Just put a large black plastic lawn/trash bag over the top of the barrels, works and you don't have to dye the water or paint the barrels.

M

That's really great to know, because when I got them home they turned out to be whiter/thicker than I had thought. I was dreading washing/sanding/painting them. but I scored 8 drums. They get disinfectant in it. Woohoo!

M, does this work as well? What is you experience? Wouldn't the air layer insulate the barrels?

I have an experiment going right now with black water, blue water, and a couple of different paint techniques. I'll see if I can add a black bag arm to the study...

I agree with not letting the water be exposed. Sure, it transfers heat better if you have evaporation, but the algae mess and mosquito breeding easily offsets that. My exposed water scared my little cousins. ;) I guess they thought it was The Blob or something. To counteract the algae, I added bleach -- but that only helped for a while, and it corroded the plastic containers until they were too brittle to use.

As for the air layer, yes, you'd want the trash bag to adhere tightly to the barrels -- otherwise, you're making it as hard for the barrels to heat up as you are slowing down its heat loss into the greenhouse. A thin film with no air space shouldn't increase the R-value too much. I just painted and sealed my barrels; I found it simpler that way.

Of course, what you really want, insulation-wise, is building a greenhouse within a greenhouse -- ideally, clear PVC around black barrels (note: I don't know if shrink wrap is thick enough to matter; it's pretty darn thin), as PVC absorbs thermal IR. It'll still reach thermal equilibrium, but it'll be at a much hotter temperature and provide a steadier day/night temperature balance, in addition to having there be less radiative heat loss out your glazing. Any sunlight that doesn't make it past your PVC simply heats it, thus heating the barrels and greenhouse, so transparency losses aren't a big deal. A potential improvement is to have a low-power fan that comes on at night to circulate air past the barrels and into the greenhouse. Of course, all of this adds complexity and cost.

Yeah, I agree with karenrei, clear is the best, air tight if you don't want fish.

I wonder whether it would be worthwhile putting an evacuated tube solar collector outside and heat a smaller quantity of water much hotter (say 400L to 85C) and bleed that heat out on demand. We can buy 20 tubes for $700 here and they work down to -40C or so. Of course, you should aim to get as much heat into the grenhouse during the day as possible first!

Money is an issue and I live in the middle of SC. It only ever gets to 20F for a few nights. There is no power to this structure, and there never will be. It's only for me to putter around in.

The coldest night we've ever had was 10F, and I wrapped my babies in rags and plastic and they made it. I keep house plants outside in the summer and move them into the greenhouse during the winter because my pets think they are a salad buffet if they are in the house. About Feb. I begin trying to start outdoor things.

Previously, I tried heat with compost, and was very displeased when a rat burrowed under the ground and came back up inside. The floor is only damaged linoleum so it did nothing to stop him.

I think I will just get the biggest trashbags I can find and tape them tightly. These barrels have an opening from a screw cap big enough to stick 2-3 fingers in. They were obviously used with some kind of pump to dispense the soap. Since they've been sitting out in the woods behind the animal shelter, they have a few dead leaves, bugs, etc, (which I am ignoring all the ones that don't float up and rush out with the water) there will be Blob growing in them. I don't think it will matter.

Rats produce a reasonable amount of heat per kg. Perhaps you should have encouraged them instead?

Does anyone have a positive experience with compost based heating? Perhaps using autumn leaves, cow poo and straw rather than putrescible waste?

There are simple formulas available to determine the amount of heat that can be collected in water filled drums. Also, putting any covering on closed water containers inside the greenhouse will not produce more night-time heat. The black plastic might get warm, but the water inside the drums will equalize with the temperature inside the greenhouse.

Here is a link that might be useful: greenhouse vegetable production

cuestaroble, firstly, advertising your business is against the gardenweb T&C. Secondly, claiming that covering drums will not produce more night time heat is clearly rubbish, as 10 seconds of thought will prove: If I can get the water hotter by controlling evaporation and convection I can store more heat per kilogram (http://en.wikipedia.org/wiki/Specific_heat_capacity). If I can store more heat, I can recover more heat.

Anyone who wants to be a consultant for greenhouse design should understand this.

Here is a link that might be useful: Businesses Using the Forums.

nathanhurst, Thank you for your response to my post. It is not clear to me how you can control evaporation any more than in "closed containers inside the greenhouse", as I stated. Also, there is no heat storage advantage by controlling convection in this situation. Finally, I am aware of the specific heat capacity of water, thus the reference to the simple formulas. The reference to my web site was to give links to other useful web sites. I should have just listed the appropriate specific links, such as the one here now. Thanks again for for your comments.

Here is a link that might be useful: solar greenhouse information

Let's see:

2. If I can heat water up further during the day (to a higher temperature), I have more heat stored.

3. More insulation means greater temperature differentials for a given heat loss power.

4. More heat stored means more heat available at night.

Ideally our tanks would have a similar design to solar domestic hot water systems, with insulated storage, insulated collectors, selective surfaces and double glazing between the water and the greenhouse. The heat wuold then be available on demand. I can heat water to 140C using evacuated tubes in mid winter (assuming enough collection area), which is a temperature differential of 120C or so compared to maybe 10C using uninsulated collectors. This means that I get 12 times the thermal storage capacity per kg of water, and maybe 4 times the volumetric storage including insulation and collectors. More importantly, I can recover far more of that heat for a given mass flow.

Evacuated tubes are so good that you can put them outside the greenhouse, increasing the collector area further. They are quite cheap and probably compete with propane heating once you factor in the fuel costs (let alone the climate change costs :). Cheaper people might use a simple design based on tarpaper, PVC film and a hydronic heating pump/controller. Our house roof is about 50m^2 to the sun, compared to 10m^2 to the greenhouse.

Practically, storing 85C water with cheap foam insulation could make week long thermal storages doable.

I'm sorry if I ambeing thick, I'm rather jet lagged atm (and thus shouldn't be posting :).

(That website quotes trombe walls as good design, which makes me somewhat dubious of the rest of the material...;)

In a few months, I'll let you know how it turned out.

Check back in a couple of weeks. I have an experiment going using a variety of different containers, painted, black ink, blue food coloring, and black plastic bag. Preliminary results show the black plastic bag technique to be inferior to even an unpainted container and 16-21 degrees inferior to painted containers. When I have good data on the black bag arm of the experiment, I'll post back.

SB

stressbaby, you really should add 'clear cover' to your collection.

I'm not sure I follow you Nathan.

Well reading your list of trials, there is no mention of whether you are considering covered vs uncovered containers. I think a winning combination would be black chrome inside, in an insulated container with two layers of clear film (with air gap) over the top. The film should be TIR blocking (such as PVC film?).

The largest cooling effect on your water is going to be evaporation. Such a clear lid lets the light enter as visible energy but not escape as TIR.

Nathan, these are covered, sealed containers 1/2-1 gallon size, therefore there should be no evaporative losses. They are, granted, much smaller than those commonly recommended for the GH, but I don't have room in my GH for an experiment with 10 different arms using 55 gallon drums. My original intent was to see if I there was a difference between black ink and black paint (so far, just a little bit). Since then, various arms have been added to the experiment, including the "black plasic bag over the container" arm mentioned above. I intend to collect some summary data and present in a new thread.

This leads me to a statistical question. Using average absolute temps for each container seems to be less than the ideal way of summarizing and analyzing the result. Differences in the amount of light or ambient air temp on a particular day may lead to great differences in the maximum temp in a given container. I wonder if it would be better to analyze based on either 1) the absolute or relative increase (or decrease) in temp over ambient air temp; 2) absolute or relative increase (or decrease) in temp over baseline morning temperature; 3) absolute or relative increase (or decrease) in temp compared to a clear container control. Just wondering if anyone has thoughts...

Stressbaby,
Assuming that the purpose of your trials is to determine which type of container absorbs the most heat, the simplest method would be to just measure the temperature of each container right after sunset. If each of the containers are in the same environment, this should tell you which is most effective in absorbing heat. The clear container control should definitely be in your study. Glad you are testing the differences. Please keep us informed.

It very much depends on what you want to optimise for. If you want to make a small amount of water as hot as possible, you might spend a lot of effort trying to keep heat in over night, but for the purpose of a greenhouse, you may want that heat to leak out just fast enough that your GH is still warm the next morning.

For a given sized container, I think it is reasonable to assume that if the collection area is black, the amount of energy absorbed is constant. The question then becomes whether you want the heat now or later.

Stressbaby,
Since your preliminary data is giving results that are actually those predicted, I wanted to give a little more input. In using plastic covers to solarize soil beneath the plastic (not unlike the idea of plastic containers to heat the water contained within), much research exists to show that clear plastic results in higher temperatures than black. The soil solarization web link is attached.

Here is a link that might be useful: soil solarization

If my glasshouse has a concrete floor, won't this act as a heat pump? Can you use a pile of bricks as a heat bank? Why is water so good?
Barbara B

barbara_b,

Anything "heavy" in there is good, bricks, old engines, planters...

Water is good because it takes so much energy to warm it up. About three times more than it takes to heat up a rock the same volume.

Also water has a magical property that is not found in other natural materials. The solid form (ice) is less dense than the liquid form (water) This magical property is what allows fish in ponds to live through the winter.

When you have ice forming on top of the water at 0C (32F) then the water at the bottom of your barrel is still at 4C!

Water in a regular greenhouse helps to buffer the hig and low temperature. Water in an unheated greenhouse is used to prevent a killing frost in there.

The main drawback of water is it is not structural, you cannot build with it. It has to be in a container.

(yeah people are yelling IGLOO!!! I yell back, water is buffering the temp in there. It may be 32F in an igloo but it is better than the temp outside!)

Cuestroble, thanks for that link. It may help to explain why the container in the black bag was actually cooler than the unpainted container. I may toss the blue food coloring and try a second container with black ink, wrapped in a clear bag.

Nathan, I have measured morning temps. These containers are so small that they give up their heat by morning. Interestingly the containers (against the south end of the GH) are consistently 3-4*F under ambient room temp by morning.

stressbaby, they are probably lower because the greenhouse got colder overnight and they are storing up some coolth. The other possibility is that they have a direct view of the sky at night and are cooling by radiation. With an insulated bucket on a cloudless night you can freeze water even when the air temp never drops below 0.

Hi nathanhurst, are you studying Jane Austen? That's the only place I've ever seen the word "coolth" used. Barbara B

I've only watched the TV shows - my wife loves them but they're too esoteric for me :) You might like to read "To say nothing of the dog" though, by Connie Willis.

Do you remove the drums of water for the summer? Barbara B

No, in summer they keep the greenhouse cooler.

Stressbaby:

My simulator actually predicts that :) It's about radiative heatloss. You have near-blackbody buckets with a great view of the outside. There's going to be a lot of IR heat exchange** with them.

You can wrap your buckets in PVC to reduce that if you want to.

** - Even when it's cold outside, the outside is radiating IR as well. Your hotter buckets just radiate more of it -- and since IR is proportional to temperature to the fourth power, it makes a big difference.

Would milk jugs work well in a GH. They are cheap and plentiful.

Yes. They have reduced my electric heat usage in my germination greenhouse. I have everything from 5 gal water bottles, to one gal. milk jugs to 2 liter soda bottles. I wanted to fill the otherwise unused area under the benches with this "thermal mass".

With all the talk about clear black and ink I was just wondering how just a plain olé milk jug would do. Since the space at the back of the shelf is not used I could line the wall with the jugs. If it don't help much I'm not out much.

gardenerwantabe, a one gallon milk jug is one of the painted containers in my experiment.

I don't have much room in the GH for 55 gallon drums, so I squeeze mine in where ever I can. I have perhaps 20-30 gallons of water underneath one bench. I also line the jugs up on the back wall, just as you say. One of the things I intend to do this weekend is make a record of the temps of these containers underneath the benches, not exposed to light, just to see how much heat they store/release into the GH...just to see what their contribution is.

Karen, my experiment containers are inside a glass GH, and glass is relatively opaque to IR. So any heat the containers emit should still be trapped in the GH, right? I figured that the GH doesn't have perfectly even temps and the temps were just a few degrees cooler up against the glass on that south end.

Stressbaby:

Interesting. Yes, glass doesn't transmit much thermal IR, so that means not much heat exchange with the outside, although you'll still be exchanging IR with the glass itself. Also, if the barrels are more of a blackbody than the rest of the greenhouse, that could account for some as well. Still, with no exchange with the outside, that makes me wonder.

These are sealed barrels, right? Because you can get evaporative cooling otherwise.

Stressbaby I sure would be interested in seeing the results from your test. Please post them here.
I think I will put some milk jugs in my GH don't plan on painting them just wash out good and fill with water. I don't know if it will do any good but I have a lot of empty jugs so it will cost me very little to try it.

Results so far are 35-40 degrees F higher than outside temps and I have not caulked the greenhouse yet. The trash bags are only slipped on over the barrels and fail to reach the floor by about 6 inches. I am very impressed.

I check temp every day at 6 pm.

Marie99,
Thanks for your update. Your results are indeed impressive. Are your plastic covered drums of water receiving direct sunlight or are they under benches?

I"m not sure that checking the temp of the GH at 6pm proves much. I live in northern Indiana it is getting cold here now and I have no water in my GH but with outside temp of 40F on a sunny day the GH was 110F
Since milk jugs are plentiful I think I will fill some with water and try them if they don't help I'm not out much.

I think that what we need to know is the degree to which the containers are warmer than the air inside the GH. This is the heat that will be reemitted at night. Theoretically, the GH could have gotten 60 degrees warmer than the outdoor temperature. If so, water 35-40 degrees warmer than the outside temp is actually a lousy result. My containers in my experiment are 20-25 degrees warmer than the air inside the GH. Marie, can you measure your temps like that?

Another way to measure and assess this is to check the temp first thing in the morning and then again in the afternoon. The difference reflects the heat gained (and therefore the heat reemitted after dark). What we're really after is daytime heat storage and nighttime heat release.

Stressbaby I agree the temp of the GH once a day proves nothing. Maybe a check of the water tamp morning and eve.
That way you would know how much the water was warming in the day time and how much it cooled at night.
With no water my GH is getting cold at night and hot in the daytime. I don't have anything in it now so it don't matter but I would like to find out if this water thing will help before I start plants from seed this spring.

All my drums are in direct sunlight. I am getting a large plank to lay over them to use as a work surface and removing it when not in use.

I too am new to greenhouse gardening so forgive my ignorance. I've painted 8 milk gallons black and plan to place them in the greenhouse tomorrow.

1) Are they to be capped or does it matter as I've thrown out most of the lids?

2) Do I fill them with lukewarm, hot or cold water?

starfan,
1- you want to cap them to stop evaporation and keep out algae, etc.
2- just use cold tap water. The real purpose is to absorb free solar heat during the day to release at night.

Thanks so much cuestaroble for your prompt response.

My Greenhouse is 10Wx12Dx10h. I currently have 36 Gallons in Covered/painted black Rubbermaid storage containers, under each of my plant benches, with 8 benches, that is just 288 Gallons of water. I have also been building a Wall of blank painted two liter bottles around the outside edges of my benches (Except on the potting bench where I need the low angle light.

I also have one painted black steel 55 gallon drum in one corner

I learned a few things right away and one of them by accident. The Water Storage being right under the plants is maintaining a very Constant temperature for my soil. I learned this by placing my temperature probe between the water containers and the plants to keep the probe out of direct sunlight.

Anyhow, on to the Computer results.

My Computer gathers the outside temperature and the greenhouse temperature every 15 seconds.
I keep a running graph of the temps displayed on my computer 24 hours a day, and then store the data.

The Data Cleary showed a Few different results.

1. Prior to putting the water in, the Greenhouse daytime Temps were easily breaking 110F to 120F

2. Prior to putting the water in, At Sundown, Greenhouse temperatures would quickly drop down to and match outside temperatures.

3. After putting in the water, Daytime temps in the greenhouse have not even exceeded 100F, even without any venting.

But here comes the real magic

4. After putting in the water, at sundown the Greenhouse temps will drop down close to outside temps (Around 65F.... but then the magic comes. As the outside temps continue to decrease, the gap between greenhouse temps and outside temps continue to increase, 5 degrees separation at 60, 10 degrees of separation at 50, and 15-18 degrees of separation at 40 (Our lowest temps so far this year have only been 39f), but I look forward to see the results this winter, It would be nice to see 20 to 25 degrees of temperature difference when we go below freezing.

All this with less than 350 Gallons of Water, that most of, was easily stored in the unused space under my benches.

I am continuously adding two litre soda bottles, and 1 gallon milk and water containers from my house and my neighborÂs house, I am hoping to get enough water in that I will not have to vent heat during the day... Heck if I get enough water in there perhaps I will not have to move my plants out in the summer, if I use some shade cloth.

I was thinking about playing with some of the Clear bottles and only painting the side the faces the greenhouse walls black, and leaving the inward facing side clear,(would that allow the heat to escape better at night?

Jimmydo, check out my experiment thread. I had clear containers with all sides black, 3 sides black, and one side black. You can see the difference in storing heat. In my GH there was no difference in the container temps by morning...all the containers (1/2-1 gallon) had dropped to ambient temp or below. I would have to do repeated measurements through the night to see how fast the temps dropped, but my guess is that they were at baseline temp in just a few hours.

Do you have a way to check the temp of the water in the containers? Maybe compare the bigger to the smaller containers? This would give us an idea of exactly how many BTU you store. Feel free to post that on the container experiment thread.

Nice job.

http://www.flickr.com/photos/98264631@N00/?saved=1

For what it's worth. Previously, I had covered the lower half of the building repeatedly with cheap plastic tarps. This time I used ruined and left over linoleum, plastic hall runners, etc. Also, the shelves were attached to the walls. I made that bench out of the shelves and got rid of the tall plastic shelf. Now nothing is attached to the walls and everything is about 10 inches out from the walls so if I do get another rat, I can let my Jack Russell Terrier loose in there and he can get them. We live out in the country, there are farms nearby and a chicken plant, so we do get rats. It's 50 outside and 90 inside and I have not caulked, ever.

I have an 8X12X9 barn shaped greenhouse, with 10 mil walls. I live in high desert. Temperatures run 30 to 40 F in the days and 10 to 25 at night. I have (4) 55 gallon barrels painted black, The barrles are on the southside of greenhouse. filled and sealed. We get losts of sunshine and attain between 85 and 90 degrees each day. It's usually 80 by noon and it begins to cool by 4:00 pm in the afternoon. I monitor my temperature remotely at night and rarely get more get more than 5 to 10 degrees above ambient outside temperatures in the middle of the night. Not enough to keep plants from freezing in Jan or Feb. I did fill these barrels in December with very cold water. I am thinking the core of the barrels may have never warmed up. Hoping for success in March. Any thoughts as to why I can't attain a greater temperature differential? I was hoping for 25 degrees?

My Dad years ago used clear plastic to seal off his carport that faced south. He had several 55 gallon steel drums. The south side was painted black and the interior side was painted white. He successfully raised plants in the carport. We lived in Memphis so it never got extremly cold.