Evaluation of the Primary Energy and Carbon Dioxide Emissions of a Passive Ventilation System with a Solar Air Heater

Improvements in envelope performance have reduced heat loss from insulation, and the ratio of heat loss through ventilation load has become relatively large. In recent years, the use of heat recovery ventilation systems (HRV) has particularly increased. However, ventilation generates not only ventilation load but also air conveying fan power, such that conserving energy for both is important. Therefore, this paper focuses on a passive ventilation system with a solar air heater (PVSAH), which is a passive ventilation system that does not use air conveying fan power and uses a solar air heater that uses solar energy. The total energy consumption of the PVSAH, the widely used mechanical exhaust ventilation system (EV), and the HRV, which has high energy efficiency, was compared with the ventilation load plus air conveying fan power. The primary energy evaluation and carbon dioxide (CO2) emissions were compared by region, and the optimal system was proposed according to regional characteristics. In warmer zones, the PVSAH saved the most energy, while the HRV increased energy consumption. The comparison of CO2 emissions by ventilation systems when using heat pumps for cooling and heating showed that PVSAH > MEV > HRV for Heating Degree-Day (HDD) 1500 and below, PVSAH > HRV > MEV for HDD 1500 to 2750, and HRV > PVSAH > MEV for HDD 2750 and above. MEV were favored in that order. As the CO2 emission factor decreases, the difference in CO2 emissions between systems decreases. If the difference in emissions becomes smaller, then considering the initial and running costs and the risk of failure of the system is crucial. A simple system configuration with low risks of failure and maintenance, such as PVSAH, may prove advantageous in the future.