2.70 total HP vs. 2.20 total HP for a spa

[beezar]

Hi everyone,

Just got my burnt out motor on my Hayward Tristar pump replaced by Warehouse pool supplies. However, the original was a one speed 2.0 HP with service factor 1.35 for a 2.70 total HP pump. The one they installed is a two-speed pump with a 2.0 HP and service factor 1.10 for a 2.20 total HP pump.

I'm worried about the downgrade in total HP and if that will affect the strength of the spa jets. Warehouse keeps telling me that I won't notice the difference at all, but I figured I'd check with you guys to make sure before I start using the motor. Thanks!

 

[mas985]

Sounds like they replaced a full rated motor with an up rated version which can create problems because the motor may be overloaded. It won't change the strength in the jets but the pump might shut off due to thermal overload and it could be damage. I would get the correct motor unless the motor has been changed before and they put too large of a motor on the first time. Which TriStar pump model do you have?

 

[adelman]

The Service Factor (SF) of a motor is the amount that it can be periodically overloaded without damage. For example, if a 2HP 1.3x SF motor is spinning a table saw blade, you can transiently overload it to 2.6HP while you're cutting. Most of the time the blade sits idle waiting for wood. Although the motor designer doesn't tell you what limited the motor to 2HP, typically it is heat buildup, while the SF overload is likely structural.

I don't see how the Service Factor would be relevant on a pool circulation pump. A circulation pump on a pool is a continuous load without such overload transients. A 2HP 1.35SF pump shouldn't be putting out more than 2HP in this situation, nor should a 2HP 1.10SF pump. So if the pump was correctly designed not to overload the 2HP 1.35SF motor, it won't be overloading the new motor either.

One test would be to measure the running current with a clip-on ammeter. The motor data plate or manual should tell you the FLA (full load amps), which corresponds to the current draw at rated output (2HP). Verify the current doesn't exceed the FLA and you're good to go.

 

[mas985]

For applications other than pool pumps, this may be true. But pool pumps are designed to run very close to the service factor load. It is the continuous load which allows for this. Otherwise, an up rated pump would have a different head curve than a full rated pump. For example a 1 HP full rated pump with a service factor of 1.65 has exactly the same performance, load and current draw as a 1.5 HP up rated pump iwith a service factor of 1.1 in the same pump line. The service factor is very relevant.

 

[adelman]

For applications other than pool pumps, this may be true. But pool pumps are designed to run very close to the service factor load. It is the continuous load which allows for this. Otherwise, an up rated pump would have a different head curve than a full rated pump.

I'm going to admit here that I'm not a pool-pump expert, but I do understand motors, and this makes no sense. If a pool pump is a continuous load and the motor is being run above the rated output into the "service factor" territory on a continuous basis, then, from the point-of-view of the motor designer the motor is already being overloaded.

For example a 1 HP full rated pump with a service factor of 1.65 has exactly the same performance, load and current draw as a 1.5 HP up rated pump iwith a service factor of 1.1 in the same pump line. The service factor is very relevant.

Aren't these constant-speed AC induction motors?

A 0.5 HP motor turning the same pump would also have the same performance curve, load, and current draw (it might just be overloaded), as would a 2.0 HP motor turning the same pump (it would just be heavier and more expensive than you need, if you only loaded it to 1.5HP). It would be up to the system designer (the guy designing the hydraulic load) to be sure that the motor wasn't overloaded, and that would mean limiting the hydraulic load so that the 0.5 HP motor, on a continuous basis, was situated on the performance curve in a place where it wasn't putting out more than 0.5 HP.

I'll stand by my comment that if the original motor wasn't overloaded, the new one isn't, but I agree that if the original motor was "a little" over loaded into the SF territory, that the new motor won't tolerate it as well. The easiest way to check this is to measure the running current.

The head-curve is a function of the pump and speed at which the pump is turning, not the rated HP of the motor. For any given head and speed, the applied shaft HP is the same, no matter what type of force you use to turn the shaft.

Ken

 

[mas985]

First an induction motor maximum load rating is actually the label HP times the service factor so a 1 HP motor with a 1.65 service factor has a maximum load rating of 1.65 THP. The actual label HP is meaningless without the service factor. The full rated vs up rated versions of the same motor have identical THP but have different label HP so it is the THP that really matters and not the label HP.

Aren't these constant-speed AC induction motors?

Yes AC induction motors are virtually constant speed. They do have a slip which averages around 4% which is why they run at 3450 RPM instead of 3600 RPM.

The head-curve is a function of the pump and speed at which the pump is turning, not the rated HP of the motor. For any given head and speed, the applied shaft HP is the same, no matter what type of force you use to turn the shaft.

True which was exactly my point. Let me give you an direct example and hopefully that will help you understand. The Whisperflo pump series has both up rated and full rated pumps. The WFDS-3 and WFDS-24 have identical wet ends so the impeller and diffusor are exactly the same and have the same head curves. However, the motors have different label HP even though the loads are the same. The WFDS-3 motor has a 3/4 HP label rating with a 1.65 service factor but the WFDS-24 motor has a 1 HP label rating with a 1.1 service factor. Both motors have a THP of 1.1 so in fact they are identical motors which is necessary since the loads are the same. This proves that in fact the pump wet end is designed for the same THP but not the label HP ratingas those are different.

If you would like to learn more about pumps, I would suggest going to Joe Evens site and read up on them: http://www.pumped101.com. He explains all of this in his article series.

 

[adelman]

First an induction motor maximum load rating is actually the label HP times the service factor so a 1 HP motor with a 1.65 service factor has a maximum load rating of 1.65 THP. The actual label HP is meaningless without the service factor. The full rated vs up rated versions of the same motor have identical THP but have different label HP so it is the THP that really matters and not the label HP.

Aren't these constant-speed AC induction motors?

Yes AC induction motors are virtually constant speed. They do have a slip which averages around 4% which is why they run at 3450 RPM instead of 3600 RPM.


[quote:3qxi5p1s]The head-curve is a function of the pump and speed at which the pump is turning, not the rated HP of the motor. For any given head and speed, the applied shaft HP is the same, no matter what type of force you use to turn the shaft.

True which was exactly my point. Let me give you an direct example and hopefully that will help you understand. The Whisperflo pump series has both up rated and full rated pumps. The WFDS-3 and WFDS-24 have identical wet ends so the impeller and diffusor are exactly the same and have the same head curves. However, the motors have different label HP even though the loads are the same. The WFDS-3 motor has a 3/4 HP label rating with a 1.65 service factor but the WFDS-24 motor has a 1 HP label rating with a 1.1 service factor. Both motors have a THP of 1.1 so in fact they are identical motors which is necessary since the loads are the same. This proves that in fact the pump wet end is designed for the same THP but not the label HP ratingas those are different.

If you would like to learn more about pumps, I would suggest going to Joe Evens site and read up on them: http://www.pumped101.com. He explains all of this in his article series.[/quote:3qxi5p1s]

I think we're arguing the same side, except...

Are you saying that pool system designers are using a WFDS-3 motor in a continuous load situation above 3/4 HP? The motor designer would tell you that this is overloading his motor. If system designers are doing this, is it somehow an accepted practice in the industry? You're not supposed to go above rated HP on a continuous basis, and I'll stand by that statement.

Back to the OP question - a measurement of the current going into that motor will tell us if it is overloaded...

 

[mas985]

Yes, again pump wet ends are matched to motors based upon the THP and not the label HP. So the WFDS-3 is designed to work with a motor rated at 1.1 THP and not 3/4 HP. And yes, this is standard practice in the industry.

The motor designer would tell you that this is overloading his motor.

Not always, it depends on the application. Service factors were initially used in industrial applications where the voltage and operating temperature conditions varied by a significant amount. In these conditions, continuous operation at the service factor would be problematic. Also, the maximum load was not always known precisely so to avoid any issues, they recommended operation below service factor. However, if the application was for short duration, they allowed for operation at the service factor rating. For a pool pump, the operating voltage and temperature is fairly stable and predictable and the loads are known very precisely so continuous operation at the service factor load is tolerated.

BTW, all pump motors now have thermal overload protection so if they are overloaded and get too hot, they will shut down. This can occur in a over/under voltage condition, bearing wear or something stuck in the impeller. But since the motors are operating close to service factor load, it doesn't take much to overload a pump motor.


Also, the definition of service factor per National Electrical Manufacturers Association (NEMA) in section MG1 - 1.43 of their manual:

"The service factor of an alternating current (AC) motor is a multiplier which, when applied to the rated horsepower, indicates a permissible horsepower loading which may be carried under the conditions specified for the service factor."

Pump motor label ratings for current, voltage, insulation and temperature are all at service factor load so they meet this definition and as long as you do not exceed these limits, you can operate the pump at the service factor load without damaging the motor.

 

[beezar]

Ok, this is a bit over my head. My pump is the Hayward Tristar SP3220EE. What makes the motor uprated? Is it the total HP or the service factor? I was under the impression that you wanted the service factor close to 1.0, but honestly I have no idea.

So my new motor (2 hp, SF 1.10 = 2.2 total HP) is uprated vs. the old one (2hp, SF 1.35 = 2.70 total HP)? If that is the case, it is definitely going back, as I don't want this new motor to burn out in 2 yrs.

Edit: ok, i think I understand better: the total HP is underpowered compared to what the impeller/wet end is designed to do, so there is a higher chance of burn out. Does that sound correct?

However, if I run my 2-speed pump at low-speed (0.33hp) most of the time with only the high speed when I use the jets, (vs. when I was running the old one-speed pump at the full speed total--total 2.70 HP all the time for circulation and for jets), the pump life may last as long as the original... possibly

I hope I'm understanding this, and I appreciate all of your help.

 

[adelman]

Ok, this is a bit over my head. My pump is the Hayward Tristar SP3220EE. What makes the motor uprated? Is it the total HP or the service factor? I was under the impression that you wanted the service factor close to 1.0, but honestly I have no idea.

So my new motor (2 hp, SF 1.10 = 2.2 total HP) is uprated vs. the old one (2hp, SF 1.35 = 2.70 total HP)? If that is the case, it is definitely going back, as I don't want this new motor to burn out in 2 yrs.

I disagree with the other poster on the notion of running the motor over rated HP. Simple way to resolve this -- measure the
running current and we'll know the load. If the load is under 2HP, then don't worry about it.

 

[mas985]

Hayward Tristar SP3220EE is a full rated pump with a service factor 1.35. You can look up the information on Hayward's site in this document: http://www.hayward-pool.com/pdf/literat ... SS11_5.pdf

The motor they gave you is for the SP3215X20 pump which is a 2 HP up rated pump with a 1.1 SF. If the operating point of the pump is 20% below full load which it could be with restrictive 1.5" plumbing, then the lower THP motor may not trip the thermal protection but at this point it is hard to tell. You could try it but if it were my pump, I would get the correct motor.

I disagree with the other poster on the notion of running the motor over rated HP. Simple way to resolve this -- measure the
running current and we'll know the load. If the load is under 2HP, then don't worry about it.

I am sorry I can't convince you that pool motors run close to their service factors but it is true just spend the time and research it yourself as I did a long time ago. A really good source are the articles on http://www.pumped101.com and specifically this article and page 73. Any expert will tell you that when sizing a motor for an existing pool pump, you must choose a motor that has a THP that is greater than or equal to the old motor. Here are a few other resources on sizing pump motors. Hopefully you will spend the time to read them:

http://www.poolsupplyworld.com/blog/how ... _motor.htm
http://www.poolsupplyworld.com/blog/Gen ... motors.htm
http://www.poolplaza.com/pump-ratings.shtml
http://blog.poolcenter.com/article.aspx?articleid=6206

There are many others too if you just search for them.

 

[adelman]

Hayward Tristar SP3220EE is a full rated pump with a service factor 1.35. You can look up the information on Hayward's site in this document: http://www.hayward-pool.com/pdf/literat ... SS11_5.pdf

The motor they gave you is for the SP3215X20 pump which is a 2 HP up rated pump with a 1.1 SF. If the operating point of the pump is 20% below full load which it could be with restrictive 1.5" plumbing, then the lower THP motor may not trip the thermal protection but at this point it is hard to tell. You could try it but if it were my pump, I would get the correct motor.

I disagree with the other poster on the notion of running the motor over rated HP. Simple way to resolve this -- measure the
running current and we'll know the load. If the load is under 2HP, then don't worry about it.

I am sorry I can't convince you that pool motors run close to their service factors but it is true just spend the time and research it yourself as I did a long time ago.

You can convince me that a pool motor runs over rated HP, but you can't convince me that this is a good idea. If it were my pump, I would measure the current at maximum load, calculate the actual HP, and size a motor with a rated HP above this number. There is no reason for the OP to replace the motor again unless we know or suspect that it is being overloaded.

Ken