York MILLENNIUM Y22, Installation Manual

Page: 73 / 140

102777-YIM-E-0206
Unitary Products Group 73
11. Economizer Option: the control directly controls the posi-
tion of the outside air / return air dampers through a 2-10
VDC signal from terminal ECO to ACT1 (economizer
actuator). The economizer is enabled only in Occupied
or Recovery mode, and after supply fan operation has
been verified (APS closed). When the supply fan is pow-
ered and there is no Y1 call or if free cooling is unavail-
able, the control opens the economizer dampers to the
minimum position setting.
The actuator maximum opening speed is 150 seconds to
full open; the control moves the actuator at the rate of
two seconds for each one % it is opening, so full open
from closed would take 200 seconds. At entry to Occu-
pied mode, the economizer is typically opening from 0 to
a minimum setting of 20%, which would take about 40
seconds. In Unoccupied mode, the economizer will close
to 0%.
With a Y1 call when the outside air is appropriate for free
cooling (see below), free cooling is used for first stage
cooling. The control modulates the economizer dampers
to maintain a SAT setpoint plus or minus one degree.
The control uses one of three methods to determine
when free cooling is available. The method used is
determined by the unit options, which function as listed
below.
Dry Bulb: the control relies on the RAT, OAT, and SAT
readings, connected to those terminals on the control.
Free cooling will be available until the outdoor tempera-
ture rises above the indicated temperature range. Free
cooling is disabled when the outdoor temperature rises
above the temperature range and cannot be enabled
until the outdoor temperature falls below the indicated
temperature range.
Single Enthalpy: The Outdoor Air Humidity Sensor is
connected to terminal OAH. When the outdoor enthalpy
is below the setpoint, free cooling is available.
Dual Enthalpy (Comparative/Differential Enthalpy):
Both the Outdoor Air Humidity [OAH] and the Return Air
Humidity [RAH] sensors are connected to the control.
When the outdoor air enthalpy is less than the return air
enthalpy, free cooling is available. The control will dis-
able free cooling and force mechanical cooling when the
outside air temperature exceeds setpoints.
12. Power Exhaust Option with Modulating Dampers: The
power exhaust controls are enabled in Occupied or
Recovery mode when the APS is satisfied. The building
pressure is sampled by a tube provided and installed by
the customer at a location in the building, connected to
the high pressure port of the pressure transducer BPS.
BPS provides a 0-5 VDC signal to the control, which
compares the reading to the pressure setpoint to control
the exhaust dampers. The exhaust damper vanes are
modulated by ACT2, from a signal from terminal EXD+.
The exhaust motor is energized by voltage at terminal
EXH to contactor 10M when the dampers are driven
above the ON setpoint for damper open %.
The exhaust motor is powered OFF when the vanes
reach the OFF % point set in control parameters. When
the power exhaust is disabled, ACT2's spring return
closes the exhaust dampers and 10M opens to shut
down the exhaust fans.
13. Power Exhaust Option with Variable Frequency Drive:
The power exhaust controls are powered through EXH /
10M with a call for the supply fan. Once powered, the
BPS sensor (Building Pressure sensor) sends a signal to
terminal 53 of the VFD. The damper vanes are gravity-
closed; motor speed is continuously variable. See sepa-
rate document for details on power exhaust VFD opera-
tion.
14. Non-modulating Power Exhaust Option: The power
exhaust motor is energized by EXH / 10M based on the
position of the Economizer damper settings in the control
parameters. Minimum run time is 10 seconds; minimum
off time is 60 seconds. The outlet pressure of the power
exhaust fan forces the barometric relief dampers open;
gravity closes the dampers when the exhaust fan is off.
VARIABLE AIR VOLUME UNIT (VFD & IGV)
OVERVIEW
The VAV units operate in one of three modes: Occupied,
Unoccupied, and Recovery. The unit operational mode is
determined by the status of the internal clock and the internal
schedules.
OCCUPIED / UNOCCUPIED / MORNING WARM-UP
OCCUPIED
In Occupied mode, all installed options enabled by the
parameter settings are available. The supply fan is operated
[controlled to the duct pressure setpoint if a VAV], optional
unit heating is available at full capacity, the optional power
exhaust system is enabled, the economizer outside air damp-
ers go to their minimum position or open for free cooling. This
operation continues until the unit enters Unoccupied mode.
When the control sees an Occupied override button push
from the thermostat or space sensor, it will go to Occupied
mode for the length of time set in the parameters, up to four
hours. If the unit is in Space Sensor operation, the fan will
operate at full speed [controlled to the duct pressure setpoint
if a VAV].
A VAV standalone unit will run MWUP the first hour of the
OCC override signal, then go to Occupied. The supply fan will
run continuously.
UNOCCUPIED
In Unoccupied mode, the economizer goes to full closed; the
supply fan will only operate if there is a call for heating or