Backyard Aquaponics
A place to discuss aquaponics

black pipe sounds expensive and ineffective. better would be to trickle water down a corrugate iron roof with a layer of plastic film over the top to stop evaporation.

janet, I don't understand why you want radiation at night? That would could your water down quicksmart.

The idea is that the heat radiates from the thermal mass (water) into the air to warm the entire greenhouse. It does cool the water, but that's not all bad. It all depends on where you want the heat.

look, I've done it with 200m of 13m (half inch) black poly pipe in various configurations, including with a fan. Do the heat exchanger calculations - it gave me something like 10W/C - it turns out that I was getting more heat from the pump and the fan than from the water!

If you want to do this properly, read my blog posts:
http://njhurst.com/~njh/blog/20061209
http://njhurst.com/~njh/blog/20061210
that does work, and works surprisingly well.

Janet, I am rather enjoying the wide variety of conversations that one topic can spawn.

I have looked at the 300 gallon Rubbermaid tanks and may go that way if I can't source a larger poly tank that doesn't cost a dollar a gallon.

I am going to have the fish tank, 6 2X8 grow beds 12" deep, and a 150 gallon return tank. A sump pump in the main tank to feed the grow beds, the grow beds will gravity feed to the return tank and a sump pump in the return tank will feed the water back to the main tank.

The S&S model uses very large capacity black poly main tanks that are above the ground and then the same grow bed setup I described for my system. The main tanks are enough to keep the greenhouse warm enough for them to grow plants year round. Now I am mindful that they have a 30 X 80 greenhouse with many main tanks and I will only have one or possibly 2 in a 16X30 greenhouse but I think it should work in a similar way.

My greenhouse walls will have on the outer surface a 10 mil clear lexan and another layer of the 10 mil on the inside. So there will be 2 layers with a 4 inch air space in between.

I can have, and don't mind having supplemental heating but if I can avoid using it as much as possible I would like to get it into the plan now.

I understand much better the passive solar concept and see the wisdom in having the tank above the ground and in fact insulated from the ground. The only issue I am having is sourcing the tank. I can get up to 8 foot in diameter tanks that are 2 feet deep and hold 700 gallons, but would I be better off to get the same holding capacity but in a deeper tank that may be only 6 feet in diameter? Would there be an advantage?

BTW, thanks to everyone for all of the input, it gives me much to consider while I am at my day job.

I agree with NJH, Foam board would seem to be the best option.

YOu need to be very careful with FG insulation bats, once they're moist or wet they are next to useless.

Af far as heat storage goes water is one of the best, so 4.5KL will do it nicely (one of the reasons i always suggest to go as big as you can with your tank.)

I've mentioned elsewhere that its having a hidden "heat exchanger" that is the pitfall, for me its my 24/7 F&D eposed sides bathtub.

Am considering turnong pump off at night, but will board up the sides first and gauge effectiveness.

Foam boards for insulation has my vote, but i think that burying the tank (as i did) is better than leaving it exposed. ground temps are often higher than the ambient air temps (overnight and when the ambient is cold)

Steve

Hey John:
Let us all know if you find a good inexpensive tank. The best thing I have found for me is a 500 gallon tank at Tractor Supply for like $400. It has a nicer aspect ratio than the less expensive 6x2 and 8x2 pools they have.

Hey John:
Here's a neat article about an inexpensive air to air solar heater on the front cover of the latest Mother Earth News, that has me all a-twitter:

http://www.motherearthnews.com/Alternat ... lar-Heater

Random thoughts on tank dimensions....

I'm afraid to fill my tank all the way to the brim for fear of the fish jumping out and the cat getting easier access to the fish. Given those fears, it makes sense to get a deeper tank rather than wider because there would be more water in it when I short-filled it by 6 inches. I don't know if my first fear is rational. I know the second one is.

The closer the tank is to a sphere, the less surface area it has to radiate/absorb from. That could be good or bad, depending on your objectives. Same statement applies to presence/absence/placement of insulation. If you do insulate, I definitely agree that foam board is better in situations where the insulation could get wet. (In case you missed it, Steve just lost a lot of fish due to freak weather and a bad temperature drop. His system is outdoors, not in a greenhouse.)

Two feet deep is the minimum I would use for a fish tank. However, if the tank is very deep, it could get difficult to maintain since you couldn't reach the bottom as easily.

The larger water capacity you have, the more stable it will be, not only for temperature, but for pH as well.

btw John, you can do it with one pump. See Mike Ferrini's setup, I think. Water in the sump is pumped to growbeds, and gravity returns it to the fish tank. The fishtank has a spillway into the sump. So water level remains constant in the fish tank, and the sump tank fluctuates. I drew a picture to help me understand it, but I think it's on my work computer. Let me know if you want me to find it tomorrow.

Also, why such narrow growbeds? Plumbing-wise, it will be easier to have fewer but larger growbeds.

Your ratio of tank to growbed is somewhere around 1:1. If you can increase your growbeds (or decrease tank size), that might be nice. 1:1 is fine, but 1:2 would be nicer.

Hehe, I just climb in my tank when it needs work - it's like having a private swimming pool! And I keep the water hot with my heat exchanger stuff....

My tank is 1.5m deep but I only fill it to about 1.2 - I once had galaxias and lost them when they all jumped out one night

Our local nursery is closing down and offering a 40% discount on stock. They have several poly fountain ponds 1800 dia and 600 deep giving a volume of 1500 litres. The price went from $380 down to $228 so I have a deposit down on one of them and I may buy two. I think it's a bargain, heaps cheaper than poly molasses troughs I priced earlier in the day.

These growbeds are actually galvanized sheep troughs and they are relatively cheap and available. The larger ones are also twice as deep so I will use these unless I find something better.

I agree about the tank to grow bed ratio but I really haven't landed on a tank yet so I will firm up the numbers once I get that part locked down.

Steve,

do you know where I can get the foam board from...and is it the same stuff you would use for rafts? Was thinking maybe using it as a lid for me tank at the same time

I live in Michigan. I built a well insulated greenhouse and built in a 3000 gallon tank 24'x5'x6' where 3' below ground and 3' above. The outter edge of my concrete foundation has 2" foam down to 4' (42" foundation). I use a heat exchanger to add more heat from a solar water heater. In Idaho I would expect to save energy by putting it into the ground. And I get the gravity flow back to the tank. I use no heater and maintain temps no lower than 35F when -10F outside. Lots of thermal mass - concrete and water. If you are heating, then tank sides may not experience much cold above ground. I guess the devil is in the details.

Best of luck and let us know what you decide.

bundaberg kid: foamex in bayswater.