Heat Pump Pool Heater Options?

[WorldwideDave]

I've proven in the last 3 months that I can run a pool pump and pool heater from solar. But the pool heater is a gas-powered, 10,000 BTU, about 60% efficient, super expensive to run because of the price of gas.
Doing this experiment, I have reduced my electric bill by just over $500 over 3 months, but by running the heater longer into the season - 2 months longer so far - I am paying way more in gas than I was in the past. About $600 more in gas bill over past 2 months, so it has effectively cost me $50 per month - $100 for 2 months - more than I spent in years past. Not bad, that's about $13 per week to keep the pool up at 90 degrees.
Having said that, I would like to reduce that gas bill from $300 a month to zero, then the savings a year from now will be $3,600.
I see some people are using heat pumps as 'dump loads'. I just don't know much about heat pumps for heating a pool. Not sure what the cost will be. Not sure if they run on 120V or have to run on 240V. Also not sure what to expect - will it raise the pool temp about 1 degree an hour, or about .25 degrees an hour? No idea how effective they would be for my installation.
I am a better plumber than electrician, so I can likely handle the installation myself.
Obliviously pool water is a bit different than house water - I can't install like a home water heater and have the pool pump circulate water through that electric element to heat it up or anything.
I did remember that when we had our farm we had these little things we floated in the water troughs for the horses so the water did not freeze that ran on 120V. Wondering if something like that exists only larger to heat a pool. No idea.
Thanks for reading as always!

 

[robbob2112]

Were it me seems like the simplest would be a plastic tank, say 50 gallons or 100 gallons, dig a pit and put in insulation under and on all sides of the tank thick as you can so as to limit losses to ground. Fix it so pool water cycles through that tank.

Then get copper tubing - maybe a bunch of 1/4in ID and a larger plenum for in and out ... large enough a quantity so as to minimize the drag of the water through the tubes. The just circulate the heatpump fluid through the tubes.... so you are transfering the heat from the air/ground (geothermal is more efficient) into the tank where the pool water is circulating.

basically a liquid heat exchanger with no electricity to connect things. Being a pool would probably have to have some sort of GFIC on the heatpump wires.

But one question - do you have an insualted cover over the pool to minumize heat lose?

 

[AntronX]

It takes 43.8 kWh of heat (without any losses) to raise 10K gallon pool by 1°C. At COP of 3 a heat pump will take 14.6 kWh of electricity to achieve that.

 

[robbob2112]

and for those of use that didn't understand that --- I got the gist but missed the details - chatgpt explains

Here’s the plain-English explanation:

• Energy required to heat water: To raise the temperature of a 10,000-gallon pool by 1°C, you need 43.8 kilowatt-hours (kWh) of heat energy. This is how much pure heat the water must absorb.
• Heat pump efficiency (COP): A heat pump works more efficiently than direct heating because it moves heat rather than creating it. The efficiency of a heat pump is described by its Coefficient of Performance (COP). A COP of 3 means the heat pump provides 3 times as much heat energy as the electrical energy it consumes.
• Electricity usage: Because the heat pump is so efficient, it only needs to use 14.6 kWh of electricity to produce the required 43.8 kWh of heat. (43.8 ÷ 3 = 14.6)

Key takeaway:​

Using a heat pump with a COP of 3, you only need to use 14.6 kWh of electricity to raise the temperature of a 10,000-gallon pool by 1°C. This is much less than directly converting electricity to heat.



I think that would leave the question open of if you can raise the water with a heat pump faster than it looses the heat to the ground/atmosphere?

 

[WorldwideDave]

But one question - do you have an insualted cover over the pool to minumize heat lose?

I did until last Thursday. Will be putting back on in 48 hours or so. It's not hot right now - probably 60 degrees. I will be warming it back up to 90 with gas starting in next 2 days. Family coming to visit. Replumbing some of the pool before I fire up the heater again.

VERY limited on space. Thinking I need to replace existing gas heater footprint with a heat pump (maybe).

I also did the DIY thing where your run a D/C pump (like a RV shower pump) fused off battery, run 1,000 feet of black landscaping PVC pipe over a white surface, and slowly warm up the pool. While water would come out at 105 degrees, the flow was so slow that it didn't seem to make too big of an impact on an inground pool after October 15 or so.

 

[WorldwideDave]

It takes 43.8 kWh of heat (without any losses) to raise 10K gallon pool by 1°C. At COP of 3 a heat pump will take 14.6 kWh of electricity to achieve that.

It sounds like the heat pump is way more efficient than an electrical only water heater. It only takes 14.6? in 48V world, isn't that 300 Amps?

 

[AntronX]

It only takes 14.6? in 48V world, isn't that 300 Amps?

Sure but that's only to raise it by 1 degree C. How cold does it get in winter and how high do you need to heat it? My guess would be 5 degrees or more. That's 75 kWh per day with a heat pump or more if your pool is larger.

 

[WorldwideDave]

Thank you. Pool is 14,000 gallons. Common size 50+ years ago.
Pool is probably 58 degrees F right now, wanting to get to 90 degrees by Monday.
I can do it with gas, but man will it cost a lot.
This is an abnormal situation, though - temps normally not this cold outside. Normally water would be 72 degrees with no heater, and the desire is 20 degrees hotter at 92 degrees. Yes, a large bath tub.

 

[WorldwideDave]

in case anyone is wondering, pool is used for physical therapy for a group of disabled senior citizens. They aren't getting in if it is under 90 degrees. Getting out when it is 60 degrees outside is not so fun, and they will not go in the pool if there is any breeze or a cloud in the sky, or the sun is not on them while in the pool. About 11 AM - 3 PM is the window that they are willing to use the pool. So yes, it is not in use most of the time, and that's okay by them. Had discussed putting a cover over the pool - a big glass enclosure like they have in florida, USA to keep bugs out - but it gets so hot in the summer it would be like a greenhouse. And, by code, you aren't allowed to put one of those covers over the pool.

 

[AntronX]

Pool is probably 58 degrees F right now, wanting to get to 90 degrees by Monday.

That's 18°C delta T * 1.4 * 43.8 = 1104 kWh thermal
May have to run a wire to Timselectric's house

 

[BentleyJ]

I think that would leave the question open of if you can raise the water with a heat pump faster than it looses the heat to the ground/atmosphere?

100% accurate. I installed a so called high COP. heat pump on a small pool (2,500 gal pond/waterfall turned into a summer wading pool just to cool off). I totally under estimated the amount of heat loss (my bad, not blaming anyone else). End result, had to operate the HP MANY more hours than anticipated into the evening and night just to hold around 80 degrees. The COP rating of 5 falls off rather rapidly at night even when ambient temps are fairly modest in the 60's. Bottom line, the HP had to run more total daily hours and during times of unfavorable ambient air temps.

Yes, it kept the pool very comfortable and enjoyable for 3 months and we used it almost daily. However, the amount of electricity consumed over that period was enormous. Heat Pumps for a pool SUCK don't do it. They heat very slowly and their COP does not live up to the advertised value.

The particular unit I received was overcharged and was consuming about 35% more electricity than the published specs. for a given set of air, water temps. and flow rate. That took about a month to figure out only being home on weekends due to work travel. You have to think about what is going to happen in a few years with regard to refrigerant leaks and maintenance on a HP.

I'm seriously considering throwing the HP in the garbage next year and installing a Nat Gas heater instead.

 

[WorldwideDave]

Hi neighbor - we are 50 minutes away.
Nat Gas bill was super high, though. If not heat pump, what are other options to heat a pool that I have not explored?

 

[Quattrohead]

Raypak by Rheem pool heat pump
These are clearance items from Rheem and have no warranty, but they are 1/3 the price of the new units.
I bought one because the pool company wanted $5k for a unit made by Jandy.
Waiting on the pool installation and then I will add it after.

 

[BentleyJ]

Hi neighbor - we are 50 minutes away.
Nat Gas bill was super high, though. If not heat pump, what are other options to heat a pool that I have not explored?

Those low cost black, solar thermal pool heaters do work if you have a suitable area like a roof near the pool or ground mount area that wouldn't look to bad. In our case there just wasn't any unshaded location close enough to the pump and plumbing to make it work.

 

[solarlab]

I wrote an hefty long post about the heat pump here

 

[Supervstech]

I've proven in the last 3 months that I can run a pool pump and pool heater from solar. But the pool heater is a gas-powered, 10,000 BTU, about 60% efficient, super expensive to run because of the price of gas.
Doing this experiment, I have reduced my electric bill by just over $500 over 3 months, but by running the heater longer into the season - 2 months longer so far - I am paying way more in gas than I was in the past. About $600 more in gas bill over past 2 months, so it has effectively cost me $50 per month - $100 for 2 months - more than I spent in years past. Not bad, that's about $13 per week to keep the pool up at 90 degrees.
Having said that, I would like to reduce that gas bill from $300 a month to zero, then the savings a year from now will be $3,600.
I see some people are using heat pumps as 'dump loads'. I just don't know much about heat pumps for heating a pool. Not sure what the cost will be. Not sure if they run on 120V or have to run on 240V. Also not sure what to expect - will it raise the pool temp about 1 degree an hour, or about .25 degrees an hour? No idea how effective they would be for my installation.
I am a better plumber than electrician, so I can likely handle the installation myself.
Obliviously pool water is a bit different than house water - I can't install like a home water heater and have the pool pump circulate water through that electric element to heat it up or anything.
I did remember that when we had our farm we had these little things we floated in the water troughs for the horses so the water did not freeze that ran on 120V. Wondering if something like that exists only larger to heat a pool. No idea.
Thanks for reading as always!

Are you certain of the 10,000 BTUH rating on the heater? Im guessing you are missing a zero.
Water takes a LOT of energy to heat, and you want 90F, so...
They do make industrial heat pump pool heaters, but as mentioned, SLOW
Now...
IF you have an air conditioning need, pools are great energy savers for dumping heat into, but for pure heating needs, heat pumps need to be dedicated to the pool job.

 

[Wibla]

A 10k BTUH heater would take forever to heat that pool up, it's probably 100k BTUH.

Napkin math:
14000 gallons and 60 -> 90 degrees gives a little over 1000 kWh of energy needed. In practice it's probably more since it takes time, so you have heat loss working against you.
Let's call it an even 1200 kWh. A 100k BTUH heat pump with a COP of 6 (which is not unusual) would use 200 kWh of energy across ~41 hours.
200kWh / 41h = 4.83 kW

E: Also a note on "heat pumps are slow" ... No they're not. They put out their rated BTUH. It's on you to pick the right size for your application. If you have a 200k BTUH gas heater, you will not have a good time with a 100k BTUH heat pump. Particularly as heat pumps lose heat capacity (and COP) as the outdoor temps go down. Do your homework and they're fine. Don't... and you get what you get.

 

[WorldwideDave]

You are asking if my pentair 10k is really a 100k BTU?

 

[Supervstech]

A 10k BTUH heater would take forever to heat that pool up, it's probably 100k BTUH.

Napkin math:
14000 gallons and 60 -> 90 degrees gives a little over 1000 kWh of energy needed. In practice it's probably more since it takes time, so you have heat loss working against you.
Let's call it an even 1200 kWh. A 100k BTUH heat pump with a COP of 6 (which is not unusual) would use 200 kWh of energy across ~41 hours.
200kWh / 41h = 4.83 kW

E: Also a note on "heat pumps are slow" ... No they're not. They put out their rated BTUH. It's on you to pick the right size for your application. If you have a 200k BTUH gas heater, you will not have a good time with a 100k BTUH heat pump. Particularly as heat pumps lose heat capacity (and COP) as the outdoor temps go down. Do your homework and they're fine. Don't... and you get what you get.

100K btuh heat pump is an 8.33 Ton heat pump... most minisplits top out at 4 ton, with multihead models.

"That’s on you" isnt really true in many parts of the country, as codes require sizing them to your A/C loads...