Barney did you look at the link I sent for titanium heat exchangers?
I am also in contact with Uponor a PEX manufacturer and trying to find out if this idea of PEX under the fish liner will in fact work. I have also contacted Aquatic Eco-Systems to find out what the BTU requirements would be for a 1000 gallon FT.
One of the company's I contacted for all of the plumbing and manifolds and PEX tubing and the water heater said that one of there customers in Boulder Colorado has been using PEX in his tanks for 6 months. I have contacted the company and I am trying to get them to have the owner contact me so I can find out for sure if this set up is in fact working and he is not paying a lot for his gas to do this process. I was told that he had 1000 gallon fish tanks with 600 feet of PEX on a separate zone and pump. 600 feet should give you a lot of heat exchange and is pretty cheap compared to a titanium heat exchanger or coils.
I will post more as I find out more.
That is true with fiberglass you may not have a way to fasten the PEX to the sides and the bottom area may not be big enough in the tanks you have. I have all wood with a liner and I can fasten pex to the bottom and side very easily.
I just got an email back from aquatic eco-systems and they are saying the the total heat requirements for the 4400 gallons I will have in my system to heat my fish tanks and troughs for a 9 degree differential will be about 119000 BTU's. The 1000 gallon fish tank itself was at 94,000 BTU's. The question is if I have a 120,000 or 140,000 water heater can I transfer those BTU's through 600 feet of PEX or not.
Does anyone know what the heat transfer for PEX tubing is? Or how to figure this out with 600 feet at 3" centers of 1/2"?
Yes i saw the link. I think having something fabricated would not be cost effective for me. If i had a sump large enough i would think about 1 large heat exchanger, however to heat 10,000 gallons it would not be sufficient. I think i am going to install a shell and tube heat exchanger. Let me know what you figure out with the pex tubing. I doubt it would work for me since i have fiberglass tanks but you know me.
If you heat the room it is in and it is a large greenhouse then to heat something to get it to 50 degrees takes a lot of BTU's. Now if you want the tank to be 75 because you have Tilapia in it then that is even more.
I have just finished getting some calculations done on my greenhouse. I have over 1500 sq feet of greenhouse. It will take 150,000 BTU per hour to keep it at 75 degrees. In our Colorado winters that means when the sun starts to go down at 4:30 to 8:30 in the morning I need to heat my greenhouse. So with a 70 to 80% efficient boiler I need about 2 gallons per hour to heat the greenhouse. With 16 hours of heating x 2 gallons per hour that is 32 gallons of fuel. 32 gallons of fuel per day is $64.00 per day or $2048 per month. If I do not have much sun in the day that means even more heat. I have to be able to grow and sell a lot of items to make that to be able to pay for the heat bill.
If I switch my fuel source to wood and purchase a wood boiler, which is better than propane as far as my wood costs( I have woods all around me) I would get free wood. The labor to cut it down would be my labor, so it costs me something to do this. Full cords go for $200 per cord for Ponderosa pine in Colorado. I would get about 15,000,000 BTU's out of a cord of Ponderosa Pine. A cord would give me 100 hours. I need 512 hours or more for the same example for propane. My costs go to $1024 exactly 1/2 if I was paying for it.
The next thing I calculated was what if I just heat the fish tanks to 75 and not the greenhouse or if I did heat the greenhouse only heat it to 40 or 45 degrees. The engineer said that because my fish tank is below ground and the ground is at 55 degrees the earth would help it stay at 55. Then he said that if I would insulate my tank with R-15 on all sides top and bottom that I would only require 400 BTUH to keep my fish tank at 75. The same cord of wood would be able to heat the fish tank for 37,500 hours. I still need 512 hours in a month to heat this fish tank but the cost is $73.45 per month.
So I think it would be better to just heat the fish tank rather than heat the whole greenhouse.
I have had him tell me and a engineer from UPANOR that using 1/2" PEX would take 400,000 BTU's to get it to 75 degrees but to maintain it would only be the 400 BTUH. The UPANOR engineer said that using 600 feet would totaly work to transfer the heat needed. They both were saying that if I used 1/2" PEX on my plywood tanks to use between 500 and 600 feet. My tanks are 4x8x4 deep. I have 1/2" plywood sides with PEX attached to the plywood. The earth is holding up the plywood and then I have a pond liner covering the PEX. A 1000 foot roll of PEX costs about $250.00. I am setting up an aquastat that will tell my heatsource that it is not 75 and I have a variable speed TACO pump that will adjust for the correct GPM's to make sure that it gets the correct amount of heated water in the PEX to keep it at 75 degrees. I can't see buying anything in my situation to heat my tanks except PEX.
Because I can't afford a boiler right now that can put out 150,000 or 200,000 BTUH I am only going to heat my fish tanks, troughs and sprouting shelves. I am hoping that I will not have that much problems with condensation because of how dry we are in Colorado. So when you look at what I need just to heat fish tanks, troughs and small shelfs I only require about 12,000 BTUH. I can do this with a 40,000 BTU hot water heater and have 28,000 BTUH left over to heat my greenhouse to what ever it gets to with that amount. I will not have everything calling for heat at the same time but worse case is I still have 28,000 BTUH left. I will experiment with this leftover and may find out it is not worth it or it does help so I will see.
I am still building everything and plumbing it all and may not get good results until next winter but because I am at the 6,000 foot elevation my nights will still get cold so I should get more data as things get going. My daytime temperatures are over 90 even in 0 degree sunny days.
Sorry to be so long but $250 in PEX to me is better than 1200-1500 in a tube heat exchanger. But you have to be able to attach it inside the tank.
Be prepared with ventilation even for winter since warm water like that in a freezing greenhouse will still experience condensation. Anywhere when it is cold out, the air is dry. That means warm water will evaporate quickly and the greenhouse being an enclosed space, the air will become quickly saturated with water and when that cold saturated air touches the even colder outer materials of the greenhouse, it will give up some of that water to condense on the outer skin of the greenhouse. Doesn't really mater how dry the outside air is. Dry air sucks up water quickly and cold air becomes saturated quickly since cold air can only hold so much water as soon as it hits a cold surface it can't hold as much water so gives it up to condensation.
During winter you will need to cover tanks to minimize evaporation but this could still cause issues with aeration since the water is still relatively warm. Depending on the cover over the fish tank, hopefully most of the evaporation can be directed to drip back into the tank rather than hitting the outside of the green house and escaping the system to drip on the floor.
I don't know if there is much you can do to avoid the evaporation from the grow beds. What kind of grow beds?