York YMC2 A, Эксплуатация и обслуживание

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JOHNSON CONTROLS
10
Form 160.78-O1
Issue date: 05/19/2021
Section 1 - System fundamentals
Regardless of chiller compressor model, the chiller
also has a mechanism called variable geometry dif-
fuser (VGD) at the exit of the impeller that was de-
signed to mitigate stall. Stall is an effect caused by
slow refrigerant gas passing through the compressor at
reduced flow rates needed for low capacity operation.
Compressor models with gas path revision level B do
not have operating prerotation vanes, but use the VGD
also as a capacity control device instead.
A final optional means to reduce capacity called hot
gas bypass (HGBP) is available regardless of compres-
sor model. When selected for an application, HGBP is
used to re-circulate some refrigerant through the com-
pressor without using it for cooling the chilled liquid.
Although this does not reduce power consumption, it
greatly reduces the capacity of the chiller for maxi-
mum turndown.
The YMC
2
uses these mechanisms in a controlled or-
der to maintain best efficiency.