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Posts: 3
Reply with quote  #1 
Hi. This is my first inquiry regarding using simple solar heat capture for a project I hope to put in place summer of 2020. The project will be located in Nova Scotia and consist of a new 20 ft x 30 ft. , PHIUS code built , non glazed hot house, incorporating a south facing glazed cold frame wall backing on to an internal 12 ft x 20 ft blackened concrete Thrombi wall . Vegetable plant growth will be through the use of focused select spectrum LED and nutrients provided via AquaPonics supplemented with required micro nutrients.
My theory, based on some readings, is to provide passive radiant heat through the Thrombi wall + naturally vented air circulation through conduits located top and bottom. To augment the process I have been thinking of sheathing the cold frame side of the Thrombi wall with Matt black corrugated steel siding, so as to further capture heat and channel it across the wall wall surface to enhance the absorption rate of the concrete heat sink.
I have also considered running some copper tubing between the concrete and steel and provide an additional in floor radiant heat sink in the concrete.

Electrical demands would be net zero leading to off grid.

Has any one have experience with such a proposal? Will it work?



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Posts: 1,109
Reply with quote  #2 
Welcome Salty. Your project is pretty complicated hard to understand from just a text description so diagrams or photos might help.

There's some information on Trombe Wall on the BuildItSolar site (our sister site):



Both temperature rise and airflow are integral to comparing hot air collectors

Posts: 3
Reply with quote  #3 
Hi. My artistic ability lacks, so hope you can make sense of it.

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Reply with quote  #4 
Hi Salty-


Great project you are working on! I would think the dark painted concrete blocks would be enough without the need for the metal. The corrugated metal sheathing may actually reduce performance since the metal would have to transfer heat to the bricks. The metal sheathing would however, heat the blocks more evenly, at least where the sun hit the metal and above. It might be something you try without the metal and see how it performs. The metal could alway be added later. The size and shape of the blocks should be considered too, as solid blocks taken longer to heat up, but would hold the heat far longer than hollow blocks. Thick, solid blocks might all but prevent heat transfer directly through the blocks, making the circulation of the air above and below the wall of primary importance. Thin blocks would heat up faster, transfer heat through the wall quickly, but would cool off faster once the sun was no longer hitting them. Once last thought about the blocks is that many concrete construction blocks are hollow. So the heat transferred through the wall might not be as high due to the void. But the hollow space would also act as a chimney, moving warmed air up to the ceiling where the opening from one side of the wall passes warm air to the other. Maybe you could use this to your advantage somehow. 

Perhaps this winter you could test some different concrete blocks to see how well they not only absorb heat, bit transfer the heat to the opposite side of the block from the sun. A small test box with a clear plastic front and made from scrap wood might give you some needed answers.

Placing copper tubing, painted black on the front of the wall sounds like a simple way to gather up some warmed water for some sort of radiant heat. It seems simple on paper, so it is certainly worth a shot. 

One last item is the actual circulation of air between the upper and lower air openings. If passive, the air will likely try to move directly from the upper opening straight down the wall to the lower vent. This could prevent warm air from circulating near the growing area. However, You don't yet know yet as to the amount of heat that will be radiated from the wall itself. If the warmed air did hug the wall and more heat was needed near the plants, perhaps a low voltage fan could be used to direct the heated air where needed. 

Greg in MN
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