Blower door and HRV question
user-1105327
| Posted in General Questions on
i just had a blower door test done on our new R-2000 build. The house is almost ready for occupancy. The initial test showed about 1.3 ach @ 50 pa but I was sure it would test far tighter.
After snooping around, I realized that both the interior supply and exhaust diffusers for the HRV were badly hemmorrhaging air. After sealing both the exterior supply and exhaust vents, the ACH dropped to .8 ach. Why is this happening?
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Is the unit installed? If so sounds like a bad job sealing the ductwork.
dan, the unit is installed. i'm a carpenter and not an hvac guy but i was meticulous in sealing the ductwork with mastic.
again, this was my first test. but when i think about it, what else was supposed to happen? the are basically two 6" diameter holes in the envelope that can't be sealed...? is the hrv supposed to be running when the blower door test takes place?
Erik when running the test the unit is supposed to be off with the dampers closed or sealed off
sean, that is a relief. it's funny, though, because i asked several people about how to prepare for the bd test and no one mentioned this. in fact, the consultant doing the test didn't even bring it up and he has performed 1000+ tests.
Right - I read the question too quickly. Also the range hood, dryer vent, etc.
is this the correct protocol for PH airightness testing?
Erik, what are the protocols for testing to the program you're in? For what I do, sealing the HRV inlets/outlets is automatic, but it's hard to imagine that someone has done 1000+ tests and never seen a HRV before. Was he not paying attention, or is he perhaps supposed to leave them unsealed for your program compliance?
Just for the sake of discussion, the difference between your two tests should be somewhat close to the total size of the supply and exhaust openings for the HRV.
Erik,
For more information on conducting a blower-door test, see Blower Door Basics.
For information on the protocol for testing a Passivhaus, see Blower-door protocol for verification of 0.6 ACH50 for Passive House certification. That document notes, "Exhaust and supply ducts of HRV systems shall be sealed."
More information here: Guidelines for Blower Door Testing of Passive Houses.
Erik:
R-2000 procedures require that every R-2000 house undergo an airtightness test according to the CGSB-149.10-M86 standard.
Under a CGSB test, intentional openings are sealed.
In the case of HRV supply and exhaust ports, the R-2000 tester must either tape off the openings OR, if the HRV has dampers on both supply and exhaust legs, the controls should be all set to off so that the unit is off and dampers closed. Unfortunately, the dampers on many models do not create a perfect airtight seal when closed, and may still leak considerably.
What make and model of HRV did you install?
As you noted, on a smaller house like you have built, intentional opening leakage (ie HRV ports) can have a dramatic effect on the ACH results. In cold climates like where I live, damperless HRVs are a bad idea.
Cheers,
Gio
thanks for the links, martin. the gba has so much good stuff it's sometimes hard to find exactly what you are looking for..
gio, we installed a lifebreath 155ecm. as you know, i need 1.5ach to meet the r2000 target and even with the vents unsealed we got 1.2ach. the official results show that after we sealed the exterior hrv vents, we got .73ach. i still thought this was leaky given the amount of time and energy we put into the air barrier. alas, the major culprit now seems to be air entering the crawlspace from around the 4" waste pipe and the water line. where THAT air is coming from is beyond me. i have read that air can make its way down the outside of the foundation and under the footing and into the house but i just figured this was an myth..
0.73...be happy!
Not just happy- be THRILLED! (That's a wicked-tight house!)
Air getting in under the slab really IS an issue, but the penetrations in the floor tend to be few. Slabs are typically poured over a very air-permeable layer of clean stone for moisture control. Even clay soils are somewhat air-permeable, and you're dealing with a very large surface area, so yeah, air even moves in soil when you give it 50 pascals of pressure differential.
Congratulations on the great air tightness results. With respect to where the air coming in around your slab penetrations is coming from, I'd be more concerned with what it contains. Soil gases coming up from under your slab can contain radon. Beyond energy efficiency, and comfort reasons for the sake of indoor air quality and occupant health it makes sense to take the time to seal these penetrations thoroughly, especially if you are in an area with above normal radon concentrations.
Gio
gio, do you know if the r2000 program requires you to balance the 'cold' side of the system?