Energy Balances and Payback Time for Controlled Mechanical Ventilation in Residential Buildings

In residential buildings, air renewal is usually entrusted to the occupants, who open windows at will. On the other hand, a controlled mechanical ventilation system (MV) may provide fresh outdoor air by mechanical means, thus diluting indoor pollutants and improving the indoor air quality (IAQ). The aim of this paper is to evaluate the technical features of controlled MV systems and their energy and financial appropriateness in residential buildings. Several configurations of mechanical ventilation system are designed for a reference residential unit located in various locations of Italy, covering a wide range of climates. For each configuration (single-flow, double-flow) the overall cost for installation is calculated. Therefore, for all the configurations of MV system, the electric energy to feed the fan and the thermal energy to counterbalance the heating needs due to the ventilation are determined, and compared to the energy needs in a building without any mechanical ventilation system. The results show that mechanical ventilation introduces considerable primary energy savings, with an attractive payback time of the investment especially in cold climates. This makes mechanical ventilation systems an appealing technology for reaching the target of Zero Energy Buildings