[Greenbuilding] A Solar Hot Tub

[Corwyn]

On Jul 09, 2007, at 17:36, Kathy Cochran wrote:

> Thanks for all your comments.  What I perhaps failed to mention is 
> that where I live there are LOTS of very interesting slate and quartz 
> rocks that could be repositioned and utilized to build the outside 
> wall of the hot tub.  I am interested in how to make this structurally 
> sound  -  for instance, do I need to start this 2 feet below ground 
> level, and support it with rebar?  Or should I use concrete blocks and 
> only SURFACE the outside with native rock?

Most modern hot tubs are made of either 1/4" or so thick plastic, or 
1-1/2" thick wood.   Concrete at all (not to mention rebar, just seems 
overkill.  All that concrete is not really very green (concrete 
manufacturing produces about one quarter of all CO2).

> What materials should I be thinking of using for insulation  ..... I 
> have a lot of sheeps wool in the garage that I haven't had time to 
> spin yet.  How would this work?  Then, I imagine that I would line it 
> with concrete and paint it black or dark blue-green to absorb the sun. 
>  Mexican tiles around the rim.

Sheep's wool could be excellent for insulation, as it maintains most 
its insulating even if wet.  Details are important, of course.

> I really like the idea of a used PV panel for heat, because the 
> logistics of placing it below the tub would work great, due to the 
> hill dropping off so quickly.

PV panels are going to be VERY expensive way to heat the hot tub.  They 
are about 10% efficient as opposed to water panels at about 60%.  And 
not cheaper per square foot.  Let's say the tub uses 500 kWh per month 
(my sister's observation), that is 6000 kWh / year, which in a sunny 
location might require 3.75 peak kilowatt solar PV panels.  Panels are 
about $4.50 per peak watt.  That $16,875 for just the panels...
>
> Any suggestions would be MOST appreciated.  This project is "on a 
> budget" which is sort of why I want to build it with the native rocks. 
> A "Green" tub, as it were.

If I were in your position, I would install some solar water panels for 
heating and hot water for the house.  Then with the surplus heat in the 
summertime, heat the hot tub.  Perhaps some manufactured hottub with a 
dry stack of stones around the outside (thus having room for the 
insulation).  A green tub, without the quotation marks.

Thank You Kindly,

Corwyn

-- 
Corwyn
Kermit didn't know the half of it...
http://www.greenfret.com/
corwyn at greenfret.com