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IM 1083-3
Economizer Control Capabilities
• Basic:
Compares the inside and outside air temperatures
using item 11 (Room Temperature Sensor) and item 13
(Outdoor Air Temperature Sensor) to determine if outdoor
air can be used for “free”, economizer cooling operation.
• Expanded:
Compares the inside and outside air
temperatures using item 11 (Room Temperature Sensor)
and item 13 (Outdoor Air Temperature Sensor) and
calculates the enthalpy of the outside air relative humidity
using item 14 (Outdoor Air Humidity Sensor) to determine
if outdoor air can be used for “free”, economizer cooling
operation.
• Leading Edge:
True enthalpy comparison economizer
that compares the inside and outside air temperatures
using item 11 (Room Temperature Sensor) and item 13
(Outdoor Air Temperature Sensor) and compares the
enthalpy of the inside and outside air relative humidity
using item 14 (Outdoor Air Humidity Sensor) and item 15
(Room Humidity Sensor) to determine if outdoor air can be
used for “free”, economizer cooling operation.
Local User Interface (LUI)
Figure 42: Local user interface (LUI)
The optional built-in LUI touch pad with digital OLED display
is located in the right hand compartment below the top right
access door. The 4 x 20 OLED display will provide a variety of
information including:
•
Operating mode states
•
Fan functions
•
Room set point temperature
•
Current room temperature
•
Fault codes for quick diagnostics at the unit
The LUI has a built in menu structure (Pass¬word protected)
with 4 keys and 2 individual LED indicators to adjust the unit
ventilator operating parameters shown in the following.
Operating Mode States (4)
•
Heat:
Heating and economizer operation only
•
Cool:
Cooling and economizer operation only
•
Fan Only:
Fan operation only
•
Auto:
Unit automatically switches between heating,
cooling and economizer operation to satisfy the room load
conditions. The current unit state is also displayed.
Fan States (4)
•
High (constant speed:
compressor on high stage)
•
Medium (constant speed:
compressor on low stage
•
Low (constant speed:
compressor on low stage)
•
Auto (part load, variable air):
Varies the fan speed
automatically to meet the room load conditions whether
the unit is in heating, cooling or economizer mode. The
current fan speed is also displayed. During low load
or normal operation (about 60% of the time) the fans
will operate at low speed. When the load increases to
an intermediate demand the fans automatically shift to
medium speed. At near design or design load conditions,
the fans will operate on high speed. A 10-minute delay
between speed changes is incorporated to minimize the
awareness of these changes. The outdoor air damper will
index based on the fan speed to maintain the required
minimum cfm (cubic feet per minute) of ventilation air.
Occupancy Modes (4)
•
Occupied:
Normal, daytime operation where the unit
maintains the room set point.
•
Unoccupied:
Night set back operating mode in which
the unit responds to a new room set point and cycles to
maintain the condition. The fan comes on when heating
or cooling is needed and runs until the load is satisfied.
The outside air damper is closed during this mode. With
direct expansion (DX) cooling units, when a cooling load
is satisfied by the refrigerant system, the compressor is
de-energized and the Unit Ventilator indoor fan continues
to run for a fixed period of time to remove possible frost
buildup on the evaporator coil.
•
Stand By Mode:
The unit ventilator maintains the stand
by mode set point temperature with the outside air damper
closed. The fan runs continuously unless it is configured to
cycle in response to the room load.
•
Bypass Mode:
By depressing the Tenant Override Switch
on a remote sensor or using the LUI keypad the unit is
placed back into the Occupied Mode for a predetermined
time (default of 120 minutes). This time can be set in
1-minute increments from 1 minute to 240 minutes through
the Unit Ventilator Service Tool, the LUI keypad or a BMS
network.
Summary of Contents for ARQ
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