Carrier AQUASNAP 30RAP010-150 Controls, Start-up, Operation, Service, And Troubleshooting

Also see for AQUASNAP 30RAP010-150: Start up & operation manual Installation instructions Installation instructions Controls, start-up, operation, service, and troubleshooting

Carrier AQUASNAP 30RAP010-150 Controls, Start-up, Operation, Service, And Troubleshooting Manual pdf 28 page image

28Capacity Control — The control system cycles com-pressors, digital scroll modulating 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 9.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 9.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.LEAD/LAG DETERMINATION — This is a configurablechoice and is factory set to be automatic for all units. The30RAP units offer an optional digital compressor. When theunit is equipped with a digital scroll compressor and enabled(ConfigurationUNITA1.TY=YES), or minimum load,then circuit A is lead (ConfigurationOPT2LLCS).If the unit is equipped with Minimum Load Valve (MLV)and option has been enabled, Circuit A will be the last circuiton as capacity is decreasing for the MLV to be active for thelast stage of capacity.The value can be changed to Circuit A or Circuit B leadingas desired. Set at automatic, the control will sum the currentnumber of logged circuit starts and one-quarter of the currentoperating hours for each circuit. The circuit with the lowestsum is started first. Changes to which circuit is the lead circuitand which is the lag are also made when total machine capacityis at 100% or when there is a change in the direction of capaci-ty (increase or decrease) and each circuit's capacity is equal.LOADING SEQUENCE SELECT — This is configurable asequal circuit loading or staged circuit loading with the defaultset at equal (ConfigurationOPT2LOAD). The control de-termines the order in which the steps of capacity for each cir-cuit are changed. Set to equal, the unit will alternate startingcompressors in each circuit as the requirement increases. Set tostaged, one circuit will load completely before the second cir-cuit is started. This control choice does NOT have any impacton machines with only one circuit or units with 2 compressors -one in each circuit.CAPACITY CONTROL OVERRIDES — The following over-rides will modify the normal operation of the routine.Deadband Multiplier — The user configurable DeadbandMultiplier (ConfigurationSLCTZ.GN) has a default val-ue of 1.0. The range is from 1.0 to 4.0. When set to other than1.0, this factor is applied to the capacity Load/Unload Factor.The larger this value is set, the longer the control will delaybetween adding or removing stages of capacity. Fig. 19 showshow compressor starts can be reduced over time if the leavingwater temperature is allowed to drift a larger amount above andbelow the set point. This value should be set in the range of 3.0to 4.0 for systems with small loop volumes.