Add a heat pump to existing gas heated pool

[Fresnoboy]

Hi folks. We have 40,000 gallon pool here in the SF Bay Area. We swim year round, and the girls really like the pool heated to around 85 degrees. The pool is 20x50, and has a pool cover on it that helps retain heat and is dark enough to heat the surface quite a bit when it's sunny.

We have a lot of solar, but our PGE bill is dominated by gas charges, which can run $600-700 dollars a month. We have a sta-rite 400K BTU gas pool heater, and when I used the calculator on the Pentair site about gas vs electric heat pump comparison, it seems like we could save a lot of money by adding an electric heat pump, even with our extreme prices from PG&E (we pay $0.25/ KWh off-peak, but gas prices are $2.80/Therm).

The goal would be to use electric heat pump to maintain pool temp during electric off-peak hours, and use the gas heater to bring the pool back to temp after we get back from a vacation or to heat the spa. Pentair heat pumps can be connected to the intellicenter system pretty easily, but the intellicenter can control a heat pump using a relay option. The control system for this may be more complicated than what my pool guy can handle, but I am an engineer, and have the pool controlled through Home assistant, and using the poolcontrollernodejs system, I can control things down to the relays pretty easily.

So some questions I'd love to get feedback one:

1) Given my energy prices and situation, does this idea make sense?

2) Is there a better gas vs heat pump calculator available?

3) Has anyone implemented this 2 heater approach before?

4) What heat pump models do folks recommend? The size of the unit would be on the upper end I think to be able to handle keep temps stable, but a scrolling inveter unit like our Mitsubishi heat pumps would be seem to be a good option to deal with both winter and summer environments. The SF Bay Area climite is very mild, so heat mumps work well here.

Thanks!

 

[setsailsoon]

Hi folks. We have 40,000 gallon pool here in the SF Bay Area. We swim year round, and the girls really like the pool heated to around 85 degrees. The pool is 20x50, and has a pool cover on it that helps retain heat and is dark enough to heat the surface quite a bit when it's sunny.

We have a lot of solar, but our PGE bill is dominated by gas charges, which can run $600-700 dollars a month. We have a sta-rite 400K BTU gas pool heater, and when I used the calculator on the Pentair site about gas vs electric heat pump comparison, it seems like we could save a lot of money by adding an electric heat pump, even with our extreme prices from PG&E (we pay $0.25/ KWh off-peak, but gas prices are $2.80/Therm).

The goal would be to use electric heat pump to maintain pool temp during electric off-peak hours, and use the gas heater to bring the pool back to temp after we get back from a vacation or to heat the spa. Pentair heat pumps can be connected to the intellicenter system pretty easily, but the intellicenter can control a heat pump using a relay option. The control system for this may be more complicated than what my pool guy can handle, but I am an engineer, and have the pool controlled through Home assistant, and using the poolcontrollernodejs system, I can control things down to the relays pretty easily.

So some questions I'd love to get feedback one:

1) Given my energy prices and situation, does this idea make sense?

2) Is there a better gas vs heat pump calculator available?

3) Has anyone implemented this 2 heater approach before?

4) What heat pump models do folks recommend? The size of the unit would be on the upper end I think to be able to handle keep temps stable, but a scrolling inveter unit like our Mitsubishi heat pumps would be seem to be a good option to deal with both winter and summer environments. The SF Bay Area climite is very mild, so heat mumps work well here.

Thanks!

Fres,
I've looked at a similar arrangement for my next pool. No natural gas at the new home and propane prices in Florida are way higher than most of the country (never could figure out why) but electric prices are half your off-peak rate (we have a high % nuclear). Part of the problem you will face with a large pool is heat pumps are less than half gas heater capacities. So they heat the pool up very slowly. Evaporation really sucks the heat out of a pool a lot. Evaporation increases significantly with wind velocity. With your cover you help offset this issue and it will be critical to use on windy nights. What does your payback calculation show? For most investments I like to see a 3-5 year payback. I think the Pentair calculator is pretty good and never could find one better. In my case with much different cost inputs and very mild winter conditions payback just isn't there for a heat pump. Solar does payback but it's at the high end of my desired payback. I'll probably stick with solar/propane plus cover to start with and see how this works.

I hope this is helpful.

Chris

Chris

 

[Fresnoboy]

Fres,
I've looked at a similar arrangement for my next pool. No natural gas at the new home and propane prices in Florida are way higher than most of the country (never could figure out why) but electric prices are half your off-peak rate (we have a high % nuclear). Part of the problem you will face with a large pool is heat pumps are less than half gas heater capacities. So they heat the pool up very slowly. Evaporation really sucks the heat out of a pool a lot. Evaporation increases significantly with wind velocity. With your cover you help offset this issue and it will be critical to use on windy nights. What does your payback calculation show? For most investments I like to see a 3-5 year payback. I think the Pentair calculator is pretty good and never could find one better. In my case with much different cost inputs and very mild winter conditions payback just isn't there for a heat pump. Solar does payback but it's at the high end of my desired payback. I'll probably stick with solar/propane plus cover to start with and see how this works.

I hope this is helpful.

Chris

Chris

Thanks. Yes, large pools have challenges with heat pump units, but that's why I am not interested in replacing the gas heater, but augmenting it with the heat pump. The Pentair calculator says I would save about 10K/year going with the heat pump with my gas prices, but that assumes I think a complete replacement, and that is with off-peak prices for electricity, so times it could run would be limited. Still, it was significant enough of a savings to get my attention!

 

[wgillette]

@Fresnoboy What did you decide? I stumbled across this thread while looking for a better/more detailed comparison calculator. I built my system last year with both a gas heater and heat pump. Someone shared this calculator with me:

Pool Heat Transfer Tools v022.xlsx

ReadMe Version:,v022 Disclaimer,These spreadsheets are provided as is without any guarantees or warranty. Spreadsheet License,By using this spreadsheet you agree to the following conditions: This spreadsheet is for personal use only and shall not be used for any commercial business without the ...

docs.google.com

If you haven't decided, this might help.

 

[Newdude]

The Pentair calculator says I would save about 10K/year going with the heat pump

Make sure you are calculating any power and delivery surcharges. They make up over half my electric bill and are never factored in when the yellow tag on a new dishwasher says it will cost me $78 a year.