Liebert CHALLENGER 3000 - Manual (Page 38)

System Performance with Advanced Microprocessor Controls
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4.1.3 Cooling Operation
1-Step Cooling, Compressorized Direct Expansion (DX) Systems
Cooling activates when the temperature control calculates a requirement for cooling of 100%. It is
deactivated when the cooling requirement drops below 50%. The hot gas bypass is energized on a call
for cooling unless there is also a call for dehumidification.
To aid in lubricating the compressor, the hot gas bypass solenoid is delayed for 30 seconds on the ini-
tial call for cooling and de-energized for 30 seconds during every 60 minutes of continuous operation.
2-Step Cooling, Compressorized Direct Expansion (DX) Systems with Part Coil (optional)
Cooling activates when the temperature control calculates a requirement for cooling of 50%. If the
system is designed for part coil operation, part coil is active and the hot gas bypass would be acti-
vated. At 100% cooling requirement, operation would be full coil and the hot gas bypass would be acti-
vated. When the cooling requirement drops to 75%, the system returns to part coil, and turns off the
compressor when the requirement drops to 25%.
GLYCOOL 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 compressor is activated at 200%. If full GLYCOOL capacity is not avail-
able, then the GLYCOOL valve will be opened proportionally over a cooling requirement band equal
to the available GLYCOOL capacity. The compressor would be activated at a cooling requirement of
100% above the available GLYCOOL capacity.
For example, if the GLYCOOL capacity is 60%, then the GLYCOOL valve would be full open at 60%
cooling requirement and the compressor would be in full cooling at 160%. In order to reduce compres-
sor cycling and prevent hunting, GLYCOOL capacity first becomes available when the entering glycol
temperature is at least 8°F (22% capacity) below the return air temperature, or 3°F below the return
air temperature for 2 hours. GLYCOOL capacity approaches 100% when the glycol temperature is 25
degrees F below the return air temperature. The system will continue to Econ-O-Cool as necessary as
long as the entering glycol temperature remains at least 3°F (0% capacity) below the return air tem-
perature. If GLYCOOL is not available, the temperature control will operate the compressor in the
same manner as a 1-step or 2-step system without GLYCOOL. The control will not permit compressor
operation if the chilled water temperature is below the minimum chilled water temperature selected
through the SETUP OPERATION menu.
Dual Cooling Source
If dual cooling is available, the sensible cooling 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 temperature is 3°F cooler than the return air temperature.
Chilled Water Cooling
The chilled water control valve is adjusted proportionally as the temperature control varies the
requirement for cooling from 0% to 100%.
Table 13 Cooling/dehumidification load status response
LLSV1
LLSV2
Part Coil HGBP
1 Step Cooling Only On Off On
2 Step Cooling Only On On On
Dehumidifying Only On Off Off
1 Step Cooling w/Dehumidifying On Off Off
2 Step Cooling w/Dehumidifying On On Off