[Greenbuilding] A Solar Hot Tub

[Nick Pine]

Frank Flynn writes:

> I have a solar hot water system in my home and it makes plenty of
> heat for the domestic hot water and a hot tub during the summer...

> 2 - Whole house domestic hot water - solar hot water panels on the
> roof heat water or antifreeze which is stored in a tank; domestic hot
> water, hot tub and possibly rooms are heated by this stored heat
> through a heat exchanger...

I like this option best, but why put the panels on the roof? Gary Reysa
and I have been working on a $500 water heater (including a tank and
heat exchanger) that goes on the ground, a work-in-progress at
http://BuildItSolar.com.

I wrote:

>... A 170 F tank with some evacuated tubes could 100% solar heat this tub 
>for 5 cloudy days with 5x3.76x3412/(170-110) = 1069 pounds of water cooling 
>from 170 to 110 F. That's 17.2 ft^2, eg a 2' tall x 3.3' diameter 
>well-insulated unpressurized tank.

Oops... ft^2 vs ft^3 would be flat water. The tank could be a single piece 
of EPDM rubber inside a 10'x2' piece of aluminum coil stock roofing material 
inside 6" of fiberglass insulation inside a 4'x4'x2' tall foil-faced 2" 
polyiso board box.

Nick