[GSBN] Straw-Bale Blower Door and Infrared Test Results
john at buildingscience.com
Fri Dec 24 08:14:25 CST 2010
Actually Ontario tract homes are closer to 3 ACH on average as of 07 but are likely a touch lower now.
However ACH is not a great metric as it makes small houses look worse and houses with basements look better.
A better metric is cfm50 per square foot of enclosure area.
The total cfm50 number is well under the average Ontario home ( less than half) because this is a small home which means its impact on the world is less than an Ontario home.
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From: David Elfstrom <listbox at elfstrom.com>
Sender: GSBN-bounces at greenbuilder.com
Date: Fri, 24 Dec 2010 02:11:28
To: <GSBN at greenbuilder.com>
Reply-To: "(private, with public archives) Global Straw Building Network" <GSBN at greenbuilder.com>
Subject: Re: [GSBN] Straw-Bale Blower Door and Infrared Test Results
The report says that flow was 617 cfm at 50 Pa depressurization.
If the house volume is (900 sqft x 10 ft avg wall height) = 9000 cuft ,
then air changes per hour at 50 Pa depressurization is 617 cfm/9000
cuft * 60 min/hr = 4.11 ACH @50 Pa. That is typical for a suburban
tract home built in Ontario today without any special attention to
detail, and easily achievable by retrofits.
Even if the volume were doubled (20 ft average wall height) it still is
considerably more than new home construction to the R2000 standard from
the 1990's of 1.50 ACH50. Passive House requires a mere 0.60 ACH50 or less.
In the report it states "ASHRAE suggest a minimum natural ventilation of
950-1200 CFM for a house of this size". I don't think so! That would be
a seriously leaky house, and would be as dry as a bone in winter. ASHRAE
actually suggests mechanical ventilation to 7.5 cfm per person + 3 cfm
/100 sqft, so a four-person 900 sqft home would require a mechanical
ventilation to achieve a mere 57 cfm for all the fresh air needed.
On 24/12/2010 12:42 AM, Dan Smith wrote:
> David and Anni, thanks for sharing this, it is a treat.
> What's the air change per hour at 50 Pa?
> Happy Holidays,
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