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Greenhouses & Garden Structures

Thermal mass, opinions?

wertach zone 7-B SC

12 years ago

I'm ordering a HFGH, 10 X 12. The greenhouses that I have had before were built, by me, from scratch with the north side heavily insulated. I'm too old for such a big project now..... I always used black 55 gallon barrels filled with water for thermal mass.

This new (to me) house has a lot of huge granite rocks that I could use instead. Since I have never used rocks, I'm wondering what are the pro's and cons of one over the other.

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Comments (12)

stressbaby
12 years ago
Hi wertach,

In my opinion, with a 10x12 HFGH, the amount of required passively managed thermal mass, rocks, water or otherwise, that you would need in SC to make a noticeable difference is not worth the space it would occupy in a small greenhouse.

The thermal mass will be giving up its heat as soon as the temp differential favors loss of heat into the GH. Generally that means that the mass is losing heat by mid afternoon and by 10pm when you need it, there is not much left.

If I were you I would put up >= 1" of reflective foamboard on the north wall. Maybe you could use the stones as flooring.
gardener1
12 years ago
without insulation between the floor and the stones. the stones will draw the heat out of the greenhouse and into the ground. Trust me mine does. Im getting ready to insulate my floor.
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Did we come to an end on this thread? ""Let's brain storm: thermal mass materials"" I think we agree for all practical purposes then water is the best for thermal storage. Several interesting issues emerged and I think they are important. "Seems to me is we may be switching our night time heating bill to a day time heating bill..." Yes, that may be a bonus in an unconventially heated greenhouse. During the day it may involve stoking up a wood, corn, straw bale, oil fired furnace to build enough heat to get through the night. In gbrendemuehls scenario you just have to do the "burn" once every three days. ""3 day storage reserve and and 50 degree termperature range, the needed volume of water is about 4600 cubic ft. or 34,500 gallons"" In the test greenhouse that is just under 2 feet deep. Why is that not practical? I admit that retro fitting a 34,500 gallon under floor holding tank in this case is not possible bit in the next one...... ""Large greenhouses are built on a grade of about 1 to 2ft per 100. Insuring the any water on the floor/ground will run out of the house."" You heard the latest the EPA are throwing at us? Greenhouse waste water is going to be classed as toxic waste. (as it should be.....) Don't ask me for a link to verify this because I have not looked. However I do know I am the only one in this area with a greenhouse because the other guy who ran a commercial setup quit when he got slapped with a $17,000 water treatment bill. Storing and re-using the run off may be a side benefit. The most important issue for us may be the fact that this thermal mass, free heat concept does not scale up to large commercial operations. We all know it works down to the "Wall-O-Water" level and up as far as 150 gallons of water under a 4x8 bench but to take it past that point you are looking at some really big heat exchangers and pumps. For Mylu, For you, the only benefit a water based heating system with the water under the benches would be is that with a prolonged power failure you would not lose your crop.
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who2ted
12 years ago
@gardener1- how do you plan on insulating the floor, my floor is dirt but I could build it up.
oakhill (zone 9A, Calif.)
12 years ago
Before you insulate your greenhouse floor, you may want to read the article at the attached link.

Here is a link that might be useful: insulating greenhouse floors
who2ted
12 years ago
great, I am not going to worry about a floor, thx.
gardener1
12 years ago
sorry i jumped to conclusions I was told thats where I was losing my heat. I am new at this and still learning. Now I will concentrate on the ceiling. And thanks for setting me straight.
wertach zone 7-B SC
Original Author
12 years ago
I disagree stessbaby, I'm in zone 7 of SC and we rarely have temps much lower than freezing. The scratch built Gh's that I have built before had water barrels under benches. They did however have the north side heavily insulated, no glass on the north side.

The temps would stay above 40 inside when the temps dropped to the low 20's or lower outside without any extra heat. If I had cloudy days with cold temps I would light my Coleman lantern and it would stay warm!
stressbaby
12 years ago
Wertach,
Questions:
What size GH have you built before?
How many gallons of water did you have?
What was your elevation?
wertach zone 7-B SC
Original Author
12 years ago
Stessbaby, My elevation is around 800' , lat. 34.62, long -82.2.

The GH I was talking about was about 14'X 20', 12' high. I had about 700 gallons of water. I used thick glass shatter resistant panels that came from a store front.

I wish that I still had the pictures of it, so that I could post them. But I lost them AND the greenhouse when I divorced! I really miss that greenhouse!
stressbaby
12 years ago
So for me, 13 55 gal barrels wouldn't be worth the space in a 14x20 house. I have 3 44 gal barrels in a 20x23 house (for rainwater) and for me, even those take up too much space! Different strokes...

Thanks for the info.

Robert
wertach zone 7-B SC
Original Author
12 years ago
Thanks for your response Robert. I'm not looking for quantity in my GH, just quality and economy. Heating a GH with fossil fuels or electricity costs too much in my opinion.

I only have 2 mouths to feed! I want to grow some lettuce and stuff for fresh salads, without worrying about salmonella. Use it for starting tomatoes, peppers, ETC. Extending some tender veggies later in the fall.

When I was younger, and had my really great greenhouse, I had tomatoes almost year round. I had a tomato that lived for 3 years! It might have lived longer, but I had to move.

I drove by about 6 months after I sold the house and the new owner had tore it down!!!!!! I felt really sad!
cheapgardener
12 years ago
THIS IS A LINK TO A VIEW OF MY THERMAL FLOOR AND IT WORKS SOME PEOPLE THINK I HAVE LOST MY MARBLES BUT I KNOW WHERE ALL 30 GALS. ARE

Here is a link that might be useful:

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