Comments on: Asthma and Poor Indoor Air Quality — The Trouble with Homes

By: Allison Bailes

Allison Bailes — Sat, 05 May 2012 14:40:08 +0000

Thanks for all the great
Thanks for all the great comments. I was hoping maybe someone would add something to what I said about moldy wood at the lumber yards in 2009. Anyone got any info on that?

By: David Butler

David Butler — Wed, 02 May 2012 06:36:51 +0000

@Peter, in large fabricated
@Peter, in large fabricated commercial HVAC systems, coil temperature is often monitored and factored into fan and capacity controls. However, This is more about dynamic latent capacity control than to prevent coil blow-off.

Coil blow-off is only an issue at very high face velocities, and frankly is not much of an issue in residential. For example, my Lennox 3 ton air handler DX coil has a surface area of 5 ft2. Even at 500 CFM per ton (rare in residential), you're still only talking about 300 FPM face velocity (3 * 500 = 1500, 1500 / 5 = 300). A residential system would have to be very poorly designed and matched in order for coil blow off to be a problem.

By: Nancy Grosvenor

Nancy Grosvenor — Wed, 02 May 2012 00:15:45 +0000

Great article!
Great article!

By: Jim Jennings

Jim Jennings — Tue, 01 May 2012 06:32:56 +0000

Interesting comments. In 1984
Interesting comments. In 1984 I was working on a lowrise building in Edmonton that had been built during the boom days. The cedar siding used had not been kiln dried and one of the tenants was constantly in the hospital with Bronchial problems due the mold on the partcle board walls behind the siding. As the siding dried it shrunkl, cracked and knotholes popped out allowing water entry into the wall assembly.As an asthmatic it takes less than 5 minutes for me to react with residences with mold issues.

Jim Jennings

C.E.O.

Canadian Academy of Building Sciences Inc.

By: Bob

Bob — Tue, 01 May 2012 06:13:04 +0000

Modulating the blower speed
Modulating the blower speed to keep a constant coil temperature is idea, but expensive and therefore impractical for most homes. A much simpler answer is to use a humidistat to switch the blower speed in cooling mode. For $50 in parts this can be implemented on a standard PSC system, no complete HVAC system required.

http://www.fluke.com/Fluke/usen/community/fluke-news-plus/ArticleCategories/HVAC/Battling+High+Humidity.htm

By: Richard Peters, P.E./CM

Richard Peters, P.E./CM — Mon, 30 Apr 2012 20:32:58 +0000

Another source of moistur and
Another source of moistur and mold is high speed air movement through an AC coil. A face velocity of more than 500 ft/min will strip water from the AC coil and down the ductwork. One of the really big contributors is the ridiculous bypass duct that relieves pressure in a zoned forced air system.

In the first case, you can reduce the indoor humidity by maodulating the blowers speed by keying it to the delivered air temperature. 10% RH reduction is common. For zoned systems, our ecMModulator modulates the blower's speed up to a set (adjustable) pressure. All the air through the coil is return air. The system's average air speed is quite a bit lower which allows all IAQ products to work at a much higher efficiency.

By: Robert Bean

Robert Bean — Mon, 30 Apr 2012 19:40:48 +0000

Allison your timing is
Allison your timing is impeccable.

This just published, “Gutarowska, B., et al, An Investigation of Allergenic Proteins Produced by Moulds on Building Materials, Indoor and Built Environment 2012;21 253-263”

http://tinyurl.com/d3v45gu 

When it comes to asthma and its potential to harm, I know of what you speak.