Solar pool heater

[bradatkins]

Hey -

I've completed my purchase of a pool!! Woohoo. Not sure what's more work, digging out or paying off :)

Anyway, I'm looking at constructing my own solar heater. There are various methods, and one of them is to take black poly-pipe and make it into a circle.

The question is, I've seen varying sizes of the pipe, 3/8", 1/2", 3/4", 1".

I'm guessing the debate is between what gets you better heat: high volume, low pressure or low volume high pressure.

My guess is high volume (ie a 1" pipe) because making x/gallons per/min at 5C is better then x-10 gallons per/min at 15C.

Anyone have any feedback?

Brad

[twizted1]

Smaller pipe will allow for more surface contact (water to pipe), which will mean that more heat will be transferred into the water for the amount of time it's in there. Think of it as if 5% of your water touches the pipe, less heat will be absorbed than if more water is in contact with the pipe. The pump that is connected to the solar heat exchanger will do best if it's piped into a larger diameter pipe that is then split off into smaller cross section pipes, allowing more thermal exchange to take place. Every joint in the pipe will also cause some turbulence in the flow of water, causing potentially more heat to be exchanged.

Plastic is not a good conductor of heat, but it will transfer more heart than the water itself will absorb. Be sure that whatever pump you use has the flow rate you need (gpm) at the head height you require to pump water through your heat exchanger. A greater volume capacity (in the heat exchanger) with a slower flow rate will net a higher amount of heat transferred to the water.

[bradatkins]

Ok, so probably 3/8's to 1/2 or so pipe then?

As for the pipe that is connected from the pump to the solar I was going to use whatever size comes off the pool pump (2" I think)

Thanks!
Brad

[twizted1]

Greater surface area with a more complete water contact will work the best. (I know I'm being vague with that answer as there are many variables not considered in what I've said thus far.)

A larger pipe going into a single smaller pipe will give you a pressure increase, a larger pipe going into a set of smaller pipes with a total cross section larger than the pipe you're going from will give you a pressure drop. A 2" pipe (all numbers here forward assume the dimension as the ID of the pipe) has an area of about 3.14 square inches (sq.in). A 1/2" pipe has an area of 0.196 sq.in, so to have no pressure increase, you would need approx. 17 1/2" pipes to flow the same volume at the same pressure.

Without some time and reference materials (that are at work), I couldn't even venture a guess at the thermal transfer you could hope for out of this system, but the idea is sound and you have the basic principals already it appears. Someone who del as with thermodynamics on a regular basis, or has more intimate knowledge of these types of thermal transfer systems could likely give you a more succinct answer and some idea of what to expect.

[BigDave]

Higher flow will provide better heating than lower. The goal is to move as many calories from the collector to the pool. Lower flow will give a higher change in temperature across the collector but higher flow will move more of the available heat into the pool. Use as many parallel tubes as possible for highest possible flow.

[bradatkins]

Higher flow will provide better heating than lower. The goal is to move as many calories from the collector to the pool. Lower flow will give a higher change in temperature across the collector but higher flow will move more of the available heat into the pool. Use as many parallel tubes as possible for highest possible flow.

You said move as many "calories" I'm guessing you mean gallons? :)

So I get the use as many parallel tubes, but what size is typically optimal? Based on higher flow, 1/2 - 1" is probably best?

[twizted1]

Higher flow will provide better heating than lower. The goal is to move as many calories from the collector to the pool. Lower flow will give a higher change in temperature across the collector but higher flow will move more of the available heat into the pool. Use as many parallel tubes as possible for highest possible flow.

Thankfully someone more knowledgeable chimed in, I'd have directed you to a slower flow with the system, but I do believe there needs to be a balance with flow rate to the heat transfer.

[BigDave]

I mean calories - units of energy - heat. It seems counterintuitive, but it's not the temperature of the water coming out of the collector but the total amount of heat you can put in the pool.

[bradatkins]

So I got the main piping in for the solar system. Unfortunately I couldn't find anyone who had good hose to use.

This is my main setup. Not as clean as I want it, but I'll do more tweaking once I get the rest of the hose.

http://farm9.staticflickr.com/8303/7926744152_6e22249053.jpg

I ended up ordering two of these from home depot:

http://www.homedepot.ca/product/1-2-inch-x-100-foot-distribution-tubing/994403

Based on the picture it looks like it can be coiled pretty tight, so hopefully that's true!

[BigDave]

I really can't see where the tubes are going, but I think the Tee closest to the filter feeds the solar loop, the Tee farthest from the filter is the return from the solar loop. The valve between the Tees bypasses the solar loop (when open) and the valves on the legs of the Tees isolate the solar loop (when closed). The line beyond the farthest Tee is the return to the pool.

How big is the line from the filter to the pool? How's the flow at the pool return? Are you planning to run parallel sections of the 1/2" tubing? Have you thought about how to lay this up for the winter?

[bradatkins]

Here's an updated picture describing the flow

http://farm9.staticflickr.com/8179/7938205676_4912e5fcf5.jpg

Here's the diagram I'm using as a general guide:

http://farm9.staticflickr.com/8445/7938211568_c1c35582e3.jpg

The main pipe coming out of the filter is 1". The loops on the roof will be 1/2". The flow is reduced when flowing up to the solar loops, of course, but still acceptable.

As for winter, I plan to leave it in place, and blow out the lines. I will be taking down the solar loops as the pipe is a little more fragile then the main system which is poly pipe.

[bradatkins]

Here's a picture of the first coil. I've only built 2 for this year. Plan to build more next year:

http://farm9.staticflickr.com/8439/7972033798_650501fc24.jpg

[CarlD]

Big Dave means calories.

A calorie (actually a kilo-calorie) is the heat energy necessary to raise one liter or one kilo of water one degree Celsius. A BTU (British Thermal Unit) is the equivalent: the amount of heat energy necessary to raise one pound of water one degree Fahrenheit.

Thin tubes can conduct more heat energy to the water flowing through them, but put up a high resistance to water pressure. Thicker tubes conduct less energy but have lower resistance. Therefore, several thin tubes parallel to each other can lower resistance AND increase conduction.

The more water you can flow through ANY system, the more heat you will add to your pool. The limiting factors are causing leaks (bad) or, possibly cavitation. Don't be fooled by the false adage that you have to run the water slowly through the panels so it can heat up. It SEEMS to make sense but actually doesn't. Again, the confusion is between heat energy and temperature, and we want our solar panels to move heat, ie, calories/BTUs. A very heavy strong flow that's only 1 degree warmer than your pool will STILL heat it faster than a trickle of hot water.

And, just to add to the confusion, as the water in the pool gets warmer, so will the water it feeds to the solar panel, that then STILL comes back warmer, even if only one degree, and warms the pool more!

I've been running solar for 11 seasons now. I've not built my own panels, but the principles are the same.

[geohec]

Here's a picture of the first coil. I've only built 2 for this year. Plan to build more next year:

If you don't mind me asking, I was curious how much your two coil system cost you?

Also, are you happy with the results this year?

I have a low lying roof next to my AGP and I am considering buying a system or building one. What you've done seems like something I could do. Any info would be helpful. Thanks.

[bradatkins]

It was $26 for the 200ft of tube and about 30$ in connectors. I built it too late in the season to take advantage of them (lack of sun).

I don't expect 2 to make any difference. I'm expecting to have to make a few more

[geohec]

It was $26 for the 200ft of tube and about 30$ in connectors. I built it too late in the season to take advantage of them (lack of sun).

I don't expect 2 to make any difference. I'm expecting to have to make a few more

Thanks for the info. So your ideal system with say 5 or 6 coils would be around $140-$200. I looks a lot more durable then some of the manufactured options out there. I see they sell a lot of repair kits which makes me think that they're fragile.

After I finish my deck, then I'll have to make a decision on which way to go. Thanks for the info.