Ventilation of buildings with heat recovery systems: Thorough energy and exergy analysis for indoor thermal wellness

Abstract

This work analyses deeply and critically the behavior of a heat recovery device of the ventilation system, in a dwelling of the Basque Country, under the energy and the exergy point of view. The aim is to show the different results that come from both perspectives. Heating period was monitored and data of the velocities and temperatures of the extracted and renovation airflows have been registered. With the data recorded, the effectiveness, energy efficiency and exergy efficiency of the recovery system have been calculated. Later, energy savings, primary energy savings and economic savings have been evaluated. Besides, the minimum difference between the outdoor and the indoor temperatures, from which the operation of the recovery system achieves a primary energy saving, an economic saving or an exergy saving were calculated. In addition to the exhaustive monitoring, the concentration of carbon dioxide in each room of the dwelling has been measured. The results obtained show the convenience of using ventilation systems with heat recovery from an energy point of view (with an energy efficiency of 89%), but not so if an exergy analysis is performed (with an exergy efficiency of 4%). After all, Second Law perspective penalizes a lot the electricity consumption for heating purposes, requiring a temperature differences (between the indoor and outdoor temperatures) higher than 32 °C in order to obtain exergy savings (not so under the energy perspective, where a difference of 1.6 °C is enough for having savings). The indoor air quality analysis confirms the adequacy in terms of CO2 concentration. This work is pioneer in terms of deep exergy application for ventilation systems.