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re: solar hot tub
1 oct 1996
andrew mckegney  wrote:
>>>if you blow air into the hot tub it is going to cool off very rapidly -

>most spas and hot tubs have air blowers to create the physical
>sensations craved by the owners. unfortunately this increases
>evapouration dramatically and cools the spa off rapidly.

perhaps they should not have air blowers. perhaps this is an undesirable
energy-wasting craving, unhealthy for the earth and the pocketbook. consider
japanese hot tubs. should this craving be more sparingly indulged? how many
cfm are needed to satisfy this craving? how much heat does 1 cfm remove from
the tub? how much power does the air pump need to move 1 cfm? where are the
spa heating professionals who know how to use numbers, when you need them? 
>>>please remember that most hot tubs are used in the evening - usually
>>>after the sun has gone down.
>the point is that you are going to need to store the heat for use
>later, rather than heat the spa with solar directly "on demand".

as i recall, we figured the cooling rate for a well-coverd tub like this
might be 0.2 degrees f per hour. so the point is, at that rate, why worry
about the amount of time between day and evening? 

>storage systems are cumbersome (at best) and expensive and ineffective
>at worst.

how does this sound?

>telephones are cumbersome (at best) and expensive and ineffective at worst.

i used to work for western union, a status-quo company whose president told
alexander graham bell that his invention was preposterously expensive
(he wanted $8,000) and useless... "why would anyone use this 'telephone,'"
he said, "if they could simply send a telegram?" when i worked there, one
major corporate goal was to "exploit the world of data communications,
at 50 baud and below." western union is bankrupt now.

this storage system does use a lot of space. but there may be lots of empty
space under the tub, inside the enclosure. this could be smaller with an
extremely efficient heat pump, like a small jet engine... compress and heat
some warm air from the storage compartment using a fan, make it flow past
the tub bottom to lose heat, and despin the air with another fan attached
to the first by a shaft, to partially power the first fan. this might also
make the solar air heater more efficient.
>if you made a living from this type of business, you would quickly
>realize what is practical and cost-effective, rather than what can
>technically be done if you have enough space, time and money.

i might just get lazy and sell what i can. but that's not my job.


      noone is exempt from occasionally uttering nonsense.
      the misfortune is to do so solemnly.      --moliere 

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