Getting rid of "Service Factor" for motors.

[JamesW]

Does service factor have any value?

In my opinion, it has no value. In fact, I think that it only causes problems and confusion.

The only number that really matters is the Total HP of the motor.

Motor makers make two identical motors and label one as 1 hp with a 1.65 service factor and the other as 1.5 with a 1.1 SF. Both have 1.65 total hp.

Then, pump makers do the same thing with pumps. They make a full rated pump and a max rated pump that are identical.

This creates inefficiency in the supply chain by making distributors and retailers carry more total inventory.

This also creates confusion for people who buy pumps and motors.

In my opinion, it's time to end service factor and only rate motors and pumps by total hp.

 

[Patrick_B]

I always found it confusing, and with everything else there is for a new pool owner, its just one more thing to muddy the already intimidating waters. What else does it boil down too in the end that really matters? I tend to agree with you James.

 

[JohnT]

I agree completely. I even get confused talking to people about it when I understand it.

Is there anything we could do on the forum to help keep it clear? Encourage everyone to use total HP and have a short PS article explaining it?

 

[JamesW]

I think that the two main challenges are awareness that it's a relevant factor when buying a pump or motor and getting manufacturers of motors and pumps to stop using it.

A person might buy a pump labeled as 1 hp and not realize that it's really a 1.65 or 1.85 total hp pump. They end up with a pump that's oversized for their pool and one that uses too much power.

Or, someone is replacing a motor labeled at 1 hp but they get a max rate instead of a full rate and the motor ends up overloaded.

An article in Pool School can help to let people know what it's all about.

Getting manufacturers to stop using it would be a challenge.

 

[JoyfulNoise]

Isn't the service factor a measure of how much a motor can be over driven for a short period of time. So a 1 HP motor with a 1.25 SF can handle a higher temporary load than a similar motor with a 1.0 SF?

Does a motor ALWAYS operate at its SF HP?

What is the relationship between the electrical HP delivered to the motor and the hydraulic HP generated by the pump wet end and motor?

Does the SF only apply to the electrical energy input or does it involve the hydraulic HP as well?

Perhaps Mark can lend his voice to this conversation.


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[JamesW]

Rated hp x SF = total hp. Total hp is the maximum permissible load the motor is designed to carry.

Choosing a motor for a pump is done by engineers. When choosing a motor for a pump, engineers will usually avoid using a motor that would operate at full load. They choose one that has a little bit room left. However, they could use one at full load. In most cases, motors are not operating at sfhp.

The correct motor choice is done by engineers.

For our purposes, the only number that matters is total hp.

For gas heaters, the power rating is the input power (ex: 400,000 btu/hr). Power delivered to the water depends on the efficiency. An efficiency of 82% delivers 328,000 btu per hour to the water.

For pumps, the rated power is the power delivered to the water. The input power is the label volts x label amps x power factor x 746. Efficiency is total hp ÷ input power.

The main problem is that, at the user level, service factor makes no sense.

When choosing a pump, it would greatly simplify things. You could compare pumps more easily. HP is not the best way to choose a pump, but at least it's closer to a fair comparison.

It makes no sense that manufacturers make two identical pumps but sell one as full rated and one as max rated. They have a full rated line and a max rated line of pumps. But they're the exact same pumps.

When getting a replacement motor, all that matters is if the total hp is equal or higher than what your replacing.

If you have a 1 hp motor with a 1.65 sf, it doesn't matter what the hp and sf are as long as they equal 1.65 when multiplied together.

 

[pooldv]

I guess the biggest question is why do they do that? What value does it bring to them to do that?

 

[woodyp]

I thought all this should have illegal a long time ago. Too many intentionally misleading smoke and mirrors.

 

[Patrick_B]

You Just talking about it in your post #6 gets me again.

 

[JohnT]

If you don't go to extremes, motor HP isn't an indication of how much work it can do, but an indication of how much load it can handle without being overloaded. If you put a 1HP motor on a pump designed for a 3/4HP motor, the motor will generate the same HP as the 3/4HP motor did and use the same amount of electricity doing it. If you put a 3/4HP motor on a pump designed for a 1HP motor, the 3/4HP motor will generate the same HP as the 1HP did and use the same amount of electricity doing it -- but it will probably overheat if you run it very long.

SF has a sort of use use in applications where a motor needs to work hard for a short time occasionally, but not when a motor runs at or near full load for hours on end like a pool pump. SF could easily be replaced by a duty cycle de-rating factor or chart in the motor specs.

Isn't the service factor a measure of how much a motor can be over driven for a short period of time. So a 1 HP motor with a 1.25 SF can handle a higher temporary load than a similar motor with a 1.0 SF?

Does a motor ALWAYS operate at its SF HP?

What is the relationship between the electrical HP delivered to the motor and the hydraulic HP generated by the pump wet end and motor?

Does the SF only apply to the electrical energy input or does it involve the hydraulic HP as well?

Perhaps Mark can lend his voice to this conversation.


Sent from my iPhone using Tapatalk

 

[JamesW]

For engineers designing pumps, there are many factors that they need to take into consideration. Continuous expected load, maximum expected load, environmental elements, service life etc.

To do this, they get statistical data about the motor and make a choice about what motor to use.

However, for people who buy a pump, the motor choice is already made. When relacing a motor, you just use one with the same total hp regardless of the rated hp and SF.

For replacement motors, all it should have is total hp.

For new pumps, it also makes sense to only use total hp. When two identical pumps are sold as if they were different, it only causes confusion.

Many people choose a pump based on label hp. For the most part, this is not a good way to choose a pump.

A better way is to use total hp. But even this is not a great way to choose. Getting rid of SF at least gets people to use total hp.

Understanding the system curves under various circumstances is a better way to choose a pump.

Plotting the system curves against the available pump curves is a better way to choose a pump. That way you make sure that the pump will deliver the flow rates needed and that it will operate in the correct section of the pump curve as specified by the manufacturer.

For example, using a WhisperFlo pump for a waterfall is usually a bad choice because waterfalls are usually low head but WhisperFlo is designed for high head.

Variable speed pumps can make things easier because you can just adjust the speed as needed.

More general info:

The total hp is generally considered the maximum load that can be put on the motor without it being considered overloaded. That's also assuming that the motor is being operated under specified conditions, such as voltage and ambient temperature.

Even if the motor is slightly overloaded, it won't catastrophically fail. It will just run hotter than it should, which will shorten it's life. The more the motor is overloaded the shorter it's life.

At some point of overloading, the motor will catastrophically fail by burning up. That's why they usually have thermal overload protection. And circuit breakers also prevent catastrophic faiure.

Maximum loading is a locked rotor, which will draw about 5 times the nameplate amps. Usually in the 30 to 70 amp range. This should quickly trip an overload protective device.

 

[JoyfulNoise]

For example, using a WhisperFlo pump for a waterfall is usually a bad choice because waterfalls are usually low head but WhisperFlo is designed for high head.

Hey! Stop making fun of my pool...I didn't know any better at the time



Seriously though, I don't think one can even come close to knowing the pool system's operating characteristics (head) a priori even if they have a layout. The plumbing subs will often deviate from plan and change things on the fly that I don't think it's possible. Unfortunately for pool builds, I think this is where you have to rely a little on a good PB's experience to say, " I've built pool type X with feature set Y a dozen times before and a 2-speed 1-1/2HP HayTair GinormoFlo 2000 pump always worked fine."

Sure, after all is said and done and your looking to change pumps, we can call in Mark and he can use his nifty calculator skills to give you a better approximation but initially you're at the mercy of the pool builder.

But to wrap it up - what is the recommendation you think TFP should give? What's the easiest way to help someone select a pump or motor?

Honestly when people ask that question, I have no clue and wait for you or Mark to chime in.



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[JamesW]

A lot depends on the specifics of the pool and equipment.

Variable speed pumps are nice when they make sense. With a rebate, they become a more attractive choice.

In many cases, pumps are oversized. So, it's always worth asking if you can downsize the motor and impeller.

Two speed pumps can be a good choice. However, two speed replacement motors cost substantially more than a single speed.

 

[JoyfulNoise]

A lot depends on the specifics of the pool and equipment.

Variable speed pumps are nice when they make sense. With a rebate, they become a more attractive choice.

In many cases, pumps are oversized. So, it's always worth asking if you can downsize the motor and impeller.

Two speed pumps can be a good choice. However, two speed replacement motors cost substantially more than a single speed.

If someone is doing a motor replacement and not a pump replacement, is the proper advice for them to find the same exact motor with the same service factor? Or can they replace a 1HP SF 1.5 motor with a 1.5HP SF 1 motor?

 

[mas985]

NEMA and only NEMA decides what goes on a motor label and given it is a standards organization, it is unlikely that they would make a change that is very specific to pool pump motors. They have a much broader view of the market requirements for induction motors and service factor is very important for some applications.

All of the specifications on the NEMA label come from one basic requirement; thermal insulation class. Each class determines the maximum temperature that the insulation should be exposed to and that combined with the efficiency of the motor, determines the maximum amps and HP. Extended operation above this range meant that the life of the motor (more specifically, the motor insulation) could be significantly shortened. However, the concept of service factor indicated to the engineer how much a motor could be overloaded (over nameplate HP) for a specified time period without compromising the insulation. It takes time for the heat to build up in the motor and that extra heat could then be dissipated when operating at the lower label HP or turned off. So for applications where the motor would only run for short periods of time or had varying loads, this allowed the engineer to size a slightly smaller motor for that application and save some money without sacrificing the life of the motor.

So you might ask how all this relates to pump motors. With pump motors, engineers found that they could operate the motor closer to the SFHP than you could in many other applications because you had a natural heat sink in the wet end. Heat can be transferred through the motor shaft and housing to the wet end and then to the water so the motors insulation life would not be significantly affected by the higher load. But this is also why wet ends melt when flow stops.

So could NEMA have a special rating for pump motors, perhaps but I doubt they would. Speaking as an engineer, I think it makes more sense to have a single standard for all induction motors. But what could be done and what I have seen some manufactures do is to place a separate sticker on the motor which is the THP/SFHP. This I think is a more practical solution to support.


But for TFP, I don't see why we would need to do anything different. The concept is explained here: Pool School - Pump Basics

Although like most TFP articles are ignored by the newbie until pointed out. The fact is, for all information on TFP, it is far easier to post a question than it is seek out an answer via Pool School.

 

[JamesW]

If someone is doing a motor replacement and not a pump replacement, is the proper advice for them to find the same exact motor with the same service factor? Or can they replace a 1HP SF 1.5 motor with a 1.5HP SF 1 motor?

As long as the hp x the sf is the same, it's the same total. A 1 hp with a 1.5 sf is the same as a 1.5 hp with a 1.0 SF.

 

[JamesW]

NEMA only requires that sf be listed if it is other than 1.

If SF is other than 1, SF has to be listed as well as hp. However, they don't specify how that combination should be done.

The problem that I see is that manufacturers take two exact same motors from the assembly line and sell one as a 1 hp motor with a 1.65 sf and the other as a 1.5 hp with a 1.1 sf.

This proves that the designation is mostly arbitrary and meaningless. All that matters is the total hp. If the numbers really had valid meaning, then there would only be one label hp and one service factor.

Pump makers make two identical pumps and sell one as a 1 hp and one as a 1.5 hp pump. It would make far more sense to just have a single 1.65 hp pump.

Here is the definition of service factor:

A multiplier which, when applied to rated power, indicates a permissible power loading that may be carried
under the conditions specified for the service factor.

It doesn't say anything about overload.

Of course an engineer shouldn't choose a motor that would be loaded to full capacity. There are many factors that an engineer has to consider when choosing a motor, but those are not relevant to the end user.

The simplest answer would be for all pumps and motors to have a 1.0 Service Factor. That way, all label hp is equal to total h.p. That's certainly within the rules pertaining to motor nameplates.

 

[mas985]

NEMA also specifies a set the operating temperature for each insulation class and it defines how that changes with service factor. This is necessary for certain applications but not pool pump motors.

NEMA Insulation Classes

The problem that I see is that manufacturers take two exact same motors from the assembly line and sell one as a 1 hp motor with a 1.65 sf and the other as a 1.5 hp with a 1.1 sf.

I agree but that that is pretty much limited to pool pump motors and mostly driven by the pool builders.

The simplest answer would be for all pumps and motors to have a 1.0 Service Factor. That way, all label hp is equal to total h.p. That's certainly within the rules pertaining to motor nameplates.

I don't disagree but I think you would expend quite a bit of energy trying to make it happen and probably still not be successful.


But I really don't think it is that difficult for people to multiply two numbers together. Initially it may cause a bit of confusion but I don't know of case where it wasn't eventually understood.

 

[JamesW]

It's not too difficult to multiply the numbers together. The problem is that many people don't realize that they need to do that. Part of my goal is to raise awareness.

As far as manufacturers go, I agree that it's unlikely to change any time soon. But, you never know. Maybe a key person will decide that it's a good idea.

I think that VS pumps will continue to increase in popularity, especially for new pools. That should help some as long as they are programmed and operated correctly to optimize performance and economy.

 

[Zurak]

It's my understanding that a motor can operate in it's SF when it's needed as a result of the following:

(1) Filter that is getting dirtier, (2) leaf, skimmer or pump baskets filling with debris, (3) water features or in-floor cleaning systems, (4) dust and/or blocked ventilation holes, etc ...

It's really not desirable to operate the pump in it's SF. A pump with a lower rated HP and higher SF will often be cheaper than a pump with a higher rated HP and lower SF. Operating a pump in it's SF often results in more heat and all it takes is for a 10 degree C (16 degree F) rise in temperature to half the lifespan of the insulation on the wiring in the motor. Is it worth saving a few bucks to shorten the life of your motor?

Continued operation of a motor in its SF will shorten the life of the motor. I would not want to see the removal of the SF from the nameplate.

Isn't the service factor a measure of how much a motor can be over driven for a short period of time. So a 1 HP motor with a 1.25 SF can handle a higher temporary load than a similar motor with a 1.0 SF?

Does a motor ALWAYS operate at its SF HP?

What is the relationship between the electrical HP delivered to the motor and the hydraulic HP generated by the pump wet end and motor?

Does the SF only apply to the electrical energy input or does it involve the hydraulic HP as well?

Perhaps Mark can lend his voice to this conversation.