York MILLENNIUM Y22, Installation Manual, Page: 80 / 140

102777-YIM-E-0206
80 Unitary Products Group
stages, or compressors are staged up, or destaged, the
economizer controls continues using the economizer damper
to "trim" the effect of the staging and to maintain the SAT as
near the middle of the SAT control band as possible.
If the unit is using hydronic heat, the control modulates the
water valve to maintain SAT at the programmed "Comfort
Ventilation Low Supply Air Setpoint". At this setpoint, the
hydronic heat control does not conflict with the economizer
control, and will prevent SAT from dropping outside of the
specified control band when the economizer can no longer
maintain the SAT at its middle-of-the-band setpoint.
HYDRONIC HEAT
The Hydronic Heat option requires locating a SAT sensor
downstream of the heating coil.
During hydronic heating, the SAT control to the selected
“Hydronic Heat First Stage SAT setpoint”, or “Hydronic Heat
Second Stage SAT Setpoint” is performed using a Propor-
tional / Integral control algorithm. The control algorithm
includes special provisions (sometimes referred to as a
“bumpless transfer” feature) that allow it to resume control of
SAT as fast as possible when it is re-activated during the ON
/ OFF cycling of the unit (cycling between a satisfied and a
heating state under control of a zone thermostat, or zone
sensor). In its OFF-state, the control algorithm continues
monitoring the SAT and performs calculations necessary to
set its output, that controls the hot water valve, to have the
same value on starting the ON-cycle as it had when it went
into the OFF-cycle (in spite of some decrease in the SAT dur-
ing the OFF-cycle).
The “bumpless transfer” feature of the hydronic heat control
algorithm essentially acts similar to a “memory” that holds the
algorithm output during the OFF-cycles. This “memory” is
reset only on unit shutdown. The effect of this “memory” can
be observed on the action of the hot water valve. After unit
startup (during the first ON-cycle of the hydronic heat), there
is no “memorized” output value and the valve moves rela-
tively slowly into a control position required to maintain the
SAT setpoint. On subsequent ON cycles, the valve moves
into a control position much faster as dictated by the output
value stored in control algorithm “memory”.
COOLING LOCKOUT ON OAT
This is the Outside Air Temperature Setpoint that the control
uses to lock out mechanical cooling when the OAT is below
this setpoint. There is a one-degree hysteresis on each side
of the setpoint. Adjustable from 0
°
F to 100
°
F, the default is
45
°
F.
The change to 0
°
F applies only to compressors # 1 and # 2
when head pressure control is installed. Cooling Lockout on
OAT may occur while the control is in an Economizer mode
and there is a demand for compressors.
WATER COIL FREEZE STAT (FSI)
This option is used only on rooftop units with hydronic heat
(Hydronic heat option is turned ON). When the FSI terminal
sees 24 VAC, the control will open the Hot Water valve to
100%. The control will continue to drive the valve to 100%
until five minutes after the switch has closed. If the control is
operating the Fan, it will close the Economizer fully until the
freeze condition is over. If the fan is off and the RAT drops
below 40
°
F, the Hot Water Valve will turn on 100%. This con-
trol sequence takes place regardless of the supply fan status
(it is expected to be used/ needed mostly in situations when
the supply fan is not running). A Hot Water Coil Freeze Alarm
is generated. The alarm is written to the Error History Buffer.
In networked applications, the alarm flag is readable by the
network.
After the valve override sequence described above is com-
pleted, the valve will revert to normal operation and the alarm
is automatically reset. The same sequence is repeated every
time the Hot Water Coil Freeze Switch opens (infinite retries).
CV OPERATION
The paragraphs below identify control modes of CV operation
and provide an overview of control methods in all modes. The
modes include Occupied and Unoccupied Heating and Cool-
ing, and differ depending on the method used to control zone
temperature (thermostat, or a space sensor). The heating vs.
cooling modes are entered under control of the thermostat,
or, in case of space sensor, control algorithm detecting zone
cooling or heating demand. The "occupied" vs. "unoccupied"
modes are controlled by an internal time clock. If a thermostat
is connected in addition to the space sensor, it takes priority
over the space sensor.
THERMOSTAT OPERATION FOR COOLING WITH
Y1, Y2, Y3 AND Y4 INPUTS
When connected to a thermostat, the Millennium Simplicity
control will apply internal rules to specific G, Y1, W1, etc.,
requests for fan, cooling, or heating; other inputs such as
SAT, economizer availability, etc., will be considered before
acting on the thermostat request.
When stage outputs are de-energized, and when the four
time delay settings in "Fan ON Delay for Heat, OFF for heat,
ON for Cooling, and OFF for Cooling" are made, the Fan out-
put will continue for the set time even if the G input becomes
inactive along with Y1 and Y2. If G does not terminate, the
controller will continue to operate the Fan.
A Minimum Run Time of up to ten minutes applies to all com-
pressors. There is a built-in five-minute ASCD cycle when-
ever a compressor is destaged. The minimum run time is
necessary to ensure that the oil in the refrigerant circuit circu-
lates back to the compressor. A minimum ASCD delay of five
minutes (nominal) applies any time compressor operation is