CVHE-SB-32A 101
1) HGBP mode, IGV Target:%
In the HGBP mode, the HGBP valve modulates capacity while the inlet guide vanes move to a
target position set by the user. The inlet guide vanes move to the target position by a maximum
of 40 steps every sample period.
2) Guide Vane Closed Travel Stop:%
In order for the hot gas bypass staging integral to begin integrating, the inlet guide vane step
position must be below a minimum step position known as the guide vane closed travel stop. In
addition, the ELWT must be 0.5°F below the chilled water setpoint.
3) Maximum HGBP Time:
When the maximum HGBP time is enabled the maximum HGBP timer is used to determine how
long the chiller is allowed to operate in the hot gas bypass mode.
Hot Gas Bypass Control Algorithm
The HGBP staging integral begins to execute once the ELWT falls below the CWS by 0.5°F, and
the inlet guide vanes are below a user specified minimum position (usually zero). Once the
HGBP staging integral has reached a preset number, capacity control transitions to the HGBP
valve. The HGBP value is modulated by converting ELWT step commands into time based (tic)
commands. Once transition occurs, the inlet guide vanes are loaded by 40 steps every sample
period until they reach a user specified target value. To exit the HGBP modulating mode, the
evaporator leaving water temperature must begin to rise above the CWS. If the ELWT exceeds
the CWS by 0.5°F, the staging integral begins to integrate. Once the staging integral reaches a
preset number, capacity control transitions back to the inlet guide vanes.
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