Cost to heat pool can anyone confirm or deny figures

[pbolden]

Hello Everyone,

I am trying to determine if I can afford to heat my inground pool during the winter months. Can anyone confirm my numbers?

My pool is very small, fiberglass, solar cover and enclosed . Location: Columbus, Ohio. Average January temp: 26F.

Volume: 2600 Gallons, 125,000 BTU gas heater (82%), cost per therm $.54, area 103 sq ft, perimeter 52 ft, average depth 4ft.

I'm looking to maintain 90F. My calculations indicate a monthly cost of about $100. Can anyone confirm or deny?

Thanks,
Paul

 

[CountyBumkin]

Here's a link to a calculator that might help http://noanderson.com/services/swimming-pool-energy-temperature-calculator/#

 

[Swampwoman]

Oops...saw that you gave te BTU Will try to get ack to this thread tonight and confirm, but if you have 10% of my water volume, 1/6 of my SF, etc. and I can run for 100/week I'm pretty certain you can run well under 100/mo if you keep the cover on, run it up past 90 (eg 96 daily, then heater off for balance of day til it drops to 90) you'd be golden
------------
When you say enclosed, do you mean indoors, or simply sheltered?

I am operating an outdoor ig pool inside a vinyl dome in Michigan and by heating for about 8-10 hours overnight, maintaining 95 for physiotherapy. That takes between $12-$14 a day to accomplish with 24k gallons and a 200k btu heater.i lose approx .3 degrees an hour when the heater is off.

Surface area of 100' doesn't quite sound right (eg mine is 600) -- can you double check that?

If you tell me the btu of your heater, gallons, and average air temp inside enclosure, I might be able to get you ino the ballpark.

The Calc in th link will assume outdoor location.

 

[pooldv]

I would also take a look at a heat pump and/or a dehumidifier. You can heat a pool and dehumidify the indoor pool space. Often it is cheaper to heat with a heat pump if you intend to maintain the water temp.

We'll see what Swampy comes up with for numbers, but I would expect it to be less than 100 bucks per month.

 

[pbolden]

Thanks for the response Pooldv. I've used a heat pump for several years. They are very economical to use to a point. Below 48F they will not function which has meant that by mid Nov. our swim season is over until mid Mar. As we approach Nov. the heat pump needs to run nearly 24hr to maintain the pool temp opposed to a couple of hours every other day or so during the summer.

 

[pbolden]

Hello SwampWoman. I am using a greenhouse as a pool enclosure. It is a permanent structure made of aluminum and clear polycarbonate windows.

Surface area of 100'? I pulled out the dig diagram from about 10 years ago and it says 103'. I will try and attach a copy of the diagram and a still of our pool before the enclosure was added. The still comes from a youtube video that I posted. It not very clear but will give you and ideas of the pools size.

The average air temp. I don't know it offhand but I will check in a couple of days when it's cold again. Crazy Winter again with temps up and down. Currently 3 days in the 50's.

Thanks,
Paul

 

[pbolden]

Thanks CountyBumkin.

 

[Swampwoman]

Okay, lets say the Air to water temp differential is
64 degrees
2600 gal
103 SF

64 x103x5= 32,960 BTU - so you'd lose about 1.51 degrees an hour (without a cover, so more like 30-40% of that) if the differential was that great, which sounds unlikely.

With 2600 gallons at roughly 8.35 lbs per gallon, it takes about 21,710 btu to heat the water 1 degree.

So with a 125x82% heater, you'd use 102,500 BTU /hour and in perfect conditions net 4.72 degrees increase each hour you ran heater.

Between the cover AND the greenhouse, im going to guess the most you could actually lose if you kept temp up and ergo pipes and ground hot like i do is about a third of a degree an hour. Your heater can get back at least 4 degrees an hour, then once you've run up to temp and are just doing daily boost heating to overshoot the mark, you'd need to run the heater about 3 hours a day worst case (but covered or all bets are off) to keep the temp up.

So 3 CCF or therms (cause you can only use 1 an hour) would be $1.62 a day or $48.60/month IF you ran it up once to past 90, didn't thermostat, and scheduled your heater on full throttle for 3 hours a day.

I actually doubt you'd even need that much...I thnk you could get it dialed down to under two hours

The trick will be to run up to temp, as the initial heating won't be terribly efficient as its working against the loss, but daytime sun in a green house setting also offsets that. Depending on your water temp, it could take a day or two to get in the 90s, but then monthly maintenance looks pretty cheap...just don't let it drop

For reference on the calcs since I couldn't remember: note to self, remember where you posted this

To calculate rate of loss, I believe you multiply air differential to pool water, multiply by square footage of surface, multiply x5 for BTUs of loss.

So with a 100 degree differential (eg -6) times 600 SF x 5 = 300,000 BTU.

It takes roughly 200,000 BTU (24,000 gallons x 8.35 lb per gallon=204,000 BTU ) to move my water temp 1 degree.

So on a -6 day, notwithstanding the insulating effect of a) the dome itself and b) my solar cover...in theory I would lose roughly half a degree more an hour than I could produce. Ergo, I couldn't keep up (heater is 266k btu x80% efficiency= 212,000 btu/hr max capability). (This also means that I can't really use much more than 2 CCF per hour even if I wanted to.

 

[pbolden]

Thanks Swampwoman obviously you're a very smart person and I appreciate all the time you took to do the calculations. If I could continue to impose, I have two additional questions.

1) I'm thinking of purchasing a 250k opposed to the 125k. If I remember high school physics and the law of thermodynamics (a long time ago LOL). If both heaters have the same performance coefficient (in this case 82%), then doubling the BTU would decrease the heat up time but the quantity heat (ccf) needed to reach the same temperature (say 90F) for the same quantity of water would be exactly the same...correct? If so, would moving up from 125K to 250K be overkill for a pool as small as mine?

2) I currently have a single speed pump. Should I upgrade to a variable speed considering Winter operation?

Again, thank you for your time.

Paul

 

[Swampwoman]

Hi Paul. My opinion, though only informed as a lay person, is that upgrading to a 250k might be overkill in that yes, your consumption per hour doubles. But that really depends on the degree differential you're aiming to overcome.

Eg. In my case in Mich, had I upgraded to a 400k btu, it could be argued that when temps are at -6, the speed of heating might increase efficiency. In my case, going with a 400k would have meant upgrading my gas meter to a million btu and redoing at least a 79' run of NG pipe, which would have been exorbitant. You never want to starve a heater of NG...you want t add up all the possible effective btu required I your home to ensure max feed...In my case, my 150k btu home boiler would have competed with a 400k pool heater in the dead of winter

In general, I expect a VS pump would not only serve you well for winter operation, but possibly offer you worthwhile savings on your kwh electric cos. If you're of a mind to replace the pump anyway, I suspect it'd pay for itself in a few years....wish I had on and that's next on m list

 

[pbolden]

Again, thank you SwampWoman for your time and advice!

 

[Swampwoman]

Much obliged