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How Do You Get Fresh Air Into Your Home?! Let's Talk About Balanced Ventilation.

Tuesday, December 03, 2019 9:55 AM | Kate Hamblet (Administrator)

The USGBCNH group was having a discussion on ventilation systems recently, and we thought it would be a good topic to share here. 

Now that winter is almost here and everyone's windows are staying shut for the next 4-6 months, the question about indoor air quality becomes a lot more relevant.  We all know how important mechanical ventilation is for our health and for the health of our buildings, but in the building industry it is still a relatively foreign concept. 

This is especially true in single family residential design, where the building code is behind where it should be on ventilation requirements.  Homes are now being built pretty air tight thanks to building code improvements, but an air tight home isn't a great solution for the occupant if no fresh air is getting inside. 

A poorly ventilated home leads to high humidity and mold growth, lack of oxygen, and toxins from materials and household products being trapped in the home.


So what do we do about it?! 

I think we are all in agreement that providing balanced ventilation systems is the way to go.  We want to bring fresh air inside the building at the same rate that we exhaust stale air.  But that doesn't go far enough to answer the question.

There are still plenty of options for providing a balanced ventilation system in a home.  I'm in the process of designing a residential art studio with one main room and a small bathroom, and I had the question, 'What's the best way to ventilate this space?'


ERVs and HRVs

We know that using an energy recovery ventilator (ERV) or a heat recovery ventilator (HRV) is a good solution because these units recover heat (and moisture if using an ERV) from the conditioned air to help temper fresh, cold outdoor air before being released in the home.  This helps reduce energy burdens.  

But now we need to decide if we're using an HRV or an ERV!  In our cold climate, an ERV needs to turn off intermittently so that frost doesn't build up on the unit.  Is this the best approach?  An ERV helps keep some humidity inside the home that our cold, dry winter air doesn't bring in.  Is that benefit worth mitigating the frost issues?  


Ducted vs Non-Ducted

And then, as in the case of my small art studio, we need to decide if the fresh air should be ducted through the whole space or if a single distribution system such as the Panasonic WhisperComfort would make more sense.  I asked this question to the group, and it turns out that this type of system doesn't function when it's very cold out.  The Panasonic unit turns off completely when outdoor air dips below 20 degrees F.  

For a home, a ducted system seems to be the best approach so that fresh air is getting into every bedroom, but is there a method that works well for a large open space (such as a studio apartment over a garage) that doesn't require ducting?

After some discussion with the energy experts in the group, it looks like the art studio is going to go with a ducted ERV so we can retain some moisture in the winter and distribute fresh air easily throughout the space.  Is this the best method?


What Would You Do?

What is your approach for residential mechanical ventilation?  Let us know in the comments below.


Comments

  • Wednesday, December 04, 2019 11:46 AM | Betsy Stefany
    Hi,
    Glad to have this question asked! SABENS Group joined NHUSGBC recently as a connection to their R & D with sensors. The question gives me the opportunity to explain why I joined and connect NHUSGBC with the educational activities. I feel that having the appropriate entry level activity and helping educators is essential as technology is progressing too rapidly for them to tackle this without support.

    The current activities developed as a segway between the past needs of the NH Dept of Ed to integrate STEM (2008-2014) with a NASA Technology Transfer Program license 2017-2020.

    The NH DOE's grant included enabling about 20 NH teachers in a variety of districts to achieve the USGBC's online Green Educators' Certification. During the grant we developed projects, aligning sensors with LEED award categories starting with light and temp. The projects continue to explore the classrooms' performance with heat becoming more formalized by connecting the output data with college/university clubs and courses.
    Glad too to notice the educational forum and will work my way to share more in that location as we progress beyond the formal classroom into community projects.
    Having actual local data WITH excellent content and an entry certification has been critical. Building a communication source to post, reflect and offer positive actions will help mellow the worries of change...and to get outdoors for some fresh air!
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  • Monday, March 09, 2020 9:59 PM | Douglas Shilo (Administrator)
    It is tempting to say things like "hire a mechanical engineer" or "go with the time-tested solution - ducted". In practice, however, small projects sometimes have budget constraints that make either one of these solutions a hardship. So, what to do?

    Short of doing your own manual J (and manual D) calculations, you could copy what thousands have done before you. As a designer, I hate to say it, but we've honed in on some pretty good rules of thumb for ventilation, which is really just based on how much volume you have (do not do this for heating & cooling!). Take a look at how GO Logic breaks down their options here: https://thegohome.us/plans-options/options/. For spaces under 1,100 SF, they use Lunos e2 through-wall HRVs. For spaces over 1,100 SF, they use a fully-ducted Zehnder Comfoair system.

    Ducting has the added advantage of dedicated supply and exhaust points. Ideally, you always want to exhaust the bathrooms and supply in bedrooms with fresh air. Ducted systems also require sizing the ducts. In theory, this requires a Manual D calculation. In practice, it usually ends up being 6" mains and 4" branches.
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