Question on Solar water heating

1 Posts
Mar 14, 2010 12:20 pm
Question on Solar water heating

I am installing a solar water heating system, I made my own collectors. I bought a storage tank with a heat exchanger (coil). I have a question, I will appreciate very much if someone can help: What is the best size tube that i should use for the loop (collector to tank)? I was thinking to use 1/2 in. cooper tube. Let me know if this is ok. I will use a Taco circulator pump, 1/25 hp.

My email: estebanv @ verizon.net

Thank you,

esteban

462 Posts
Mar 15, 2010 12:16 pm
Re: Question on Solar water heating

Esteban, for water flow through a tube Q = V * A, or volume flow rate equals velocity times the area. So with a constant flow rate in gallons per minute the velocity will increase as the area of the pipe decreases. In solar hot water, the slower the flow the longer the water stays in the collector. So basically you can use whatever size pipe you want but if you want to have the water flowing slower, use a bigger diameter pipe.......

1 Posts
May 4, 2010 05:44 pm
Re: Question on Solar water heating

Esteban, Tom's equation for water flow through a tube is correct.  However, with a constant flow rate in gallons per minute, both the velocity and flow of water through the collector would be exactly the same regardless of tubing size.  This is because the cross sectional area of the collector does not change.

Your circulating pump does not produce a constant flow rate in gallons per minute.  Smaller tubing creates more resistance to flow and would reduce pump output.  The velocity of the water in the tube would be higher but the velocity of the water in the collector would be lower!

Factors to consider when sizing tubing for the collector loop include the length of the loop, circulating pump specifications, system type (open/closed loop), and controller type.  My best guess for your closed loop system is 1/2-inch copper.

Good Luck!

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