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Control Training and Service Manual
2-Stage or 4-Stage control method. If the chilled water temperature is not cold
enough the valve control band is replaced by the compressor band.
Dual Cooling at 100% Capacity – No Dead Band
Temp Set Point: 70°
Proportional Band: 8°
70 71 72 73 74 75 76 77 78 79
Increasin
g
Temperature
Band 1 Chilled Water
Valvel
Band 2 Compressors
Valve
Closed
100%
Open
Cool 1 On
Cool 2 On
Temp Set Point + (1/2 Proportional Band + 1/2 Proportional Band)
An addition program available with the Dual Cooling option is called Minimum
Chilled Water Temperature. This program allows the end user to select the
minimum chilled water temperature that permits simultaneous operation of the
chilled water control and compressor control. When the supply chilled water
temperature decreases to this programmed value ONLY the chilled water valve
control is operational, the compressors are locked out.
Staged Electric Reheat
The basic temperature heating control band is established at the temperature set
point with the length equal to ½ of the programmed temperature proportional band
divided by the number of reheat stages.
The Liebert DS units are supplied with three (3) reheat stages (elements), each
stage is rated at 1/3 of the unit capacity. The three (3) stages will operate in an
on/ off configuration to reheat the unit discharge air as it enters the space.
The temperature controller activates the first electric heating stage when the return
air temperature decreases to 33% of the heating proportional band. The second
electric heating stage activates when the return air temperature decreases to 66%
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