Functional exergy efficiency and exergy consumption behaviour for air-to-air heat exchangers operating at near-environmental temperatures

This paper investigates how temperature changes affect the efficiency of thermal exergy transfer at near-environmental temperatures. Depending on the combinations of heat exchanger and environmental temperatures, different values of functional exergy efficiency can be obtained for the same heat transfer effectiveness. Some temperature combinations can lead to unexpected values of functional exergy efficiency. A dimensionless temperature T′ is proposed to identify and analyse patterns in the temperature sensitivity of functional exergy efficiency. T′ is combined with the notion of warm and cool exergy to explain the results, and to identify exergy-efficient temperature combinations for heat exchange at near-environmental temperatures.