Heat exchanger can't handle solar panel water temperature

[J.P.M.]

Thanks for the dtailed reply. However, I obviously did not make my original post clear.

I intended using the solar panel flow as a closed loop, passing over a heat exchanger (the solar flow never mixes with the pool water). The pool flow also goes via the heat exchanger but does not mix with the solar circuit (like an indirectly heated hot water tank).

In this configuration the input and output temperatures of the pool water are not the issue. It is the input temperature of the flow from the solar panels to the heat exchanger.

I think I understand what you have in mind. If the goal is to heat pool water by taking solar heated water (or other fluid) and heating pool water with it via a heat exchanger, then, for a lot of reasons, that's a very inefficient way to accomplish the task. It can sure be done as you have in mind, but you better have some deep pockets. To a first approximation, and partly because of the temp. differences involved and the design you have in mind, the heat exchanger you will need will require about the same or more surface area as the solar collector you have in mind. It will also need to of a design type that can be disassembled (if not replaced) on a regular basis due to the fouling from mineral deposits that will precipitate out of the pool water.

Read up on common methods of heating pool water. Simple technology and quite low tech is commonly that's quite effective for pool water heating applications.For most such applications, unless you are operating the solar pool collector when freezing conditions are likely/common, what you have in mind could be called a misapplication.

Good luck.

[bernie4253]

Thanks for the dtailed reply. However, I obviously did not make my original post clear.

I intended using the solar panel flow as a closed loop, passing over a heat exchanger (the solar flow never mixes with the pool water). The pool flow also goes via the heat exchanger but does not mix with the solar circuit (like an indirectly heated hot water tank).

In this configuration the input and output temperatures of the pool water are not the issue. It is the input temperature of the flow from the solar panels to the heat exchanger.

[J.P.M.]

If by heat exchanger you mean a fossil fuel fired pool water heater, most, but not all, heat a relatively small amount of water passing through them, and recombine that heated water with the rest of the inlet water and return an equal volume of what entered the heater to the pool, warmer than it went in.

A solar pool water heater as you will find them will never see an outlet temp. anywhere near 70C. Maybe a few deg. F above the pool water temp., but no more than that.

Solar pool heaters work differently, usually by heating a larger quantity of pool water, sometimes/often the entire pump flow, though flat plate collectors that turn solar energy into heat energy and in so doing transfer that energy to a relatively large amount of water that gets pumped through the collectors with that water getting a relatively small temp. increase, but still returning to the pool at a higher temp. than it left the pool. Fossil fuel fired pool water heaters and solar pool water heaters work differently.

Do not confuse temperature with heat. Adding one degree of temp. to 100 gal. of water will require just as much heat input as adding 100 deg. of temp. to 1 gal. of water. Adding 1 deg. of temp. to 100 gal. of water will be an easier task from an efficiency standpoint.

The fossil fueled heaters function as they do because of fluidmechanical, heat transfer and thermodynamic considerations.

Solar pool heaters do it as they do for reasons having more to do with something called Entropy as manifested by enabling lowered thermal losses to the environment by high flowrates of heated fluid, thus keeping the temp. increase lower, but adding heat more efficiently than if flowrates were lower (and thus water temps. higher) with the accompanying higher thermal losses to the environment.

If you feed the output from a solar pool heater to a fossil fuel fired heater, provided the flowrate into the fired heater is sufficient, you should have no problems, but the two devices operated in series may not be as cost effective as operating them in parallel, or with the fossil fueled heater's turn on temp. higher than the approx. solar pool heater return temp. (and so maybe above the desired pool water temp.). Two heaters make the control logic of maintaining desired water temp. a bit more tricky than either device on its own.

Get a good pool cover and use it. You'll save the most money, both on equipment and fuel. Been there. Done that. The motorized and tightly fitting cover eliminated ~ 2/3 to 3/4 of an inground pool's heat loss in Albuquerque.

FWIW, in effect, a solar pool heater is a heat exchanger of a specialized type and designation, but not really. It sort of defies description a bit in that sense. But one perhaps poor analogy is that it might loosely have some thermal-hydraulic analogy to a mix/mash of some of the elements of what are called transformers and/or gyrators in the areas of modeling of dynamic systems. But that's way off topic.

[Bala]

"Tempering valve" is used in houses to limit hot water temp at the taps. I don't see why it would not work for this application.

[bernie4253]

You'll have to forgive me if this is a stupid question, but ...

I am installing a heat exchanger for my swimming pool. Almost every exchanger that I have looked at says input water temperature of around 70C. I expect (from all that I have read), that the hot water feed from solar panels,could be significantly higher than that. If my understanding is correct, how do I deal with this?