Carrier AQUASNAP AIR COOLED CHILLERS WITH COMFORTLINK CONTROLS 30RAP010-060 Operation And Service Manual

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Carrier AQUASNAP AIR COOLED CHILLERS WITH COMFORTLINK CONTROLS 30RAP010-060 Operation And Service Manual Manual pdf 29 page image

29Energy Management Module (Fig. 12) — Thisfactory-installed option (FIOP) or field-installed accessory isused for the following types of temperature reset, demandlimit, and/or ice features:• 4 to 20 mA leaving fluid temperature reset (requiresfield-supplied 4 to 20 mA generator)• 4 to 20 mA cooling set point reset (requires field-supplied 4 to 20 mA generator)• Discrete inputs for 2-step demand limit (requires field-supplied dry contacts capable of handling a 24 vac,50 mA load)• 4 to 20 mA demand limit (requires field-supplied 4 to20 mA generator)• Discrete input for Ice Done switch (requires field-supplied dry contacts capable of handling a 24 vac,50 mA load)See Demand Limit and Temperature Reset sections onpages 41 and 37 for further details.Loss-of-Cooler Flow Protection — A proof-of-cooler flow device is factory installed in all chillers. It is recom-mended that proper operation of the switch be verified on a reg-ular basis.Electronic Expansion Valves (EXV) — All units areequipped from the factory with EXVs. Each refrigeration cir-cuit is also supplied with a factory-installed liquid line filterdrier and sight glass.The EXV is set at the factory to maintain 9° F (5.0° C) suc-tion superheat leaving the cooler by metering the properamount of refrigerant into the cooler. The superheat set point isadjustable, but should not be adjusted unless absolutelynecessary.The EXV is designed to limit the cooler saturated suctiontemperature to 50 F (12.8 C). This makes it possible for unit tostart at high cooler fluid temperatures without overloading thecompressor.Capacity Control — The control system cycles com-pressors, digital scroll modulting solenoid (if equipped), andminimum load valve solenoids (if equipped) to maintain theuser-configured leaving chilled fluid temperature set point. En-tering fluid temperature is used by the main base board (MBB)to determine the temperature drop across the cooler and is usedin determining the optimum time to add or subtract capacitystages. The chilled fluid temperature set point can be automati-cally reset by the return fluid temperature, space, or outdoor-airtemperature reset features. It can also be reset from an external4 to 20-mA signal (requires energy management module FIOPor accessory).The standard control has an automatic lead-lag feature builtin which determines the wear factor (combination of starts andrun hours) for each compressor. If all compressors are off andless than 30 minutes has elapsed since the last compressor wasturned off, the wear factor is used to determine whichcompressor to start next. If no compressors have been runningfor more than 30 minutes and the leaving fluid temperature isgreater than the saturated condensing temperature, the wearfactor is still used to determine which compressor to start next.If the leaving fluid temperature is less than the saturated con-densing temperature, then the control will start either compres-sor A1 or compressor B1 first, depending on the user-configu-rable circuit lead-lag value. For units with the minimum loadcontrol valve, the A circuit with the minimum load valve is al-ways the lead circuit. The A circuit is also always the lead forunits with the digital compressor option. On units with the dig-ital scroll option, the A1 compressor operates continuously,providing close leaving chilled water control. For this reason,on/off cycling of the unit’s compressors is dramatically re-duced, which in turn reduces wear associated with compressorstart/stop cycles.The EXVs will provide a controlled start-up. During start-up, the low pressure logic will be bypassed for 21/2 minutes toallow for the transient changes during start-up. As additionalstages of compression are required, the processor control willadd them. See Table 19.If a circuit is to be stopped, the compressor with the lowestwear factor will be shut off first except when a digital compres-sor is used. The digital compressor is always the last compres-sor to shut off.The capacity control algorithm runs every 30 seconds. Thealgorithm attempts to maintain the Control Point at the desiredset point. Each time it runs, the control reads the entering andleaving fluid temperatures. The control determines the rate atwhich conditions are changing and calculates 2 variables basedon these conditions. Next, a capacity ratio is calculated usingthe 2 variables to determine whether or not to make anychanges to the current stages of capacity. This ratio valueranges from –100 to +100%. If the next stage of capacity is acompressor, the control starts (stops) a compressor when theratio reaches +100% (–100%). If installed, the minimum loadvalve solenoid will be energized with the first stage of capacity.Minimum load valve value is a fixed 30% in the total capacitycalculation. The control will also use the minimum load valvesolenoid as the last stage of capacity before turning off the lastcompressor. A delay of 90 seconds occurs after each capacitystep change. Refer to Table 19.MINUTES LEFT FOR START — This value is displayedonly in the network display tables (using Service Tool,ComfortVIEW™ or ComfortWORKS® software) andrepresents the amount of time to elapse before the unit will startits initialization routine. This value can be zero without themachine running in many situations. This can include beingunoccupied, ENABLE/OFF/REMOTE CONTACT switch inthe OFF position, CCN not allowing unit to start, DemandLimit in effect, no call for cooling due to no load, and alarm oralert conditions present. If the machine should be running andnone of the above are true, a minimum off time (DELY, seebelow) may be in effect. The machine should start normallyonce the time limit has expired.MINUTES OFF TIME (ConfigurationOPT2DELY) — This user-configurable time period is used by thecontrol to determine how long unit operation is delayed afterpower is applied/restored to the unit. Typically, this time periodis configured when multiple machines are located on a singlesite. For example, this gives the user the ability to prevent allthe units from restarting at once after a power failure. A valueof zero for this variable does not mean that the unit should berunning.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. Asignal isolation device should be utilized if a full wavebridge signal generating device is used.