infiltration rate

Mike Thomas_2

Yes, 50 pascals, a unit of pressure, is the standard for blower door testing. At 50 pascals it simulates a 20 mph wind blowing on all sides of the building at once. I know, impossible for wind to blow on all sides at once, but pressure on one side leaves vacuum on the other, suck and blow and the same time and air is going to move. The Canadians and Alaskans do achieve .3 ach at 50 pascals during a blower door test. When you talk about natural infiltration, that can be tested using tracer gases. Usually a building that is tested with a blower door at 50 pascals and acheiving 3 to 4 ach will have a natural infiltration rate of 0.19 to 0.26 ach, on a calm day. Now don't design around 1 ach natural, thinking that it would correlate to about 12 to 16 ach at 50 pascals. It is not a direct, straight line correlation, it is a parabolic curve.

The point I'm leading to, is 20 mph is not unusual, and "natural infiltration" varies from day to day. If also varies from season to season. A home that leaks like a seive during the heating season because of a condition called "stack effect", warm air rising and pulling cool air in around the sill plate and other penetrations, usually cools just fine in the summer, because cold air falls, diminishing the stack effect. The cold air just wants to sit in this box, called the house.

The heating and cooling contractors I work with get in trouble with their customers when the leaky house won't heat on that week or two of really cold weather in the middle of the winter. You can explain how you sized the system for the other 351 days of the year, and you are saving them money, but they still want to be warm. If you want to size the system for assumed excellant construction techniques and low infiltration rates, and save your customer money, I applaud you for that. But cover your butt and spec those infiltration rates in your proposal. It would be best to spec it stating that the building would pass standard blower door test, at 50 pascals, because if someone takes you to court, that is the standard for testing air tightness in a building.

pat_3

infiltration rate differences

what is the average infiltration rate difference(new constuction) between a radiant heated room and an identical room heated with finn-tube baseboard? thank you in advance for any responses

Ken_40

Mmmmm...

The IR (infiltration rate) is the infiltration rate - period.

The method of heating will not change the IR. A few have suggested radiant heat is less affected by IR than HWBB, but that flies in the face of science and the two are essentially unrelated.

Those desperate to sell radiant systems and products have made the claim of "effective" IR being reduced with radiant, but no one actually believes that.

It simply isn't true.

Most typical new homes run around one A.C. (air change) per hour. Our new house however is made using ICF and SIPS construction and we have one A.C. per 20 hours! If you have an ICF or SIPS home, you may also be in that range?

Brad White_9

What Ken said, sorta...

The construction standard (in Canada anyway, ay?) is 0.33 or 0.35 ACH and is tested with blower doors. In older construction or as a default, I use the 1.0 ACH that Ken stated. It is in my opinion, conservative for new construction..... BUT- your house is only new once. 20 years from now you have a 20 year old house, with all the settling and cracks that can open over time.

Ken is absolutely correct on the effect versus radiant. While there is a physiological advantage to radiant versus convective (and God knows FHA), the infiltration losses are just that, a factor in your total heat loss.

Now, here is a twist on calculating using the infiltration rate, some food for thought: Air leaks in on two sides and out on the other two sides, plus the roof. Air infiltration is often 1/3 of your total heat loss profile, higher especially in new conventional construction because by comparison the walls and roof are so well insulated.

Every room gets calculated with 100% of it's infiltration rate. It will see it from time to time....


If you were to take the sum of all room heat losses, each with their appropriate infiltration rates, there is some overlap. All of this loss could not really occur at one time, house-wide. When air is leaking OUT of a room on the leeward side, it is only leaking in on the windward side or at the bottom leaving by the top...make sense?

So what I always do is to size the radiation for 100% of each room of course. But then I take the sum of room heat losses and back out the infiltration number so it is just transmission losses.

THEN, building-wide, I take 2/3 of the per room Air Change per Hour (ACH) rate but for the house as a whole. If each room had 1.0 ACH, I take 0.67 ACH for the house. Add that to the sum if transmission to size the boiler.

I suspect this compounding of infiltration losses as simultaneous is a contributor to over-sized boilers...

My $0.02, sorry of not entirely to your question.

Brad

Mike Thomas_2

3 to 5 is more what I see

I do blower door testing here in Iowa. I see more like 3 to 5 ach in new construction, and these are pretty good contractors, doing a pretty fair job. You really have to work to get 1 ach. As a heating contractor you can size for 1 ach, but you better put it in your contract, 'cause your gonna eat it, if the house don't heat or cool properly, and it would be nearly impossible to retrofit a home with 5 ach to make it only 1 ach.

[Deleted User]

Excuse me???

3 to 5 air changes per hour? That may be what you are seeing during your test, but it can NOT be indicative of expected "natural air changes per hour". Our heating systems would NEVER be capable of keeping the spaces conditioned at that rate. That is more than is required for commercial spaces with sweaty human beings in it...

Conversely, if your contractors are designing their systems for that much infiltration, their physical plants would be about 5 times bigger than needed, even at design condition.

I say build it tighter than a ducks butt and then put an air to air HXer on it so yo KNOW what the infitration rate is.

THe best way to cover your butt in the design arena is to put the oweness of air changes per hour squarely on the builder or the architect. We as comfort contractors have absolutely NO control OR say so over the infiltration rates. Put it in your contract that "Per conversation with builder, infiltration rate is anticipated to be "XX" air changes per hour. THis way, if THEY are wrong, YOU don't pay, THEY pay.

Heres a link explaining blower door testing information.

http://homeenergy.org/archive/hem.dis.anl.gov/eehem/94/940110.html

ME

Weezbo

Mark he must mean 3 -> air exchanges per hour with

controled ventilation. maybe?

D107

It's got to be a missing decimal point

must mean .3 or .5 ach. My old 1924 house pre-cellulose in the walls with only old attic floor insulation was .9 ach. The lowest I've heard of is .2. New construction with 5?? Must have only three walls.

David

Brad White_9

Mike-

Close the door!



Blower doors I have seen and used could not produce that kind of CFM.... what am I missing?

Weezbo

that is right...Brad ..

Larry Weingarten

There is a convention...

... in the use of blower doors, which is the number of air changes per hour when using a 50 pascal differential pressure between indoor and outdoors. Perhaps that is what we're talking about. Natural air changes will be far less and will depend on wind, stack effect, etc.

Yours, Larry

Brad White_124

That would make sense

if the ACH 50 standard were used. In that case 5 or more ACH would make sense. Thanks for clearing that up, Larry!

Mike Thomas- is that the standard and terminology you meant, ACH 50? Sorry to jump on you; I think that settles what you meant.

Brad

Brad White_9

Excellent

I like the idea of making that part of the proposal.

Some years ago I did tracer gas measuring (sulphur hexafluoride) and was amazed at how accurate it was once set up.