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Reach4

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I guess I'm just a little late to discover how far removed the value of input electrical power is from the nominal values we use to describe pumps.
I think the nominal HP may be the power the motor needs to deliver to the wet end of the pump when the pump is pumping at its nominal gpm. So it may be more a spec of the wet end than the motor end.

Not sure, and I don't have references along those lines.
 

Pawpaw

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The more surprising surprising part to the engineer/physicist is the service factor aspect. It's like having an engine putting out 130% of its rating.
I feel like I've encountered scenarios where the service factor was left as a safety margin. Here though, it seems like pumps are in the service factor region for a good part of their curve.
 

Valveman

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Sure, it matches the one I found on the Grundfos site, which I've also attached. Though the attached chart uses kilowatts (0.75kW ~= 1HP), you can see that the same power and efficiency curves from your chart in post 11 are in this chart.

My concern is the P_1 curve. According to Grundfos (see post 14 or attached images (same source)), the P_1 power would relate to the electricity consumed (and billed!). Perhaps I'm the only one surprised to find this "0.75kW pump" (with a 1.4 service factor), has a peak power consumption of ~2.6kW (~3.5x). Without published P_1 data, is it reasonable to assume other pumps have similarly higher P_1 power, relative to their nominal power rating?

You have certainly educated yourself on this subject. You know more about this than the majority of pump guys, and even more than the engineers at the pump manufacturers. You have been able to put your finger on the real issues, and there are only a small handful of people who understand it as well as you do. If you figure out the P1 power thing you will be way ahead of me. A 1HP with a Service Factor of 1.4 can draw as much as 1.4HP, but not 2.5HP. That has never made sense to me. And yes, all submersibles are loaded well into the service factor. Being submerged in water I believe they can take a higher SFA than an air cooled motor. But mostly, I think they just want to get as much as they can for the horsepower.
 

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TL;DR: The only direct questions in this post are at the bottom, and are not reliant on the info in this post. However, I'm hoping folks will corroborate or pull apart what else I've written.

To recap, I've got a short-cycling problem. In this specific situation, merely installing a CSV has been ruled out. Since then, I've been (slowly) checking out matters related to the VFD, larger pressure tank, and pump change plus CSV options.

1) The VFD option
Since the last post, I started a new thread about VFDs (VFD installers: Mix & match brands? Use 1-phase motor? Test well pumping level?), and presently I'm not thrilled about that route.

2) Relevant power
I think the nominal HP may be the power the motor needs to deliver to the wet end of the pump when the pump is pumping at its nominal gpm. So it may be more a spec of the wet end than the motor end.

Not sure, and I don't have references along those lines.
I read more of the Grundfos pump handbook (a rather nice document), and it backs you up:

"Normally, pump curves in data booklets only cover the pump part. Therefore, the power consumption, the P_2-value, which is listed in the data booklets as well, only covers the power going into the pump – see figure 1.1.4. The same goes for the efficiency value, which only covers the pump part (η = η_P)." (page 9)

Motors on the other hand seem to be referred to by their output power, which all makes it seem rather straightforward to pair a motor & pump. As a result though, non-specific "power" then becomes a source of trouble when one is concerned with the inputs & outputs (electrical power & hydraulic power respectively (or what you pay & what you get)) of the motor + pump assembly.

The Goulds/Xylem technical support number was perpetually busy, and they did not respond to my voicemail or form request. Fortunately, their documents do list the electrical specs of their motors, giving the following power requirements for the motor I think I have (CentriPro M10412, generation 2, post November 2015, CSIR):
Full load: 1.175kW (~1.6HP)
Service factor: 1.590kW (~2.1HP)
Thus, the normal maximum running electrical input power of my "1HP" submersible pump is just over 2HP (note the service factor is only 1.4x).

3) Geothermal profile
I finished assembling measurements I collected from the geothermal unit on a few mid-to-high-40s (°F) days:

Runtime: The thermostat is programmed with a nightly setback window of 10 hours & I recorded the geothermal unit running for about 15 hours each day, with a large off period during the night. The greater than 14h runtime may be explained by the temperature reaching the nighttime setpoint and/or the thermostats "adaptive" feature that tries to REACH an increased heating setpoint AT the programmed time.

Water demand: It seems 5-6000 gallons per day were used while I recorded (that's ~9ft cubed!). During the geothermal's operation, the distribution of flow rate looked somewhat like this:
5 GPM: 1%
6 GPM: 59%
7 GPM: 13%
8 GPM: 12%
9 GPM: 12%
10 GPM: 3%
Weighted average: ~6.8 GPM

The runtime duration will likely increase in colder weather and decrease in warmer weather. I suspect the water demand distribution will change based on the weather. Since I am not sure how or by how much these will change, I will treat the data I have as the average. With the following approximations, my yearly water demand for the geothermal alone is:

6 (months) x 30 (days/month) x 15 (hours/day) x 60 (minutes/hour) x 6.8 (gallons/minute) = 1.1 million gallons per year (for only 1/2 year usage!)

Approximations:
Geo operates 6 months per year (not much cooling is done in warmer weather)
30 days per month
Geo operates 15 hours per day on average
Geo demands an average of 6.8GPM when running

4) Larger pressure tank option
If I were to solve my short cycling by installing a bigger pressure tank, the pumps operating point (presently ~15 GPM) would not change. Since this operating point is near the limit of this pump, I assume the motor is operating at full service factor (1.590kW (~2.1HP) electrical input)). Thus, I estimate the yearly electricity cost to supply geothermal water is:

1,100,000gal x (1min/15gal) x (1h/60min) x 1.59kW x ($0.076/kWh) = $148

Of course, with normal household water use included, the total pumping electricity cost will be a little higher.

If I added a 119gal tank (for a combined drawdown of ~32 gallons (existing tank is 22gal, all operated 50/70PSI)), the pump would end up cycling ~105 times per day when the geothermal is used. This is close to (but does exceed) the 100 maximum number stated by Goulds/Xylem. The additional household water usage may increase or decrease the cycle count a little (depending on whether each use of household water brings the combined flow closer to or farther from half the ~15GPM max refill rate). I'm estimating a 119gal tank will cost roughly $1k and last 15 years, for an average cost of ~$67/yr.

When my existing motor/pump finally dies, I might be able to install a "3/4 HP" pump such as the Goulds/Xylem 10GS07 or 13GS07. I expect it will operate near full service factor as well, which will need electrical power of 1.335kW (~1.8HP)(according to data for the CentriPro M07412 motor). The yearly electricity cost would then be $124. So, the larger pressure tank option would have a yearly cost of ~$215 (148+67) in the near term and potentially ~$191 (124+67) in the future (again, just considering geo water).

Edit Dec-10-2020: I made a mistake in the calculations of the above paragraph by neglecting that the pump curves of the 10GS07 & 13GS07 are different than my 10GS10. Replacing my current pump with either would result in a different operating point, and thus they would take different amounts of time to produce 1.1 million gallons. I still have not had a pumping level test performed on my well, but using the 10GS10 curve and working backwards from the observed 15 GPM operating point, it seems my system needs 140' of head. This should be predominantly static head, and thus won't change much as the flow rate changes. At 140' head, the 10GS07 would produce ~14 GPM, and the 13GS07 would produce ~15.4 GPM. The costs are then:

1,100,000gal x (1min/14gal) x (1h/60min) x 1.335kW x ($0.076/kWh) = $133 (10GS07)
1,100,000gal x (1min/15.4gal) x (1h/60min) x 1.335kW x ($0.076/kWh) = $121 (13GS07)

It's interesting that the larger pump actually ends up cheaper, and in fact it's probably even a tad cheaper than shown. The assumption that the 13GS07 would draw full service factor power is probably less accurate than the 10GS07/10GS10 case, because the 13GS07 is rated for up to 20GPM, and the 15.4 GPM operating point is significantly below that.

So, the larger pressure tank option would have a yearly cost of ~$215 in the near term and potentially ~$188-200 in the future (again, just considering geo water).

5) Pump change + CSV option
With a CSV installed, the pump will operate at whatever flow is demanded (above the minimum threshold), so a P_1 power curve is necessary to calculate electricity usage. Unfortunately, of the discussed pumps, the only P_1 curve I'm aware of is for the Grundfos 16S10-10 (see attached, it's the same data as the one attached to post #17, but with feet & GPM, and smaller because Grundfos changed their site). Reading values from that curve, I get:

5 GPM: 1.4kW
6 GPM: 1.5kW
7 GPM: 1.65kW
8 GPM: 1.75kW
9 GPM: 1.85kW
10 GPM: 2kW

The yearly electricity cost contribution of each flow rate is then:

5 GPM: $2.87 (6 x 30 x 15 x 0.01 x 1.4 x 0.076)
6 GPM: $181.60 (6 x 30 x 15 x 0.59 x 1.5 x 0.076)
7 GPM: $44.02 (6 x 30 x 15 x 0.13 x 1.65 x 0.076)
8 GPM: $43.09 (6 x 30 x 15 x 0.12 x 1.75 x 0.076)
9 GPM: $45.55 (6 x 30 x 15 x 0.12 x 1.85 x 0.076)
10 GPM: $12.31 (6 x 30 x 15 x 0.03 x 2 x 0.076)

For a total of: $329.44

Thus a "1 HP" Grundfos 16S10-10 is a costly choice, even before considering the cost of a CSV. Nonetheless, the use of a "3/4 HP" pump may make this option favorable.

6) Questions:
1) What manufacturers / brands / product lines of single-phase submersible pumps do you folks consider good quality, trouble-free & long lasting?
2) Of those, which will I likely be able to acquire P_1 power curves for?
 

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Valveman

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Thus a "1 HP" Grundfos 16S10-10 is a costly choice, even before considering the cost of a CSV. Nonetheless, the use of a "3/4 HP" pump may make this option favorable.

Like you say the 3/4HP Grundfos will make the CSV system more favorable. Your comparison shows the CSV using a 1HP and everything else using a 3/4HP, which is not apples to apples. Here is a curve for a 3/4HP Grundfos. I could not get the Grundfos web site to work with the variable speed option. But losing head by the square of the speed you can see this pump can be slowed only slightly and still produce the head required. My math shows reducing the speed to 2500 RPM would only reduce the power required from the 0.75HP caused by the CSV on a full speed pump to 0.62HP when varying the speed. If you add back the loss of motor efficiency at reduced speeds and the loss from harmonics or dirty power caused by the VFD, it will basically be a wash. There certainly won't be enough savings differences between the CSV and VFD to every pay for the extra cost of the VFD.

The 100 cycles per day maximum is just to get the pump/motor to last past the warranty date. If you go that route you should probably add the cost of a new pump every 5 years or so.

Good luck getting any useful info from Goulds or anyone else. You night try National, Unitra, Meyers, and there are a few others who make the Stainless Steel copies of the Grundfos that might be able to help you.

16S07-8 curve 6.8 GPM.png
 

Reach4

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I suspect that a 1/3 HP or 1/2 HP pump would supply plenty of water for the heat pump, and maybe even supply water to the house. The pump should be 3-wire and have a run capacitor in the box.

I think you could maybe have two pumps with two pitless adapters. Or have one pump, but with a pressure pump up top for supplying higher-pressure water for general house use.
 

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From everything I've read, P_1 is the electrical power to the motor and P_2 is power transferred via the shaft (i.e. power produced by the motor and given to the "wet end"). The mere existence of power values greater than P_2 would seem to indicate that P_2 can't be the total power entering the motor.

P_1 data is needed to calculate cost for the CSV option, and I was only aware of P_1 data for the 16S10-10 when I wrote post 24. For unknown reasons, the "3/4 HP" 10S07-12 does not show a P_1 curve. However, the "3/4 HP" 16S07-8 Valveman just showed does have a P_1 curve (see attached, in kW not HP). From that I read:
5 GPM: 1.25kW
6 GPM: 1.4kW
7 GPM: 1.5kW
8 GPM: 1.6kW
9 GPM: 1.7kW
10 GPM: 1.85kW

The yearly electricity cost contribution of each flow rate is then:
5 GPM: $2.57 (6 x 30 x 15 x 0.01 x 1.25 x 0.076)
6 GPM: $169.50 (6 x 30 x 15 x 0.59 x 1.4 x 0.076)
7 GPM: $40.01 (6 x 30 x 15 x 0.13 x 1.5 x 0.076)
8 GPM: $39.40 (6 x 30 x 15 x 0.12 x 1.6 x 0.076)
9 GPM: $41.86 (6 x 30 x 15 x 0.12 x 1.7 x 0.076)
10 GPM: $11.39 (6 x 30 x 15 x 0.03 x 1.85 x 0.076)

Total: $304.73
Thus, the 16S07-8 is not much better than the 16S10-10.

Something doesn't seem right though. Why is there such a large difference between electrical input power of Goulds/Xylem & Myers/Pentek vs Grundfos pumps of comparable nominal power? Are the motors on the Grundfos just inefficient or am I missing something?

"3/4 HP" pump
Goulds/Xylem 10GS07 (or 13GS07): M07412 motor: 1.335 kW electrical power at service factor ("Motor Application and Installation Data Manual", BMAID-R11.pdf, page 9, see link in OP)
Grundfos 16S07-8: MS402-type #79453103 motor: ~2.5 kW max P_1 (curve attached to this post)
Myers/Pentek Rustler 3NFL72-12-P4 (or Predator 3ST72-12PLUS-P4), P43B0007A2 motor, 1.381 kW (Pentek Electronics Manual, page 13, CSIR)

"1 HP" pump
Goulds/Xylem 10GS10: M10412 motor: 1.59 kW electrical power at service factor (same source as 3/4HP Goulds/Xylem)
Grundfos 16S10-10: MS402-type #79453104 motor: ~2.6 kW max P_1 (curve attached to post 24)
Myers/Pentek Rustler 3NFL102-12-P4 (or Predator 3ST102-12PLUS-P4), P43B0010A2 motor, 1.672 kW (same source as 3/4HP Myers/Pentek)

Unitra didn't say much about motors; it looked like the UP series was just "wet end", while only a motor width and length were listed for the SP series. National didn't seem to have 4" submersibles.

I can roughly estimate electrical costs of Goulds/Xylem motors & a CSV by crudely scaling down the Grundfos electrical costs by the ratio of max P_1 between Grundfos and Goulds/Xylem:

$304.73 * (1.335 kW / 2.5 kW) = $162.73

That is far more favorable, but it remains to be seen how realistic the approximation is.

The 100 cycles per day maximum is just to get the pump/motor to last past the warranty date. If you go that route you should probably add the cost of a new pump every 5 years or so.
That's a very important consideration. I'm going to split that out into a thread of it's own: Submersible turbine pump lifespan formula?

I have not given much thought to dual pump options at this point.
 

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Valveman

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Yeah with a dual pump set up you could use a 16S05-5, which is a 1/2HP well pump, running with a CSV setting of 20 PSI and using a 10/30 pressure switch. Then another 1/2 or 3/4HP jet pump could boost the pressure enough to use 50 PSI setting for a CSV and a 40/60 switch. The 1/2HP well pump would save a lot of energy for the heat pump, and the extra boost pump would only run about 30 minutes a day when the house needs water.

DUAL PUMP_HEAT PUMP-2 PK1A.jpg
 

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I made an edit to some calculations in topic 4 of post 24.

Reach4 & Valveman, that dual pump setup is intriguing, and I hope to consider that more later. First though, I need to make sure I'm adequately estimating pump replacement intervals, and electricity costs of a CSV'd pump.

"3/4 HP" pump
Goulds/Xylem 10GS07 (or 13GS07): M07412 motor: 1.335 kW electrical power at service factor ("Motor Application and Installation Data Manual", BMAID-R11.pdf, page 9, see link in OP)
Grundfos 16S07-8: MS402-type #79453103 motor: ~2.5 kW max P_1 (curve attached to this post)
Myers/Pentek Rustler 3NFL72-12-P4 (or Predator 3ST72-12PLUS-P4), P43B0007A2 motor, 1.381 kW (Pentek Electronics Manual, page 13, CSIR)

"1 HP" pump
Goulds/Xylem 10GS10: M10412 motor: 1.59 kW electrical power at service factor (same source as 3/4HP Goulds/Xylem)
Grundfos 16S10-10: MS402-type #79453104 motor: ~2.6 kW max P_1 (curve attached to post 24)
Myers/Pentek Rustler 3NFL102-12-P4 (or Predator 3ST102-12PLUS-P4), P43B0010A2 motor, 1.672 kW (same source as 3/4HP Myers/Pentek)
Any insight on those wildly different service factor electrical powers between Grundfos & other?
 

Valveman

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SFA or Service Factor Amps are just the max the motor can safely deliver. The motor will still only draw as many amps as the pump end requires to pump the amount of water being used.

Having a motor with a higher SFA than the pump is drawing will make the motor run cooler. That is the point of putting a 1HP motor on a 3/4HP pump end.
 
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