Heat Recovery Units in Passivhaus Housing on the Spanish Mediterranean Coast: Energy Efficiency and Return on Investment

Abstract

Regulatory demands for indoor air renewal in buildings entail high levels of energy consumption. This is the only way to provide minimum indoor air quality (IAQ) and avoid some common lesions and pathologies. In Passivhaus standard (PHS) houses, a heat recovery system is required between the indoor–outdoor air masses of the air renewal system. This configuration substantially reduces energy consumption. In addition, the obligation to reduce envelope air leakage below the n50 value of 0.60 ACH usually allows for a decrease in the energy consumed to less than 15 kWh/m2y in winter, as required by the PHS. It is complex, however, to quantify the energy demands of a building, whether in the project phase or in the operational or use phase. The present study focuses on the application of the PHS in Spanish Mediterranean housing. The aim was to assess whether it is suitable to use heat recovery systems by quantifying the energy savings obtained, execution costs, infiltration air flow, ventilator power usage, and maintenance. To this end, we performed a study on an existing PHS house in Abrera (Barcelona, Spain). It was found that heat recovery systems are always cost-effective in cold climates such as that of Central Europe but are only profitable in Spanish Mediterranean houses when the system costs less than approximately EUR 2500. In this case, the investment is covered over a period of 9.4–12.8 years and over 14–18 years when the equipment costs more than EUR 3000. Annual savings range from EUR 184.44 to 254.33 in Abrera compared to EUR 904.99 to 934.82 in a city like Berlin, that is, a 400–500% increase in savings. Moreover, leakage air energy accounted for 13% to 15% of that of renewal air, −1.348 kWh/m2y and 2.276 kWh/m2y compared to 8.55 kWh/m2y and 17.31 kWh/m2y, respectively. Lastly, recovery system average efficiency or ηt performance—which is usually between 82% and 95%—did not play a relevant role in deciding whether the system should be installed or not.