Calling all heated pool junkies....we have questions :)

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RazorbackFan78

RazorbackFan78

0
May 13, 2013
19
Bentonville, AR
A few questions for you pool heater junkies!

1. Any idea how to estimate how much water temp loss we should expect between now and mid-October? Or as an example: water tends to stay X degrees above avg air temp.

2. What water temp would you recommend for comfortable swimming when the avg outside temp in October is 58F?

3. Would it worth it to get a solar cover just to keep the water temp higher from now til the party? Knowing that we're only heating it for one day of use?

Curious to hear your comments and feedback. We're kicking around the idea of throwing a heated-pool party for our niece's birthday, Oct 18th ror 19th
 
1. No idea. A good rule of thumb is the water will be close to the average air temperature if you are not supplying any extra heat.

2. Warm as you can make it (mid 80s?) since the air is going to feel VERY cold.

3. Most heat loss is through the surface evaporation and radiation. A cover will most certainly help retain heat.
 
1. My water is generally the average of the high and low temps without a heater. I have a cover but don't use it because it is too bulky for my middle aged, petite female body and my pool is too large. My propane heater can raise my pool about a degree an hour depending on the wind.
2. I like mid 80s (84-86). I've heated my pool to he mid 80s and the air was too cold (low/mid 70s) and nobody got into the pool.
3. Depends on the cost of your gas to heat the pool. For me, the cover pays for itself for one party because I pay out the nose to get propane trucked in. Having a cover will help and you can always use the cover next year in the spring.
 
$150 to heat up once? You should recheck your math. Maybe $150 to keep it 85 for the whole month...

But yes, my water temp drops back to the average of the high-low a day or 2 after turning off the heat.
85 is just about right- but I've gone up to 90 for a pool party with kids, they loved it and never turned blue even on a cloudy/drizzly day.
 
I found this calculator on https://www.discount-pool-supplies.com/heatingcosts.php

By their estimates - I'd spend $47 do raise the temp 30deg. Not too shabby, and we'd only be maintaining that temp for 6hours or so. Their results are below.

Total Gallons = 18700

Wind Speed Average = 3.5 MPH

Desired Temperature Rise = 30 degrees

Heater BTU's = 265000

Heater Efficiency = 80%

Fuel Cost per therm = $.8


Our calculations based on your information shown above are as follows:


Total therms required = 58.41

Time (in hours) to raise 18700 gallons of water 30 degrees = 22.04

Time (in minutes) to raise 18700 gallons of water 30 degrees = 1322.58

Cost to raise 18700 gallons of water 30 degrees in 22.04 hours @ $ .8 per therm = $46.73
 
Appreciate that physics isn't everyone's favorite subject (I mean, what's wrong with you people? :) )


Skipping some sticky details, the envelope math says...
A "Therm" is an amount of gas that produces 100,000 BTUs
A BTU (British Thermal Unit) is the amount of heat it takes to raise one pound of water by one degree Fahrenheit.
A gallon of water weighs eight pounds (a pint's a pound the world around)

19,000 gallons = 152,000 pounds

152,000 pounds x 30 degrees = 4,560,000 BTU's

4,560,000 BTU / 100,000 BTU/Therm = 45.6 Therms

Lots of loss terms ignored- heater efficiency, evaporative losses, raising the surrounding pool shell and ground temperature, etc. I'd estimate about 50% higher to cover all that.

Gas prices vary, but $0.50 to $1.00 seem to be the range.

So expect $60-70 worth of gas to heat your pool 30 degrees.
 

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prs said:
Are you sure? In the rest of the world a gallon of water weighs ten pounds. :eek:
Click to expand...
I can not tell if this is a joke or not :scratch: Water weighs a little over 8.3 pounds per gallon

Although I assume you are referring to a UK gallon which is 10 pounds which has no relevance to this discussion as in AR, I highly doubt he was referring to 18700 UK gallons of water ...
 
It's a joke!! Desterline wrote

"a pint's a pound the world around"

Well, it isn't in the UK and much of the British Commomwealth. There a pint is 1.25 lbs.

And that comes in handy when ordering pints in pubs. :p
 
prs said:
It's a joke!!
Click to expand...

I wish it all was. :-(

So apparently I just got schooled over a basic assumption I've been using for the better part of thirty years. I was under the belief that a "fluid ounce" was defined as 1/128 of an US gallon and was one avoirdupois ounce (mass) of water at some specified purity, temperature and pressure. And since 128/16 = 8, I've been using 8lbs per gallon as the mass of water. After the trip down this rabbit hole, all I can say is is that I've been about 4% off most of my life. My wife will not be at all surprised by this as she's maintained that I'm "a little off" since I've known her. :)

Interestingly enough, this link shows the density of water as a function of temperature:
http://www.engineeringtoolbox.com/water-density-specific-weight-d_595.html
So water _is_ 8.0 lbs per gallon, but only just below boiling or well below freezing. Probably not close enough for me to plausibly claim that I was right all along...

On the plus side, I can claim that the whole mess is pretty darn complicated with at least two different size "gallons", six different size "pounds" and eleven different sizes of "ounce" in use somewhere around the world throughout history.


As to the original post above - I'm sticking to my numbers. I might be 4% wrong on the mass of the water, but I did include about 50% tolerance to cover ignored loss terms- I just didn't realize that included my bad assumptions about the size of an ounce.
 
Desterline said:
I wish it all was. :-(

So apparently I just got schooled over a basic assumption I've been using for the better part of thirty years. I was under the belief that a "fluid ounce" was defined as 1/128 of an US gallon and was one avoirdupois ounce (mass) of water at some specified purity, temperature and pressure. And since 128/16 = 8, I've been using 8lbs per gallon as the mass of water. After the trip down this rabbit hole, all I can say is is that I've been about 4% off most of my life. My wife will not be at all surprised by this as she's maintained that I'm "a little off" since I've known her. :)

Interestingly enough, this link shows the density of water as a function of temperature:
Water - Density, Specific Weight and Thermal Expansion Coefficient
So water _is_ 8.0 lbs per gallon, but only just below boiling or well below freezing. Probably not close enough for me to plausibly claim that I was right all along...

On the plus side, I can claim that the whole mess is pretty darn complicated with at least two different size "gallons", six different size "pounds" and eleven different sizes of "ounce" in use somewhere around the world throughout history.


As to the original post above - I'm sticking to my numbers. I might be 4% wrong on the mass of the water, but I did include about 50% tolerance to cover ignored loss terms- I just didn't realize that included my bad assumptions about the size of an ounce.
Click to expand...
Good post, I just want to say if need want to know more about density of water or calculate it look here What is the density of water lb/ft3 by Temperature and Unit
 
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