Points, (T1/P1;T2/P 2) . These points have defaul t settings as defined on t he Service1 table, or
on Table 4. These settings and the algorithm funct ion are graphically dis played in Figure 21 and
Figure 22. The 2 sets of load point s on th is graph (default settin gs are shown) describe a line
which the algorithm use s to determine the maxim um lift of the compressor. Whenever the actual
differential press ur e be tween the cooler and con denser, and the temper at ure difference
between the entering and le aving chilled water ar e ab ove the line on the graph (a s def ined by
the MINIMUM and MAXIMUM Load Points) the algorithm will go into a corrective actio n mode. I f
the actual values are bel ow the line, the algorithm t akes no action. Modifi c at ion of the default
set points of the MINIMUM and MAXIMUM load points is described in the Input Service
Configurations section.
Corrective action can be t aken by making one of 2 choi c es . If a hot gas bypass line is
present, and the h ot gas is configu red on the Servic e1 table, then the ho t gas bypass valv e can
be energized. If a hot ga s bypass if not present, then the action taken is to hol d the guide vanes.
See Table 4, Capacit y Overrides. Both of the s e c or r ec t ive actions will reduc e t he lift
experienced by the comp ressor and help to preven t a surge condition. Surg e is a condition
when the lift beco mes so high that the gas flow across t he impeller reverse s. This condition c an
eventually cause mach ine damage. The surge pre vention algorithm is in tended to notify the
operator that machin e ope rating conditions are marginal, and to take act io n, such as lowering
entering conden ser water tempe rature, to help prevent machine damage.