|Why use a Fresh Air Ventilation System?|
Any true energy-efficient house constructed in New England must have a fresh air ventilation
strategy. In the early years of air tight construction, designers and builders concerned
with energy efficiency had problems with uncontrolled humidity levels and
poor indoor air quality in their projects. In the early 1980's, it
was realized that the way to overcome this problem was to install a Fresh
Air Ventilation System (FAV). These systems can be as simple as a bathroom
fan running continuously at a slow speed with make up air being provided
through dampened ducts built into living area's exterior walls. (This
is known as an exhaust only system.)
The next step up is a simplified ventilation system where stale air is exhausted from the bathrooms and kitchen through a heat recovery ventilator (HRV) and fresh air is supplied to the bedrooms. We have also built whole house ventilation systems that have an exhaust and a supply built into every inhabited room. In both of those options, the heat recovery ventilator preheats the supply air on its way from the outside to the occupied rooms of the house.
When the heat exchanger is designed to exchange moisture as well, it's known as a enthalpy recovery ventilator (ERV). This is used primarily in homes that require more air conditioning than heat.
We use either Imperial or Lifebreath heat recovery ventilators that pre-heat supply air with
the exhaust air being removed from the house. The exhaust air from the bathrooms passes
through a heat exchanger (which is part of the HRV) where some of the heat energy is
transferred to the supply air (from the outside). This preheated air is then introduced
to the supply side of the
air heat pump distribution system for delivery to the bedrooms. The HRV runs continuously
at approximately 106 cfms, supplying controlled and preheated air to the living
spaces of the house.
In addition, there is a boost switch in all the bathrooms which temporarily runs the HRV at a high speed (150 cfms) when bathroom venting is needed.
When shopping for a heat recovery ventilator you need to look for:
1. It's capacity in cubic feet per minute (10CFM per occupant).
2. A thermal efficiency of at least 70%.
3. Electrical efficiency of at least 1 CFM per watt.
4. Recirculating defrost mode.
5. Quiet and easy to service.