How fast a tween screw compressor start up to maxima capacity?

Dear all
We all know that a recip compressor respond faster than a screw compressor to a step change of load.

I have the experience that a tween screw compressor with slide valve control goes from 0 to 100% load in 5 min.
In case the compressor is driven with a VFD How fast it should go to 100% load?
Normally in some industries like soft drink beverage the load could change 200TR or more from one moment to another. The compressor and the refrigeration system should be fast enough
I appreciate your coments
Regards
GWAPA

Screw loading rate is restricted by drive motor capacity to handle high compressor capacity change, rapid load rates can also be governed by condensing capacity.

Some machines can load & unload quicker than others.
If it was a MYcom I would say 0 to 100% 10-15 seconds
& unload 15 to 20 seconds.
They are not really designed for that purpose, so a false load valve generally used to give more reaction time & sudden load changes in your example of soft drink plant.
High pressure cool gas taken off top of liquid receiver or discharge line & injected into main suction line at a pressure slightly lower than normal suction pressure.
Unloading can occur slower.
If slide valve used excessively it will wear out for sure.
VSD good for instant reduction of capacity, 60 to say 25 Hz in a few seconds.

Compressor should take 60 Seconds from 00 to 100 percent .

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Originally Posted by gwapa

Dear all
We all know that a recip compressor respond faster than a screw compressor to a step change of load.

I have the experience that a tween screw compressor with slide valve control goes from 0 to 100% load in 5 min.
In case the compressor is driven with a VFD How fast it should go to 100% load?
Normally in some industries like soft drink beverage the load could change 200TR or more from one moment to another. The compressor and the refrigeration system should be fast enough
I appreciate your coments
Regards
GWAPA

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Of course a reciprocating compressor would react faster to load changes if we are talking about simple load stages.
A reciprocating compressor can go from 33% capacity to 66% capacity at the switch of a solenoid valve...
(I am not familiar with the term of TR so if someone would explain, please...)
This switch will give an instant result in change of capacity, a change in capacity that may be to high, so the reciprocating compressor will reduce back down to 33%, and you end up caught in an endless inefficient loop...

Having a screw or a reciprocating compressor, what you should do is fit a vfd.

A compressor works best when it is at 100% mechanical load... how you get the most out of a compressor is by using a vfd to to get the most out of a compressor while it is at 100% mechanical load but at 50% speed...

Quote:

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Originally Posted by ranger1

the best way to make this work is a vfd

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