POOL HEATER USING PEX COIL MOUNTED ON ROOF

[tellydad]

I have built two boxes containing PEX coil, each w 150 feet of 1/2 inch pex coiled in boxes sealed / plexi covered, placed on roof . There is a 25 foot vertical and 75 foot horizontal of PEX to deliver water from my pool to the boxes.
I put valves before and after the collectors, (maybe not close enough to the boxes.)
I thought once I fill the panels, the siphon effect would take most of the burden, but so far have not had success moving water thru the system. When I hook a garden hose, fills and goes thru the system easily. Any suggestions welcome. What am i doing wrong?

 

[HRTKD]

Sounds like you're going to need a pump.

PEX pipe is not rated for UV exposure. I'm not sure how long it will last under full sunlight. Probably a few years.

 

[Rider]

I thought once I fill the panels, the siphon effect would take most of the burden, but so far have not had success moving water thru the system.

I tried that method many moons ago. Hot water rises, so as the water is heated, it rises from both sides, effectively negating the flow. You'll need a pump. I used a small 12V bilge pump.

 

[tellydad]

Sounds like you're going to need a pump.

PEX pipe is not rated for UV exposure. I'm not sure how long it will last under full sunlight. Probably a few years.

painted the pex pipe black. it will last longer than i will be around i hope.
i got the system flowing by using house water pressure to fill the run and the coils, then switched to a submersible pump i use to lower the pool level in the fall. but the flow is one gallon per minute, the temperature rise is tbd, because i have to insulate the pex for the long run back. (55 feet) to the pool. right now the temp rise is about 10 degrees. Not sure how i determine if i want to get a stronger pump, build another box, or just accept that this system will never do that much. any suggestions are welcome.

 

[Rider]

Slowing down the flow rate will allow the water temp to rise higher. More water flow will not allow the water temp to rise adequately in the PEX. But a slower flow rate may lose more heat getting back to the pool, and the pool will probably lose heat faster than it gains from the heated pipe.

Been there. Just keep experimenting until you get it working.

 

[tellydad]

David Iselin <d.iselin@gmail.com>

Sun, Aug 9, 9:13 PM (9 hours ago)

to DIY

thats why i am wondering if i build another solar box (i have room and its part of the plan if it makes sense) it gives the water a little more time to heat up a little more, but will it reduce the flow dramatically if there is another 150 feet of pex to travel through?
I can return the water much sooner to the pool, i was just trying to hide the pex a little more.
I think i can get another 5-10 degrees, (shorter retrun, insulate the pex) but is it worth it to drive more water thru more coils, to get just a small improvement?
maybe not.

 

[Rich Palmisano]

My profile pic is my box, 100' of 3/4 pex, painted, in a tracker. I didn't want water on my roof. Too heavy.

Anyway, if you slow your flow, you gain heat. I can push the box to 180F and get a 13 degree heat gain at about 0.75 gal/min. Mine is tied directly to the pool pump return and supply with two valves so I can adjust flow.

 

[tictag]

painted the pex pipe black. it will last longer than i will be around i hope.

Using a black pigment-based paint will simply absorb more visible light from the sun but would likely have no impact on reducing either UV transition through the paint, nor the material's resistance to UV exposure. My guess is that the paint will be transparent to UV. You can buy UV resistant paints/lacquers, they usually have a polyurethane base to make them flexible. I am not a materials scientist but I would at least check your assumptions here.

And I do hope you're around for more than a few years!

 

[Supervstech]

To get flow from convection alone, the heated section needs to be the lowest point.
Because the hot water rises... if the hot is at the top, you get no flow.

 

[fat_old_sun]

I have built two boxes containing PEX coil, each w 150 feet of 1/2 inch pex coiled in boxes sealed / plexi covered, placed on roof . There is a 25 foot vertical and 75 foot horizontal of PEX to deliver water from my pool to the boxes.
I put valves before and after the collectors, (maybe not close enough to the boxes.)
I thought once I fill the panels, the siphon effect would take most of the burden, but so far have not had success moving water thru the system. When I hook a garden hose, fills and goes thru the system easily. Any suggestions welcome. What am i doing wrong?

For the dimensions you're proposing (1/2" dia 150 ft length), there's insufficient surface area for heat gain - it works out to about 6.5 sq ft (0.65 sq m). Even at 100% efficiency, the coil wont collect more than 650 Watts, a 'drop in the bucket' considering what it takes to heat a pool.

Editing to correct my math: OP states two sets of 150 ft PEX tubing. The max heat gain is 1300 W, "2 drops in a bucket" worth.

 

[HRTKD]

For the dimensions you're proposing (1/2" dia 150 ft length), there's insufficient surface area for heat gain - it works out to about 6.5 sq ft (0.65 sq m). Even at 100% efficiency, the coil wont collect more than 650 Watts, a 'drop in the bucket' considering what it takes to heat a pool.

Editing to correct my math: OP states two sets of 150 ft PEX tubing. The max heat gain is 1300 W, "2 drops in a bucket" worth.

So what you're saying is that a couple of fat chicks with an endless supply of Twinkies will do a better job at heating the pool?

 

[Fred S]

To get a feel for the watts needed: I used to heat an 18' aboveground pool (7500 gal) just a few degrees, over 8 hours or so, using two 4500w heating elements. Say, to raise 85F water to 90F.

 

[fat_old_sun]

So what you're saying is that a couple of fat chicks with an endless supply of Twinkies will do a better job at heating the pool?

Yes, but there may no space left for you in the pool!