Heat pump feasibility for Nov-Feb in Phoenix

[itfargo]

Hi all. I've read back about a year on the forums and searched the internet as well, but don't quite have a full picture of how a heat pump will work for us.

We have family that would like to be able to swim while visiting Phoenix during the winter months (Oct - Mar). I wanted to get some feedback from others (hopefully in the Phoenix area) on how well heat pumps or other heating methods work for their pools. We'd also get a cover to help with heat retention. Our family is from way north and 80F is likely great swimming temp for them. But the swim season here is about late April through October without a heater or cover.
We got one quote for a Pentair 140k BTU heat pump, and my questions are mainly about how likely that will be able to heat the pool for visits in the colder parts of our winter, Dec - Feb.

The Facts:
- 11,500 gallon in-ground pool, 5ft max depth, plaster
- Pentair Intelliflow v2 primary pump
- Single speed pump for in-floor cleaning system
- Only electric available, no gas feed to the neighborhood
- Would target for swimming days being 70-75F at the coldest for the daily high
- Pool temp target 80F or higher
- Assume we also get a pool cover
- Quoted heat pumps are Pentair 140k BTU and Aquacal 126k BTU

The questions:
- For weeks where the highs are only around 70F, how likely can we get and keep the pool temp to 80F or higher?
- Are the quoted pumps sized right, or overkill?

Really, that's about all the questions. My family wants to go in on it since it'd be for the whole family, but I don't want to waste any money if it's not going to let them swim when they visit in the winter.

Thanks for any insights!




Thanks for any input!

 

[Jd5996]

Our temp hit a low of 48* last night and I only lost 2 degrees of water temp...our daytime temp yesterday was 77 and today will be 76.

My pool temp is at 84* with a 95K BTU heat pump, machine temp is about 88* and has been running 24/7 since Nov 1.

I imagine with a 126 or 140K I would be in the high 80's to low 90's.

Its really more about the lows than the highs IMO, my machine continues to increase in temperature at +64-65* ambient air temp...lower than that and it maintains at best or loses a few degrees depending on how cold it gets overnight.

I would imagine our temps are somewhat similar, we are fortunate that our coldest overnight temps only last about 4-6 hrs.

Hope that helps a little

 

[Jd5996]

On second thought let me rephrase...I think HIGHS & LOWS are equally important. Your lows will determine how much you lose overnight and your highs how much of that you recuperate during the day.

At 70* with a 126 or 140 I would think you would recover about 3* during daytime operation

With 95K I am recovering about 2* at 75* temps. So essentially I am breaking even when our lows hit in the high 40's...

Tonight our low is only going to be 65* so I might even gain .5* overnight!!!!

 

[itfargo]

Thanks for the info. Ideally I would like to be able to only run it for the week or so prior to family visiting to get it up to temp, but I'm not sure if that will work at all at the coldest parts of the year.

 

[PoolGate]

I don't think you will be happy with a heat pump in your climate for winter months. I'd be surprised if you got 1 degree rise per day running it 24x7 and I doubt you could maintain that at night. You have a dry climate. I'd bite the bullet and go propane with a buried tank. Since the pool is smaller you could also consider a resistance style electric heater. Have you swam in 80 degree water? That is way too cold for me!

 

[Jd5996]

I would have to agree with PoolGate. 70 is about the absolute minimum these things will produce any gains.


Yesterday my daytime temp was 75* and I picked up about 1.6 degrees during daytime operation. Fortunately, my overnight last night was 65 so I actually maintained that 1.6 degrees...had my overnight dropped below 60 I would have lost all those gains and more depending on how low it dropped.

Again though my pump is only 95K...I would imagine a little better performance from 126 or 140... but thats just an assumption.

 

[JoyfulNoise]

You’ll be fine with a heat pump and cover. You might find it hard to maintain the higher temps during the deep parts of the winter where overnights can get down to freezing. There was actually a thread by a guy in Canada who kept his pool in the high 80’s/ low 90’s all winter long by using a gas heater and a cover. He was able to run the pool all winter, swim in January with piles of snow all around and keep the pool warm. He developed a few procedures that enabled the water to stay warm. One point is that you DON’T run the pump at night because you want to keep the water as still as possible and not pump water through cold ground. Then you heat throughout the day. I’ll see if I can find the link.

Given our weather is A LOT warmer than Canada, you should be fine.

 

[JoyfulNoise]

Here you go - FAQ: Cheaply Keeping a Pool Hot -- 90F,95F,100F -- How we ran till Jan 11th in Canada

Not quite the same as they had a gas heater BUT you may be able to adapt some that poster’s ideas to keep the pool warmer.

Again, not running the pool when the air temps are too cold for the heat pump will help conserve heat in the water. The gunite shell is a very good insulator and so what you need to do is keep the gunite and surrounding dirt warm so that it buffers the pool water. At night, you don’t want to draw warm water out of your pool and flow it through your equipment pad and heat exchanger when it is exposed to cold air. If you do, then you’re radiating heat away. With a good fitting bubble cover, you should be able to keep the temperature loss down to no more than a degree or two and then you want to add that back in (and more if you can) during the day.

 

[Jd5996]

IMHO your best opportunity for success is to fire up the heat pump towards the end of the season before water temp drops below 75 at most (the higher the better) and ambient temps drop below low 80's/high 70's.


Get that water temp up to 92-95 (or higher if you choose) degrees then when the colder weather hits you will only have to maintain the temps you have already built up. Make sure you are covering it as much as possible!


I'm certainly not a guru and am only speaking from personal experience but...


I don't see how you can expect to turn on the heat pump, for example, the week before christmas when the family will be coming down, with day temps at 70* and overnights around 55-60( guessing) water temps probably around 60-62* and pick up 20 degrees in one weeks time.


With a gas heater, as JoyfulNoise has referenced, sure...I could see that. With a heat pump which relies on ambient air temps to generate its warmth, I don't see it...not in a weeks time at those temps.

It's much more feasible to get the temps up before the cold weather hits and then just maintain from there.


Just my 2 cents


If I have a chance tonight I will post all my numbers from this month. I have documented everything since firing up my heat pump. When I say everything I mean everything lol

 

[JoyfulNoise]

As jd5996 says, you need to run heat pumps over a long period of time. You need to have the heat pump running to maintain the heat in the water. But I suggest you DO NOT run your pool after the sun goes down. You want to avoid pumping warm water outside of the pool where it will radiate that heat away. Stick to heating the pool during the sunny daylight hours and then shutdown the pump at night. That’s your best chance for heat retention. As it is anyway, heat pumps lose their efficiency as the ambient air temps decrease and the COP can go below 1 at air temps lower than 40F. The more modern heat pumps have an anti-freezing mode to avoid causing frost and ice from building up on the coils. So your just better off running it during the day when the air temps are higher and your efficiency is greatest.

Be prepared for a MUCH BIGGER winter electric bill.