Recommended ACH for health

jb9

Hello,

I am confused by what a healthy ACH value should be in a tight SIP enclosed home. I am seeing a lot of different numbers (.66, .50 are two I have seen). From a health standpoint, what is recommended? And from an energy efficiency standpoint, what is recommended? How does a person reconcile these two values if they aren't relatively close?

Thanks.

Jamie Hall

When I was inspecting schools -- many many years ago now! -- we required two air changes per hour as a minimum. I'd be sort of happy with 1. I'd be pretty unhappy with less in a house; indoor air quality suffers and so does your health with anything less -- in my humble (?) opinion.

If you are concerned about energy efficiency and your health, and your structure is tight enough to need fresh air supplied, you can reconcile the two rather easily -- although at some cost: an air to air heat exchanger on the fresh air intake/building exhaust. Use the variety which is sensible heat only; I have found that the latent heat heat exchangers, though more efficient, seriously impair the intake air quality.

If you have to choose between the health and energy efficiency, perhaps because you don't have the money or the duct work, may I suggest choosing health? It's all very well to be very green, but being alive and healthy has its points...

SWEI

http://www.residentialenergydynamics.com/REDCalcFree/Help/ASHRAE6222013.aspx

jb9

Thanks SWEI. I tried to use the calculator but had some problems. Earlier today, I think I finally have a better understanding of the difference between ACH50 and ACHnat. ACH50 is done under controlled circumstances against an existing structure. ACHnat takes into account natural circumstances that aren't going to be as rigorous as the blower test. After talking to a SIP manufacturer, he told me SIPs can get between 1 and .5 ACH50 results. He divided those by 7, so let's take .75 divided by 7 and get .10 as ACHnat for my designed structure (not built). Then, if I run the infiltration, I see I don't get nearly what I need for fresh air, so I supplement it with an HRV. I guess I wasn't quite sure how to use the calculator because one of the fields would not accept my very low measured leakage of 204 cfm (based on my total volume of 16,402 cu. ft). It said my leakage was too low and forced me to increase it to a range that it found suitable. Perhaps I wasn't using the calculator correct or perhaps it isn't designed for a SIP project. BTW, my values were 1500 sq. ft., 29ft tall, 2 occupants (I laughed because it wouldn't let me live there as a bachelor).

I also specced out the HRV to run at 250 cfm so that it won't be running at its highest rpms for noise mitigation.

Any ideas?

SWEI

62.2 has been through a lot of changes over the years, and I suspect there may be more coming.

http://www.achrnews.com/articles/print/127235-ashrae-standard-622-gets-a-makeover explains the 2013 version pretty well.
Not everyone agrees http://www.buildingscience.com/documents/special/ventilation-new-low-rise-residential-buildings

Rich_49

The BSC standard is a better standard in my opinion . balanced ventilation is always better . How many stories is the home , bedrooms , people residing ? We can nail down the BAS ( building air standard ) . 250 sounds a bit high but maybe not .

RobG

Has anyone ever used the LifeBreath Clean air furnace? If yes, what did you think of it.

jb9

The house will be 2 stories with 3 bedrooms (on the 2nd floor). I have run the numbers through ASHRAE's formula and BSC's formula to get ranges of required cfm of mechanical ventilation between 91 (manual ACHnat calc using .60 air changes per hour in the house), 161 (ASHRAE) and 66 (BSC). It has been recommended that HRV's be specc'ed out so that their fans/motors are not running at 100% for the sake of noise and wear/tear. That's how I got that 250 cfm number. I didn't mean to imply that it would run at 250 cfm. Hope that helps. If anyone has any good guidelines for locations to install an HRV, please feel free to make a suggestion.