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SCXF-SVX01Q-EN
static pressure within an adjustable user-defined range.
The range is determined by the supply air pressure
setpoint and supply air pressure dead band, which are
set at the HI panel.
VFDs provide supply fan motor speed modulation. The
drives will accelerate or decelerate as required to
maintain the supply air static pressure setpoint.
VFD with Bypass
Bypass control is an option that provides full nominal
airflow in the event of drive failure. The user must
initiate the bypass mode at the HI panel. When in
bypass mode, VAV boxes need to be fully open. The
self-contained unit will control heating and cooling
functions to maintain setpoint from a user-defined zone
sensor. Supply air static pressure limit is active in this
mode.
For more detailed information on VFD operation,
reference VFD technical manual that ships with the
unit.
Airside Economizer Option
Units with the airside economizer option are equipped
with the necessary control sequences to use outside air
for the first stage of cooling, in occupied or unoccupied
mode and when ambient conditions are favorable for
economizing. Inherent in the unit controller is the
ability to suppress the setpoint below the normal unit
setpoint. This allows the building to improve comfort
levels when possible, and at the same time, optimize
building mechanical cooling operation for peak
operating efficiency. An outside air temperature and
relative humidity sensor are provided to allow
monitoring of reference enthalpy and are field
installed.
If the unit has the ECEM board, economizer operation
enables when the outside air enthalpy is less than 25
BTUs/lb. default (adjustable 19-28 BTUs/lb). During
occupied mode, the outside air damper opens to 15%
(adjustable 0-100% at the HI) for ventilation purposes.
Also, the ability to alter the outside air damper position
to compensate for VAV supply air modulation is
inherent in the unit controls, and can be enabled by the
operator.
If the unit does not have an ECEM board, it will
economize when the O/A temperature falls below the
O/A economizer setpoint.
The mixing box fabrication is galvanized steel.
Opposed low leak damper blades are fabricated from
galvanized steel and rotate on rustproof nylon
bushings. A factory installed 24V modulating spring
return actuator controls both damper positions.
When outdoor conditions are not suitable for
economizer cooling, the enthalpy control disables the
economizer function and permits the outdoor air
damper to open only to the minimum position.
On water-cooled units, compressor operation lockout
will not occur at low ambient air temperatures.
However, lockout will still occur via low condenser
water temperature.
The outdoor air dampers drive fully closed whenever
the supply air fan is off, provided there is power to the
unit.
Comparative Enthalpy Control
Comparative enthalpy controls the economizer
operation and measures temperature and humidity of
both return air and outside air to determine which
source has lower enthalpy. This allows true
comparison of outdoor air and return air enthalpy by
measurement of outdoor air and return air
temperatures and humidities. A factory-installed
control board, with field-installed outside and return air
temperature and relative humidity sensors, allows
monitoring of outside and return air.
N
No
otte
e:: If comparative enthalpy is not ordered, standard
method is to compare outdoor air enthalpy with
the fixed reference enthalpy. The reference
enthalpy is set through the human interface
panel.
Units with comparative enthalpy control are equipped
with the necessary control sequences to allow using
outside air for the first stage of cooling, in occupied or
unoccupied mode and when ambient conditions are
favorable for economizing. Inherent in the unit
controller is the ability to suppress the setpoint below
the normal unit setpoint. This allows building to
improve comfort levels when possible, and at the same
time, optimize building mechanical cooling operation
for peak efficiency.
Economizer operation enables when the outside air
enthalpy is 3 BTU/lb less than the return air enthalpy.
During occupied mode, the outside air damper opens
to 15% (adjustable 0-100%) for ventilation purposes.
Also, the ability to alter the outside air damper position
to compensate for VAV supply air modulation is
inherent in the unit controls, and can be enabled by the
operator.
The mixing box fabrication is galvanized steel.
Opposed low leak damper blades are fabricated from
galvanized steel and rotate on rustproof nylon
bushings. A factory installed 24V modulating spring
return actuator controls both damper positions.
Airside Economizers with Traq Damper
Outside air enters the unit through the Traq
™
damper
assembly and is measured by velocity pressure flow
rings. The velocity pressure flow rings are connected to
a pressure transducer/solenoid assembly, which
compensates for temperature swings that could affect
the transducer. The ventilation control module (VCM)
utilizes the velocity pressure input, the RTM outdoor air
temperature input, and the minimum outside air cfm
Summary of Contents for IntelliPak SCRF 25
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