[Greenbuilding] first certified Passive House in Canada

[jfstraube]

Hi John
Your answer appears to be a riddle wrapped in an engina.  So the 0.6 is based on the use other arbitrarily chosen and unexplained measures, like I must heat the house with ventilation air, or I must reach 10 W/m2?
But even then it is odd because you say "because at this point after optimising the fabric heat losses". What does optimising heat losses mean?
The peak heat loss, Q, of any house due to conduction and air leakage is:
Q = (U A + c L + c (1- e) V) (Tin - Tout)
Where U A is the U-value (1 / R-value) of the shell times the area of the shell (we normally calculate each component and add them all up)
c is the volumetric heat capacity of the air (In metric units thanks to the French for inventing SI this is 1.20 kJ/m3/°C)
L is the air leakage rate (m3/s in metric )
V is the ventilation rate (m3/sec in metric)
e is the efficiency of heat recovery (in decimals, eg 0.70)

This is basic and well agreed physics. As you can see it does not depend on some point of optimisation as claimed: for a given climate (Tout) and a given area of building enclosure A, I can vary U and L amd e at will to get to the same heat loss Q.
So it is not true that there is a heat loss physics reason for the 0.6 ACH at 50 number.
PH has simply fixed L at 0.6 at 50 PA.  L can be estimated to be about ACH at 50/20 in service or 0.03 ACH.  There are detailed models that will get the answer more carefully, but this is pretty close.
Hence, now Q can only be reduced by reducing U not by trading off between L and U. Why this is done is the root of my question. Building physics shows that it cannot be to avoid condensation.  I could decrease U (add more insulation) and reduce Q, but PH wont let me.  

Another question is, why is it necessary to heat with the ventilation system? This is not a requirement of PH, and many certified PH use heat pumps, pellet stoves, electric heaters etc.
The 10 W/m2 does not work either.
ASHRAE 62.2-2007 is the north american ventilation standard.  It recognizes that both people and houses produce pollutants and hence recommends minimum ventilation of 7.5 cfm/person + 0.01 cfm per square foot of house area.  This is 50 cfm for a 3 bedroom 2000 sq ft (186 m2) house. PHPP 2007 states that the “average air change rate should not fall below 0.3 ACH.” This ACH based ventilation is no longer used in North America because research showed it was inadequate: it is the people and the building that need ventilation, not the volume. For a 3-bedroom 2000 square foot single family home, this results in a PH ventilation rate of 80 cfm versus 50 cfm (25 l/s) for ASHRAE 62.2- 2007.
So if I properly ventilate at 25 l/s, and limit heating to 50 C, then the heating power will be 0.025 m3/s * 1.20 kJ/m3/°C * (50C-20 C) = 900 Watts.  This is 4.8 W/m2 (for the 186 m2 house), not 10 W/m2.  Of course PH uses different ways of measuring area so maybe it is actually 6.5 W/m2.  In either case, it is only 10 if you over ventilate.  Why build a super tight house with an efficient HRV and then over ventilate?? This over ventilation is also one reason I think they want such high efficiency expensive HRVs.

But let us pretend that we want to ventilate at a higher rate and can deliver 10 W/m2.  First, what part of the environment is protected that is not included in the 120 kWh/m2/yr value? I dont even understand why this 10 W number is beneficial.
Second, refer back to the original equation.  As the outdoor temperature gets lower, Q will get larger in step.  If you are building in a climate with a design temperature of -30C, it is very difficult to imagine how to reduce the required peak heating power to 10 W/m2.  In Darmstadt, with Tout of may -15C you might be able to do it when you meet the overall 120 target. But they are not connected directly.

I know that the way some people in colder climates are meeting that number in some projects is to increase the outdoor temperature they design to (by saying "thermal mass will carry me through") although PHPP does not tell me how to account for thermal mass on an overnight level.  People are also including the heat from occupants, appliances and pets to meet the Q required, even though these people may not be there, and when they come home the house will take a long long time to get back up to 20C again. I also know numerous Europeans that are saying "10 is just a recommendation it is not required".

Must of this has been hashed out before elsewhere. Check out the two on line documents at buildingscience.com on PassivHaus.  BSI-025 and BSI-026

So, I am back to, "why 0.6ACH at 50".  And we can add, "and why 10 W/m2" or "why is heating with ventilation air desirable" or "where is the science that shows that 50 C is the limit for air heating".  
More questions than answers I am afraid. 


On 2011-01-27, at 5:20 PM, John Daglish wrote:

> Bonjour John,
> 
> Why 0.6 because at this point after optimising the fabric heat losses
> you can use an the HRV heat recovery
> ventilation as the heating source, the peak load 10W/m2 with less than
> 50°C heating elements avoiding burnt dust particles at around 0.3 ACH
> air changes per hour. Higher
> air changes in the continental dry winter climate leads to the air
> being too dry to maintain comfort (albeit there are other mechanisms
> that can mitigate this problem).
> 
> The peak heat /cooling load of 10W/m2 is an alternative but preferred metric to
> the 15kWh/m2.yr, it being used to fit into existing German / European
> energy metrics.
> 
> Regarding the PHPP planning package (calculation sheet) and calculation there is a copy
> here (I think it may be a little disabled) :
> http://www.passive-on.org/CD/
> 
> 
> Cordialement
> 
> -- 
> John DAGLISH
> www.batirsain.org
> 
> 
> 
> Wednesday, January 26, 2011, 5:45:14 PM, you wrote / vous ecrirez:
> 
> JS> Hi Shawna! (sorry I had no time for a visit...)
> JS> So how do we answer the question "Why 0.6ACH at 50, not 0.5?"?
> JS> Would you agree then that all the homes that you built and tested from 0.61 to 1.0 are not good low-energy houses?  I bet they are.
> JS> I would also argue that it is the primary energy use of the home that matters.  I do not understand why a house with 0.2ACH at 50 and one with 1.2 ACH at 50 with the same primary energy use are not
> JS> considered equal, because the environment will consider them so.
> JS> Now if the house is 3.2ACH at 50 we know from experience that comfort, condensation and performance problems result so clearly that is too high for our climate and much warmer climates.
> JS> We also know from experience that 1.5 of the R2000 spec is pretty safe on all these levels.
> JS> So the limit is somewhere around 1.5.
> JS> For energy, the goal should be 0.0
> JS> Back to "Why 0.6, not 1.2, or 0.9".
> 
> JS> On the PV topic, I agree that one cant make the ROI of PV pay (in Ontario or anywhere) without subsidies.  They dont make sense on ROI. Period.  
> JS> I cant make a 0.6ACH at 50 single-family house get its annual heating load down to under 15 kWh/m2/yr (the PH max) in North Bay, or Winnipeg without spending a lot more than 25K. And if any of your
> JS> ground floor walls is shaded by neighbouring buildings, fences, trees, etc, it becomes darn near impossible. Neither NZE or 15 kWh/m2 heating use makes any ROI sense for single family homes in
> JS> cold climates.  Rowhouses, apartments OK, duplexes in Halifax and Windsor, maybe.    Note that several houses have shown than solar hotwater systems (SHW) can cost as much to generate hotwater as
> JS> unsubsidized PV run through a heat pump.  So PV is expensive, but SHW aint cheap either.  PH lets me use SHW to reduce energy, but it wont let me use PV ragardless of cost.
> 
> JS> The CMHC Equilibrium NZE homes spent an awful lot of money getting the heating load down to the 25 to 35 range in Calgary, Edmonton, and Ottawa.  Reducing the heating load to half that (when you
> JS> already have R60-80 in the roof, triple glazed fiberglass windows, etc) is quite expensive.  Those same houses, dropped into Darmstadt Germany, would meet the PH space heating and annual primary
> JS> energy targets. 
> 
> JS> PS (most NZE designs with 200-300 m2 of floor area in Northern US and Southern Canada require 6-8 kW PV arrays, which costs more than 25K, I would estimate closer to 50K).
> 
> 
> JS> On 2011-01-26, at 9:31 AM, Shawna Henderson wrote:
> 
>>> Hey Ross and John,
>>> 
>>> Here in NS, we have several small production builders who consistently come in at <1 ACH at 50, Keith Sawlor hit 0.29 (I personally did that test, about 15 years ago!!). On all of our custom design
>>> jobs, 0.5ACH @ 50 is the target on our bid documents. While not all builders hit that, they are consistently coming in at less than 1 and some are bang on, because they have long-standing crews
>>> who can do the air sealing work. Ross, I'm with you on the NZE house $25,000 PV extravaganza, which might make sense where there is a decent FIT, like ON, but here in NS, where ComFIT comes into
>>> play April 1, there is still no real business case for it (ie, ROI sucks). We ensure that the design and planning allows for 3 to 7 kW PV on the roof and with conduit (not wiring) in place and
>>> wall space in the mechanical area for inverter and controls, roof mount and any extra bracing etc in place as homeowner dictates. When it's affordable/cost-effective, homeowner can have it
>>> installed.
>>> 
>>> I agree with John on the issues around the energy modelling, and that a set of dogmatic rules leads us right back to the one-size-fits-all approach, which leads us right back to the problem of
>>> large tract builders and 1,000s of spec homes in GTA every year that are not meeting the +20-year-old R2000 standard, but are building to a one-size-fits-all approach, just using a different set
>>> of dogmatic rules driven by a different set of requirements ($/sf vs W/sf).
>>> 
>>> Cheers from mighty chilly Halifax
>>> 
>>> Shawna
>>> 
> 
> 
> 
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John Straube
www.BuildingScience.com