Carrier AquaSnap 30MPA Series Controls, Start-up, Operation, Service, And Troubleshooting

Also see for AQUASNAP 30MPA: User manual Operation and service manual Installation instructions

Carrier AquaSnap 30MPA Series Controls, Start-up, Operation, Service, And Troubleshooting Manual pdf 34 page image

34Demand Limit — Demand limit is a feature that allowsthe unit capacity to be limited during periods of peak energy us-age. Three types of demand limiting can be configured. Thefirst type is through 2-stage switch control, which will reducethe maximum capacity to 2 user-configurable percentages. Thesecond type is by 4 to 20 mA signal input which will reduce themaximum capacity linearly between 100% at a 4 mA input sig-nal (no reduction) down to the user-configurable level at a20 mA input signal. The third type uses the CCN Loadshedmodule and has the ability to limit the current operating capaci-ty to maximum and further reduce the capacity if required.NOTE: The 2-stage switch control and 4 to 20-mA input sig-nal types of demand limiting require the energy managementmodule (EMM).For units with the digital compressor option, digital opera-tion is ignored when determining capacity limit of the machine.Since Demand Limit controls the number of compressors oper-ating, the requested demand limit must allow for the corre-sponding capacity of the full digital compressor capacity plusany remaining compressors. For example, a 30MP045 unitwith a digital compressor will require a demand limit of at least33% for the first compressor to be energized. No compressoroperation will be allowed prior to this demand limit level. Dig-ital operation below 33% will require a demand limit of at least33% to allow a compressor to start. Digital operation between33 and 67% will require a demand limit of at least 67% to al-low 2 compressors to be operating. Finally, for digital operationabove 67%, demand limit must be at 100% to allow for allcompressors to be operating.To use demand limit, select the type of demand limiting touse. Then configure the demand limit set points based on thetype selected.DEMAND LIMIT (2-Stage Switch Controlled) — To con-figure demand limit for 2-stage switch control, set the DemandLimit Select (ConfigurationRSETDMDC) to 1. Thenconfigure the 2 Demand Limit Switch points (Configura-tionRSETDLS1) and (ConfigurationRSETDLS2)to the desired capacity limit. See Table 31. Capacity steps arecontrolled by 2 relay switch inputs field wired to LVT as shownin Fig. 4.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 (DLS1). Closingcontacts on the second demand limit switch prevents the unitfrom exceeding the capacity entered as Demand Limit Switch2 set point. The demand limit stage that is set to the lowest de-mand takes priority if both demand limit inputs are closed. Ifthe demand limit percentage does not match unit staging, theunit will limit capacity to the closest capacity stage.To disable demand limit, configure DMDC to 0. SeeTable 31.EXTERNALLY POWERED DEMAND LIMIT (4 to20 mA Controlled) — To configure demand limit for 4 to 20mA control, set the Demand Limit Select (Configura-tionRSETDMDC) to 2. Then configure the DemandLimit at 20 mA (ConfigurationRSETDM20) to themaximum loadshed value desired. Connect the output from anexternally powered 4 to 20 mA signal to terminal block LVT,terminals 7 and 8 (+,–). Refer to the unit wiring diagram forthese connections to the optional/accessory energy manage-ment module and terminal block. The control will reduce al-lowable capacity to this level for the 20 mA signal. SeeTable 31 and Fig. 23.DEMAND LIMIT (CCN Loadshed Controlled) — To con-figure Demand Limit for CCN Loadshed control set the De-mand Limit Select (ConfigurationRSETDMDC) to 3.Then configure the Loadshed Group Number (Configura-tionRSETSHNM), Loadshed Demand Delta (Configu-rationRSETSHDL), and Maximum Loadshed Time(ConfigurationRSETSHTM). See Table 31.The Loadshed Group number is established by the CCNsystem designer. The ComfortLink controls will respond to aRedline command from the Loadshed control. When theRedline command is received, the current stage of capacity isset to the maximum stages available. Should the loadshed con-trol send a Loadshed command, the ComfortLink controls willreduce the current stages by the value entered for LoadshedDemand delta. The Maximum Loadshed Time is the maximumlength of time that a loadshed condition is allowed to exist. Thecontrol will disable the Redline/Loadshed command if noCancel command has been received within the configuredmaximum loadshed time limit.Cooling Set Point (4 to 20 mA) — A field suppliedand generated, externally powered 4 to 20 mA signal can beused to provide the leaving fluid temperature set point. Connectthe signal to LVT-10,8 (+,–). See Table 31 for instructions toenable the function. Figure 24 shows how the 4 to 20 mA sig-nal is linearly calculated on an overall 10 F to 80 F range forfluid types (ConfigurationOPT1FLUD) 1 or 2. The setpoint will be limited by the fluid (FLUD) type. Be sure that thechilled water loop is protected at the lowest temperature.CAUTIONCare should be taken when interfacing with other manufac-turer’s control systems due to possible power supplydifferences, full wave bridge versus half wave rectification.The two different power supplies cannot be mixed.ComfortLink controls use half wave rectification. A signalisolation device should be utilized if a full wave bridgesignal generating device is used.50% CAPACITY AT 20 mA75% CAPACITY AT 12 mA100% CAPACITY AT 4 mA0 2 4 6 8 10 12 14 16 18 20DEMAND LIMIT SIGNAL – 4 - 20 mA INPUT100806040200MAX. ALLOWABLE LOAD (%)Fig. 23 — 4 to 20-mA Demand Limiting