Basic Solar Water heater design?

Markymark

I searched this Topic, but didn't really search hard on the forum. What I would like to know is if anyone has done this type of thing for heating the water.

Now I am not talking about heating the water to keep Tilapia alive (or warm water fish), what I'm talking about is just keeping the tank warmer than it normally would be with little investment and minimal additional electricity.

Using it with a Fish tank would be something like this (IMO):

Pump -> One way valve -> Solar Water Heater -> Temperature Probe -> Fish Tank

So the pump could be a small separate pump, or a split from the tanks main pump, one way valve is to make sure for some reason hot water doesn't cycle back into the pump in case of failure. Some kind of temperature probe in your tank to make sure it doesn't get too warm, and should it reach a certain heat to either close the valve or stop the water from flowing into the tank. I'm thinking this would be something mainly only used during the winter months, and it's just supplemental heating, so in the winter in my area I was talking to the Local Fish Nursery and the gentlemen told me his tanks can get down to about 50 degrees, and bluegill for example can tolerate such temperature but it can slow their growth. So with this setup if I could get the temperature of the water let's say to 72ish degrees during the day, and during the night it cools down to mid or low 60s/upper 50s I think given that rough estimate of fluctuation would be worth maybe attempting this setup.

Also this setup wouldn't be on during the night, so this would only be running during daylight hours. So I figured a timer would be connected to a small pump or on/off valve would protect the tank from getting cooler. I presume if you don't want 160 degree water coming out the end it could be coiled less to decrease the exit temperature for small type tanks, but mine is going to be quite large so I would assume as soon as the hot water enters the tank it would decrease dramatically. A basket could be installed at the exit point so hot water wouldn't come in contact with a fish.

Also if there is another post related to this topic where a solution has been drawn please if you have it handy post it for me as I would like to read up more on it.

SuperVeg

I'm pretty sure there is a thread about someone trialling an evacuated tube system with a custom made water cistern. Insulating the tank with a lid etc is vital too...

ThommoPerth

My neighbor has some sort of water heating for his swimming pool, I don't get along with him so it's a bit hard to get a decent look at it. However I do see black tubes slung over his small garden shed.

Markymark

I was pretty sure this was talked about somewhere on here, I used the search function but didn't turn up a whole lot. I don't plan on insulating it or anything like that because my summers get pretty hot and I wonder if the tanks could get over heated. I just kinda wonder if I could alter the winter temps let's say between 15c to 20c (60F to 70F) during the night. I'm more interested in altering the temperatures than worried about having it at a consistent 72 or 74 degrees. I was just wondering if you guys knew what type of parts could fit in those locations for the probe and timed shut off valve.

Sterfire

I think TCLynx, did something like this.

But with few extra materials you could make a more effective solar collector. Framing it in scrap lumber, paint the inside all black and covering it with any type of semi clear plastic would drastically improve heat gain.

There is a website that has LOTS of info about DIY solar heaters and examples of people using them to heat their house water in very cold areas. http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm

Lots of reading, was planning on making a system for the winter for my system so i can keep tilapia alive year round ( with a back up heater) along with a compost heater.

IMelting

Here is a link that describes a DIY solar radiant heating system for a home in Montana. If you were to adapt this for AP you would want to be careful about exposing your AP water to copper. Maybe separate pump to send water from your thermal storage through a poly coil in your FT.

http://www.motherearthnews.com/Do-It-Yourself/2007-12-01/Solar-Heating-Plan-for-Any-Home.aspx

Markymark

Well, once the water makes it around that irrigation hose it ends up at 130 degrees, to increase the temperature you increase the hoses length. I want something small and CHEAP. That project there could be only around 50 bucks depending on how everything is setup. I was aware of the water heater type system, but I think this one is much easier to setup and takes limited parts.

Sterfire

IMHO, If you add a dark backing (extra plywood, painted black) and covered the whole thing clear plastic (Saran wrap). It will absorb more energy from the sun and trap it in the hose better then if left to the open air. The open air will cool the hose, so the more insulated you can make the black pipe, the hotter it will run. A longer hose might not increase the temp much, but insulating it would make any length perform better.

But some one did some math before, a small system like this would only change the temp like 1F in the day time.

Here is a tread. http://www.backyardaquaponics.com/forum/viewtopic.php?f=8&t=3344&hilit=poly

DuiNui

I have done pretty much exactly what the guy in the video did.
Only difference was I just ran the pipe up the garden and back.
Actually I run one pipe up the garden, split it then run 2 pipes back to the ST.
One end is in a FT the other in the ST it just slowly siphons.
It needed a small pump to prime it, but now it just runs all day heating the water.
At a guess I'd say I have increased the average temp by about 3 degrees C with 100m of pipe.

KeenasFish

We have a similar thing set up for our household hot water. Initially we had black plastic underneath and then covered it all in laserlight. We had to remove the laserlight because it started melting the black plastic. It concentrated the light like a magnifying glass and was an extreme fire risk. For winter we'll cover it in some flat clear plastic but it's working fine for now without it.

We have also got some FT water running through black poly for our Barra at the moment. It does help increase the temp by a few degrees on a warm day. We have it running through quite fast as possibly, if the water in the pipe gets too hot it could harm bacteria.

Markymark

I was going to split it off my main tank pump, now if you don't know my system will be quite large and the pump I'm getting will be capable of 4200 GPH, now that is of course I think at 1 foot of lift. But I presume it should move water through the 1/2 hose quick enough to heat the water up properly. Do you guys allow the water to cycle through the solar heater during night hours? I'm trying to figure out a good way to cycle it off during night hours. I presume something like sprinkler timer maybe?

KeenasFish

Yes we turn ours off at night. The pump is on a timer.

DuiNui

Markymark wrote:

But I presume it should move water through the 1/2 hose quick enough to heat the water up properly.

I have wondered about the thermal dynamics of even a simple system like this.
Is it better to pump more water raising the temperature by just a tiny bit, or run it more slowly and heat up less water to a higher temperature....
I don't know if heat transfer is linear, i.e. if the theoretic maximum temperature was 50C, will it heat from 20-30 and from 30-40 in the same time?
If it's linear, then I don't think it makes much difference whether it's flowing quickly or slowly, you'll be adding the same amount of energy.
Guess I should experiment with that, with a small tank of water.

Markymark wrote:

Do you guys allow the water to cycle through the solar heater during night hours? I'm trying to figure out a good way to cycle it off during night hours. I presume something like sprinkler timer maybe?

It's quite cold at night here, relative to the day time temps 10C/35C peaks.
So yeah I turn mine off at night, which involves putting a small plastic bag over the end of the pipe.
I need to automate it somehow as I sometimes forget to do it

Sterfire

DuiNui wrote:

I don't know if heat transfer is linear, i.e. if the theoretic maximum temperature was 50C, will it heat from 20-30 and from 30-40 in the same time?

I believe it is not linear, other wise it wouldn't matter what temp your oven was when you bake cookies (try it :lol:

). The larger the difference in temp, the faster the transfer of heat will happen. If your water moves to fast, it wont have enough time to absorb the heat, but then the solar collector will get hotter.

Realistically, if you have some sort of enclosed collector, and its hot to the touch, but your water coming out is not AS hot, you are pumping too fast. If they are both the same temperature your flow rate is slow enough and you are collecting all the available heat possible.

DuiNui

Sterfire wrote:

I believe it is not linear, other wise it wouldn't matter what temp your oven was when you bake cookies (try it :lol:

). The larger the difference in temp, the faster the transfer of heat will happen. If your water moves to fast, it wont have enough time to absorb the heat, but then the solar collector will get hotter.

That's my belief too.

Sterfire wrote:

Realistically, if you have some sort of enclosed collector, and its hot to the touch, but your water coming out is not AS hot, you are pumping too fast. If they are both the same temperature your flow rate is slow enough and you are collecting all the available heat possible.

But if it's not linear, the faster you pump, the bigger the temp difference between the sun and ultimately the water will be, therefore transferring more heat (overall) to the water.
Bearing in mind that we are talking about a closed loop system, not a hot water heater for a shower etc.

BTW I have no collector, the pipe just runs up the garden and back.
I was thinking of putting on the roof of the house.
This is absolutely all guess work, based on no research or experiments whatsoever.
I can fairly easily set up an experiment, today is overcast and muggy, so not ideal conditions.

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