MANUAL VFDs

[nanuuk]

WE ARE ABOUT TO PUT IN LEESON VFDs IN TO OUR PLANT AND THESE VFDs WILL HAVE TO BE MANAULLY SET. THE PLAN IS TO RUN THESE VFDs AT IETHER 50 OR 100%. THE EQUIPMENT IN THE PLANT IS 40 YEARS OLD WHICH CONSISTS OF 6 AND 8 B MYCOMS AND ROTARY BOOSTERS.WE ONLY RUN 1 SHIFT FOR ENGINEERS HERE DAYS BUT HAVE A SECOND SHIFT IN THE AFTERNOON FOR THE WAREHOUSE MEN. SO MY QUESTION IS WHAT PROBLEMS MAY OCCUR WHEN WE INSTALL THESE VFDs WE RUN THE REFRIGERATION ON A OLDER DELTA COMPUTER CONTROL BUT IT WILL NOT RUN WITH THESE VFDs. THEY WILL BE STAND ALONE.

[RANGER1]

nanuuk,
6&8B Mycoms minimum speed is 800 rpm at compressor flywheel.
You can run them down to 700 rpm, but need low speed oil pump (now below 700 rpm not recommended by Mycom).
Can't see the benefit as why can't you just unload cylinders, as its still efficient?

The rotaries you would have to check, but certainly possible.
Have seen 2 speed motor on rotary with no problems, so as long as its in manufacturers limits.
You will have to work out min Hz for compressor min speed.
Also check that lubricator can work with enough oil being supplied if belt driven off compressor shaft.

[nanuuk]

Thanx for the reply good advise another question what if we where to put them on our evaporators the high temp and low temp. We have 1 freezer with a floor mounted coil with 4/ 7.5 h.p. fans at 47 TR the duct work coming out of the top of the coil that goes up 20 ft and along the ceiling for 140ft and the motors have to push the air also through the coil. So will there be enough push if you will to maintain a contsant room temp through out the room which is 413,000 cubic ft. Another question is at 50% how will that effect the high temp coils they are DX coils at 5.4 TR and there are 6 of them room sixe is 357,000 cubic ft seeing how you are now changing the rate of evaporation will the coils freeze up at this speed?

[Segei]

Do you want to put VFDs for evaporator fans or for compressors as well?
DX coils and 50% speed. It can work if you reduce condensing pressure and capacity of TEVs will be reduced and it can match to fans speed of 50%. Coils won't freeze up, because temperature of the coil controlled by compressors(suction pressure setting) or by back pressure regulator.
Your floor unit isn't suitable for VFDs, because it requires good throw.
What is the reason to install VFDs for old plant?

[nanuuk]

LOOKING TO CUT DOWN ON THE TR FROM THE COILS IF WE SPIN THE FANS AT 50% WHICH IN TURN CUT DOWN THE H.P. IN THE ENGINE ROOM. ON THE DX COILS WE RUN OUR HEAD AT 120 PSI I AM TOLD IF WE GO ANY LOWER THAN THAT THE TEVs MAY NOT WORK PROPERLY IS THAT TRUE? AS FOR CHANGING THE CAPACITY OF THE TEVs DO WE CHANGE THAT AT THE V/V OR DO WE HAVE TO DO SOMETHING ELSE AND IF WE NEED MORE CAPACITY SAY TO SATISFY ROOM TEMP THEN WHAT DO WE NEED TO DO CHANGE THE FAN SPEED, HEAD PRESSURE AND CAPACITY AT THE V/V AGAIN? THANK YOU FOR YOUR REPLY.

[Segei]

What do you mean by v/v?

[nanuuk]

Sorry Segei v/v means valve.

[Segei]

I don't see any connection between H.P. cut out and 50% fan speed. 50% fan speed you can use during periods of cool weather when refrigeration load much less than 100% that you have at summer time.
At condensing pressure below 120 psig capacity of TEV will be reduced. During periods of cool weather it can be coincident with lower refrigeration load and this TEV can work fine.
When you run VFD at 50% and low refrigeration load capacity of TEV should be 40% or lower. At this capacity operation of TEV will be unstable or it can slightly overfeed.