Hot Gas Bypass; Install And Enable - Trane CVHE Troubleshooting Manual

During HGBP, the normal differential to stop is obeyed. If the differential to stop or the
"Maximum HGBP Time" timer requires the Centravac to shutdown, the HGBP valve will be
held while the inlet guide vanes are driven closed. When the inlet guide vanes are fully
closed, the Centravac will shutdown.
Hot Gas Bypass Valve Operation:
The HGBP valve is constantly driven closed when neither in the HGBP mode nor under
manual HGBP valve control. During this time, the I/O module will be checking for a valve
closed indication from the HGBP valve switch input and will issue a valve diagnostic if the
valve is not found to be closed. Upon seeing a transition from either HGBP mode or manual
HGBP valve control, the I/O module will allow 3 minutes to expire before calling out a Hot
Gas Bypass Valve closure overdue diagnostic.
Manual Hot Gas Bypass Valve Control:
The HGBP valve is capable of manual control while the unit is running and during the stop
mode. The manual HGBP control is based on a load, hold, or unload signal from a user
specified duration setpoint every 5 seconds.
Design:
The HGBP feature is designed as specified above. The following is added for further clarity.
Hot gas bypass (HGBP) is a control option designed to avoid chiller cycling during low load
conditions while still maintaining the chilled water temperature set point. This is accomplished
by artificially increasing the load on the compressor. The compressor load is artificially
increased using the hot gas bypass valve to divert refrigerant gas from the condenser back
into the suction side of the compressor. The hot gas bypass valve is modulated by
appropriately scaling the output of the ELWT control algorithm.
HGBP Control Actuator Characteristics: Single phase induction motor moving a butterfly valve
HGBP Control Algorithm Inputs: ELWT control error, IGV target position
HGBP Control Algorithm Output: number of tics to open/close the hot gas bypass valve
HGBP Control Algorithm Sample Rate: Sample Rate: = 5 sec

Install and Enable

To get the HGBP control option to function it must first be installed. To install the HGBP control
option enter the Machine Configuration Group. In this group make sure to
1 Install Hot Gas Bypass Control.
Installing HGBP control sets up the display features associated with HGBP. However, for the con-
trol algorithm to be operational it must be enabled. To enable the HGBP control algorithm enter the
Field Start-up Group.
2 Enable Hot Gas Bypass Control.
In addition, this group also has three user adjustable setpoints associated with the HGBP control
option. The three setpoints are:
CVHE-SB-32A 100