the first wofati greenhouse design

Here's a sketch of what I envision, not at all to scale but just to show induced convection during daytime. Night time convection reverses once trombe releases its heat...

Borehole directly under glass, framed in such a way that air can pass through the frame but loads passed to borehole casing. Dry stack, square bottle bricks, insulations, etc to face the outer portion of stub wall foundation (you all are way ahead of me in what this should be). Smaller pipe inserted into top of borehole feeding into trombe wall at front of front bed. Nitinol spring operated louvers at top end of glazing for overheat dump. Heat pipe based condensation collector at the rear (would work better if heat pipes were stuck into a high mounted water tank...). Air and splashed water sinks into cold trench, compost or worm bed absorbs some humidity and first chance reheat. Air that stays cold drains on an angle forward to borehole. Warm air rising through borehole and sinking coldest air don't have to pass by each other due to pipe in pipe effect.

Greatly reduces the chance of people, flip-flops, or keys going down the borehole. Always a chance for warm and cold air to pass by each other segregated in the borehole...

David Haight wrote:

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?

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...

I forgot acetone as a possible working medium also...

If methanol in copper pipe passes the group's "not toxic enough" test, that pulled to .6atm partial vacuum is what I would go with for the condensation medium / heat pipes. The more I think about it, the more the complexity increase from having a water tank up high and the heat pipes stuck into the tank is worth it, in my opinion. Second bonus is gravity-fed water to the beds if you wanted to do that, con is having to get the water into the high tank, maybe a fill port from the outside on the roof hill?

I liked the innovation of the de-stratification pipe in the deep temperature well. Looks like it should help move air at the two times it needs it the most. However, we all know air is a fairly slow and low effectivity medium for moving heat. A heat pipe can bring up ground heat and radiate it into the greenhouse space, with less of the heat being transferred to the leaky air mass. Basic vertical heat pipes have to be "gravity assisted", aka only move heat well upwards away from gravity. But this also means you could take excess summer heat from the interior of the greenhouse and lift it up into the dry umbrella soil or water mass as well. Loop heat pipes and oscillating heat pipes have a better, though not unlimited, ability to push heat down against gravity, though some designs require taking some heat away in a gravity assisted direction too. Here again, having thermal mass above the growing area makes this possible.

So my question to Paul and the other designers is, was a heat pipe (basic vertical, loop, or even oscillating) considered for this greenhouse design? If it was ruled out, how come?

I’m new to this. Seems like the primary purpose of the heat pipes isn’t to move heat up (that happens naturally). It’s more to help circulate the air and move heat down (not natural) to prevent greenhouse from becoming too hot. Likely will do some of both.

I believe for heat pipes to function they will need to be dry. Might be problem in my soil. During wet springs soul is saturated and I get standing water in a 1-2 foot hole. Perhaps the umbrella would prevent this.

Kelly Pridgen wrote:I’m new to this. Seems like the primary purpose of the heat pipes isn’t to move heat up (that happens naturally). It’s more to help circulate the air and move heat down (not natural) to prevent greenhouse from becoming too hot. Likely will do some of both.

I believe for heat pipes to function they will need to be dry. Might be problem in my soil. During wet springs soul is saturated and I get standing water in a 1-2 foot hole. Perhaps the umbrella would prevent this.

It sounds to me like you are using "heat pipe" like I would use the words "thermal borehole". I'm taking about this completely closed pipe (which would actually work better in wet soil with more thermal conductivity): https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Ftse1.mm.bing.net%2Fth%3Fid%3DOIP.oa75lEKrkjwIbwKf6z6A5wHaE3%26pid%3DApi&f=1

Kelly Pridgen wrote:I’m new to this. Seems like the primary purpose of the heat pipes isn’t to move heat up (that happens naturally). It’s more to help circulate the air and move heat down (not natural) to prevent greenhouse from becoming too hot. Likely will do some of both.

I believe for heat pipes to function they will need to be dry. Might be problem in my soil. During wet springs soul is saturated and I get standing water in a 1-2 foot hole. Perhaps the umbrella would prevent this.

I also wonder if a dry thermal borehole would move heat up better or worse than the same size borehole filled with water. Might have to go look for scientific research on that now...

Just ran across a design from homesteaders with 40 years experience, I don't quite know if this is meets all the design criteria but it may, I'll have to look at it more closely.  Just pasted it there.  It was on Facebook.  Maybe some useful food for thought?  They're running a pipe for geothermal 10 feet down, appears to cool and warm passively.

https://selfsufficient-backyard.com/my-book/?utm_source=facebook&utm_medium=cpc&utm_campaign=t11-interest-l1-conv-pur&utm_term=l1-int-tiny-house-us-25up-mf-all-mix-072820&utm_content=img-illustration-v1-copy-v6-h6-138899287767182&fbclid=IwAR3duFZ4kCig496pfAgr1RqlwkrOT53wqOxFxnDA4nI4tk-Iq4Btg1XzfZw

There’s several (maybe dozens) of YouTube videos along those lines. What most designers have found is they need several air exchanges Per hour for it to work effectively, which of course requires fans and power for the fans, ie- not passive. But still a great design!

Sorry for having to go quiet at the end of the meeting, I was not able to keep the coughing at bay... Here's some more detailed reactions, ideas, ravings, and possible gibberish...

Bathtubs: I like the idea of separating moist growing soil from structural and insulative soil. I am a bit worried about the bottom of the bathtubs going anerobic. Consider a full blown wicking bed setup in the bathtubs? Also, the outside of the bathtub may have "sweaty toilet" syndrome in the warm and humid period of the year, so having a plan to harvest that condensation would be good. Also, harvesting condensation from the windows straight into the wicking bed reservoir would be passively awesome.

Gravel around posts: Nailed it. They do the same thing on fence posts here in wetter clay soils and even though they get rained on periodically, the bottom of the posts rot at least 2-3x slower to non-gravel protected ones...

Earth tubes / cooling tubes / ventilation tubes: Yes, the more the merrier. As Reximus Prime said in the meeting chat, you can always cap them off initially or to reduce the number of variables that you are testing. They are hard to retrofit in later, but easy to install in the initial build. If nothing else, they are cheap insurance against some of the potential achilles heels we have been discussing. Folks living in earthships do cover/cap these in the winter to not draw cold air through the berm or into the space. Vent up high to create stack effect to pull new air into the space through the ventilation tube is a must.

Instead of building a greeenhouse v0.7 then 0.8 then 0.9 ... I think it makes a lot of sense to be able to use this structure to test various configurations from one build cost. Could multiple thermal boreholes be drilled, one under the cold sink and one up front? Earth contact tubing between them that could be opened or closed?

That being said, I think it would be smart to come up with a thesis statement for this one to guide the initial setup of what is opened vs closed off (i.e. "a single thermal borehole and destratification pipe is enough to heat and cool an earth sheltered greenhouse in Montana"), a set of potential problems and negative results (humidity, mold, low CO2 levels, overheat, etc), potential mitigation steps (like opening the upper vent, opening the upward sloping ventilation tube, etc), and trigger points for each mitigation (interior reaches 99F the first time, mold is sighted on plants, etc). Then, the final design for this build can have these mitigation elements in place or at least the structure where the mitigation will go already installed...

I think a thesis is a good idea. here is my first crack at it.

"A combination of:

    An 8 foot deep cold sink

    Two well casings extending 19 feet deep below the cold sink fitted with passive air circulation units

    Dry earth thermal mass on the roof, as well as the North, East, and West walls that is disconnected from surrounding soil by a polyethylene membrane “umbrella”

    Inflow of household greywater at or above room temperature

    A south facing glass wall measuring 10 feet by 5.5 feet, sloped perpendicular to the angle of the sun at solar noon on February 1st

Will be sufficient to keep a greenhouse with interior dimensions of 10 feet by 9.5 feet above 50 degrees and below 92 degrees year-round in Western Montana at an elevation of 3200 feet above sea level."

For wooden beams, what about charring them before installing with gravel?

In critique of the strategy of capping things off for later testing, I will relay two things that Paul has told me.

thing one, instead of testing each innovation independently with controls, paul likes to heap ten or more innovations into one experiment and then if the experiment is successful, you can successively divide the innovations in half to sort for relative influence.

thing two, the annualized thermal inertia aspect of wofati structures takes years to test. It may take 2 or more years for the mass to be fully charged and operating in semi-stable seasonal temperature fluctuations. So capping and uncapping earth tubes within the first 5 years muddies the results of the thermal inertia. That being said, If it takes several years for the greenhouse to start working, then it's not very attractive as a design solution.

Josiah Kobernik wrote:I think a thesis is a good idea. here is my first crack at it.

"A combination of:

    An 8 foot deep cold sink

    Two well casings extending 19 feet deep below the cold sink fitted with passive air circulation units

    Dry earth thermal mass on the roof, as well as the North, East, and West walls that is disconnected from surrounding soil by a polyethylene membrane “umbrella”

    Inflow of household greywater at or above room temperature

    A south facing glass wall measuring 10 feet by 5.5 feet, sloped perpendicular to the angle of the sun at solar noon on February 1st

Will be sufficient to keep a greenhouse with interior dimensions of 10 feet by 9.5 feet above 50 degrees and below 92 degrees year-round in Western Montana at an elevation of 3200 feet above sea level."

Excellently specific! The map is not the territory and the measurements are not the thing measured... BUT... having facts and figures  and temperature numbers does help those of us who are not in your specific spot adapt your design to our context, compare why it worked in one context and not another, etc.

List of what counts as failure, negative result, type 1 error, etc next?

And would you please verify the time for the next zoom meeting today? Thanks

Josiah Kobernik wrote:In critique of the strategy of capping things off for later testing, I will relay two things that Paul has told me.

thing one, instead of testing each innovation independently with controls, paul likes to heap ten or more innovations into one experiment and then if the experiment is successful, you can successively divide the innovations in half to sort for relative influence.

thing two, the annualized thermal inertia aspect of wofati structures takes years to test. It may take 2 or more years for the mass to be fully charged and operating in semi-stable seasonal temperature fluctuations. So capping and uncapping earth tubes within the first 5 years muddies the results of the thermal inertia. That being said, If it takes several years for the greenhouse to start working, then it's not very attractive as a design solution.

I agree that changing too many things too fast is not helpful for comprehension, invites instability through over-management, etc. Having the discipline to not touch the controls until a certain point is just as hard as having the discipline to go check on it every day. Hence why I think having defined trigger points for intervention by someone in the group of observers / managers / recorders of this thing makes a lot of sense...

What's the hoped for lifespan of the building beyond the initial annualized thermal inertia testing? 50 years? 100? more? Climate could do funky things in that time frame for 100 different reasons. For our greenhouse here, I will try to plan in enough passive, active, etc buffer for things to change say +2 USDA zones and -2 zones in climate. I will be watching with interest to see what you all decide for this one.

Tonight's design meeting is at 6 p.m. mountain time

Here is a more complete first draft description of the greenhouse experiment, I think the language is specific enough and also vague enough to lend itself to making the mitigation decisions with better data when the failure mode arises.

"the WOFATI greenhouse 0.7 experiment posits that a combination of:

An 8 foot deep cold sink
Two well casings extending 19 feet deep below the cold sink fitted with passive air circulation units
Dry earth thermal mass on the roof, as well as the North, East, and West walls that is disconnected from surrounding soil by a polyethylene membrane “umbrella”
Inflow of household greywater at or above room temperature
A south facing glass wall measuring 10 feet by 5.5 feet, sloped perpendicular to the angle of the sun at solar noon on February 1st

Will be sufficient to keep a greenhouse with interior dimensions of 10 feet by 9.5 feet above 50 degrees and below 92 degrees year-round in Western Montana at an elevation of 3200 feet above sea level.

Possible failure modes and potential mitigation steps include:

If the internal temperature of the greenhouse drops below 50 degrees while all vents and doors are appropriately sealed, then we will begin installation of either an active thermal curtain to reduce radiative heat loss from the glazing, or an active air circulation system.

If the internal temperature of the greenhouse rises above 99 degrees with all the vents and doors appropriately sealed, then we will begin installation of either a passive heat dump ventilation system, or an active air circulation system.

If condensation is occurring in a location that it cannot be appropriately harvested and removed from the structure and is thereby threatening the longevity of structural components of the greenhouse, or productivity of plant systems is being diminished by excessive levels of humidity, then we will begin installation of either passive dehumidifying units (fog harps, and or heat pipes angled up into the north wall mass), or an active air circulation system."


Each of the mitigation steps listed above could help the greenhouse function in the event that the annualized thermal inertia is either insufficient, or insufficiently charged.
The active air circulation system that I am referring to is something like a solar panel and fan that pushes air through the well casing to help store that thermal energy. This is something that Paul is expressly opposed to, however, I think that it is worth consideration if it can be installed as an automatic failure preventative and therefore not an essential aspect of the greenhouse thermal regulation.  

Josiah Kobernik wrote:  instead of testing each innovation independently with controls, paul likes to heap ten or more innovations into one experiment and then if the experiment is successful, you can successively divide the innovations in half to sort for relative influence.

What if the experiment isn’t a success? How do you then decide which innovations to delete? Same system or? And if it is a success, how do you know which of the ten innovations is doing what? Or how much? How do you even know that any of them except maybe one or two is doing anything? That seems really un-scientific to me. And you also now potentially have unneeded things interacting (for better or worse) with needed things. I’m not criticizing the logic, just not fully comprehending it.

Dry earth thermal mass on the roof, as well as the North, East, and West walls that is disconnected from surrounding soil by a polyethylene membrane “umbrella”

A poly membrane creates a moisture barrier, but not a full disconnect. How thick is the layer of surrounding soil? For the dry earth to act as a thermal mass, it needs to be below frost line and separated from any source of conduction. So the barrier will prevent moisture migration, but not thermal transfer. If the barrier does not also include insulation, the surrounding soil would need to be much thicker than whatever frost depth is, no?

Julie Reed wrote:  

What if the experiment isn’t a success? How do you then decide which innovations to delete? Same system or? And if it is a success, how do you know which of the ten innovations is doing what? Or how much? How do you even know that any of them except maybe one or two is doing anything? That seems really un-scientific to me. And you also now potentially have unneeded things interacting (for better or worse) with needed things. I’m not criticizing the logic, just not fully comprehending it.

Julie, yes, the same system could be used if the thing is a failure. It is worth noting that in any scenario, standing in the completed structure and observing would give a hint regarding which innovations function to which degree. This approach is suited more for gaining experience in uncharted waters than for refining well understood techniques. We are in effect, trying to invent outliers.

Julie Reed wrote:  

A poly membrane creates a moisture barrier, but not a full disconnect. How thick is the layer of surrounding soil? For the dry earth to act as a thermal mass, it needs to be below frost line and separated from any source of conduction. So the barrier will prevent moisture migration, but not thermal transfer. If the barrier does not also include insulation, the surrounding soil would need to be much thicker than whatever frost depth is, no?

That sounds correct. A layer of dry duff such as sawdust has been used between the umbrella membrane and the dry soil beneath it to help insulate, but even with that technique the main insulation is simply the sheer thickness of the mass. So not much of a disconnect.

I'm not sure to what extent this factors in, but the membrane is usually 5-10 layers of repurposed billboard tarps. What I have seen is that even after the mass has settled, the membrane still has cushion to it as not all the air is expelled between the tarps. Their creases prevent them from laying flat together.