Variable speed hydronic circulator pump 1

[alternety]

I have had a bit of trouble figuring out where to ask this. Pump forum seems a bit pumpy. HVAC feels wrong. So I will try here.

I have a residential hydronic system that was designed with a variable speed pump to control system flow. The pump supplied by the contractor is a Grundfoss UP-26-96 F/VS. This is about a 200 W unit. Maximum operating point is 12.2 GPM @ 10.8 ft of head. 1 1/4" flanges.

The problem is that it is too noisy for the residential application. It is louder than the boiler and 3 other smaller pumps combined. Without this one pump you can barely hear the system running. This pump generates vibration that can be heard everywhere in the house. A replacement unit of the same model does the same thing. It is not a faulty pump; just a feature.

In addition, what appears to be a simple TRIAC controller built into the pump, can not deal with low flow rates without even more noise and stalling.

The application requires a very wide range of flow. It really needs to be able to go down to only a couple of percent of full flow. There are some very small zones. The pump is controlled by external equipment and the system is designed to control system pressure drop by controlling the pump speed. That is another topic.

I have been searching for a replacement pump. At this point (i.e., winter is approaching) I have instructed the contractor to replace the variable speed pump with a quiet fixed speed unit and a pressure bypass valve. People familiar with this pump and the same motor without variable speed indicate there is a radical difference in noise. Why this is true, particularly at full speed, is unknown and not really the question at this point.

My thinking is that I can install the new pump now and next summer I can try to reconfigure for varaible speed again. I need a pump that can deal with a wide range of speed/flow. My supposition is that I should use a PM DC motor or something along those lines and use PWM for control (using an external PLC).

I have been searching the web and have been unable to find anything that will replace the Grundfoss pump but have a quiet and properly controllable motor. The heating people that the contractor and I have talked to have no information on a suitable device.

Can anyone point me to a suitable unit or vendor. I would also be interested in your opinions of what type of motor/speed control to use. Pumps for this type of use tend to be integral units, but some older and usually bigger circulators had seperate motors and pumps. I understand they tended to be less reliable overall because of the seals, but this is also a possible solution.

Thanks for any help you can provide.

 

[ScottyUK]

Depending on whether you can find a suitably small pump, a type with a three-phase motor should have low inherent vibration because the torque ripple is low. Such a unit coupled to a cheap variable frequency drive from any of the countless manufacturers would give you a good range of continuously variable pump control. Most types accept either a 4-20mA or 0-10V reference input. Speed ranges of better than 10:1 are easily achieved even with the cheapest types. There would be much benefit in this application spending a lot more money on a high end drive. The small VFD's rated below about 2.2kW accept single phase domestic power input and produce a reduced voltage 3-phase output. You'll need to check that the pump motor is compatible with the voltage output of the VFD.




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One day my ship will come in.
But with my luck, I'll be at the airport!

 

[Barry1961]

If you really need a "couple of percent", 50:1 speed range, of full flow you may need to use multiple pumps. This is the standard practice in pumping stations for water and sewage to handle peak loads and save energy during slow times. Most pumps become inefficient at low speed and very nonlinear.

There are several people who make controls for multiple pumps and a lot of good information online about the theory of operation and even schematics. If you do a google for “pony pump control” you should get a lot of hits. The pony pump is the little pump that runs during slow times.

If this seems like a good solution you should try to find information on the flow of the pumps across the speed range. Try to size the pumps so as the efficiency of the big one starts to drop the pony pump takes over. Here is some general info.

http://www.eere.energy.gov/femp/technologies/eep_centrifugal_pump.cfm

Barry1961

 

[LionelHutz]

As Scotty said, sounds like you need a small 3-phase pump and a VFD.

That pump does appear to be 1-phase so you're likely right about operating with a triac type controller which is just controlling the voltage on the motor.

 

[ScottyUK]

There would be much benefit in this application spending a lot more money on a high end drive.

I seem to have missed out the word 'not' from the above statement!

There would not be much benefit in this application spending a lot more money on a high end drive.

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One day my ship will come in.
But with my luck, I'll be at the airport!

 

[jraef]

That pump has an integral motor, meaning the motor and pump are sealed together as a single unit. You will not be able to replace just the motor. Hard to say what they are doing for variable speed, Grundfos does not show that version on their website. They do show a UP-26-96-F and the data for it shows it only as a 1 phase 115V motor with a run cap, so most likely a split phase. You cannot vary speed on those with a VFD, or a triac controller for that matter, so your version must have a different motor.

UP 26-96 F Click for website
The pump is of the canned rotor type, i.e. pump and motor form an integral unit without shaft seal and with only two gaskets for sealing. The bearings are lubricatd by the pumped liquid. The pump is characterized by:
* Ceramic shaft and radial bearings.
* Carbon axial bearing.
* Stainless steel rotor can and bearing plate.
* Corrosion-resistant impeller, Composite, PES.
* Cast iron pump housing.

The motor is a 1-phase motor. No additional motor protection is required
Electrical data:
Max. power input: 205 W
Mains frequency: 60 Hz
Rated voltage: 1 x 115 V
Max. current: 1.7 A
Capacitor size - run: 10 µF/180 V
Insulation class (IEC 85): F

That type of pump (centrifugal vane pump) should not be making a lot of noise, maybe a little high pitched whining if it uses a VFD, but it should just be a normal pump whirring noise. If you click on the link, it even says "Whisper quiet operation". Vibration in any kind of a pump usually signifies something wrong. If you have replaced the pump and it didn't change, I'd look next at the installation. BTW, you should post this in the Pump forum, I seriously doubt this is an electrical problem.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[Warpspeed]

I am thinking this is a rather special application, and a complete "off the shelf" solution may not be readily available.

If it has to be truly silent, an oversized centrifugal pump would probably be best run at unusually low Rpm, and pulley driven by an appropriate motor. Pulley ratio and motor size can be optimised for most economical operation. The motor itself may then be fitted to some very soft vibration isolating mounts.

 

[ScottyUK]

good points jraef,

Grundfos do make some small 3-ph pumps, although they're not listed as domestic circulators. The 3-ph ones on the European website are listed as 380/415V which may mean that they're star connected but the starpoint is buried or that they're delta wound. I suspect the former case. Alternety could either butcher the motor of his new pump - thus invalidating the warranty - or look for a separate motor-pump combination.

An aside: could the noise be due to resonance in the mounting? Do I recall that the pump is in the loft? Large planar surfaces - especially wooden ones - can make insignificantly low levels of vibration produce quite unreasonable amounts of sound. Have you tried decoupling the pump from the rest of the structure using anti-vibration mountings and flexible hoses to the pipework?


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One day my ship will come in.
But with my luck, I'll be at the airport!

 

[alternety]

WISPER QUIET IT AINT. The pump is not readilly identified from Grundfoss information. They do not easilly acknowledge that it exists. The specs posted above for the motor match rather well with the label information on the pump. Yes I know I can not replace just the motor. It is an integrated motor/pump.

Resonance could be an issue. As noted, the pipes are mounted on anti-vibration mounts but I am not aware of a usable flexible pipe that would provide vibration isolation while meeting code or reasonable durability for a hydronic system.

If anyone could identify a suitable motor/pump product (manufacturer/part number) I would be grateful. This is what I am after.

 

[ScottyUK]

Alternety,

I can't comment on US codes, but British CH and DHW systems are allowed to use flexible hose with a braided stainless steel outer. Similar to:

http://www.hydralectric.co.uk/detai...Ref=2877&Ref=1509&Category=Hoses+and+Fittings

They are commonly used with pump-fed showers to help isolate them from the rest of the system - those pumps are typically 1HP or greater and have a lot of scope for making noise.


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One day my ship will come in.
But with my luck, I'll be at the airport!

 

[MikeHalloran]

If space permits, I'd try to isolate the noise, e.g. by supporting the pipes immediately adjacent the pump on rubber mounts.

In the supply and discharge pipes, instead of hoses, install a really big high- index (D/d>>20) coil spring, constructed from the pipe itself.




Mike Halloran
Pembroke Pines, FL, USA

 

[stardelta]

Has it been noisy from the start? if so it could be cavitation which is causing the problem in which case the pump is not idealy suited for the system characteristics. I would post the question in the Pump Engineering forum and get some feedback from there. Another thing to consider, certain circulating pumps must be mounted with the shaft down to allow the weight of the rotor to be supported by a thrust bearing at the impeller end.

 

[alternety]

All the rigid piping is supported by rubber isolated mounts. The pump motor also directly emits a lot of noise. There is not very much room to alter things around the pump location. The pump is mounted acording to the manufacturers specifications.

Well established software was used to calculate the necessary pump characteristics. With all the valves open, the current draw of the pump is consistient with the 200 watt rating. In addition, the contractor is experienced and does not believe there is cavatation noise.

The pump of this size should not make this much noise. I should be nearly silent.

I need a quiet, energy efficient, controllable replacement. That is what I am trying to find.

 

[stardelta]

Has the noise been there since the start or developed over a period of time?
Have you noticed a coresponding drop in performance/efficiency of the system?
If your experienced contractor says its not cavitating what does he say is generating the noise and why cant he suggest
a fix or an alternative pump.
Have you considered speaking directly to Grundfoss to get their comments on the noise issue?
Have you considered (if possible) moving the pump to an area where the sound is not as obtrusive or attempting to insulate it?
Have you tried a websearch and looked for alternative manufacturers of circ` pumps and see what they can offer?

You need to post your original question in the Pump Engineering Forum.

 

[Warpspeed]

Reinforced rubber hose similar to automotive radiator hose installed next to the pump, should be able to handle the temperature and pressure well enough, and isolate any conducted vibration along the pipework.

 

[itsmoked]

??

These things are silent! If they made noise they wouldn't be the de-facto standard....

You obviously have it installed properly. Rubber mounts, an experienced installer, beat dead horse, etc, etc, etc.

IMnHO your system has a problem. You need to focus on that not the pumps.

In my town relief valves have caused two microbrewers to be shut down. Horrible incapacitating noise throughout the entire facility that boiled down to a singing relief valve in the energy recapture systems. TWICE!

Now I think you said you don't have one, having gone with the variable speed pump instead. If I'm wrong check any relief valves first.

Next most likely bad noise problem is cavitation... And I don't mean a few bubbles in the system. I mean screwed up pressure gradient cavitation. You have a humongous system that just may have exceeded your installer's knowledge base. You could be running the suction side of your pump into a vacuum. You could be asking the pump to develop too much pressure from too small an impeller, etc., etc.

I would try some experiments like running your system open.
Provide the pump inlet with a 5 gallon overhead pail or a garden hose. Let the system return to a pail or the lawn. See if the pump doesn't instantly drop to inaudible.

I would try anything else you can think of that doesn't include another pump change.

You need to start getting data on your system's boundary conditions. What is the discharge pressure? What is the suction pressure?

Is the return manifold actually the correct size?
Is the supply manifold the correct size?
Confirming this NOT thru your installer!

Does the sound change as you open each and every zone one at a time until they are all open?

This would be my approach. I would definitely NOT look at the pump anymore since you have gone through two of them.

You need more info.

 

[alternety]

itsmoked

You must have taken a laptop up to the attic.

I completely agree about the potential noise from pressure bypass valves. One of the reasons I avoided it. If you use a constant speed pump you have to put one in to bypass varying amounts of water back to the supply side of the pump. This is different than a relief falve for system overpressure. I have those and we tripped on while filling. Made an exciting noise. The water pressure from the water filter is much higher than the normal system static pressure.

The system right now is configured so all valves are open. The pump is seeing the minimum backpressure for any given speed. I have shut down many of the zones and the noise does not chage noticibly. I will see if we can get water through and right to a drain. I am not sure how we can get it fed non-pressurized water. Have to be careful too because it has water lubricated bearings.

I am looking into some of the other things you mention.

 

[itsmoked]

Great let us know! And yeah, I couldn't conjure up "bypass" so I finally went with "relief". Prolly fiberglass poisoning.

 

[alternety]

I forgot to mention - the pressure sensor that was supposed to do the control shows absolute system pressure and the pressure across the pump.