McQuay WSC Operating Manual page 54

SET UNIT SPs (12)
SET UNIT SPs (13)
Units = ° ° ° ° F/psi
Lang
SET UNIT SPs (14)
Protocol =
Ident Number +
Baud Rate =
SET UNIT SPs (15)
Ex Valve Gain = 100
Offset(Slope) = 271
Prs Ctrl Dout = 10° ° ° ° F
Screen 15 controls the electronic expansion valve (EXV) and is set as close as possible to known
job operating conditions. Ex Valve Gain values less than the default of 100 pivot the curve slope
to the right (downward). Values greater than the default of 100 pivot the slope upward, resulting
in a greater valve opening for a given condenser delta-T, with the effect increasing as the delta-T
increases. Very little effect is seen at low delta-Ts (low loads). See Figure 30.
Offset (Slope) values above 271 move the curve upward parallel, increasing the valve opening the
same amount regardless of the condenser delta-T. Values less than 271 have the opposite effect.
Prs Ctrl Dout (pressure control dropout) setting determines the leaving chilled water temperature
at which the EXV transitions from pressure control based on chilled water temperature to program
control based on condenser delta-T (trimmed by lift). This pressure control mode provides a
controlled pulldown of the chilled water temperature on system startup.
Figure 30, EXV Control Parameters (Program Control Mode)
1,000
EEX
OPENING
+ OFFSET
54
CLOCK
dd/mmm/yyyy
hh:mm:ss
= ENGLISH
0
0
CONDENSER
LESS
GAIN
10
T and LIFT FACTOR
OM Centrif Micro ΙΙ-5