OMM TGZ-1 TGZ 040A through TGZ 190A 21
Figure 1, Staging/Starting Temperatures
If the Condenser Leaving Water Temperature stays below 138.5°F, all three (or five)
remaining compressors will eventually stage on after the Stage Up Timer times out between
each stage. At some point, the Condenser Leaving Water Temperature will be rising and begin
to approach the point when compressors should begin staging off, which is the Active Heat
Leaving Water Temperature set point plus ½ of the Control Band, 141.5°F in this case.
If the Condenser Leaving Water Temperature remains above the Active Heat Leaving Water
Temperature set point plus ½ Control Band and the Stage Down Timer times out, additional
compressors will stage off. The last compressor will stage off when the Condenser Leaving
Water Temperature raises above the Active Leaving Water Temperature set point plus ½ the
Control Band plus the Stop Delta T. The Stop Delta T is in effect for only the last compressor
running.
If the condenser leaving water temperature falls below 141.5°F, all running compressors will
remain on. No compressor staging occurs within the Control Band. The next-on compressor
will start when the condenser leaving water temperature drops below 138.5°F and the Stage
Up Timer times out. In the example shown in Figure 7, the Shutdown Temp (last compressor
off) would be 143.5°F.
Manual Compressor Disable Logic
Logic is available that allows the operator to manually enable and disable compressors. When a
compressor is disabled, it is considered unavailable to start in the staging logic. This allows a
damaged compressor to be taken offline while the remaining compressor can still provide some
cooling
• The Compressor Disable set points are found on Compressor Set Points screens three and
four.
• A running compressor cannot be disabled until it has been shutdown.
• If all of the compressors on a circuit are disabled, then the circuit will be disabled.
• If both circuits have all of their compressors disabled, the Unit State will remain Off
Leaving Water Temperature
Set Point
Entering Water Temperature
Condenser Delta Temperature
Set Point
140º F
130º F
10º F
½ Control Band
½ Control Band
141.5º F
138.5º F
Stop Delta T
143.5º F
Start Delta T
133.5º F
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