Applying Passive House Standards in the Southwest
Hi all – I’m still learning about the Passive House standard. How well do you think it applies to homes in hot climates like the American Southwest?
I ask because it originated in Germany, and in general resources on green building tend to have an East Coast or northern climate bias. Tucson and Phoenix are very different from those climates, and our main concern is cooling during the long summers. We also tend to not have basements or attics. Are there any standards focused on hot desert climates?
We also want our home to have lots of natural light. This probably comes with an energy efficiency trade-off. In any contest between natural light and energy efficiency, we choose natural light. In general, we’d choose well-being over energy use. Any standards that balance natural light and fresh air with energy efficiency? Does Passive House do so? I figured it might since northern climates would want warming light, but I’m not sure since a thick insulated wall is always better than any window from an energy standpoint…
Thanks for your feedback.
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Hey Blue Solar.
There are lots of opinions on whether the Passive House standard makes sense at all. There's an interesting discussion of that in this article: Lessons From a Practical Passive House
And here's a look at three Passive Houses built in the southwest: Passive House Meets Pueblo
I think at least one splinter of the Passivehaus/Passive House movement has adopted their standard to account, at least in some ways, for climate. Start reading here, for instance:
https://www.phius (dot) org/phius-2015-new-passive-building-standard-summary
Also, I think that at some point GBA solicited some regional ideas for the PGH. Not sure if any of those got back to the semi-official PGH organization website: https://www.prettygoodhouse (dot) org. Some searching here on GBA might find those...
One bonus of building in the desert SW is that slabs do better, from an energy standpoint, if they don't have any insulation underneath, so that avoids a big point of discussion that often comes up. NB: I think you still need to insulate slab edges, and do so with termites in mind.
Goals are great but the most important thing is to set the right goal.
I could never get behind the Passive House idea. A group somewhere decrees your house shall not consume more than X number of BTU divided by its area regardless of where on earth the house is located no matter what it costs to build and it does not count unless you have paid a certified consultant to design and inspect its construction.
LEED also never made sense to me. You select from a menu and collect point. Get enough points and you get a medallion. Some of the menu item make economic sense, other deliberately do not economic sense. Again you pay certified consultants to design and inspect the construction.
Energy Star homes I got turned off when I discover one of the requirements was no more than X number of square feet per resident. I wanted more elbow room than allowed.
Pretty Good House (PGH) This standard is more or less whatever you want it to be. For me this meant spending money on the building that is likely to be recovered in energy saving while I expect to own the building given the buildings location and fuel costs. Using the BEopt computer program allows you to model your house and tune your options.
https://beopt.nrel.gov/home
Walta
Walter,
I agree.
There are aspects of each program the may be useful as resources, but thats about it.
I bought Joe Lstiburek's book, Builder's Guide to Hot-Dry & Mixed-Dry Climates. Its not specifically about Passive House but it is a good general guide for building a sustainable structure that will meet some or all of the Passive House standards.
Generous overhangs, well shaded patios on the south side, courtyards, mass walls and night time ventilation ...
There's so much that can be done by intelligent space planning, even before going to technical solutions. I was in a hot/dry part of southern California, visiting one of the old Spanish Missions. There was a side structure, one room deep and very long in the east-west direction, with a deep patio all along its southern length. It was 96 degrees in the sunlight, but just stepping onto the patio it cooled by a good 8-10 degrees, from the cooling effect of the shaded adobe wall. I then stepped inside the room. It was uninsulated. You could see pinholes of light through the clay tile roof over the open wood framing. The room was perfectly comfortable, another 8-10 degrees cooler than the patio. It must have been in the mid-70s.
All done without the benefit of air conditioning or the burning of fossil fuels. Unfortunately building like this is no longer an option with our current codes. But we can still learn a lot of lessons from these old structures.
I was mildly obsessed with the idea of building a truly passive house here in Phoenix, a few years ago -- this would be a house that had no active heat and no air conditioning. I concluded that it's simply not possible. Maybe in Tucson or out in the desert, outside of the metro area.
The key component to a truly passive house would have to be a huge amount of thermal mass, mostly in the form of gigantic adobe or concrete or similar walls. The idea would be that the temperature pressure from the Sun during the day wouldn't have quite enough time to make its way through the walls before the nighttime temperature inversion would reverse the heat flow. Add some good ventilation and pervasive shading and that's how houses were built in the desert for hundreds of years.
Alas, that technique no longer works for much of the year here in Phoenix due to the "heat island" affect. The thermal mass technique demands that the outside temperature would eventually revert to below the desired interior temperature, thus reversing the heat flow... but in Phoenix, in the summer, the nighttime temperatures may only dip below "room" temperature for an hour or so and often not even that. The high thermal mass walls get hot and essentially stay hot.
I do wonder if a combination of thick thermal mass walls and notable amounts of insulation would help out, in this case, but I haven't seen any research done on that topic.
The small house I'm building now is going to have very wide patios coupled with large overhangs where there aren't patios; R-30 insulated walls; R-60 insulated attic; radiant barriers with low thermal emissivity in all the walls (with rain gap) and on the underside of the roof sheeting; and tile floors on a concrete slab. The goal is to hopefully require zero heat during the winter and only minimal cooling with a mini-split in the summer. I will say that with the house still in the framing stage, it's already MUCH cooler than the outside air or any other unconditioned enclosure on my property, due largely to the radiant barriers.
Kurt,
I'd be really interested in an update once you finish and see how it performs.