ERV Efficiency
CT shoreline, Zone 5, newly renovated old home.
We recently moved into our all electric renovated 1850’s home with a Mitsubishi Hyper Heat Pump and a GE ERV. For the first week, the ERV was not connected and the HP did quite well. We were extremely comfortable and even had to damper down some rooms to lower temps here and there. The house is testing less than 1 ACH, with no problems so far with us feeling ill or the fireplace drawing properly, unless we run the kitchen hood with a fire going. An open window solves that problem.
Today the HVAC tech came to make some adjustments and get the ERV up and running. The unit is either on or off and not controlled by the air handler. It feeds the return ducts. It’s only been half a day, but the ERV may be circulating the air in the house better and helping the HP run less….don’t know yet.
So here’s my question:
Why run it? If we’re getting enough fresh air with 1 ACH, it seems to me I’m sending hot air out of the ERV and only getting a percentage of that heated air back. Why bother?
Thanks in advance.
Nick
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Replies
Nick,
What's your indoor RH, and have you done any IAQ testing?
This does seem very reminiscent of the situation in your last project where you had humidity issues and were similarly resistant to providing ventilation.
https://www.greenbuildingadvisor.com/question/70-humidity
RH is 43-50. Humidity isn't a problem in this one.
The RH in the ADU was, I think, a function of new construction drying out. It seems to have settled down quite a bit up there, with the dehumidifier running infrequently.
I guess I like to second guess the projects. I have not done any IAQ testing.
Nick,
That tight houses need either mechanical or natural ventilation is what I'd call a central tenet of building science. Our code has required continuous mechanical ventilation in all residential units for almost a decade now.
https://www.greenbuildingadvisor.com/article/a-beginners-guide-to-ventilation
You may also find this current discussion interesting. The amount of outside air that enters a tight house like yours through the enclosure may often be next to none.
https://www.greenbuildingadvisor.com/question/n-factor-checks-out
and
https://www.northernbuilt.pro/building-science-ach50-achnat/
If you are monitoring your indoor CO2, VOCs, PM2.5 etc. And all those numbers are normal then why bother with an ERV. But with a house below 1 ACH 50. It seems unlikely you wouldn't have at least some level of diminished indoor air quality, even if it's not something that you notice right away.
Thanks guys. I'll look into air quality monitors to see what my levels are like.