It sounds like it would work, but I haven't tried it yet. I was wondering about doing something similiar using plastic barrels filled with water. I have seen this done in greenrooms where they are put onto the back wall, filled with water in the winter and drained in the summer. They also "gain" heat from the heater in the space.

Moke: Yes, I've seen water walls and they do indeed act as you describe, but they seem best suited to very large GH's, in which giving up at least 2 1/2 - 3 ft. of floor space on every wall they are stacked against isn't an issue.

That's why I was thinking of those panels. They would fit between the aluminum channels and not take up any floor space at all.

When I mentioned the notion to my husband, he speculated on using clear polycarb to double glaze the entire GH. So far, it's just speculation, but I'm willing to explore every avenue.

Maybe the two of you could bat around the idea of doing both! Put the opaque down low, where other than the morning/evening low angled sun, you won't lose that much photo energy coming in to your plants or providing you with solar gain onto your floor and any mass you have under the floor. Then put the second layer of clear on the inside like he suggested for a means of trapping the air. The only problem might be one of humidity getting trapped between the panels. I hope I have been of help to you.

Birdwidow, I also thought of a solution for any potential humidity between the sheets of polycarb. Have a squirrel cage fan mounted up near the ridge, then run ductwork (3 or 4 inch PVC pipe) from the fan to the outside walls. Install a heating duct connector (round to rectangluar) on the inside polycarb and the duct. Install a set of self opening shutters on the bottom near the floor. Then have the electrician install a thermostat and timer to turn the fan off and on. This away when the GH heats up, the blower fan kicks on and blows hot air out of the top of the GH and back down, between the polycarb, and onto the floor. Thus helping with the air/heat flow in the GH. Then in the summer time just have it set on a timer so that it runs on a preset schedule. I hope this might help.

Moke: good ideas, but I really don't know about additional fans, vents and tubes. There are a lot of panels in a 12 X 16 ft. GH. But air circulation in general won't be an issue, with 4 roof vents on automatic openers, 2 powered intakes set at the base at one end and an exhaust fan set high at the other, coupled with my "ultimate continual air movement weapon": 2- 52" ceiling fans, turning in opposite directions 24-7, will privide a lot of circular air movement.

If the surface of the GH wall panels are perfectly dry, and the inside ones are sealed on all sides; if they were then sealed against the GH panels, would they STAY dry?

Or- leave a few inches at the tops and bottoms open, to allow moisture a place to run off? Or- and this is one my husband and I discussed: cut the inside panels to fit just between the channels on the polybars, as not to block them, and seal the interior panels against the metal, creating dead air space between them and the exterior panels?

I could also use that shrink plastic used on windows, but I'm really looking for a more permanent solution.

Frankly, if I had thought more about this issue, I'd had given up my desire for the sloped roof on my lovely Cross Country, and just gone with triple wall polycarb and now, I'm sorry I didn't.

But... the R value still isn't all that different between double and tripe, until you get into the ultra heavy, commercial weight polycarb panels and for that cost, you might just as well blow it all, and go with thermopane glass.

Oh well, the months ahead should give me some time to develop more nutty notions. The GH gets some decent dappled shade, and between the trees, misters and all those ventillation gadgets, I'm hopeful of keeping it reasonaly cool, but do want to come up with something better than draping the whole thing with that heavy solar pool cover again.

All notions nutty sounding or not, are welcome. BTW: my "electrician" (and carpenter, plumber, etc,) is my husband, and one of the reasons why I'm anxious to find a better solution than climbing ladders to haul that cover onto the GH. It worked, but oh, what a chore, and the wise old wife simply does NOT tell her 73 year old farmer he's too old to climb ladders; she just tries to avoid the need for him to get anywhere near one.

If you get the chance look at the website for KCPT Public Television in Kansas City. Charles Gusswelle, a long term columnist for the Kansas City Star newspaper, does a series which is loosely based on his column. One of them has to do with him and his wife putting up Christmas decorations and a step ladder. It clearly illustrates what you are talking about.

The idea with the fan and duct work is to just have some air movement between the panels. I know that the exterior panels are weather tight, but the space between the two panels will not be sealed, or very difficult to. So the chances are there will be some humidity build up between them. What I am afraid of is what my brother had on a patio door many years ago. (In fact it happened on two different ones, both south facing.) The humidity built up between the glass, and since there was very little means for it to escape, it wound up mildewing between the glass! Something I know you don't want to have happen.

I am sure you and your husband will come up with a solution, and a way to add insulating value to your GH. Today, being the first day of spring, means you've got 5 months to come up with a plan before fall!