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.