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500 sq ft. Passive Solar House Design Considerations  RSS feed

 
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Greetings -

I posted this at Green Building Adviser (see the thread here: webpage ) and the consensus was that this is 1970's design and not relevant to modern building techniques. I'm curious to learn what the community here thinks.

It seems to me there are sort of two factions: passive solar enthusiasts and net zero enthusiasts, the latter being more focused on super-insulated, tight envelopes with minimum windows, PV + heat pump + HRV.

Another point made was that full southern glazing is excessive - the target should be closer to 9-12% southern glazing unless there is a surplus of thermal mass to soak it up. I love glass. I love the outdoors. I get that it's a terrible insulator, but if we can add more by adding thermal mass, I am intrigued.

The final question is whether insulated concrete forms count as thermal mass or not? Seems like it would be better than stick framed for sure, but how much better. My uncle builds with pumice-crete a lot which is locally sourced.

The original thread follows:

My partner and I are building a small (500 sq ft) house in climate zone 5B (NM/CO border). When we lived in Colorado, we had friends who built commercial passive solar greenhouses using south-facing glazing and water tanks for thermal mass. Using their formula, we calculated that we would need approximately 1500 gallons of water to meet their design specs for a self regulating high desert (7k ft elevation) house of this size.

The design specifics of storing that much water in an already very limited living space is an obvious practical constraint. As such, we were considering a couple of strategies, including:

1. A dark colored in-ground hot tub in the living room floor with a reinforced plexiglass cover. This could yield ~500 gallons of water thermal mass.

2. A dark 4" stamped concrete slab floor over 3" rigid foam. Since water is 4x as efficient for thermal mass, call this 1200 gallon concrete slab equivalent to an additional 300 gallons of water.

That brings the total up to 800 gallons, so to hit the target we would need an additional 700 gallons of water storage. Some potential options are:

a. Call it good enough, supplement with solar thermal radiant floor heat and a heat pump and propane water heater. I'd like to avoid the expense of a boiler. We plan to do this regardless.

b. Add another in-ground tub for rainwater storage, same design as above but with a fixed cover.

c. Add a covered rainwater cistern below the slab, possibly tied into solar thermal panels, either outdoor or built into the floor. This could easily start to get elaborate and expensive.

Another major consideration for all of the above are building code considerations. While the thermal mass is desirable, we would prefer not to jeopardize our ability to pass inspection.

I also asked on this forum about solar thermal plate collectors and got some great info and design considerations. See here: https://permies.com/t/76915/Solar-Thermal-Plate-Collectors


 
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One scheme for thermal mass water that I have not seen discussed on Permies is the Skytherm roof designed and built in the 1970s.
Idea is to have a roofpond that is covered/uncovered as appropriate to gain/lose heat depending on season.
Supposedly this maintains the otherwise normal house in the 70s year round in a hot summer/cool winter location in Atascadero CA.
Practically this means having some kind of water container from bottles or gallon milk jugs to larger ones like commercial bladders for liquid foodstuffs in/on your roofspace.
The roof is glazed with a transparent cover such as polycarbonate corrugated panels.
To gain heat in the winter you uncover the water containers during the day and cover at night with insulation to block radiating heat away.
To lose heat during the summer you do the reverse, cover during the day to prevent thermal gain, and uncover at night to allow heat to radiate away.

http://www.solarmirror.com/fom/fom-serve/cache/30.html
 
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Zane Bridgers wrote:Greetings -

It seems to me there are sort of two factions: passive solar enthusiasts and net zero enthusiasts, the latter being more focused on super-insulated, tight envelopes with minimum windows, PV + heat pump + HRV.



Thermal siphon or convection can be used to circulate water passively. all that's needed is to have water storage above the panel as well as the house.
 
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