Tight homes, such as Passive House, make for very efficient structures. However, where old homes could depend on small cracks to let in fresh air, new tight homes must integrate a mechanical ventilation system to ensure a healthy interior. Heat and Energy Recovery Ventilators (HRVs and ERVs), do this, and more:In a tightly built home, ideally every corner, crack, nook and cranny is sealed and insulated so that no unwanted air flows in or out of the house. While this is good to minimize energy costs, it means that extra attention must be made to ensure a proper ventilation system is integrated into the building design. Ventilation is important to keep a fresh and healthy interior, minimize odors and pollutants and maintain proper humidity levels.
While it is possible to rely on other types of ventilation, such as kitchen and bath exhaust fans, the best system would be a whole house balanced supply and exhaust system that uses and HRV or ERV. These units are connected to a home's HVAC system to bring in fresh outside air and exhaust stale interior air. Inside of these units is a heat exchanger, and when the exhaust and supply run through two separate chambers within the HRV, heat is transferred from the warmer air stream to the cooler air stream. Therefore, in the winter, incoming air is preheated by the exhuast, and conversely in the summer, incoming air is precooled by the exhuast. This reduces the energy demand on a home's HVAC system, and according to the US Department of Energy, most energy recovery ventilation systems can recover about 70% - 80% of the energy in the exiting air and deliver that energy to the incoming air.
The difference between and HRV and ERV, is that in addition to transferring heat, and ERV is also able to transfer moisture from humid air, which is particularly ideal for certain climate regions and seasons. There is some controversy on when it is best to use and HRV and ERV, particularly when it comes to controlling humidity levels. Therefore, it is important to consult with a HVAC professional to determine which system is best suited for your home.
While HRVs and ERVs can be more expensive than a lower tech ventilation system, they are the ideal solution to integrate into a green building. They are a reliable source of fresh air and aid in controlling the heating, cooling and humidity levels of a home.
Read More: US Department of Energy
(Images: Terese Maring/Re-Nest; Efficient Air Conditioning)