Spa Pool Geekery

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jonherries

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Topic # 113918 1-Feb-2013 12:03

We have just moved into a new house and it has a spa. We were going to sell it on Trademe but after testing it to make sure it was working, we want to keep it.

The only problem is I am not loving the thought of maintenance costs.

So I have some ideas and some questions:

Firstly, it uses power to heat and filter the water, so reducing this to a minimum should increase efficiency. I am thinking I can time the on/off using one of the new wemo switches from Belkin. But I figured turning it off too much means the pool would get too cold and I would have to spend lots to reheat it. So:

We have a hard cover, but I read on a US website that you should have a floating blanket too, so I thought maybe I could make one out of say 4 layers of bubble wrap duct-taped together? Any thoughts about thermal efficiency and longevity certainly cheaper than buying one at ~$400?

One of the longevity questions is using chemicals, I have had a look on the intertubes and there is a guy in Akaroa selling ozone filters on trademe and on his website www.aquazone.org.nz. Any thoughts about whether these are good?

Thirdly, because it has been hot in Wellington and there is a roof over the spa I could put a solar collector on the roof. On the whirlpool.com.au forums I read about some principles of swimming pool solar heating, which said to use large diameter hose to and from the roof and small diameter hose on the roof to minimise heat loss during transfer and maximise heat gain on the roof respectively. I looked at the fountain pumps available and thought there is bound to be some thermal siphon effect. Could I get away with a 0.9 maximum height pump if I start a siphon (manually) and add in the thermal siphon effect? The actual height of the head will be about 2-2.5 metres.

Obviously I want a cut off for all this, so I was thinking the wemo option is probably to simplistic unless all run off the same relay or I buy more than one or they all run at the same time during the day? The alternative is a arduino to power some relays for which I probably need a temp sensor for the roof heating. I have one in the garage but I think this is going to be much more cludgy.

Thoughts?

wellygary

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Reply # 754361 1-Feb-2013 12:32

I am pretty sure that most modern pools have a built in thermostat

(otherwise if you left them on they would heat to a point you could not get in)

Adding an additional one may be troublesome,

nickb800

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Reply # 754377 1-Feb-2013 12:50

Could be worth talking to your power company/electrician about connecting the spa on a controlled tariff.

With a smart meter it is possible to some variation in time-of-day rate, or the old school option is ripple control which would turn off the circuit during peak morning & evening hours.

The workability of this solution would depend on separating the heating power supply from the rest of the electronics - pumps etc

jonherries

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Reply # 754388 1-Feb-2013 13:15

wellygary: I am pretty sure that most modern pools have a built in thermostat

(otherwise if you left them on they would heat to a point you could not get in)

Adding an additional one may be troublesome,

Yeah it does currently, would be interesting to know how much heat the solar option would add. If it isn't too much then I could just let it run, with the spa itself taking care of temp regulation.

Jon

jonherries

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Reply # 754390 1-Feb-2013 13:25

nickb800: Could be worth talking to your power company/electrician about connecting the spa on a controlled tariff.

With a smart meter it is possible to some variation in time-of-day rate, or the old school option is ripple control which would turn off the circuit during peak morning & evening hours.

The workability of this solution would depend on separating the heating power supply from the rest of the electronics - pumps etc

It is on a separate circuit, at the back of the house, outside in it's own little house, with the heater integrated into the pump solution, so might be difficult to separate out. Appreciate the thought but that sounds like a lot of cost and I am not sure that the ripple control would be more effective than a wemo switch and the primary problem of doing that is monitoring the water temp (ie. trying to keep the temp stable).

I think I need to understand the thermal efficiency of the pool to know if there is any efficiency I can get out of better timing of the heater. I guess I figure this out by turning it off and figuring out given the ambient temp, and the starting water temp, I can calculate how long it needs to be off to be worth turning off and then reheating the water later. I think I need a arduino and a temp sensor!

Ha, this is like the spa pool equivalent of working out whether you should turn your car off at the traffic lights!

dolsen

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Reply # 754405 1-Feb-2013 13:53

We used genesis energy day/night plan for our spa pool in Wellington. The spa was only on for a few hours just before 7am and a half hour top up about 5:30 and that was enough to keep the spa pool warm. Night power was only 11.3c / kW/h.
If it's a "plug in" spa you might get away with a timer but for our one we had a timer controling a relay (which has a big air gap) to switch the heater & pump as just the heating element was a 6-8kW load.

Spa already has its own thermostat on the heater to control the water temp.

jonherries

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Reply # 754411 1-Feb-2013 14:01

dolsen: We used genesis energy day/night plan for our spa pool in Wellington. The spa was only on for a few hours just before 7am and a half hour top up about 5:30 and that was enough to keep the spa pool warm. Night power was only 11.3c / kW/h.
If it's a "plug in" spa you might get away with a timer but for our one we had a timer controling a relay (which has a big air gap) to switch the heater & pump as just the heating element was a 6-8kW load.

Spa already has its own thermostat on the heater to control the water temp.

Hmmm nice thinking about the relay, I think (from memory looking briefly at the smart meter last weekend) the whole house when it was on heating from cold, was drawing ~3.5kW so I am going to have to do a bit more checking as the relay limit on a wemo is 3.1kW...

Jon

jonherries

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Reply # 754413 1-Feb-2013 14:08

dolsen: We used genesis energy day/night plan for our spa pool in Wellington. The spa was only on for a few hours just before 7am and a half hour top up about 5:30 and that was enough to keep the spa pool warm. Night power was only 11.3c / kW/h.
If it's a "plug in" spa you might get away with a timer but for our one we had a timer controling a relay (which has a big air gap) to switch the heater & pump as just the heating element was a 6-8kW load.

Spa already has its own thermostat on the heater to control the water temp.

Re: the thermostat and why a timer might be useful, if we only use it 2-3x per week, it might be cheaper to heat the water for those dips rather than keep it hot all the time. I need to figure out whether that would be the case.

Measuring the change in temp over time (with it both off and on) should let me estimate how long it takes to get to usable and ambient temperature respectively, and therefore how much heating is required, how often and the cost.

Jon

jonherries

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Reply # 754414 1-Feb-2013 14:09

Does anyone have any thoughts on the solar heating or the blanket ideas?

Jon

chevrolux

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Reply # 754415 1-Feb-2013 14:11

Ozone is not a filtering system but a treatment system. Some of the best pools in the world use Ozone - Kilbirnie pool in wellington for example. It is so clean that in an emergency it becomes a backup water supply.

The issue is though you are wanting to get the ongoing costs down. Ozone is made by electrolysis so that would be yet another unit that would be running in your spa. Perhaps look at a passive filtering solution like silver wool. It isn't actually silver wool but is like a filter pack sort of thing that has soluble silver in it that treats the spa. Not sure where you would get it from but have seen it in a few spa's and it they looked great.

jonherries

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Reply # 754429 1-Feb-2013 14:45

chevrolux: Ozone is not a filtering system but a treatment system. Some of the best pools in the world use Ozone - Kilbirnie pool in wellington for example. It is so clean that in an emergency it becomes a backup water supply.

The issue is though you are wanting to get the ongoing costs down. Ozone is made by electrolysis so that would be yet another unit that would be running in your spa. Perhaps look at a passive filtering solution like silver wool. It isn't actually silver wool but is like a filter pack sort of thing that has soluble silver in it that treats the spa. Not sure where you would get it from but have seen it in a few spa's and it they looked great.

Yeah wrong word, should have talked about santisation. From the advertising it reduces significantly the need for chlorine, so presumably this would save me some good $ on chemicals?

Jon

bazzer

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Reply # 754430 1-Feb-2013 14:48

jonherries: Does anyone have any thoughts on the solar heating or the blanket ideas?

Jon

Solar heating gets the pool (with a cover) up to over 30 in the summer months. Not sure what it would do for your spa in the winter months when you want it the most.

Bubble wrap is cheap as so give it a go!

chevrolux

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Reply # 754436 1-Feb-2013 15:04

jonherries:
chevrolux: Ozone is not a filtering system but a treatment system. Some of the best pools in the world use Ozone - Kilbirnie pool in wellington for example. It is so clean that in an emergency it becomes a backup water supply.

The issue is though you are wanting to get the ongoing costs down. Ozone is made by electrolysis so that would be yet another unit that would be running in your spa. Perhaps look at a passive filtering solution like silver wool. It isn't actually silver wool but is like a filter pack sort of thing that has soluble silver in it that treats the spa. Not sure where you would get it from but have seen it in a few spa's and it they looked great.

Yeah wrong word, should have talked about santisation. From the advertising it reduces significantly the need for chlorine, so presumably this would save me some good $ on chemicals?

Jon

Ozone is a replacement for Chlorine. So yea would save on that but again, you need to run the unit all the time. So you would have to weigh up what costs more. Some little chlorine tablets or an ozonator.

gzt

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Reply # 754437 1-Feb-2013 15:06

My guess is chlorine will degrade bubble wrap.

Jaxson

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Reply # 754445 1-Feb-2013 15:21

I would have thought Ozone was out of reach price wise? Pool chlorine is likely to be cheaper.

Filtering gets the big lumps out, but it also transfers the water past the heating element, so the transfer pump does have to run in order to maintain the heat.

Fundamentally these things just cost a lot to run, and you don't want to use a poorly maintained unit.