Experimental Performance Analyses of a Heat Recovery System for Mechanical Ventilation in Buildings

Nowadays the increasing trend to make buildings more and more energetically efficient leads to an improvement of the thermal performance of the elements such us walls, windows and doors, making the envelope a strong barrier between the indoor and outdoor environment, also for air infiltrations. If this circumstance results useful for energy consumption reduction, it constitutes a problem for indoor air quality and comfort. Mechanical ventilation systems are often provided, and, at the aim of abating the thermal (or cooling) loads linked to the inlet of air from the external environment, heat recovery systems became more and more popular; for high values of air mass flow treated, many national regulations make the installation of heat recovery systems compulsory. An experimental test bench was built at the Thermal Engineering Laboratory of the University of Perugia, aimed at evaluating the performance of air heat recovery devices. The first measurements were carried out on a commercial plate-type heat exchanger, made of polystyrene. This plastic material is characterized by a low value of thermal conductivity, but its easiness of workability allows to increase the heat exchange surface, overcoming also issues linked to the weight and the cost of the product. The flow-rates, the pressure drops, and all temperatures of interest for the heat exchanger were acquired. The energy efficiency index of the heat recovery system was assessed with several tests conducted with different boundary conditions of the indoor and outdoor ambient, as well as different air flow rates. Results were compared with data gathered from the manufacturer, highlighting the points of contact and the differences between the experimental outcomes and the company information sheet, providing further details that are commonly not available.