DIY solar heater

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I just ran a new set of numbers today at 2pm. Note there was a typo in my original post about the BTU output and I omitted a zero. [emoji51]

Today's result:

Starting pool temperature was measured at the skimmer (where the water feeds to the pump).

Flow rate measured by directing all solar output into a 5 gallon bucket and timing how long it took to fill to the brim.

Final temperature gain measured with same pool thermometer.

Initial temp: 80 degrees F
Final temp: 85 degrees F
Flow rate: 5 gallons in 2:03. We'll call it 2 mins for easy math~2.5 gallons/minute.

BTU output = (flow rate gpm) x (8.2lb/gallon) x delta T x (1 BTU/lb-F)

=(2.5gpm) x (8.2lb/gallon) x (5 degrees F) x 1 BTU/lb-F

=102.5 BTU/minute

= 6150 BTU/Hour

We have direct sun on this panel from 11am - 5pm. After 5pm the temp output drops way off.

I will run the actual numbers this afternoon to see when the output drops off.
 
Water temperature is measured from the solar panel output before it hits the pool water.

No question the surface area of the pool adds FAR more heat to the pool than the panel does. At the current flow rate it would take over 11 hours to turn over the pool volume one time through the panel. We only get maybe 5-6 hours of actual solar heating on that panel per day.
 
Oh, I misunderstood. Your post said you were measuring the temperature in the skimmer.
So I thought your initial and final temps were of the pool water at the same place after a long period of solar running.

Now I understand that you are actually measuring the inlet and exit temp of your solar system.

As mentioned before, ideally you only want a couple of degrees on temp increase. So if you would increase the flow rate through the solar so that the temp rise was less, you would be adding more heat into the pool.
 
The only numbers that count when trying to keep track of pool water temp is the 24 hour gain. Measure temp today at whatever o'clock and measure it tomorrow at the same time. Continue to do so for a week to see if you are making progress. If the temp is higher you are winning!
 
pooldv said:
The only numbers that count when trying to keep track of pool water temp is the 24 hour gain. Measure temp today at whatever o'clock and measure it tomorrow at the same time. Continue to do so for a week to see if you are making progress. If the temp is higher you are winning!
Click to expand...

Or ... was the weather just more favorable to have less cooling ... :poke:
 
Poolzzz said:
6150 btu/h = 1800 watts/h.

If your panel is 200' x 0.5" (8 square feet or about 0.8 square meters) that exceeds the energy output from the sun which would be about 800 watts.:confused:
Click to expand...

Those were the actual temperature measurements and flow rate. Please correct the math as if I'm mistaken, I'd like it corrected.

I've been looking into reasons why this "doesn't add up" and the only possibility are conductive heat gains from the area of the panel that doesn't have tubing on it. The surface temp of the wood panel gets to about 130 degrees in peak sun. Ambient air temperature probably also contributes--if pool temp is 75 degrees, but air temp is 79, gains should be expected there as well.

Here is a pic of the setup and surface temp of the wood.

52beea7ff5c9f0eb930768efa6d0a556.jpg


feb34b452b1c9b38766bb2505d802f9f.jpg
 

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jblizzle said:
Oh, I misunderstood. Your post said you were measuring the temperature in the skimmer.
So I thought your initial and final temps were of the pool water at the same place after a long period of solar running.

Now I understand that you are actually measuring the inlet and exit temp of your solar system.

As mentioned before, ideally you only want a couple of degrees on temp increase. So if you would increase the flow rate through the solar so that the temp rise was less, you would be adding more heat into the pool.
Click to expand...

The restriction of the 1/2" tubing doesn't allow for any more flow using the pool's main pump. Having 4x50' coils could reduce the head somewhat but I don't know if I will go down that path...2.5 gpm is the max flow rate available. This is with the sand filter on recirculate.
 
all of these facts sound good. all i know for sure is when i turn on my ball valve the water that comes from my solar heater is measuring 155. i can run my solar heater from 10am to 7pm. when i turn it off the temp coming from the solar heater is still at least 150. i have actually had to shut it off and turn on my fountain twice this year because my pool water was so hot it almost felt like a hot tub. the last week or so, i have not even thought to turn on solar heater because we are getting at least 103 each day. having to run fountain to keep water under 90. i think the solar heater works. is it gonna warm your pool 10 degrees in an hour, NO, but it will warm it up over the course of a day or so, more than just the sun alone. this has been my experience.
 
Eureka moment!!! Thanks to everyone for fact checking, I think I found the problem!

My memory of four years ago (when the collector was built) isn't great. I ASSumed I had bought 4 - 50ft lengths of tubing. Without tearing the panel apart to measure each length, I did some measuring and number crunching. The total actual physical area measured of poly pipe is just about 2 square metres for both coils.

200 ft (~61m) of pipe at 5/8" OD ~17mm (1/2"ID) gives a calculated flattened surface area of 1.036 square metres...

So it turns out I likely bought 4 - 100ft rolls giving a theoretic area of just over 2 square metres with ~7000 btu/hr potential.

The best gain at full flow I have seen is 5 degrees from in to out. Today is partly cloudy and we're seeing a 3 degree increase through the system which is about 3700btu/hr.
 
Just an interesting exercise. I figure the solar accounts for maybe a 1-2 degree gain each day max. Yesterday the pool overall climbed from 75 degrees to 84. Converting this heat gain into BTUs that's just over 125000btu from all sources for the day. I expect no more than 20,000 of that was from the solar heater.
 
Our solar heating system is from youtube (I think the inspiration was from the "red neck solar pool heater" video!) and has worked fabulous for us. I included a picture below. I'm in Central WI where we rarely see 90 - mine is a 22' Sofpool (10,500 gal) and the pool temp, with solar cover hovers around 84-88. We just had a cold snap/rainy weather for a few days and the pump was off - and the pool dropped down to 74 as of Saturday morning. It's Monday afternoon now - and for the past 3 days we've had highs of 78-81...and my pool is @ 82 as of an hour ago.

It's not pretty - it's made up of a old piece of plywood (4x4) and the black is just 4 Hefty garbage bags. :) But it works for us!

37930196_10155383890481097_2209909666207498240_n.jpg
 
Sun hitting the pool is adding more heat than the hose. And the cover is helping greatly to retain the heat.

You have roughly 11 sqft of black tubes. A rough daily (under full sun) available heat from the sun is 1700 BTUs/sqft.
So that is adding about 18700 BTUs. In a 10,500 gallon pool (87465 pounds of water), the solar collector will raise the pool water by: 18700/87465 =
1/4 degree F per day.

Physics for the win :mrgreen:

1700 BTUs/sqft comes from here: Solar Energy - How Much Energy Comes From the Sun
 
Why does everyone continue to trash these folks whom are working hard on a project, something they did on their own, etc. If they found something that works for them, that's great! But continuing to constantly trash, bash, and run them down with opinions is getting really old and just plain rude.

Sorry for the rant, but I had to spit it out. And I am NOT targeting anyone specific either, just a general overview.

I also started with the black pipe, and it worked decently, and heck of a lot cheaper than the panels. After 2 years, we got a bigger pool and then decided to get the panels. Ended up being $600 Cdn, and somedays they are a real pain due to the leaks they spring in the tubes. I have 2 Enersol, and 2 Sunquest panels, and they both spring leaks. Trying to patch these is difficult as finding a glue that will work well with polypropylene. So if one wants to test the waters on the cheap, then doing the black hose is a good starting point until they decide to go better/bigger.

- - - Updated - - -

Awesome! Glad it works for you.
 
No one is trashing and bashing anyone.

We are simply pointing out that there is a flaw in people's perceptions based on physics. Just like we will point on flaws in thinking regarding pool chemistry, we are going to point out flaws in people's thinking about other pool related products.

Yes, these DIY solar heaters "work" in that they add heat ... but they are often not doing nearly as much as people think.
This thread is proof that there is a large misunderstanding about what these small collectors are actually doing to their pools.
Should we not try to teach the truth?

If the founders of BBB and TFPC just accepted the pool industries teaching of the way to maintain pools and ignored the science, this forum would not even exist.
So why should we ignore the science behind solar heating?
 
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