Debating All Aspects of Passive Houses - And May the Best Argument Win!
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Hi
This is possibly not the key focus of the forum, but I thought I would write up my ideas anyway
I have been interested in building a warm, very well insultated home that uses only a small amount fo heating for some time appropriate to both New Zealand conditions and also to my budget. I've come to the conclusion that I would need to build such a house, and so in my mind I have been formulating a reference design. Ideally in fact (from my narrow point of view) the people on this forum would contribute to such a reference design.
I've looked at the German passive designs and they seem to be very boxy and not really suited to the typical Kiwi section which is long and thin. They also cannot be built here - there just are not builders available.
I've loked at ebode houses, which I quite liked. They have really good material choices and nicely slanted roofs to catch the sun, but they are very expensive and also include items such as solar panels which I am not happy with. I feel solar panels are a false move environmentally - they consume more resource than they put back - and also are very poor economics. Ebode also seem to treat their designs as religious - they won't modify them at all.
The best design seems to be that of energy efficient homes. I think they are using a Canadian mdel which features the following:
- six inch walls with both insulation and plywod
- 30cm of insulatation in the roof
- lots of attention paid to thermal breaks
- use of UVPC double-glazed windows
They have a Titorangi design / kitset that has a nice set of windows. And it seems to have a pretty good price point. And it can be built by a kiwi builder.
However it is deficient in several respects.
- it does not slant the roof to catch the winter sun
- it does not feature any thermal mass
- it does not cater for "still cold air" spaces to act as air locks
- it has no built in heat pumps nor any concept of an air exchanger
So ideally my reference design would be all the features mentioned above.
I'd be interested in other people's thoughts about a reference design for a passive house of say 150 square metres, 3 bedrooms, study, lounge/kitchen, laundry, air lock. Is anyone else interested?
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Hi Peter,
There is absolutely no reason why Passive Houses could not be built on a long and narrow section. Actually, the section my house in Germany is on is 5.80 by 20 m, and it is a near Passive House standard (at the time it was built, some components needed for Passive Houses in central Europe, like triple glazed windows were still way too expensive, and the standard wasn't as well tested as it is now, so we didn't go all the way - which I regret now).
Also, while I believe that the accuracy needed to avoid air leakages and thermal bridges doesn't come naturally to most builders (anywhere in the world) I cannot see any reason why good kiwi builders couldn't build a Passive House. After all: the main ingredient is insulation, and installing insulation correctly needs some care, but is nothing that requires particularly special skills, that you can only obtain overseas.
Take another look at Passive Houses. www.passivhausprojekte.de has a database with worldwide projects. You will find they come in all forms and shapes and are available for all sorts of uses, too. Passive Houses are a performance standard - not a design standard.
As for roof slants and overhangs: this IS really hard to get right - getting the winter sun in, without risking overheating in summer. I cannot see the stupid sun diagrams any more that make it look simple. It isn't. There's topography, adjacent buildings, vegetation, depth of openings, optical performance of glazing and a lot more to consider to get this right.
As for thermal mass: the influence of thermal mass is most likely totally overrated. I know for sure for NZ conditions end of July (when the results of our research are in), but research for the Mediterranean and central Europe is pretty clear: thermal mass has very little positive effect, and can be a rather negative factor in your energy balance, particularly when - as it mostly is the case in NZ - heating happens intermittent.
As for still, cold air spaces: no need for anything like this in a Passive House; same goes for heat pumps (unless you use them for hot water generation, then a combination of HRV and heat pump might be useful to have. There are combi systems on the market in Europe that perform well in this instance).
Not sure what you are referring to regarding solar panels; if it's PV then yes: there was an issue with the usable/embodied energy ratio in early system, but that is not the case any more. They are still quite expensive, though, and I wouldn't use them were grid connection is available. Good solar thermal systems on the other hand never had that problem; there are however some not-so-good system on the market as well, so it pays to be a sceptic. As for solar thermal systems in general: this is a really good, cost effective way to get hot water in a new build. Cost effectiveness is of course less in a retrofit.
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