Sunday, September 26, 2010

Colorado PassivHaus? almost...

This morning brings us a great New York Times article about where we are headed in green building design.  Bravo, people!

Here is a shot of Green Line Architects' recently completed Off-grid PassivHaus!  (Passive House to us Americans)  

The Living Room trusses are made of reclaimed timber and steel, and you can see a section of the 12" thick, R-60 SIP's (structural insulated panels) being installed above for the roof.  High insulation values, coupled with a very airtight "envelope" and proper ventilation make for an extremely energy-efficient home.  This one is estimated to be 94% more energy efficient than a standard home.  That's very near Net-Zero Energy!

Stay tuned for more news about this terribly exciting new home...


Turns out this house is 105% more energy-efficient than the standard home, which means that it is a Net-Zero Energy or NZE Home!!

Technically, it falls just short of being a true PassivHaus.  See notes from our energy consultant, Megan Gilman, of Active Energies, Inc. below:

Performance Characteristics

PassiveHaus Standard 1 • Airtight building shell ≤ 0.6 ACH @ 50 pascal pressure, measured by blower-door test.
This home had 0.1 natural air changes per hour and an ACH@50Pa of 2.14.  LEED and other programs have started using ACH@50Pa (LEED has three tiers of infiltration for this climate – required 5.0 ACH@50, 2 points for 3.5 ACH@50, and 3 points for 2.0 ACH@50.  These figures make sense… we were very close to LEED’s most stringent level.  
PassivHaus Standard 2     • Annual heat requirement ≤ 15 kWh/m2/year
(4.75 kBtu/sf/yr)
            Our annual heat requirement (according to HERS) is 12,000 kBtu/year, so this would be 5.96 kBtu/sf/year.  This might be a hangup, if it doesn’t meet their requirement.  However, they specifically say that it has to get this energy use in their software, which has specific weather and conditions, which could be a bit different
PassivHaus Standard 3 • Primary Energy ≤ 120 kWh/m2/year (38.1 kBtu/sf/yr)
Our total is 7,200 kBtu/year.  Yeah, I know that it’s weird that this is lower than the heating requirement, but this is because the PV production knocks down the total energy requirement.  I suppose the specific heating requirement is to ensure that you don’t just have a home with bad insulation and windows and slap a bunch of PV on.  Anyway, this total energy use would be 3.58 kBtu/sf/year.
In addition, the following are recommendations, varying with climate:
PassivHaus Recommendation 1  • Window u-value ≤ 0.8 W/m2/K  Window U-value is 0.213 in English units (Btu/hr-sf-degree F).  To convert to SI units, the conversion factor is 5.678, resulting in a value of 1.21 W/m2K.  They say this varies by climate, but I’d bet we’d be in one of the more aggressive climate zones.
PassivHaus Recommendation 2   • Ventilation system with heat recovery with ≥ 75%  
   efficiency with low electric consumption @  0.45 Wh/m3  I believe the HRV has an efficiency right around or above 75%.  My records show there is a 500 cfm unit (really two 250 cfm units) that runs 2.5 hours per day at 300 watts total, which is a total of 31.25 watts-hours per day, divided by 907.16 cubic meters is 0.034 W-h/m3.  This seems really low, but they wrote cubic meters, so that’s what makes it so low.  I don’t believe this item would be a problem.
PassivHaus Recommendation 3 • Thermal Bridge Free Construction ≤ 0.01 W/mK
I believe that with a SIPS shell, that this house is on par.

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