Backyard Aquaponics
A place to discuss aquaponics

I found these on ebay, we have just gone into Spring and managed to get our Barramundi through Winter ok.

http://www.ebay.com.au/itm/Premium-Qual ... 19d14c7d4b

Not trying to promote this guy either.....

Interesting Rosey... hadnt seen that before... how hot do they get?

It's basically linear, based on the BTU's put into the system. The only time when the temp change is not linear is when there is a phase change; ie to melt, vaporize, or turn the heated material into plasma. The reason 15° water has a larger temp change when mixed with 100° water, than when 75° water is mixed with 100° water is because the 15° water is taking more BTUs from the 100° water. There are quite a few variables that cause this to not be strictly linear in application though when we are talking about solar energy collectors.

The reason for temps in cooking is to produce the desired chemical changes, at the desired time. Less heat = lower rates of chemical changes and possibly no chemical changes or elimination of some of them. Actually some may be basically eliminated with higher cooking temps as well. (ie turning the collagen to gelatin in a beef brisket, as higher temps cause the water to boil off before the change can happen)

I disagree.
Basically the faster you pump the water the better.
Like you said heat transfer is greatest when the temperature difference is the greatest.
So allowing the water to heat up in the collector will reduce the amount of heat that is transferred to the water. Also if you allow water to heat up in the collector, as soon as it leaves the collector more heat will be wasted via the pipes etc (because the water is hotter, heat transfer AWAY from the water will be greater)

(I think I got that right)

Yes I looked at these and Id need 2 x to help much. Thought a 12v DC pump (also from Evil bay) could run the thing from Solar, ie on during sunlight hours, only 20+ watts I think
If you were to leave OUT a check valve the water in the collector could drain back to sump hence not cooling overnight.
I was also going to setup second main pump which bypasses grow beds at night
Anyway winter now past so on the plans for next year!!

I worked for a company in melbourne that did solar hot water for swimming pools. what we put on the roof was essentially long loops of 5 or 6mm rubber pipe (hundreds of them, they came in strips of 8 or so), attached to a PVC manifold at one end. pump the cold water up one side, collect the hot water on the other.

Apparently, they worked magnificantly. They actually pumped the water quite slowly, using High Head, low volume pumps (apparently they tried all sorts, the these worked the best). They also sold thermal blankets for the pools to help keep heat in at night (possible for a pond i'd think). One thing they did say was that fountains or slplashing water returns significantly decreased the efficiency. apparently the cool the system more than the system can heat it.

Orcy do you have any info on the high head low flow pumps?
I have been wondering what is available in this format..

SuperVeg, unfortunately I have no details at all, but they were made by davey. proper pool pumps, generally with a strainer pot on the front. I was slave labor for that company, so I didnt really take that much notice of what we were doing except that I did enough to get paid the pittance they were offering.

no worries

Normal pumps, like used in AP, do not have enough pressure to force water through the system. You need a pressure pump (like on a rain water tank supply). I have 300mtrs of 19mm poly and have it on a timer to come on every 1/2 hour. It takes 10 mins to run through at a temp between 45 - 50 deg. I only run it between 9:30 and 4:30 on sunny days.

Small pipes will clog with junk in AP water, no chlorine to keep them clean.
high pressure = high running cost
Pool pumps arent very high pressure though but volume? I guess higher Pressure than aquaria pumps many are used to

AP pumps your wasting your time, as I said a household rainwater tank pump (dont need a pressure switch on it) pumps at 40 psi and ensure you clamp the joints. Would not not use less than 19mm tho.

Can that poly tube handle those temperatures? Would it leech out any nasties?

Hi guys, first virgin poster here (great place for info btw). Just wanted to address the debate on thermals and flow (Mechanical Engineering and Business Administration student). All the quotes I saw on this thread regarding heat transfer are completely true, but nobody seems to be thinking of heat in the way that you're supposed to in a system like this. Here's my 2 cents:

1) Rate of heat transfer is absolutely and completely irrelevant.

- What you actually need to be thinking of is the QUANTITY of thermal energy retained in proportion to the initial investment and the operating costs. It doesn't matter how fast or how slow your water is getting the heat, it just matters that it gets as much heat as possible.

2) A separate tank for the solar heater is absolutely and completely irrelevant.

- That tank is used in solar water heaters in which hot water is required at a higher temperate (AKA to give you a limited hot water supply at home). The tank serves no purpose in AP because we are just taking the hot water and diluting it in colder water at far too fast a rate for it to matter. It's actually HURTING your efficiency because it's just added surface area to your system in which heat can escape.

3) A separate pump to feed specifically into the solar water heater is absolutely and completely unnecessary (unless you're barely getting by on your current pump).

- The main pump that runs water from your sump to your FT (or your grow beds or filters, depending on how you have it set up), should have a little bit of untapped potential left. Feeding a small line straight off of this pump going to the solar water heater is a cheaper, more efficient, and more productive way of heating your system, rather than getting a gazzilion GPH pump separate just for the job.


Now, what do I mean by "Think about quantity of heat retained"? Here it is:

- If you pump too fast you will lose heat through the pipes. This is simply because you are running water that is 60-80 degrees through pipes that go outside your greenhouse, usually sitting in ambient air that is colder than the water you are trying to heat. If the rate of flow is too high then the solar array will not add enough heat to offset the loss induced through piping, and you'll have a net negative impact on temperature.

- If you pump water too slow you won't be maximizing your efficiency. Your solar array will only heat up so much. It will heat up to the point at which it is losing heat through ambient air attrition at the same rate as it is gaining heat through sunlight. Basically the hotter the solar array gets, the greater the rate at which it loses heat to the ambient air (due to the temperature difference increasing).

So what's the punchline?

- As in any engineering system, there are far too many variables for me to give standard advice across the board; each person's set-up is different from the next, so what might be the right flow for someone would definitely not be the right flow for the other. Here's my general advice:

1) The best money spent on a solar array is money spent on a) heat gain (surface area; make it bigger, painting black) and b) insulation (Insulate the housing of the array, insulate any pipes that leave your greenhouse going to the array, etc.)

2) It's better (especially in colder weather) to run water through the array at a lesser rate rather than a greater one, due to the explanation provided above. This is why I suggest running a very small line (with a valve, preferably with a timer so it shuts off at night automatically) from your main pump to your solar array, and try to avoid running all of your water through it. The best way to gauge what rate is the most efficient is to find a similarly-sized commercial array and observe/ inquire about their flow rates. Bear in mind that these systems are used to heat a tank (may even use a siphon system) and your flow rates typically will be higher, just nothing too crazy.

3) Insulate, insulate, insulate...

4) Did I mention insulate?

5) If you are running a larger system (commercial or otherwise), do not FOR A SECOND think that you can get away with pure solar heating. An appropriately-sized solar array may provide you with adequate heat for 364 days out of the year, and then one cold sad day when the sun don't shine and your water temp drops to near freezing, all of your fish will die. You NEED a backup. fortunately, backups don't cost all that much initial investment, they just use up lots of electricity and that's why we're only using it to supplement our solar heater. A few pool heaters will do just fine, but make sure it doesn't have anything that would hurt the fishies. Also make sure that you have adequate backup heat to fully heat the water. Nothing is worse than losing an entire harvest due to bad planning.

6) I may have mentioned this before, but INSULATE. By far the best way to heat your water is to not lose heat in the first place. Double-insulate your greenhouse, insulate the solar array, insulate the piping that goes out of your greenhouse, insulate your cats and your dogs and your kids. If you do it right you'll save a lot in future operating costs.

I was thinking of using evacuated solar tubes directly in either the FT to ST to maintain heat. The system would use thermal syphoning to move the water around. No pump needed. To accomplish this, the collector panel would have to be completely "burped" or all air removed. This can be done by submerging the collector panel during assembly. To keep the water from losing heat at night, a swing check valve would be installed at the inlet to prevent backflow. And a spring check valve would be installed at the outlet. The spring check outlet would double as a thermostat. As the water is heated, the pressure in the evacuated tubes builds, the heated water is pushed through the spring check valve outlet (which is operating as a thermostat), and is displaced by the water coming in from the inlet swing check valve.
Aside from the collector panel/manifold which will have to be glued together, a stand could be dry fitted and assembled over the FT/ST to allow this solar heater to stand directly in the FT or ST. This can be removed during the hotter months and reassembled as needed. I have no doubts that this would work. The only variables would be to determine if the solar heater would collect enough heat to get me through the winter. The intention is to warm the water just enough to keep the fish alive not necessarily active.

Thoughts?