Assessing the exergy performance of heat pump systems without using refrigerant thermodynamic properties

• Published in: International journal of refrigeration 2018-09, Vol.93, p.1-9
• Main Authors: Saloux, E., Sorin, M., Teyssedou, A.
• Format: Article
• Language: English
• Subjects: Alternative energy; Capacitors; Chauffage de locaux; Destruction; Efficacité exergétique; Energy consumption; Evaporators; Exergy; Exergy efficiency; Exergy reference state temperature; Heat pump; Heat pumps; Irreversibility; Irréversibilité; Pompe à chaleur; Refrigerants; Space heating; Température de l’état de référence exergétique; Thermodynamic properties; Thermodynamics
• ISSN: 0140-7007; 1879-2081
• DOI: 10.1016/j.ijrefrig.2018.06.005

•The exergy destruction highly depends on operating conditions.•Assessing exergy losses of non-renewable flows reveals different optimal conditions.•Varying the exergy reference temperature has low impact on the exergy destruction.•The exergy efficiency with varying reference temperature properly assesses heat pumps. This paper tackles the assessment of the exergy performance of heat pumps. This work is based on a modeling that does not require the evaluation of refrigerant thermodynamic properties and is applied to two commercial (water–water and air–air types) units for various operating conditions (i.e., temperatures at the inlet side of the evaporator and the condenser). The total exergy destruction and the irreversibility distribution into the components are estimated and cover a broad range of values. As well, the nature of the sources of exergy destruction, divided into non-renewable (electrical) and renewable (thermal) energy flows, is also investigated. This distribution, which allows the use of electricity that is really paid by the user to be clearly identified, provides different optimal operating conditions, as compared with the total exergy destruction. Finally, the influence of the exergy reference state temperature (either constant or variable) is examined; in particular, with the air–air heat pump that permits the space heating demand of a building to be achieved. Although the effect on the exergy destruction is relatively low, varying the exergy reference state temperature strongly affects the exergy efficiency, which then appears to appropriately evaluate the use of energy in heat pumps.