HRV needed? Tied into HVAC ducts?
We are renovating a 1950’s home in the SF Bay area (climate zone 3). We hired a consultant to design the ducting and HVAC system after we air sealed the house using Aerobarrier– ACH50 dropped from 12 to 4.
He suggested adding in an HRV (Broan HRV250TE) as follows:
“HVAC contractor shall incorporate HRV to run at high speed whenever the comfort system is running, weather heating or cooling. This should increase comfort and boost total air flow by a minimum of 200CFM to from 1,676 CFM design to 1,876CFMm when equipment is running. Broan HRV250TE or equivalent, drawing air from the system central return and exhaust it outside and drawing air from outside and delivering tempered outside air to the central supply plenum”
Do we need an HRV in our climate zone at ACH50=4?
Details of HVAC from report…
“HVAC Contractor has requested Bryant Equipment. HHP defers to HVAC contractor’s installation experience in the final choice but recommends Bryant Model 987M66100V21, or better, to provide adequate heating & cooling air flow for the long duct runs incorporated in this design. Evaporator coil shall AHRI match the furnace and be a maximum of 3.5 Tons, with fan flow preset/locked to high speed when unit is in cooling mode.”
Outside air temp range: 32-91
Inside air temp range: 68 heating, 75 cooling
Humidity: 50% inside and outside
Conditioned Area: 4322 sq. ft.
Heating Load: 51,477 BTU/H
Cooling Load: 45,032 BTU/H
Heating AVF: 1600 CFM
Cooling AVF: 1600 CFM
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Replies
The wording makes it seem like he thinks the purpose of the HRV is basically a fan booster for the heating/cooling. This is definitely not the case. It's supposed to supply fresh air. And why would the desire for fresh air go away when the heating / cooling is not active?
That heating load seems high for a delta T of only 38 degrees F.
Thanks Trevor
Yes the heating load is likely due to the long duct runs. It’s a single story house.
HRVs aren’t common here. Maybe it’s he was trying to keep the load balanced within the plenums. You make a good point about wanting fresh air all the time not just while the system is running.
Not really sure we need this HRV thing at all.
Sean,
I'm in favor of HRVs, but this is one of the worst HRV specifications I've ever read. The author of this specification (a) doesn't understand the purpose of an HRV, (b) doesn't understand ventilation air flows or commissioning, and (c) doesn't understand HRV ducting.
Hi Sean -
there is good info on HRV installs on GBA, starting here:
https://www.greenbuildingadvisor.com/article/integrating-hrvs-with-air-handlers
Peter