Solar Heater Performance??

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traxx2003

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Jul 6, 2011
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Hello everyone! I need some experienced opinions about the performance of my solar heater setup. First let me start by describing some details about my setup. I currently have an Intex Ultra Frame 24' Round pool equipped with a Hayward EC-50 DE filter rated at 50GPM, in addition I also have two (2'x20') a SunHeater collectors in parallel and everything is hard piped using PVC schd 40 pipes. To direct the flow of water to the collectors I installed a "mixer" valve that allows me to choose between directing the water flow between the pool or collectors or a combination of them both. Today the current temp outside is 97 F, the water temp in the pool is 84F and the temp of water from the return is 86F. The collectors are cool to the touch. and I currently have the water flow at a rate of 50/50 between pool/collectors. And lastly The filter has been running for about 3 hours. The pool's temp before I turned on the pump was at 83F. Does this sounds about right? considering the details I have included above? Or is it really to early to tell? Sorry if my questions are a little unrealistic, I just want to have an idea if my system is working at an optimum potential.
'I appreciated any opinions on this!!!
 
I'm far from an expert. I can only tell you my experience. I have a 26K gallon inground plaster pool. I installed some solar heaters and while they do work well, you will lose most if not all your heat over night if you don't use a good solar blanket as well.
It takes some time to see results from the amount of solar panels you have. In my case, I installed 4 panels and in Febuary and March of this year, I could see a gain of 5+ degrees per day but I'd lose most of that at night. I got a solar blanket and I would usually gain 5 degrees per day and lose 2 degrees at night with the solar blanket giving me a net gain of 3 degrees per day. Once the weather warmed up a bit, those figures were higher but the heat loss was about the same. I would gain 6, or perhaps 7 degrees and still lose 2 or 3 degrees so over the course of about 2 weeks, I was able to get my pool from the low 50's into the mid 80's and hold it there with proper use of the solar blanket as well as the solar heaters but if I forgot to roll out the solar blanket at night, I'd lose virtually all of my heat gain.
The solar system I have installed works and should lengthen my swim season from about 5 months per year to 9 months per year. Maybe even 10 months if I'm lucky.
I'm in the Phoenix Arizona area so we get a lot of sun but even with the massive amounts of sunshine we get here in the winter, the high temps are only about 68 in December and January so I'm not expecting my solar heaters to be able to keep the water as warm as I'd like it to be but they are worth the effort if you ask me.
On a side note, if you get a solar blanket, get a solar blanket reel. You'll be glad you did. The reel makes life a lot simpler.
 
Okay!! First let me thank you both for responding to my questions. My other concern is, if I run the risk of over pressurizing my panels given the size of my filter's pump (50GPM) if I were to divert 100% of the water flow thru the panels? My panels are seating about 2-3 feet higher than the filter pump and I have about 15 feet of piping between filter outlet and the inlet for my panels. Thanks once again!!!

P.S I would also used a solar blanket to minimize the loose of heat at night, the problem I have is that here in California City Ca, the wind is a major factor during the summer. On average I have to deal with 10-20 mph winds on a daily basis. My solar blamket wold always be blown completely out of the pool by the wind.
 
That's what I thought when I installed my blanket but it seems to stick to the water very well as long as the ends aren't flopped up. It gets windy here in Arizona as well but my cover has never come off or even moved when it's windy.
I have a valve on my solar panels as well and I can regulate the flow to the solar heaters. I usually do about 50% and that seems to be where I get more heat. You just have to play with it until you're satisfied.
 
Thanks!! Hey a little update, since my last post its been about tw0 hours +-, I just went outside, and the pool water temp is already 2 degrees higher. Its is currently @ 86F. WOW!!!! I might be able to see 87-88 by late afternoon. It is 450pm right now, and my collectors still have about 2-3 more hours of sunlight left today.
 
traxx2003 said:
Thanks!! Hey a little update, since my last post its been about tw0 hours +-, I just went outside, and the pool water temp is already 2 degrees higher. Its is currently @ 86F. WOW!!!! I might be able to see 87-88 by late afternoon. It is 450pm right now, and my collectors still have about 2-3 more hours of sunlight left today.
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You should be able to run 100% through the panels. What's the manual say? I have 2 panels of 2' x 20' in parallel and only get a 3lb. pressure rise at 100% flow through the panels.

My manual states "If the pressure is above 30 psi or if it is 10 psi higher than the pressure reading you took before installing the solar system, install the optional bypass valve per the next step. "

It goes on to say "slowly turn ball valve handle until pressure gauge reads below 10 psi (SOLAR ON)"

You'll get the greatest efficiency by running as much flow as the panels will handle, which in my case is 100% at only 3lb. of extra pressure over my normal 14 psi.
 
cramar said:
I run my panels at about 75% or so, it's a balance between heat VS volume.
Click to expand...

BINGO!
I produce more heat by slowing the water a bit than by forcing it through so quickly. I played with mine for months trying to figure out what the best scenario is. Full volume with lower heat output or lower volume with higher heat. It's a give and take situation but I finally settled on 50 to 70% of the water going through the panels and it has worked out well for me.
 
Mesamav said:
BINGO!
I produce more heat by slowing the water a bit than by forcing it through so quickly. I played with mine for months trying to figure out what the best scenario is. Full volume with lower heat output or lower volume with higher heat. It's a give and take situation but I finally settled on 50 to 70% of the water going through the panels and it has worked out well for me.
Click to expand...
Generally solar panels will be most efficient at high flow. The Ops 2 degree rise is pretty ideal, so I would not change how it's set up. High temperature difference between the pool water and the return water is inefficient.
 

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If you look at the equation backwards it becomes a little clearer that the greatest flow through the panels equals the greatest heat extraction. Not trying to be argumentative or a know-it-all but it's a fact.

By backwards I mean let's look at the situation in reverse. Instead of looking at it like trying to heat the water, look at it like trying to cool the panels. What will cool the panels better--more water flowing through them or less water running through them? A cooler panel means greater heat extraction and warmer water overall.
 
Mesamav said:
cramar said:
I run my panels at about 75% or so, it's a balance between heat VS volume.
Click to expand...

BINGO!
I produce more heat by slowing the water a bit than by forcing it through so quickly. I played with mine for months trying to figure out what the best scenario is. Full volume with lower heat output or lower volume with higher heat. It's a give and take situation but I finally settled on 50 to 70% of the water going through the panels and it has worked out well for me.
Click to expand...

Yup about 50-75%, I monitor it and if I think it's not adding as much heat as it can I'll increase/decrease the flow accordingly. At 100% I personally have found that the water is not picking up enough heat even considering the increased water through, but that's just my set up.

My Sunsaver manual says they should add 3-5 psi at the filter, this puts me at the 50-75% mark. I'm sure glad I bought them, they've made a HUGE difference in pool temp.

PS, I have a dedicated return for the solar panels so I can throttle independently.
 
cramar said:
Yup about 50-75%, I monitor it and if I think it's not adding as much heat as it can I'll increase/decrease the flow accordingly. At 100% I personally have found that the water is not picking up enough heat even considering the increased water through, but that's just my set up.
Click to expand...
It simply doesn't work that way. Higher water flow always means more total heat extracted. Above some flow rate the additional heat extracted gets to be very small and there starts to be a risk of damaging the panels due to the higher pressures required to achieve the higher flow rate, but you will still always get more heat out at the higher the flow rate. This is true even though the temperature increase you get passing through the panels goes down as the flow rate goes up. The additional volume of water getting heated more than makes up for the lower temperature gain.

Lets try some imaginary numbers to see if I can make this clearer. Say I have a panels such that I can run 10 GPM through them and get a 2 degree temperature increase. That means in one minute I have heated 10 gallons of water two degrees, thus adding 20 degree*gallons to the pool. Now lets say we move the valve so we now have 30 GPM moving through the panels, and in this setup the water temperature after passing through the panels only increases by 1 degree. In this setups in one minute 30 gallons have been raised by 1 degree so 30 degree*gallons have been added to the pool. Even though the temperature gains is smaller, the total heat added to the pool is larger.

This leads to the slightly counter intuitive result that lower temperature gains are more efficient. The panels are actually most efficient when they are as cool as possible to the touch and you can barely notice any heat gain in the water going through the panels.

The upper limit of flow rate is determined by the panel design. As the flow rate increases, the pressure in the panels increases. At some point the pressure gets to high and strains the plastic, which eventually leads to damage and leaks. So you want a high flow rate for efficiency, but a lower flow rate for increased panel lifetime.
 
I appreciate you point, my results don't support the final conclusion.
If I send 100% of the flow to my panels I don't find as good a performance in the end of day temperature increase as when I throttle it back a bit.
Also, I'm not advocating having the return as hot as possible, but I suspect that perhaps at 100% of water thru the panels I may not always get any net temperature gain at the pool return, under certain conditions (mixed clouds, wind - which we get a lot of) I may be cooling the water at times, thereby offsetting/reversing the minor temp gain.

The one caveat I'll give are those stifling hot days, massive humidity, no clouds and intense heat.....where I live we don't get many days like that, but when we do, ya, I could see running 100% flow thru the panels.
 
Regardless of whether someone believes in an immutable law of physics or not, it sure is nice to swim in a warm clear pool. :p :-D

One of these days I'm gonna get some automation. I hate giving back those BTUs when there's no net gain or worse when running through the panels.

Here's something interesting. Or not. :) My panels are on the ground. A couple weeks back I decided to insulate them from the ground. I put 3/4" Styrofoam underneath. Efficiency dropped like a stone. It cut my heat gain dramatically. Should have measured the soil temperature first. Didn't realize that the ground heats up very fast and is a good heat sink for those partially cloudy days.
 
Well, I really appreciate everyone that has contributed their experiences and opinion to my question!!!! Just wanted to update everyone with what I have experienced so far. In the last couple of days here in California City Ca, the highest temps we've had have been in the mid to high 80's, not common for our area during this time of the year, and a lot of wind (15-25 mph sustained). In the mornings, when I get home from work, for the last two days my pool's water temp its been reading right at 70F. My panels are facing west (due to space limitations) and with the wind and relatively low ambient temperatures during the day, my water has gained between 6-8F running my system for 6-8 hrs a day. I'm not sure how much water flow I am sending thru the panels, I do have a selector valve, and what I've been doing is dividing 50/50 the water flow between panels & the pool. O, and I'm not using a solar blanket to keep the heat at night, although it looks like I'm going to have to use it. I'm hoping that once the ambient temp gets back into the 90-100+ (normal for around here) I will be able to keep my water at the very confrotable 86-90F without having to deal with a solar blanket. We will see!!!! Thanks again everyone!
 
I have a similar setup except we are not hard plumbed and have a regular AGP. My solar heaters are lying on the ground on the east side of my pool. My pool was 102 when we got home at 4:40pm today. The solar blanket is staying off tonight. I have 100% of the water going through the panels. Likely, by morning my water temp will be 10 degrees cooler.

I have never had my solar cover blow off - even in tornadic winds that blew shingles off my roof. The solar cover stayed adhered to the water. Luckily, that tornado left only minor damage to our property.
 
yeggim said:
Regardless of whether someone believes in an immutable law of physics or not, it sure is nice to swim in a warm clear pool. :p :-D

The immutable law of lay mans physics.

Thermodynamics and fluiddynamics are very complicated and can not be mastered by thinking about your pool filter. Flow speed will affect heat transfer mechanisms between the water and the solar collector. Try googling heat transfer and flow rate for automotive radiators. You would need a PHD from MIT to truly understand everything that is going on. Life is not so simple. There is definitely and optimal flow rate and some point where more flow is worse.
Click to expand...
 

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