Re.:- VSD for chiller pumps

19 January Query from Ferry Marfang -

I want to ask what data must be completed before installing variable speed drives on chiller pump, because I was afraid would happen abnormal conditions on the chiller when installing VSDs on the pumps. As additional information that the data are available only electrical measurement data. Because the flow meter and pump characteristic curve is not available. another question is how to choose the right inverter.

This is the technical specification of chiller and pump:

No	Parameter	Chiller 1,3,4	Chiller 5,6
		30GBN400	30GTN420
1	Refrigeran	R22	R22
2	Chill water pump	90 KW	30 KW
3	Chiller capacity	400 Ton Ref	420 Ton Ref
4	Power input compressor	45 kW	45 kW
5	Chill water temperature	-	-
6	In let	13 oC	13 oC
7	Out let (setting)	5 oC	6 oC

20 January, SLA wrote -

Is it possible that 30 kw mentioned for Chillers 5,6 is 'per pump' and 90 kW mentioned for Chillers 1, 3, 4 is for 3 pumps together ? That will make all pump and chillers identical.

The difference in refrigeration capacities 400 and 420 seems marginal.

In fact there is no logic for pump(s) in 400 T refrigeration capacity to be 90 kW whereas the pump(s) in 420 T (higher) refrigeration capacity are 30 kW (1/3 of 90 kW).

The VSD is never common. It is always dedicated to each motor. Selection of VSD is primarily dictated by motor-rating and the range of speed-variation required in an application.

Also, VSD is useful for energy-saving and to avoid too many pumps in an installation. A combination of having number of pumps and having also VSD may not help much. It may rather complicate O&M by the increase in number of engineering devices in the system.

20 January, Ferry wrote -

the reason I installed VSD on chiller pumps is due to the percentage loading capacity of 90 kW pump is maximum 60%. with this condition discharge valve closed 50% this is because the pressure chilled water in Air Handling Unit (AHU) is very high.

Here I attach a detailed layout diagram of chilled water systems.

With a record for the booster pump outlet after the header on the image attachment does not use anymore.

20 January, SLA wrote -

Your query was about method of selecting VSD. My answer was that selection of VSD is primarily influenced by the motor rating. If you have already installed VSD with due diligence, your query is answered by yourself.

Now when you say that percentage loading capacity of 90 kW pump is maximum 60%, I wonder whether the system was over-designed and in turn the pump also became selected with excessive capacity.

Since the pumps cannot be replaced as easily, your logic of installing the VSD seems logical.

24 January, Ferry wrote -

my intention to install a VSD on the pump is to reduce energy consumption at the pump, the current state of the pump rotation speed constant while the chiller cooling load vary. I want to ask for input consideration what should I look for when installing the VSD so that the VSD to work as expected.

28 January, SLA -

Since you have number of pumps in parallel and now you also want to have VSD, I wonder whether you can incorporate VSD in the common control panel, maybe, with a properly programmed PLC. That should save you from having VSD dedicated to every motor.

With a PLC it should be possible to link operation of the VSD to correspond to the variation of load on the chiller. With today's advancements in technology, everything that is technically logical should be possible ! Check with a smart PLC guy !

I know that in hydro-pneumatic systems (called also as pressure-booster systems) they do have more than one pumps, cutting in and out of standby pumps and VSD and pressure-switch mode all integrated using PLC. What is pressure-switch mode in that system will be chiller load in your system. Yes, parametric control of operation of VSD should be possible. In fact that will give best energy-saving.

On 24 January Ansari wrote -

Most importantly the motor should be compatible to be fitted with a VSD. Speed reduction involves lot of heat generation and a suitable means of dissipation of the same should be present to avoid motor burnt out.

Mr. Abhyankar: I hope, I am right. You can comment on this a little more.

28 January, Response by SLA -
Dear Juned,

You are right. As with any other device, VSDs also have their pros and cons. I just did google search on "Problems with VFDs". And I got "1,430,000" results in 0.45 seconds".... !

-o-O-o-