Heat exchanger can't handle solar panel water temperature

[LucMan]

Before we all get too heated (sorry about the pun), here is what I now propose having read all the responses and looked at other options.

I have 2 Bosch Worcester (as they are branded in the UK) solar panels FKC-1S, and all the associated gear so wish to make the best use of it. My current thinking is this.

Using a dual-coil indirect tank (one purpose designed as a heat store), probably 500 litres, I can heat the water in the tank using standard closed loop circuit from the panels, via the tank and back to the panels. I'll put a heat dump on the closed loop. This means the tank water heats up when the panels get the most direct light and the heat is stored for the night time when the pool pump runs, the electricity is cheaper, and the pool heat loss is greatest.

Using the second coil in the tank I will set up a closed loop from that coil to the pool heat exchanger. As its a pool heat exchanger, its designed to deal with chlorinated water. As before, the pool water never mixes with anything other than pool water and taking J P M's advice about efficiency, I can keep the heating water to the heat exchanger, at an optimal temperature.

Any excess in the heat store, I will use to feed my electrically heated domestic hot water tank.

Will this work, am I crazy, or can you suggest better use of these panels (which I already own, long since paid for) which I hope to benefit from?

I'll give you a short answer- save your money on the heat exchanger and just use your panels for domestic HW. Those 2 panels won't raise the temperature of your pool water, they don't produce sufficient BTU's. You can calculate the BTU's stored by your indirect tank, and the BTU's produced by the solar panels. I don't know how many liters of water are in your pool, do the math and you will see your wasting your time and money.
I have installed HX's on pools, they are usually rated at 250K BTU's "PER HOUR" or above depending on the size of a pool and that rating is with boiler supply temps of 85 C.
Two panels will be lucky to produce 120K BTU'S "PER DAY" in optimum conditions.

[J.P.M.]

A lot of words... If the solar panel fluid is isolated from the pool water, did someone point out that "water" may not be the best choice? Think about shutdown modes.. Freezing... Overheating when the pumps aren't running while the sun is still shining. I looked at a "Duda Solar" dudadiesel system a month ago. Has a good installation manual freely available, might help you gain more knowledge. Forget that it is for home water, i think you are seeking the knowledge there.

Yea, folks with short attention spans sometimes think that. Sometimes things need more than one sentence. Life's a bitch, but sometimes that's the price of completeness. Nice feature: Folks get to ignore what you don't think you need.

To your point about water perhaps not being the ideal fluid for the collector loop, I didn't bring it up because, for the most part, it's not part of the conversation. If the OP has a collector system that hasn't frozen, and plans on using the same system but adding another component to it (a heat exchanger), looks like if freezing hasn't been a problem so far, it won't become one with what he is looking into.

Appropriate solar pool water heating systems are available and have evolved that can be cost effective and also SOMEWHAT freeze tolerant. See Fafco and others for more info.

Solar pool water heating is very low tech. It does not need to be complicated. Information only or something else, that system/site you reference is peddling a product that's way overboard in terms of complexity and price, and anyone who knows anything about the subject sees it for the ripoff it is. I'm calling B.S. on it.

Bernie or anyone else that's curious about the basics: A much better reference and a primer of sorts for pool heating can be found at the Florida Solar Energy Center web site under pool heating. Probably less useful for the U.K. etc., but still informative.

Also see the "Build It Solar" website. lots of info there, but it may need a bit of caution/interpretation.

[QuantumSlice]

A lot of words... If the solar panel fluid is isolated from the pool water, did someone point out that "water" may not be the best choice? Think about shutdown modes.. Freezing... Overheating when the pumps aren't running while the sun is still shining. I looked at a "Duda Solar" dudadiesel system a month ago. Has a good installation manual freely available, might help you gain more knowledge. Forget that it is for home water, i think you are seeking the knowledge there.

[J.P.M.]

J P M and Ampster, thanks for everything

For anything I wrote that you found helpful, you're most welcome. Respectfully, more self education will point the way forward for you better and before any forum or other social media.

[bernie4253]

J P M and Ampster, thanks for everything

[J.P.M.]

You are correct I do not have in depth knowledge of what is the best way to heat a pool, that is why I did not offer any advise other than what I did. I have followed many of your posts have no doubt your know your stuff and would reply to the thread.

For my hot water systems I have had two different types the Solarhart forst then the Edwards now, and both will bring water to boiling. They have both been 300l systems and with only two of us in the house and living in the tropics there is ample sun to heat water.

The first one was a Solahart 302SP

The 302SP Series is a 300lt roof-mounted, closed-circuit system utilising the new revolutionary Envelope solar collectors.


The one I have now is an Edwards brand, the Edwards brand is now owned by Rheem. This one is basically the same as the Solarhart one but it has a stainless tank and is an open loop system. We have good water and dont get frost so no need for a closed loop system.

They both have safety valves standard that let pressure out if needed. Both are commercial systems and have been fitted as per instructions so I assume they are safe??.

Besides your units being batch heaters, which is fine, I don't know what your particulars are, but if I was you, and as a cheap and expeditious safety measure, I'd first (and soon) cover a portion of the inlet side (the bottom) of one or both the collector surfaces during times of the year when high daily insolation is likely to the extent that the system temp. and pressures stay below the set points on the relief valve.

Using a P & T. relief valve as a regulating device is not a good idea. If a high solar input causes the relief valve to see either a pressure and/or temp. that's too high, the valve will lift (operate/open). That's what it's supposed to do. But that action is meant to cover upset or unusual conditions (such as stagnation from blocked or no flow conditions for example), not as a daily or regular temp. regulating mechanism or control method. Doing so is sort of analogous to using the emergency brake on a vehicle as an everyday means of slowing the vehicle down. Besides, and is likely with common P. & T. valves, too much use (and it doesn't take much) will cause the valve to leak and worse, maybe get stuck, unable to either open or close fully. If/When that happens, and it will, you'll have a safety issue on your hands.

The systems may be plumbed and set up per instructions, but those instructions do not cover all operating conditions. Cover a portion of the collector surface with something like a corrugated fiberglass roof panels found at big box and affix them with bungee cords.

Back on topic to the OP's thread.

[J.P.M.]

Before we all get too heated (sorry about the pun), here is what I now propose having read all the responses and looked at other options.

I have 2 Bosch Worcester (as they are branded in the UK) solar panels FKC-1S, and all the associated gear so wish to make the best use of it. My current thinking is this.

Using a dual-coil indirect tank (one purpose designed as a heat store), probably 500 litres, I can heat the water in the tank using standard closed loop circuit from the panels, via the tank and back to the panels. I'll put a heat dump on the closed loop. This means the tank water heats up when the panels get the most direct light and the heat is stored for the night time when the pool pump runs, the electricity is cheaper, and the pool heat loss is greatest.

Using the second coil in the tank I will set up a closed loop from that coil to the pool heat exchanger. As its a pool heat exchanger, its designed to deal with chlorinated water. As before, the pool water never mixes with anything other than pool water and taking J P M's advice about efficiency, I can keep the heating water to the heat exchanger, at an optimal temperature.

Any excess in the heat store, I will use to feed my electrically heated domestic hot water tank.

Will this work, am I crazy, or can you suggest better use of these panels (which I already own, long since paid for) which I hope to benefit from?

Questions: How much water is in the pool ? And, is it above/below ground ?

Here's the deal: Yes it will probably work if done safely and in a well designed fashion. Whether or not the results will be noticeable either in terms of how much the pool temp. goes up or how much the pool heating bill go down as a result of what sounds like a lot of work and added maint. is a different question.

Trying to be professional about this, if you have ~ 4 m^2 of solar domestic water heater surface as I think 2 ea. of the FKC-1S panels have (at least as best as I can surmise with the limited info I could find), you can do what you want, but for all the heat you'll get out of them, it may not be noticeable as an increase in the pool water temp., or as much of a reduction in the fuel used to keep that water at desired temp.

My guess is that you are unaware of the limitations of solar energy to provide the quantity of heat necessary to maintain a desired pool water temp. or effect a noticeable change in pool water temp. or the means available to achieve any form of safe and cost effective solution that may be currently available. Read up on solar pool water heating requirements and what's available for a primer on the scope of what you want to do.

I'll get you started: As a rough rule of thumb and a dart throw for preliminary design, a solar pool water heater usually needs to have a surface area of very roughly and approx. 2/3 or so of the surface area of the pool. That's when used in relatively warm summer conditions. And that's for pool water heaters made for the purpose. Such heaters operate at very low temps relative to what solar flat plate collectors operate at, and because of that low temp., operate without glazing and are usually constructed frameless. As an aside, and because of those factors including the low operating temps, such collectors operate at relatively high efficiencies of something approaching. Because of all that, such collectors are less expensive than panels used for potable water heating as the Bosch equipment you have.

Bottom line: Depending on the size of the pool - actually the daily or design heat load in terms of the daily heat loss from the pool that needs to be replaced - your solar collectors are probably: 1.) Quite undersized for the task. 2.) Not, or at best less appropriate for what you want to do. 3.) Fixed in size and so fixed in long term annual output, meaning any heat you do add to the pool that gets supplied by those collectors will come at the expense of a lower quantity of heat that gets supplied to the potable water heating system which I'm assuming here is the intended and original duty of the Bosch system.

That is, on an annual basis, you will have, for all intents and purposes a fixed amount of heat from the solar thermal system you have. So, the panels will only supply so much heat. If the current solar water heating system is oversized, maybe at some times of the year, you might make a case for shunting the excess solar heat to the pool during those times of excess generation, but for the added expense, I'd sure be doing a lot of homework to try to ensure I wasn't spending a bunch of time, toil and treasure on a scheme that will produce little more than maint. problems and maybe a few pounds sterling/yr.

Put bluntly but straight, and not meant as anything more than opinion and information, your ignorance of the situation is causing you to think some things are viable and practical that most other folks more experienced and knowledgeable in such matters know to be the folly of such ignorance. That ignorance is the enemy here. Get educated. Based on the limited information you supply, my guess is what you suggest above, or some form of it, will work, but my opinion is that it will not come to a good end or produce measurable results or anything near what may be the desired outcome. But don't shoot me, I'm only calling balls and strikes as I see'em.

Take what you want of the above. Scrap the rest.

Good Luck

[Ampster]

.....

I have 2 Bosch Worcester (as they are branded in the UK) solar panels FKC-1S, and all the associated gear so wish to make the best use of it.
......

If I had two of those panels and a pool I would do the same. If you have plumbing skills, and can program the controllers, you can accomplish the goals that you set out. Or you can hire those services. The concept is to store energy from the sun and use it to top off your pool and use any excess energy to preheat your domestic hot water.

In my way of thinking, anytime you can use free energy from the sun you are getting a benefit. You are saving money on whatever you would otherwise spend on purchased energy. You have probably researched the costs of doing that and you undoubtedly know the cost of energy that you would otherwise purchase. As others may point out the devil is in the details but you get to decide if the payback is acceptable to you. There are a number of concepts of efficiency that can be used to justify or negate your concept.

[bernie4253]

Before we all get too heated (sorry about the pun), here is what I now propose having read all the responses and looked at other options.

I have 2 Bosch Worcester (as they are branded in the UK) solar panels FKC-1S, and all the associated gear so wish to make the best use of it. My current thinking is this.

Using a dual-coil indirect tank (one purpose designed as a heat store), probably 500 litres, I can heat the water in the tank using standard closed loop circuit from the panels, via the tank and back to the panels. I'll put a heat dump on the closed loop. This means the tank water heats up when the panels get the most direct light and the heat is stored for the night time when the pool pump runs, the electricity is cheaper, and the pool heat loss is greatest.

Using the second coil in the tank I will set up a closed loop from that coil to the pool heat exchanger. As its a pool heat exchanger, its designed to deal with chlorinated water. As before, the pool water never mixes with anything other than pool water and taking J P M's advice about efficiency, I can keep the heating water to the heat exchanger, at an optimal temperature.

Any excess in the heat store, I will use to feed my electrically heated domestic hot water tank.

Will this work, am I crazy, or can you suggest better use of these panels (which I already own, long since paid for) which I hope to benefit from?

[Bala]

My understanding of what the OP wants or has at this time:

He wants to heat swimming pool water with output from an (existing ?) solar water heater of some as of now unspecified size, type and orientation. Apparently, the solar heater is operating at an elevated temp. at least some of the time that's greater than 70 C. The OP thinks a HX can be used to lower that temp. to 70 C.

Aside from the OP, and apparently you, not understanding why inlet temps., but most often minimum delta T's (temp. differences between two fluids in a HX) are often specified, there might be some value and a better design attained by rethinking what's the best way to meet the OP's needs. On the min. temp. the OP writes of: In short, too small a delta T will mean the HX will have what's probably a lower probability of not meeting the duty (the required amount of heat transfer). Actually, and often but not always, a lower delta T results in a somewhat safer design at the expense of a lower duty (in this case, lower heat transfer with less heat going to the pool water).

Sure, a tempering valve may work. But, depending on the duty (the required range of daily heat input to the pool), and the size of the (existing ?) solar thermal system, it may or may not be useful or practical or even possible to use a tempering valve.

Before any talk of a tempering valve, a lot needs to be known about the OP's situation, the existing equipment and what's available on site to reuse/modify.

For all the hassle and cost including the separate hassle of even preliminary sizing and design of a suitable HX, not to mention it's cost and service/maint./cleaning requirements, it'll likely be more cost effective to consider a separate solar thermal pool water heater.


As for your boiling heater - and I'm telling you this as a retired P.E. who claimed proficiency in boiler and pressure vessel design and also claimed knowledge of solar energy applications as they relate to HVAC and power generation applications : Whether you choose to recognize it or not, have a potentially dangerous situation on your hands.

Get it checked out.

You are correct I do not have in depth knowledge of what is the best way to heat a pool, that is why I did not offer any advise other than what I did. I have followed many of your posts have no doubt your know your stuff and would reply to the thread.

For my hot water systems I have had two different types the Solarhart forst then the Edwards now, and both will bring water to boiling. They have both been 300l systems and with only two of us in the house and living in the tropics there is ample sun to heat water.

The first one was a Solahart 302SP

The 302SP Series is a 300lt roof-mounted, closed-circuit system utilising the new revolutionary Envelope solar collectors.


The one I have now is an Edwards brand, the Edwards brand is now owned by Rheem. This one is basically the same as the Solarhart one but it has a stainless tank and is an open loop system. We have good water and dont get frost so no need for a closed loop system.

They both have safety valves standard that let pressure out if needed. Both are commercial systems and have been fitted as per instructions so I assume they are safe??.

[J.P.M.]

Before we all get in a twit, perhaps it might be useful to find out a little more from the OP before we drill so deep into Carnot's theories. It seems someone here is trying to define the problem to fit his skillset and the result is another thread hijack.

And why do you think I stated what I think I understand of the problem from what the OP has shared so far if not to get a better understanding from the OP of what he has in mind ?

As I stated previously, except to point out errors as I see them in your statements, I'm not going to waste time on commenting to your stuff, beyond stating I probably forgot more about the matters of this thread than you will even know or even imagine.

In the spirit of pointing out your errors as I see them and that it also seems a bit of maybe the pot (you) calling the kettle (me) black on a thread hijack, I'd call attention to your incorrect and off thread reference to Carnot.

I'd point out that while his better known and essentially only work is indeed one of the foundations of classical Thermodynamics, Carnot's work dealt with the maximum theoretical efficiency of heat engines running on a theoretical cycle and, believe me on this, has nothing to do with the matters of this thread. For the most part the real meat of matters of this thread deal with heat transfer, not Thermodynamics. That's a difference I'd suggest is unknown to you and maybe part of the cause of your ignorant and irrelevant reference to Carnot who, BTW, had only one theory (not plural as you mistakenly state) on the efficiency of heat engines and little else, especially of the finer points of heat transfer and it's mechanisms which is what most of thes thread is about, particularly as it relates to heat exchangers. Others later refined and formalized Carnot's seminal work but that's off topic.

You may not care, and I sure don't, but you just embarrassed yourself to anyone who does know anything about the subject. You know squat about Carnot and why Thermodynamics has nothing to do with this thread. If there's a hijack, it's on you. Get in a twit if you want, but screw up by throwing crap around that's out of your league and expect to get called on it.

I'll be more than willing to answer any questions the OP may have about his system, how it operates, or some informed opinions about how to perhaps get to the stated goals as safely, efficiently and economically as possible.

[Ampster]

Before we all get in a twit, perhaps it might be useful to find out a little more from the OP before we drill so deep into Carnot's theories. It seems someone here is trying to define the problem to fit his skillset and the result is another thread hijack.

[J.P.M.]

Op asked how to lower water temp from a solar hot water system so I offered an option. My system often boils and I run a tampering valve at 60c, I think?, and it works fine.

I did not think it would be efficient way to heat pool water but op did not ask for opinions on that.

I

My understanding of what the OP wants or has at this time:

He wants to heat swimming pool water with output from an (existing ?) solar water heater of some as of now unspecified size, type and orientation. Apparently, the solar heater is operating at an elevated temp. at least some of the time that's greater than 70 C. The OP thinks a HX can be used to lower that temp. to 70 C.

Aside from the OP, and apparently you, not understanding why inlet temps., but most often minimum delta T's (temp. differences between two fluids in a HX) are often specified, there might be some value and a better design attained by rethinking what's the best way to meet the OP's needs. On the min. temp. the OP writes of: In short, too small a delta T will mean the HX will have what's probably a lower probability of not meeting the duty (the required amount of heat transfer). Actually, and often but not always, a lower delta T results in a somewhat safer design at the expense of a lower duty (in this case, lower heat transfer with less heat going to the pool water).

Sure, a tempering valve may work. But, depending on the duty (the required range of daily heat input to the pool), and the size of the (existing ?) solar thermal system, it may or may not be useful or practical or even possible to use a tempering valve.

Before any talk of a tempering valve, a lot needs to be known about the OP's situation, the existing equipment and what's available on site to reuse/modify.

For all the hassle and cost including the separate hassle of even preliminary sizing and design of a suitable HX, not to mention it's cost and service/maint./cleaning requirements, it'll likely be more cost effective to consider a separate solar thermal pool water heater.


As for your boiling heater - and I'm telling you this as a retired P.E. who claimed proficiency in boiler and pressure vessel design and also claimed knowledge of solar energy applications as they relate to HVAC and power generation applications : Whether you choose to recognize it or not, have a potentially dangerous situation on your hands.

Get it checked out.

[Bala]

It might, but probably not or most likely unnecessary and unworkable for any reasonably designed system for heating swimming pool water. The goal of heating pool water works best, most efficiently, most practically and most economically when the fluid going through the collectors is as close to the pool water temp. as possible (and BTW, sometimes/often below ambient air temp.) Tempering valves will not be needed or even work properly with such small temp. differences.

Op asked how to lower water temp from a solar hot water system so I offered an option. My system often boils and I run a tampering valve at 60c, I think?, and it works fine.

I did not think it would be efficient way to heat pool water but op did not ask for opinions on that.

I

[J.P.M.]

"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.

It might, but probably not or most likely unnecessary and unworkable for any reasonably designed system for heating swimming pool water. The goal of heating pool water works best, most efficiently, most practically and most economically when the fluid going through the collectors is as close to the pool water temp. as possible (and BTW, sometimes/often below ambient air temp.) Tempering valves will not be needed or even work properly with such small temp. differences.