[Greenbuilding] PHPP Flow Rates

Tue Mar 5 20:48:07 CST 2013

I don't want anyone to think that the 7.5 /person or 0.01/sq ft are chiseled in stone.  The approach of per person and per square foot is what I am advocating.  And those numbers have worked on huge numbers of homes. Those values could 8 and 0.015 or some variations.
It is also assumed that a bath fan of intermittent boost capacity of 50-75 cfm per bathroom, and maybe 75-150 cfm per range to deal with local pollutants.
I agree with John S: the F326 standard can be a problem, and often over ventilates (which we notice by complaints of overly dry indoors during cold weather).

John

On 2013-03-05, at 9:42 PM, John Salmen <terrain at shaw.ca> wrote:

> Using the highest air flow by room is biased to larger houses. Canada’s F326 ventilation code has a room requirement which for a small house can easily double or even triple the amount that would be required by JStraube formula (7.5 per person / .01 per sq. ft.). An extreme example is a small detached suite I just designed (about 600 ft2) which by F326 (based on room req.) would require approx 75 cfm. That is close to 1ach and with limited infiltration (by scale) would require over 60cfm for supply. A reasonable amount would be 20-25 cfm for that size of space with makeup of about 10 cfm.
>  
> ERV/HRV are generally designed for larger spaces in terms of efficiency – I think the smallest run to min 40 cfm or so – designed for multiunit applications. Those type of housing units have poor air quality if depending on infiltration so a good application for health but probably not for energy efficiency.
>  
> Building volume at .3ach is a throwback only as it refers to housesize (works well up to about
> 1200 sq.ft).
>  
>  
> From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of Alan Abrams
> Sent: March-05-13 5:20 PM
> To: Green Building
> Subject: Re: [Greenbuilding] PHPP Flow Rates
>  
> This came up in the course of PHIUS's evaluation of a current project.  The following comment is from Lisa White, Certification Manager:
>  
> "The max [PH] Design Air Flow rate is determined by the highest of either extract requirements by room, supply air requirements by people, or a volumetric requirement" 
>  
>  
> Alan Abrams
> certifed professional building designer, AIBD
> certified passive house consultant, PHIUS
> certified passive house builder, PHIUS
> Abrams Design Build LLC
> sustainable design for intentional living
> 6411 Orchard Avenue Suite 102
> Takoma Park, MD 20912
> office  301-270-NET- ZERO (301-270-6380)  
> fax      301-270-1466      
> cell     202-437-8583
> alan at abramsdesignbuild.com
> www.abramsdesignbuild.com
>  
> 
> On Tue, Mar 5, 2013 at 3:20 PM, JOHN SALMEN <terrain at shaw.ca> wrote:
> Agree on ashrae Canadian standard uses rooms which can have the result of over equipping small houses 
> Sent from my BlackBerry 10 smartphone.
> 
> From: John Straube
> Sent: Tuesday, March 5, 2013 10:35 PM
> To: Green Building
> Reply To: Green Building
> Cc: Joe Lstiburek
> Subject: Re: [Greenbuilding] PHPP Flow Rates
>  
> I think the PHPP approach is a bit of a throwback to the old days when people measured required ventilation by ACH.
> A more sensible approach, and the one used by the most common north American standard ASHRAE 62, is to assess the need for ventilation based on the number of people (since they produce pollutants) and the square footage served (since building pollutants, including cleaning supplies etc are roughly square foot based).
> A good approach is 7.5 cfm per person plus 0.01 cfm/Square foot. Real simple, time tested, logical.
> So for a 1500 sq ft 3 BR home, that would be assumed to be 4 people, and hence 30 cfm. Then there is the 15 cfm added for the 1500 sf of building to get 45 cfm. This is continous operation. A 90 ccm HRV would be set to run 30 minutes on the hour to achieve this.
> We often install more capacity than this (hence your paraphrase of Joe's), but commission it at these rates in tight houses (and lower rates in leaky production houses), thereby allowing for a higher rate to set if the occupancy demands it.
> Recently, the ventilation rates in 62.2 have increased, and these are not in my opinion justified IF you do a good job of mixing and filtering incoming air. IF you do a bad job of mixing and don't exhaust large concentrations of pollutants (kitchen range hoods, bathrooms etc) then you would need to increase the baseline rate. But that is bad design and should not IMO be recommended.
> 
> Many people want to increase the ventilation rate despite the initial cost and operating cost penalty to improve indoor air quality. While there is some logic to this, it is usually better from a health, economics, and environmental point of view to manage the production of indoor pollution through material choices and sensible operation than try to solve pollution with lots of dilution.
> 
> my 2 cents worth
> John
> 
> On 2013-03-05, at 1:13 PM, John Salmen <terrain at shaw.ca>
> wrote:
> 
> > Maximum flow rate is generally the maximum of your supply and exhaust
> > requirements (based on occupancy, assumed volumes, leakage, etc.) As I
> > understand it PHPP however calculates this just as volume (interior building
> > volume) multiplied by .3 ACH (air changes/hour) multiplied by 1.3 (real
> > world factor?). So oversizing by 1.5 keeps it in the real world and ensures
> > adequate ventilation.
> > 
> > -----Original Message-----
> > From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org]
> > On Behalf Of Bob klahn
> > Sent: March-04-13 7:21 PM
> > To: Green Building
> > Subject: Re: [Greenbuilding] PHPP Flow Rates
> > 
> > Eli,
> > I can't answer your question directly. I am dealing with a situation where
> > I'm pretty sure the ERV flow is low and am equally frustrated. 
> > However, I recall a recent posting by Joe Lstiburek saying that they
> > oversized ERV's by 150%.
> > 
> > Given what my memory has done to me lately, you might want to find that
> > posting for the rest of the story. Check the BSC site.
> > 
> > I hope the lead helps. This thread should be interesting.
> > Bob
> > On 3/4/2013 4:38 PM, Eli Talking wrote:
> >> I am trying to make sense of Ultimate Air spreadsheet describing how 
> >> to size ERV flow rates. It references the Ventilation maximum flow 
> >> rate as determined from PHPP.
> >> 
> >> Does anybody know how to find Ventilation maximum flow rate PHPP?
> >> 
> >> Eli
> >> 
> >> 
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> Prof. John F Straube, P.Eng.
> www.BuildingScience.com
> 
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John Straube
www.JohnStraube.com