Basic HRV concepts/design
We are building a SIP panel [house], open concept, vaulted living room, with a second floor. Radiant in floor heat. 1500 sq ft main, 500 sq ft upstairs.
Our local HVAC contractor (small community, not many contractors to draw from) is telling us we must have an HRV supply and a return for each room. Ie: each bedroom is to have a supply and return, each bathroom is to have a supply and return. We thought the basic concept was more like each bath would have a return and each bedroom was to have a supply.
Is there harm in the way our contractor is suggesting it be set up? Or is it more advantageous to have returns in moist areas and supplies in drier living space?
Thank you 🙂
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Your HVAC system should be based on a Manual J. Has he done one? If he hasn't or doesn't know how to complete the calculation, you should hire an independent HVAC engineer and also ask him/her to specify the system. (Really, that is the best approach in most markets.)
On another related topic, have you developed a plan for ventilating your new (probably much tighter) home? Here is an article you should review: https://www.greenbuildingadvisor.com/blogs/dept/musings/designing-good-ventilation-system
Sorry my wife typed this out for me and it should have been HRV concepts/design. We have had a heat load analysis completed and the boiler for the radiant warmboard, heat is sized correctly. The only problem I have is the HRV ducting lay out, supply and return locations. I had Zehnder design a layout and system for our house but it was quite a bit more expensive than we would have liked but it called for supply into the bedrooms/living space and returns from bathrooms/wet locations. My plumbing and heating contractor recommended a Venmar HRV and wants to put a supply and return in every room and living space. I just want to ensure that I put the correct ducting layout in.
It certainly sounds like you HVAC contractor has no clue about a sensible and reasonable design layout for an HRV system for your home. Don't get sucked in and ripped off. Do your research on this site. You do not need more HRV ventilation than required by ASHRAE 62.2, and such low volumes of air would not possibly require a supply and return in each room. I am also specifying a Venmar (now sold in the US as a Broan unit) for my new 1500 sq' ft. SIP home. For a 2000 sq' house the ASRAE requirement is likely between 60 and 85 CFM depending on the number of bedrooms. That is for the WHOLE HOUSE, not each room. Do your research and you will be more informed than your HVAC contractor. Many good articles on this site, and quite a bit of information on the Broan site as well.
Rebecca,
The standard method used for ducting an HRV is to supply fresh air to the living room and bedrooms, and to pull exhaust air from the bathrooms, laundry room, and sometimes the kitchen. (Note that the exhaust grille for the kitchen should be as far from the range as possible -- not from the range hood.)
If your HVAC contractor has any doubts on these issues, the contractor should read the installation instructions provided by the HRV manufacturer. These installation instructions can almost always be found online.
For more information on these issues, see these articles:
Designing a Good Ventilation System
Ducting HRVs and ERVs
-- Martin Holladay
While the forced-air registers delivering heat or cooling to a bedroom might be blowing at 100 or 200 cfm, an HRV will be delivering 10 to 15 cfm. It's an order-of-magnitude difference. There are no pressurization concerns arising from ventilation systems.
Not having a HRV supply and return in a closed door room means that the room will be pressurized or depressurized to some additional extent (never ideal). You should have a minimum of 1 square inch of free area opening per 1 CFM of supply air or verification that it causes less than 3 pascals. 1/8" under the door won't do it, even with the low CFM of a HRV.
https://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/ENERGY_STAR_V3_HVAC_Quality_Installation_Guidebook.pdf