Dual Heat Pumps on LI?

[JamesW]

The manual might say that dual heat pumps need to be done in parallel, so you would possibly violate warranty if you do it in series.

In my opinion, it is not necessary, but you have to decide if you want to go against the installation manual which is generally not recommended.

In any case, you need to follow the manual or do your own research before doing it a different way than the manual requires.

If there is a problem, you would bear the burden of proof that the installation did not cause the warranty issue.
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2. Multiple Heat Pump Connections.

All plumbing on multiple heat pump installations must be done in parallel (see next page).

An equal flow of water to each heat pump is important for optimum operation.

Note: It may be necessary to adjust the water pressure switch if a unit is installed below the water level.

Refer back to page 6 for details on when and how to adjust the pressure switch.

Each heat pump in a multiple unit installation allows a maximum flow rate of 100 gpm (380 lpm) and requires a minimum of 30 gpm (110 lpm).

https://www.pentair.com/content/dam/extranet/nam/pentair-pool/residential/heaters/ultratemp/manuals/ultratemp-heat-pump-installation-and-users-guide-en-fr-sp.pdf

 

[ajw22]

Pentair recommends parallel...

https://www.pentair.com/content/dam/extranet/nam/pentair-pool/residential/heaters/ultratemp/manuals/ultratemp-heat-pump-installation-and-users-guide-en-fr-sp.pdf

 

[JamesW]

Pentair recommends parallel...

Yes, they actually say "must", so probably best to do it that way.

The pump power cost is 8 times as much, so maybe 1,600 watts vs. 200 to 250 watts.

You can do it either way, but you take the risk of warranty issues not being covered based on "improper installation".

Also, some local code uses language that says that installations need to follow manufacturer's installation Instructions, so it could be a building code issue as well.

 

[JamesW]

Pentair does not need to pay for the additional power required for parallel plumbing vs. series.

So, it is easy for them to ignore that cost.

If they had to pay for the additional cost of power for a parallel setup, they would probably be pretty quick to say that series was ok.

 

[JamesW]

Each heat pump is 7,200 watts for a total of 14,400 watts.

Each heat pump uses 33 amps for a total of 66 amps.

2 in series at 40 gpm is about 8 psi of head loss (18.5 feet).

2 in parallel at 80 GPM is about 4 psi of head loss (9.25 feet).

 

[NYR56]

With parallel heaters, the flow requirements are additive. If each heater needs 40 GPM, then your pump needs to run at 80 GPM. You will be running your pump at fairly high speed when the heaters are on, so consider that in your electrical cost.

@NYR56 your signature contains no information about what pump you have or any automation. Good automation can help reduce electrical consumption when the full blast of both heaters is not needed but is another expense.

Good point about the flow requirements. I have a IntelliFlo VS+SVRS Variable Speed pump, with no automation. Pool guy gave a quote on automating things with a NG heater when I first priced this out last year but it was nearly 10k for features that, although cool, don't seem really necessary. With two HPs though, maybe it would be worthwhile to route water to one or both if plumbed in parallel.

One other thought I have is installing one, since the pool is already plumbed for a heater (old propane one the prior owner had died), and seeing how it performs. I have a 50amp panel out there now, so I think I have capacity for one heater? Then if we need a second, we can run another line out there and install automation at that later date to save a bit this year. Although I'm not sure one heater is even worthwhile with the size pool.

 

[JamesW]

Air.....Water............BTU/Hr. (Loss)
80.........80....................40,000 (20 x 2,000)
80.........85....................55,000 (27.5 x 2000).
80.........90....................70,000 (35 x 2,000)

70.........80...........100,000 (50 x 2,000).
70.........85...........140,000 (70 x 2,000).
70.........90...........180,000 (90 x 2,000).

60.........80...........160,000 (80 x 2,000).
60.........85...........220,000 (110 x 2,000).
60.........90...........290,000 (145 x 2,000).

50.........80...........220,000 (110 x 2,000).
50.........85...........280,000 (140 x 2,000).
50.........90...........340,000 (170 x 2,000).
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Air.....Water.....Btu/Hr gain.
50........80.............90,000
60........80...........105,000
65........80...........115,000
70........80...........130,000
80.......80............140,000


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Breakeven for one heat pump to maintain a water temp of 85 degrees.

Heat Loss Data
Air............BTU/Hr. (Loss)
80..............55,000
70.............140,000.
60.............220,000.
50............280,000.
Heat gain data.
Air..........Btu/Hr gain.
50.............90,000
60...........105,000
65...........115,000
70...........130,000
80..........140,000


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Breakeven for two heat pumps to maintain 85 degrees with no cover and zero wind.
Heat Loss Data
Air............BTU/Hr. (Loss)
80..............55,000
70.............140,000.
60.............220,000.
50............280,000.
Heat gain data.
Air..........Btu/Hr gain.
50.............180,000
60...........210,000
65...........230,000
70...........260,000
80..........280,000

 

[JamesW]

For a minimum air temp of 72 degrees, you can maintain about 85 degrees with no cover and zero wind with one 140,000 btu/hr heat pump.

For a minimum air temp of 62 degrees, you can maintain a water temperature of about 85 degrees with no cover and zero wind with two 140,000 btu/hr heat pumps.

 

[JamesW]

One heat pump to maintain 80 degrees.

Heat pump running 24/7 with zero wind and no cover and a minimum air temp of 67 degrees.

7.2 kwh per hour = 172.8 kwh per day.

172.8 x $0.15 = $25.92 per day.

Heat Loss Data
Air............BTU/Hr. (Loss)
80..............40,000
70.............100,000.
60.............160,000.
50............220,000.
Heat gain data.
Air..........Btu/Hr gain.
50.............90,000
60...........105,000
65...........115,000
70...........130,000
80..........140,000

____________________________________________________________________________
Two heat pumps to maintain 80 degrees.

14.4 kwh per hour = 345.6 kwh per day.

345.6 x $0.15 = $51.84 per day.

2 (140,000 btu/hr) Heat pumps running 24/7 with zero wind, no cover and a minimum air temp of 54 degrees.

Heat Loss Data
Air............BTU/Hr. (Loss)
80..............40,000
70.............100,000.
60.............160,000.
50............220,000.
Heat gain data.
Air..........Btu/Hr gain.
50.............180,000
60...........210,000
65...........230,000
70...........260,000
80..........280,000

 

[NYR56]

Thanks James, those charts are very helpful. I guess the problem is at night, even in June, the temp falls below what the pump can keep up with, so I would have to wait until morning to start being able to heat the water. Based on @1poolman1's numbers, I can only get roughly .35 deg/hr at ideal conditions, so 15 hours for 5 degrees, makes it sound pretty much useless except for heating the water a bit for the after work dips (which is probably not worth the expense of running it that long). I suppose in July/August it could keep the water in the 80s though. Alternatively, it could heat the attached spa pretty quickly to a comfortable temperature, but that would require automation for me to route the water there during the week.

 

[ajw22]

You should run all the numbers to get a complete cost picture:

• Pentair MasterTemp 400 for 320,000 BTUs all the time at all air temperatures - $4,000
• Pentair UltraTemp 140 x2 for 280,000 BTUs at 80/80/80 and BTU output drops at colder air temps - $6,000 x2 = $12,000
• Running 200 foot gas line - $10/foot = $2,000??
• Running 50 amp or 100 amp service to 1 or 2 HPs -??
• Pump Operating cost:
  • 40 GPM for gas heater is about 800 watts
  • 80 GPM for two HPs is about 2,000 - 2,500 watts for longer runtimes

What is your payback time for the HP acquisition costs in electrical versus gas savings?

Those charts you posted do not give the complete economics and are biased toward making HP look better.

In the Northeast, I think gas heaters, which can be heated on demand when needed, are the most economical long-term solution.

 

[JamesW]

A 400,000 btu/hr gas heater can maintain a temp of 85 degrees; it just depends on the runtime required.

Note that loss rates are at zero wind and wind can double or triple the loss with no cover, so that needs to be considered.

If you double the heat loss rates, then the runtime doubles and the breakeven will be at an air temp of about 65 degrees.

To maintain a water temp of 85 degrees.

Heat Loss Data
Air............BTU/Hr. (Loss)...........Runtime %
80..............55,000............................16
70.............140,000...........................42
60.............220,000...........................65
50............280,000............................83

Gas Heater gain rate = 400,000 x 0.84 = 336,000 btu/hr.
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Gas heater maintain 80 degrees.

If you double the heat loss rates, then the runtime doubles and the breakeven will be at an air temp of about 60 degrees.

Heat Loss Data
Air............BTU/Hr. (Loss)...........Runtime %
80..............40,000...........................12
70.............100,000............................30
60.............160,000............................48
50............220,000............................65

 

[Bill1974]

Plumbing in parallel would would be more efficient that in series. If run in series you run the risk of the second unit never outputting as much heat as it could. You may also want to check your flow of your current plumbing to make sure you have enough flow to allow the HPs to achieve their max output. Not enough flow and they will reduce output.

Is solar an option for heating your pool? Yeah you are going to need a lot of panels but should help with the running costs.

When I redid my pool I looked at putting in a NG line for a heater and looked at the operating cost. A HP was much cheaper on both. I did the numbers based on LI gas and electric rates and NG was about double to cost per BTU.

A 200A service to your house it likely not going to be enough to support two pool HPs and the house unless your house is tiny and mainly have gas appliances. It's likely cheaper to run one larger service to the pool equipment pad than running two seperate line for each HP. But that going to depend on where you main panel is and where the pool equipment is.

You are going to fighting an uphill battle maintaining the temp without a cover.

 

[JamesW]

2 heat pumps maintaining 85 degrees with some wind (Assumes double heat loss of precious examples with no wind).

Minimum air temp = 72 degrees F.

Heat Loss Data

Air............BTU/Hr. (Loss)

80..............110,000

70.............280,000.

60.............440,000.

50............560,000.

Heat gain data.

Air..........Btu/Hr gain.

50.............180,000

60...........210,000

65...........230,000

70...........260,000

80..........280,000

 

[JamesW]

Gas can maintain a water temperature of 85 F with low wind at an air temp of 67 degrees running 24/7.

Heat Loss Data

Air............BTU/Hr. (Loss)

80..............110,000

70.............280,000.

60.............440,000.

50............560,000.

Heat Gain = 336,000 btu/hr.

 

[JamesW]

 

[JamesW]

Multiple heat pumps can be plumbed in series or in parallel. Please contact us for advice on the best method to use for your situation.

Pool Heat Pump Installation Tips

Swimming Pool heat pump installation tips. Best practices, how to install, electrical reqirements, clearances, bypass and plumbing etc..

heatpumps4pools.com

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Multiple unit installations should always be in parallel circuits and no closer than 12 inches apart.

https://builtrightpoolheaters.com/wp-content/uploads/2024/10/2017-2018-Owners-Manual.pdf

 

[JamesW]

For an air temperature of 65 degrees, here is the heat loss vs. water temperature.

The breakeven is about 82 to 84 degrees for a 400,000 btu/hr heater at 84% efficiency (336,000 btu/hr).

Heat Loss Data

Water Temp F..........BTU/Hr. (Loss)

65.................................68,000 (34 x 2,000).

80..............................260,000 (130 x 2,000).

85..............................360,000 (180 x 2,000).

90..............................470,000 (235 x 2,000).

Heat Gain = 336,000 btu/hr

 

[JamesW]

For two heat pumps at 65 degrees air temp, the breakeven water temp is about 75 to 77 degrees degrees.

Heat gain data.
Air..........Btu/Hr gain.
50.............180,000
60...........210,000
65...........230,000
70...........260,000
80..........280,000.

Note that wind speed, humidity etc. affect temp gain and loss, so the numbers can only give you a general sense of what is possible.

 

[NYR56]

I just did some rough calculations after reviewing my electric and NG bills. Our total electrical rate is actually $0.235/KWH, and our NG rate is $1.338/therm. If I assume the pump runs at the exact same speed, a HP cost $1.12/therm assuming 100% efficiency and a NG heater, assuming 85% efficiency, costs $1.57/therm of heat output. If the VS pump uses an extra 2kw for the required flow through 2 pumps, the cost is essentially equal. Further, the HPs will not run at 100% efficiency at all times, so unless I made a mistake w/ my math, both heater solutions cost similar amounts to operate. Considering NG can be used slightly more like an on demand heater w/o regard to air temps, I'm starting to think that is the way to go. Our electric bill for July of last year (without any heaters) shows 2800KWH used, so even if we got a new roof and covered it in solar, I don't think we could even come close to producing enough power to offset our electric usage anyway. If you guys think I'm missing something, let me know, but HPs are sounding less and less appealing in my situation unfortunately.