Efficiency: Full Rated vs Up Rated

[wpb]

Hi all,
I believe I understand the difference between Full-Rated (and) Up-rated pumps, and I've read the excellent post on them @TFP, however, I've always wondered whether an up-rated pump would be more energy efficient than a full-rated pump, considering the motor in an up-rated pump is smaller yet it pumps the same volume. OR... whether the up-rated motor is working harder, it would be equal or worse in efficiency?

Reason I ask, I'm replacing my recirculation pump and I'm looking for energy efficiency.

I don't want to go with the expense of a 2-speed pump, but I'm hoping to determine the most efficient route with a conventional pump.

We have a 1,000 gallon swim-spa. Our original pump (Whisperflo 1.5HP SF=1.1) cycles the entire spa about 4 times in that 45 minutes. I had originally chosen the 1.5HP, because it appeared to be the best amperage-to-pump volume ratio. However, I'm now wondering if I went too big, based on articles that claim that a smaller pump will be more efficient, with all volume being equal (eg 5k gallons of recirculation is going to be less total amp hours for a 0.5 HP pump than a 1.5 HP pump, in what I've read).

In my application, the recirculation plumbing is 2", with roughly 60' of head (including all elbows), behind the pump is a Hayward 2400 DE filter, which I believe may be too small for the 1.5 HP pump as well.

This is for recirculation only (unless you count using it for a vacuum line).

The only real value the larger pump offers, being the better suction when using it as a vacuum. Other than that, I'd prefer to go with energy efficiency above all else.

Thank you in advance for any ideas,
RKM

 

[JamesW]

The only difference between a "Full Rated" and an "Up Rated" pump is the service factor. A Full-rated pump will have a larger service factor than an Up-rated pump. There is no difference in efficiency.

For energy efficiency, you want a motor rated as "Energy Efficient". An energy efficient motor will use a run capacitor, which improves the Power Factor of the pump.

How many gallons is your pool?

 

[mas985]

There is no difference in efficiency if you are comparing two pumps of the same THP (service factor * label HP). However, if you are comparing two pumps of the same label HP, then the uprated version will be more efficient simply because it will have a lower THP. And when I talk about efficiency, I mean gallons pumped per watt-hr consumed.

 

[wpb]

Thank you for the replies.

I'm sorry, I had originally included the number of gallons in the post and I must have accidentally deleted it when editing.

It's a small 1,000 gallon swim-spa.

According to what you've stated, if all amperage is the same for identical Braking Horsepower, and if those always push the same amount of water -- that indicates that the SF will never have any relation to efficiency relative to the amount of water it pushes, so I can stop worrying about that.

However, regarding the size -- will I see greater efficiency if I go with a 1hp and run it longer, than a 1.5hp run shorter, for example?

 

[wpb]

I should also mention that I'm noticing that if I buy the motor in a GE/Marathon model, that the exact motor is available in both switchless and standard. I'm not sure if "switchless" is better or worse for a pool pump?

 

[JamesW]

Yes, running longer at lower flow rates is more efficient. With only 1,000 gallons, even a 1 H.P pump is going to be too much. I would suggest a pump that will supply a flow rate of about 24 gpm (unless the heater requires more). You only need about 1/8 H.P total.

Switchless usually refers to a permanent split capacitor motor, which uses a run capacitor. Either way, you want to look for a motor rated as "Energy Efficient".

What heater do you have (make model)?

 

[wpb]

I have an AquaCal T120 heat pump. I believe it's 120k BTU. The whole thing is plumbed like a large pool, I wanted to do it right even though it's just a small swim-spa. I even threw in a salt-chlorinator ;-).

I believe my heat pump requires 30-70 GPM. They Hayward 2420 DE filter, on the other hand, shouldn't run over 48 GPM, it seems.

I suppose the ideal size would be about 40-45 GPM, so that I still have some suction for vacuuming. With 2" plumbing and 60' head (total w/elbows), but staying with the Whisperflo pump (so that I can simply change the impeller/motor), I'm not sure I can get small enough. I think the smallest Whisperflo is 1/2HP * 1.90 or so, for THP of 0.95.

 

[JamesW]

The WFE-2 is the half horsepower energy efficient Whisperflo and has a SFHP of 0.95, but I think that that would be too much.

If you can get a pump in the 35 to 40 gpm range, then that would be ideal. For vacuuming, you shouldn't need any more than about 20 to 30 gpm.

I think that you might be misunderstanding system head. The system does not have only one head; it has a different head for each flow rate. The higher the flow rate, the higher the head. To get a flow rate of 35 to 40 gpm does not take a lot of horsepower.

At 30 gpm, you will probably be near 10 to 15 feet of total dynamic head. At 48 gpm, you will probably be closer to about 24 to 36 feet of total dynamic head. I think that you would do well to choose a pump that delivered about 40 gpm at about 25 to 30 feet of head.

Of course, you need to be careful not to get a pump that is too small to supply an adequate flow to the heater. You also have to size the pump large enough so that it will still supply enough water flow when the filter gets a little dirty.

Is your heat pump an "AT120" or a "T120"?

What is your normal filter pressure?

http://www.haywardnet.com/pdfs/Pump_filter_sizing.pdf

http://www.pentairpool.com/pool-owner/p ... mp-193.htm

http://www.pentairpool.com/pdfs/whisperDS.pdf

http://www.aquacal.com/heat-pump-inform ... /index.php

 

[wpb]

@JamesW,
I understand what you're saying about the head, I was strictly referring to the more simple, static measure in feet, because I don't know enough to calculate the true head. Basically I have 40' of 2" pipe run, with 3 elbows.

The heat pump is the T-120 or TT-120, it's very similar to the H120 you mention, but it's no longer made / no documentation available.

I do not know what PSI it was running, because I have everything disassembled at the moment. With the original 1.5 HP pump, I think it was hovering around 25 PSI (on the DE filter, running clean), but I could be wrong.

I did not have a problem with the original 1.50 HP, so I thought the 3/4 (1.2 SHP) might be a good compromise. The smalled option, the 0.95 SHP you mention, should not hurt anything, right? I am just a little worried about a pump that runs 1.95 SF. Wouldn't it be bad for a pump to run nearly a full 200% of its rated HP?

What I mean by that .. here in South Florida, where pumps have relatively short lives .. wouldn't I get longer life out of a 1.00 SF than one that is so high, constantly running at nearly 200% it's base rate?

I apologize in advance if that's a stupid assumption .. I may be a bit overparanoid with how short-lived our pool pumps are in this area!

 

[mas985]

The smalled option, the 0.95 SHP you mention, should not hurt anything, right?

No it won't hurt anything. Running a large pump on small pool may be inefficient but won't do any damage unless you exceed the flow rate rating of the filter.

I am just a little worried about a pump that runs 1.95 SF. Wouldn't it be bad for a pump to run nearly a full 200% of its rated HP?

The motor is designed to run at full load which is 1.95 * 1.2 HP or 0.975 THP. However, it will probably never run at full load. One of the reasons that the SF is so high is that it is difficult to build an efficient motor that is much below 1 THP. So manufactures will tend to use the smallest motor they can find and simply underload it. You can underload an induction motor quite a bit before you lose much in efficiency. So a 1/2 HP pump is likely to be under loaded around 50%.

wouldn't I get longer life out of a 1.00 SF than one that is so high, constantly running at nearly 200% it's base rate?

No. A 3/4 HP motor with a 1.65 SF is identical to a 1 HP motor with a 1.2 SF in the same pump line. The only difference is the label. SF is fairly meaningless for a pump motor except for identifying the THP which is the true rating of the motor.

My recommendation would be for a two speed or variable speed pump. A 3/4 HP two speed run on low speed most of the time would work fine for that application and they are fairly easy to find. A variable speed would give you a bit more flexibility in choosing your flow rate but that is more of a luxury.

Another option would be to downsize the impeller and/or motor of your current pump. This will save you money and give you the nearly the same performance as a new pump. You can probably replace the motor with a two speed motor and the impeller for less than the cost of a single speed pump.

 

[wpb]

@mas985, thanks a million, that's exactly the information I need to complete my research.

If purchasing a two-speed, I would only be using it at the 1725 RPM. Would it be any more efficient -- when you compare the actual volume of water it pumps? In other words, if I pumped a total of 1,000 gallons on a 3/4 HP running at 1725 RPM, would it be noticably more efficient than, for example, a 1/2 HP running at 3,450 RPM to pump a total of 1,000 gallons?

 

[mas985]

Yes, a two speed on low speed is about double the efficiency of high speed. Flow rate goes down by a factor of 2 but energy use goes down by a factor of 4!

Comparing a 3/4 HP on low speed to a 1/2 HP of full speed here are a few numbers using Curve-C of the CEC data:

WFDS-24 High Speed: 78 GPM @ 1592 watts - 2.94 gallons/watt-hr
WFDS-24 Low Speed: 42 GPM @ 380 watts - 6.63 gallons/watt-hr

WFE-2 Single Speed: 68 GPM @ 1190 watts - 3.43 gallons/watt-hr


The WFDS-24 on low speed is close to twice the efficiency of the WFE-2.

 

[wpb]

Wow, that's incredible! You've sold me on the 2-speed despite the extra cost. I'm amazed it's possible to achieve 6+ gallons/watt-hour.

I wonder if running a pump at 1725 RPM is also going to result in added longevity versus running at 3450.

 

[JamesW]

My concern with the WFDS-24 (or the WFDS-3 (same pump)) is that the high speed easily exceeds the filter capacity. If you're only going to use it on low, that's fine, however, I think that the flow rate might be borderline if the filter gets dirty. Although, being such a small pool, the filter should not be hard to keep clean.

The head curves on low speed are pretty flat, so it doesn't take too much of a pressure increase to drop the flow below the minimum.

Also, on low, the heater's pressure switch might not be triggered to allow it to turn on. You might need to install a flow switch in the plumbing and wire it into the heater control in place of the pressure switch.

I think that you could use the Power-Flo II. Either the SP1750 (1/2 HP -0.37KW) or the SP1775 (3/4 HP - 0.56KW). The Power-Flo II should be roughly the same efficiency as the Whisperflo, it will cost much less and it has a better pump curve.

http://www.hayward-pool.com/prd/Above-G ... 017__A.htm

http://www.hayward-pool.com/pdf/literat ... ochure.pdf

 

[mas985]

The flow specification listed for the Hayward 2420 is based upon the NSF recommendation of 2 GPM/sq-ft for public pools. The recommendation for residential pools is a little higher at 2.5 gpm/sqft (60 GPM). But still these are only recommendations to maintain proper filtration and don't really reflect the maximum flow rate the filter can tolerate.

But if you are concerned about damage to the filter, then I would recommend the SuperFlo series of pumps. They have about the same efficiency as the Whisperflo but a lower head curve which will result in a lower flow rate. Curve-C for Superflo has the following operating point for the 3/4 HP two speed:

High Speed: 59 GPM @ 1130 watts; 3.13 gallons/watt-hr
Low Speed: 30 GPM @ 280 watts; 6.43 gallons/watt-hr

So high speed is slightly below the NSF recommendation for residential pools.

 

[wpb]

My original goal was to use the same pump apperatus I have now (Whisperflo) and simply replace the impeller, difuser, and motor.

My plan was to use the impeller/difuser from the WFDS-24 if it's available. I think I might be limited to ordering the WFE-3 because the WFDS-24 does not seem to be available.

I am a little worried about the heater's flow switch when running at 1/2 speed. I do not plan to run at full-speed, so the flow-switch is my greatest concern.

I can't tell you how much I appreciate all of your great insight. I'm going to attempt to order the pumps on Monday based on all of the great assistance I've received here.

Speaking of ordering pumps... I had made a call to an Internet vendor, Pump Warehouse on Friday. They appeared to have good pricing, however, they appear to have some sort of weird scam going on there. They rarely ever answer the phone, and when they finally did, they said "we don't have that in stock" and immediately hung-up without so much as asking if I would be interested in an alternative. Very strange.

Thank you again for all of the great help!

 

[mas985]

Ok, then it might be helpful to figure out what your old pump's operating point was so that I can figure out what the new operating point will be. So I need a bit more information about your current setup.

Old Pump Model #
Filter Pressure
Hieght of the pump relative to the spa water level (+- feet).
Number of suction pipe runs and their diameter from pump to spa
Number of return pipe runs and their diameter from pump to spa
Number of return eyeballs in spa and their diameter

Also, that manufacture of Heat Pumps also made a 120 HP which would work down to 20 GPM so is there a way to confirm which model number you actually have?

Note too, it is also possible to just change the impeller to a 1/2 HP WFE-2.

 

[wpb]

Old Pump Model #
Pentair Whisperflo WFE-6 (1.5 HP * 1.47 SF = 2.2 HP)

Filter Pressure
Unfortunately I do not know for certain, everything is dismantled at the moment. I believe it was around 25 PSI, but if you can estimate without this, it would be better because I'm just not sure.

Height of the pump relative to the spa water level (+- feet).
Top of spa waterline is 1" above the top of the Whisperflo pump.

Number of suction pipe runs and their diameter from pump to spa
1x Suction Pipe, 2" - coming from a skimmer and 4 x 2" suction intakes

Number of return pipe runs and their diameter from pump to spa
1x Return Pipe, 2"

Number of return eyeballs in spa and their diameter
4x Return Eyeballs (approx 1/2" eyeball jets)

Confirm Heat Pump Model#
Yes, the number mentioned above is accurate, it's the AquaCal TT120 aka T120

Thank you in advance!

 

[mas985]

Sorry forgot one more question. How far is it from the circulation pump to the spa?

Also, I am only interested in the plumbing that is used for the circulation pump and not for the swim spa high volume pump. So are the 4 x 2" intakes used only for the swim spa pump or are they used for the circulation pump as well? Are these basically bottom main drains?

The TT120 seems to be a TropiCal HP and has the following specs:
http://www.poolheat.com/new_site/images ... _SPECS.gif

Which shows a minimum flow rate of 20 GPM. But you might want to give AquaCal a call just to make sure.

 

[wpb]

Oh you're right, sorry, I had forgot the 4x 2" intakes & skimmer are shared among all three intake likes (1x Recirc, 2x Jets). So the recirc pump shares 4x 2" intakes + Skimmer, with two other 2" intakes. However .. It's extremely rare that I run the recirc pump when the jets are running, so in 95% of the cases, the recirculation pump has access to all 4x 2" intakes + skimmer.

Wow, I don't know how you located that information. I purchased the heat pump used and was never able to find the exact specs, so thank you for that! Yes, that appears to be the correct model. And you're right, it looks like the cutoff is 20 GPM, but I want to be sure I don't get close to that.

The piping run is: 40' of 2" pipe run, with 3 elbows (instake) and 4 elbows on the output side.

Thanks again for the great insight!