Carrier 48FC Series Controls, Start-up, Operation And Troubleshooting

Also see for 48FC 04: Installation instructions

Carrier 48FC Series Controls, Start-up, Operation And Troubleshooting Manual pdf 24 page image

24Free CoolingThe economizer will be enabled for cooling (OK TO FREE COOL?= Yes) if the supply air temperature sensor reading is valid, there areno applied lockouts, and economizer is operational. EconomizerOperational (ECON OPERATIONAL?) indicates if an economizer isinstalled (VENT METHOD = ECON) and feedback indicates it isoperational. The three economizer lockouts that determine if freecooling should be used to help with cooling are: Dry Bulb Lockout(DRY BULB LOCKOUT), Enthalpy Lockout (ENTHALPYLOCKOUT), and Unoccupied Free Cooling Lockout (UFCLOCKOUT?). Any one of these lockouts will disable economizer freecooling. See below for how each lockout occurs.When the economizer is available for free cooling (OK TO FREECOOL? = Yes) and the compression is not on, the damper will startopening from the damper’s minimum Position in Effect(EFFECTIVE MIN POS) based on the supply air temperature(SUPPLY AIR TEMP) to provide free cooling. A low coolingdemand (DEMAND = LOW COOL) will utilize the Low FreeCooling SAT Setpoint (LOW COOL SAT SP) as the Free CoolingSetpoint (FREECOOL SAT SP) to control the economizer. Amedium or high cooling demand (DEMAND = HIGH COOL) willutilize the High Free Cooling SAT Setpoint (HIGH COOL SAT SP)as the Free Cooling Setpoint (FREECOOL SAT SP) to control theeconomizer.During free cooling the fan will start at the dedicated free coolingspeed (FREE COOL IDF SPD). After the economizer (ECONCMD POSITION) reaches 100% (or Max) for 5 minutes, the fanwill be changed to the High Cool Speed (HIGH COOL IDFSPD). When a high cooling demand (DEMAND = HIGH COOL)is active the control will use the High Cool Speed (HIGH COOLIDF SPD). The compressor will be allowed for use after the fanand economizer are 100% (or Max) for 5 minutes. Oncecompression is turned on the economizer and fan will remain at100% until the call for cooling is removed or until the unit is nolonger allowed to free cool (OK TO FREE COOL = No).Dry Bulb LockoutDry Bulb Lockout (DRY BULB LOCKOUT) occurs when any ofthe following are true:S The Outdoor Air Temperature (OUTDOOR AIR TEMP) is invalid.S When Differential Dry Bulb Control is disabled (DIFF DRYBULB CTL = Disable) and the Outdoor Air Temperature(OUTDOOR AIR TEMP) is greater than the configured FreeCooling Maximum Temperature (FREE COOL MAX OAT) orless than the configured Free Cooling Minimum Temperature(FREE COOL MIN OAT).S When Differential Dry Bulb Control is enabled (DIFF DRYBULB CTL = Enable) and the return air temperature (RETURNAIR TEMP) plus the Differential Dry Bulb deadband (DIFFDB DEADBAND) is lower than the outdoor air temperature(OUTDOOR AIR TEMP).Enthalpy LockoutThe control uses the Outdoor Air Temperature (OUTDOOR AIRTEMP), Outdoor Relative Humidity (OARH LEVEL), andBarometric Pressure (BAROMETRIC PRESS) to calculate theOutdoor Enthalpy (OUTDOOR ENTHALPY). The control usesthe Return Air Temperature (RETURN AIR TEMP), ReturnRelative Humidity (RARH LEVEL), and Barometric Pressure(BAROMETRIC PRESS) to calculate the Return Enthalpy(RETURN ENTHALPY). Enthalpy Lockout (ENTHALPYLOCKOUT) occurs when any of the following are true:S When Differential Enthalpy Control is disabled (DIFFENTHALPY CTL = Disable) and the outdoor enthalpy(OUTDOOR ENTHALPY) is greater than the MaximumOutdoor Enthalpy limit (ENTHALPY HI LIMIT).S When Differential Dry Bulb Control is enabled (DIFF DRY BULBCTL = Enable) and the outdoor enthalpy (OUTDOORENTHALPY) is greater than the return enthalpy (RETURNENTHALPY). The Differential Enthalpy deadband (ENTHALPYDEADBAND) is use in the case of unlocking the Enthalpy lockout(ENTHALPY LOCKOUT).S The Enthalpy switch input (ENTHALPY SWITCH) is readinghigh.Unoccupied Free Cooling LockoutUnoccupied Free Cooling lockout (UFC LOCKOUT?) occurs whenthe unit is in the unoccupied period (OCCUPIED NOW? = No) andthe Outdoor Air Temperature (OUTDOOR AIR TEMP) is less thanthe Unoccupied Free Cooling low temperature (UFC LOW TEMP).Unoccupied Free CoolingThe unoccupied free cooling algorithm attempts to maintain thebuilding space half way between the Occupied Cool Set Point (OCCCOOL SETPOINT) and Occupied Heat Set Point (OCC HEATSETPOINT) using only the economizer when the conditions in thebuilding and the outdoors are suitable, during unoccupied periods.Three different points define this algorithm: Unoccupied Free Coolingconfiguration (WHEN TO UNOCC FC), Free Cooling PreoccupancyTime configuration (UFC PREOCC TIME), and Free cooling allowed(OK TO FREE COOL?).WHEN TO UNOCC FC = 0 (Disabled)Free Cooling will only occur if the space exceeds the unoccupiedsetpoints.WHEN TO UNOCC FC = 1 (Preoccupancy)Unoccupied free cooling can only occur when the time until thenext occupied period is less than the Unoccupied Free CoolPre--Occupancy Time (UFC PREOCC TIME) in minutes.WHEN TO UNOCC FC = 2 (Unoccupied)Unoccupied free cooling can occur throughout the entireunoccupied period. The space temperature must be higher then themid--point between the occupied cooling and heating setpoints.Power ExhaustPower Exhaust is a function used to assist in the building exhaustair if the barometric relief damper is not enough. It can be one ortwo motors which can be controlled independently to provide 2stages of exhaust. These two power exhaust stages are controlledby relays on the Main Base board, and therefore need to beconfigured on relay channels. To assign the channels set the PE1RELAY CHANNEL and PE2 RELAY CHANNEL as needed.NOTE: Factory installed power exhaust is only one channel and ison Relay 06.When a power exhaust 1 relay channel is configured, the controlwill create a PE1 curve, example shown in Fig. 17. This curve iscreated by applying the difference of the power exhaust stage 1 atmaximum fan speed (PE1 POS @ MAX SPD) and the Economizerminimum at maximum fan speed (MIN POS @ MAX FAN) inrelationship to the minimum position curve. When a power exhaust2 relay channel is configured, the control will create a PE2 curve,example shown in Fig. 17. This curve is created by applying thedifference of the power exhaust stage 2 at maximum fan speed(PE2 POS @ MAX SPD) and the Economizer minimum atmaximum fan speed (MIN POS @ MAX FAN) in relationship tothe minimum position curve.Power exhaust 1 (PE1 RELAY) and power exhaust 2 (PE2RELAY) are controlled using their respective curves as a threshold.When the operating point of the Commanded Fan Speed (IDFSPEED OUTPUT) and Economizer Commanded Position(ECON CMD POSITION) is above the power exhaust 1 curve,the Power exhaust 1 (PE1 RELAY) will be turned on. When theoperating point falls below the curve minus the power exhaust turnoff deadband (PE OFF DEADBAND) the Power exhaust 1 (PE1RELAY) will be turned off. Power exhaust 2 operates the same asPower exhaust 1 except using the PE2 curve.