One of the most frequent questions we are asked from people in the know is: what are you doing for ventilation?
Before I answer, let me quickly explain why ventilation is important. Ventilation brings in fresh air, and exhausts stale or polluted air. They are necessary in every house. In green buildings, which should be air tight, they are especially important. The mantra of most green builders is “build tight, ventilate right.” For LEED, we are required to meet ASHRAE 62.2 standards, which basically says to have a vent fan in each bathroom and kitchen, and to have a whole-house ventilation strategy.
A quick side note: When I’m talking about ventilation, I’m not referring to an attic ventilation fan, like a solar powered attic fan. Those tend to do far more damage than good. If you really think you want one, I have two pieces of advice. First, don’t do it. Second, if you really, really want to install one, get a home energy audit first and see what that professional tells you (it’ll probably be don’t install one, or at least air seal the attic floor first).
Ok, now we can continue.
What we are doing (Upstairs)
We have installed a Broan energy recovery ventilator. An energy recovery ventilator mixes incoming air with exhaust air, and is able to recover much of the heat and moisture of the outgoing air to keep it inside the house - in this unit’s case, 69% recovery efficiency. It also filters the air with a HEPA filter for improved indoor air quality. In our opinion, ERVs are the ideal ventilation solution for DC’s mixed-humid climate.
We have primarily seen ERVs installed onto the return side of the central heating/cooling duct system. This is fine, when done properly, but most HVAC installers don’t properly damper the system, and can’t handle the more sophisticated controls. In addition, any time the ERV is on, the air handler fan must also be on, which significantly lowers the recovery efficiency do to the increased electric load.
For those reasons, we separately ducted our ERV. There are 4 supplies
– one in each upstairs bedroom, one on the main floor – with returns in each of the 3 bathrooms. The ERV actually replaces our need for bathroom exhaust fans, enabling us to recover a large portion of the energy that would normally have exhausted from them. We also have fewer penetrations in the building envelope (than having an exhaust vent for each bathroom), which saves even more energy.
Because this ERV only needs to be on for about 12 hours a day, per ASHRAE 62.2 standards, anytime we need to use it for bathroom ventilation, we flip a switch and a boost turns on the ERV if it happens to be off. We’re using the American Aldes Zone Register Terminal as the boost in each bathroom.
In short, what we are doing is the most foolproof and high end mechanical ventilation strategy.
What ARE we doing? (Basement)
Because we are planning on renting out the basement, we wanted to keep our systems separate, to minimize air and odor transfer, even though the Broan ERV is big enough to provide ventilation for our entire house.
For the basement, we choose to use a Pansonic WhisperComfort. Since we installed it in our bathroom, this also provides spot ventilation along with the whole-unit ventilation. It’s a small ERV that provides between 36% and 66% energy recovery efficiency.
Because it operates at about 40 cfm, we’ll leave it on 24 hours a day. Panasonic recommends that this unit be used in a single open space – compared to the 3 rooms in the basement – so we’ll install a jumper duct between the bathroom and the bedroom to provide better air transfer.
Since we haven’t turned on this system yet, the verdict is still out on how effective it will be. Stay tuned for results.
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