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A surge condition occurs when the lift becomes so high the gas flow across the impeller reverses. This condition can eventually cause chiller damage. The surge prevention algorithm notifies the operator that chiller operating conditions are marginal and to take action to help prevent chiller damage such as lowering entering condenser water temperature. The surge prevention algorithm first determines if corrective action is necessary. The algorithm checks 2 sets of opera- tor-configured data points, the minimum load points (MIN. LOAD POINT [T1,P1]) and the full load points (FULL LOAD POINT [T2,P2]). These points have default settings as defined on the OPTIONS screen or on Table 4. The surge prevention algorithm function and settings are graphically displayed in Fig. 21 and 22. The two sets of load points on the graph (default settings are shown) describe a line the algorithm uses to determine the maximum lift of the compressor. When the actual differential pressure between the cooler and condenser and the temperature difference between the entering and leaving chilled water are above the line on the graph (as defined by the minimum and full load points), the algorithm goes into a corrective action mode. If the actual values are below the line and outside of the deadband region, the algorithm takes no action. When the point defined by the ACTIVE DELTA P and ACTIVE DELTA T, moves from the region where the HOT GAS BYPASS/SURGE PREVENTION is off, the point must pass through the deadband region to the line determined by the configured values before the HOT GAS BYPASS/SURGE PREVENTION will be turned on. As the point moves from the region where the HOT GAS BYPASS/ SURGE PREVENTION is on, the point must pass through the deadband region before the HOT GAS BYPASS/SURGE PREVENTION is turned off. Information on modifying the default set points of the minimum and full load points may be found in the Input Service Configurations section, page 55. The state of the surge/hot gas bypass algorithm on the HEAT_EX DISPLAY SCREEN (Surge/HGBP Active?). Corrective action can be taken by making one of 2 choices. If a hot gas bypass line is present and the hot gas option is selected on the OPTIONS table (SURGE LIMIT/HGBP OPTION is set to 1), the hot gas bypass valve can be energized. If the hot gas bypass option is not selected (SURGE LIMIT/ HGBP OPTION is set to 0), hold the guide vanes. See Table 4, LEGEND ECW — Entering Chilled Water HGBP — Hot Gas Bypass LCW — Leaving Chilled Water .P = (Condenser Psi) – (Cooler Psi) .T = (ECW) – (LCW) Fig. 21 — 19XR Hot Gas Bypass/Surge Prevention with Default English Settings LEGEND ECW — Entering Chilled Water HGBP — Hot Gas Bypass LCW — Leaving Chilled Water .P = (Condenser kPa) – (Cooler kPa) .T = (ECW) – (LCW) Fig. 22 — 19XR Hot Gas Bypass/Surge Prevention with Default Metric Settings 39 Capacity Overrides. Both of these corrective actions try to reduce the lift experienced by the compressor and help prevent a surge condition. Surge Prevention Algorithm with VFD — This is an operator configurable feature that can determine if lift conditions are too high for the compressor and then take corrective action. Lift is defined as the difference between the pressure at the impeller eye and at the impeller discharge. The maximum lift a particular impeller wheel can perform varies with the gas flow through the impeller and the diameter of the impeller. A surge condition occurs when the lift becomes so high the gas flow across the impeller reverses. This condition can eventually cause chiller damage. When enabled, the Surge Prevention Algorithm will adjust either the inlet guide vane (IGV) position or compressor speed to maintain the compressor at a safe distance from surge while maintaining machine efficiency. If the surge condition degrades then the algorithm will move aggressively away from surge. This condition can be identified when the SURGE/HGBP ACTIVE? on the HEAT_EX display screen displays a YES. The surge prevention algorithm first determines if corrective action is necessary. The algorithm checks two sets of operator-configured data points, the lower surge point (MIN. LOAD POINT [T1,P1]) and the upper surge point (FULL LOAD POINT [T2,P2]). The surge characteristics vary between different chiller configurations and operating conditions. The surge characteristics are factory set based on the original selection with the values displayed inside the control panel of the chiller. Since operating conditions may affect the surge prevention algorithm, some field adjustments may be necessary. The surge prevention algorithm function and settings are graphically displayed on Fig. 21 and 22. The two sets of load points on the graph (default settings are shown) describe a line the algorithm uses to determine the maximum lift of the compressor for the particular maximum operating speed. When the actual differential pressure between the cooler and condenser and the temperature difference between the ente...

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