Heat pump heating much less than expected - but maybe normal?

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Ticojpunk

Ticojpunk

Well-known member
Apr 4, 2023
51
New York
I’m a little frustrated so far but writing to see if maybe this is normal. Getting tired of my family saying “why is the pool still cold didn’t we get a heater?!”

Yesterday the pool started at 62.8. It was in the 70s all day and my pool gets a lot of shade during the day. Only an hour or two is direct sun. Running the pump from 9am to about 10pm, I was up from 62.8 to 69. I lost a degree or two over night. Today it’s in the 80s but a bit cloudy. Pump turned on around 8am (starting at likely about 68). It’s now 2pm and I’m up to just about 72. 6 hours for 4 degree on a pretty warm day.

Feeling the return with my hand the water is generally only slightly warmer than the overall pool temp. It’s subtle for sure.

Does this seem like normal electric heat pump operation or should I expect a little more out of this thing?

21’ round above ground and heater is Aquacomfort ACT750.
Hayward pump is single speed at about 70gpm.
 
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You have a 10,000 gallon pool, which is 88,000 lbs. of water. Your heater is 55,000BTU/hr. 1BTU raises 1 lb. of water 1*F.

So you would expect a 1.6*F temperature rise per hour under ideal circumstances and 100% efficiency. You're getting 1.5*F per hour.

I would say it's working just like it's supposed to.
 
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Thanks. Hopefully someone else can take a look at the numbers. Would a diverter valve help if I slowed the flow actually going through the heater? I think in my heater specs it mentions up to 50gpm being the optimal max? It'd then be combined with the non-heated water, so not sure if it'd then break even. Just trying to get things in place before swim season fully kicks in.
 
MITBeta said:
Unless the heater output is somehow related to flow, changing the flow shouldn't matter. Heat is heat.
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I do think slower flow allows more heat to be transferred to the water. But again, combined with unheated water back into the pool I might just break even.

If there a way to slow the flow of your system either pre filter pump, or after the filter, or does that put a strain on the filter pump itself and not a good idea?
I know a multi-speed pump would probably be a good idea, but my pump is single speed unfortunately.
 
No, slower flow allows more temperature rise, but in less water. Changing the flow does not change the amount of heat.

My suspicion is that the rating on the heater is for ideal condition and you are not operating under ideal conditions. The website for your heater says: 80* water, 80* air, 80% humidity. Once you move off those numbers, you start derating. How fast, I can't say.
 
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MITBeta said:
No, slower flow allows more temperature rise, but in less water. Changing the flow does not change the amount of heat.

My suspicion is that the rating on the heater is for ideal condition and you are not operating under ideal conditions. The website for your heater says: 80* water, 80* air, 80% humidity. Once you move off those numbers, you start derating. How fast, I can't say.
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I’ll be patient for now. So far, I’ve yet to get to that target temp to maintain it. And lots of cooler nights, overly mild days. So it’s been a struggle. Hoping once I get to 85 and it’s more consistently warm out maintaining that 85 won’t be hard.
 

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80 deg air, 80% humidity, 80 deg pool water is that HPs sweet spot. 55,000 BTU heater seems real small for a pool w/ that many gallons. Solar cover would definitely help, especially if the temps drop overnight. HP's are good for maintaining temp, not getting there quickly.
 
Ticojpunk said:
Thanks. Yesterday I ran the pump approx 12-13 hours though, gaining about 7 degrees. (.58F per hour)
Today it was 6 hours for 4 degrees. (.66F per hour).

Am I missing part of the calculation?
Click to expand...
deltaF = 55,000 / (10000 * 8.34) = 0.66 dF/hr

This of course is without heat loss.
 
Newdude said:
It'll do GREAT at 85. I found mine didn't like 70 degrees or below.

You're using a solar cover, right ?
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Still figuring out out to manage a solar cover. I’ve got no help for putting it in and taking it off. Using liquid solar cover for now for what’s it’s worth. Only lost 1-2 degrees last night and it got down to the 50s so not terrible.
 
Newdude said:
It's worth none with the pump running. Or with a slight breeze with the pump off.

Heck, either will push a solid solar cover to one end, much less a liquid solar cover. 🤷‍♂️
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Completely understand the downside. A lot of the time it’s pretty still at night. It’ll help when it can. Overall I’m just checking to make sure what I’m experiencing with the equipment I’ve got is normal behavior and that I don’t need to look into possible issues with the heat pump or glaring configuration problems.
 
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Ticojpunk said:
I’ve got is normal behavior and that I don’t need to look into possible issues with the heat pump or glaring configuration problems.
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No problems. :) It takes many BTUs to heat, and HPs need favorable weather on top of being shortchanged in the BTU department.
 
Newdude said:
No problems. :) It takes many BTUs to heat, and HPs need favorable weather on top of being shortchanged in the BTU department.
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An hour or so ago the pool water hit 75 and climbed a bit more to 75.5. At THAT point, I can feel with my hand a difference in the output temp. I really do think with water below 75 and humidity relatively low outside, even when it's low 80s out (and pool is in shade most of the day), it's just by nature unimpressive. I think when it gets into those upper 70s, lower 80s water temps It'll perform a lot better. It's just be a frustratingly cool start to the pool season here in NY, and NE US in general. Low overnight temps, not many days above 80. Gotta just keep fighting for that 87ish target I want and run the heater consistently in order to stay there. Fingers crossed.
 
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Ticojpunk said:
I’m a little frustrated so far but writing to see if maybe this is normal. Getting tired of my family saying “why is the pool still cold didn’t we get a heater?!”

Yesterday the pool started at 62.8. It was in the 70s all day and my pool gets a lot of shade during the day. Only an hour or two is direct sun. Running the pump from 9am to about 10pm, I was up from 62.8 to 69. I lost a degree or two over night. Today it’s in the 80s but a bit cloudy. Pump turned on around 8am (starting at likely about 68). It’s now 2pm and I’m up to just about 72. 6 hours for 4 degree on a pretty warm day.

Feeling the return with my hand the water is generally only slightly warmer than the overall pool temp. It’s subtle for sure.

Does this seem like normal electric heat pump operation or should I expect a little more out of this thing?

21’ round above ground and heater is Aquacomfort ACT750.
Hayward pump is single speed at about 70gpm.
Click to expand...
Really good explanation by a company that specializes in heating large bodies of water.
ej-bowman.com

Why doesn’t my pool heat up faster? - EJ Bowman

Do you want to know why your pool doesn't heat up? There are several reasons for swimming pools not reaching temperature - find out more.....
ej-bowman.com ej-bowman.com
 
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