Well, I just googled "heat transfer" and "soil". The first page I find is: http://www.wtamu.edu/~crobinson/SoilTemp/index.html "Conduction is the primary mode of heat transfer in soil." Do you have a better link? Conduction was what I assumed was the primary heat transfer method when I wrote my simulator, so if it's not, I'll need to modify my simulator a bit. As for heat balance. Let's assume that the PVC's diameter is 0.1 meters. That's a circumference of ~0.31 meters. Times 50, that's 15.7 square meters. Assume a metric R-value of 0.2 (American R=1.14). Conduction is (Temp1 - Temp2) * Area / Insul_R, so Delta-T * 78.5W. 10 degrees average temperature difference will unload 785W into the soil. I would anticipate, as well, that with soil's low R-value, heat will flow much faster through the soil than from the PVC to the soil, thus equalizing temperatures (I'd have to write a simulator to check this out). My heat balance simulator shows, for such a greenhouse (simply adjusting my greenhouse to be the proper length and width; your geometry will be important), a peak input heat of 1458W added to the air. This happens early in the day, when the sun is bright but the greenhouse is still quite cold. By high noon, it's down to 1237W, and by 3:00 PM, it's actually cooling because of the less optimal sun angle. I can get you a breakdown of the calculated heat inputs and outputs if you'd like. By these numbers, at peak heating time, the PVC will be sapping half of the greenhouse's incoming energy. At non-peak heating times, it will be reducing the heat input even more. Again, I could do a more detailed simulation if you thought it necessary, but a rough look at it appears that this system would do a very good job at heat storage. As for heat capacity (the other issue), my research indicates that soil specific heat ranges from 800 to 1500 (lets say 1100) J/kg*K, and soil density is typically around 2000 kg/m^3 (although highly organic soil can be much less). Assuming a pipe depth of 0.5 meters, we're looking at 6 cubic meters of soil. This translates to 12,000kg of soil, storing 13.2 MJ of energy per degree, I.e., 3.6kWh/degree, meaning that the soil would only change less than 1 1/2 degrees in 6 hours. Now, this a very rough calculation for a number of reasons. It assumes even soil heating, which is false (this works against soil energy storage). However, it also assumes that no soil will be heated below the pipes, which is also false (this works in favor of soil energy storage). Assuming that the factors roughly cancel out, the soil temperature should fluctuate very little between day and night. I already know, by my pipeless-greenhouse simulation, that this indeed is the case. About 1 foot down, I show the temperature shifting only about one degree between day and night. Of course, since you have some complaints about the conduction-dominated soil heat transfer model, I'm open to changes in this. As for water usage, the areas downriver from us are rainer than we are (east Texas, Louisiana, etc). The US's water problems are mostly in the rockies and especially the desert southwest. Phoenix is subsiding from the overtapping of its resevoir. LA has basically terraformed the Owens Valley by the amount of water it's diverted. Etc. However, we have little to no effect on them out here. As I stated, the world doesn't have a water shortage; rather, there are regional water shortages. Conserving water in an area that doesn't have a water problem doesn't help with water problems in areas that do. As for mold, that's certainly an issue to consider; however, I'm not concerned. Sealed PVC will only have the moisture from your greenhouse affecting it. As mold doesn't grow very quickly on the walls of a PVC greenhouse, I see no reason to expect quick mold growth in the underground PVC pipes. If mold does become a problem, with the "auger-slant" approach, what's the difficulty? All pipe segments come up to the surface, so you can clean them out, or even potentially replace them (if your soil is compact enough that the hole won't collapse) without any digging. As for water collection, the PVC will only be colder than the inside air during the daytime. At night, it will be hotter. As the PVC will have air actively blown past it, if there's any water in the system, the air should reach the saturation point with ease. If, by some accident, water accumulated, I could take a few joints off and blow each row out with a leaf blower (I doubt one could blow water out of the whole system at once, but a single row should be doable. If not, a half row, a third row, a quarter row, or whatnot). I'm not knocking you, only trying to get a reality cheque for the problem Oh, by all means, do! I'm actually enjoying this discussion. Some things I actually hadn't considered before, such as mold. Naturally, I'd start out with just a single row of PVC and see how it works out. And while I certainly don't see anything close to a showstopper here, who knows what the future will bring. By the way, your water system sounds nice -- making use of your heat-sink water as a fish pond. I'll have to consider that for the future. ;) All of my simulations show that the water tends to stay at a nice comfortable temperature even when if air temperature gets uncomfortable, so fish should be in good shape.

Hi Chuck, I love my HFGH 10x12, but I think splitting it in two to make a 5x20 lean-to would require a huge amount of rethinking and re-engineering. The roof pitch in the kit is predetermined by angle brackets at the corners, and by a formed angle in the framing piece at the top of the side wall; I don't think you could use that major component if you changed the roof pitch. The framework really doesn't lend itself to cutting the structure in two as far as critical bracing. Not saying it couldn't be done (anything is possible for hard workers!) but personally my husband and I think you'd be better off to consider building your own structure (which would allow you to go wider than 5' if you wanted.) It's nice you will have a solid structure to anchor to. I now know the twinwall polycarbonate panels that come with the HFGH kits will not last more than a few years in my own sunny climate, due to (in my opinion) a lack of UV protection, even though HF continues to advertise otherwise. The panels represent a huge part of the value of the kit, since true UV protected twinwall polycarbonate is expensive, so I now advise folks to take this into consideration, depending on climate, when they consider the kit. Some of the close-up photos in my blog may help you see what I mean about the pre-formed angles in the aluminum framing at the GH corners: Mudhouse blog for 10x12 HFGH Also, here's a link to a helpful site with many links to info about building your own greenhouse: Free plans for building greenhouses and solar spaces I also agree, I'd encourage you to start a new thread to get more opinions from other folks...lots of folks here more knowledgeable than me, and some of these older threads with many slow-to-load pics get skipped by folks who might be very helpful to you. Sheri

We are having a big wind storm and I'm worried about the greenhouse. This morning my husband drove down to see it and frankly I was expecting to hear it was destroyed but it is fine so far. The winds at our house which is about 20 mile away are very strong and luckily the greenhouse hasn't been hit as hard. The wind gusts last night are reported to have reached 51 mph. I was working late and felt the house shake as the gusts hit so you can see why I expected the worst for the the greenhouse. We did screw down all the panels with stainless screws including the roof vents. The corners are all firmed up using Gardenwantobe's brace system but the rear wall has some flex in it and it needs immediate help. I'm thinking of putting in the bench framing using the galvanized pipe - just not sure how to attach the pipes to the greenhouse frame. Lazerfan I looked at your photo of the cross beam you added to your greenhouse and I'm wondering how you attached it to the frame. I read that you welded L brackets on to some of the pipe and I'm trying to think of how to install the pipes (for both the cross brace and bench frame) without welding. I guess I could bolt an L bracket to the wall stud, drill the pipe and attach the pipe by bolt to the L bracket. If there is a better way please let me know. Our neighbor who is building the greenhouses is out of town until the 3rd and I want to be sure there is something left when he returns. It is so cold and windy out that it is hard to get myself motivated to deal with all this - for now I think the worst part of the storm is over. I live in Pacifca, CA (hence my name) and you may see us on the news as the surf here is very high and the local news stations keep coming down from San Francisco to film the waves. Mary

Wow, I haven't been on Garden Web in 7-8 months and what a surprise to find this thread I started several years ago back on the first page, LOL. Last year we moved in December and left my greenhouse at our farm for the rest of the winter. DH installed two "new" propane heaters in my greenhouse before we moved, and I have to admit they worked great on their own all winter without any help from me. I went back about twice a week to check on the greenhouse, water my plants, etc., but the greenhouse was basically on its own all winter. The plants didn't really thrive with the propane heat, but at least none of them died. My problems from the previous year had been caused from those piece of shi+ Northern heaters, which were defective from the very first day they arrived. I bought three of them, and it seems strange they were ALL defective. I highly recommend you don't buy your heaters through the mail from Northern. I do believe electric heat is a much cleaner source of heat, and better for my plants. I know this is a big argument here on this forum, but that is how I feel. If I could afford it, I would use electric heat and only use propane for a backup in case of power outages. But our electric rates have sky rocketed here, so even at $1.90 a gallon, propane is still cheaper to heat with. So that's what I'll be using this winter. Hopefully my experience here using propane will be more successful. We finally got the greenhouse moved here to our new home this week. I sure hope to get it up and running before freezing weather gets here. I'm looking forward to enjoying it again soon since I didn't get to last winter due to our move.