Air Change Question...

Constantin

Here is another brain teaser for the long weekend...

Imagine a house that is being retrofit with new glass windows and foamed insulation. This should cut down infiltration signifcantly (currently my biggest heat loss). However, how to account for it in the heat loss / heat gain programs I own?

Does anyone have ACH experience with homes that have benefitted from spray-in icenyne or closed-cell urethane foam?

Furthermore, how do I go forward with calculating the effects of HRV's? Do I simply assume a number of air changes per hour times a recovery efficiency?

Why do I ask? Well, let's just say I hope my energy costs will be less than what Siggy's software suggest they will be. I still have time to upgrade the foam being used in the house-wall cavities... 4 inches of closed-cell vs. open-cell foam could make a big difference.

Unknown

welcome to the world of heat load calculations

someday it will be an exact science. Until then, I'm sorry to say, everything is a "rule of thumb" for estimating infiltration.

For a standard, modern home we assume .35 ACH infiltration unless we have any cause to doubt the builder or area.

For an icynene'd home, you could probably get away with .1 or .2 ACH. We have a foam contractor around here who does blower door tests and it comes out loooooow.

for the vent your sustained ACH should small, multiplied by the recovery efficiency you aren't adding very much. don't figure on the "boost" ACH if it's boostable as that will only be intermittant.

dconnors

Air changes are not guesswork

If you really want to know the air change rate of your house, you need a blower door test. Energy Conservation Professionals is just one company that does this. Not sure if they will do a residence. Not even sure its worth the money to find out this info. Remember that everything you do has to have a reasonable payback.

Unknown

maybe I should have said

air changes on non-existing homes are guesswork. You can't blower door test a set of blueprints! In retrofits/renovations of course that no longer is necessarily true, however not many people actually get blower door tests, so in effect it's still guesswork for most people.

It only makes sense to blower door test if you are going for some kind of certification, or if you suspect you may have a problem with excessive leakage in an existing home.

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dconnors

blueprints?

i thought he asked about an existing home, sorry, my fault.

dconnors

blueprints?

i thought he asked about an existing home, sorry, my fault.

Unknown

you're right

no need to apologize; I caught that after I posted and edited my comment accordingly.

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Constantin

Blower Tests Work great...

....once you have a buttoned-up house. Considering that I can see through several walls at this point, a blower test probably wouldn't indicate much more than "lots of holes". Ditto for the house prior to the gut job considering there was no wall insulation, etc.

In the meantime, I've done the heat-loss calcs and am trying to figure my heating needs for the year. If, as folks suggest, HVAC-Calc does overstate the heating needs by 10%, my heating needs per degree-day are 1106BTU. Considering the climate up here, that about $2k per winter at current fuel prices.

Seeing that infiltration numbers currently account for about 20% of total heat loss, the question then came up whether the house would be as leaky with foam as it would be with other insulation types like the pink-panther special.

Based on my analysis, it is doubtful that paying 3x for closed-cell foam instead of icenyne is worth it.. this is based solely on the analysis of HVAC-Calc. Our current wall losses are about 1/4 of the total, or about $500 a year. The delta for a all-closed-cell urethane foam system is likely to approach $30,000... probably not worth it... though we are considering its use in areas where the walls/celings are very thin or the exposure is great.

dconnors

infiltration

Actually the sheetrock and good caulk does more for infiltration than insulation. The pink is horrible as an air barrier. But that is not the question. I would only foam the wall to ceiling connection and possibly the floor to wall joint. If you think you have other large cracks that need filing you could do that as well. The best of all worlds is to control air intake based on co2 levels and code requirements.

Constantin

That's what the Lifebreath DCS units are for...

...they should offer plenty of air changes while maintaining a even 86% recovery efficiency on the low speed setting. They'll take care of all the bathrooms and also interface with the duct system to keep the house air happy.

Or so I hope.

[Deleted User]

.35ach is very generous

While living in Alaska, we became certified for blower door testing, energy rating homes, and hrv system design. We now live in Iowa and work with suppliers who have designed and then sold equipment to contractors in both residential and commercial applications. We get called in when the building won't heat or cool properly. We determine whether it is the fault of the system, the design, or construction of the building. To assume that the modern new construction is .35ACH is way off the mark. You had better figure .5 to .6, and that is if the contractor did a really good job. In order to achieve.35 your contractor will need to use some of the best materials and techniques used in energy efficient design. In order to meet the ACHP/Canadian/Swedish standards of .1 you are looking at some pretty extensive training and what most consider extreme measures in order to make that. I have tested new homes, that looked great, but had 2 to 3 ACH. You can't tell by looking, only by testing...

Unknown

well

there is such a thing as overdesign, and I don't do my clients any favors by assuming the worst-case scenario. We've never run into situations that would indicate a 2 or 3 ACH even in log homes (judging by the fact that the heating systems are actually heating the homes and would not be able to under such extreme situations).

I think one thing to keep in mind... and maybe I'm off the mark, so if so please correct me... is that as a blower door professional, you aren't really seeing a cross-section of houses. You are seeing only problem houses. Correct?

The .35 ACH assumption is one used by many professionals in our area. We of course adjust this if we have any reason to doubt the tightness of the home, but for our standard known builders or DIY clients that are going through herculean efforts to make their homes tight, we've found it to be pretty workable. Just went through the coldest winter in quite awhile up here with no complaints, at least.

If I'm missing something of course don't hesitate to let me know... just sharing our side of the discussion!

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