How to heat pool?

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I live in central Texas and want to heat a yet-to-be-built 12' X 28' X 4.5' exercise pool for year around use. The water temperature needs to be about 80 degrees F. The pool would be used about 1 1/2 hours per day, preferably early in the morning. I am having difficultly getting reliable information on the most cost effective way to heat the pool. The people I have talked to have a vested interest in the products they sale. Natural gas and electricity are available as well as adequate roof area for solar heat. Any unbiased help would be appreciated.
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On Tue, 17 Oct 2006 02:06:42 GMT, "Craig Davis"

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With RC = R1x4.5x62.33 = 280 hours, the pool temp would drop from 80 F at 9 AM to 48.8+(80-48.8)e^(-6/280) = 79.3 by 3 PM on an average January day in Austin :-)
Nick
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On 17 Oct 2006 12:17:54 -0400, snipped-for-privacy@ece.villanova.edu wrote:

Those are nice numbers but I doubt they hold up in a real life situation. We have lots of solar heated pools here (SW Florida), covered and uncovered. I can only report what they see. On a windy day that heat will really go fast, particularly when you pull the cover off and start swimming around. You also have to be very consciencous about putting the cover back on. If you have kids that is usually a problem. Never swim in a partially covered pool. Without the cover the best you can usually hope for is the ambient afternoon air temperature and that is only good for a while in the afternoon.
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That's because you are ignorant :-)
Nick
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On 17 Oct 2006 18:00:52 -0400, snipped-for-privacy@ece.villanova.edu wrote:

I have a solar heated pool and a thermometer, (as do several neighbors) you have a sliderule
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And a vast supply of ignorance? :-)
This is 300-year-old physics.
Nick
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On 18 Oct 2006 03:58:14 -0400, snipped-for-privacy@ece.villanova.edu wrote:

Ther problem is not with the physics, it is with the real world performance of the cover and other places where the heat escapes. I agree the heat all started in the water but keeping it there is not as simple as your numbers would indicate. A degree or 2 makes all the difference when you actually get in the water. I can swim in 27c water, 28 is better but 26c is too cold. I suppose folks in the frozen north are more tolerant of cold water.
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Well sure. We need to cover the whole pool surface with no exposed water, and no gaps for airflow nor leaks in the cover.

I disagree. It's pretty simple :-)
Nick
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On 18 Oct 2006 13:24:23 -0400, snipped-for-privacy@ece.villanova.edu wrote:

That's a man without a wife or kids. The cover never gets put on perfectly and a cloudy day really screws up the heating. A little rain really puts you in the crapper. As they say on the sticker on a Hummer "Your mileage may vary but it will certainly be less than this"
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How sloppy can you be? Wrinkles are OK. Leaving less than 10% of the pool uncovered is probably OK in Texas...

No. That's OK, the pool cools slowly, with a 280 hour time constant.

That could be a bummer, with a large puddle on top of the cover. Maybe the cover should have a few leaks, eg a 1/4" hole every 2'.
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

I fail to see why you find it necessary to insult someone who questions or doubts your analysis.
btw if add some white space to your posts........
those of us who might have the ability & desire to check your calcs could do so w/ less frustration
also you might consider the use of units.
cheers Bob
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OK.
With RC = R1x4.5'x62.33lb/ft^3x1Btu/lb-F = 280.485 hours, the pool temp would drop from 80 F at 9 AM to 48.8F+(80F-48.8F)e^(-6h/280.485h) = 79.33967251 F by 3 PM on an average January day in Austin :-)
US R1 (the pool cover thermal resistance) is 1 ft^2-F-h/Btu, and 1 cubic foot of water weighs 62.33 pounds, and 1 Btu can warm 1 lb of water 1 F. Everything but "hours" nicely disappears in the rest of the RC calc...
Happy now?
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

Dear Nick-
Thanks for the effort but you don't have to go out of your way to try to make me happy. :)
I wasn't unhappy but typically your post filled with runon calcs that are very hard to follow...even for an ME with 30+ years of experience.
I doubt if any other ng readers even attempt to make sense of them
The units did help but I like lots of white space......improves the readability.
If you want people to take your calcs seriously you need to make an effort to make them understandable. ......
otherwise it's just "another a stream of numbers.from that obnoxious, know-it-all guy from villanova"
You also might consider using an unafilliated email address...IMO a lot of your posts reflect poorly on your organization.
cheers Bob
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Craig Davis wrote:

Craig-
Here are some random thoguhts that will hopefully help with the process.
The cost of heat (electirc vs gas) is dpeend on the $/ kwatt-hr & the $/therm in your area.
Gas is typically cheaper than electric
Your exercise pool will hold ~11,000 gallons. ~92,000 lbs
The sizing of your heating system will depend on local day to day weather conditions (I have no idea of the local weather in your area)
I do know that keeping a pool at 80F in SoCal year round would cost a LOT, you would need heat in the winter and the summer. The heat losses to the air & gorund would be very large.
I had a small (~500 gal) above ground spa, well insulated, electric heat. I kept it turned down during the day but heated it up (about an hour or so) to spa temperature. I figured it only cost about $20 or $30 per month.
You've got a much larger mass of water so you need a very large capacity heater to bring the temp up very quickly. An 100,000 BTU/hr heater would be able to raise you pool 1 deg F per hr. A LARGE gas heater (400,000 btu / hr) would be able to heat the pool faster.
So conceivably you could yo-yo the water temp on a daily basis; bring the temp up for use, then turn the heater off & let the water cool naturally; repeat the process every morning (heater on a timer).
I seriously doubt that electric would be cost effective unless you've got really low rates
3415 btu = 1 kwatt-hr
a gas therm is 100,000 btu ~80% of the heat value of a gallon of gasoline.
I doubt that you could get an elctric heater any larger than a 100,000 btu/hr gas equivalent.
A standard concrete pool looses heat to ground & air; a cover (large bubble wrap types) really helps cut loss to the air. It is possible to insulate between the pool & the ground. The concrete pool wall has an R-value of ~.5, 2" of foam would boost the R value to ~15. This would greatly reduce the heat loss.
Foam costs about 1 to $2 per sq ft depending on thickness. You have to discuss these issues with the pool designer. Adding a foam layer will complicate the construction but GREATLY reduce the heating costs. The integration of the cover into to the pool system needs to be done prior to construction.
You've got to do the trade off......construction costs vs heating costs
cheers Bob
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Craig Davis writes:

OK. Here's the unbiased truth.
Tell us honestly, how much are you willing to pay for this heat, per year?
If it is not in the multiple $1000s, then you're wasting your time.
How often will you really use this pool? For how many years? Not how often do you imagine you might.
The typical new pool is built, and then after the novelty wears off, sits unused. Think of it as a treadmill that costs $25K or $50K. Except you can't just put it out on the curb when you grow bored of using it. It must be maintained constantly at significant expense, and you cannot discard it or just turn it off. If you blow $35K on a boat, at least you can park it and not pay any more for it when you're not using it, and sell it when you haven't been out in a year. Not so with a cement pond.
The typical pool buyer uses it every day for some months, then falls off to once a week, then occasionally, then hardly ever. The maintenance is faithfully with you every day, as is the financing (or opportunity cost) of a $35K investment. Total true cost per swim, over the life of the pool: $150/swim or more.
Swimming pools are not a middle-class entitlement.
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Considering the fact that you replastered your pool yourself, you definitely know how much 'fun' a pool can be... <evil-grin>
A previous house that I owned had a pool... If the water had been cooler, I might have been more inclined to think that it was worth it, but it's difficult to get all that enthused about jumping into the water when it is 90F or more... These days, I chalk it up as a learning experience... I made sure that the next two houses that I bought did *not* have a pool... If a person is considering adding a pool to their house, they should think it over very carefully... It's not like they are going to get their 'investment' back out of it when they sell the house... They'll pay $35K for the pool and maybe get a $15K increase in the value of the house when it is time to sell it...
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snipped-for-privacy@gmail.com wrote:

Craig-
I approached a reply to your post from a strictly technical / egineering point of view.....but I must say that the two additional replies you got at right on the money.
I grew up in SoCal with a pool; this was pre-pool man days. I swept it, kept the chems, vacuumed it, flushed the filter. I swore I'd never own a pool. I even bought my folks a "pool sweep" to take my place when I went to college.
Unfortunately, my wife bought a house w/ a pool & for ~ten years we paid for a pool man, replaster, new filter, etc. I bet I went in less than 10 times per year.
My kids had awesome parties when we were out of towns, so they really liked the pool.
An in-gorund water feature can be a liabilty rather than a selling point.
My above ground spa was another story......I got a lot of use (nearly daily) out of it & I did the up keep on it.
btw a lap pool doesn't need to be 12' wide
cheers Bob
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BobK207 wrote:

I really didn't want a house with a pool, but we ended up with one. The maintenance is much less than what it used to be. With the large filters (require cleaning only once per year), good sweeps (Dolphin), and automatic chlorinators, the time requirements for maintenance are low.

That's the deal. the kids really like it. Our house is very popular in the warmer months. My wife likes doing lap swimming. It's probably a $1500/year expense for the power to run the pump, and for the chemicals, but this doesn't include the resurfacing every 15 years or so, which adds another $500-1000 per year in cost.

Depends on the area. In Florida, Arizona, and Texas it's probably a break-even proposition. In Northern California it probably adds no value at all to the house.
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Craig Davis wrote:

You'll want to do a combination of things:
-Some sort of cover is essential, and on a new pool I'd get it integrated into the design rather than use an after-market bubble-cover. An automatic cover will be more likely to be used than a manual cover.
-Solar panels, as many as is practical, since you want the water pretty wram.
-Gas heater for the times when the solar is insufficient. A gas heater isn't expensive to install, just expensive to run.
I've never heard of an electric heater for a pool, the power requirements would be overwhelming.
In California, our pool is a six month a year pool, May to October. Heating it would be way too expensive. We get good use out of it during the warmer months, but it would cost about $50 a day to heat it, as it's about 40,000 gallons.
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