[Greenbuilding] ACH50 or ACHn

[jfstraube]

Again, where is the logic or evidence that 0.6 ACH at 50 will stop this "short circuiting" you speak of?  0.7 wont work, must be 0.6?
There are thousands, tens of thousands of homes in Canada with 1.5-2 ACH at 50 with HRVs that dont have this "short circuiting problem"
And condensation can be controlled by wall design and insulation placement.
0.6 ACH in a double stud wall will still result in condensation on the exterior sheathing.


On 2011-01-30, at 3:23 PM, John Daglish wrote:

> Bonjour elitalking,
> 
> 0.6 ACH at 50 is the test level for infiltration that will garantee that
> in normal use there will be no problems of short
> circuits by infiltration that will diminish the effiency of the
> HRV nor create problems of humid air entering into the structure
> and condensing (interstitial condensation) and that you will be able to
> use the ventilation air with 10W/m2 peak heat demand in a continental european climate.
> 
> It works.
> 
> Now in cooler climates or hotter climates some modulation is needed.
> See the PassiveOn project :
> www.passive-on.org
> 
> 
> Cordialement
> 
> -- 
> John DAGLISH, B.Arch,1984
> 
> 
> 4, rue des Coteaux  
> F-91370 VERRIERES LE BUISSON, France
> Tél / Fax: +33.(0)1.60 11 12 10
> 
> 
> 
> Saturday, January 29, 2011, 3:21:59 PM, you wrote / vous ecrirez:
> 
> e> John Straube writes:
> 
> e> PassivHaus requiring 0.6 ACH at 50 as a voluntary program.  No problem.  But 
> e> when they claim this number is scientifically based, it distorts, well, 
> e> science.
> 
> 
> 
> e> My comment:
> 
> e> As a test protocol to demand a certain level of performance from a built 
> e> thermal envelope, testing at 50 pascals pressure difference makes sense. 
> e> However, this exagerated pressure difference is not a relavent in real world 
> e> performance under natural conditions.  Where as the 50 pascal measurement is 
> e> precise, assessing whether your site is well shielded, normal or exposed, 
> e> expecting some variations within a zone, and different height stories 
> e> resulting stack affect differences, the use of the n factor (ACHn=ACH50/n) 
> e> is back to an estimate.  Though less precise for measuring, in my modeling I 
> e> use natural conditions because I can estimate the volume of air that must be 
> e> conditioned during normal operation.  With historical data, then ACHn can be 
> e> used to estimate the energy cost accounting for various energy delivery 
> e> approaches.  The environmental reaction (estimated or real) would follow 
> e> (condensation et).
> 
> 
> 
> e> JF Straube writes:
> 
> e> ASHRAE 62.2-2007 is the north american ventilation standard.  It recognizes 
> e> that both people and houses produce pollutants and hence recommends minimum 
> e> ventilation of 7.5 cfm/person + 0.01 cfm per square foot of house area.
> 
> 
> 
> e> My comment:
> 
> e> Do you know the science behind this recommendation?  It does not recognize 
> e> the variations of occupancy.  Also, it uses area instead of volume for 
> e> recomending a volume of ventilation.  It strikes me that we need to move 
> e> towards a qualitative assessment of conditions of air (humidity, co2, co, 
> e> particulate matter) such that the ventilation can be adjusted according to 
> e> the environmental conditions.  Assembly use spaces do include co2 sensors to 
> e> adjust ventilation according to sense the occupancy needs for O2.  This is 
> e> beyond me to invent this technology.  Therefore, I rely on "the experts" 
> e> like ASHRAE 62.2-2007 to give me safe bases for my design goals.
> 
> 
> 
> e> The dilemma for codes and best practice recommendations is that knowledge is 
> e> an evolving revelation.
> 
> 
> 
> e> Eli
> 
> 
> 
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John Straube
www.BuildingScience.com