Carrier 45J Installation, Start-up And Service Instructions Manual
Also see for 45J: Installation, Start-Up and Service Instructions
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9Balancing Carrier Fan TerminalsCarrier fan terminal units contain primary air damperswhich, under the control of a volume controller, regulate theamount of cold air distributed to the space.45J,K,Q SERIES FLOW UNITSThe 45J,K,Q series flow terminals direct all primary airthrough the unit fan. The terminal is designed to operate with thefan supplying airflow equal to or greater than the airflow sup-plied by the VAV damper. To balance the unit, therefore, it isnecessary to first set the fan flow, and then the VAV damper (pri-mary) flow.Each control option has specific procedures required for bal-ancing the unit, but some steps are common to all 45J,K,Q units.The fan box adjustments described below must be made in con-junction with the adjustments described in the Speed Controllerand Control Adjustments section.The VAV damper airflow may be set at the factory, but the fanairflow must be set in the field as described in “Setting of VAV(Primary) Airflow.”Setting Fan AirflowNOTE: If the unit has electric heat or hot water heat, temporarilydisable these functions before balancing the fan.If unit has optional electric heat disconnect downstream offan motor connections to power, open disconnect.If unit does not have optional electric heat disconnect, re-move one electric heat power line connection. Be sure to insulateloose line from ground wire or other wires.1. Set the controller to provide heating airflow demand only.Typically, this is accomplished by setting the thermostat tothe highest possible temperature setting.NOTE: A minimum of 0.1 in. wg downstream static pressure isrequired in the duct to ensure proper heater operation.2. Determine that the VAV valve is fully closed and that thefan is rotating in the proper direction. (If the VAV damperis open when the fan is started and there is primary air inthe system, the fan may start and run backward.)3. Using a flow hood or duct traverse, determine the deliveredfan airflow (cfm).NOTE: Both flow hood and duct traverse are subject to measure-ment errors. Be sure that all applicable measurement precautionsare taken.4. Compare the actual cfm in heating mode to the designedairflow. If there is a minimum setting for the VAV damperin heating mode (as recommended by ASHRAE [Ameri-can Society of Heating, Refrigeration, and Air Condition-ing Engineers] Standard 62), this quantity is included in thetotal measured heating airflow to determine if the desiredinduction airflow level has been met.5. Adjust the fan SCR at unit control box to achieve the de-sired airflow rate. Refer to the performance data tables (Ta-bles 9-11) to ensure airflow through electric heaters meetsthe requirements before operating the heater.Setting of VAV (Primary) AirflowAdjustment of Set PointsEach 45J, 45K, and 45Q supplied with controls is equipped witha pneumatic or electronic volume controller which regulates thequantity of cold primary air entering the terminal and the condi-tioned space. If required airflow levels are specified with the joborder, the minimum and maximum cfm levels will be set at thefactory where applicable. If minimum and maximum levels arenot specified, a default value of 0 is used for minimum setting atthe factory. Other settings of minimum and maximum primaryairflow must be set in the field. Airflow (cfm) ranges for the pri-mary air damper are shown in Tables 9-11. The minimum pri-mary airflow (other than zero) is the minimum flow ratecontrollable by the unit volume controller. The primary airdamper can be set at zero for shutoff or at the minimum cfmlisted.Field Adjustment of Minimum and Maximum Airflow SetPointsEach 45J, 45K, and 45Q unit is equipped with a centerpointaveraging flow probe which provides an amplified differentialpressure that is proportional to the unit airflow. Output from thisprobe is used to provide a flow signal to both pneumatic andelectronic controls. Unit airflow (cfm) can be read directly fromthe flow probe on the unit (refer to Fig. 8).1. With the unit airflow from the fan set, turn on primary(VAV) air supply.2. To set cfm in the field, connect a gage to the flow probe atthe provided ‘T’ taps, and check the differential pressure.(Alternately, the total flow may be measured, and the previ-ously determined fan induction flow rate may be subtractedfrom the total flow to determine VAV flow. However, forlow primary settings, this may not be as accurate as theflow tap method.)3. If a minimum VAV flow is required in heating mode, adjustthe volume until the differential pressure corresponds to thecfm required.4. Set the controller to provide maximum cooling demand.This is typically accomplished by first setting the thermo-stat to the lowest possible temperature setting.a. In most series fan boxes, the primary airflow rate isequal to the fan induction flow; in these cases, adjustthe volume controller until a balance is achievedbetween fan induced airflow and primary airflow.When a balance exists, a strip of paper hung at theinduction port should hang straight down, and nei-ther be blown in or out of the unit.b. If the primary airflow desired is less than the faninduction flow, adjust the volume controller until thedifferential pressure (measured through the flowprobe as described above) corresponds to the cfmrequired. Verify that induction exists through theinlet ports, using the paper strips as described above.When induction exists, the paper strip should bepulled into the unit.5. Return all reheat options to normal connections.6. Cap the ‘T’ taps.7. Reset the thermostat to a normal setting.NOTE: It is normal for the total airflow to the room to increaseslightly in full cooling mode. |
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