[Greenbuilding] Aggressively Passive: Building Homes to thePassive House Standard

[George J. Nesbitt]

Dear John,
     I have enjoyed your critiques of PH, your BS (that's Building 
Science) Insight articles, your posts here on this forum, as well as 
your presentations in SF (San Francisco) this past, oops, last year. I 
agree with much of what you have to say, and agree that some some 
changes could help make PH more assessable in NA (North America).
     I had dinner with Dr. Feist in December which was great and I had a 
chance to clarify a few issues.
     I was recently elected to the Board of PHCA (Passive House 
California) and have been a certified Passive House Consultant since 
June, and my invitation to you, and perhaps Joe too to come and talk to 
us on a 4th Sunday at Pyramid Brewery in Berkeley still stands. We could 
changes meeting dates too to accommodate you.
     You have pickup up and understood some of the details better than 
some who have been through the training. I have made some clarifications 
below as needed.

On 1/10/2011 7:44 AM, John Straube wrote:
> As you may know, there are 3 numerical requirements of PH, with a 
> bunch of recommendations that vary with whom you speak to (of which I 
> dont think any are required) and what day you speak to them.
> 1. 120 kWh/m2/yr of source energy
This is for your all of your energy at your building site. And using the 
U.S. DOE average for source energy conversions need to be entered 
replacing the E.U. #'s. And the appropriate #'s for Canada should also 
be used.
> 2. 15 kWh/m2/yr of annual space heating demand
and 15 kWh/m2/yr for space cooling, this and heating are based on site 
energy use (as opposed to source energy)
> 3. 0.6 ACH at 50 air tightness
This is a multipoint pressure & depressurization test, and must pass 
both, equivalent to our ASTM-E779
> and you should have a mechanical ventilation system.
Correct, and wrongly assumed to have to be a balanced HRV or ERV, it can 
be exhaust or supply only. If you install a balanced system you can't 
have more than a 1Pa delta between rooms (this is a requirement per Dr. 
Feist)

To be Certified, you have to submit plans, pictures & other 
documentation showing your project was built as it was modeled in the 
PHPP. You have to test the mechanical system and have it balanced to +/-10%

A note on square meters, the EU m2 TFA (treated floor area) is a net 
usable square footage, it does not include stairs, and is only a % of 
other spaces. We typically use a gross exterior floor area, so without 
making an an adjustment to the floor areas the #'s can be off (I made 
this mistake 3 years ago, before I knew better).
> You have to meet 120 kWh/m2/yr site energy regardless of PV. 
Correct, end of sentence
> Sort of. In fact, the PHPP spreadsheet uses a factor of 0.7 to when 
> calculating the factor for PV: I assume this means in an all electric 
> house you could use up to 120/0.7= 170 kWh/m2/yr.
No, there is no adjustments to any of the numerical requirements for PV 
generate electricity. There has been discussion about a small house, 
cold climate, and retrofit modifications, but I am not clear on if they 
are official yet and the exact details.
>  I do not know why PV is rated this way, since in a grid 
> interconnected system like PV, the best factor one would think was 
> possible is 1.0.  Anyway, the problem is that the PHPP software 
> basically ignores the PV generated electricity in its verification: 
> you can add PV but it does not reduce the energy accounted for in the 
> 120 number.
>
> So yes, this limits the size of the PV array and would avoid very 
> large PV arrays on small houses.  That is good.  We can still have 
> largish PV arrays on large houses.
> For a large house in Sonoma California, this results in an absurdly 
> bad house, even if it met the other two requirements of PH. A 300 m2 
> house (say 4500 sf) could use 300*120=36000 kWh. This is a large 
> amount of energy which could be provided by a 28 kW PV array, and 
> render the house net zero.  This would meet PH's 120 requirement. But 
> it may not meet the 15 requirement for space heating and has nothing 
> to do with the airtightness.  Meeting 15 is easily possible in Sonoma 
> (where heat pumps work very well).  The only hard part is getting 0.6. 
>  Of course, in Sonoma, 0.6 is a pretty stupid measure, since the 
> energy saved going from 1 to 0.6 is truly trivial.  But if you want PH.
My rough calculation based on actual output of PV in the SF Bay area 
would say it's an 18kW PV system to get to net zero source energy. Still 
honking large! Net Zero Site energy would be much smaller, and net zero 
Time Dependent Value (California's modified source energy) would be even 
smaller. Net Zero is not a trivial pursuit, especially in large house.
>
> Sensible economics would reduce the size of PV arrays on most house, 
> eg if it is cheaper to save energy in a specific project than it is to 
> produce it, a sensible design would choose to save energy. This is one 
> of the requirements that the Building America research program tries 
> to convey: use the lowest cost means of saving energy, and every home 
> reaches a point where PV is more economical than, for example, adding 
> another 2" of foam to a 12" thick layer under your slab (to pick a 
> favourite example).
>
> Now lets look at a small house in a cold climate like Minneapolis. 
>  Say a 1500 sf house plus a basement, which would have a PH area of 
> maybe 130 m2.  Thus we can only use 15600 kWh of energy of all types, 
> which would be 5770 kWh for an all electric house using the PHPP US 
> values.  This would be hard to do all electric! Also total space 
> heating demand would be limited to 1950 kWh (=66 therms) regardless of 
> how this heating demand is met.  This is really hard and kind of crazy 
> to achieve in a cold climate small house.  Meeting this 15 number is 
> what drives many of the extreme and non-obvious decisions, not so much 
> the 120 number.  At least this the case in cold climates and small houses.
I think this is why they have considered a cold climate adjustment to 
the 15 kWh/m2/yr budget.
>
> For example, I currently live in a medium size house (1500 sf raised 
> ranch with a fully finished basement) in a coldish climate (7500 HDD 
> F). I cannot meet the 15 kWh/m2 demand number for space heating, 
> although I could likely meet the 120 number, and could reduce the 
> blower door number from 1 ACH at 50 to 0,6 ACH at 50 by spending another 
> $5000 or so (I looked at this during the retrofi: the payback for this 
> option was in the order of 100 years, and it was 4 times cheaper to 
> use PV to generate the energy saved than saving it this way).  But I 
> could not get certification if I wanted to because I dont meet the 15 
> number: I am over twice this with R45 walls, R80 ceiling, R30 basement 
> walls, triple glazed R6.5 windows, etc.  There is zero benefit to me, 
> society or the environment, to meet that 15 target but it is required 
> for PH.  For a townhouse in a 5000 HDD F climate in, say Frankfurt 
> Germany, 15 would be a nice guideline (oh, I guess that is where PH 
> was developed..) but it still would not matter to the goals of good 
> buildings like the 120 number does. Oh, and I heat primarily with wood 
> from my own property, so the fact that I use more energy for heating 
> is pretty irrelevant.
My congratulations to you if you are under the 120 kWh/m2/yr total 
source energy budget (without PV) even if you don't meet the 15 
kWh/m2/yr heating budget.

You have achieved an equivalent level of performance, an energy 
efficient house, and that's is what we all should be trying to achieve, 
no mater what we call it!
>
> Just some more thoughts.
>
> On 2011-01-09, at 9:08 PM, Rob Dickinson wrote:
>
>> Interesting post, John.
>>
>> I'm afraid I need clarification on a few points.
>>
>> If I understand correctly, in PH you can't increase the amount of 
>> total kWHs available by adding a solar PV array beyond the energy 
>> allotment specified by 120kWh/m2/yr.  To me, this makes some sense 
>> because it avoids the examples of very inefficient houses 
>> compensating by installing enormous solar PV arrays.
>>
>> But if one had an all-electric house and the exact amount of 
>> electricity allowed by the area formula (i.e. 120 kWh/m2/yr) were 
>> produced on-site using PV, wouldn't that that be more of a 1:1 source 
>> energy/site energy, and allow the full 120kWh/m2/yr?   That would 
>> seem sensible.  Or is PH not that sensible?
>>
>> Hopefully I have expressed my question clearly.  I look forward to a 
>> response.
>>
>> Rob
>>
>>
>> On Sun, Jan 9, 2011 at 5:44 PM, John Straube <jfstraube at gmail.com 
>> <mailto:jfstraube at gmail.com>> wrote:
>>
>>
>>
>> -- 
>> "I still find each day too short for all the thoughts I want to 
>> think, all the walks I want to take, all the books I want to read, 
>> and all the friends I want to see." — John Burroughs (1837-1921) 
>> American naturalist, writer
>>
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>
> Dr John Straube, P.Eng.
> Associate Professor
> University of Waterloo
> Dept of Civil Eng. & School of Architecture
> www.buildingscience.com <http://www.buildingscience.com>
>
>
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