[Greenbuilding] Passive House Overheating

christian corson chris at ecocor.us
Thu Aug 16 15:12:06 CDT 2012


Whoa......

John,Corwyn, and whomever else is on this DOS based list from 1995.

Pump the breaks folks.

First of all, I did not report anything. Ted Cushman did. Furthermore, what
I said is being spun and twisted into some sort of malignant half truth.

Its funny to me to walk through life and have people comment on your work.
Funny in a good way. After all, at one point I was hanging out on Shakedown
Street trying to get miracle’d. It never happened for mem(although I have
seen the Dead a hundred times), and like the lottery, that was a lesson in
knowing that  I would always have to work for it (whatever arbitrary thing
"it" could be).

That work is designing and building high performance,healthy homes.

So, at least, lets keep things real. Starting with not using words like
Dogma. Seriously. I'm meta religious anyway, so we can all give that a
rest. PH dogma? WTF?

Now, I can assure you that there are example of PH's in the Northeast that
overheat. That is for sure true, and for the sake of being polite I will
refrain from pointing them out. They are NOT mine.

My own house even with high SHGC 0.494 windows barely overheats. Once more.
It is not even finished. The final design calls for exterior shading in an
already heavily shaded area. The house isn't even completely sided yet.The
point I was making to Ted was that even with out shading and
de-humidification the house is still within PH limits for overheating.
Those limits stretch what I consider to be comfortable. Ironic since PH
comfort criteria are so stringent and they are totally focused on heating
dominated climates, but can be applied both ways.

Yes, the shoulder seasons are rough. especially when counting
on deciduous trees for shading. Ext shading is always best whether active
or passive with active being superior. It is a retro fit that has gone from
1200 gal/oil yr for DHW and space heat to less than 100gal/oil  for DWH
only. The mini split is not yet installed either so I have 3/4 of a
EnerPHit retro. Flame me, but I dig breaking the house away from the
thermal envelope too.


High solar heat gain windows are fine. This isnt a PH thing, its an energy
balance thing. If you are creating 20,000Kbtu/yr with tons of south facing
glass and SHGC's of .62 , you better god damn well put some shading up.
I'll wont ever argue that. I will argue shading on the interior. Once the
radiation is in the house its in the house.

The house I designed and built in Knox is performing just fine. Now I just
need to get paid for it. It Doesn't overheat. Its comfortable, and so is
mine. It will just be better when the shading is up and the mini-split is
installed...........in two years....or whenever.

A few points

AHD-  is not arbitrary
SPED- is
PHPP is fine when used properly. It does account for overheating ,but like
ANY model it is just that. A tool for design guidance. Shading is often
improperly entered. If you can meet PH in New England with 4" of eps
everywhere you model is frigged up. Its not the model but the data enrty
that is the key here.
a PH like any super-insulated home should be well designed, that
includes balancing loads, with money,with best practice,with research, etc.
BALANCE.
Daylighting is a good thing



John, Thanks for all of your hard work,NESEA talks, and acerbic wit. Maybe
you'll invite me to Sommerville some day. I have all kinds of stuff for the
hot box. Including our wall assembly.

Corwyn, Thanks for the heads up.

Everyone else, thanks for a real good time!

small windows suck
c










*Christian Corson*
*EcoCor Design/Build*
ecocor.us
chris at ecocor.us
207 930-5088



On Thu, Aug 16, 2012 at 3:17 PM, John Straube <jfstraube at gmail.com> wrote:

>  I dont understand what you are suggesting then Corwyn if not 1-4.
> So you say: 1. dont lower the window SHGC, 2. dont use operable shades and
> 3. dont change comfort expectation.
> Sounds like that is exactly what Corson has, and he reports, to no
> surprise to me, that there is overheating.
>
> I am arguing against the dogma of "high SHGC windows are generally a good
> solution for low energy homes".  I beleive they are generally a bad
> solution.
> Also I am arguing that current models dont properly predict overheating
> (even the much lauded PHPP) and that fixating on a specific space heating
> target rather than a total primary energy target can lead one to poor
> designs than otherwise.
>
> Your 1. You are making a major assumption that a house with a SHGC of 0.23
> (pretty low, probably too low to get decent daylight) is a bad house.  What
> tools do you use to support that and what metric do you use to measure this?
>
> Your 2. I was proposing 3-5 time reduction in primary energy use of homes.
> Who said anything about status quo?  Where did I ever suggest that this was
> good enough or the right direction?
>
> Your 3.  All energy targets are dependent on occupant choice. People can
> choose to run their homes at 74 or 65F for example.  The target is a
> modeled number using fixed specified inputs to avoid this.  They can
> however install, gasp, curtains, and reduce solar gain or they might even
> plant trees outside.  No target is immune from this.  While we as designers
> have more control over space heating and cooling than, say hot water or
> computers, I do not think there is much evidence to support the contention
> that rigorous space heating targets are much easier to hit than rigorous
> primary energy targets.  In fact, if you look at the measured space heating
> usage of the famous Krongsberg study, which was a PassivHaus development of
> a row of townhouses, the actual space heating energy use varied by a factor
> of over 5 from lowest space heating usage to highest space heating usage
> even with a consistent target of the same building design built by the same
> people, eg almost all of this variation was due to occupancy. This is MORE
> variation than one would see for houses built to the same total energy
> use.
> It is not my experience that a heating target gets more attention from a
> builder than a total energy target.  Having a target is what seems to
> matter.
> And of course the environment cares only about total energy use and energy
> type, not wether that energy is used for heating, lighting cooking or TV.
>
>
>  Dr John Straube, P.Eng.
> www.BuildingScience.com
> On 12-08-16 2:28 PM, Corwyn wrote:
>
> On 8/16/2012 12:17 PM, jfstraube1 at bell.blackberry.net wrote:
>
> This whole thread started by mean pointing out that an obsession with
> hitting an arbitrary heating number can result in overheating and high SHGC
> are part of the problem.
> Without asking people to make many changes in their comfort and their
> lifestyle superinsulated homes can make very large reductions (eg 3 to 5
> times less energy that code built) in their energy use.
> Yes one may be able to get to 5.5 times less energy by asking people to
> accept higher temperatures, operate shades or pay 10K for automatic shades.
> My argument is that there are small benefits to some of these approaches
> and high social or economic costs.
> Low SHGC windows, tighter comfort, giving up the arbitrary 15 kwh/m2
> heating limit while still accepting the 120 kWh primary energy number
> hardly seems like that flawed of a way forward.
>
>
> I did not say:
> 1) People should accept higher temperatures
> 2) Operate Shades
> 3) Pay 10k for automatic shades
> 4) Make ANY changes in their comfort level
>
> I am not sure what you are arguing against.
>
> My points:
>
> 1) Low SHGC windows in the house under discussion would *increase* total
> energy usage, at the *same* comfort level.  I never recommend compromising
> comfort levels; I often recommend improving them.
>
> If he replaced his high SGHC windows with ones with s SHGC of 0.23 or
> lower, the windows would no longer be energy positive, and he would be
> better off with a wall instead (which would do nothing to cause
> overheating).  In general, from a heating/cooling standpoint, having
> windows which aren't energy positive is counter-productive, especially if
> we expect that people can't be bothered to open them.  (There are, of
> course, other valid reasons for having windows.)
>
> 2) The status quo is not sustainable.  Attaining something sustainable
> might require a live style realignment.  Not attaining something
> sustainable will definitely require a new life style.
>
> 3)(new) I agree that the arbitrary heating limit might not be ideal. For a
> builder like Chris Corson, it really isn't, when he is renovating, and
> hitting the limit is impossible, he gets as close as he can.  When he is
> building new, he sees how far *past* it he can go.  For other builders,
> having that goal actually gets them to go out of their way to improve
> heating efficiency; without the goal they would not have any incentive.
> For yet others, it might be a spot where they say 'eh, good enough', when
> without it, they would have gone further.  My guess would be that most
> builders around here fall into category 2, YMMV.
>
> A total energy limit does not accomplish quite the same thing, in that it
> is so dependent on changeable occupant choices.
>
>
> Thank You Kindly,
>
> Corwyn
> Topher Belknap
>
>
>
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