# Pool Heating



## Kevingr (Mar 10, 2006)

I have a small pool for the kids in the back yard and would like to experiment with some solar to heat it. It's only about 4200 gallons and has a small pump and filter system. Currently it's not heated. I was thinking about getting some black plastic barrels to hook in series with the pump/filter system. I'm not really worried about the cost effectiveness of this system, it's just an experiment to show the kids how solar heating works.

My question though, is how many barrels would I need to make a difference in the water temperature of the pool? Is there some kind of calculation for this? I'm not looking to keep it at 100 degrees F, just comfortable. I live in central MN on 12 acres with plenty of unobstructed southern exposure. The pool is covered overnight, and I could make some kind of insulated cover for the barrels overnight.


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## MELOC (Sep 26, 2005)

jak, we need you here, lol.


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## SolarGary (Sep 8, 2005)

Hi,

Here is a rough way to look at it:

A 55 gallon barrel has an area that the sun shines on of about 10 sqft.

Each barrel on a sunny warm day might collect about:

(1500 BTU/sqft)(10 sqft)(0.7 efic) = 10500 BTU

This will warm the 4200 gallons by:

dT = Q/W*Cp = (10500 BTU/day)/((4200*8.2lb)(1 BTU/lb-F)) = 0.3F

So, by this rough calc, 3 barrels might take the pool temp up about a 1F in a day.

Having a cover on the pool will reduce the heat loss at night a lot, and help keep you from lossing all you gain during the day.

In pool heaters, area is the big thing. The problem with the barrels is they have a lot of water mass (which really does not do much for you), but not much area. The very very rough rule of thumb is that you would like to have around half the pool surface area in collector area. 

There is a potential very simple pool heating collector here on my site that you might be able to adapt to your situation:
http://www.builditsolar.com/Projects/PoolHeating/pool_heating.htm
Search down the page for "Mears" -- this was developed as an ultra cheap greenhouse heating collector, but (it seems to me) might work well for a pool. It could probably be simplified even further -- e.g. you might forgo the inflated cover feature. The one in the article is huge, but you could make a much smaller one that worked the same way.

Please let us know how it comes out.

Gary
www.BuildItSolar.com


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## Kevingr (Mar 10, 2006)

Great information. Seems to me maybe making a solar collector (with help from the kids of course!) would be a better alternative, plus more educational. I have a copy of "Handmade Hot Water Systems" by Art Sussman and he has plans and directions for a fairly cheap collector to build. Maybe I'll look at that a little closer.


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## SolarGary (Sep 8, 2005)

Kevingr said:


> Great information. Seems to me maybe making a solar collector (with help from the kids of course!) would be a better alternative, plus more educational. I have a copy of "Handmade Hot Water Systems" by Art Sussman and he has plans and directions for a fairly cheap collector to build. Maybe I'll look at that a little closer.


Hi,
That might be a good way to go. But, one thing to consider about pool heating solar collectors is that unless you live in an area with unusually cold summers, the collectors don't have to be glazed. This is because the pool water is usually cooler than the air, so even without glazing, the collector does not lose heat to the air.

So, pool collectors can be simplier (no glazing) and cheaper and use materials that would not hold up to the temperatures that a conventional collector for heating water for you house would experience.
If the Sussman collector is for heating water for a house, then it may be more than what you need for a pool collector. But, certainly worth a look.

Most of the commercial pool collectors are basically rubber mats with many little tubes for the water to flow in molded right into the rubber. You just roll them out, anchor them down, hook up the header pipe at the top, and drain pipe at the bottom and thats it -- no glazing or enclosing box. 

Gary


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## ericjeeper (Feb 25, 2006)

My neighbor used to serpentine a couple hundred feet of black garden hose up on his roof.. He had it hooked to the pool pump. he swore by this basically free way of heating his pool. Think about picking up a garden hose that has been laying in the sun.. Hot water for a few seconds.. so if the hose is long enough and flow is slow enoughm you can pick up a lot of heat.


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## SolarGary (Sep 8, 2005)

Hi again,

Don't know if you have seen this type of pool heater:
www.smartpool.com/website/sunheater/s220.htm

Pretty simple and inexpensive -- about $100 for the 2'X20'.

They claim 80,000 BTU/day for the (larger) 4'X20', which should raise the 4200 gallon pool temp by about: 

dT = (80,000 BTU/day)/((4200*8.2lb)(1 BTU/lb-F) = +2.3F per day

If you don't have a pool cover, that can make a huge difference -- about 70% of pool heat loss is by evaporation, and a cover cuts that way down.

Gary
www.BuildItSolar.com


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## JAK (Oct 15, 2005)

I would start by looking at all the heat losses and gains.

Solar Gain by Day = Radiative cooling at night - Evaporative cooling when uncovered

Some dimensions: 4200 gallons = 33,600 lb = 540 ft2 ~ 10' x 15' x 3.6'
To raise the temperature by 1 degF requires 33,600 BTU ~10 kwh ~ $0.80

http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/serve.cgi
Solar Gain by Day = 6 kwh/m2/day x 150ft2 / 3.28^2 ft2/m2 = 84 kwh/day
So you are already gaining $6.72/day, but you are also losing it by day and night.
So you might want to fix the gate before you add any more horses.

Evaporative cooling is a big one, expecially when humidity is low.
Pretty much any cover will do. Make sure it is safe though.

Radiative cooling at night is significant also, you might need two covers.
You need a thin dark or transparent cover by day, that floats on top.
I would be worried about a transparent cover though, for safety.
Perhaps a light covered tarp at night. It doesn't need to be thick.

Like SolarGary said, covers make a big difference.
You already have an excellent solar collector, you just have to stop the leaks.
After a week of sun your pool can be significantly warmer.
The garden house on the roof is a good idea also.


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## cowgirlone (May 9, 2002)

ericjeeper said:


> My neighbor used to serpentine a couple hundred feet of black garden hose up on his roof.. He had it hooked to the pool pump. he swore by this basically free way of heating his pool. Think about picking up a garden hose that has been laying in the sun.. Hot water for a few seconds.. so if the hose is long enough and flow is slow enoughm you can pick up a lot of heat.



This is the way my nephew heats his large pool. Seems to work great for him!


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## SolarGary (Sep 8, 2005)

cowgirlone said:


> This is the way my nephew heats his large pool. Seems to work great for him!



Hi,
I like the simplicity of it.

I just wonder how much heat it actually adds?
If you figure 200 ft of hose with a 3/4 inch outside diameter, you get at total of about 13 sqft of collector/hose area. This is a pretty small collection area. Most pool heating system use a collector area around half the pool surface area. If pool is around 10' by 15' (as JAK suggests), then you would want something like (10)(15)/2 = 75 sqft. So, I guess 13 sqft seems on the small side, but, maybe enough to help a bit.
It would be interesting to test it. This would be easy -- just measure pool temperature, the hose outlet temperature, and the flow rate (by timing how long it takes to fill a 5 gallon bucket). This would be a neat experiment to do with the kids.
You can calculate the pool temperature rise from the three measurments above by:

Heat Gain for Day from the hose 
= (HoseFlow)(collection time)(Temp Rise through hose)(Specific heat water)

and,

Pool Temperature rise due to hose
= (Heat Gain for day)/((Weight of pool water)(Specific heat water))

So, for example, if Tpool = 60F, Thoseout = 65F, HoseFlow = 1 gal/min = 8 lb/min

then,
Heat gain for Day (from the sun heated hose) 
= (8 lb/min)(60 min/hr)(6 hrs) (5F rise)( 1 BTU/lb-F) = 14,500 BTU/day

Pool Temperature Rise 
= (14,500 BTU)/((4200*8.2 lbs)(1 BTU/lb-F) ) = 0.4 F rise per for a sunny day

It would also be interesting to see if it makes much of any difference if you distribute the hose on the roof vs laying it out on the ground. It might work a little better on the roof by picking up some heat from the roof surface.

The pool cover would be key to making sure you don't lose this overnight.

Gary
www.BuildItSolar.com








Gary
www.BuildItSolar.com


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## JAK (Oct 15, 2005)

Depending on the roof though the roof might capture some heat and tranfer it to the hose. That might double its effective area, but perhaps not much better than that. Still, 25-30 sqft is getting up there. Cools your roof also. Great idea for an experiment, especially with kids. Anything that involves water, a bucket, and a stopwatch has to be a great idea for an experiment.


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## WisJim (Jan 14, 2004)

Latest issue of Home Power magazine has an article about pool heating.


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## ericjeeper (Feb 25, 2006)

you never have to mow around it when it is placed on the roof.plus does not work the pump very hard as it pumps it up then the water pulls itself back down from the roof..


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## JAK (Oct 15, 2005)

Would think this 2" ribbed PVC might work very well.

200' x 2" / 12 = 33.3 ft2
200' x 3.14 in2 / 144 = 4.36 ft3 = 34 US.gallons
$312 for 200' = ouch! ???

http://www.pondtechnology.com/pages/hoseandpipe.html


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## highlands (Jul 18, 2004)

Kevingr said:


> I have a small pool for the kids in the back yard and would like to experiment with some solar to heat it.


We have been doing this for years. The pool's pump pushes water up about 18" into 80' of 1" black plastic pipe that lays on top of a stone wall next to the pool. A timer turns the pump on in the morning about the time the sun hits the pipes and off in the evening when the sun goes off the pipes. This heats the pool very nicely so that we can swim in it comfortably (72Â°F to 84Â°F water temperature) from May 1st through October 31st. Some of us go longer than that. In the middle of the summer if the temp gets too high I adjust the timer.

We also keep fish in the pool (commets & a koi) so there is no chlorine. I do a water change about twice during summer and then in the fall and again in the spring. In the winter the pool freezes about a foot thick leaving space below that for the fish to make it through the winter. We're in northern Vermont in the mountains zone 3.


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