Buildings must be treated as a system, and any time one component of the system changes it can affect how many other parts of the building perform. As energy efficiency improves and homes become tighter, ventilation becomes much more important to maintain healthy indoor environmental quality.
There are several ventilation strategies that will perform adequately in Michigan, including exhaust-only systems and balanced heat recovery systems.
Exhaust-only Systems
Exhaust-only systems utilize a properly sized fan that usually operates continuously at a relatively low speed and volume. These fans must be rated for continuous duty and often double as the bathroom exhaust fan. This creates a small amount of negative pressure in the home and the incoming fresh air is generally controlled through the home's duct system. This incoming air is not preheated and can cause uncomfortable cold spots if not designed properly.
Heat Recovery Ventilation Systems
Heat Recovery Ventilation (HRV) technology offers the benefits of balanced air pressure, better climate control, and increased energy efficiency while supplying fresh air to the home. An HRV can recapture the otherwise wasted heat energy in the conditioned air that is exhausted from the home.
As stale conditioned air is pushed outside, fresh air is introduced with little or no mixing of the two air streams. The heat energy of the outgoing air is transferred to the incoming air via a heat exchanger thus preheating (or precooling) the incoming fresh air. In some types of these units, the incoming air is also pre-humidified or dehumidified.
For adequate ventilation, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommends replacing indoor air with at least 15 CFM per occupant.
("Energy Efficiency Makes Homes More Affordable". Energy Techinical Bulletin. SouthFace Energy Institute. Accessed 24 July 2009).
What is the Difference between a HRV and a ERV?
A Heat Recovery Ventilator (HRV) can help make mechanical ventilation more cost effective by reclaiming energy from exhaust airflows. HRVs use heat exchangers to heat or cool incoming fresh air, recapturing 60 to 80 percent of the conditioned temperatures that would otherwise be lost.
Models that exchange moisture between the two air streams are referred to as Energy Recovery Ventilators (ERVs). ERVs are especially recommended in climates where cooling loads place strong demands on HVAC systems. They transfer moisture from the humid air stream (incoming outdoor air in the summer) to the exhaust air stream.
HRVs have been more commonly used in homes where the primary concern is high humidity in winter. ERVs are typically recommended where moderating between humidity extremes is a year round concern.
Fantech HRVs and ERVs are available at a discounted rate through Gifts in Kind.
("Energy and Heat Recovery Venilators". ToolBase Services. http://www.toolbase.org. Accessed 24 August 2009.)