Fresh air on a budget?
shedworkshop
| Posted in General Questions on
What are some budget-minded ways to supply balanced ventilation to a tight envelope room?
I was originally leaning toward an exhaust only system using a bathroom exhaust fan, but now I’m re-thinking it and wondering whether I should look into other options. Size is about 100 sq ft (backyard workshop/office space).
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https://www.supplyhouse.com/Panasonic-FV-06VE1-WhisperValue-DC-20-30-40-50-CFM-ERV?utm_source=google_ad&utm_medium=pmax&utm_campaign=geo_pmax_test&gad_source=1&gclid=Cj0KCQjw6PGxBhCVARIsAIumnWbgipBUDObPSqpRcdl4nTWv8FLuMNQi_rQazbeNFqK--RcsqyD80UYaAoakEALw_wcB
shedworkshop,
With an interior space of about 85 sq ft, it's in the range where any mechanical ventilation would be overkill. I just finished a 120 sq ft backyard office for an architect. She opted for two windows she could crack.
Seems like a good option. I'm wondering if it would still be fine if the space was unoccupied for a couple of days with the windows closed though.
shedworkshop,
We provide ventilation to either keep down humidity, or improve air quality for the occupant. In an insulated, heated shed, when it isn't in use there is no source of moisture, or air quality concerns.
Is the filtration on the WhisperValue good enough to even be considered? Can the core be swapped to something of higher quality?
Edit: Looks like it has a MERV 13 core. I think it is a decent idea if you are spending a decent amount of time in the room. $500 plus the need to replace filters may be a bit steep though.
I seem to recall reports that some big-box stores were selling what I interpreted as a less expensive, knock-off of the Lunos in-wall HRVs - like this Pioneer unit: https://www.pioneerminisplit.com/products/pioneer-ecoasis-50-ductless-wall-mounted-single-room-wi-fi-energy-recovery-ventilator?variant=41087954518058¤cy=USD&tw_source=google&tw_adid=&tw_campaign=16138532077&gad_source=1&gclid=CjwKCAjwi_exBhA8EiwA_kU1MhLStQ4coR1gLaGlVTnKq3pS_xGRVrcjt6uTlHAcFMCTVICM__5PIhoCq2sQAvD_BwE
I have a friend that's very happy with his Lunos system. If the budget-version is reliable, it's likely the least expensive and easiest to install option.
This looks interesting. I like that it's cheaper than the Panasonic ERV. Will have to do more research to see whether it is worth it or not.
I want to know why you think exhaust-only isn't sufficient.
DC,
Given that the interior is only about 680 cu/ft, what cfm fan you you suggest?
I'd be thinking 15 CFM per occupant. If there's a bathroom, the ability for higher sporadic ventilation, maybe 100 CFM. If there's a kitchen, 300. Ideally variably and sensor driven.
From what I understand, exhaust-only tends to be frowned upon because there is no way to control where the intake air is coming from. So moist air could be drawn into places it shouldn't be.
I'm curious to find out where you're hearing that.
In an inhabited building the interior air always has a higher moisture content than the outside air.
Also, just because you have a makeup vent doesn't mean air is going to use it.
Moist air may not be drawn in but cold incoming air will lead to condensation at air leakage points. If you're exhausting 15-300 cfm from a 10'x10' building, the makeup air has to come from somewhere.
I know you like to be a contrarian, but arguing against balanced ventilation is an odd hill to die on. Balanced ventilation is always preferable to single-direction ventilation, for a bazillion reasons that any fan of building science should know and that have been posted here on GBA regularly for 14 years. The only reason not to have balanced ventilation is cost.
Is cost not a valid reason?
In discussions we have about balanced ventilation, most people:
* dramatically over-estimate how much a house is depressurized by ventilation
* dramatically under-estimate how tight even a "tight" house is
* assume that air goes where you want it to go, not where it wants to go
Most people have no intuitive sense of what 50 Pascal is. We've had posters ask here if it would cause the traps in their plumbing to get sucked out. (Answer: no). It's a level of pressure difference that is undetectable, the difference in pressure that you would experience walking up a six foot flight of stairs.
And tight houses aren't submarines, they're not hermetically sealed. So even if you have that makeup air vent, and even if it's powered, there's no way to guarantee that all of the air that comes in comes in through the makeup vent, nor that all of the air that goes out goes out through the ventilation vent.
It's well-known that combustion appliances that rely on gravity to exhaust their combustion products and don't have a dedicated source of air are very sensitive to negative pressure, and can backdraft if it exists. They are the reason that make-up air requirements got put into the code, and it's a good reason. But somehow make-up air has taken on a life of its own. It's just ridiculous that we're talking about make-up air requirements for a 100 SF accessory building.
https://buildingscience.com/documents/building-science-insights-newsletters/bsi-012-balancing-act-exhaust-only-ventilation-does
Also, https://greenmainehomes.com/blog/2020/4/1/building-science-101-ventilation (shout out to Michael Maines above who authored this blog post).
So the Building Science article is entirely concerned with drawing air from one part of a structure to another and that causing undesirable effects. Almost the entire article is about multi-family dwellings or attached dwellings, which are structurally the same thing. Single-family dwellings get two sentences: "In single family detached houses this leads to contaminants being pulled from attached garages – especially houses with bedrooms over garages. Contaminants are also pulled from under slabs – if radon was valuable we would mine it this way – and what better way to bring soil gas, herbicides and pesticides into a home?"
Not a word on the purported evils of cold outside air infiltrating the walls.
I'm a big fan of super-tight air sealing between garages and living spaces, and in basements.
Needless to say, none of this is going to be a problem in a 100-square-foot accessory building.
My $0.02.
I have a small bunkie near the cottage that has a cupula on the roof with a damper at the ceiling. Opening that with a combination of cracking a window works. Not efficient but who cares for a small structure like this.
If you want better and don't mind a bit of DIY. Get a low flow rate quiet exhaust fan, a DC muffin fan is probably your best but could use something like a WhisperValue DC on low as well.
Step down the exhaust to 3" and use semi rigid aluminum. Run this (preferably spiraled) inside a 5" duct to the outdoors as a simple heat exchanger. Longer the better.
It won't be fully balanced and It won't be efficient but better than zero. You can also put a filter on the 5" duct to get some fresh air filtering.
Akos, how would the exhaust fan pull in intake air? Is it from the 5" duct? Is the 5" duct a passive intake?
Yes. Basically making a DIY heat exchanger.
Hard to say how much flow you'll get trough the passive intake, lot of it depends on how tight the structure is and where the passive intake exits. Make sure to slope the 3" pipe to drain since you'll get some condensation in the winter.
My thinking would be to mount the fan near the ceiling on the wall, have the duct run down along the wall and exist near mid wall at the neutral pressure point (maybe a bit bellow middle to get a longer run). This also gets you the drainage you need. You'll have to do some fancy sheet metal work on a 5" wall cap to also add the 3" exhaust to it.