tsmith-
What temperature do you maintain in that greenhouse?

You might try storing solar heat.

Get hold of a 55-gallon drum and paint the outside FLAT black. Then position in the greenhouse and fill with water. The idea is that the black paint will absorb solar heat and heat the water during the day and then release the heat slowly at night.

I intend to try this, but haven't yet.

Sue

One BTU = 1 degree increase for one pound of water.
One gallon = 8.35 lbs.
55 gallon = 459.25 lbs = 459.25 BTUs

Assuming you can increase the water temperature by 20 degrees, that is still very little BTUs.

The thing to consider is the following:

After a night's cold temperature, the tank of water gets very cold, the next day the sun is not out, then the tank of cold water will take away heat that's in the greeen house.

My point: water tank is a good idea, but design your system carefully.

dcarch

I pretty much agree with dcarch's comments. The heat in one Btu is about equivalent to burning one kitchen match, so 460 Btus isn't much. However, remember that that is 460 Btus for every 1 degree rise in the temperature of the barrel; how many degrees the barrel would go up is heavily dependent on a number of factors. Mainly, however, I am concerned that in such a small (6' X 6') greenhouse, putting a barrel in there is not too practical.

I would think covering it at night would help a lot...get some big blankets or sew something up...

franktank-
I presume you mean cover the GH, not a water barrel...

HD now sells ($12.00) 4' x 8', 1/2" thick form insulation boards with shinny aluminized reflective film on one side.

Beautiful stuff to use behind the greenhouse:
1. In the day time, they bounce sun light into the greenhouse (sunlight = 200+BTUs per SF).
2. Best insulation in the night time.

Also, have the floor in the GH as dark as possible to serve as geothermol source.

dcarch

I have just built 10 X 12 6M double layered hoop house. I have ordered bubble wrap for the North and west walls. I have a planter box on the North side then the South side plants are in black molasses tubs with 3-4" of gravel and drainage holes. I have installed 2- 55 gallon drums (water filled).

I thought the heated water might do the trick, but with the gloomy clouds lately, I'm starting to think I will need more heat. I have been trying to find a SOLAR way to heat the GH. I personally have a problem with paying to heat a GH when there has to be a better way for our environment and the checkbook.

I have looked into using the water heater sticks :) URL below. I was thinking this might use the least electricity. Does anyone have any other suggestions I could try? There has to be some great Solar ideal out there I haven't stumbled across yet.

Here is a link that might be useful: Sunleaves HeatWave 300

Hi there- these are all good thoughts and ideas, many of which I have toiled with myself. You can read about my greenhouse winterization and some solutions I've come up with on my blog...

Here is a link that might be useful: winterizing my GH and compost furnace

Sorry, I didn't come back to your post until tonight. Here is a good example: It is currently 35* outside and supposed to go down to 29*-31*. We have a possibility of 1 inch of thankfully rare snow tonight. Somewhere around 7:30 pm, over 2 hour after sundown, I recalled I had failed to light the heater. This is the first night I've needed to heat this season. That is in the back of the greenhouse, 15 feet away from the heater. So it was 39* when I started the heater and it has risen to 55* in the back of the gh @ 9 pm. I bought the heaters from WalMart for about $100 each. When the temps drop below 20*, I use two heaters, one in the back and one up front. I have two fans moving the warm air around. The fans are mounted near the roof. The front fan is an stove/oven vent fan salvaged from our kitchen remodel. The vent fan was probably 20 years old when we remodeled and has been running in the greenhouse about 12 years. The other fan is a small 8 inch fan I bought at the Thrift Store for $5. I also have a 20 inch box fan that I sit on the floor on really cold nights to circulate air down low. My gh is 22 ft x 9 ft. The front 16 feet has an 8 feet height and the back 6 feet has a 10 feet height. I hope this is helpful.

The temperature you want to maintain is important. I had 400 litres of water in my greenhouse this spring. I found that inside temperatures dropped in sync with the outside temperature until the freezing point. Then the temperature in the greenhouse stabilized. Water gives up a lot of heat before it freezes. I found that my starts survived even if they weren't always happy. I did lose some tomatoes that sprouted during a cold snap. I had a rain barrel, garbage cans, 5 gallon containers, and put a layer of ice cream pails in black garbage bags on my shelves with the planting trays on top. Next year I am using a 130 litre storage container that will double as a low shelf.

I'm beginning to think the most cost-effective method to heat a GH is geothermal, but I'm flexible by what I mean by "green house"! Certainly if you are heating it, you'll want to have some way to retain that heat, either with a 2nd layer (interior curtain, bubble wrap, foam panels) or structurally (think circa 1970's 'greenhouses' - buildings with a south wall of windows, the rest looks more or less like a conventional building.

To get heating and cooling via geothermal you have to plan ahead and size the system appropriately however, and I have no clue yet how to do that. But then heating and cooling costs go to fans to move the air instead of $$ for fuel and such.

Just a thought.

Geothermal would be ideal but the initial expense would be costly. Most geothermal is a result of drilling a "well" into a hot spot in the earth's crust and pumping water into the hot spot to create steam or pumping out hot water. If you had a warm artesian well, that would be ideal because you wouldn't have to pump water at all.

I have wondered about solar heating using an underground tank. Heat water using the well known roof-type solar water heater system. Circulate it with a small 120 V pond pump. When you need heat, you would recirculate the warm water through a non-pressurized radiator with a small pond pump and with a fan behind the radiator.

My view - and I'm doing garden trials now - is that hot water underground in tubes is cost-effective. A solar-powered pump is inexpensive and the other cost is 1/2" poly tube and the fittings. You can get a free barrel and heat the water in that by whatever and pump it around the floor of the GH. My setup is different but am moving water around pipes. Well below zeroF here last night and no problems this morning in the cold frame. I also see the high-end method of taking the hot air at the top of the GH and putting it underground to heat the soil. I also use dark-colored water in containers to absorb solar radiation to help things along.

Dan

"My view - and I'm doing garden trials now - is that hot water underground in tubes is cost-effective. "
I am not sure how this is to be executed. Will the hot water be in a container and insulated?
Otherwise most of the heat will be lost to the earth.

"A solar-powered pump is inexpensive"
Solar cell generates not much power. Depending on many hydrostatic factors, I think a water pump about at least 100 watts will be needed, A 100 watt solar panel is very expensive with other electrical and electronic to go with it. When you need it the most when the sun is not out, you donÂt have the power to operate the pump.

" I also see the high-end method of taking the hot air at the top of the GH and putting it underground to heat the soil. "
Not easy to make this practical at all.

Geothermal, where there is no hot spring type of underground heat source, I believe is a concept works best with a heat pump system to extract the small amount of BTUs in the soil.

"I also use dark-colored water in containers to absorb solar radiation to help things along."
Water does not have a lot of heat storage capacity (One BTU per lb per degree F) unless it goes thru phase change (144 BTU/lb of ice). Whatever heat it gives up in the cold nights, it will take away in the day time in your greenhouse.

dcarch

Hot air moved under the floor is easy and not too expensive. I used 3"sewer pipes with a 3" computer fan in the top of each pipe. Pipes are in the wall and air is pushed under a raised floor..trying to attach pictures

Here is a link that might be useful: trombe wall

Here is a picture of the raised floor, I have since removed the insulation and heat the ground directly...

Here is a link that might be useful: raised floor

It was 22 degrees this morning and my GH (192 sf.) was 52. I used about 3/4 gal of kerosene, running from 9PM until 11AM. Today, it warmed up to 25 outside and inside - without any heater, it got as warm as 83. On a completely overcast day I gain about 22-30 degrees running a 1200 watt heater, 600 watts gives me 15-20 extra degrees.

BTW, the temps inside are measured just a few inches above the ground - it always feels much warmer at my waist or head.

Mike

dcarch,

A number of different solar pumps exist for such an application already, and pipe under, say, an 8x12 GH, you are only running maybe 3-6 gal of water around at any one time - not much weight at all. Not a problem.

My coldframe setup - necessarily vague as I want to patent - is indeed a sealed and insulated reservoir and I WANT to lose heat to the soil, as that is the point.

I also use water to store and release heat to the GH (the point) at night. There is much precedent for such a setup, which was expanded to many GHs in earnest in the 1970s. Not perfect, but it helps.

My next big project (family hasn't approved) will be a GH with something like a trombe wall like polcat did. There is much precedent for this as well.

Returning to the OP, a drum heated however - drop an element in there and plug in and heat for maybe 10.00/month and then run 1/2" poly under the floor and run water thru there and your soil will be warm enough at ground level in the winter to grow greens. Pump, barrel, pipe, mesh for protecting pipe and time should be 150.00 tops.

Dan

I agree with Dan. My entire set-up is solar. With a small 3 panel PV array (harbor frieght for $169) and a couple of deep cycle batteries you would be surprised what you can run. I'm using a Recreation Vehicle pump (12 V) to circulate water from 2-55 gallon drums, no problem. It may even run a couple of misters in the summer :-) It was 4 degrees the other night and between the trombe wall and 55 gallon drums I was just above freezing. Thing is I don't have any plants or other thermal mass in there yet, so I'm hoping with the addition of a small propane heater I will have this thing heating (above 40 deg) for cheap.

Just an idea:

Get an electric generator and run it inside a greenhouse. Making sure that exhaust is completely safe to outside thru a heat exchanger. You get free heat when you supply power to the your home.

dcarch

polcat, are you using your solar array to heat your drums and pull water thru the pipes? Any light?

Dan