Carrier 17 Start Up & Operation Manual

Contents

Demand Limit Control Option (RequiresOptional 8-Input Module) — The demand limit maybe externally controlled with a 4 to 20 mA signal from anenergy management system (EMS). The option is set up onthe Config table. When enabled, the control is set for 100%demand with 4 mA and an operator configured minimum de-mand set point at 20 mA.The Demand Reset input from an energy management sys-tem is hardwired into the number one, 8-input module. Thesignal may be internally powered by the module or exter-nally powered. If the signal is externally powered, the signalis wired to terminals J1-1(+) and J1-2(–). If the signal is in-ternally powered, the signal is wired to terminals J1-3(+) andJ1-2(–). When enabled, the control is set for 100% demandwith 4 mA and an operator configured minimum demand setpoint at 20 mA.Surge Prevention Algorithm — This is an operatorconfigurable feature which can determine if lift conditionsare too high for the compressor and then take corrective ac-tion. Lift is defined as the difference between the pressure atthe impeller eye and the impeller discharge. The maximumlift that a particular impeller wheel can perform varies withthe gas flow across the impeller, and the size of the wheel.The algorithm first determines if corrective action is nec-essary. This is done by checking 2 sets of operator config-ured data points, which are the MINIMUM and the MAXI-MUM Load Points, (T1/P1;T2/P2). These points have defaultsettings as defined on the Service1 table, or on Table 4. Thesesettings and the algorithm function are graphically dis-played in Fig. 21 and 22. The 2 sets of load points on thisgraph (default settings are shown) describe a line which thealgorithm uses to determine the maximum lift of the com-pressor. Whenever the actual differential pressure betweenthe cooler and condenser, and the temperature difference be-tween the entering and leaving chilled water are above theline on the graph (as defined by the MINIMUM and MAXI-MUM Load Points) the algorithm will go into a correctiveaction mode. If the actual values are below the line, the al-gorithm takes no action. Modification of the default set pointsof the MINIMUM and MAXIMUM load points is describedin the Input Service configurations section on page 55.Corrective action can be taken by making one of 2 choices.If a hot gas bypass line is present, and the hot gas is con-figured on the Service1 table, then the hot gas bypass valvecan be energized. If a hot gas bypass if not present, then theaction taken is to hold the guide vanes. See Table 4, Capac-ity Overrides. Both of these corrective actions will reducethe lift experienced by the compressor and help to prevent asurge condition. Surge is a condition when the lift becomesso high that the gas flow across the impeller reverses. Thiscondition can eventually cause machine damage. The surgeprevention algorithm is intended to notify the operator thatmachine operating conditions are marginal, and to take ac-tion, such as lowering entering condenser water tempera-ture, to help prevent machine damage.Surge Protection — Surging of the compressor can bedetermined by the PIC through operator configured settings.Surge will cause amperage fluctuations of the compressormotor. The PIC monitors these amperage swings, and if theswing is greater than the configurable setting in one second,then one surge count has occurred. The SURGE DELTA PER-CENT AMPS setting is displayed and configured on the Serv-ice1 screen. It has a default setting of 25% amps, SURGEPROTECTION COUNTS can be monitored on the Maint03table.A surge protection shutdown of the machine will occurwhenever the surge protection counter reaches 12 counts withinan operator specified time, known as the SURGE TIMEPERIOD. The SURGE TIME PERIOD is displayed andconfigured on the Service1 screen. It has a default of2 minutes.Lead/Lag Control — Lead/lag is a control system pro-cess that automatically starts and stops a lag or second chillerin a 2-chiller water system. Refer to Fig. 16 and 17 for menu,table, and screen selection information. On machines thathave PSIO software with Lead/Lag capability, it is possibleto utilize the PIC controls to perform the lead/lag functionon 2 machines. A third machine can be added to the lead/lagsystem as a standby chiller to start up in case the lead or lagchiller in the system has shut down during an alarm condi-tion and additional cooling is required.LEGENDDP = (Condenser psi) − (Cooler psi)DT = (ECW) − (LCW)ECW — Entering Chilled WaterHGBP — Hot Gas BypassLCW — Leaving Chilled WaterFig. 21 — 17/19EX Hot Gas Bypass/SurgePrevention (English)LEGENDDP = (Condenser kPa) − (Cooler kPa)DT = (ECW) − (LCW)ECW — Entering Chilled WaterHGBP — Hot Gas BypassLCW — Leaving Chilled WaterFig. 22 — 17/19EX Hot Gas Bypass/SurgePrevention (SI)401197→