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

Also see for 48LC 05: Controls, Start-Up, Operation and Troubleshooting Service and maintenance instructions Service and maintenance instructions

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Carrier 48LC Series Controls, Start-up, Operation And Troubleshooting Manual pdf 27 page image

27IAQ (Analog Input)When IAQ assigned channel (IAQ SENSOR CHAN) is set for ananalog input that input channel will be mapped to the Indoor AirQuality (IAQ LEVEL). The control is configured for indoor airquality sensors which provide 4 to 20 mA signal for 0 to 2000 ppmCO 2. If the sensor being used has a different range, the ppmdisplay range must be reconfigured by entering new values for theIAQ Sensor Value at 4mA (IAQ PPM @ 4MA) and IAQ SensorValue at 20mA (IAQ PPM @ 20MA).ANALOG IAQ CTRL = 0 (No IAQ)This signifies that there is no IAQ sensor installed. The economizerdamper will operate based on the minimum position curve.ANALOG IAQ CTRL = 1 (DCV)During Demand Controlled Ventilation (DCV), the dampermodulates on or between two ventilation curves depending uponthe difference between the Indoor Air Quality (IAQ LEVEL) andthe Outdoor Air Quality (OAQ LEVEL). The lower of these twocurves is referred to as the IAQ Minimum Position Curve, and thehigher curve is the Minimum Position curve discussed in theMinimum Ventilation section under Economizer Operation. Referto that section on how the minimum Position curve is created. SeeExample Curves in Fig 19.The IAQ Minimum Position curve is created by applying thedifference of the IAQ position at maximum fan speed (IAQ POS @MAX SPD) and the Economizer minimum at maximum fan speed(MIN POS @ MAX FAN) in relationship to the minimum positioncurve. The IAQ position at maximum fan speed (IAQ POS @MAX SPD) should be set to an economizer position that brings inenough fresh air to remove contaminates and CO 2 generated bysources other than people. The Economizer minimum at maximumfan speed (MIN POS @ MAX FAN) should be set to aneconomizer position that brings in fresh air to remove contaminatesand CO 2 generated by all sources including people when theindoor fan is operating at the IDF Maximum Fan Speed(MAXIMUM IDF SPEED). The Economizer minimum atmaximum fan speed (MIN POS @ MAX FAN) value is the designvalue for maximum occupancy.The economizer Min Position in Effect (EFFECTIVE MIN POS)will follow the IAQ Minimum Position curve while the Indoor AirQuality level (IAQ LEVEL) is less than the Outdoor Air QualityLevel (OAQ LEVEL). The control will begin to open the dampermore than the IAQ Minimum Position curve when the IAQ levelbegins to exceed the OAQ level by a configurable amount. Thisamount is referred to as AQ Differential Low (LOW AIR.QDIFF). When the differential between IAQ and OAQ reaches AQDifferential High (HIGH AIR.Q DIFF), the economizer MinPosition in Effect (EFFECTIVE MIN POS) will follow theMinimum Position Curve. When the IAQ/OAQ differential isbetween AQ Differential Low (LOW AIR.Q DIFF) and AQDifferential High (HIGH AIR.Q DIFF), the control will modulatethe damper between the IAQ Minimum Position Curve and theMinimum Position Curve in a linear manner as shown as theshaded area in Fig. 19. As a simple example Fig. 21 shows the MinPosition in Effect (EFFECTIVE MIN POS) relationship while theCommanded Fan Speed (ECON CMD POSITION) is held at themaximum speed.ANALOG IAQ CTRL = 2 (Override IAQ)Override IAQ is reserved for a future release.ANALOG IAQ CTRL = 3 (Control Minimum Position)An external 4 to 20 mA source is used to set the Min Position inEffect (EFFECTIVE MIN POS). The 4mA signal corresponds to0% and the 20 mA signal corresponds to 100%. In this mode,configuration such as Economizer minimum at maximum fanspeed (MIN POS @ MAX FAN), IAQ position at maximum fanspeed (IAQ POS @ MAX SPD) and the economizer minimumposition and DCV minimum position curves in Fig. 19 and Fig. 21are not used. If the indoor fan is not operating, the economizerposition will be zero. The actual damper position may exceed theeconomizer Min Position in Effect (EFFECTIVE MIN POS) toprovide economizer cooling.VENTILATION FOR PEOPLEVENTILATION FOR SOURCESINCREASING VENTILATIONMIN POS @MAX FANIAQ POS @MAX FAN100 700 INSIDE/OUTSIDE CO2DIFFERENTIALLOW AIR.Q DIFF HIGH AIR.Q FIFFC14328Fig. 21 -- ExampleOutdoor Air Quality (Analog Input)The default for the Outdoor Air Quality (OAQ LEVEL) is 400ppm CO 2 when the OAQ sensor is not assigned an input channel.When OAQ Assigned channel (OAQ SENSOR CHAN) is set foran analog input that input channel will be mapped to the OutdoorAir Quality (OAQ LEVEL). The outdoor air quality sensorprovides a 4 to 20 mA signal corresponding to 0 to 2000 ppmCO 2. If a field supplied sensor has a different range, the ppmdisplay range must be reconfigured by entering new values for theOAQ Sensor Value at 4mA (OAQ PPM @ 4MA) and OAQ SensorValue at 20mA (OAQ PPM @ 20MA).Pre--occupancy PurgeThe control has the option for a pre--occupancy purge to refresh theair in the space prior to occupancy. This feature is enabled bysetting PREOCC PURGE ENBL to Yes. This function is alsoreferred to as the IAQ purge function.The IAQ Purge will operate under the following conditions:S Purge is enabledS the unit is in the unoccupied stateS Current Time is validS Next Occupied Time is validS time is one hour prior to next occupied periodS the OAT is greater than the lockout (PREOCC LOW LIMIT)The IAQ Purge Position curve is created by applying the differenceof the IAQ purge position at maximum fan speed (PURGE POS @MAX) and the Economizer minimum at maximum fan speed (MINPOS @ MAX FAN) in relationship to the minimum position curve.The IAQ purge position at maximum fan speed (PURGE POS @MAX) should be set to an economizer position that brings inenough fresh air over an hour period to remove contaminates andCO 2 during the unoccupied period. When the preoccupancy purgefunction is active (IN PREOCC PURGE?), the economizer MinPosition in Effect (EFFECTIVE MIN POS) will follow the IAQPurge Position curve.Temperature Compensated StartSpace control set points are usually set to 2 different levels forunoccupied period and occupied period. Unoccupied set pointssaves energy, while occupied set points provide occupant comfort.The time period it takes for the RTU to bring the space from itscurrent condition in unoccupied mode to its occupied set point is