Backyard Aquaponics
A place to discuss aquaponics

Last couple days I've been tinkering with thermosiphon solar water heating. I learned that it does work, but only in pretty specific situations.

What I was trying to do is get a little more heat into my aquarium system without using any added electricity. I had already moved the sump just outside the window from the system so it could pick up some of the free heat this time of year. That helped but not enough, I still needed about 4-6 more degrees F to get a good breeding temperature for the tilapia.

I found that the thermosiphon idea that had worked yesterday on the ice chest water just would not happen with the barrel sump.

So, tinkering around whit what was to hand and the configuration of this set up, I came up with something.

The barrel sump is a blue barrel laying on it's side with a hole cut in for plumbing and pump in the side facing up. The bung holes are one near the ground and the other near the top side. I plumbed a 3/4" ball valve through the bung near the ground and attached the 3/4" black potable water safe pipe to it. That runs out and there are a few coils and the pipe comes back through the top bung hole (which I simply removed the bung.) This is attached to the bottom of a T attached to the drain line that comes through the window. This way the water flows down first filling the black pipe and any excess will flow out the side and fall into the sump so as not to impede the drain action that would mess up the loop siphon on the grow beds inside.

Clear as mud? I've now got 86 F water for the breeding aquarium system. Now I will just have to work out how to keep it warm overnight.

For the testing I wound up putting the tubing over on the west side of the house but I think it will be better to bring the tubing around front to get the best early morning sun and some afternoon shade. That way I may not need to shut it off before evening. Now perhaps, if I were to cover it over with some plastic, I would not even have to shut it off at night.

I do not expect this to be in operation for the coolest part of winter though unless I really insulate the barrel well. I will probably switch back to the indoor sump for winter and just expect the fish to deal with 70 F water.

Clear as mud any chance of a picture Lynx?

Let me see if I can work out a diagram since there really is no way to get a picture that would really show much (too much stuff in the way like shrubs and the barrel etc.)

ok, for what it's worth.

Use the same thing to passively heat the water in the shed at our last place. If you have a header tank the water can get very hot. In winter its warm. A lot better than ice cold for washing your hands.

If it was in a situation where the tank was up high and supplied by some small bit of main water pressure, then it could totally be a Thermosiphon thing. Now if it is being supplied by say the water off the roof, then I see what you are getting at.

Ok, at about 9 this morning the indoor and outdoor temps aligned at 79 F The fish tank is right at about 79 F.

It is just now time to go out and see if turning on the drain heater would be a good idea since the sun has just started hitting it.

11 am fish tank at 80 F Outdoor temp at 85 F Solar heater tubes valve opened just after earlier post.

12:40 pm
Fish tank up to 82 F
Outdoor air temp 88.5 F

It is an overcast day.

splendid idea, TC
But the tank shouldn't be a sump or you risk troubles with the pump: that would have to pump warm if not hot water
All submerged pumps are cooled by the water,
which is good in a heating system, since the wasted energy will be transposed into heat, but they need water with a cooling capacity.

So it should be an overflow tank so as not to need a pump

And that gives the possibility to go thermosiphon all the way, as it will be up high (or at least the top of it)
connect the coil to the bottom and to just below overflow level and watch the thing perform all by itself

The coil will perform better if set at an inclination rather than horizontal or vertical

the disadvantage of an inclinated coil is that you would have hot water in the top (wanting to stay up) and colder water in the bottom (wanting to stay down) of each circle, so thermosiphon will not be optimal

why is it so difficult to get all factors right ???

Frank

You are right that if I was using this to make really hot water, I would definitely not want to use the sump for it. Currently I don't want to let any of this really get much warmer than the fish and pump will be comfortable in. There really is no heat exchanger involved or temp controls other than me shutting the valve when it gets warm enough or when the sun goes down. I will also leave such a thing shut off when I'm not around to check on things.

Now for something that might really heat things up, I don't think we want to go totally passive.

Anyway, your comments about an overflow tank up high with a thermosiphon. Can you elaborate what you mean on this one a little more since I don't think I'm getting my mind around it quite right. For a thermosiphon to work reliably I think you need a pretty well sealed system. (Perhaps discussion on this should go back to the Thermosiphon experiment thread since if you have a way to make a thermosiphon heater work in a passive way, I'm quite willing to go back and tinker with that experiment some more.)

As to the incline. I think it would probably get the sun better at a slight incline but the gravity drain method though perhaps not perfect seems to work ok for the mild heating I want with the coils flat on the ground. Actually the incline would be very appropriate for a collector that doesn't use coils but say a grid or zig zag or vertical tubes.

2:25 pm
90 F air temp
84 F aquarium temp

Shade will soon cover coils.

From Wikipedia:
"Simple thermosiphon
Convective movement of the liquid starts when liquid in the loop is heated, causing it to expand and become less dense, and thus more buoyant than the cooler water in the bottom of the loop. Convection moves heated liquid upwards in the system as it is simultaneously replaced by cooler liquid returning by gravity. In many cases the liquid flows easily because the thermosiphon is designed to have very little hydraulic resistance".

Water tends to stratify (= form layers) when heated:
The hottest water will always want to go and remain at the top, the coldest water will sink to the bottom

The trick is to have your tank (or at least part of it) higher than the solar heating system so that the solar warmed up water can easily escape from the heating system
Where the bottom of your tank rests is less important: gravity will always push the colder water into the system as long as there are no air locks in the system (another possible disadvantage of a coil).

But once the system is primed, its functioning will be totally automatic

So you need the highest possible stratification and the least possible mixing to have the system perform at best: temperature differential will be the highest and so will water density difference
logically that means a narrow high tank is better than a wide shallow tank

also you need to avoid forcing the warmed water to go downwards on it's way: it doesn't like to do that.
it wants up, up, up.

hope this helps

frank

Yes Frank, I do understand what a thermosiphon is. I actually managed to get it to work the other day. See this thread on the experiment.
http://backyardaquaponics.com/forum/viewtopic.php?f=8&t=4130

I just couldn't get it to work in the situation of a fluctuating tank level with bubbles in it with less elevation to work with in the situation of this sump heater. The passive drain heater seems to be working well so far. At least for what I want it to do for this time of year.

I have been following this thread, no worry
this subject fascinates me
so thanks for experimenting and posting

the problem is hat your ice chest is shallow and white
for better performance it should be high and narrow
all boilers are constructed that way

frank