If you’re in the process of building a home and want to keep it filled with fresh, healthy air year-round, then you have an important decision to make – which ventilation system to add to your HVAC package.
The most effective ventilation options available for residential homes are HRVs and ERVs. In order to choose the right one for your home, it’s important to understand the differences between the two products.
Both HRV’s (such as models produced by Greentek/Imperial Group) and ERV’s (like those produced by Solar & Palau – S&P) perform the same basic function in your home, essentially removing stale indoor air and replacing it with fresh outdoor air. Both products include exhaust and supply fans, along with a plate-type energy transfer cell/core that both the exhaust and supply air streams pass through. The outgoing air stream tempers the incoming air stream in a process referred to as an “energy transfer”.
In HRVs, the heat in the stale exhaust air is used to raise the temperature of the incoming outdoor air as it enters your home during the heating season. This process reduces the energy used by your home’s heating system to raise the outside air up to the temperature set point on your home’s thermostat. HRV cells are made out of non-permeable materials such as aluminum or a plastic composite which doesn’t allow any cross-contamination of the exhaust or incoming air streams.
An ERV, also known as an enthalpy recovery ventilator, differs from an HRV because the material the cell is made out of is permeable (often a paper composite), allowing some of the moisture in the exhaust air to transfer into the incoming outdoor air which is often moisture deprived during the heating season in cold climates.
In more technical terms, the more humid indoor air equalizes the humidity of the drier air in order to make the humidity level in a home more comfortable and healthy (the HVAC industry recommends maintaining humidity levels in living spaces between 35-45%. In the cooling season, the ERV will reverse the transfer to remove humidity from the incoming fresh air before it enters a home. This saves energy by reducing the load on your air conditioning system and/or dehumidifier.
Both HRVs and ERVs help reduce the stress on your HVAC system compared to other ventilation methods. Both options are sound, and the decision really comes down to your climate, lifestyle, and home design. A general rule of thumb is an HRV is more effective in cold climates and an ERV is better suited for hot humid climates that require considerably more cooling than heating.
Since outdoor air during the heating season is most often considerably drier than a home’s indoor air, running an HRV can significantly reduce humidity levels, thus requiring a humidifier to maintain the 35-35% humidity in a home.
On the other hand, cold temperatures are a concern with ERV’s because the moisture in the cell will freeze at what is referred to as the dew point (frost point) which can occur in many cold climates – the colder the winter design temperature is for a specific area, the more likely an ERV cell will be exposed to freeze up; a condition where ice forms within the cell and air flow is either reduced or completely inhibited from passing through the device. Most HRV’s have built-in defrost systems which keep their cells from freezing up while functioning in cold climates.
No matter which system you choose, installing one or the other will help reduce energy consumption and costs while ventilating your home. Both types recommend a continually running fan, but the amount of energy saved is much greater than what it takes to keep the fan running. Energy efficiencies for both types can range from the mid-55’s to over 90%, though the most efficient units come at a much higher cost. However, when you factor the value of energy savings over the unit’s full life cycle, choosing the most efficient model can often make it a financially and ecologically sound investment.
In the end, there is not one right choice. The choice between a Greentek HRV and S&P ERV is not as important as the decision to incorporate mechanical ventilation into your home. The leaky houses of the past simply cannot compare with the airtight house designs of today.
Current homes entrap airborne contaminants like bacteria, allergens, viruses, mold spores and toxins (such as formaldehyde gasses from glues used in many household materials). HRV or ERV ventilation systems help to reduce the concentrations of these contaminants in an effective and efficient manner. Since your family’s health is likely at the top of your priority list, don’t overlook the important role that proper ventilation in your home can play.
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