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Controls Training and Service Manual
Glycool at 50% 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
Glycool
Valve
Band 2 Compressors
Valve
Closed
100%
Open
Cool 1 On
Cool 2 On
Temp Set Point + (1/2 Proportional Band + 1/2 Proportional Band)
Dual Source Cooling
When supplied with the Dual Cooling option, the basic unit is supplied with an
additional coil, piping, valve and a Glycol Fluid Sensor (AQ), which is mounted to
the unit supply fluid line and serves as control interface in determining the system
operation. Selection of the chilled water or compressorized operation is controlled
by microprocessor using this aquastat to sense the water temperature.
The Dual Source Cooling program establishes two distinct control bands for
cooling control operation in the same method as Glycool. The first band controls
the operation of the chilled water valve and the second controls the operation of
the compressors, either 2-stage or 4-stage.
The microprocessor checks the return air temperature and the entering chilled
water fluid temperature to determine a cooling capacity. The chilled water cooling
capacity is considered to be 100% if the entering Chilled Water fluid temperature is
8°F lower than the return air temperature.
When the microprocessor decides that the return chilled water temperature is cold
enough the first cooling band is the modulating valve control method, and the
second band, added to the first band, is for the compressors as in the normal
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