Quote:
Originally Posted by fotofashion
...I understand your concern about space vs. economizing on the heating costs. Are you considering buying the polycarbonate panels that will give you the maximum insulating value? I know they are more expensive but if they will lessen your heating costs it would be worthwhile to consider them.
Winter is not that far away for you. You need to get cracking on your new GH so you won't get caught building it while it is snowing. 
Beverly A. |
Twin-wall polycarbonate panels aren't worth it in my application. These:
Polycarbonate Panel, 10mm Clear - Polycarbonate Panels | Greenhouse Megastore, have an R-value of 1.89. A layer of inflated double poly has a R-value of 1.7 (
R-value & U-value). The polycarbonate panels cost $64.44 for a 4'x8' sheet, polyethylene is $78 for a 12'x55' roll. The South face in the above plan measures 10'x21'. I would need 8 polycarbonate panels at a total cost of $515, or one roll of polyethlyene at a total cost of $78. That's a difference of $437. The polycarbonate has an R-value only .19 better than the film. Plugging that into my heatcalc spreadsheet, worst case scenario it would costs me $38 more per year to heat the greenhouse if the South wall were covered in polyethlyene. It would take 11.5 years for the polycarbonate to pay itself back. Plus I wouldn't be able to remove the polycarbonate during the summer for ventilation.
Even the panels with the highest R-value,
16mm Polycarbonate, Clear - Polycarbonate Panels | Greenhouse Megastore, wouldn't be worth it. They have a R-value of 2.36 and cost $130 for a 4'x10' sheet. I'd need 5 of those, for $650. The difference in R-value is .66. Which saves $107 a year. It would take 5.5 years to pay for itself. Which is better except I don't plan to use this GH for that long.
Hey I got a good 2 months yet before there's a chance of snow. How long could it take to build an itty bitty greenhouse like this
Quote:
Originally Posted by DavidCampen
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Hey I like those too!. I hadn't thought too much on the shelves, I was going to build them myself out of wood and hardware cloth, but those pre-made wire shelves would be a lot sturdier and not cost much more. Did you buy them from that website?
Quote:
Originally Posted by msaar
A few comments (re solar scheme):
-You don't mention terrain. Is your site flat or sloped? If flat, you will have to consider control of ground water. do you know where the water table is? If your site is sloped, which way? Are you planning steps?
-While the water will store a specific amount of heat, a lot of factors will affect the absorption and release of that heat: the volume:surface area of the water mass, the material of the water containers, the exposure of the surface area of the water mass to free air and sun. Your cube-shaped water tanks present concerns on those accounts.
-You will need a means of removing watering water from the GH-sump pump, drain to grade, etc.
Food for thought....
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I'm glad you asked. The site I'm looking at right now is about 50' away from the house. It's close to our satellite dish, which has an underground line (18" deep) for elec to it, I can run another one for the GH easily. I would have to put in a line for water 48" deep, and for propane if I tied it in with the house. The area is at the top of a hill. Eastwards is flat, to the South is gradually slopes downwards. To the North it is level for 20' behind the wall of the GH, then slopes down steeply. And to the West it slopes steeply. Where the greenhouse would be, it wouldn't slope N-S, but E-W the West end is ~18" lower. I was going to pile excavated soil around the West end to make it a bit more level. If I don't sink the GH 3', I'll need to level the site before building. My dad owns a tractor with a backhoe and grading blade.
It is true that large bodies of water isn't the most efficient way of storing heat. The hot water will rise and there will be a gradient of hotter water over cooler water. This reduces solar gain of the hotter water at the surface, which is where the sun usually hits it. Large water bodies also don't release the heat as fast compared to smaller containers. But over a 10hr night, it shouldn't be a big difference. The Solar Greenhouse Book suggests stacking small containers, like milk jugs, against the back wall. When stacked on their sides, the jugs contact each other well and transfer heat readily throughout the entire water body. But without a good source for a couple of thousand milk jugs, I opted for 55 gallon drums and IBCs.
Hybrid Mode
