Looking into this a little more, "R-value per ASHRAE 90.1-2016 Section A9.4.2. Airspaces less than ½” thick shall have no R-value. The Rvalue for airspaces between 3.5” and 12” thick shall use 3.5” thickness as basis." So a 30" air gap would give you something around R-8.5 if you can trap the air. Anyway, this is an interesting idea. I am just concerned about its effects on the soil in case of a leek.
ok... a bit more awake now... It looks like there are working examples been running for 17+ years now, so the low temp behavior is not an issue. They build a trench that recaptures the bubble solution. What little I have read does not look into the soil/tox issue at all. Have you seen any discussion on what soaps work in this application and have been tested to not harm soil organisms or pollinators?
@C Letellier, the soap bubble system looks interesting but there are a number of things that I would want to see worked though before I would consider it, and also cautionary tales I would suggest --
* the type of soap is crucial. May soaps contain anti-bacterial additives, and that could really mess up the soil organisms. So could just regular soap itself if it gets on the soil at all. I do not know if you know, but one anti-mosquito trick if you have open non-potable water sources like a smithy quench tub, is to put a couple of drops of soap on it -- it changes the surface tension on the water and the mosquitoes drown. I would be seriously concerned about all the beneficial insects, detritivores, and bacteria. This would completely mess up the soil organisms unless you could recapture basically all of the soap, and you have to plan for dealing with the consequences of the inevitable tear or leak.
* working out how it behaves after the temperature drops below freezing. Do you know at what temperatures the materials in the bubbles freeze and become a frozen shell? How sharp would those shells be in a storm when the wind pushes against the exterior surface of the glazing and they break and rub against the plastic. It is possible that they might remain flexible throughout, but this would have to be tested. That said, if this was set up as an emergency measure to save a winter crop, it might be worth the cost to re-glaze if you saved enough produce to cover the cost of re-glazing. This would be a cost benefit analysis.
Hmmm... I just realized that I might have come down as a nay-sayer/downer. Not my intent. If you could work through the issues of recapture, potential toxicity to soil and pollinators, and mechanical strength, this could be a simple solution to a really nasty problem. If you could find a way that would pass organic certification I would definitely go for it. Maybe there is someone at one of the ag extension research universities that could help you work through these issues.
There are likely other issues as well, but I bumped into this at 2:45 in the morning after waking up, and I have not had my first cup of tea and not all of the 8 cylinders are firing -- feels more like the old single cylinder hit-and-miss <https://www.youtube.com/watch?v=euIMiSaYPX0>...
@Mike, Here is an updated (version 2.0) of the calculator http://www.ecosystems-design.com/uploads/2/5/1/9/25191018/climatebatterycalculator2.0.xlsx Apparently they did not take into account the displacement of the hoses and some other things. I am not sure what the difference is between 1.2 and 2.0, but maybe since you have the numbers handy you can rerun them. Yes you are correct with the Citrus in the Snow using air outside. For some reason I thought that it also circulated air and brought it back in, but you might be right. Also to think of, and probably not experimentalable is something I was taught back in New Mexico working with adobe -- the thickness of the walls are not random, but chosen because of the temperature lag as it migrates through the material. It has been 40+ years since I was told this and I could have the information wrong, but... at 9" thick walls, the heat will migrate through the adobe in 12 hours. So the max heat of the day will actually migrate through into the interior by the middle of the night, and the cool of the night will might through to the heat of the day. The thick walls (I forget if they were 24" or 26", but that would migrate through in 1.5 days. All that said, the head does not travel in one direction, but all, so you would get this attenuated fluctuation due to the thermal mass. I always loved living in adobe homes, but you *must* make sure you have a good roof and a good foundation -- everything in between is negotiable.
@Mike, if you know of any good engineering books/materials going over the earth battery, please post here. I have not seen any. All I have seen is very rough numbers from the Citrus in the Snow guy, and soil temperature profile normals. The Citrus in the Snow guy uses something like 4 to 8 pipes running something like 200' to get the temp to stabilize. I would use plastic underground, and try to use stainless above. I have read people using perforated pipe underground so that any condensation will leak out.
Derating the estimated 100A @90C capacity of 2-2-4 aluminum SER wire is a very good idea. Also use niloc (or whatever it is called -- which keeps the connections from oxidizing). Your electrician shoud do that, but know that if you are in a place that will allow you to do your own wiring to read through the code books and comply with at least the residential standards, if not the commercial ones. Like I tell people "every sentence of the code book represents someone being injured, maimed, or killed". Following the code is not just the law, it is a VERY good idea. Also, run another separate ground wire (unless the 2-2-4 is shielded). Also, go ahead and wire up the an extra outlet circuit (or a special outlet near the door for 240V and 120V). You never know when you need to run an extra fan, emergency heater, water pumps, welder, etc. It is easy to wire up when you are starting, and a pain later. Also, make sure that the ground and commons are *not* tied together in the breakout panel, but *are* in the main panel where you took the power from -- tying both can create a ground-loop. Oh yea, and this is likely very important also, use GFI's where it makes sense, but know you should not use them on circuits with GFI's...
Before putting in a inflation fan (that will const constantly), try just installing a wax-filled vent piston (see: https://www.amazon.com/Univent-Automatic-Solar-Vent-Opener/dp/B0083IZG0A for a good one that would work close to the ground, but I would look for one that can be set to open near 90 or so for a vent near the apex). Once you know what can be done with passive means, you know what you have to operate actively.
I probably forgot a dozen things off the top of my head, but this should be a decent start. Hope this is a good start.
Well... looks like you have your priorities about right ;-) meaning do what you need and you know first... I have the embedded electronics and similar stuff sitting in my room to poke at when I wake up and have a moment to play. BTW, it looks like the house part of my renovation will *finally* get done in a week or three...
@Mike, do you have any of the temp probes up and plotible? I forget your background, but if you need help setting up some code to generate plots (and maybe also display details from local weather forecast, etc.) let me know and I will try to break away some time. Actually I have plans for doing the same for myself...
Mike! Good to be back. Lots on my end, but that is for another discussion.
I agree with Cristo. I remember reading about a rare high elevation plant that daily survives freezing temperatures at night, and very hot during the day. Very few plants can withstand that, much less food crops. Realistically we need to help you keep the temp range down.
I thought I posted this a few days ago, but it did not show up in the thread, so here it is again...
re: minor air leaks in the system...
I remember reading that even very small air leaks can completely destroy your ability to keep the heat/cold where you want them. In my readings I remember someone writing about how much cold air came into his house through the electrical plug boxes in an old house where the walls were either inadequately insulated behind the receptacle boxes. Try sealing all holes you can with plastic, or however, and see if that helps. Maybe you already got that done, but...
re: thermal mass...
I forget how far down you went with your insulation along the walls. But as you mention the mean annual temperature is ~40F in your area, and is why you did not want to go with a low grade geothermal like the Citrus In The Snow and similar greenhouses, and why you made a comment about a heater putting out 40F air, and the outside air being -20F then the house would not be 40F in the morning. Ok, but also consider this -- if you did not insulate the soil under your greenhouse then you have a constant heat sink sucking the temperature in the greenhouse soil (basically in an insulated box) down to that temperature. I remember reading about someone that built a greenhouse back in the 70's -- insulating just the underground perimeter walls and not the bottom. They were hopping to keep the soil temperature high. They found that all the heat was being sucked out of the bottom. That said, this is part of what makes the climate battery and low grade geothermal work, or at least as I understand them. So all of this said, I would be surprised if you could keep the greenhouse soil much above the mean temperature year around.
I also found the following: "The 24-hour cycle of air temperatures disappears at a depth of one-half foot; five feet down, ground temperatures lag three months behind seasonal air temperatures. The lag is six months at 15 feet. Soil temperatures are constant below 30 feet, and, incidentally, about equal to the average annual air temperature." At first I thought the 12" to 18" depth was to little, but then read in the context of pumping the soil temp up makes sense. That said, if you are growing plants in the same soil, they will get down to where your are heating the rootzone, and that might cause some issues depending on the temperature fluctuation. But with a 115+F between inside and outside (as reported a -6F and +110F previous)I am guessing you really need a lot more thermal mass to stabilize. I could be wrong.
re: changing the design from an arch to triangular/rectangular...
Just remember this. Every sentence in the code was written because someone was injured, maimed, or killed. Fundamentally, it is all about safety and then efficiency, and even efficiency can be about safety some times -- given the population and how areas population are expanding, if you do not make buildings more efficient that you can have power outages, water outages, etc.
With rainfall collection, check your state and county programs. In PG County, Maryland it is not only encouraged but they actually have a grant program to help you pay for it! Take a look at Maryland's Rain Check Program. Finding examples and explanations from other locals should help a lot.
As for other building codes. I am surprised that you did not start with a LEEDS certified architect. There is going to be a point where they are going to want certified drawings. Hiring the architect up front will actually help with that. They will be able to give the permitting folks what they need to OK you. Also keep in mind what I said about safety before. If someone is injured, maimed or killed in/from a building that they have inspected and signed off on, then they can be held legally accountable.
All the above said, I really do with you the best of success in moving this forward!
I would suggest getting the temp sensors up, or whatever other sensors you have, and running as soon as possible. You may find that the information is useful, and also might run into a bug as it is collecting. Better to find sooner than later. Also if you are initially worried about the barrels freezing, only fill them 3/4 of the way. If you have some temp sensors set up you can track the outside/inside air temp as a function of how much water you have in the barrels. As a note, water stores a LOT of energy and can release it as it starts to transition to freezing. So if you get enough solar gain to keep things just above freezing, the barrels will help with any dips in the night.
@Brian, can you post some pictures of the beds you are referring to? Are the ones you lined with pond liner for hydroponics, or are these fiberglass beds just plant beds, and if so why are they closed off? Is there no drainage?
As for the flattening the glue problem... On thing that could be done, but it will be tedious to set up, is to use use screws or bolts as stops. The basic idea is that you have something which adjusts the heights of different pieces in the assembly so that the only parts touching the truss pieces are the screw heads. THe problem is how to adjust the head heights. Probably a better way is to take one of the assembled beams, mark out where the glue joints go, carve/route a glue channel,m and then wax everything up so that glue drippings do not stick so easily. That way you have flat pieces parts and no smushed glue berries.
Mike, if i am following you correctly you should be able to correct that by clamping the pieces in two planes -- if you clamp the piece from the wall sticking out, you can force the rib to lay flat against the jig, and the other one parallel to the wall to pull the two ribs and the spacer block against it.
Mike. Regarding the cuts for the ridge beam, are you going to have the truss overlap at the meet or but-joint so they are in the same plane?
If they overlap at the top, then have the blue line make a left angle under the ridge beam like the red line does. That way you have wood supporting under both sides.
If you intend them to meet inline, I would split the difference of the angle cut so that they meet in the middle of the beam, and also cut some plywood gusset plates -- so that you make sure the joints go *nowhere*.
Also one way to rough out a curve is to flip over a belt sander and use the flat to grind quick curves (both concave and convex). It does not have to be perfect. In fact I am not sure you *need it, but I would ask someone that has more experience with building trusses.
If you wanted to still install a bond been, I do not think it is to late. You could probably form one up for say 4"around the top.
Oh, one thing -- if you fill the cells with dirt, have something separate the dirt from any wood just in case termites or something gets in them. You should be able to easily cap the dirt filled cells with a little concrete to make sure.
BTW, this all looks great, and I wish you the best of success!
Oh, almost forgot... If you really want to boost the mass and also deal with several types of issues you might think of filling the open cells with dirt or something (just as a thermal mass), and then pour a short bond beam around the entire perimeter http://imiweb.org/02-410-0142-u-block-cmu-bond-beams/. It will strengthen the structure and give you more thermal mass cheaply. Just a thought...
I would suggest looking at the plans they publish for the Deep Winter Greenhouse at U. Minnesota's Extension https://extension.umn.edu/growing-systems/deep-winter-greenhouses. The plans have details near the end how they handle the foundation/framing interface and other important features. I would give you the link, but last I checked you have to register to get the plans from them, but they are free and the info is really good.
I'll write more later -- just found some more termite damage in the house renovation...
@Mike, you might want to take a look at BlueMax and similar elastomerics <https://www.youtube.com/watch?v=i7F3C4MsQwE>. You can actually use it to both glue the joints together before filling with cement, and also keep the moisture on the respective sides of the walls. I would not leave it with just the elastomeric, BUT it would be a nice way to lay them out.
Sorry if the name 1-wire was confusing. Yes, they actually need ground, power, and one for data. I did not know that the RPi's were made in the UK. But I prefer them over Arduinos because they are a full running OS if you want it, or you can strip it down to a single program as well. Much more versatile.
@Mike, There are lots of possibilities for the controller. Arduino is perfectly acceptable, so is RPi, BeagleBone, UDOO, and many others. Also, for every platform there are many different versions. One of the first things that you need to do is figure out how many input and output lines you will need, how much storage, etc. Then there is an idea of connectivity.
So, starting with the number of lines. If you connect 4 or more in a group wired together, then you will need at least 4 input lines. You will also want several output lines I would imagine -- unless you are looking at logging only. With that, even an Arduino nano would likely handle it. You would have to look into it more deeply to make sure that it will do everything you need, but it is likely that all of these will work.
For my own work I would also want to have ethernet connectivity -- I use POE for security and device control.
@Charli thank you for that brilliant report. I will have to go through it in detail, but I like how you suggest testing and some idea of the root cause. I usually use metal conduit for anything exterior above ground -- precisely because of the trimmer experience you mentioned.
Thinking ahead I would put in 3 different conduits (one to sleeve PEX for water), one for a high voltage line, and another for low voltage lines. None of those three should ever mix, and unless you choose not to have water, 120/240VAC electricity and data lines, I would install conduits for all of them. It is not much more money at this stage of the game, and you might regret it later.
I installed 3/4" for my security cameras, and 1" EMT for all the regular data lines except the ones that I had to run flex. The POE connectors on the end of the camera lines basically fill the space, and I am sure that is all I will ever get. The 1" lines will fit several data lines, but if you are running cat6, then you can run a hub (as long as there is power). For my own I will likely install 1-1/2" conduit lines into the greenhouse and if I *ever* run out of space with that then I need to completely rethink everything. On another job site I think we used 1-1/2" conduit for a 100A 3-phase line they installed for one of the lathes at an old shop I worked in.
Also remember that they make rubber plugs that seal around the wires coming out the conduit.
As for what to install now and later... I would read what people have found useful and not. At only a couple of bucks each I would install a couple of extra -- this just off the top of my head, and not thought through:
temp probes at 6", 12", 24" and 48" (which is below my frost line). I would install these inside and out. Above ground I would install then at 2", 12", 24" and at the top of the inside of the greenhouse. The reason I would do this is that I do not know the soil temp or exactly how the foundation insulation will behave. This will allow me to at least try to analyze it. If you have it both inside and out you can see the effects of the insulation on the foundation wall, and the effects of the insulation on the interior soil temperatures.
I would also look at installing soil moisture probes in a couple of places, as well as humidity sensors near the ground and up at the top of the greenhouse.
Sorry for the late reply. I found another modeling package called RC_BuildingSimulator which I am trying to set up to model the passive solar DWG greenhouse mentioned before. I have it working, but I am not sure that I have set it up correctly. Is there anyone with thermodynamics background that is willing to help set up an initial model? As a note, one of the researchers will be sending me some performance data to validate the model with. With a little work I am hoping that we can validate the model and then optimize various parameters against site specific data.
Sorry for disappearing for awhile. Lots going on...
While doing some more background research I came across U. Minnesota's Extension program design of their Deep Winter Greenhouses (DWG-v2) <https://www.extension.umn.edu/rsdp/statewide/deep-winter-greenhouse/> . They include plans, and other useful information. While I have not had time to read through all their documentation, it is really informative stuff. I also have a little more to report on the modeling front, but will wait to give a report when I sort out what I got working and what I did not...
I would have to look at the LVL's that were put in my house, but as I recall every other layer is oriented 90 deg which increases the strength overall. Also, I have seen joints in LVLs laminates. I think you could build them up the same. Regardless, if you find something that works for you then you have rung the bell ;-)
Before spending the money to purchase LVL, cut them in strips, and glue them back together (at least that is what I think you are planning to do here), why not build them up from plywood laminated on our own jig using exterior grade adhesives and make your own LVLs? Then you can make something similar to these Gothic arches http://www.starwoodrafters.com/gothic-rafters.html
If you use pieces cut out of plywood, then you can also, with a bit more work, laminate in the cross bracing, or make something more akin to a curved version of an I beam truss https://www.apawood.org/i-joist
Could you post the citations? These look interesting. I agree with the insulation -- more is better, but how much is cost effective... Also, changing the amount on one side or another is a research project. I would be surprised if the burred insulation made much of a difference, but then again, the north side will never see daylight and I would expect it to be colder.