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the first wofati greenhouse design

 
steward
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I need a thread so people can make their design suggestions.
 
paul wheaton
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this came in through my email:

Many problems I see with your kickstarter idea. I have been dwelling the past several months on a much bigger idea, yet much smaller as well.

Here's my take so far on what I'm trying to research the idea for.

A fireproof, rustproof, rotproof, rustproof, insectproof, rodentproof, waterproof, hopefully fireproof and bulletproof all in one house which heats itself, provides its own water and hopefully even(still a long ways off on this) provide its own source of power(non solar, wind, or hydro). Everything will be contained in a structure which is secure, not a homestead but a securestead.

My idea as it currently stands, it keeps on evolving all the time into something much better:

Fiberglass structure, no wood(wood burns) and very little to no metal(rusts). The fiberglass is waterproof and can be structural enough when used with regular sheet insulation to make it so you can make non standard walls(not vertical but slanted walls).

This is a small house, under 32 sq ft, no permit necessary and no property tax assessment.

The bottom level will have an air gap between the ground and the floor of the compost pile/house. The air gap prevent any worries about radon gas(5-6 miles north of where I live is known for uranium deposits).

The compost pile will sit with a lightly insulated fiberglass housing. It will have a door on one side for removable of compost and also to let the heat out during the summer months.

Above the compost pile will be storage space, probably 2-3 feet thick, this is closet space for the house right above it.

Right above the storage area will be the main room of the house, no walls. other than the outside walls which both inside and outside are made of fiberglass with R50-60 insulation between them. The outer wall would be much thicker than the inner wall. The heavy insulation is for both keeping the house warm but also to make sure the heat wants to move one direction only, upwards.

The walls of the house turn lean outward at an angle. The angled walls are used for both shade against the walls to keep the UV light down, since UV likes to break down fiberglass, but the angled walls also help to create more garden space up on the roof. of the house. The angled walls also make it harder to try to climb the walls to get to the door into the house which is on the roof.

There are no windows in the walls, and the front door is also not in the walls. This makes it difficult for someone to break in and steal anything or take any of your food unless they bring a nice big ladder with them so they can get up on the roof. Being built out of fiberglass it won't burn as easy as it would if was built out of wood. Also by being built out of fiberglass you aren't limited to the confines for insulation like you are with wood and you don't have the heat loss due to the wood interrupting the insulation in the walls.

On top of the house you have the rooftop garden which can be covered like a standard greenhouse. Only now it is protected from prying thieves due to it being up on top of the house. You have quick easy access to it while in the house since you go right by it every time you come or go from house since the front door is up on the roof. You need to manufacture a quick release/quick(small) storage ladder scenario so you can easily remove the ladder and take it with you anytime you leave. This further protects the house and greenhouse/garden from thieves, and animals.

Down in the compost pile you have a tank, which receives all liquid waste from the house this liquid waste gets heated up and rises up into the house and recondenses into fresh drinking water. At the same time a pipe through the floor/storage area which goes down into the compost pile receives all your shit for the compost pile/wastewater tank.

Everything is compact in design and the flow of everything works the way it is supposed to and gets rid of all the complex plumbing and heating problems associated with standard houses today.

The heat from the compost pile rises to heat the house. The heat from the compost pile warms the grey water tank and causes it form condensation which also rises into the house where it recondenses into fresh water. The heat from the house continues to rise to the ceiling(still not sure how much insulation I would want in the ceiling given the rooftop garden). Once the heat from the house leaves the ceiling it warms the rooftop garden which is also helping to insulate the structure underneath it. Now put a simple greenhouse on top and you should have close to a year round greenhouse out of reach of most people and animals. The only trouble would be providing enough sunlight during the winter months to keep anything growing all winter long.

This is a day and age where protection is far more important than having an item. You can have a car but if you have no electricity or gas supply, what good is the car to you. You can have the garden/greenhouse but if your neighbors/rioters/looters can come and take everything from it and leave you with nothing--than what good is it?

The biggest problem with your design shown on the kickstarter page is the simple fact of it sitting partially buried in the ground. That leaves it totally unprotected from troublemakers, which there are plenty of anymore, with many more being added each day. Your design needs a secure method of protecting the garden/greenhouse or what is the point of building it in the first place? You can't make a point of the idea being feasible if everybody has stolen all the food from the greenhouse.

Remember your old forum posting about cutting your heat bill by 87%. Why not get rid of it entirely. The trouble with your way of approaching it is space. Space is the dumbest frontier, not the final frontier. The more space you have the more it takes to heat up the space. I have lived in a 468 sq ft shack for 20 years now but stumbled into the tiny house concept back in '13 or '14. I trimmed my living/heating space down to 48 sq ft and wrapped the 6 walls with R60 pink panther insulation. I spent a couple of years in that room before shrinking it on down to 32 sq ft and lived in it for two years. Both years included R30 in the ceiling with the second year also including R30 in the floor. Last summer thanks to your 87% posting I shrank the room down to around 50 cubic ft with R60 completely surrounding the room. Unfortunately I didn't get the chance to try the room out this past winter since right after finishing the room I moved in and started full time caretaking for a friend of mine. I've been hoping to completely get a setup made where I could 100% eliminate the heating bill other than body heat and stray electricity from lights and a laptop computer. Typically during the summer months I only use 4-6 Kw /month, aka laptop and light. I need to get rid of the heating bill 100% and then I'm doing pretty good, but not until then.

I think the idea I'm looking at now is far more along the lines of what I'm hopingto accomplish with a lot of side benefits to it as well since I live with plenty of deer which love to eat the garden. I also have tons of mosquitoes and I have recently heard of the possibility of getting rid of the mosquitoes by moving everything up off the ground. I hear they don't like it much above 5-6 feet above ground. If I could garden or sit outside on a nice summer day and enjoy without having to deal with the bugs, because I'm above them then I win.

Still not sure about the electric generation but I am thinking something along the lines of using the evaporating/condensing water cycle for it, not sure how I could though with such limited production.  Everything, in this day and age, needs to be completely self-contained and secure or else you have nothing.

 
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Interesting project. I am concerned about the deep hole. Someone is bound to drop their car keys inside. So there has to be a maintenance ladder of some sort which leads to the likelihood of a soil collapse when someone is investigating the sudden dampness at the bottom. Will the walls be braced?
 
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It sounds a lot like living in an inground pool.
A living space sandwiched between an active compost pile and a working greenhouse sounds rather uncomfortable .
The material choice seem incompatible with previous design choices.
The security concerns might be personal.

I do like the idea of a compost pile beneath the working green house, but I can't see how it can work passively long term.
Maybe a Solvia style vermiculture filter could work,  it is said the early if ever need emptying.
 
William Bronson
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My own idea concerning a the green house project is related to walls and shoring,  etc.
Maybe leave the internal wall sloped rather than vertical.
Most soil will slump into a naturally dictated angle if it isn't reinforced.
When we berm above ground  walls we are using this to our advantage.
We could dig a slopped walled hole with a flat bottom, tamp the soil and cover these "walls" as we normally would in a WOFATI
There the will be very little pressure against the wood and sheeting of the wall.
Build bleachers on this slope and grow in containers sitting on the bleachers.
This is especially good for hand dug holes, because less soil needs to be removed yet it is a safer hole to be in.

If we dig a strait sided hole maybe we can still use an internal berm.
Build your walls as usual but add a layer of sheeting to protect the wood from your internal berm.
This sandwich of plastic and wood could be a problem,  but not necessarily.
Borox or wood ash could be applied to the wall to help stave off decay.
In any case, berming against this wall gives more support for the wall.
We can build this berm as we like,  layering in drain tile, hugel materials, earth tubes, PEX loops,  geofabric , biodigesters, rainbarrels, rocket stove bells or whatever.
When we have built the berm to within a two feet of the top of the wall,   we stop.
Against the top of the wall we set diagonal braces that parallel the surface of the berm.
In addition to bracing the wall,  they also offer support for a layer of glazing, insulating or pest exclusion material that will sit about 2 feet from the surface of the berm.
By laying a board across the bracing,  we can lean in and lay   within 2 feet of the berm surface, for harvesting,  planting and weeding.

Any of these berm ideas could be used above ground,  but the key is to berm on both sides of a wall, the wall itself being less structural support and more a form for the earthworks.

 
gardener
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Thoughts to kick around:  

I understand the 5' pit under the walkway from an evolutionary design perspective, but with the 20' pipes do you really need that pit or is it just vestigial?  It means a lot more digging and materials as well as a future hazard if the walkway should give.  The air in the greenhouse will likely be humid which could lead to rot at some point years down the line and an unexpected 5' drop could make for a really bad day(s).  Being lazy, I also like not digging/building it.  I suspect that you could have the walkway over perhaps a 6" deep bottom that is sloped to the pipes so that the cold air would just drop into the walkway and down into the pipes while eliminating the future hazard.  When I was thinking about something like this I was actually thinking of just having a gravel floor (perhaps mildly sloped to the pipe openings) at the bottom of the walkway with cast drain grates over the pipe openings to let air in and out, but not keys or what not.  I was also thinking that the beds to either side of the walkway pit would be sloped towards it such that cold air drains into the walkway volume, and then into the pipes.  I think sloping the beds towards the walkway also may make them easier to work with when standing in the walkway.
 
steward
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My design suggestion is to massively increase the surface area between the deep soil and the greenhouse interior.  Much like Travis Johnson's idea about keeping stock tanks from freezing in Maine with a Geothermal Culvert.  He uses a 10' length of 15" culvert to passively allow warmish deep earth temps to come up under his stock tanks.  

I'm suspecting one (or 5) of these in the cold sink, or in the place of the cold sink, could really make a difference.

It would be really nifty if there was a way to connect two of them at the bottom and then encourage the air to travel down one and up the other.  Maybe if one end was in the cold sink and the other was higher and in the sunlight?  During the day the sun hitting the culvert might make the air want to rise?  At night with the coldest air settling into the cold sink it might want to push down into that culvert and help slightly warmer air come up through the other duct.  A similar concept could be done with clay chimney liners but connecting them at the bottom (safely) may be a challenge.

The attached crude sketch is the view from the south looking into the greenhouse.

With any underground tubing, I think we can learn a lot from the Citrus in the Snow and the CRIMPI approaches.  They have fans and TONS of ductwork in contact with deeper soil.  This application is completely different but it's worth keeping in mind the scale of what they need to do to harvest heat from soil.  Many many many square feet of surface area.  With forced air movement.
A-second-grader-could-do-better-than-this-artwork.png
A second grader could do better than this artwork
A second grader could do better than this artwork
 
Edward Lye
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I read this book about the construction of China's railway line to Tibet. "Methods included using pipes called thermosiphons along the sides of the tracks to refrigerate vulnerable parts of the soil along the highest parts of the plateau, an area that comprises the largest continuous sub-Arctic permafrost region on the planet. These cooling sticks are 7.6-meter-long steel tubes drilled into the soil; they contain ammonia, which draws latent heat out of the soil as it evaporates. " Might this be an alternative to that hole/trench? It has no moving parts.
 
Greg Martin
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Edward Lye wrote:I read this book about the construction of China's railway line to Tibet. "Methods included using pipes called thermosiphons along the sides of the tracks to refrigerate vulnerable parts of the soil along the highest parts of the plateau, an area that comprises the largest continuous sub-Arctic permafrost region on the planet. These cooling sticks are 7.6-meter-long steel tubes drilled into the soil; they contain ammonia, which draws latent heat out of the soil as it evaporates. " Might this be an alternative to that hole/trench? It has no moving parts.


So it sounds like their thermosyphons are a form of heat pipe?  Heat pipes utilize gas phases to very rapidly move heat in the vapor phase from a warm source and deliver the heat to the cold spots by condensing into liquid, which delivers the heat through the phase changes.  If ammonia were to leak it would kill you, so another fluid would be desirable, but one that works at the right temps.  The CRIMPI system relies on water vapor to deliver the heat to the earth battery, which provides the added benefit of dehumidifying the greenhouse air.  Using water is very attractive.  For example, you could channel water down the inside glazing at night into a rain gutter that would deliver it back down into one of the pipes.  Since this system is a greywater treatment system their should be a good supply of water into the system to make up for any lost to the deeper ground.  Paying close attention to the water cycling in this system would be a VERY good idea as it may be critical to the efficiency of the system.  I'd very highly recommend using sensors that measure and log both temperature and humidity in the key locations of the system to understand how it's really moving heat.
 
Greg Martin
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Alternatively you can capture the water and send it back to the house for reuse, creating a loop of water to the house, greywater to the greenhouse.
 
pollinator
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I don't understand how the thermosiphon works to cool the greenhouse.  A bit of air is in the hot part of the tube, it gets heated up to so that it is hotter and less dense than the air outside the top of the tube so it moves up and out.  The bit of air behind it is siphoned up but it wouldn't move up and out of the tube until it is hotter and denser than the air outside the top of the tube.  So it would only work to heat the air.

Does it need to be shaped like an upside down J?  Maybe you wouldn't get the siphon part without gravity pulling the cooler denser air out of the tube.
 
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Mike Haasl wrote:My design suggestion is to massively increase the surface area between the deep soil and the greenhouse interior.  



That is my thought as well.  I don't think a 1 or 2 or 3" pipe is going to move enough air to do much.  I read Mike's greenhouse book years ago.  My first thought was, what if the cold pit was 30 or 40 feet deep instead?  I understand the safety issues involved.  It still seems to me that having the area underground much larger than the greenhouse itself would be necessary.  I'm not an engineer though, so I could be way off base.
 
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I wonder if you've heard of Tim Meyers of Bethel Alaska? He had greenhouses working in Alaska, and if I remember correctly from what I read back in 2009, used compost heat kind of like this, (not Tim Meyers)  


NPR on Tim Meyers https://www.npr.org/sections/thesalt/2015/02/26/389011370/alaska-farmer-turns-icy-patch-of-tundra-into-a-breadbasket

Update on local public radio in 2019, https://www.alaskapublic.org/2019/10/08/bethels-meyers-farm-shuts-down-market-focuses-on-internet-sales/

Direct link to Meyers Farm, http://meyersfarm.net/
 
pollinator
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Mike Haasl wrote:With any underground tubing, I think we can learn a lot from the Citrus in the Snow and the CRIMPI approaches.  They have fans and TONS of ductwork in contact with deeper soil.  This application is completely different but it's worth keeping in mind the scale of what they need to do to harvest heat from soil.  Many many many square feet of surface area.  With forced air movement.


I hate to sound pessimistic but I’ve watched dozens of YouTube videos about heating greenhouses this way, and they all point to the need for a lot of surface area and a lot of air flow. In John Hait’s book Passive Annual Heat Storage the main factors seem to be moisture control, massive storage/heat tubing, good air flow, and heat retention (insulation). The concept itself is sound. I’ve discovered that with zone 3 winter it takes about r60 to keep the ground from freezing. I now have a greenhouse which doesn’t freeze, but is still not warm enough to grow anything between November and March. As Mike mentions, extensive tubing either deep down or under an insulated umbrella, plus good air flow, is key to having sufficient warmth to overcome the heat loss that will occur at the glazing. Multiple layers of glazing would help. Elliot Coleman grew winter greenhouse crops in Maine using multiple glazing- essentially a cold frame in a double glazed greenhouse.
I think the ultimate success of this Wofati greenhouse project may not even be whether it works as designed, but the resulting conversations, brainstorming and further experimentation that occur around it.
 
pollinator
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Love this idea!!!  Is there a link we can use to put on Facebook or other sites to let people know abou this?   And thanks for offering so much at even the 1 dollar level.  Even if someone didn't want the greenhouse moive, That is a prize in itself.   I think this is one of the best greenhouse Ideas I have seen, I just want it connected to or a part of a Wofati house.  
Sorry I should have read the whole email and then I would have know .... so disreqard my question about a link.  
 
Julie Reed
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Kyle Bob wrote:I don't understand how the thermosiphon works to cool the greenhouse.



Good point! I don’t think this system as currently conceived will do that. To cool, you need a stack that exits at the highest point, so the hot air is exhausted, drawing cooler air up from below. But that does nothing to charge the mass. Paul says in the Kickstarter that “When the sun hits the greenhouse, the pipe would pull cold air from the bottom. Eventually the hot air at the top of the greenhouse would be pulled into the trench and warm the trench.” I see that as extremely optimistic. Hot air by nature has no interest in falling. It takes effort to force it to sink, more than just air flowing passively. I don’t think cold air being pulled up will pull hot air down. In fact, even if the tube was an inverted “J”, for air to return to the trench (passively) it would need to be colder than the air in the trench. It seems, as Kyle describes, more like a cycle of warming cooler air with hotter air, creating more warm air overall. Somehow that hotter air needs to be returned to the mass all summer, if you want to charge it up for the winter. I’m also not seeing that in this design.
That said, I don’t think the mass, if kept dry and properly insulated, would need to be charged to accomplish success here. It’s part of a larger mass (the earth around and below) and will likely maintain 50 degrees year round, given how small the greenhouse is in comparison. And it’s easy enough to get excess heat out in the summer with a vent and wax filled cylinder to open and close it.
 
Edward Lye
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Looking at the roof, what if a few Cybetruckers get lost and decide to drive up to the roof to get their bearings and enjoy the view? Would the "roof" collapse? So a fence with the warning "Danger! Loose Earth." would be in order or a fake radio antenna mast with guy ropes all around. I still don't like the trench. If lost hikers seek shelter there and the earth then decides to give way ... . A locked door would be unfriendly. There is a guy who who makes earthships. He said one of his designs had too many windows and everything inside overheated even when snowbound. An outdoor curtain perhaps? Just some more food for thought.
 
Mike Haasl
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Kyle Bob wrote:I don't understand how the thermosiphon works to cool the greenhouse.  


I think the idea of the original thermsiphon is to dig one well casing hole and get the air to move in and out of it in a way that helps the greenhouse out.  So a 6" casing with a smaller pipe inside could conceivably do that.  If you can get the air to want to move up or down in the smaller pipe.  I can see how if the sun is hitting the small pipe, it would heat up the air inside and make it want to rise.  If it did rise, something has to replace it and the coldest air in the greenhouse is in the cold sink which is where the larger pipe's opening is.  So maybe the cold air will drop down into the well casing as the smaller hot pipe draws air out the top.

I don't know what would happen at night.  No sun on the small pipe.  Greenhouse flirting with 35 degrees.  Well casing sitting at 50 degrees.  The air in the casing would want to rise but it needs cold air to fall past it down the casing.  Or down the small pipe.  Or up the small pipe and down the large one.  In any case, I'm not sure it would move any air at night.

I think a wofati greenhouse at Allerton Abbey with no well casing at all would probably go below freezing at night in the depth of winter.  I'll guess 25-30 degrees for the low.  I suspect that the thermosiphon won't really change that.  BUT it's worth trying!  Turn it on and off to prove if it works or not.

I think a wofati greenhouse at Allerton Abbey with a 40' deep cold sink would probably stay above freezing at night in the depth of winter.  I'll guess 35-40 degrees for the low.  That is based on the vast majority of the greenhouse's interior surface being in contact with warmer soil as compared to the little bit in contact with frozen glass or a door.  The more surface area against the "warm" soil, the more balanced out the temperatures will be day to night and summer to winter.

A 40' cold sink isn't practical but large culverts might be.  They'd certainly be safer.

With the deep cold sink or culvert idea, I'm not expecting to "charge" the mass at all.  Just use the thermal energy in the ground.
 
Mike Haasl
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Another idea for consideration:

If increasing the contact area of the greenhouse with the subsoil is a good idea...  How about adding culverts or a man-made tunnel system like shown below?  Culverts could horizontally exist the cold sink and go back into the mass.  They'd be connected to additional culverts that connect up to the back wall.  I doubt air would flow in one and out the other but they'd still have the effect of buffering the temps in the greenhouse by significantly increasing the surface area.  
Great-place-to-lose-a-cat.png
Great place to lose a cat
Great place to lose a cat
 
Edward Lye
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Greg Martin wrote:
So it sounds like their thermosyphons are a form of heat pipe?  Heat pipes utilize gas phases to very rapidly move heat in the vapor phase from a warm source and deliver the heat to the cold spots by condensing into liquid, which delivers the heat through the phase changes.  If ammonia were to leak it would kill you, so another fluid would be desirable, but one that works at the right temps.  The CRIMPI system relies on water vapor to deliver the heat to the earth battery, which provides the added benefit of dehumidifying the greenhouse air.  Using water is very attractive.  For example, you could channel water down the inside glazing at night into a rain gutter that would deliver it back down into one of the pipes.  Since this system is a greywater treatment system their should be a good supply of water into the system to make up for any lost to the deeper ground.  Paying close attention to the water cycling in this system would be a VERY good idea as it may be critical to the efficiency of the system.  I'd very highly recommend using sensors that measure and log both temperature and humidity in the key locations of the system to understand how it's really moving heat.



https://www.arrow.com/en/research-and-events/articles/how-does-a-thermosiphon-work explains the differences between a heat pipe and the thermosiphon and claims a superior performance. Basically we want the earth heat wen the interior is cold and to heat the earth when the interior is warm. Either way we have a temperature differential to drive a circulation with a couple of check valves. Ultimately the best solution is a superconducting rod which has the property that the temperature throughout the rod is exactly the same temperature. Again no moving parts.
 
Edward Lye
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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.
 
Mike Haasl
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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...
 
Edward Lye
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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
 
Julie Reed
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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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