Carrier 48/50HC04-28 Controls, Start-up, Operation And Troubleshooting

Also see for 50HCQ04---12: Controls, Start-Up, Operation and Troubleshooting Instructions Service and maintenance instructions

Carrier 48/50HC04-28 Controls, Start-up, Operation And Troubleshooting Manual pdf 22 page image

22Supply FanThe RTU Open supply fan may be configured for 1 of 3Fan Control modes:S Single -- The fan operates at one speed only andprovides on/off operationS Two Speed -- The fan operates at 1 of 2 speeds dependingon the mode of operation and load conditions. During fanonly or single stage cooling, the fan operates at low speed.During heating, dehumidification, second stage cooling, orif maximum economizer operation is required, the fanoperates at high speed. This control mode is used with48/50TC(Q), 48/50HC(Q) and size 04--06 48/50LC unitswhen Staged Air Volume (SAV) option is provided.S Variable Speed -- The fan operates at a variable speed tomeet the load conditions and SAT safety requirements toprovide maximum energy savings by minimizing fanhorsepower consumption. Fan speed is NOT controlled bystatic pressure. This setting is default for LCWeatherExpert size 07--26 units and when WeatherExpertis selected under Unit Type configuration.The RTU Open supply fan may be configured for 1 of 3Fan Modes:S Auto -- The fan cycles on/off in conjunction withheating or cooling.S Continuous -- The fan runs continuously duringoccupancy and intermittently during unoccupiedperiods with heating and cooling.S Always On -- The fan runs continuously regardless ofoccupancy or calls for heating and cooling.Occupancy can be determined by Linkage, BACnetschedules, BAS schedules, or in response to a remoteoccupancy switch.A Fan Off Delay allows the supply fan to continueoperating after heating or cooling stops.If the following alarms are active, the fan turns offimmediately, regardless of the occupancy state or demand:S Fire ShutdownS Safety chainS SAT sensor alarmS SPT sensor alarmsThe RTU Open does not include smoke--control functionssuch as a smoke--purge, zone--pressurization, or smoke--vent-ilation. Each of these modes require a field--designed circuitto operate the following by local fine codes:S RTU supply fanS RTU economizerS RTU power exhaustThe RTU Open many be configured to accept a SupplyFan Status input to provide proof the supply fan isoperating. When enabled, a loss or lack of fan status willstop heating and cooling operation.A supply Fan Alarm Service Timer function is availableto track the number of supply fan run hours and generatean alarm when the accumulated runtime exceeds the setthreshold.EconomizerThe Economizer dampers are used to provide free coolingwhen the outside conditions are suitable and Indoor AirQuality, if optional CO2 sensor is installed.The following conditions must be true for economizeroperation:S Indoor Fan is on.S Enthalpy is Low if the Enthalpy input is enabled.S SAT reading is available.S OAT reading is available.S SPT reading is available.S OAT <= High OAT economizer lockout configuration(default = 75).S OAT <= SPTIf any of the mentioned conditions are not true, theeconomizer will be set to its configured minimum position.If the RTU Open is configured for VFD or 2--speed fan,and the fan is on or at the highest speed, or if the unit isconfigured for single--speed fan, then the economizer willuse the Vent Dmpr Pos/DCV Min Pos setpoint as theminimum economizer position when occupied. If the unitis configured for VFD or 2--speed fan, and the fan is on orat the lowest speed, the economizer will use the Low FanEcon Min Pos.NOTE: For LC WeatherExpert units or any unit withVariable Speed fan control, the RTU Open will determinethe required minimum economizer position (CalculatedMin Econ Pos) based on the fan’s actual operation speed.The minimum damper position can be overridden by theIAQ routine described later in this section.If the above conditions are true, the Economizer controlwill calculate a damper position starting with a minimumvent position and based on current space temperature anda setpoint that is one degree less than the effective coolsetpoint. If the SAT drops below the cooling low supplyair setpoint (+ 5_F), the economizer will close as requiredbut not to less than the to minimum position. TheCalculated Min Econ Pos used for control is displayed inthe Maintenance section.RTU Open provides Fault Diagnostic and Detection(FDD) for economizer operation in compliance withCalifornia Title 24. The FDD logic will detect aneconomizer that fails to close, fails to open, stuck fullyopen, and fails to fully open. Each condition will cause anEconomizer Operation alarm to occur and the specificcondition will be displayed.Enthalpy ControlYou may use an enthalpy switch to indicate the suitability ofoutdoor air for economizer cooling. You can use either anoutdoor air or differential enthalpy switch. A differentialenthalpy switch has a sensing device in both the outdoor andreturn air streams. A differential enthalpy switch indicateswhen outside air is more suitable to be used than the returnair and is available for economizer cooling. If no enthalpyswitch is configured, a network point (Object Name: oae) isavailable. This point is displayed in the i--Vu application andEquipment Touch as Enthalpy (BACnet).48 ---50LHTCQ ---01T