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Black Tubing Coil for Solar Water Heating  RSS feed

 
Posts: 38
Location: Halifax, Nova Scotia
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Hi All,

I'd like to hear from anyone who is using a setup for heating water that similar to the one pictured in my attachment.

Ideally, I would like to know what the ID and length of the tubing is that you are using and some measurements of temperature input/output, ambient temperature, exposure and weather conditions.

I'm looking at building a solar pool heater and I'm estimating that 1000' of 1/2" ID tubing can increase the temperature of approximately 4600 gallons by around 6*F assuming that the water in the tubing will increase by about 27*F in approximately 50 minutes of full sun exposure. My pump will then push cold water from the bottom of the pool through the tubing and back into the pool continuously for 10 minutes before shutting-off to allow the water and tubing to reheat for another 50 minutes before the pump comes back on. The tubing will be laid east-west on a south-facing roof of dark grey asphalt shingles. Both ends of the system will be submersed to avoid allowing any air into the system once it's up and running so if I'm correct the pump will only need to be powerful enough to move water up to the roofline and it should siphon back down into the pool on it's own.

I made my calculations in metric and converted to imperial so they may be off by a bit!

A-DIY-Flat-Coil-Solar-Water-Heater.jpg
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pollinator
Posts: 1804
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I went to a pool heating seminar at an energy fair. Thats the limit of my knowledge but picked up some tidbits.

Surface area of collectors should equal to surface area of pool. Surface area being more important than gallons cause that is where heat is lost.

A solar pool cover is as good as a solar heater.

Solar pool heaters dont need additional pumps. Use the filter pump in pool with 2 solenoids and 2 thermostats. If the collector is higher temp than pool, it opens solenoid so filtered water is diverted to collector before going to the pool. If theres no temp gain achievable it quits sending it to the collector. It can also be used to cool the pool (run through it at night to dissipate the heat)

The automation means the pool is ready if conditions are right. Whereas a manual system, be it propane or whatever, you have to think "hey i might want to swim in 3 days so let me turn this thing on"
 
Posts: 114
Location: Boston, Massachusetts
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The Fafco pool heater has a bunch of tubes in a ribbon form, two ribbons (supply and return) joined at the ends by manifolds (1-1/2" MPT each end for connections) and is 4 feet by 16 feet in size .
On one manifold there is a butterfly valve to select for flow-through collector ribbons OR bypass collector, and like Wayne says... meant to use filter pump.
So this would be the manual control version...

I think you would get better results with Wayne's automation scheme, rather than your start/stop method.
As long as the return temp is higher than the pool temp, you are gaining pool temp, and getting better efficiency in the collector loop.
Also preventing stagnation temperatures that might be problematic to materials used, and return water at scalding temperatures! (think safety)
 
Posts: 596
Location: Bendigo , Australia
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1/2 inch tube has a good balance between volume of water and the surface area of the pipe, consistent with overall costs.
I have seen 6mm used but its fiddly.
I can back the pool cover suggestion, they are amazing.
 
Jay Colli
Posts: 38
Location: Halifax, Nova Scotia
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Thanks for the replies fellas!

Sounds like a solar pool cover is a must. I have one for an 18' pool so I'll start using it right away. Would I be correct in assuming it is also useful to keep on at night for insulation?

As far as using the existing pool pump to move water through a heating system goes... I'm skeptical about the pump's ability to move the water as far as it'll need to go. It's an Intex pool pump that came with the pool itself and doesn't appear to have a lot of power to spare. With the way that the house and pool are positioned on the property I will need to pump the water up to my roof before it can get direct all-day sun, which is at least 12'.

I'm interested in the dual solenoid/thermostat setup but I don't think I'm capable of building it myself. Is there a unit like this on the market?

Just as a side note my pool has a surface area of ~177 sq. ft. and in order to get the same surface area of black tubing I believe I would need over 1300' of tubing, assuming that 1" of tubing has an exposed surface area of 1.57 sq. inches. Having the runs of tubing on my asphalt shingle roof spaced a few inches apart might even make up for the shortfall in length.
 
wayne fajkus
pollinator
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If the cover is clear it will increase gain at day and decrease loss at night.

I personally think the nightime loss is the biggest key. My gauge for swim season is nighttime temps over 70 degrees f.

The technology is out there on the temp triggers.. Ill do some poking around. Even if it had a separate pump, its worth it. No preplanning to swim. Its just ready.

Oh, the other thing is being realistic about your goals. They said a well designed system will increase swim season by 2 months.  You can swim a month earlier and a month later.
 
wayne fajkus
pollinator
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Check this out at Amazon.com
Differential Temperature Controller T2-T1 Thermostat Water Heater, Pool Solar Panel Pump 2 Sensors Fahrenheit Celsius https://www.amazon.com/dp/B01ETRIZUG/ref=cm_sw_r_other_apa_KBkzBb23F4A54
 
wayne fajkus
pollinator
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Dont fret on size of collector.  These are guides but there are so many variables. Glass covering, a heat absorbing bottom that would transfer heat to the pipe, etc.
 
wayne fajkus
pollinator
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I think this is what Kenneth was referring to. The volume flow stays equal so it flows through your pool pump. The ends are equal to the pool pump pipe diameters. The "ribbons" (small pipes crossing over) in total has same volume as the end pipes. Designed right it just flows through with no bottlenecks that increase or decrease pressure on either side.
20180803_141419.jpg
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Kenneth Elwell
Posts: 114
Location: Boston, Massachusetts
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Wayne, that's basically it, just add a valve in the center of the "IN" manifold, and plug both ends of the "OUT" manifold.
Flow is IN-->down half the ribbon-->back up the other half of the ribbon-->OUT the opposite end of same manifold as the "IN".
OR...open the valve, and flow is IN-->OUT, bypassing the ribbons. Presumably for cold/night time filter use.

This also allows IN and OUT plumbing to be short/near the filter, or at least routed together.

There's lots of information over at Build It Solar... careful you don't fall in! ;-p
 
Posts: 583
Location: In the woods, West Coast USA
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I use 5/8th" tubing, but not on a big scale.  

The trick is that any day that is even slightly overcast the water in the tubing won't get very hot.   If one week has even 50% sunny days, the water doesn't stay hot.

Once the days start to get short, there's only heated water for a handful of hours.  Where I am that's October - April, northern hemisphere, so I suspect the pool water will cool off by mid to late afternoon.  Not sure where you are and if you empty the pool in the winter.

I think a black solar cover is the best bet, and it also helps keep it clean and keeps the cold summer rain out of it.  
 
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