Free Greenhouse Heat

[Millet]

In order to raise 1-lb. of water up one degree requires 1 BTU of heat.  Conversely, when 1-lb. of water loses 1 degree of heat it gives off 1-BTU of heat. If you put one 55-gallon barrel of water (456-lbs. of water) inside your greenhouse it will give off 456 BTU of heat for every degree  the water inside the barrel drops over night.  For instance lets suppose after a day in the sun by evening the water inside the barrel has a temperature of 79 degrees F.  By the next morning the water has cooled down to 64 degrees.  That is a drop of 15 degrees. Therefore, the barrel has given off 15 X 456 = 6,840 free Btu's of heat into your greenhouse.  My greenhouse is 32-ft. wide and 72-ft. long. I have one hundred black plastic 55-gallon drums lining the side walls of the greenhouse. That is 45,600-lbs. of water in total.  Therefore, for every one degree that the water in the barrels cools down over night the greenhouse gets 45,600 free BTU's of heat .  So for even a 10-degree over night drop in water temperature 456,000  free BTU is given off into my greenhouse every night. Additionally, the water also helps to even out the greenhouse temperature during the heat of the day by absorbing much of the heat.  - Millet

[Millet]

Forgot to add that container plants grow well setting on top of the warm sun heated barrels due to the bottom heat the root system gets. - Millet

[sugar land dave]

So that's your trick!   

[gunnar429]

this may be an amateur question, but are the barrels sealed with a lid on top or open to evaporate and give humidity as well?

Thanks

[Millet]

Jeff all drums are black plastic 55-gallon drums tightly sealed. - Millet

[jmc96]

I'm interested to know how many degrees above ambient did your system keep overnight?

I had the same idea, and only an idea at this stage, (I'm still constructing the polyhouse) using 250 gallon IBC's. My poly house is 36ft long x 18ft wide x 12ft high in the middle. The IBC's are roughly a cubic yard in size, and stackable if necessary. My plan is to install 12 IBC's  along the back of the polyhouse, all interconnected into eventually several second hand  solar panels on the lower front, to boost the heat during the day. The heat generated by the solar panels will migrate upwards into the tanks. I will lose 12 square yards out of 36 in total, but can use the top of the square tanks as a bench, so not all space is lost. That's the plan, but your 55gal drums plan might be enough, and your hothouse is massively larger than mine.. I'm in zone 10 here in Aus.

[Millet]

jmc, your plan sounds interesting, it would be nice if you would keep us up to date as you proceed with your solar system.  My passive solar drums does help allot in lowering my greenhouse heating cost, but as my greenhouse is in zone 5 and additionally at an elevation of 5440 feet above sea level (1,800 M) still requires additional heating during our cold winter months. The 100 drums actually have not cost me the loss of usable greenhouse space, because I use them as a bench with containerized plants on top of them.   The best to your plans. - Millet

[chester copperpot]

I was looking at doing something similar, with a cold frame. Maybe some passive solar work would help increase the water temperature a little.

I live in a warm spot, so in the winter, I think a modified version of this might help:
http://www.thesietch.org/projects/solarthermalpanel2/

[Millet]

Chester copperpot, welcome to this forum.  Your post was really quite interesting. As shown with a little effort, one can build a solar collector and save money at the same time. The guy who wrote the article had a good sense of humor. - Millet

[chester copperpot]

Thanks for the welcome.

I have been looking into building something cheap for a greenhouse or coldframe and the water barrels seem to be a good solution to the winter nights. Obviously this project would work in summer, but I wonder if there would be enough solar energy to raise the water temperature enough to make a difference.

I just need to get my hands on an old refrigerator now to test it out.

My goal with growing food (including citrus) is to try and save money off of our food bills. It had worked with our garden, it has been consistently giving us more food value than the cost of maintaining it. So, I decided to branch out to fruits and berries. I am pretty far in the hole right now, but it's my first year. So, projects like this are really intriguing to me. I bought a cheap, pre-fabricated greenhouse and loaded that thing up with buckets. It kept pretty warm, even through the night the lowest temperature recorded was still 20-25 degrees above ambient, but it couldn't hold up to the wind.

[Daintree]

So, I just now saw this string.
Because my greenhouse costs as much to heat as my house, I am always looking for ways to make "free", or even "cheap" heat. 

I am wondering if I can use the refrigerator coolant pipe method and hook a whole bunch of them together in a series, position them along the north wall of my greenhouse (thus not taking up any floor space, which is at a premium...) and cycle the water through my 150 gallon pond in the greenhouse? 
The pond has a small fountain pump. 

Right now I heat the water to help heat the greenhouse, but I am using two really large aquarium heaters.  So I have basically reduced my gas bill by increasing my electric bill!
Has anyone here actually built one of those water heaters from refrigerator tubing, like the ingenious guy on that website?
Any other ideas for heat that does not take a lot of floor space?  I tried the barrels, but they didn't help much... 

And another thing - I use the water in the pond to water my plants, and my little parrots like to bathe in the fountain.  So how do I clean the coolant pipes really REALLY thoroughly?  And then, should I have the water tested?

[jcaldeira]

Millet, how much temperature drop do your barrels actually experience on a typical winter night?  I realize there's a lot of variables, but I'm just looking for a rough range.

By the way, one million BTUs, when generated by electricity, costs  over $25 USD so you have some good daily savings there!

[jmc96]

I've had my doubt's over refrigerant radiators, in my opinion, I think the diameter of the pipes are too small especially if you are wanting to heat a glasshouse of good size.  I'd be happy to be proven wrong. 
Have you encountered those evacuated tubes? man are they efficient. If you are not familiar with them Google will reveal all. You can purchase them individually  or a hundred or complete solar hot water units. They have a bulb on one end where the heat collects and  can be glued directly into a water reservoir, or what is really neat, they sell cheap portable versions complete with a reservoir on top that you can modify to suit.  These tubes will burn your hand on an overcast day, they are that efficient.

[Daintree]

Wow!  That is really cool!  I mean, hot!

[Mark in Texas]

I am pretty far in the hole right now, but it's my first year.

Don't feel bad.  My first avocado cost me $30,000. 

[chester copperpot]

I started a spreadsheet to see how long it would take once they broke even. I think it was a bad move. I know exactly how much I spent.

Oh well. We'll just see how it goes ...

[bangkok]

https://www.google.co.th/search?q=solar+water+heater&espv=2&biw=1366&bih=643&tbm=isch&tbo=u&source=univ&sa=X&ei=JSerVKWZOsXauQS33oLgDg&ved=0CDYQsAQ

Those things work very well. The refridgerator pipes are too thin, you can also use a black hose for it with a bigger diametre. Add a (solarpowered) waterpump to this system and you can heat loads of water in daytime. A pond would be ideal to heat up but connected waterbarrels will also do fine.

[Millet]

jcaldeira, I just noticed your question concerning how much the drop in water temperature is over night with the drums of storage water inside my greenhouse.   The solar heat up of the water barrels inside the greenhouse, and the drop in the water's temperature over night varies daily and also from season to season.  However, to answer your question I took the water temperature yesterday at dusk, and again the following morning.  Note that in the northern hemisphere during January the sun is very low on the horizon during the day, so January's solar production is the lowest of the year.   Anyway, the water's temperature at sunset was 61.5 F, the next morning it was 57.5 F, a drop of 4 degrees.  This translates to a release of 4 free BTU's of heat into the greenhouse for every one pound of water inside the barrel. Each 55-gallon drum contains 551 pounds of water. There are 100 drums (acting as benches) inside the greenhouse   Therefore, 100 barrels of water inside the greenhouse last night gave of 4 X 551 X 100 = 220,400 free BTU of heat. Note, I had the greenhouse propane heaters set at 55- F, so the water would not go much lower.  One could get 10 or 15 times more free BTU's by setting the propane heaters at 35 F night temperatures, but I want the extra winter growth, from the trees by maintaining the higher temperature range.  The amount of released solar heat will increase in February, March, and April.  From May through August the water storage actually helps cool the greenhouse during the hot summer days by absorbing the daytime heat. - Millet

[jcaldeira]

jcaldeira, I just noticed your question concerning how much the drop in water temperature is over night with the drums of storage water inside my greenhouse.   The solar heat up of the water barrels inside the greenhouse, and the drop in the water's temperature over night varies daily and also from season to season.  However, to answer your question I took the water temperature yesterday at dusk, and again the following morning.  Note that in the northern hemisphere during January the sun is very low on the horizon during the day, so January's solar production is the lowest of the year.   Anyway, the water's temperature at sunset was 61.5 F, the next morning it was 57.5 F, a drop of 4 degrees.  This translates to a release of 4 free BTU's of heat into the greenhouse for every one pound of water inside the barrel. Each 55-gallon drum contains 551 pounds of water. There are 100 drums (acting as benches) inside the greenhouse   Therefore, 100 barrels of water inside the greenhouse last night gave of 4 X 551 X 100 = 220,400 free BTU of heat. Note, I had the greenhouse propane heaters set at 55- F, so the water would not go much lower.  One could get 10 or 15 times more free BTU's by setting the propane heaters at 35 F night temperatures, but I want the extra winter growth, from the trees by maintaining the higher temperature range.  The amount of released solar heat will increase in February, March, and April.  From May through August the water storage actually helps cool the greenhouse during the hot summer days by absorbing the daytime heat. - Millet

Excellent!   Even your low January 220,400 BTU heat yield is equivalent to near $5.50 per night, or $165/month at average U.S. electricity prices.  It is a more even heat that most other heaters, too, doesn't pollute or dry the air. I hope you'll collect and share more data as time goes on.

Your water barrel heat recapturing method is something that many gardeners can learn from.   Do you have any photos to share?

[Millet]

Now that it is April I once again checked on the solar heating barrels of water inside the greenhouse to see how much free heat I am getting.  At the end of the day yesterday the water temperature in the barrels was 80-F (26.5 C).  This morning the temperature of the water was 69 F (20.5 C).  This is a drop of 11 F. Therefore, to calculate the BTU release from the 100 barrels of water inside the greenhouse it is.....
11 (drop in temp) X  456 (lbs. of water/barrel) X 100 (# of barrels in Greenhouse) = 501,600 Free BTU's of heat for the night of April 5. 2015.

Millet
(For the definition ob BTU see the beginning post of this thread)