Exergy efficiency of a ventilation heat recovery exchanger at a variable reference temperature

Abstract

The purpose of this paper is to develop the application of exergy analysis for assessing the performance of building mechanical systems. When exergy analysis is applied to thermal processes in HVAC systems, this method faces the conditions when variable reference temperature is placed below, above and across the operating temperatures of working fluids. Using the derivative status parameter from enthalpy and entropy, the methodology for calculating the exergy efficiency for HVAC equipment is proposed. The capabilities of this method are demonstrated in the case study of exergy analysis of a ventilation heat recovery exchanger. Thermodynamically justified numerical values of the universal and functional exergy efficiencies for variable reference temperatures are shown. The proposed method is distinguished by its universality and can be applied on other HVAC equipment. Results from this study could be useful for creating exergy optimized design and developing efficient control of HVAC systems operating at variable reference temperatures.