From what I’ve read,these are not very structurally sound and pieces may come apart in a strong wind.
It looks like ross has put in some added support.
There are many videos about doing that on You Tube. Brady
Very true. You really have to reinforce this thing, @Susu. I just put in a support beam for the roof today in preparation for snow.
@ross it really depends on what you intend to use the GH for, and how long during the winter you intend to use it and at what temps.
Heat balance and storage needs and solutions vary quite a bit in different climates. Unless your climate is very similar to someone else’s, it probably won’t work to use their solution.
Climate batteries, SHCS systems and other similar GH heat storage plans do work to varying degrees, but they have their limits. If you intend to store heat in the soil under your GH, you need a means to move the heat down there and bring it back, natural movement thru the ground/air interface isn’t going to be enough for either (but it will do some). You also need to insulate and isolate that soil, otherwise any heat down there will be lost to the outside. One of the problems with very small or very large GHs and subsoil storage is that there isn’t a good match volume and heat capacity-wise. Small to medium sized GH seems to do best, but even those cannot go all winter just on stored solar heat in most climates.
Ground heat storage is a possible way to go, but you will need to have insulation around the soil under your GH (3-4" of extruded styrofoam, 4’ down or so). And you need a grid of air tubes which you can blow air thru to bring heat down on sunny days and back up when you need heat. Not something that is easy to add after the GH is up.
I do have one GH which I put a SHCS in. It works fairly well for a sunny zone 5, but I do vent some in the summer and heat some in the winter too. Without supplemental heat one can expect a heat storage system like this to extend the growing season a month or so at each end with no additional heat. But to go thru a full winter with growing plants you need supplemental heat. Your area is a bit warmer but likely less sunny than here so I’d rough guess you might expect similar results with the same size GH as mine (16x36’). Smaller GH’s tend to be harder to keep heated because their surface area to volume ration is much higher.
Another option (perhaps not for you since your GH is in place already) is to attach the GH to your home or other heated building. You can vent excess heat during the day to the building and get some heat at night from it. This does limit what you can spray and do in the GH a bit, but can work very well. I have a smaller GH which is attached to my home at the garage level. No additional heat and typically stays above freezing, tomatoes and peppers live and fruit there year round.
It really comes down to what are you planning for this GH. Do you just want to start some plants a bit earlier in the spring and have a place for your tomatoes for a month or two longer int the fall? You going to grow orchids or citrus year round in it? Something in between? Depending on what you answer, your heating needs and what you will want to do with the floor will likely change.
This subject has been on my mind for quit a while and there is a lot of different information out there, it can be quit confusing. I have a question if anybody knows… What is the advantage of a SHCS system versus an under ground “walipini” style greenhouse? For both you will have to dig a large hole and insulate the walls down to a depth, what I imagine to be the hardest part of building them. Maybe the light hits the plants better in the SHCS, not down in a hole? Also it is hard to build a passive greenhouse that functions well in the winter but wont over heat in the summer does one of the above systems work better? Thanks Greg
I guess a simple answer you may be looking for is thermal mass for the sun to heat up during the day, and then give off that heat during the night. You’ll want to insulate this mass from the cold ground beneath it. The mass can be anything heavy; concrete pavers, bricks, even water. Rigid insulation on the ground with a layer of pavers over it is still better than nothing.
1 Like
I’m no expert but if you’re primarily using this for winter storage, I would get aluminum insulation rolls to lay across the entire floor and put my plants on it. You could also put pea gravel down first followed by the insulation. Remove the insulation and store it away until winter again. Then during the growing months you’d have pea gravel to walk on.
I use this stuff all the time for growing applications including blocking sun away from my grafts; I use it as a sub-floor under above ground pools; And I use it under a heat mat as well as above a heat mat to put my growing flats on. It’s a great product. If you feel the need to tape the joints, use duct tape. You won’t need to tape it for a temp floor in your greenhouse, however.
Dax
1 Like
@gregkdc It’s a good question, and a pretty broad topic. I have built and run a couple of GHs, one a SHCS one, but don’t have any first hand experience with subterranean ones (although I have toured some and chatted with the owners).
As always, it all depends on what one is trying to do with the GH and your climate. Just starting annuals in the spring, year round orchids and tropicals, extend a season for tomatoes and peppers, etc etc. Much of what is written needs to be filtered with this info in mind: what is the climate where the author lives and what are they trying to do. Once you know those answers I think it starts making more sense and being more consistent.
Years ago I took a SHCS course with John Cruickshank (aka Sunny John) the original designer of the SHCS. It was very useful and helped me set a reasonable set of expectations. At that time John was in the front range, and he stated that for large commercial sized GHs, the SHCS could extend the season a month at each end without supplemental heat. If the grower had plants to keep alive and producing, the SHCS would help some outside that, but another heat source is needed. If you do the numbers they pretty much back that up, the volume of soil directly under a GH cannot hold enough heat to carry a GH through an entire winter in zone 5 (or 6 too I would guess) at growing temps. It is also true that the “passive” heat transfer (blowing air thru underground tubes) cannot move enough heat fast enough to eliminate the need for other cooling (venting) in the warmer months, and probably also could not bring enough heat up to sustain the plants on really cold nights (say -20F).
I think this more or less accurately summarizes what can be done with a SHCS GH in my climate. Others here have had similar experiences. For my purposes, SHCS is well worth it. I need a GH to get crops from tomatoes, peppers and the like. The SHCS system alone extends my growing season enough to do that. I also have potted citrus in the GH, near to a supplemental heater, and the SHCS system helps lower my heating costs as well. I am not personally aware of how SHCS works in other climates, but there are several sites online of people who are using them elsewhere.
The subterranean GHs I know of here are mostly used for winter and early spring plant propagation. I don’t know anyone who is trying to use them year round, but that does not mean they couldn’t be. Here at least, it is much more economical to move your plants outside once the weather permits. I suspect that they would have issues with enough light, at least for light loving plants in an underground GH.
What does work well is a small GH attached to a heated (or partially heated) structure. A variant of sorts on the Earthship concept. You use the heated structure as your heat storage, pushing your excess heat in there during sunny days, and pulling heat back from there at night and cloudy days. I have such a GH, and it has stayed above freezing with no additional heat for 10+ years during the winters (with one exception during an extreme cold snap). The “room” it is attached to is an otherwise unheated garage at the basement level of our house. The GH keeps itself and the garage heated most of the time. No active air movement or heater just an open door between the GH and garage. There is however a power vent, because it can and does get too hot in the GH without venting (even in the winter). This GH has worked very well as far as heating is concerned. No supplemental heat required and can grow plants year round (although there is not much growth in Dec-Jan when light is limited, but plants stay alive). If I was designing my house again, I would expand this GH to run along the entire S side. Although if one is really using the GH actively I am not a fan of the Earthship practice of making your GH part of the living space. An active GH needs to have things done to it (sprays, etc) that you don’t want in your living room; putting the GH at the basement/garage level with a means of closing it off solves that. It also helps that I don’t care how hot the garages gets, 80F+ is just fine down there; would not be in my living room.
It’s a real eye opener to do the BTU calculations for how much heat a GH uses when you try to keep it at growing temps in a climate with some real winter. On the surface it seems there is so much extra heat in most GHs that get vent to the outside. But storing and retrieving that heat passively (without a heat pump) becomes a challenge. It is hard to do especially if you want your plants to make it thru the coldest nights.
@Steve333
Thanks for the long write up it is good to hear how well these systems really work versus what your told by salesmen. What I have read in reports from universities matches your experiences. It seems like you need to employ all kinds of mechanisms to regulate the temp and no one thing is going to get you through. Sometime in the future I will have a greenhouse that hopefully I will be able to grow year round tropicals in, that I my goal at least. Greg