Electric heat pumps - how do they work?

[merentha]

Hi! I'm pretty new to pool equipment - we moved into a place with a pool two years ago, and I've learned to keep up with cleaning, chemicals and testing over the summers, but that's about it. I live in Massachusetts, and we're having some work done on our pool before we open it sometime in June. It's around 21000 gallons, 18x36, rectangle, in-ground, vinyl liner. There's a step that's collapsed, and in addition to having that repaired we're having a new liner put in (the old one has some serious issues inherited from the last owner).

We're also looking into warming solutions. We'd like to keep it nice and toasty, but we can't do that with our existing propane heater - we've tried, and it costs a fortune. We don't have a gas line to the house, and getting one put in would cost quite a lot because the nearest main is a good distance away. The really nice gentleman who opens/closes/repairs our pool has recommended switching to a 125000 BTU Raypak electric heat pump. (We also plan to install and use a solar blanket on a reel.)

We're on board, but we don't know a lot about how this will work. Is a heat pump essentially on all the time, maintaining the pool at a set temperature? We would have to sell the house to afford doing that with our existing propane heater. Will the cost of doing that with an electric heat pump be outrageous? I've looked through the forum at some of the heat pump posts, but I'm not clear on what level of use the calculators are assuming - constant, like running an A/C in the house to keep a certain temp? Or just powering it up before we swim?

Any tips on this would be very welcome!

 

[JohnA902]

When it works I run mine only in spring and fall. The solar cover gives me 60% of my heat in the summer. It is slow to heat so when I want it warm I will be running it for 12-15 hours easy for 4-5 days to get it to be warm. I never like doing 24hour pump runs just because it seems like too much.
To answer your question you will need to run your system often to get the benefits. There are calculators online to see how many hours it takes for 1 degree depending on your pool volume. It’s sad to see how slow it is if you are used to gas.

 

[ajw22]

Pentair has a Heat Pump Calculator to determine the appropriate size Heat Pump for your location. Pentair seems to do honest calculations based on the physics and efficiencies of each type of pump and energy source.

To get the most accurate cost comparison you should change the default electric kwh, natural gas price, and propane price to actual prices in your area.

A 125K will heat your 21K pool 1/2 to 3/4 degree per hour. So to get a significant temperature rise takes a while with a HP.

 

[merentha]

Thank you for the replies! I tried the calculator, but I couldn't tell if the savings it showed over other types of heater were based on periodic use, or "always on" use. Our propane heater, for instance, was only used when we knew we'd be in the pool, and would heat the pool to a swimmable temp in one day. But my understanding is that the heat pump is not used that way.

I was under the impression that people ran electric heat pumps all the time to maintain a given temperature - at least, all the time during the months they might be swimming. Kind of like an air conditioner, which you set to maintain a specific temperature rather than turning it off and on manually all the time. Is that not the case?

 

[JamesW]

When do you want to start and end heating (month/day) and what temperature do you want to maintain?

What is the pool surface area?

Will the pool be covered?

 

[merentha]

Hi, James - We plan to start sometime in June - there's work to be done first - and maybe through September. We do plan to cover the pool using a solar blanket on a reel.

The pool is 18 x 36, so 648 sq feet surface area. I'm guessing we'll want to keep the pool at around 80...ish...? Last year we barely used it because it was often too cold at around 70-75 degrees. So we'll have to experiment a bit to find the sweet spot. The pool is usually at least half in shade by 2-3pm in the afternoon, which doesn't help. Last year we experimented with a solar blanket, but didn't have a reel, and it was kind of an annoying nightmare to haul it in and put it back out again.

 

[Hootz]

There are pros and cons of both. It depends on your type of usage. You already know roughly how a gas heater would work as you now have a propane heater. If you are the kind of family that wants to start the heater in the morning so you can use it in the afternoon you probably do not want an electric heat pump. At our house we tend to use the pool more on the weekend so Thursday evening I will fire up my heat pump to be ready early Saturday afternoon. I have a spa and can heat it to temp by isolating circulation to the spa only, in about 3 hours. Most will say a heat pump is slightly more economical but the biggest issue in choosing a heater is your utility situation and type of use.