Re:Dedicated Outdoor Air Systems: Rx for Sick Buildings

[Guest guest]

Barb and Gil,

I have always been a fan of dedicated outside air with separate temperature

and humidity controls for HVAC systems. It makes no sense to have only a

thermostat (and no humidistat) to control indoor air.

One idea in the article seems quite odd to me: radiant cooling. How can this

possibly avoid mold problems. Imagine having large cool panels in the

ceiling. On some days, the panels will have to be below the dew point and

condensation will occur on the surfaces, leading to mold growth.

I believe that the problem people may be having with outside air intakes is

not necessarily the outside air itself (unless the spores therein bother

you) but is rather that mold grows in the intake duct.

It is essential that any outside air system have an exterior design that

avoids rain intake; a screen to prevent insect intake; and an efficient

indoor filter to prevent the accumulation of dust in the duct. The filter

must be close to the outdoors, but far enough indoors to avoid getting wet,

and should have a MERV rating of 11 (such as an Air Bear or Aprilaire).

The idea of bringing in fresh air into homes has been around for some time

and the heat recovery or energy recovery ventilation (HRV or ERV)embodies

this principle. Yet almost every $2,000+ HRV or ERV system I have inspected

had a mold problem within 3 years due to the lack of adequate filtration.

In the case of HRVs and ERVs, supplemental MERV 11 filtration has to be

added to the house air intake side as well as the fresh air intake side. The

filters that come with the ERVs and HRVs are a joke! They are inefficient

and leaky, certainly not up to the task. Since there is not room inside the

units for decent filters, these must be added to the ductwork at the outside

of the unit.

The only HRV that has adequate filtration is one with a built-in HEPA

filter. VanEE makes the THH 1.0 that has a HEPA filter but I am not sure if

the filter cleans both the outside air as well as the house air. (There is

only one HEPA filter.)Both air intakes MUST be filtered to prevent the

accumulation of biodegradable dust on the heat exchanger.

So long as the interior of the HRV or ERV is spotlessly clean, there should

be no mold problems. This means monthly checks and cleaning 3 or 4 times a

year). Only purchase an HRV with a heat exchanger core that can be easily

removed for cleaning.

Drainage should also be provided for these units, as condensation can occur.

The interior should contain only wipe-able surfaces, NO exposed fiberglass

liners whatsoever (because these are guaranteed to get moldy).

SO check the inside of your intake ducts. If dirty, they are moldy. Replace

them and give your outside air intake system another chance, but filter the

incoming air.If you have an HRV or ERV, replace dirty intake ducts, clean

the interior and add MERV 11 external filters.

As an aside, I coughed every time I entered our first-floor bathroom. Turned

out that the seller's son used the shower in the full bath with the exhaust

on. Moisture filled the cold duct. When the exhaust was off in winter, air

infiltrated (due to the stack effect). All the dust on the inside of the

duct was moldy. I replaced the duct and sealed it off; no more coughing.

C. May, M.A., CIAQP

May Indoor Air Investigations LLC

3 Tolkien Lane

Tyngsborough, MA 01879

617-354-1055

www.mayindoorair.com

www.myhouseiskillingme.com

>Re: Dedicated Outdoor Air Systems: Rx for Sick Buildings

>Posted by: " barb1283 " barb1283@... barb1283

>Date: Wed Aug 15, 2007 6:26 am ((PDT))

>I have to agree with this also. I put fresh air intakes into my

>house and *at first* we all felt really great, 2004. I thought

>everything was solved by that but every year house culture kits

>showed more and more mold, even in winter. Finally I realized that

>I was dragging in a tremendous amount of mold in fresh air intake,

>particularly in summer when mold counts are extremely high here, as

>well as humidity which I had to add additional dehumidifiers to

>overcome. Finally I closed off fresh air intakes in summer. Even

>so, I discovered that outside air was STILL getting into house,

>coming into attic in summer and coming down into house through the

>tops of interior walls, which were not sealed at top like newer

>buildings, dragging summer humidity and mold through the insulation

>and into house...so also carrying dangerous insulation fiber

>particles incidentally. I have now capped off wall tops that are

>exposed to attic air so the outside air cannot get down into them,

>or at least very little can, but I now have to test these wall

>cavities to make sure this humid, moldy air that has been coming in

>since 2001 (when I *vented attic for first time*- it was unvented

>attic when originally built 1924)...(air) from outside didn't creat

>a problem inside the walls. I'm still enthused about having a fresh

>air intake system but it needs some work to make it help and not

>hurt the indoor environment.

>>

>>

>> This article implies that a system bringing in fresh air will

solve all

>> the problems.

<http://www.ehponline.org/members/2003/111-13/innovations.html>