VFDs on a compressor

[meoberry]

The VFD stores energy in capacitors and then uses transistors or triacs (electronic switches) to pass that power at the desired frequency. Those electronic switches convert about 3% of the energy that passes through them into heat. That is why all the VFD controllers have large heat sinks (aluminum fins) in order to shed that heat created by the electronic switches. So you are correct that the VFD should only be used when it is desirable to trim the load by greater then 3%. However, some VFDs can also be used to convert a single phase power supply into three phase power supply, in which case they might be used even in full load applications just for the phase conversion capabilities.

Did not know about the phase conversion. Did know about the heat they generate though. Also found they do not like salty air. As for the power loss just simple phisics. Takes energy to create heat. So there has to be a loss. But we have a chiller that cools a hospital. this time of year it runs at about 40%. Heat of the summer it runs at 100% and have two smaller chillers for backups. We firing them up just to keep them limbered up and give the big one a break. Usually for maintenance. Clean the barrels, filter and such. Before they added on to the hospital the two smaller ones was it. Took all they could do just to keep up. They added the big one with the vfd which was supposed to handle the whole building. Which does 9 months out of the year. Reduced their power consumption by 20% for cooling.

[NANOTECH]

Can anyone explain sequence of operation for these VFDs The two mounted on the rack seem to be doing the CFMs and the one oon the wall is doing the R22 Bitzers. How are these set up? How does it know when to reduce or speed up? Also any info on the oil system setup on these LT Bitzers would be great! Oil coolers and what the solenoids are doing in the oil line?

http://youtu.be/aPrPg5iz5G4

[BDOLIN]

VFDs can increase efficiency on almost every motor driven device. The is another thread about how they may be used.
On compressors the big concern is lubrication- slowing the pump will slow the oil to the bearings. Standard compressors, especially scrolls do not tolerate VFDs very well.
Fan overall can save about 50% on condensers but even then safeties should be put in place to prevent motor damage. Non-VFD rated motors can survive if the VFD is programmed correctly.
Careful when trying to measure amps on the output of the VFD. What comes out of a VFD is a DC voltage chopped up 2-15 thousand times per second and may be further modulated. Even its voltage is changing. Most drives can display output amps

[NANOTECH]

But, does anybody know how these are wired in and sequence of operation with diagrams specifically to a rack with multible compressors? Looking for help! Especially from the EDUCATION COMMITITEE! I sent pics and model # If there is no support to be found please state!! I thoughly understand the theory of a vfd, but i'm looking for information on this particular one! And the technical aspects of how it works --- step by step ( SEQUENCE OF OPERATION) If you will. Do not mean to be rude but I know all you old timers can feel me eg: in the trenches not familar with the equipment got to get it going!!!

[Icefixer]

I have a customer that has one 5hp Carlyle compressor run with a yaskawa vfd. It uses a teletrol controller and it requires a windows 98 computer to access. It's obsolete. The guy that designed it told me that the Carlyle compressors don't lose oil pressure at the lower rpm's. It's been in there for 13 years. Same compressor. But when it goes down, both walkins, four make tables and beer coolers all go down. That's the down side.........anyone else see any other compressors out there on vfd's 5hp or lower?

[Phase Loss]

NANO, for the most part the sequence of operation should follow.

The line voltage wiring usually goes like this...from the compressor breaker, to a compressor contactor (probably has some aux contacts used for VFD ready proof) then to the VFD, then out to the compressor.

Some systems do not use an additional compressor contactor, they just use the VFD as the contactor.

Some systems use 2 contactors. 1 for VFD mode and the 2nd for a bypass mode.

Then you have your control wires. You will most likely have 2 wires for an EMS fault detection going from the VFD to a DI point.

2 wires for your 0-10VDC speed reference going from an AO point to the VFD input

then you will have at least 2 wires going to the VFD's digital input that is setup as a run command that puts the VFD in a ready mode when the EMS calls for that compressor (usually this part involves more wires typically jumped at the VFD into other digital inputs that put the VFD in forward mode or reset and other such functions)

This is all assuming that you have an EMS system that does the thinking part...some systems are setup independent of EMS systems and the VFD makes all the decisions...I cant tell your setup with the information given.

but here's how it works.

Suction group calls for compressor to run. It closes an RO point which tells the VFD to go into a ready mode (most VFD's use an internal 24VDC signal to prove digital closure), then it waits for a 0-10VDC speed reference from the EMS system. As the suction pressure reaches setpoint, the VFD will slow the compressor down , as the suction pressure raises above setpoint, the VFD will speed the compressor up

[NANOTECH]

Wow thats what I'm talking about!!! Awsome, thank you Phase!! I'm hands on, I like to pull wires see what is hooked in series, paraellel, and series paraellel. Put power on and watch the stageing I'll play with these today!

Thank you Phase!!!

[icemeister]

The VFD description given by Phase Loss reminded me that the Hussmann Atlanta Rack Manual has a pretty good section on them showing typical power and control wiring:

http://hvac-talk.com/vbb/showthread.php?t=163158

(See p.4-13 through 4-16)

[rcbuddy]

I have a customer that has one 5hp Carlyle compressor run with a yaskawa vfd. It uses a teletrol controller and it requires a windows 98 computer to access. It's obsolete. The guy that designed it told me that the Carlyle compressors don't lose oil pressure at the lower rpm's. It's been in there for 13 years. Same compressor. But when it goes down, both walkins, four make tables and beer coolers all go down. That's the down side.........anyone else see any other compressors out there on vfd's 5hp or lower?

Steve's Pizza??