[Greenbuilding] Hot tubs and recirculating pumps

[Kevin Dalley]

Thanks for the analysis, George.  And healthy is fun, perhaps.

Some of the 75-85W 24 hour/day pumps can be shut off for 8 hours
during the day, to remove usage during the hours of the day when
energy costs are highest, and temperatures are highest..  Of course,
these tubs still heat at 4AM, when outside temperatures are low and I
won't be using the tub.

Why is it so difficult to get good data on energy usage for so many
items?  Do the manufacturers mislead on purpose?  Or do they not care?

"George J. Nesbitt" <geoedb at idiom.com> writes:

> Fun is healthy! isn't it?
>    An 85W pump running 24 hrs/day 365 day/year will use 2.04 Kwh/day
> or 744.6 Kwh/year. This will require an additional 0.434 Kwh AC (CEC
> rated) of PV capacity (4.7 hrs average hours sun per day Oakland CA).
>    The 3.2 amp 230V (736 Watts) pump running 6.5 hrs/day will use 4.78
> Kwh/day or  1746 Kwh year. This is 1.02 Kwh AC of PV capacity.
>    If you can reduce the filter run time you can reduce the energy
> use, whether you can get down to 3 hrs or 2.21 Kwh/day is hard to
> know. (it will depend some on amount of use, and how clean you keep
> the water).
>
>    This is just the filter pump and not even the hot water heating! 
> How much it will cost depends on the price of electricity. In some
> parts of the country people pay $0.04 Kwh for all their use. Here in
> California you pay a minimum of $0.12+/- Kwh and up to $0.55 +/- Kwh
> for summer afternoon use if you use lots of electricity.
>
>   The 85W pump running 24 hrs looks like it uses less energy that the
> larger pump running longer hours. But I have inside information ;-)
> and I know you are on time of use rates with a PV system. Since you
> get credit at a higher rate if your PV production exceeds your use
> from 1-7pm in the summer, you might be better off using more
> electricity, but off peak.
>
>    We had a hot tub at my parents house years ago. It was electric
> resistance heating, 110V. My parents have excess solar hot water
> production in the summer (4 to 6 25 yr old panels, 80g tank). We made
> a copper pipe heat exchanger, placed it in the hot tub (had to remove
> to use), connected with garden hose to the storage tank, ran a pump to
> heat hot tub (no controls, manual operation only, delta T controller
> would have been an improvement). In the summer we heated it
> exclusively this way. I don't remember how long we had to run the
> filter, or how much total energy we use.
>
>    To minimize energy use buy as small a tub as possible. Pay extra
> for more insulation around the inside of the tub (have them spray it
> full). Buy as thick of a cover as you can.