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the first wofati greenhouse design

 
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Mike Haasl wrote:
I think the idea of the original thermsiphon is to dig one well casing hole  .



How about horizontally? A tiny hill behind the roof might supply the neessary earth mass and deter lost cybertruckers from resting on top of the hidden roof. I just don't like deep holes. A fear of premature burial.
 
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Yup, that's what I was trying to get at with my second sketch.  Since they'd be digging up the area anyway, it's easier to lay pipe horizontally than to dig down.
 
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WOW,

All these remarks seem Well thought through and are about Heat,materials, danger,...
But not much about growing.

Here is my thought,
In the current design, there is only glass to the South. Wouldn't that get the plants growing to the glass? Stretching for light (especially in the back?)

The main goal is to grow year round right?
IT would be a shame if You get the right tempetature but the plants dont grow well because off "wrong" light.

Strange Idea: some mirrors on the back wall?

Appart from that, verry interested in dimensions as i dont have much room in my garden (7meters wilde) and migt try this in the future...
 
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Faber vanmolkot wrote:
IT would be a shame if You get the right tempetature but the plants dont grow well because off "wrong" light.
Strange Idea: some mirrors on the back wall?


Right, here is the Caia heliostat:  
Caia



I think the original Indiegogo prototype enclosed this in a transparent globe thus snow-proof. It is solar powered thus supposedly no external power source and wiring. You can then line the ceiling with silvered mylar to scatter this sun re-beam. Another heliostat is the Sunflower which has open petals like unfurled satellite solar panels. thus subject to rain, hail, wind and snow damage. An alternative would be to puncture the ceiling to allow a light pipe. For a dirt cheap solution, there is the Philippine  



This also needs holes in the ceiling. The heliostat does not disturb the structural integrity of the greenhouse.
 
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Ok, I recently inherited a big metal frame greenhouse; and in short order, I have realized how inefficient it is.  So I am excited about this wofati greenhouse idea!  Especially since I am looking at a potential growing site on a fairly steep SW facing hill...  This would be perfect ~ built right in!  

I have seen youtubes of Oranges growing in Northern Nebraska by using angled earth birmed North wall with reflective insulation material, and long expansive deep earth ventilation systems. I like Mike Haasl's idea of adding additional horizontal deep earth tubes inside the wofati umbrella!  The dirt is always going to be warmer under there  Spread that love around more!

I have one important question. How much is this going to cost to build?  (Will you be drilling the 20' shaft?). Since you're raising money with a kickstarter, would it be cheating to build 10 or 20 of (something like) these solar cooker tubes into the wall (probably with cob?) just above a stem-wall on the South Side, protruding from the front of the building at a degree angle ideal for Winter Sun?  They would not take up any space inside, and their opening could be positioned under the growing tables on the South side of the walkway, increasing convection from the cold pit, and heating the massive growing beds on the tables right above the tubes. These evacuated glass tubes are dark colored on the outside, but reflective on the inside, so heat is captured really well inside.  With no lid, this heat would flow right into the greenhouse.  I have one of these, and it gets piping hot, even on cloud-covered days!  You might even be able to fit the parabolic reflector under each tube. The whole array could easily be covered in the summer.  (Forgive my Amazon link!  Maybe these can be sourced used somewhere?)  GOSUN Survival Gear Solar Oven Sun Cooker https://www.amazon.com/dp/B00KLKJB72/ref=cm_sw_r_cp_apa_i_EtB7EbF8P3JH7

I also love Faber's idea!  Add angled mirrors to the North Wall! (Forget the reflective insulation!). Mirrors will reflect the light onto the plants, and the dark dirt they are growing in, thus heating the ground (a better place for the heat to be than on a dark colored North Wall).
 
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Mirrors to reflect light into the greenhouse would be spiffy.  I think for the plants to be truly happy, there would need to be a lot of mirror surface area.  So to light up a 3' by 8' growing bed I'd suspect that you'd want a 3' by 8' mirror.  

What about berming the ground to the south of the greenhouse and covering the berm with reflective rocks.  Then they may bounce a lot of light in while not needing to be motorized.  The challenge would be to select a berm angle to give you light at the times of the year you most need it.  

I suspect in winter the sun will enter directly, in summer it may need redirection.  Plus if there's snow on the ground it will help reflect light in winter.

Another mirror idea would be white corrugated roofing metal.  Put it on a frame so you can adjust the angle up and down with the seasons.  Collect the rainwater off of it.
Wofati-reflector.png
Wofati reflector
Wofati reflector
 
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Mike Haasl wrote:  The challenge would be to select a berm angle to give you light at the times of the year you most need it.  

I suspect in winter the sun will enter directly, in summer it may need redirection.  Plus if there's snow on the ground it will help reflect light in winter.

Another mirror idea would be white corrugated roofing metal.  Put it on a frame so you can adjust the angle up and down with the seasons.  Collect the rainwater off of it.



One thing that struck me after reading your comments and looking at the rendering, is how cave-like this greenhouse is. So getting light to the rear, especially in summer, may be problematic. Painting the entire interior white would be inexpensive and very effective at reflecting available light.

“ Put it on a frame so you can adjust the angle up and down with the seasons.”
Yes. Light will reflect at the same angle it hits, so if you had a frame work (with notches maybe, or holes for a peg) that you could adjust up and down a couple inches at at time maybe once a week, you could maintain a continuous stream of light coming in year round.

Regarding horizontal tubes going into the earth- my crazy idea (seems like it might work well) is a horseshoe shaped loop, maybe 1’ diameter ducting, with one side angled up a few degrees, and the other angled down a few degrees, and the rear of the loop being level. Both ends would enter/exit the rear wall of the greenhouse. What ‘should’ happen (passively)- when the air in the greenhouse is cooler than the earth, it falls into the tube angled down into the earth, thus forcing warmer earth air out through the tube angled down into the greenhouse (this is a way that I think cold air would push warm air in a downward direction). When the greenhouse is hot, the direction reverses, and the warm air flows naturally into the tube angled up into the earth, with cooler earth air coming out the other side. Now you are using warm air to push cold air in an upward direction. I don’t think air will move through horizontal tubes that are level without using fans. But if the tubes were at maybe a 5 degree incline, it should happen the same way cold and hot air moves up and down a slope?
 
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I like your idea Julie for the tubes with a slope to them.  I think that would work well outside but I'm not sure about inside.

If they're buried behind a wofati or wofati freezer I can see how cold air will want to sink out of them, drawing in warmer ambient air and charge a mass.

Inside the greenhouse I'm thinking all the air will just sit and stratify.  I'm having trouble seeing how air will move in or out of big tubes passively.  If it's 100 degrees in the planting area and it's 50 in your horseshoe tube (or my sloped horizontal tubes), I think the warm air will just travel a little way into the top of the tubes.  This might push a bit of colder air out into the cold sink but I don't think it will cause an ongoing flow.  The coldest air will still sit down low.

If it's nighttime and it's 35 in the greenhouse, the 50 degree air in the tube system may want to rise.  And as it rises, the cold will replace it at the bottom.  Hmm, that might actually start to cause ongoing flow...  

I'm not sure why my intuition is telling me the air will stratify during the day and flow through the culverts at night but that's what I'm thinking...
 
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Heat is much the harder factor to handle than light, in my unerstanding.  That's what Ben Falk said about his greenhouse.  

This reminds me of a concept that is kinda totally off topic but maybe there's something worth remembering in it--and I can't remember the name of the person who invented it, but all the websites I find seem to have invented the same concept without illustrating it (or possibly they took it from him without giving credit?), so I'm not %100 clear if they're talking about the same thing.  

You have an east-west-oriented, ^ shaped roof for your greenhouse.  Basically in winter you blow soap bubbles up along the wall of one side of the greenhouse, the west / side in the morning, the east \ side in the afternoon, in winter, to reflect extra light back into the greenhouse and get supplemental heat and light onto the plants.

Now I know you don't want more moving parts, and having to supply soap is another cost, but maybe there's some aspect of the concept that can be translated for the wofati.  

What about frost?  In winter, frost forms on windows when you have a warm interior and a cold exterior.  Condensation, and then it freezes occasionally.  I guess that would take a little while to melt on the east side in the am, and by evening it would be gone on both sides.  in the a.m., the frost on the west side would act as a bit of a mirror bouncing some light into the growing area.

I'm not quite sure I can picture what's east and west in the design, the glass is not a pitched roof, correct?  so you're going to have frost on the one south wall, and that will slow down the warming on the coldest days.

I guess this is a problem that needs to get handled in some way.

Does the Oehler greenhouse get frost on the windows??

Mirrors outside the greenhouse might help--they won't frost, but they'll get pounded by the weather.

Maybe a TEFA pond that never melts...

https://smallfarms.cornell.edu/2011/10/soap-bubbles-to-insulate-greenhouses-a-new-approach-to-energy-conservation/

"Over the period of operation, gas use was 25% less in the house with the bubble system and 7% less in the house with the curtain than in the unimproved control house. " [they were heating the thing with natural gas, that's what the "gas" refers to here.

Oh found it!  Chris Marron was the inventor of it.  It's a very different context, but there are some really unusual ideas in here:

https://midwestpermaculture.com/self-study-more/permaculture-greenhouse/greenhouse-description/

And some odd observations--that the CO2 level increase for 3 hours each morning helps plants grow faster (if you could vent your rocket stove into the greenhouse somehow, not for heat but just for added CO2, each morning you make breakfast, that would be a great add-on that isn't necessary for the plants to live but just makes them happier).

Again, I know this is almost entirely off-topic, but it's worth looking into this if you want to see some outside-the-box thinking.


Faber vanmolkot wrote:WOW,

All these remarks seem Well thought through and are about Heat,materials, danger,...
But not much about growing.

Here is my thought,
In the current design, there is only glass to the South. Wouldn't that get the plants growing to the glass? Stretching for light (especially in the back?)

The main goal is to grow year round right?
IT would be a shame if You get the right tempetature but the plants dont grow well because off "wrong" light.

Strange Idea: some mirrors on the back wall?

Appart from that, verry interested in dimensions as i dont have much room in my garden (7meters wilde) and migt try this in the future...

 
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Hmmm...one of these in Canada claims to need no conventional heating at night, but the bubbler must consume some energy:

The liquid bubbles provide a thick blanket of insulation at night that is able to reduce the heat loss by a factor of ten times as compared to standard double polyethylene covered greenhouses and is about 15 times improvement over a single glass covered greenhouse. The renewal of the bubbles brings the stored solar gain from the liquid thermal mass system to the building envelope so that no conventional heating is required inside the solar controlled environment space during cold nights.

http://www.solaripedia.com/13/231/solaroof_keeps_it_cool_and_hot_(canada).html .

Also, you can submit a project to solaripedia, and i guess they do some sort of open source collaboration.  
 
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First off....I love the look of this in the artwork.  This may be minor, but it seems like heat lose could be reduced with sloped retaining walls (which would also reduce the force on them) and by moving the door away from the main greenhouse and making an airlock....of course that adds to the build.  An alternative to make a sloped retaining wall that I've been considering is terracing since that side is south facing and some nice goodies can grow there (this could take the place of herb spirals :) ).

wofati-greenhouse.png
sloping the retaining walls, moving the door to reduce exposed surfaces and to add an air lock
sloping the retaining walls, moving the door to reduce exposed surfaces and to add an air lock
 
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I might be totally wrong here but I think the wall you put the red slope in front of is just holding back dirt, not the interior of the greenhouse.  

I like the idea of the airlock and having the door come in from the side.  Then there's more room for glass and solar gain during the day.

And the artwork is looking really awesome!  Great job to everyone involved with that!
 
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Mike Haasl wrote:I might be totally wrong here but I think the wall you put the red slope in front of is just holding back dirt, not the interior of the greenhouse.  


No, you're right Mike.  This was just to minimize the exposed wall that is 90 degrees from the glazing.
 
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From a walapini design website:

"At the summer solstice this
angle will have the opposite effect and maximize reflection and minimize penetration.
This angle can be
varied, but will change the basic design of maximizing heat during a winter solstice and
minimizing it during the summer solstice. " (http://www.solaripedia.com/files/1257.pdf)

The angle they're referring to is the angle of the roof window (plastic in their case).  They're saying that it reflects more in summer.  This is already in the design, I believe.

I wondered however is there a roof overhang that can augment this effect? and then can that roof add more to the thermal battery while not adding to the heat of the air inside the greenhouse (overheating the plants in summer)? in other words, can that roof overhang conduct some heat into the thermal battery under the waterproof umbrella part? Maybe you've already done this.

Or, can there be a wax cylinder overheat escape valve from the greenhouse that vents into another chamber that's in contact with the thermal battery sub-umbrella roof of the structure?  The biggest question I'm hearing is will the stratification idea work.  So far, I'm assuming it will just because Paul.  But overcoming the hot-air-wants-to-rise thing seems big, and the problem is the solution.

 
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Also, they point out about obstructions outside the greenhouse--how about a deciduous tree on the south side or southwest?

A mock tree stand-in for testing purposes for the first summer (building a whole tree is a lot of work, maybe just some cloths hanging on a clothes rack that blow around a bit in the wind?)
 
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I think someone with more experience and design knowledge might want to take a look at this and see if any of what they say would inform the design choices for the wofati greenhouse.  Although it's a very different climate and latitude, they've got experience and some of it may cast light on factors for the wofati greenhouse.  http://www.solaripedia.com/files/1257.pdf.  I'm just a novice in this stuff.
 
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Greg Martin wrote:

Mike Haasl wrote:I might be totally wrong here but I think the wall you put the red slope in front of is just holding back dirt, not the interior of the greenhouse.  


No, you're right Mike.  This was just to minimize the exposed wall that is 90 degrees from the glazing.


Ahh, good point, I didn't see that.  You da man!
 
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I've been mulling this over for a couple days, and the more I think about it, the less I am convinced that the pipe will do anything, or is needed.  The idea of Mike's greenhouse was that the cold air will naturally fall into the cold sink.  That should happen whether there is any kind of pipe or not.  The heat will naturally stratify and that is exactly what is needed in the greenhouse.  At night when the air temperature cools the inside of the greenhouse, that colder air is going to fall into the cold sink no matter what.  The warmer air from deep in the ground will rise.  I think the same will happen with the pipe installed.  Nothing short of a fan is going to force hot air from the greenhouse down into the cold sink area.

I think the best way to do this might be to take the idea of using culverts and expand it.  If you could use bigger culverts, the largest that could be installed, and put in as many as will fit, you could still have the cold sink that was 5 feet deep or so, and then in the floor of it, you could put in the culverts.  They could have steel covers to ensure that no one or nothing could fall in.  I'm picturing something like manhole cover with holes drilled all over them.  That should handle the safety issues and it can't really get more passive than that.  As long as the volume of the cold sink is much larger than the volume of the greenhouse, It seems like it could keep the greenhouse from freezing.  
 
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Trace Oswald wrote:I've been mulling this over for a couple days, and the more I think about it, the less I am convinced that the pipe will do anything, or is needed.


Trace, the idea, as I understand it, is that the light entering the greenhouse will heat the air in the upper portion of the greenhouse, but the air in the blackened pipe will heat much more than that and will rise into the upper portion of the greenhouse where it will get diluted back to the same temp it would have achieved if the pipe hadn't been there.  But the rising hot air in the pipe will pull air up from the bottom of the 20' wells.  This will, in turn, pull in air from the 5' air space in the walkway zone, which will, in turn pull down air from the greenhouse.  So the pipe will passively turn the air over in the greenhouse.  The big question is how efficiently.  It would be very interesting to add some sort of air flow meter on the pipe or else somewhere in the flow path, though the end result can also be measured by with pipe/without pipe temperature measurement differences.  They could also build multiple greenhouses :)

I had earlier suggested that the pipe end in a trombe wall, so that that thermal mass could extend this effect to both day and night.  Having said that, it would also reduce the maximum temperature of the pipe, which would be expected to reduce the air flow rate during the day.  Lots of good iterations that can be made to test what works best once they have this greenhouse up!  

If they put more 20' wells in up front they can always cap some of them off to see what the return on investment is for what number of pipes, though that might not be an attractive proposition work wise up front....but it's all an investment in learning.  Maybe that could be a stretch goal if they reach a certain level of fund raising?
 
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