On the thinner overcast days and during sunbreaks, the sun's energy still reaches earth's surface as clouds are transparent to some radiation (why you can get a sunburn on a cloudy day). During the thicker overcast days you'll have a problem. 3 mm single-layer not much insulation...

Dan

Here is my advice.

Do NOT insulate the floor. If you want to know why, I can explain, or you could just search this forum.

Use water barrels to store rainwater, not as heat sinks. Even with the sun, you will not find them worth the trouble if you want to stay at 55F for citrus. I can explain, or you can search the forum.

Mist at night is asking for disease.

Be very careful with the wall of your house that is inside the GH. Water damage is a significant risk.

Tubes run through the cavities not likely to help much. I don't think that the heat will be transferred efficiently enough if most the tube, regardless of the material, is surrounded by air.

Total energy-wise, you would be much further ahead if you upped the R-factor of your glazing. Also, acrylic allows a LOT of direct light, very clear. Plants very much favor diffused light. I have some direct experience with this given that I have a single pane glass GH. The plants do a lot better with a layer of poly which diffuses the light...much less burn and perhaps better growth.

My two cents.

I'm not very good at being subtle, now that the ice has been broken, when I lived in Wallingford I couldn't grow peppers, and when I moved to Enumclaw it was worse. You can gather solar radiation. But is it worth it? Rich people grow citrus. You can extend your season, but 6 days in a row of broken at600 and overcast at 1000? Energy is required. It can be done. There are pluses and minuses to living there. Maybe I'll change my standard answer here..

Dan

A couple things to note:

I haven't much choice on the acrylic vs poly for diffusion. Mandatory clear as glass, since this sits in the main window of the house (need to see out through it for view). Roof is diffused poly though (no need to see upwards). I am open to ideas on what GH would do what the Rion Sunroom does in this case, but with better glazing R-Value. I need a kit, dont want to custom build.

No choice on a lean-to model either... no other place on the property for a GH. Not sure how to mitigate water damage yet, nor how big a prob it will be.

I have grown citrus in this area indoors for 2 years, so far so good (terrible lighting, even in the south window). Depending on the variety, artificial light is needed. I was hoping to put them in the GH, but maybe it would require way more power than my current indoor light setup - this is what I am investigating and hoping to solve.

One alternative to forcing the GH temp to 55 is to just heat the soil of the individual citrus containers.

The ironic bummer about greenhouses is that you'd think the whole point is to create a fully controlled artificial environment. But, what you get is almost no temp difference to outside without forced heat, or at least lots of fancy work. With no way to efficiently use the energy of earth and sun, a GH is near pointless in my mind. Well, there is a way to do nearly anything with the right budget, but then that kills the fun too.

Still learning, and sorting out... :)

"...almost no temp difference to outside without forced heat..."

...at night.

If you need to know how big of a problem water damage in the house wall might be, I can hook you up with a buddy of mine who is knee deep in it right now. And he was careful. Built a GORGEOUS greenhouse. I believe his GH was well into the 5 digit $ range and it sounds as if the total may be the same on his water damage. Just be really careful.

Why can't you go more than a foot or two down for geothermal?

I am curious... What's the issue with growing citrus there? Seems i remember UW having a palm tree growing outside of their greenhouses.

I find here in New England that citrus easily survive our winters stashed away in the unheated garage (We've had temps in the negative double digits). This year i tried keeping some of them in an unheated greenhouse and, while they are not doing well at all, they appear to be still "alive". The point being, i'd think citrus would be easy to grow in your area.

I am unfamiliar with any palm trees in the free air on the UW campus.

Nonetheless, the overall idea needs work, as two feet down is not nearly far enough to collect geothermal 'heat'. Misting will cause mold and fungal issues. The thickness of the glazing is insufficient R- value to retain what tiny amount of heat is collected on the third day of overcast at 600 ft and rain where the temp hasn't changed from 41 degrees F either. Surely a greenhouse film that diffuses light, and has anti-condensation properties and reflects IR is needed for those purposes and to create an air gap to insulate. Energy input will be needed, either to heat water in tubes in the floor or electric cables or heater of some sort. And you'll have to dig down much farther than 6" for your base for cinder blocks - you'll want to go the library to get a book to understand how to lay a masonry floor/patio.

The bottom line is that you will be paying to heat the structure. Insulating the ground and replacing the glazing and adding an air gap will help. But you'll get scant help from the sun, and you don't want to pay the price to do geothermal correctly.

Dan

^

Agree with everything but insulation of the ground. Maybe insulate the perimeter.

Maybe insulate the perimeter.

That's what I meant. I'm in the market for a new editor. ;o)

Dan

stressbaby:
yes, please contact me about what went wrong with your friends water damage. I updated my profile to allow email.

I was just looking at your profile, and WHOA!!! you grow Lychee in zone 6!!?? Wow, I tip my hat to your mega awesomeness. :) I want to learn from the master.

poppa
Citrus does grow here if you know the tricks. However, outdoor winters would kill em for sure. You cant allow the soil to drop below 55 or leaves drop, plant dies. Bringing them into the garage in the winter is ok for survival, but not thrival... so I use artificial light in the winter indoors (they are fine without it in the summer, outdoors, even in seattle)

dan:
good tips all around.

Thrival... I like that. The trees i have are now over 6 feet tall which is why i tried a couple in the GH. They are getting too heavy to move. They're about 9 years old and they started flowering last year. It was only my ignorance that caused them to suffer in the winter. I stopped watering them and i thought the leaf drop was due to the cold. Now that i water them, they don't drop their leaves. Hopefully i will get fruit next year. I set them out too early this year and a late frost killed all the flowers. Since i do get ice on the floor in the garage, i have to assume it gets below freezing in there at night.

The palm tree was there in '81' when i was a student.

It is pretty apparent that given the environment (overcast and 44F avg all year), AND the fact that Clear glazing is mandatory in my specific case, heating will be mandatory.

Insulating ideas:
-Find different Clear panels that have more insulation (likely difficult, or surpassing the point in buying a Rion kit)
-Insulate at night with foam panels inside (have to put up and down constantly)
-Insulate 24/7 with clear film mounted inside (a poor mans dual layer, see link)
-Insulate with a solar blanket outside each night (have to put up and down constantly)

I will definitely add as much thermal mass as possible, with fully concrete floor and water barrels. I am also thinking, radiant heating under benches via water tubes, as opposed to just heating the air. Proper geothermal is just not achievable for me (bummer).

Taking ya'lls advice, I will not mist at night and not insulate the ground except maybe the perimeter.

Other thoughts? I also have to avoid condensation with the 3mm Acrylic, but I figure that is doable with the proper temps and air/humidity control applied.

Here is a link that might be useful: Clear Shrink Film

Technically you will want outdoor film not indoor. Indoor will likely last a little while then come off (sez the voice of experience). You will likely not avoid condensation on that glazing. Simply too thin. You may want to look at an anticondensate greenhouse film and figger out how to attach it. Nonetheless, now you are starting to understand how hard it is to make these work without energy input, esp inexpensive kits. I've got several GH books from used book stores in Wallingford & big annual sale @ Sand Point, you may want to do same. And search this forum for similar tales of difficulty.

Dan

Agree about the condensation, you will have it. The key is controlling where it drips. Better greenhouses have channels, little gutters if you will, which keep the condensation from dripping on the plants.

And again, don't bother with water barrels. The value of the water is the latent heat. The water gives off a lot of heat when it freezes, and that is of no use to you if you want the GH 55F for the citrus. The water will just be taking up space. Better off heating a smaller greenhouse.

Roachslayer, read this.

Here is a link that might be useful: Attached Gh tale