View Full Version : Heat/cool, water?? Air?? or both??

07-07-2013, 04:27 PM
Well, as the title says, What is your opinion or what has your research turned up as the best, or most efficient way to heat your greenhouse.

heat/cool the water ??
heat/cool the air??
heat/cool both??

I am in the process of final plans on my greenhouse. I started out with the idea of subterranean air movement for h/c transfer. I have since, been giving it second thoughts. I am now concentrating on h/c the water. I believe this will be a more efficient use of electricity and the water will make a better, longer lasting h/c sink, than the air, which has no mass to act as a sink. I also found the air ducts were taking up valuable space in my Greenhouse, where space is at a premium.
I have my own track hoe, so either way is readily accessible, I have just decided from my research that my money on hardware (pumps plumbing etc.) would be better spent insulating the foundation better and digging a trench for subterranean water cooling and relying on solar heat in the winter. Both from heat trapped by the water in the grow areas and fish tank, and from a circulating solar panel heating system
I am certainly interested in any ideas some of you have from your research or experience, whether it backs my idea up or disputes it, I am interested. My design changes will be cheap now, they are on paper, one month from now, they will be more expensive, they will be in a building. Much more expensive to change then!!
Thanks for your input

07-07-2013, 05:04 PM
This has been discussed here before. Poke around with the search engine.

If you use Deep water culture....you'll hold in the heat with the styrofoam rafts. Especially if the sides are insulated top some degree.
Media beds will lose heat and NFT would be the worst way to go.

That would be sweet if you were near the hot springs... 8-)

07-13-2013, 04:05 PM
Ok, Since this topic has not received any replies, well, I will state my opinion on the subject, if you think otherwise, I welcome your opinion.
I have decided through my research that unless you have a free source of heat ( I don't) then trying to heat the air is a waste of resources. The air is a terrible heat sink because it has no mass. Yes, I can dig a bunch of holes and put pipe in to hold some hot air during the day, but then I still must use electricity in the way of fans to move it down there and get it back out. I am planning a DWR system, so I will have lots of water. Lots of water means i have lots of MASS. I think I will spend my money on a pump instead of a fan and I will move my water to a place it can get heat in the sun the pump it back to my FT and DWR to store it. If I have us some kind of stove etc. then I will also move water via. a pump to the heat source and back to the DWR and FT. The mass of the water should do a fine job of giving off a bit of heat to the air in the green house. If it does not and all I do is keep my water warm, well, I think my plants will be just fine as they will be basically sitting in a hot tub with their roots. That's my opinion anyway, what is yours???

07-13-2013, 05:25 PM
you're in arkansas, and i really have no idea what your weather is like.. up here in the great white north, i'd go with a wallampini style gh, with lots of barrels full of water painted black on the north wall

07-13-2013, 08:00 PM
I am considering using a solar collector to heat water that heats the soil surrounding a buried fish tank.

07-14-2013, 05:14 AM
Thanks guys for the input, but I have to ask some more questions concerning this. Why are we adding additional water in barrels to heat, when we have a AP system full of water already? I know traditionally, greenhouses did this because they were not AP systems, so they had no large mass of water to heat and had to add it, but we have a large AP body of water already? With Green house space running on average of $50.00 per square foot to construct, each barrel is taking up approximately 4 square feet, which means each barrel is costing $200.00 in non-productive space. This would mean if we add 10 barrels we have to construct $2000.00 worth of additional green house space, just for the barrels. Of course we could offset that, by building grow beds above it? But now we are adding extra cost to support all that weight that normally could be supported by the ground?
When it comes to heating the soil around the fish tank, I go back to my original question. What are we, in the end, trying to heat?? The AP water? So why not heat it directly with a heat exchanger?? A heat exchanger in the FT or sump tank has the advantage of directly heating the water, therefore there is no transitional loss of heat to the soil. The other advantage is, if there is a problem we can easily access it for repair, no so easy if the piping is buried in the dirt under and around the tank.
Look guys do not take this the wrong way. I do appreciate the input. I am just trying to fully understand what the benefits are to these different methods, compared to a simple heat exchanger directly heating the AP water?? Working out problems here in our discussions is cheap compared to constructing something, then finding out it is not as good as we thought.

07-14-2013, 08:07 AM
I plan on having a bank of 15 gal barrels with a shelf/table top on top of them. In addition I plan on using a electric water heater either tank type or point of use. I am going to run the hot water thru a pex coil in the tank and then to the barrels. I may apply the same method to cool by using a drinking fountain condensing unit. with all that said could you do the same only bury the barrels?

07-14-2013, 10:11 AM
I have to ask again, Why are we trying to heat water in barrels, that has no other use than to try and store heat, when we could be heating the AP water directly and storing our heat in the hundreds or thousands of gallons of water in our AP system????
DB, I am just not sure what you would gain, by burying a bunch of barrels then heating the water up in them?? I understand since you are planning to use electric heaters and electric water fountain coolers, efficiency is not your main goal, but I am still not sure why you would not simply forget about all the barrels and heat up the water in your AP system, or cool it, depending on the season? What is to be gained by heating water in barrels then trying to transfer that heat to the water in your AP system?? If you have the ability to heat water in barrels, you should have the ability to heat water in your AP system. Efficiency wise it only makes sense that it would be more costly to heat more water ( barrel water, plus AP water) than it would be to heat less water, just AP water??
I think people are missing the fact that the reason they used big black barrels with water, as a heat sink in green houses in the past, and still today, is because they lacked the AP system, that has a large water mass and acts as a heat sink all by itself.

07-14-2013, 04:20 PM
I understand what you are saying, but in my opinion I think you would have to heat the water in the ap to much to keep the greenhouse warm and constant. the more mass will give you a more even heat at a lower temp. For example: you may have to heat the ap water to 100 degrees to maintain 70-75 degrees in the greenhouse. I think if you had more water (storage barrels) at say 85 degrees your heat transfer from both the ap and barrels would be more stable. I too am concerned about efficiencies. I want the most solar storage as possible during the day. my heated water will hit the ap first then cycle thru the barrel back to the heater. I could be full of it but that's my plan. I need to maintain at least 60 deg during the winter. Do you have other thoughts

07-14-2013, 05:23 PM
I am glad you did not misunderstand me, I certainly do not claim to have all of the answers. To be honest, I am not all that concerned with air temps in the greenhouse, if I can maintain water temp. Having said that, I think the water temp will have to swing some, but I think that can be kept to a temp. that will not be detrimental to the plants or fish. I am fairly convinced, if I can maintain water temp. in a growing range 65 to say 75 during the winter. Then even if the air temp falls, as long as it stays above freezing, the plants should do fine, because their root system will be in warm water. They are not growing at night anyway, just sitting and waiting for the sun to come back up. I would also be surprised if I was able to keep the water temp. I am shooting for, if the air temp fell very far. I am planning a fairly well insulated Chinese style greenhouse with both end walls well insulated and the north wall well insulated and planning a insulating kilt on a cable system on the inside of the ETFE roofing at night to hold in temp. I will also be insulating under the concrete slab around my DWR troughs and very well around my FT. I will be building it next month and i will post some pics when I do. My plans are for my fish tank to be partially down in the ground, not because I think that is better, but because of space, I do not want to build any more space than I have to which is not being used for grow beds.

07-15-2013, 05:23 AM
your growbeds will be the biggest transferor's of heat into and out of your system..they act like a damn good heat sink.. so heating the water, every pass through the growbeds cools it, or visa versa..
that and the surface of your ft unless you cover it with insulation..

07-15-2013, 07:12 AM
I agree, media grow beds transfer a lot of heat/cool to the surrounding air, especially in flood and drain systems where the water draining pulls in the surrounding air down into the media. I am planning a DWR system, the troughs will be insulated on bottom an sides and a 2" raft on top will actually provide insulation for all 4 sides of the grow area.
Sorry, I may have used the wrong terminology and miss led someone into thinking I was planning a media bed system.

07-15-2013, 11:13 PM
Sorry, I may have used the wrong terminology and miss led someone into thinking I was planning a media bed system.

DWR system = Raft system :mrgreen:

07-28-2013, 02:21 PM
I have a background in greenhouse construction, and have built the so-called "Chinese" model in Texas back in 1980 and more recently.
Your thought path and mine are parallel. Cooling is primary for me. The mass in the water has to been very beneficial. I am designing my raft beds, sump and fish tank out of concrete to introduce more mass. I will use "Thoroseal" to waterproof the concrete or CMU so that I can avoid using plastic liners. (Just can't wrap my mind around plastic) Since complex systems tend to fail, I am leaning away from Phase Change Materials and heat/cool tubes but the jury is still out. First greenhouse to be 48' x 32' x 20' tall.
There is a solid roof on the North that you can walk on to make putting on the plastic and 60% shade cloth safe and easy. I'll have 1 media bed 48' x 3' ; one raft 42' x 6' and a sump dug into the ground. Fish tank to have view window. About 1000 gallons (+ or-).

07-28-2013, 08:54 PM
I personally have a huge problem with Chinese style greenhouses, but I will leave that for another thread when I have the time to dispel it and verbally tear it down.

Then I will introduce and build my American Aquaponic style greenhouse (designed especially for Aquaponics - commercial or backyard), on paper naturally.

No bucks for a greenhouse at this time, but I have built them before and I do have the knowledge and experience necessary to prove my thinking. :mrgreen:

07-29-2013, 03:03 PM
It would be interesting to hear your issues with the "Chinese" style greenhouse. I personally have operated one with very little energy input.