: Division of Energy and Climate, Danish Technological Institute, Kongsvang Allé 29, DK-8000 Aarhus C, Denmark ' Department of Mechanical Engineering, Technical University of Denmark, Nils Koppels Allé, Building 403, Room 007, 2800 Kgs. Lyngby, Denmark ' Department of Mechanical Engineering, Technical University of Denmark, Nils Koppels Allé, Building 403, Room 007, 2800 Kgs. Lyngby, Denmark
Abstract: The use of zeotropic mixtures in well-designed heat pump cycles enables considerable performance improvements. Temperature glide matching of the heat exchange processes and recovery of expansion losses by internal heat exchange decrease the exergy destruction yield higher cycle performances. A case study for supply to district heating is presented, indicating increases in COP from 4.3 for a pure fluid in a standard cycle to 5.2 for a zeotropic mixture in a cycle with optimised internal heat exchange. As these improvement potentials are difficult to quantify by conventional and advanced exergy analysis, a new approach was suggested. For deriving a meaningful benchmark for cycle optimisation, the exergy destruction was distinguished into a contribution describing the irreversibilities from the respective components operating with an ideal working fluid and cycle design and another contribution resulting from the cycle and working fluid being non-ideal. In addition, the exergy destruction was related to the COP, enabling an intuitive interpretation of the exergy-based analyses.
Keywords: cycle design; exergy; exergy destruction; heat pump; irreversibility; Lorenz cycle; refrigerant; temperature glide matching; working fluid; zeotropic mixtures.
International Journal of Exergy, 2021 Vol.35 No.2, pp.173 - 194
Received: 19 Mar 2020
Accepted: 31 Aug 2020
Published online: 15 Jun 2021 *