[Greenbuilding] A Solar Hot Tub

[dantonioli at earthlink.net]

> 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.

For clarification, this would be a thermal panel and not a pv panel.



>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...


I'm new to the world of hot tub ownership, but 500 kWh per month is well
beyond what our tub is using thus far. I'll get an average and get back to
the list on this. We only run our tub two hours a day. Once it's heated up,
and properly insulated, it will hold hot water all day long. When the timer
kicks the heater/pump on, it only heats the tub up to whatever additional
degrees it needs to get to 104.



>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.

In order to heat a hot tub with thermal you need to have either a dedicated
system, or have a large storage tank with heat exchangers. Either way, you
can heat your tub year-round with a thermal system, using a conventional
heater as a back-up the same way you would use it for a regular solar hot
water system. If you need more capacity to heat the hot tub, add an
additional thermal panel. 


Remember also that even with a thermally heated hot tub you still need
electricity to power the pump for circulation through the filter, lest you
get dirty water sooner than later.

Dan Antonioli