Heating Hot Tub Water

[voyager]

I have recently moved from Alaska to Hawaii and have now purchased a new [to me] home.
It came with a spa, hot tub or what ever you want to call it.
Knowing how high the cost of electrical power is here, the tub was of no consideration in the purchase,
other than assuming that I'd have to tear it out eventually.
Now that I've been walking by it for a few months, I'm beginning to scheme on getting it up and running.
I will NOT heat it with electricity!



The roof is 8-1/2' above the concrete slab and about 6-1/2' above the water surface.
The tub holds 210 gal of water.
The water temperature is holding at 75°F +/- 1°F using the insulated cover 24 hrs.
The roof is 12' long from left to right.
The grooves in the roof panels run left to right.

There are 55 "grooves" [low areas] along length of the panels.

Now, every time I open the garden hose nozzle I get a stream of very warm water until the cooler water reaches the nozzle.
This has me thinking of going solar to heat the tub's water.

So, what I'm thinking of is to lay 200' of black garden hose in the grooves of the roof panels.
Then, add a small 12v pump that can push about 3gpm through the hose.
Finally, power it with a solar panel in such a way that it powers the pump only when it is light enough to produce enough power to run the pump.
I do not want to go to the trouble and expense of using storage batteries.

Is this possible, or am I off in La-La-Land?

[Naptown]

given your location it is very possible.
gettng to 105^o may not happen but it will heat the tub.

[russ]

heater http://rimstar.org/renewnrg/solar_po...ter_diy_fp.htm

A black plastic water pipe pool heater - like Naptown said it might not get you all the way but it will be a super help.

[Mike90250]

black poly irrigation tubing.
Figure if you need 1/2, 3/4, or 1" . How many gallons per foot, and how much weight it will add to the roof.

[Wy_White_Wolf]

http://www.builditsolar.com/Projects/PoolHeating/pool_heating.htm

Solar pool heating. Some of them are along the idea you have.

WWW

[voyager]

Thanks guys.
I am getting ready to move on this.
I have several other projects to finish first,though.
But, I am beginning the planning process right now.

1.
So, I'm thinking of using this pump as the basis:

http://www.lightobject.com/Solar-water-pump-40Lm-635GPH-DC24V-High-Temperature-100-39C-P570.aspx#

The reasons being that it is rated for 12v and 24v.
Plus, it is rated at 6gpm @ 12v.
It should be able to circulate at least 3gpm.
With the addition of a small pot, the motor's speed can be controlled, if needed.

2.
And, I believe it should be able to be powered directly by one of these solar panels:

http://www.amazon.com/All-Black-30W-30-Watt-Polycrystalline/dp/B00G4JCV1W/ref=pd_sim_sbs_lg_42?ie=UTF8&refRID=1H87CCBF7FJGKF7MKZHQ

http://www.amazon.com/Goliath%C2%AE-Solar-Module-Battery-Charging/dp/B00DQF3JF4/ref=pd_sim_sbs_lg_44?ie=UTF8&refRID=1H87CCBF7FJGKF7MKZHQ

3.
I'm very green at this.
But, I think, if I understand things correctly, either of those solar panels should be able to power that motor from a direct connection to the motor.
I should not need a voltage regulator or other "current conditioner" to protect the motor or panel?

4.
If I'm right about that, my only concern is about low voltage during twilight periods.
Is this anything that I need to worry about?

5.
Then, if I go with irrigation pipe, I could get as much as 660' of pipe on the pergola's roof.
If I use 1" pipe it should come to less than 250# on the roof.
It is built with 4x4s and 2x6s.
It should be able to handle that weight easily as it will be distributed evenly over the entire roof.
Would there be any reasonable advantage to running as much as 660' of pipe?

6.
The inlet and outlet on the pump are 1/2".
Will 1" dia pipe be overkill?
It should lessen the friction of the water moving through the pipe compared to smaller diameters?
Plus, if I have to mail-order it, it is cheaper than the smaller dias.

7.
Running pipes in series between inlet and outlet headers would probably be the easiest to setup.
But, I'm wondering if running the piping in a serpentine pattern might be a better method?

Any comments, corrections, or slaps up along side the head?
I do have other questions but they don't come to mind right now.

[J.P.M.]

Thanks guys.
I am getting ready to move on this.
I have several other projects to finish first,though.
But, I am beginning the planning process right now.

1.
So, I'm thinking of using this pump as the basis:

http://www.lightobject.com/Solar-water-pump-40Lm-635GPH-DC24V-High-Temperature-100-39C-P570.aspx#

The reasons being that it is rated for 12v and 24v.
Plus, it is rated at 6gpm @ 12v.
It should be able to circulate at least 3gpm.
With the addition of a small pot, the motor's speed can be controlled, if needed.

2.
And, I believe it should be able to be powered directly by one of these solar panels:

http://www.amazon.com/All-Black-30W-30-Watt-Polycrystalline/dp/B00G4JCV1W/ref=pd_sim_sbs_lg_42?ie=UTF8&refRID=1H87CCBF7FJGKF7MKZHQ

http://www.amazon.com/Goliath%C2%AE-Solar-Module-Battery-Charging/dp/B00DQF3JF4/ref=pd_sim_sbs_lg_44?ie=UTF8&refRID=1H87CCBF7FJGKF7MKZHQ

3.
I'm very green at this.
But, I think, if I understand things correctly, either of those solar panels should be able to power that motor from a direct connection to the motor.
I should not need a voltage regulator or other "current conditioner" to protect the motor or panel?

4.
If I'm right about that, my only concern is about low voltage during twilight periods.
Is this anything that I need to worry about?

5.
Then, if I go with irrigation pipe, I could get as much as 660' of pipe on the pergola's roof.
If I use 1" pipe it should come to less than 250# on the roof.
It is built with 4x4s and 2x6s.
It should be able to handle that weight easily as it will be distributed evenly over the entire roof.
Would there be any reasonable advantage to running as much as 660' of pipe?

6.
The inlet and outlet on the pump are 1/2".
Will 1" dia pipe be overkill?
It should lessen the friction of the water moving through the pipe compared to smaller diameters?
Plus, if I have to mail-order it, it is cheaper than the smaller dias.

7.
Running pipes in series between inlet and outlet headers would probably be the easiest to setup.
But, I'm wondering if running the piping in a serpentine pattern might be a better method?

Any comments, corrections, or slaps up along side the head?
I do have other questions but they don't come to mind right now.

Just a thought: Don't know about powering this setup, but I wonder if you might be just consider a pool heating panel or two of about 30 ft.^2 each, provided they could take the temp. Seems like the plumbing might be easier and better and the weight would likely be a bit less. From a heat gain standpoint, sticking with the hose, the more hose (area) exposed to the sun, the better. 660 ft. of 1" hose will give you something like ~~ twice as much heat gain as 330 ft. of 1" hose because you'll have, in effect about 2X the collector area. That would be an advantage. The hose as you describe it will pretty much pick up solar heat due to its cross sectional area exposed to the sun, sort of like 1'' O.D. hose 12 ft. long equals about 12" X 12" = 1ft.^2 of solar collector with a fairly high ability to remove heat. What the hose lays on however will add some heat, but probably not a lot to the amount of heat picked up by the hose due to poor thermal contact between the hose and its supports. Honest. FWIW.

[SunEagle]

Thanks guys.
I am getting ready to move on this.
I have several other projects to finish first,though.
But, I am beginning the planning process right now.

1.
So, I'm thinking of using this pump as the basis:

http://www.lightobject.com/Solar-water-pump-40Lm-635GPH-DC24V-High-Temperature-100-39C-P570.aspx#

The reasons being that it is rated for 12v and 24v.
Plus, it is rated at 6gpm @ 12v.
It should be able to circulate at least 3gpm.
With the addition of a small pot, the motor's speed can be controlled, if needed.

2.
And, I believe it should be able to be powered directly by one of these solar panels:

http://www.amazon.com/All-Black-30W-30-Watt-Polycrystalline/dp/B00G4JCV1W/ref=pd_sim_sbs_lg_42?ie=UTF8&refRID=1H87CCBF7FJGKF7MKZHQ

http://www.amazon.com/Goliath%C2%AE-Solar-Module-Battery-Charging/dp/B00DQF3JF4/ref=pd_sim_sbs_lg_44?ie=UTF8&refRID=1H87CCBF7FJGKF7MKZHQ

I see an issue with matching the pump to your suggested solar panels.

First the pump data is not correct. It states the pump draws 3.5 amp at 24 volt and 1.6 amp at 12 volt. It also states the pump is rated 85watts/19.2 watts. That is a contradiction on motor stats.

More than likely the pump draws 3.5 amp at 12 volt and 1.6 amp at 24volt. That would calculate to about 42 watts at 12 volt and 38 watts at 24 volt.

So if the pump draws 42 watts, those 30 watt panels will not be enough to run the pump. And running the pump directly from the panel will not get you consistent water flow due to the panel output changing as the sun moves.

You need to size a battery system to run the pump which will give you a constant voltage and then size your panels to charge the battery.

[voyager]

@ J.P.M.
I'm beginning to see a few problems with just laying the collector's piping in the grooves of the roof.
I'm on the windward side of the island.
We get something on the order of 150+ in/yr of rain.
Those grooves are where the rain water collects to run off the roof.
That water will draw off a lot of heat from the piping.
The collector will probably need to be protected from the rain water.
I will have to ponder on it a bit more, ... Maybe cover it with a clear version of that roofing material?

I am finding the idea of coiled collectors to be aesthetically unpleasing.
I may have to get over it.
We'll see.
And, I am now considering 1/2" piping for the collector.

@ SunEagle
Thanks.
I am not very knowledgeable on electrical subjects.
But, I was bothered by the huge difference in power requirements between the 12v and 24v applications.
It didn't feel right.
Your observations sound logical to me.
I'm much more comfortable with 38w and 42w rather than 19w and 84w.
I will check into it further.

I thank you both for your input.
It makes me glad I didn't just dash out and start buying everything.

[J.P.M.]

@ J.P.M.
I'm beginning to see a few problems with just laying the collector's piping in the grooves of the roof.
I'm on the windward side of the island.
We get something on the order of 150+ in/yr of rain.
Those grooves are where the rain water collects to run off the roof.
That water will draw off a lot of heat from the piping.
The collector will probably need to be protected from the rain water.
I will have to ponder on it a bit more, ... Maybe cover it with a clear version of that roofing material?

I am finding the idea of coiled collectors to be aesthetically unpleasing.
I may have to get over it.
We'll see.
And, I am now considering 1/2" piping for the collector.

@ SunEagle
Thanks.
I am not very knowledgeable on electrical subjects.
But, I was bothered by the huge difference in power requirements between the 12v and 24v applications.
It didn't feel right.
Your observations sound logical to me.
I'm much more comfortable with 38w and 42w rather than 19w and 84w.
I will check into it further.

I thank you both for your input.
It makes me glad I didn't just dash out and start buying everything.

You're Welcome !

Thoughts:

You probably won't be gaining much heat from a solar coll. be it hose/pipe/collector when it's raining, so there may not be a lot of heat drawn off. I probably wouldn't worry about that.

Solar devices can take a rainstorm.

FWIW, Way back in the day of experimentation when I thought I knew something, I copied something I read about and built a simple hot tub water heater out of corrugated aluminum roofing panels, 2 ea., 2' X 8'. Painted them flat black, mounted them over the tub tilted 10 deg. or so to the south, plumbed some of the pump outlet to the top of the panels and distributed it to each groove via a hose which was capped at the far end and had holes drilled to match the ridge pitch in the panels. The return was from a gutter/downspout arrangement at the bottom of the panels. Wasn't to code, looked a bit funky and the paint wore from the groove bottoms after a while, but that seemed to not affect performance much. I was after proof on concept info anyway. I forget the #'s I got, if any, but I remember the H2O coming back warmer than it left.

[voyager]

Update:

It has been a while since I began this thread.
Not much has happened with this since the last post.
I have other considerations that relate to this.
They have priority because their outcome will affect how this one gets done.

SO, why am I back here?
I have been taking the insulated cover off during the day for several weeks now.
The water temp had stabilized at about 84°, still a bit cool for my tastes.
Three days ago I placed a sheet of visqueen over the surface of the water and continued covering at night and uncovering during the day.
The water's temperature has steadily climbed until today it reached 90°.
I'm going to continue on to see just how high it will go.

[J.P.M.]

It has been a while since I began this thread.
Not much has happened with this since the last post.
I have other considerations that relate to this.
They have priority because their outcome will affect how this one gets done.

SO, why am I back here?
I have been taking the insulated cover off during the day for several weeks now.
The water temp had stabilized at about 84°, still a bit cool for my tastes.
Three days ago I placed a sheet of visqueen over the surface of the water and continued covering at night and uncovering during the day.
The water's temperature has steadily climbed until today it reached 90°.
I'm going to continue on to see just how high it will go.

Just a thought: If it's not already, a brown or black or otherwise dark piece of opaque plastic will work as good or better than clear. And/Or, probably a bit more effective as a cover - "bubble wrap" or pool cover material may be even better.

[Mike90250]

the visqueen is likely stopping cooling evaporation from the water.

[CraziFuzzy]

the visqueen is likely stopping cooling evaporation from the water.

This is correct. If a body of water is exposed to the air, it will naturally tend to cool down to the wet bulb temperature of the air. This is lower than the dry bulb (thermometer) temperature unless humidity is at 100%. A near air-tight cover will stop this evaporative cooling, and limit heat drop down to the dry bulb temp only.

Most heavy hard spa covers, however, are pretty air tight, so they, if in good repair, should be sufficient to fight the evaporative losses.

Solar heating will likely never get your spa up to 'hot tub' temperature, as the higher the water temp gets, the higher the losses in the solar collector get. The only way to get water appreciably higher than ambient temp, is to use an evacuated tube collector, which allows the solar energy in, but prevents the heat loss back out.

Regarding your worry about losses during rain, the fix is to not run the pump while it's raining. Ideally, you'd have a control system on this that will run the solar pump only when:

- Temperature in the spa is lower than your desired spa temp, AND
- Temperature in the collector is a couple degrees higher than current spa temp.

[Edward45]

It is always best to keep the covers on if the temp outside is cold. Make sure your cover is in good condition. Most of the people don't give much notice to the condition of the cover, but if the cover is damage, its insulation property is lost. If you have a damaged hot tub cover, get a good quality cover which has the capability of saving the heat. If you need to get a cheap but better quality covers try Buy Factory Direct, -URL deleted--
It is best to stick to the basic, nullify any chance of conduction through any form.

--Mod note: please no clickable links to vendors in your recommendations.