Comments on: Rats to You, Daniel Bernoulli! – Understanding Air Pressure

By: Allison Bailes

Allison Bailes — Wed, 09 Jul 2014 00:18:54 +0000

Colin:
Colin: Fluid flow can be complex. Yes, you can have positive and negative pressure, and in fact you always do. It just depends on what you're measuring relative to. Your hypothesis about mold around supply vents is certainly reasonable.

By: Colin Jones

Colin Jones — Tue, 08 Jul 2014 00:07:12 +0000

I thought about this video
I thought about this video this weekend while I was blowing up balloons for a friend's birthday party this weekend at a house that I know to have some issues with the duct leakage particularly around the boots. What I saw was really interesting. Two semi-large balloons fighting for space and hovering over a single floor register the rest of the balloons fell into clumps around other supplies and the return.
My question to you is can we have a simultaneous negative and positive pressure at the boot and register? The balloons had to have been pulled into the register by negative pressure and then once there it remained in balance above the register due to Bernoulli's principle.
Couldn't that also explain why you will see black fungal growth around supply ceiling registers in houses? Because of the negative pressure pulling in hot attic air around the boot and immediately meeting cool conditioned air and reaching the dew point?
This kind of makes me want to fill houses up with a bunch of balloons full of smoke and turn on and off HVAC systems to show clients air movement as tangible information tool.

By: Jamie Kaye

Jamie Kaye — Mon, 20 Sep 2010 04:34:25 +0000

Thanks for another good
Thanks for another good article Allison.

By: Allison Bailes

Allison Bailes — Sat, 11 Sep 2010 00:09:38 +0000

Thanks for reading and
Thanks for reading and commenting, B. Pagel & Todd. I'm glad you find our blog helpful.

By: Todd

Todd — Thu, 09 Sep 2010 17:25:33 +0000

I have enjoyed all your blogs
I have enjoyed all your blogs and thanks for another great one. You have been a great voice for our industry, keep up the great work and posts. Thanks again

By: B. Pagel

B. Pagel — Thu, 09 Sep 2010 15:23:25 +0000

Wow , its about time someone
Wow , its about time someone else talks about static pressure . I have been working with statics for years now , but I still haven't found the perfect trunk / branch designs . Over all HVAC needs more room in attics/crawlspaces to include their static pressure caps..

By: Allison Bailes

Allison Bailes — Thu, 09 Sep 2010 15:01:59 +0000

That sounds like the logical
That sounds like the logical choice, Matt, but I think the amount of venting we put in most attics isn't enough to keep the roof on. When the wind is blowing 130 mph outside, the air in a vented attic won't be moving anywhere near that fast, so the roof can still blow off. That's why hurricane clips are part of the building code in high-wind zones now.

I believe that opening the windows can reduce the pressure difference between inside and outside the house enough to keep the windows from blowing out, however.

By: Matt

Matt — Thu, 09 Sep 2010 14:09:40 +0000

Good stuff. So it sounds
Good stuff. So it sounds like a vented attic is the wiser choice over a non-vented attic when one lives in a high wind-, hurricane- or tornado-prone region.

By: Hunter Dendy

Hunter Dendy — Wed, 08 Sep 2010 23:42:39 +0000

Great post. Thanks for
Great post. Thanks for bringing some good science into the week. I look forward to learning more soon!