[Greenbuilding] PHPP Flow Rates

Tue Mar 5 20:42:17 CST 2013

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
 <mailto:alan at abramsdesignbuild.com> alan at abramsdesignbuild.com
 <http://www.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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