Energy demand and indoor air quality in low-energy apartment buildings: A simulation-based comparison of ventilation systems

Energy-efficient buildings require efficient ventilation to achieve low-energy demand while maintaining good indoor air quality (IAQ) and comfort. This study analyses the impact of different ventilation systems (i.e., automated window ventilation, extract air system and mechanical ventilation with heat and enthalpy recovery) on heating and electricity demand, IAQ and thermal comfort. Multi-zone dynamic simulations are conducted and benchmarked against monitoring data from similar flats in Innsbruck for the mechanical ventilation with heat recovery case. Both constant and CO 2 -controlled airflow are evaluated, alongside a simple sensitivity analysis addressing uncertainties such as infiltration, occupancy, and door position. Three locations -Navis (AT), Innsbruck (AT), and Bologna (IT)- are analysed. Results indicate that mechanical ventilation with heat recovery consistently achieves the lowest energy demand. However, the absolute savings, compared to systems without heat recovery, diminish in warmer climates, with higher infiltration rates, or when CO 2 -based control is applied in sparsely occupied flats. Under the adopted pollutant-generation assumptions, relative humidity and CO 2 are found to dominate the IAQ performance indicator. In cold climates, an enthalpy heat recovery system mitigates excessive dryness. Systems without heat recovery often supply excessively cold air, risking thermal discomfort. Reducing airflow to prevent this can lead to inadequate IAQ.