Is a DIY solar heater worth it?

[DigitalGuru]

I built a solar heater using 200 ft of 1/2-in PEX tubing that I cut in half for two 100-ft spirals on the same 4x4 board. The submersible sump pump I have is supposed to be able to do 1500 gallons a minute but a 5 gallon bucket test running through the solar heater only yields about 150 gallons a minute. At a little over a thousand gallons an hour on a 4500 gallon pool, does the water actually getting warmed enough for the hassle of electricity use if it's running for 6 or 7 hours at most? The water coming out from the tubes feels warmer, but likely only 2-5 degrees more.

 

[mas985]

The amount of heat transferred to the pool is related to both the temperature difference between the inlet and outlet of the panels but also the flow rate of the panels. In fact, heat transfer is proportional to the temperature difference times the flow rate.

The other factor is heat loss. The higher the water temperature in the panels, the more heat that is lost to the environment. Some mistakenly believe that a larger temperature difference between inlet and outlet results in more heat getting transferred to the pool but the exact opposite is true because more heat is lost to the environment when flow rate is reduced.

I built a solar heater using 200 ft of 1/2-in PEX tubing that I cut in half for two 100-ft spirals on the same 4x4 board.

1/2" tubing is only about 10 sq-ft so it won't be adding much heat to the pool. SW MI, this time of year, the incident energy on the panels, assuming they are flat, is about 2500 BTU/sq-ft/day. Assuming a panel efficiency of 80%, results in about 20k BTU/day or a temp rise of 0.5F.

The submersible sump pump I have is supposed to be able to do 1500 gallons a minute but a 5 gallon bucket test running through the solar heater only yields about 150 gallons a minute.

There is no way that pump produces 1500 GPM. More likely it is 1500 GPH (gallons per hour). Most sump pumps are rated in GPH.

Also, you can't push 150 GPM through a 200' of 1/2" tubing as it would likely rupture. Plus 150 GPM would fill up a 5 gallon bucket in 2 seconds so again, I think you have your units wrong.

 

[DigitalGuru]

There is no way that pump produces 1500 GPM. More likely it is 1500 GPH (gallons per hour). Most sump pumps are rated in GPH.

Yeah, that was a mistake or auto correct. It's a 1500gph pump.

 

[DigitalGuru]

Thanks for doing the math. I have a probe thermometer that graphs and I could barely ever see an increased rate of heating if any. Too many other factors, outside temp, how sunny, wind, etc. to factor in. I'll likely abandon this idea for now. The amount of square footage needed and the pump, hoses running around, panels killing the grass, electric usage, it's just not worth it.

 

[1poolman1]

I built a solar heater using 200 ft of 1/2-in PEX tubing that I cut in half for two 100-ft spirals on the same 4x4 board. The submersible sump pump I have is supposed to be able to do 1500 gallons a minute but a 5 gallon bucket test running through the solar heater only yields about 150 gallons a minute. At a little over a thousand gallons an hour on a 4500 gallon pool, does the water actually getting warmed enough for the hassle of electricity use if it's running for 6 or 7 hours at most? The water coming out from the tubes feels warmer, but likely only 2-5 degrees more.

Once you try to pump water through that 1/2" PEX, there is no way you are moving even close to 1500GPH with that pump. It can't do that much through the filter alone. That very inflated rating might be on an open line with next to zero head.

Heating any pool with solar requires that you run the system as long as it takes to get the temperature rise in the pool that you want. Six or 7 hours a day won't do it with that tiny system. You're not heating enough water hot enough. The pool is losing any minimal temp rise overnight.

Also, PEX is a great insulator but doesn't transfer heat to the water the way a black poly tubing would. Also, from one PEX manufacturer:

"PEX pipe is not approved for outdoor applications and is not approved for continuous UV exposure. PEX pipe should not be stored in direct sunlight."

Sorry.

 

[DigitalGuru]

I did paint black for uv coverage, but you are right on not long enough exposure and not enough overall heating. In between timer issues, possible draining and other hassles, I'm glad to have it out of the loop.