[Greenbuilding] Hot tubs and recirculating pumps

[George J. Nesbitt]

    I was going to suggest that the 85W pump 24hrs/day could probably be 
reduced in run time to avoid peak, as long as adaqate water quality is 
maintained.
    The water temperatures should be able to be put on a timer too, so 
you only heat it up to temperature before and while you use it. If you 
use it regualarly and at the same/simular times, you just need to learn 
how long it takes to run to bring it up to temperature (will vary with 
season). I do not know how easy it is too set up this way. You might 
have to modify the wiring for the filter and heater so they can be 
controlled separately, alhough the filter probably needs to run when the 
heater is on.
    I wonder if anyone has a variable speed pump, they work great for 
pools, you have to run them longer, but you cut energy use in half or more.
    I don't have much hands on experience or training on spas at the 
moment, so I'm winging it.
    I don't know if you have looked at natural gas spas, usually less 
expensive to run. The instalation cost will depend on if you have to 
wire the spa for 110V or 220V, and the cost of running a gas line and 
electric.
    220V is more energy efficent, and will/should heat quicker.

    Manufactures, may be affraid of loosing a sale, customers don't 
demand the information enough, or they don't care, or all of the above 
and more. Most people don't buy pools and spas thinking about the cost 
to run, but can be surprised when their bill goes up. I wish good 
information was more acessable to me in the field. I don't have any good 
numbers for spas at the moment. I looked spas up in the ACEEE Consumer 
Guide to Home Energy Savings and electric spas are 1500-4000 Kwh/year, 
wide range, but from some of the numbers we crunched seems likely.

    Pools can cost a fortune to run the filter and skimmers, especially 
if you have high use otherwise, and here in California with higher 
prices and a tier structure.



Kevin Dalley wrote:
> 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.
>>     
>
>