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Thread: Passive solar wall

  1. #1
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    Default Passive solar wall

    Way back, I came accross "solar walls" for the first time in a Harrowsmith Reader. Recently, I have stumbled accross the topic again and it got me thinking. We have some south facing wall ... .

    A solar wall is not that complicated - you paint the wall in a dark color, put some glass in front of it and have something that provides shadow in summer when the sun is standing high and lets the sun rays through to the wall in winter when the sun is low.

    Now, the concept I recently saw is a warm air heating, where you have inlets into the room at the top and outlets from the room into the solar wall at the bottom. In summer, you close the openings to the room and open ventilation to the outside. Doing it like that, you probably will not have mould growing between the glass and the wall.

    Now, I would not like to make holes in our outer wall ... . Just heating up the wall together with having it insulated from the winds would be all I would be looking for at the moment. Ventilation in summer would be easily doable, but in winter, the air in the solar wall would be standing. And likely, there might be condensation and mould. Now - does anyone know more about solar walls without holes in the building shell and tricks to avoid condensation and mould?

  2. #2
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    Default Re: Passive solar wall

    I have seen internal water tanks used the same way. Fabricated to whatever shape you need.

    https://www.youtube.com/watch?v=A0fLm7YmbkU
    https://www.youtube.com/watch?v=IJ0Bn1KurS0

    Hope this helps a bit. A bloke I knew used a mud brick wall as the spine, and the heater-cooler of his house.
    The floor can be used as a heat/cooling bank if the house is suitably oriented using angled slats on a verandah to let in sun in winter, shut it out on summer.

    I'm sure youtube will be your friend there too.

  3. #3
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    Default Re: Passive solar wall

    A solar absorbing floor may be a better use than a light-blocking wall during low light periods in the winter.
    R
    Sleep with one eye open.

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    Default Re: Passive solar wall

    Quote Originally Posted by Ron Williamson View Post
    A solar absorbing floor may be a better use than a light-blocking wall during low light periods in the winter.
    R
    But when the sun is low, a floor will absorb less radiant heat owing to the angle.

    This is a good reference on various solar designs. A passive double wall setup is known as a Trombe wall.

    https://en.wikipedia.org/wiki/Double_envelope_house
    We're merely mammals. Let's misbehave! —Cole Porter

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    Default Re: Passive solar wall

    Makings of an interesting thread here…..

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    Default Re: Passive solar wall

    I've learned a thing or two about solar stuff. This has been going for 11 years at 8000 ft. in a very cold part of the US.



    It's self-heating year-round. When the night temps get 30 or 40° below zero, I fire up a little propane duckblind heater. Otherwise it collects and stores enough solar heat to grow tomatoes, etc.








    We're merely mammals. Let's misbehave! —Cole Porter

  7. #7
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    Default Re: Passive solar wall

    Passive solar is not just get some gain from the sun. Not saying you can't retrofit something, but it requires some thought & planning. The major piece is thermal mass - IOW a place to store the heat.

    I built a passive solar house that worked very well, even in cloudy northern VT. Friends in Maine had a passive solar house that a "builder" designed & it had no thermal mass. On a sunny January day, it'd get to over 100 degrees during the day. They had to open some windows to cool it down, then close them & fire up the woodstove to stay warm at night.

    A properly designed passive solar house has ratios of cubic footage to glazed area to thermal mass. My 1600 sq. ft. house (10' ceilings) had thermal mass of gravel covered in brick: 8' x 60' x 20" deep. I was about 6-8 tons shy of what it should've been.

    Common materials for solar walls are dyed water in gear glass, solid masonry, and - if getting fancy - eutectic salts.

    Lots of good books on it out there - do some reading - it's cheaper than building a mistake...

    ETA: Not trying to be a naysayer! Just that it requires some thought.
    Last edited by Garret; 09-21-2020 at 01:43 PM. Reason: grammar
    "If it ain't broke, you're not trying." - Red Green

  8. #8
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    Default Re: Passive solar wall

    I've studied this subject some, have built two passive solar heated houses, the first one worked ok, much warmer than the usual house, the second one is spectacularly warm, even on a cloudy day. Daughter and her family live there now and she tells me that in the winter she leaves windows open a bit during the day to stop the place overheating, and that the insulated slab heat sink inside the big windows is still warm to the feet after a couple of rainy days.
    Although I went down that route, I am considering a Trombe wall for the next place I build, thats really what the OP is proposing, lots of information on line on those.
    https://www.google.com/search?q=trom...hrome&ie=UTF-8

    John Welsford
    An expert is but a beginner with experience.

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    Default Re: Passive solar wall

    We started by digging a meter down and setting a foam-insulated foundation.





    With the dirt floor level, I laid down a couple inches of gravel and then 2-inch foamboard. Then it was filled with coarse sand, with a maze of PEX tubing for radiant floor heat.



    With the beds framed, I laid dark pavers and put soil in the center..



    Under the black rubber mat at the near end is a 400 gallon stock tank for a heatsink, filled with water. A small AC pump (bottom, blue intake tubing) pushes the water through a maze of PEX tubing under the floor. A DC pump hooked to a 20W PV panel drives a loop of PEX tubing (red) filled with 50% ethanol antifreeze at about 20 psi.



    A salvaged flat plate hot water collector (first photo) warms the water/antifreeze solution, which in turn warms the water in the heatsink, often up to 125°F. Pumped under the floor, it stores quite a lot of heat and the main thermal mass seldom gets cooler than 50° in the depth of winter when it can drop to -40°F outdoors).

    There are also four passive heatsink tanks on the south-facing wall, which can get up to 65-70°F in winter and shed about 10-15° at night. I added shelving for the tenderest plants, herbs, etc.



    I've long wanted to start on a house from scratch, as the one we live in is not well built for solar heating. There's a limit to what you can do with double-windows, insulated blinds and similar upgrades.
    Last edited by Chip-skiff; 09-22-2020 at 12:30 AM.
    We're merely mammals. Let's misbehave! —Cole Porter

  10. #10
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    Default Re: Passive solar wall

    Hi Henning
    Regarding the question of condensation and mould there is an online calculation sheet http://www.hygrothermik.de/ . To instruct you how to use it and about some other points of "Solarthermie" please contact me (Impressum, email) if you want.
    Gruß, Günter

  11. #11
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    Default

    Used to live in house here in Seattle that we rented from the architect who designed it and built it. It was designed as passive solar. 2-story glass front facing south. Living room was in the front, 2 story high ceiling. Master bedroom was a open loft facing the glass wall. Thermal mass was the concrete slab the house was built from and the brick floor the ground floor had.

    Had a little Vermont Castings wood stove as a backup, and radiant electric baseboard heat as a backup for that.

    Electric heat ran very infrequently even in the dead of winter, though we did run the wood stove fairly frequently. Seattle does get pretty dark and dismal November through January.

    Summertime was a different deal. The glass wall was sliding patio doors all the way up, we had a pole with a hook that allowed us to open them to regulate ventilation. And the whole glass front was rigged with polished aluminum Venetian blinds to control light admission. Even with all the doors (windows?) open in the summer, one still needed to keep all the Venetian blinds closed so as to minimize light admission and heat.
    You would not enjoy Nietzsche, sir. He is fundamentally unsound. — P.G. Wodehouse (Carry On, Jeeves)

  12. #12
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    Default Re: Passive solar wall

    The key idea is to design your solar application for the local climate. Here, that includes extreme cold, with bright winter sun, and low humidity. I used 6-wall polycarbonate (R 3.8) for the roof and 3-wall poly otherwise. Since the sun is intense in summer, with frequent high temps in the low 80s, it's got a passive low/high vent setup with automatic thermal openers on both the corner inlet vents and the clerestory outlets. I also stretch reflective shade cloths. When a day is 85°+ and still, I use a couple fans for circulation.

    It's nice to have heating and venting that's largely automatic, so I'm not scrambling out there in panic mode.
    We're merely mammals. Let's misbehave! —Cole Porter

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    Default Re: Passive solar wall

    Good stuff, thank you! The house is existing, first half of the last century. So, no chance of Trombe walls and stuff like that. The roof has been insulated around 10 years ago. The basement still needs insulation. We have been postponing this, partly as the basement windows (double glazed) are still pretty good although around 50 years old and a good insulation would require new ones. Whatever. I have researched a bit in the meantime and found, that there is 7 and 10 wall polycarbonate around in the meantime. There is even aerogel filled 3 wall polycarbonate out there ... This stuff already has pretty good thermal insulation properties, best the aerogel filled 3 wall with apparently 0,5 W/(m²*K), the 10 wall 0,8 and the 7 wall 1,1. This put in front of a dark painted wall. External ventilation (automatic) and shadow in summer. Thermal insulation from the multi wall PC plus a bit of external solar warming of the wall in winter. That is the idea. What could go wrong? I am sure a lot of things could go wrong ... At the moment, it is just the idea. I guess I should fire up the spreadsheet this winter ...

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    Default Re: Passive solar wall

    Quote Originally Posted by Henning 4148 View Post
    At the moment, it is just the idea. I guess I should fire up the spreadsheet this winter...
    You might build a small-scale model of your idea, and test the concept with real sunlight.

    I've built solar cookers, largely with recycled stuff, and they work really well.




    Also, a solar space heater (basically, a portable Trombe wall) with black corrugated roofing and polycarbonate, rigged with a PV panel and 12v fan to boost the output.



    Tinkering with stuff is lots of fun.
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  15. #15
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    Default Re: Passive solar wall

    You can build a Trombe wall outside in the garden, using a pool of water as a reflector helps boost it. Pipe the heated water into an insulated box buried in the ground, and pull that warm water inside and through a radiator as required.

    We've a number of examples of that system in houses in our alpine regions in the far south, they're very effective. ( remember that for us, the "far south" is further away from the equator)

    John Welsford
    An expert is but a beginner with experience.

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    Default Re: Passive solar wall

    Thanks! All interesting stuff! Storage in the garden might be an option. I guess I really have to crank up the olde spreadsheet machine this winter. Together with the pocket calculator.

    The insulated box (of water) in the ground - I once calculated that for our current energy consumption and came out at around 200 m³ IIRC - to save the surplus heat from the existing solar from summer for winter. Feasible in theorie but a bit out of reality, digging out and removing 200 m³ of soil. So, insulating of the ground floor walls is a must anyway. Which is where I come back to transparent thermal insulation and a dark painted wall with shadow in summer. Or hanging thermal solar on the walls and feeding a storage tank from them. Or ... But the thermal insulation is a must.

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    Default Re: Passive solar wall

    The idea of storing heat in a buried water tank depends on ground temps at your location and how deep the frostline goes. Here, even with insulation, you'd have severe loss of heat in winter. The heatsink in the floor of the greenhouse is surrounded by foamboard and also double-layered with Reflectix (aluminised bubble wrap). The plywood cover has Reflectix underneath and is topped with 1.5-inch foamboard.



    Even so, it loses heat in winter. But since that heat goes to the overall thermal mass, it's not a problem. But it seems like a good idea to place the tank under the house or in some structure.
    We're merely mammals. Let's misbehave! —Cole Porter

  18. #18
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    Default Re: Passive solar wall

    Quote Originally Posted by Henning 4148 View Post
    Thanks! All interesting stuff! Storage in the garden might be an option. I guess I really have to crank up the olde spreadsheet machine this winter. Together with the pocket calculator.

    The insulated box (of water) in the ground - I once calculated that for our current energy consumption and came out at around 200 m³ IIRC - to save the surplus heat from the existing solar from summer for winter. Feasible in theorie but a bit out of reality, digging out and removing 200 m³ of soil. So, insulating of the ground floor walls is a must anyway. Which is where I come back to transparent thermal insulation and a dark painted wall with shadow in summer. Or hanging thermal solar on the walls and feeding a storage tank from them. Or ... But the thermal insulation is a must.
    The Arahiwi house on the mountainside above Alexandra in our far south has, according to an architect I know who was involved in its design, a pit 22 cubic metres in volume, with 600mm of foam insulation on all sides. He tells me that a key factor in its ability to store heat is that its filled with slabs of granite, layered in such a way that the water follows a path through it rather than just being dumped in at one point. He makes the point that the higher the total density of the storage medium, the more heat it will hold.
    Note though that this area has very high sunshine hours, even in winter which helps it a lot.

    John Welsford
    An expert is but a beginner with experience.

  19. #19
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    Default Re: Passive solar wall

    Back in the late 70's, I designed a passive solar home to go on my 2/3 acre lot. A Trombe wall was a big component. Thought I'd jump into the market early. Use the house as a 'model home'. Maybe even sell it or use it to leverage another couple on spec. Lots of early interest, but then the recession of the early 80's quashed the financing, and I had to sell the property to survive. <sigh>

    But it certainly works, and our execution of the concept has only gotten better.
    David G
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