Chilled water Pumps

[vecnaj1978]

hello

can someone please advice me on why do we select the chilled water pump in the closed loop at 1500 RPM
Why cant we select the pump at 2900 rpm??

Why consultants always suggest with 4 pole motor

is it ok if we use 2900 RPM and then run with VFD

Pleae advice me on this

regards
VEC

 

[DubMac]

Slower pumps will last longer. Wear increases as the cube of the speed increase. It is a trade off, as slower pumps are larger and more expensive. You must decide, "Pay me now, or pay me later".

 

[willard3]

You may do better posting this in "Pump Engineering"

 

[ScottyUK]

From the motor's point of view DubMac got it in one. Two-pole machines have a significantly shorter life between bearing changes than four-pole types.

 

[KiwiMace]

Yes, but it is not just wearing out faster, it is the cost of downtime. We use 2-pole motors only when the pressure requirement demands it.

 

[NXTCOLD]

The VFD 2900 RPM motor idea is a good one if your operating conditions allow you to back down while maintaining sufficient cooling performance,

 

[Artisi]

vecnaj1978: Why run 2900RPM and VFD, what is your reason for this?

There is nothing inherently wrong with operating at 2900 RPM, a chilled water service pump has a pretty easy life in which you wouldn't expect to see much wear and tear on the pumps. Also bear in mind, what pump manufacturer you are choosing to use, many pumps have been designed to operate at 3600rpm 60Hz and when applied to 50Hz 3000 rpm they are only operating at about 80% of their max. design, a point worth considering in your analysis.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[EnergyProfessional]

unless you can design and pick the perfect pump, you always will run the pump slower than rated speed. In the old pre-VFD days a balancing valve was used to run pump at full speed and make up for the oversizing.

As far as the 1750/3500 rpm pump discussion goes, I would suspect (or hope) a good pump manufacturer uses better bearings in the higher rpm pump.

Why your engineer selected that pump? - you need to ask him/her. If you select the pump the manufacturer sometimes just has that one for the given flow/pressure. Maybe often the high-pressure pumps tend to be high rpm pumps. If you don't like it, look at a different manufacturer.