[Greenbuilding] A Solar Hot Tub

[Nick Pine]

> The tank could keep the tub hot for 169x8.33(159-110)/13274 = 5.2 cloudy 
> days in a row, or more, if we...  2) add some calcium chloride and a $10 
> 1"x100' HDPE black plastic water pipe to the tank as a heat exchanger and 
> lower the average-day water temp to 140 F max (an upper limit for the 
> plastic pipe) and evaporate water on sunny days and add water back to the 
> tank on cloudy days with a solenoid valve (scrounged from a dead washing 
> machine :-) and a $10 snap-disk thermostat and Tractor Supply's 21-70322 
> $8.55 float valve, when the tank temp drops below 110 F.

Some data to help find the equilibrium concentration of a CaCl2 solution 
maintained at 140 F for a long time and the enthalpy of dilution:

http://www.mrc-eng.com/Downloads/Aqueous%20LiCl&CaCl2%20Solution%20Props.pdf

Nick