Hi,

I don't have experience with removable roofs but I have some other ideas . . .

Have you heard of using phase change materials to control temperature extremes? Here is a blog about it:

http://greenhousefashions.blogspot.com/

The blog is written by some people at a company that sells phase change materials for other more conventional applications and the blog is meant to show that PCMs can work great in greenhouses too. We are building our greenhouse now and considered installing PCMs but decided to wait to see how our greenhouse functioned without them first which will help us in estimating how much PCM material we need.

Another reason why we did not go with PCMs immediately is because we are building a Subterranean Heating and Cooling Storage system into our greenhouse which is a phase change system. It is possible we'll have all the heating and cooling we need from the SHCS. For more information about SHCS see this blog:

http://www.roperld.com/science/ymcasolargreenhouse.htm

Have you looked at "Pit" greenhouse designs? That could really help maintain temperatures passively:

http://www.amazon.com/Earth-Sheltered-Solar-Greenhouse-Book/dp/0960446400

Here is another great book. In it, it talks about a variety of passive solar designs that work well. The best combination of strategies seems to be an attached passive solar pit greenhouse:

http://www.amazon.com/Solar-Greenhouse-Book-James-McCullagh/dp/0878572228/ref=sr_1_7?s=books&ie=UTF8&qid=1385082426&sr=1-7&keywords=passive+solar+greenhouse

One thing that I wonder is if you should glaze the roof at all or at least do it minimally. We opted to go with really tall south-facing windows, a few skylights and tons of insulation. This should help with too much solar heat gain in the summer (along with the SHCS) while allowing more solar heat gain in the winter when we need it. For a short article from a green building site that is focused on energy efficiency see:

http://www.greenbuildingadvisor.com/blogs/dept/energy-solutions/sunspaces-solar-heat-and-place-grow-plants

In case you don't already know about this, check out this site that has tons of peoples' experiments with all kinds of solar greenhouses:

http://www.builditsolar.com/Projects/Sunspace/sunspaces.htm

Best of luck! Looking forward to hearing what you end up designing. Where are you located?

I've got a sunroom that heats my house wonderfully. I've grown figs and blueberry in there in winter but that requires heat at night, or a move indoors at night. Just heating the house is easier.

All you need is a greenhouse covered with 6 mil IRAC greenhouse poly during the heating season. Heating season should be about the same as the season where frost is an issue. The poly could be easily removed during the frost free season and even replaced with shade cloth if needed. The same fastening system will work for both, ie wriggle wire. A shade cloth could also be held in place with simple ropes.

A more typical design would be a fixed roof in the GH, with removable (or open-able) side walls. Those could be roll up ones, or window/sash units that you remove for the summer. I think you'd find keeping the roof in place and just dealing with the walls easier.

A general rule of thumb is that you can use your winter GH heat to heat your house, or grow plants in the GH, but not both (without an additional heat source). That is generally true in my climate, but obviously will depend upon the plants involved, your climate, and the details of your home/GH.

Might be worth running some heat gain/loss numbers to see just how much extra heat you have in your GH that would be available to heat the house. Since you are in a warmer zone than I am, you will probably have extra heat to play with, but a first pass at the BTUs should tell you quite a bit about whether you'll have extra GH heat or need to be adding. Of course with an attached GH, the house heat is available to heat the GH too, when needed.

In zone 7b-8a, same as mine, the winter heat available is amazing. My sunroom hits 110F even when I'm pulling off as much heat as possible to warm the house. I think I've figured out about 15,000 watts output for a collection area that is about 15 meters squared.

In January starting at 9am the sunroom heats the house almost as fast as turning on the furnace.

It's true that roll up sides are easier than removing the top. But with sides rolled up a greenhouse would still hit 110-120F here in June. That's too warm attached too a house. It would need heavy duty shade cloth even with sides rolled up in summer.

Interesting Fruitnut. I have no experience with GHs in that climate, but it sounds impressive in terms of the amount of heat available, year round.

I just got my 34'x15' GH enclosed, and on a sunny day here, it was running 110F while outside it was mid 40'sF. That without any windows/vents or heat capture. Heat capture (SHCS) in a primitive form (just subsoil, no upper soil layer yet, and very low humidity) lowered the peak temp ~10-15F. I am expecting more once there is a full depth of soil, some more humidity and plants in there. And of course vents and the fans will help too.

I am surprised though that you think with no side wall the GH temps would be 120F in the summer. I would have thought they'd come to rest 5F or so above ambient outside temps. Is the air that still in your area that this can happen?

I defer to the folks living in that climate, but I would still think that shade cloth and removable sides would be far easier a task than a removable roof.

Shade cloth or the temporary shade paint both sound a lot easier. Or you could make the roof panels all open just a little as vents; then at least the very top of the roof would be open. I think shade cloth would work better, though.

It's not that hard to remove attachment of poly on three sides and then pull it over to the attached side and tie it off in a rolled up bundle. I've done this with shade cloth for seasonal use.

As to temperature rise it takes one air exchange per minute to hold temperature rise to 10-15F. I can open one side on my sunroom early or late in the heating season and it still warms up substantially. The reason I open it up is that closed off it still warms the house too much through the walls and windows on those days I don't need/what extra heat.

I do agree that sides that open combined with ~50% shade cloth would work in summer both for citrus and house cooling.