the first wofati greenhouse design

Greg Martin wrote:

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?

I agree Greg, I think that is exactly the intention.  I'm just wondering if it is necessary if it does work.  I think the real question is if you are indeed trying to heat the mass for the wofati-type flywheel effect, or if having a large enough cold sink would work well enough on it's own.  Either way, I'm really looking forward to this project and seeing how it turns out.

Out of curiosity, what is the plan to ensure the greenhouse doesn't overheat in the summer months? I know most of the focus is keeping it above freezing (or better) in the winter, but there's still summer to contend with. I'm assuming passive wax or oil cylinders on a vent opening would be used since they are a pretty proven zero-energy solution, but I didn't see any mention about it, one way or the other.  

Does anyone have any thoughts about combining a root cellar into the design. Somehow. Space is at a premium for us, and we'd like to combine the two if it's possible. Any of those clever engineering types out there with thoughts on this?

Regards
Lesley

Another question. We dont have a source of logs on our property but we do have loads of granite and sedimentary rocks plus we could buy cinder blocks. Is there any engineering reason why the berm retaining wall couldn't be constructed with these alternatives? Or for that matter earthbags?

Thanks
Lesley

lesley verbrugge wrote:Another question. We dont have a source of logs on our property but we do have loads of granite and sedimentary rocks plus we could buy cinder blocks. Is there any engineering reason why the berm retaining wall couldn't be constructed with these alternatives? Or for that matter earthbags?

Thanks
Lesley

I think that would work much better.  Logs will eventually rot.  That should probably be it's own thread though, instead of being in this one.  Maybe start a thread for that with design ideas?

lesley verbrugge wrote:Does anyone have any thoughts about combining a root cellar into the design. Somehow. Space is at a premium for us, and we'd like to combine the two if it's possible. Any of those clever engineering types out there with thoughts on this?

Regards
Lesley

The bottom of the tench should stay around 50 degrees.  If the humidity is kept low and sides of the trench are properly reinforced (and that's a big if), in theory, that could make a pretty good root cellar. Add an access hatch and a ladder down, perhaps a set of selves set low along the walls, and voila!

Standard disclaimer as I have no idea how practical would actually be, just throwing out the possibility. Though I would love to see the bottom of the trench instrumented to see if this does turn out to be the case. I feel like moisture is going to be your biggest issue with this method. It could be a very useful case of function stacking, if it works out however.

Yes to what Derek said except for one thing.  You want a humid root cellar so the hope would be for higher humidity down there.  Which I think you'd have.  

Seems like having a removable floor in the walkway with stairs or a ladder down to the food would be pretty neat.  If the whole greenhouse works as intended, it should be a bit too warm for a root cellar down there.  Ideal root cellar temps are 33-35 degrees and 95% humidity.

Just burying carrots and beets in the floor of the cold sink would likely work.

Do we have a clear description of how the well casing and 1" pipe will work?  My understanding is that it will be a 6" casing that goes 20' down and the top of it ends at the bottom of the cold sink (the area 5' below the gardener's feet).  Within the casing is a 1" pipe that travels from near the bottom of the casing up through the cold sink and jogs over next to the glass of the greenhouse.  Then it travels along the inside of the glass till it's near the roof.  The part that is in the sun is painted/colored black for solar gain.  

Did I get that right and/or is there a better description out there somewhere that I missed?

I believe the intent is that the sun-warmed 1" pipe will induce air to rise within it.  This would draw air down into the 6" casing to replace it.  By doing this enough when the sun is out, the daytime warmth of the greenhouse will be forced down the casing to heat the dirt around the casing.  At night the only forces at work would be the warmish air in the casing wanting to rise if the air in the greenhouse is colder than it.  Cold air might flow down the 6" pipe and warmer up the 1" or they might face the same temperature gradient and the cold air will just have to tumble past the warm air.

Before I/we theorize about how this will function, I'm hoping to determine if my understanding of the layout is correct in the first place...

Just thought of something.  

If you end up putting in multiple well casings and maybe multiple de-strat pipes, you could without much extra cost incorporate a valve in each de-strat pipe, so it can easily be shut or open, so you can easily change from 1, 2, 3 or however many you make.

My gut feeling is that a single 1" or 1.5" de-strat pipe isn't going to create as much flow as you want - but that could easily be wrong, so if you install more, adding valves would give you a way to switch them off or on, depending on the results - and would even allow testing with no de-stratification.

your existing WOFATIS have been working largely by how dry it is all maintained. Not so for a greenhouse that is designed to treat gray-water. Moisture will be a big problem. Consider using gabion baskets to encompass the log posts. Mechanically connect the log to the basket and fill with rocks. This will provide an avenue for moisture to escape, keeping the logs dry.
> I understand the cooling concept, but notice Oehler's design has an exit for hot air at summer peaks. This would be more important if the next point was considered
> the sun infiltration is limited by the wing walls (maybe open to the sun with a 120degree angle?). Consider angling the wing retaining walls to open more to the sun, including solar gain to the east and west - which would then have the difficulty of too much heat in the summer, thus the previous point
> gray-water needs wet-land plants to gobble up all the nutrients that are available. I have a design of 4 bathtubs that drain by gravity into each other. The gray-water is introduced into the top-most 1st tub of wet-land plants (full of pea-gravel) which then flows into the 2nd, and so forth. The end result should be very clean water (which can be safely discarded onto solidly frozen ground outside). The important calculation is to determine how much gray-water needs to be treated, keeping in mind that gray-water turns to stinky black-water in a matter of hours, so you cannot store gray-water - it must be 'immediately' treated.
> If you develop this huge infrastructure and have very little growing space, then the point might get lost. The sketches show a very insignificant growing area.
> I'm super excited about your project because I've had a gray-water treatment greenhouse concepts for over 10 years, but no money. Another consideration is buried barrels of water which can store the heat from the summer. Water is a fabulous material to hold and move heat.
>
> I'm way late to the design party, and maybe these points have been considered. If so, sorry for the interruption and I'm excited to see progress. I believe I saw a stretch-goal of adding devices to record the data, deep inside the build. I highly encourage this.

Mike, your description of the well casing thermal destratifier is accurate.

After living in Allerton Abbey for the last 9 months, I'm not so worried about the winter heating aspect of the greenhouse design. It has solar gain, thermal mass, and a cold sink. I'm very confident it won't freeze. I'm reasonably confident it will come up above 50 degrees F in the winter, at least during the day. Maybe Paul's thermosiphoning well casings will work and add a few degrees. That would be cool. I doubt that they will do much in the way of really circulating air or cooling the greenhouse for all the reasons that have already been discussed, however, I'm looking forward to testing them and playing with pipe diameters and different head attachments to increase airflow. There are optimizations to be made here for sure.

Tim, you are spot on with the moisture problem. Are you thinking that the rocks will provide a medium for the humidity to condense onto instead of the posts, or simply to provide drainage around the buried portion of the posts?

I would be curious to see what we can come up with in the way of a passive dehumidifier that collects the water and routes it out of the greenhouse. I suspect that the well casings will condense a lot of water.

Summer cooling is a legitimate concern. My thought is that the mass walls will suck up excess heat, giving us a lot of buffer. Additionally, having part of the greenhouse shaded during the summer will help prevent overheating. If these two are not enough, then the automatic vent is a good safety feature.

The concern about growing space is legitimate. All I can say is that I hope we get to double the size, and if not, at least we will get to test the design and iterate a larger greenhouse for winter food growing later on.

Greg, I like your idea of bumping the wingwalls forward and including an airlock. The only downside I see is needing to extend the eaves over the bumped out wingwalls which will increase shading a little bit.

Conversely, we may end up glazing the small triangular walls to the east and west to increase morning and evening light.

I think you'll quickly learn if you need ventilation or not.  Even in the fall with a full sun day you'll figure it out pretty fast.  And the wax cylinder vent openers are very available and quite cheap.

I'm fairly worried about summer sun angle.  Will the plants get enough light?

Here’s some drawings of sun angles

The front growing bed gets full sun exposure year round. For a few months in the summer, about half of the cold sink/pathway is shaded. I don't think that this will kill the plants in the greywater system. The whole thing is only 7.5 feet wide, so  roughly 3.5 feet of shade means that there will still be a lot of indirect light all the way to the back in the summer. Despite this, light may still be a limiting factor for biomass production from the greywater system during the summer.

I'd like to put in solar tubes or some diffused light reflection, but maybe its worth coming back to these options after we determine that it is actually a problem.

Tim, Do you have any pictures or information to share on your bathtub greywater systems?

Our current design sounds pretty similar to that and it would be great to learn from your experience.

Cool, I'm glad you're thinking about it.  One detail from your sun angle sketches.  In the second one the summer sun is not being blocked by the overhang like it is in the first picture.  

The second drawing is an alternate design where the glass wall has been moved one foot forward so that there is no overhang. This increases the size of the front planting bed.

Oh, good!  I like that one much better.

With the talk of how much sunlight gets to what part of the greenhouse, it's worth noting that some plants don't want too much sun.  

Here in Portugal, part of our effort goes to trying to create enough shade that those plant don't give up and die 'cos it's too sunny.  
It's also come to my attention how clever the builders of our house were, the roof on the front (sun-facing) side is extended just enough that the sun doesn't shine directly in through the windows in the hot part of the day.

Hi,

Reading through this thread, I'm relieved to see some discussion about the angle of the summer sun and the earthen roof / overhang.

Up here (north of 60), I need a well-insulated greenhouse but I also need to take advantage of all the sunlight I can. The frost-free season is very brief (sometimes only 90 days) and any plant which needs to come to fruit needs to do it in a short window.

I don't have any solutions to propose, but just a keen knowledge that I won't be putting a ton of energy into a greenhouse with that much of an overhang.

Cheers

I’m with you on that El. Also at a high latitude and will take all the sunlight I can get. The excess heat can be vented or, preferably, stored somehow. I do not get enough sun from late November until late February to grow much of anything. But to keep the greenhouse warm all winter is ideal, as it’s ready when that sunlight does return adequately in early spring. I would modify this project to include earth tubes with solar powered fans, which is still 100% passive, but puts all that excess heat to good use. I hope I’m wrong, but I think this design will require venting, which is a waste of usable heat. I realize the project is primarily about treating greywater all winter, not growing tomatoes. But in my case if I put forth this much labor and expense, I’d be a fool to only care about treating my relatively small amount of greywater (10 gallons a day tops, most days less than 2), despite it being a very real need in winter. The value to me is an extended food growing season, with water treatment as a bonus. I’m really looking forward to what can be learned from this project, and then modify that to my own situation.

I came up with a better ( I think) floor plan for the wofati greenhouse. I moved the door to the side and pulled one wing wall back a little bit, while also pushing the glass wall forward 1 foot. This allows for more garden space, as well as more light in all seasons.

Probably pushing the envelope too much, but what if you made the greenhouse area twice as wide? You double the growing space, double the potential greywater treatment area. Don’t need twice the greywater area? Make half into a compost bin. More heat from that than you will likely ever see from a few gallons of warmish greywater (which really will be close to ground temp by the time it reaches the greenhouse). An extra ten minutes with the excavator to make a longer trench, a few more roof poles, a couple upright supports in the middle, a few extra yards of dirt and epdm for the top, and 10’ more glazing. Maybe that’s already been discussed and vetoed, I don’t know. But it seems like it’s not much more in materials, and probably less than a week in extra labor. There’s extra Kickstarter money now, and the additional food that could be grown would provide a fairly quick payback as well, a factor for those deciding how much to pay for one of their own. A further benefit is you are doubling the total solar gain, for approximately the same mass, banking that much more heat for winter.

Julie, I believe doubling the size is a stretch goal

Hi Mike, I wasn’t sure, as I did see that, but then thought maybe it was in reference to Josiah’s altered plans shown above.

hi guys!, I have been interested in Wofatis for a while, i backed the greenhouse and am super excited! I originally found you guys looking for earthen bermed houses.

Here is my struggle, i am looking for a 100% self-sustainable build. which for me makes metals and plastics a no go. the biggest struggle has been trying to find an alternative water barrier. I would love to see if this could be a project the labs seeks to solve, I've toyed with the concepts of mucking the umbrella area, or various waterproofing methods before backfilling, and using gravel around the house walls to guide moisture, but they all seem to be insufficient. i hope this can be a future project!

Just had a thought--once I visited a community that had greenhouses, and someone had left the door open and everything froze.  Twice.  I recall the door to the greenhouse was from the outside, and a second door led from greenhouse to interior.

Human error attacks again.

Since this present design seems to have only one door, the door you use to get in and out of the house, that problem is mostly eliminated, right? Is there anything else that needs to be human-proofed about that aspect of it? What if you run out in a hurry and the door doesn't close?

Then I realized there may be no fire exit from the wofati?  It seems worth acknowledging for the future designs.  Fire is unlikely to happen in an earth-bermed structure I would imagine, but it's

How much light is going to make it to the back once there are plants in the front? I think it might be an idea to mock up the roof and some front planting and check how much light gets in. For us here heat is not the major problem in winter but light is. I can't grow houseplants in a full unshaded south-facing window without them stretching for the light so I'm very concerned there will be enough light even at the front of that design never mind the back.

Anthony Dougherty wrote:
Here is my struggle, i am looking for a 100% self-sustainable build. which for me makes metals and plastics a no go. the biggest struggle has been trying to find an alternative water barrier.

I’m not sure there is anything in nature that is waterproof to make the envelope layer, except clay. And that might be a chore, to make a clay umbrella. But consider this- you really don’t need to keep the mass dry! Water holds heat better than anything, so a wet mass obviously holds much more heat (or ‘cool’). What you need to prevent is Migration. That means the wet needs to be the same ‘wet’ every day, not water that is moving through the mass (migration) robbing the heat. That may make your dilemma greater or less, I don’t know. It definitely gives you a major potential mold issue, depending on how the mass relates and connects to the dwelling. I say that because I sense you are talking about a home, not a greenhouse. But what you wouldn’t want is drainage, because that means water will enter your mass, have a quick fling with the heat there, and elope with it. The only way I can think that ‘might’ be acceptable is if you could somehow trap that water and return it to the mass. But in the process, some heat will be lost. Part of the answer also depends on your location, and just how much heat you need to store, and for how long. The other issue is insulation. Water conducts heat far better (and faster) than dry earth. So a wet mass needs better insulation on the exposed areas.
One last thought- you could, with enough slope to the mass, build a shake roof over it. That’s waterproof and natural.

Julie Reed wrote:

Anthony Dougherty wrote:
Here is my struggle, i am looking for a 100% self-sustainable build. which for me makes metals and plastics a no go. the biggest struggle has been trying to find an alternative water barrier.

I’m not sure there is anything in nature that is waterproof to make the envelope layer, except clay. And that might be a chore, to make a clay umbrella. But consider this- you really don’t need to keep the mass dry! Water holds heat better than anything, so a wet mass obviously holds much more heat (or ‘cool’). What you need to prevent is Migration. That means the wet needs to be the same ‘wet’ every day, not water that is moving through the mass (migration) robbing the heat. That may make your dilemma greater or less, I don’t know. It definitely gives you a major potential mold issue, depending on how the mass relates and connects to the dwelling. I say that because I sense you are talking about a home, not a greenhouse. But what you wouldn’t want is drainage, because that means water will enter your mass, have a quick fling with the heat there, and elope with it. The only way I can think that ‘might’ be acceptable is if you could somehow trap that water and return it to the mass. But in the process, some heat will be lost. Part of the answer also depends on your location, and just how much heat you need to store, and for how long. The other issue is insulation. Water conducts heat far better (and faster) than dry earth. So a wet mass needs better insulation on the exposed areas.
One last thought- you could, with enough slope to the mass, build a shake roof over it. That’s waterproof and natural.

right originally that's what sparked the idea of mucking out above the shelter before completely backfilling, that mucked area would be anaerobic. I just don't know if it would work and for how long. My latest thought is to char a wooden roof to preserve it, as you suggested, but I don't know that this will protect the walls... youre right its for a home, maybe i should start a new thread i guess lol

In response to the sunlight issue:

Plants do weird things when they only have access to directional light (like that which comes through a south facing window), yet the earthship folks have shown that south facing angled glass walls provide plenty of light for growing plants. Mike Oehler had glazing on the roof of his greenhouse as well as the south wall, but we have chosen instead to tilt the roof towards the north and make it insulative and shading. This is an intentional innovation to reduce solar gain during the summer and increase thermal mass and insulation. Many of the greenhouses that I have managed have needed shade cloth in the summer to prevent sun scald on tomatoes and peppers.

We will find out if light becomes a limiting nutrient for the greywater system. I'm pretty curious.

One problem that I'm working on has to do with cultivating living soil inside a natural building. So much of what we do with the structure is focused on keeping water out. And then we are going to bring water in and pour it on the ground regularly to keep the soil at the appropriate moisture level for life to thrive?

This kind of relates to Anthony's question about natural envelopes because, in my experience, a wet mass leads to rot and fungus and lots of beautiful little critters moving in with you.

I drew up a doodle of how we are planning to partition the living soil from the definitely not rotting posts

Tomorrow at 6pm ranch time is our first design meeting with Kickstarter supporters. A lot is changing as we pour attention into the design details. Here are the most recent drawings that will be discussed tomorrow.

Here are a few more drawings showing stub wall design ideas

Hi All -

I caught the last half of the design meeting, joined just as the fog harp was being discussed. If I'm understanding a standard fog harp, the only driver of condensation is the heat difference between the metal surface and the dewpoint of the air, right? If so, your going to run out of "stored cool" in the fog harp metal very quickly.

What if the "fog harp" was actually made of angled heat pipes stuck into the rear mass, fairly high up on the wall. Then, the rear mass will be continually drawing daytime heat away from the air via the heat pipes, keeping their surface temperature similar to that of the rear mass. If the rear mass gets charged to say 60F, that means the dewpoint of the air in the greenhouse would have a tough time getting much higher than this. There is probably some way to texture the surface of the heat pipes to increase condensation potential, like the desert beetles that can make drinking water on their shells. Daytime temps above 80F with a dewpoint near 60F is very comfortable for working inside and should cut mold and rot issues of the wood and etc in my opinion. The cooling and dehumidification and therefore densification of the air at the rear plus daytime solar heat at the front means you have a "convective cell" destratifying and moving air twice a day. Effect direction will be reversed at night, with a small amount of heat leaking by conduction down the copper walls of the heat pipes (without re-adding humidity). This effect would be greatly increased if proper wicks were in the heat pipes allowing better downward flow of heat out of the rear mass.

The question is where to direct the generated condensation? Into the greywater tub? Into a "cleanish water" barrel for watering front plants (but probably not drinking unfiltered)? Down the borehole to humidify the soil at the bottom and increase thermal transfer?

What if the "fog harp" was actually made of angled heat pipes stuck into the rear mass(?)

David, I woke up thinking about heat pipes this morning. I was trying to figure out how heat pipes from the mass could cool the fog harp, but I think you nailed it by having the heat pipe itself be the condensing surface.

Anyone have design ideas for DIY heat pipes that are filled with non toxic material?

Earlier in the thread, Greg mentioned using water. Do you think that would suffice in this scenario?

My next thought:

What if the borehole(s) was not under the cold sink trench, but instead moved toward the glazing, meaning that the borehole casing could become a structural element and hold up the glass? Definitely gets you below the frost line! Might take multiple boreholes or some creative wood or stone work to connect the load back to the borehole for the entire length of glass. Also, by moving the borehole top closer to the glass, I think there would be more temperature differential to drive convection into/out of the borehole.

Consider also 6" casing split into 2 or more smaller pipes, at least one of which would go through a trombe wall on the front face of the front bed. Use the front bed and its moisture as a thermal mass that drives more daily solar heat storage / release. The front face of the bed will get more perpendicular sun in the winter (when we need to drive more night time convection) and less in the summer when night time temps do not matter so much, and daytime overheating is more of an issue... I'll sketch it up after breakfast once the idea engine between my ears settles down just a bit...

Josiah Kobernik wrote:

What if the "fog harp" was actually made of angled heat pipes stuck into the rear mass(?)

David, I woke up thinking about heat pipes this morning. I was trying to figure out how heat pipes from the mass could cool the fog harp, but I think you nailed it by having the heat pipe itself be the condensing surface.

Anyone have design ideas for DIY heat pipes that are filled with non toxic material?

Earlier in the thread, Greg mentioned using water. Do you think that would suffice in this scenario?

There are a ton of youtube diy videos about this. Here's one of my favorites: https://www.youtube.com/watch?v=60PctdoRHd0

Any working fluid can be tweaked to the right temperature range by getting the internal pressure right. For water, this means pulling a vacuum to get the pressure way way way down so that the water is boiling at room temp. Means either pulling the vacuum as you seal it up, or having a service port were the the vacuum can be pulled after sealing the pipe and re-pulled as leakage occurs. Ammonia and propane are two other possible working fluids but as someone else mentioned the toxicity potential, especially in a closed environment, might be a no go. Ethanol and Methanol might also work, I'll have to consult my reference to see if they will work with copper or aluminum pipe material...