15
Fan Powered Terminal Units IOM
BALANCING KRUEGER FAN TERMINALS
Krueger 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.
BALANCING SERIES FLOW UNITS
KLPS, KQFS & QFC 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 supplied by the VAV damper. To balance the unit,
therefore, it is necessary to first set the fan flow, and then
the VAV damper (primary) flow.
Each control option has specific procedures required for
balancing the unit, but some steps are common to all KLPS,
KQFS & QFC units. The fan box adjustments described
below must be made in conjunction with the adjustments
described in the Speed Controller section, 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 below.
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, remove 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” w.g. 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 measurement 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 [American
Society of Heating, Refrigeration, and Air Conditioning
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
desired airflow rate. Refer to the performance data
tables (Tables 8 and 9) to ensure airflow through electric
heaters meets the requirements before operating the
heater. Setting of VAV (Primary) Airflow
ADJUSTMENT OF SET POINTS
Each KLPS, KQFS and QFC unit, 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 conditioned 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 primary
air damper are shown in Tables 8 and 9. The minimum
primary 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 KLPS, KQFS and QFC unit is equipped with a centerpoint
averaging airflow sensor, which provides an amplified
differential pressure that is proportional to the unit airflow.
Output from this sensor is used to provide a flow signal to
both pneumatic and electronic controls. Unit airflow (cfm)
can be read directly from the airflow sensor labels on the
unit (refer to Figure 8, Flow Chart).
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
previously 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
thermostat to the lowest possible temperature setting.
a.
In most series fan boxes, the primary airflow rate is
set so the maximum primary CFM is equal to the fan
CFM; 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 neither be blown in or out of the unit.
b.
Primary CFM airflow is less than the fan induction flow
cfm, 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.
Summary of Contents for KLPP
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