Operation
24
Figure 20 Second cooling source and two-step compressorized cooling
Minimum Chilled Water Temperature
—This feature permits the user to select the minimum
chilled water temperature that allows simultaneous operation of the second cooling source (chilled
water control) and compressor control. This feature is enabled in the Service menu under Setpoints,
parameter Minimum CW Temp.
If the water temperature is below this minimum chilled water setpoint, parameter Minimum CW
Temp Value, (Service Menu, Setpoints), the control will operate ONLY the second cooling source con-
trol, i.e., the compressor is locked out. Above the minimum chilled water setpoint, assuming the fluid
temperature is below the return room air temperature (delta T between room and glycol = true), the
control will operate the second cooling source control and compressor control simultaneously if
needed.
If the Minimum CW Temp is disabled, the second cooling source temperature is ignored, the control
will always operate the second cooling source and compressors simultaneously when the load requires
it.
GLYCOOL
™
Cooling—Free-Cooling
When GLYCOOL cooling is available, the temperature control will calculate a total cooling require-
ment of 200% rather than 100%. Assuming that full GLYCOOL capacity is available, the GLYCOOL
valve opens proportionally as the requirement for cooling rises from 0 to 100%. If more than 100%
cooling is required, then the compressors are activated at 150% and 200% respectively (133%, 163%,
180% and 200% for a four-step system). If full GLYCOOL capacity is not available, then the GLY-
COOL valve will be opened proportionally over a cooling requirement band equal to the available
GLYCOOL capacity. The compressors would be activated when the GLYCOOL capacity is exceeded.
For example, if the GLYCOOL capacity is 60%, then the GLYCOOL valve would be full open at 60%
cooling requirement and the compressors would activate at 110% and 160% cooling requirement. In
order to reduce compressor cycling and prevent hunting, GLYCOOL capacity first becomes available
when the entering glycol temperature is at least 8°F (4.4°C) (22% capacity) below the return air tem-
perature, or 3°F (1.7°C) below the return air temperature for two hours. GLYCOOL capacity is 100%
when the glycol temperature is 25°F (13.9°C) below the return air temperature. The system will con-
tinue to operate in Econ-O-Cool mode as necessary as long as the entering glycol temperature
remains at least 3°F (1.7°C) (0% capacity) below the return air temperature. If GLYCOOL is not
available, the temperature control will operate the compressors in the same manner as a two-step or
four-step system without GLYCOOL.
Dual Cooling Source
If dual cooling is available, the system operates in the same manner as a GLYCOOL system, except
that it is assumed that 100% chilled water capacity is available any time the chilled water tempera-
ture is 3°F (1.7°C) below the return air temperature.
75
71
72
73
74
70
Increasing Temperature
Cool 2
On
Cool 1
On
+ 100 %
Cooling
Valve 100%
Open
Valve
Closed
½ Dead-
band
76
77
78
79
+ 200%
Cooling
0%
Cooling
2nd
Source
Comp
½ Proportional Band
½ Proportional Band
Band1: 2
nd
Source
Band 2: Compressors
Temp Setpoint: 70°F
Proportional Band: 8°F
Deadband: 2°F
Summary of Contents for Liebert Challenger 3000
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