HRV or ERV and incorporation of bath vents
I have just started building a new single story 3898 sq ft, 3 BR, 4.5 Bath home in Sisters, OR (Zone 5B). I am planning to install a Mitsubishi Hyperheat Ductless HVAC system throughout the house and want to incorporate an HRV or ERV. I also do not want to have separate bath fans and would like to incorporate a boost function with the HRV or ERV. I anticipate an ACH 50 of approximately 1 based on how it will be constructed. I am working with Earth Advantage locally and will have blower door testing done before insulation and again later.
My only ceiling penetrations will be the plumbing vent stacks and a single vent for the direct vent gas fireplace. Everything is electric so there will not be other combustion units in the home.
I originally planned to install an HRV in my high desert climate, but the HVAC contractor I have been working with (the only one in the area who actually runs room by room Manual Js) is suggesting an ERV. He also is recommending two Trane Fresh Effects Units because I want to use a boost function during showers and eliminate the bath fans.
Does anyone know who manufactures these Trane units and how they perform in comparison with other manufactures? Also, does anyone have any suggestions on the best approach to utilizing HRV/ERVs to eliminate bath fans?
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Replies
Why don't you want bath fans? They are cheap, even for the nice ones, and work well by ventilating the location you want. I would personally use them in any bathroom with shower.
If you want to use a boost mode ERV/HRV I would figure out how to use these to increase ventilation only where needed with these:
https://aldes.us/wp-content/uploads/2017/12/vz_spec.pdf
If ventilation can be done with only one ERV/HRV and a mix of bath fans, consider that approach as it may be the simplest overall design.
Not using bath fans won't save much energy as they are used for short periods of time.
I'm not familiar with the Trane Units specifically. We have similar plans and requirements though.
We're building in Terrebonne, OR (Zone 5b, deschutes county) 1300sqft, Mini-split, and ERV.
We're going to be using a Zehnder exhausting from the bathroom and kitchen, Boost feature for showers.
Continuous ventilation will provide the air exchange for the house. It should be enough for the bathroom and shower. But not worried about exact CFM for exhaust from the bathroom, because the operable window is what meets code requirements. ERV exhaust is because we care about humidity control.
I wanted to avoid the bath fans because I wanted to limit my outside penetrations and I was concerned that in a very tight house the use of the fans would depressurize the house. Since I am using a HRV or ERV it wouldn't be able to provide make-up air when bath fans would be in use. If I was able to use an HRV/ERV with a boost function for the bath areas my reasoning is that I could exhaust the humid air to the outside while bringing in air without causing pressure differences.
MS,
Consider no bath fans and no boost function. Instead, run the ERV 24/7 and pull 20 cfm from each bath. That's 100 cfm 24/7, which is a about right for your size house (depending who you listen to). This meets code and works well for me. I'm also in a high dry climate (Colorado at 9,400').
Bill
I'd review your ERV supply plan to assure that closed door rooms get 20 cfm/person.
I'd use typical bathroom fans instead of a second ERV. You want lots of air movement to get rid of all the humidity quickly.
My preferred approach is to use bath fans in high moisture areas. HRVs for bathroom exhaust generally doesn’t meet customers expectations in my experience. Even if your house depressurizes it shouldn’t be a big deal if your house is all electric. At 1 ACH50 it will equalize pretty quickly. If you are still worried about it use a product like the panasonic intelibalance and run your house at a slight positive for your continuous or semi continuous ventilation
The Trane ERV is a mediocre product. For something that runs 24/7, best to spend a bit extra on a better ventilator.
You want at least an ERV with an ECM blower (consume 1/2 the electricity). A cross flow core (looks hexagonal in the pictures) is more efficient especially when it comes to humidity transfer. Something like a Vanee G2400E or Panasonic Intellibalance are much better products.
Since your house is all electric, without combustion appliances depressurizing is not an issue. Even a passive house has enough leaks no to get much negative pressure with a bath fan. They work much better in this application.
I have both ERV and bath fans. In the thunder room, the ERV even on boost is just not up for the job.
EDIT:
Seeing there are a lot of baths, best is a compromise. Install a fan in the baths used most often, no ERV return there. ERV return from the rest of the bathrooms. Installing a boost switch on those baths doesn't hurt either.
If you want to minimize the number of outside holes, install a larger ducted bath fan that can service multiple bathrooms.