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Old 08-06-2020, 01:13 PM   #1
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Pressure sensitive duct/vent


Hello-
I'm working on a passive whole-house fan system for a green home and wondering if anyone knows of a vent that opens when air pressure inside drops and closes when stabilized (ideally passively with gravity, not with pressure sensitive switches and servos). The purpose is to have a few of these spread throughout a house so that a whole-house fan can have air to pull into the house without having to manually windows. The fan will be lower power and quieter than a typical high CFM whole house fan and is designed to automatically turn on when air temperature outside is more desirable than temperature inside.

I haven't been able to find this kind of product and may end up designing and fabricating my own. It may quite simply be some rigid insulation hanging in a duct by a rudimentary hinge and light spring. In the winter I'd block it off with a cube of rigid insulation. Screened vent on the outside, normal air register cover on the inside.

Anyone have experience with something like this or other ways for whole house fans to be "smarter" and not require manually opening windows?

Thanks!
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Old 08-06-2020, 05:55 PM   #2
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Re: Pressure sensitive duct/vent


Well, whole house fans have passive registers exactly like this at the fan. Whether there would be enough airflow to open passive register further away from the fan is an unknown.
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Old 08-07-2020, 12:05 AM   #3
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Re: Pressure sensitive duct/vent


Are you looking for a make up air solution?

Something like:
https://www.fieldcontrols.com/make-up-air-system/

Or one of the products offered by a company such as Fantect?
https://www.fantech.net/fileadmin/us...ions_US_EN.pdf
They offer a air pressure differential sensitive switch inside a duct for an application like a dryer exhaust, but I don't think that is what you are after.
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Old 08-08-2020, 09:51 AM   #4
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Re: Pressure sensitive duct/vent


Quote:
Originally Posted by erichm5 View Post
The purpose is to have a few of these spread throughout a house so that a whole-house fan can have air to pull into the house without having to manually windows.

It may quite simply be some rigid insulation hanging in a duct by a rudimentary hinge and light spring. In the winter I'd block it off with a cube of rigid insulation. Screened vent on the outside, normal air register cover on the inside.
If I am understanding, you want to put additional through-wall, stand alone vents on the exterior of each room. Lets assume each one being around 3 or 4SF in size to meet the purpose of what most people use a "whole house fan" for - to feel the cool breeze on your skin, dissipate heat quickly, and control CFM within each room and what rooms. When not in use, those vents will be huge leaks in your insulation barrier, and cannot be air sealed at all, even with your proposed blocking with rigid foam in the winter. It seems to kinda defeat the energy tenet of a 'green' house. At least a window pane has insulating value and although not perfect, the unit provides air sealing.

You can wire a damper to a fan control, there are products for that. But if you do individual dampers based on it's particular air pressure, there's no guarantee the vent will only open when the fan is on, it may open when not actually desired and the fan remains off.

Maybe thinking along the lines of a ducted system, like HRV/ERV or one of the versions of the Fantech systems Rust linked, might better serve at least the part of having fresh air from a fan, and still meet the energy goal of a 'green' house.
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