Is a solar heater the best option for my hot tubs?

[justkirkers]

Hi, my wife and I are planning on opening a health spa in here in Colombia. The average temperature where we are is a constant 22 degrees celcius (72 farenheit) all year round. The temperature drops just a few degrees at night. We want to have a series of 2 or 3 connected hot tubs, that will stay warm late in the evening after the sun goes down.
Are solar heaters suitable for this purpose?
If so, what's the best way of going about it (we are solar novices so go easy with the tech speak please!!)

[Mike90250]

You will need to look for a product that can stand the warmer temperatures and chemicals of a spa (swimming pool products may not last long above 80F)

Or even going with solar electric Grid Tie will help with the bills for the pump motors.

Insulation will be a big factor too, if when you install the tubs, you can get some insulation around them, not just dirt and sand. Don't forget the pipes and filters need insulation.

Look for variable speed pumps, that can operate more efficiently and are sized right for your tub, not some big honking pump the store has in stock.

[Mike90250]

You will still need backup heaters, for night time and cloudy days.

[Naptown]

The solar will work best during the day. the problem I see is storing the heat to use during the evening hours. Running the jets with air injection will cool the tubs off quickly. If you can build enough storage into a separate storage vessel and run a reheat exchanger through that it may work. How big are the hot tubs in gallons and how long do you want them hot after dark in use with pumps and jets operating. It is also helpful to know the average ambient temp during use and relative humidity and set temperature of the tubs. Evaporative losses will be the greatest losses and a liquid pool cover may help at least during periods of inactivity.

[justkirkers]

more details on the tubs..

Thanks for the interest folks. It's all still in the planning stages but I guess we want about three 400 gallon tubs. We don't want jets, just plain hot baths. It get's dark around 7pm and we'll want them warm until around 10pm. The temperature doesn't drop below about 65F.

[Mike90250]

Without jets and air bubbles, 400 gal should stay pretty warm for a long while.

[russ]

To follow up on Mike & Naptown's suggestions -

Without jets or bubbles the pools should stay warm into the evening without backup.

1) Well insulated is very important - around and under - 100mm of Dow XPS foam or similar

2) Night time covers to conserve heat - to be closed each evening when use is done

3) You do not want the spa water going through the panels - you have to have two separate loops with a heat exchanger between. The spa chemicals would ruin a panel shortly.

Russ

[justkirkers]

No chemicals if possible

Like I say, it's all still very much in the planning stages, but we are building a natural swimming pool and were planning on using pool water (no chemicals) to fill the tubs. I'm not sure how at this point; probably by having them all connected, then disconnecting/blocking off the tubs during opening hours, warming them using a solar heater, and then after closing time reconnecting them allowing the tub water to circulate with the pool water.
Is this do-able??

[russ]

You will have to use chemicals for sanitation, pH control etc - no way around it - spas are worst case.

If you mix the spa water with the general pool water you would have to heat far more water - probably make the idea unusable.

Russ

[justkirkers]

Well I didn't mean heat the pool water, just the water in the tub, then let the water circulate with the pool water at night.

[justkirkers]

What I want to know is this:

If water from a natural pool (ie no chemicals but clean) is used to fill a hot tub, can people safely use the hot tub for a day? The hot tub water will be replaced every night with fresh clean pool water.

[Naptown]

What I want to know is this:

If water from a natural pool (ie no chemicals but clean) is used to fill a hot tub, can people safely use the hot tub for a day? The hot tub water will be replaced every night with fresh clean pool water.

Uh no

[russ]

For people to swim in a pool or relax in a spa water treatment is mandatory.

If you dump the spas every night your solar heating requirement will skyrocket - making it very unattractive.

This is one place where natural has a bad meaning - there are many things like that actually.

Russ

[Mike90250]

100f spa water breeds nasties instantly, and faster when you get 1 person in there. There are some Silver ION sanitizers and ozone bubblers that can keep the water clean, but warm plain water, is a lab experiment in disease.

But the solar will heat it on a sunny day !

[justkirkers]

Back to the drawing board..