Carrier AQUASNAP 30RB060-390 Controls, Start-up, Operation, Service And Troubleshooting Instructions

Also see for AQUASNAP 30RBA315: Installation instructions

41Demand Limit — Demand limit is a feature that allowsthe unit capacity to be limited during periods of peak energyusage. There are three types of demand limiting that canbe configured. The first type is through 2-step switchcontrol, which will reduce the maximum capacity to 2 user-configurable percentages. The second type is by 4 to 20 mAsignal input which will reduce the maximum capacity linearlybetween 100% at a 4 mA input signal (no reduction) down tothe user-configurable level at a 20 mA input signal. The thirdtype uses the CCN Loadshed module and has the ability tolimit the current operating capacity to maximum and furtherreduce the capacity if required.NOTE: One-step Demand Limit is standard.The 2-step switch control and 4 to 20-mA input signal typesof demand limiting require the energy management module(EMM).To use demand limit, select the type of demand limiting touse. Then configure the demand limit set points based on thetype selected.2-STEP SWITCH CONTROLLED — If using 2-step de-mand limit control, an energy management module must be in-stalled. One-step demand limit control does not require the en-ergy management module. To configure demand limit for2-step switch control, three parameters must be configured:Demand Limit Select (ConfigurationRSETDMDC),Switch Limit Setpoint 1 (SetpointsMISCDLS1) andSwitch Limit Setpoint 2 (SetpointsMISCDLS2). In thefollowing example, Demand Limit Switch 1 is 60% and de-mand limit Switch 2 is 40%. Demand limit steps are controlledby two relay switch inputs field wired to TB5 for Switch 1 andTB6 for Switch 2. See Table 31.For demand limit by 2-stage switch control, closing the firststage demand limit contact will put the unit on the first demandlimit level. The unit will not exceed the percentage of capacityentered as Demand Limit Switch 1 set point. Closing contactson the second demand limit switch prevents the unit from ex-ceeding the capacity entered as Demand Limit Switch 2 setpoint. The demand limit stage that is set to the lowest demandtakes priority if both demand limit inputs are closed. If the de-mand limit percentage does not match unit staging, the unitwill limit capacity to the closest capacity stage without exceed-ing the value. To disable demand limit configure DMDC to 0.EXTERNALLY POWERED (4 to 20 mA Controlled) — Theenergy management module is required for 4 to 20 mAdemand limit control. To configure demand limit for 4 to20 mA control three parameters must be configured. They are:Demand Limit Select (ConfigurationRSETDMDC), mAfor 100% Demand Limit (ConfigurationRSETDMMX)and mA for 0% Demand Limit (ConfigurationRSETDMZE). In the following example, a 4 mA signal is DemandLimit 100% and a 20 mA Demand Limit signal is 0%. The 4 to20 mA signal is connected to TB6-1 and TB6-2. The demandlimit is a linear interpolation between the two values entered.See Table 32 and Fig. 24.In Fig. 24, if the machine receives a 12 mA signal, themachine controls will limit the capacity to 50%.CCN LOADSHED CONTROLLED — To configure demandlimit for CCN Loadshed control, the unit Operating TypeControl must be in CCN control, (Operating ModesSLCTSP.SE=2) and be controlled by a Chillervisor module.The Chillervisor module can force the demand limit variableand directly control the capacity of the machine. Additionally,the unit’s set point will be artificially lowered to force the chill-er to load to the demand limit value.Remote Alarm and Alert Relays — The 30RB chill-er can be equipped with a remote alert and remote alarmannunciator contacts. Both relays connected to these contactsmust be rated for a maximum power draw of 10 va sealed,25 va inrush at 24 volts. The alarm relay, indicating that thecomplete unit has been shut down can be connected to TB5-12and TB5-13. For an alert relay, indicating that at least 1 circuitwas off due to the alert, a field-supplied and installed relaymust be connected between MBB-J3-CH25-3 and TB5-13.CAUTIONCare should be taken when interfacing with other controlsystems due to possible power supply differences such as afull wave bridge versus a half wave rectification. Connec-tion of control devices with different power supplies mayresult in permanent damage. ComfortLink™ controlsincorporate power supplies with half wave rectification. Asignal isolation device should be utilized if the signalgenerator incorporates a full wave bridge rectifier.001020304050607080900102816141210186420DEMAND LIMIT SIGNAL (mA)DEMAND LIMIT (%)Fig. 24 — Demand Limit