Pool Heater Calculations

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R

rwx

0
Jul 10, 2010
15
I had some friends ask me about the cost to heat and maintain temperature for a pool. I made up the attached Excel spreadsheet to estimate the cost to initially heat a pool, and the cost to maintain the heat.

It's basically fill in the appropriate blanks in column A, and the results appear in column B.
 

Attachments

  • PoolHeating.zip
    5.9 KB · Views: 56
For Excel users who do not want to open the .xls file, here is the same thing in a text file that can be imported into a clean Excel file. It is tab delimited.

I will also write this up showing the formulas.
 

Attachments

  • PoolHeating.txt
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I actually opened the file up and wanted to review it before asking questions. Safe to open. With me, I purchased a heat pump (long story), which works well and have done some studies. I really feel that a lot that there are many variables, including temperature, humidity, sun exposure, wind speed, etc. Below is a link to the heat pump. I would love to see something like this for a gas heater, etc. In addition, my pool could be larger than I believe, but really hard to tell. This is what I was told originally, but suspect about 16,000. For my signature, will keep as is though.

Heat Pump recommendations - Gulf Stream - Page 2

Post # 30
 
You are right, there are a lot of variables that can affect the energy calculation, but I boiled it down to simplify the calculation. Although have not taken the data you have, I know the energy required to heat the pool is pretty accurate.

WRT the energy required to maintain the temperature, this calculation was furnished to a friend who wanted to determine how much it would cost to heat a pool at a rental house he had, and he said it was very close.
 
Your heat pump rating is too low. I don't have one, but most of them are 100,000 - 150,000 BTU per hour, and with a heat pump you have to look at the COP for the ambient temperature.

I'll be happy to do some research for you -- what is the heat pump model number, and your pool dimensions.

Edit: I mis-read your post -- I took the 16,000 as the BTU of the heat pump -- sorry.
 
rwx said:
Your heat pump rating is too low. I don't have one, but most of them are 100,000 - 150,000 BTU per hour, and with a heat pump you have to look at the COP for the ambient temperature.

I'll be happy to do some research for you -- what is the heat pump model number, and your pool dimensions.

Edit: I mis-read your post -- I took the 16,000 as the BTU of the heat pump -- sorry.
Click to expand...

COP is 6.3. My pool dimensions are 17*33, but it is a free form pool with an 8' deep end (liner pool). You can safely guess that I am around 14,700 because the pool goes from 17' to (13' in the middle) and 16' in the shallow end. A 3' shallow with a slope to deep end and concaved walls. I would assume that the pool is no more than 15,700, but can use 16,000. The heater is a 125,000 output and the specs are here.

HE125 and HI125 MODELS

- - - Updated - - -

Gulfstream HE125RA - 117K BTU Heat Pump

- - - Updated - - -

TEMP outside/HUMIDITY outside/DEGREE of Pool Water Desired

80/80/60 = 6.3 @ 117,000
80/63/80 = 5.9 @ 109,000
50/63/80 = 4.1 @ 74,000

If the temperature is 50 degrees outside, no one is going swimming and the pool will be more likely than closed for the season. We had a cool spell this year where daytime temperatures were 75* and water was 85*, which was not fun at all. The manufacturer really should do testing at 85 degree desired water output, which is more realistic.
 

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To: Catanzaro

Thanks for providing all the data in your link. If you can give me the pool dimensions, I can re-calculate the pool volume.

It did show that I should include the cooling effect in the calculation, and that heat pumps are rated in BTU output, where gas heaters are rated in BTU input.
 
The heat loss constant that you are using will have an extremely high variance with conditions so I am not sure that is going to be all that accurate. Plus the heat loss of a pool is primarily drive by the temperature difference between the water and the dew point temperature and not air temperature.

Some time ago, I put together a heat transfer spreadsheet that takes into account the local weather conditions, solar covers and all of the heat loss components as well as including heat gain from the sun, solar panels, NG and/or heat pumps. The spreadsheet can be found here:

Hydraulics 101 - Have you lost your head?
 
The intent of this was to provide a simplified calculation to estimate the times and costs to heat a pool over an extended period, like a week or a month.

It's true that the heat loss coefficient is the result of a lot of variables -- I have seen values as low as 4 and as high as 10.5, so the actual values could vary significantly from the estimate.
 
To Catanzaro

Although I came out with a result about the same as your data sheet (I calculated 6 degrees pool temp increase in 6.8 hours with a 117,000 BTU per hour input), I think when you get into the technical details there are some environmental effects that probably cancel each other out. (Cooling of the pool due to the ambient temperature difference and evaporation, and heating of the pool due to solar radiation, etc.)

I have a gas heater and a small pool, so the heater output and the small pool volume tend to outweigh any environmental effects.

I have a pool at a rental house that I can get 24/7 data from, so I'll get some data from it to see how what happens when you don't have a heater running -- the actual pool temperature change over a 24 hour period.
 
I was brave and opened it

real cost per ccf for natural gas here based on 12 month average from bills is $1.23

We heated our ~20k gallon pool up from in the high 70s to the high 80s for one weekend and it raised our bill by over $120

The sheet shows $43.34 to raise the temp 20 degrees and $0.85 per hour to maintain based on 20 degree temp delta - worst case

I don't think we tried to maintain it for 50 hours but maybe

When I was researching my new raypak heater I found they have a really comprehensive calculator on their site

Pool Heater Sizer
 
Thanks for the data. I'm trying to duplicate your calculation. Is the pool surface area the sum of the 16x31 and 11x7?

(the calc for heating the pool to temperature uses the pool volume, and the calc for heat loss per hour uses pool surface area)
 
using your dimensions, $1.23 per CCF, .85 heater efficiency, 20 degree rise for initial heating and 20 degrees temperature differential, I get:
$53.63 to heat the pool
$1.29 per hour maintain the temperature.

However, the high cost may have to do with the cost of gas, which depends on how you are billed. For Texas, the residential cost has gone from $1.24 per CCF in March 2017 to $2.38 per CCF in August 2017 (US Energy Information Administration figures).

Where I live, they charge the actual cost for the gas, then add in the piping charges, and other service charges, so a double in the price of gas will not double the bill.
 

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