9
Balancing Carrier Fan Terminals
Carrier fan terminal units contain primary air dampers
which, under the control of a volume controller, regulate the
amount of cold air distributed to the space.
45J,K,Q SERIES FLOW UNITS
The 45J,K,Q series flow terminals direct all primary air
through the unit fan. The terminal is designed to operate with the
fan supplying airflow equal to or greater than the airflow sup-
plied by the VAV damper. To balance the unit, therefore, it is
necessary 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 Controller
and Control Adjustments section.
The VAV damper airflow may be set at the factory, but the fan
airflow must be set in the field as described in “Setting of VAV
(Primary) Airflow.”
Setting Fan Airflow
NOTE: If the unit has electric heat or hot water heat, temporarily
disable these functions before balancing the fan.
If unit has optional electric heat disconnect downstream of
fan 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 insulate
loose 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 to
the highest possible temperature setting.
NOTE: A minimum of 0.1 in. wg downstream static pressure is
required in the duct to ensure proper heater operation.
2. Determine that the VAV valve is fully closed and that the
fan is rotating in the proper direction. (If the VAV damper
is open when the fan is started and there is primary air in
the system, the fan may start and run backward.)
3. Using a flow hood or duct traverse, determine the delivered
fan airflow (cfm).
NOTE: Both flow hood and duct traverse are subject to measure-
ment errors. Be sure that all applicable measurement precautions
are taken.
4. Compare the actual cfm in heating mode to the designed
airflow. If there is a minimum setting for the VAV damper
in heating mode (as recommended by ASHRAE [Ameri-
can Society of Heating, Refrigeration, and Air Condition-
ing Engineers] Standard 62), this quantity is included in the
total measured heating airflow to determine if the desired
induction 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 meets
the requirements before operating the heater.
Setting of VAV (Primary) Airflow
Adjustment of Set Points
Each 45J, 45K, and 45Q supplied with controls is equipped with
a pneumatic or electronic volume controller which regulates the
quantity of cold primary air entering the terminal and the condi-
tioned space. If required airflow levels are specified with the job
order, the minimum and maximum cfm levels will be set at the
factory where applicable. If minimum and maximum levels are
not specified, a default value of 0 is used for minimum setting at
the factory. Other settings of minimum and maximum primary
airflow 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 rate
controllable by the unit volume controller. The primary air
damper can be set at zero for shutoff or at the minimum cfm
listed.
Field Adjustment of Minimum and Maximum Airflow Set
Points
Each 45J, 45K, and 45Q unit is equipped with a centerpoint
averaging flow probe which provides an amplified differential
pressure that is proportional to the unit airflow. Output from this
probe is used to provide a flow signal to both pneumatic and
electronic controls. Unit airflow (cfm) can be read directly from
the 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 at
the 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 subtracted
from the total flow to determine VAV flow. However, for
low primary settings, this may not be as accurate as the
flow tap method.)
3. If a minimum VAV flow is required in heating mode, adjust
the volume until the differential pressure corresponds to the
cfm 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 is
equal to the fan induction flow; in these cases, adjust
the volume controller until a balance is achieved
between fan induced airflow and primary airflow.
When a balance exists, a strip of paper hung at the
induction 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 fan
induction flow, adjust the volume controller until the
differential pressure (measured through the flow
probe as described above) corresponds to the cfm
required. Verify that induction exists through the
inlet ports, using the paper strips as described above.
When induction exists, the paper strip should be
pulled 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 increase
slightly in full cooling mode.
