Design and analytical investigation on air-to-air cross flow heat exchanger of an industrial heat recovery ventilation system

Abstract

Energy consumption based on the building heating, ventilation, and air-conditioning (HVAC) systems is sharply rising daily. At this point, heat recovery ventilation systems save energy while contributing to indoor air quality and thermal comfort. This work mainly focuses on designing the air-to-air cross-flow heat exchanger system and duct lines. First, the ducts, bends, vents, and heat recovery ventilation unit are placed around the selected domain complying with the ASHRAE 55 and 62.1 standards. The requirements on temperature levels of the cold and hot streams, air flow rates, number of vents, velocity at the supply air vent outlets are considered. Then, calculations are conducted for the cross-flow air-to-air heat exchanger to determine the number of layers, heat transfer surface areas, flow regime, and heat transfer rate. Thermal calculations of the recuperator system are initially performed by effectiveness-number of transfer unit (ϵ-NTU) method as the outlet temperatures are not known at the beginning of the design. In addition, the findings are compared and validated via logarithmic mean temperature difference methodology. The results show that the fresh air temperature can increase from 5 °C to 13.32 °C when the exhaust air temperature is at 26 °C in winter. Furthermore, the heat transfer rate of air-to-air heat exchanger system is analytically calculated as 1806.7 W and 1807.5 W via ϵ-NTU and logarithmic mean temperature difference (LMTD) methods, respectively.