IDENTIFYING THE LOCATION, MAGNITUDE AND SOURCES OF THERMODYNAMIC INEFFICIENCY IN A WASTEWATER SOURCE HEAT PUMP BASED ON ADVANCED EXERGETIC ANALYSIS

Abstract

In contrast to conventional exergy-based methods, advancedexergetic analyses can evaluate exergy destructions due tointeractions among components of the energy-conversion system and the real potential for improving system components. Application of the advanced exergetic analysis to a wastewater source heat pump with wastewater heat exchanger providing space heating in variable operation modes is proposed in the work. In order to determine thermodynamic parameters of the refrigeration vapor compresion cycle a special simulation model was used. The so-called thermodynamic-cycle-based approach was applied to split the exergy destruction within each component of a heat pump into unavoidable, avoidable, endogenous and exogenous parts. It is shown that in the investigated conditions, the biggest part (76%) of exergy destruction in the compressor and all exergy destructions in throttling valve can be avoided by reducing irreversibilities in the remaining components of the system. 90…97% of exergy destructions, which can be avoidedin the condenser, evaporator and the wastewater heat exchanger, are mainly caused by irreversibilities within these components. Thebiggest part (40%) of avoidable exergy destruction in the heat pump is due to thermodynamic inefficiencies (caused by temperature differences) in the wastewater heat exchanger. The condenser and the evaporator have fewer possibilities (respectively 29 and 24%) for improving exergy efficiency of the system. The compressor has the last priority for decreasing irreversibilities. Based on the applied advanced exergetic analysis it is possible to receive more precise and useful information for better understanding and improving the design and operation of the analyzed energy-conversion system.