I am trying to size a heat exchanger for a solar water heater. It seems that most people online tend to either buy a prebuilt exchanger with some arbitrary "good for 3 people" rating or just wing it. I googled to death but either google is to dumb or I am too dumb to find the answer.

 

Id like to take what I know which is:

 

temperature of incoming water

temperature of water in holding tank

volume / second of incoming water

heat volume of water (4.18 kj/kg) where 1kg=1liter

 

so if I have 40*F incoming water (using *F for degree symbol) and have 160*F water in the holding tank, how many square feet of surface area do I need to get the 40*F water up near 160*F?

 

I would be using copper coil. I can get 1/2" OD copper coil for the best surface area to price ratio so I would use that. 1/2" OD copper has a surface area of 18.5" per 12" length. it has a volume of .0386 liters per 12" length.

 

can someone help me on a formula for the heat transfer from the holding volume to the incoming water over a length or coil or surface area.

 

there are some assumptions here. The holding tanks temperature can be assumed to not be affected by the incoming water. The 160*F goal temp is over the needed temperature as I will be using a tempering valve at about 102-106*F so the the drop in temp in the holding tank from the heat exchange should not be noticed.

 

thanks in advance.

You should not find difficulties in finding heat calculations if stay with kilograms, litres, joules units... and do not toss farenheit, square feet, inches, btu units ... into the mix.