Head Pressure Control; Description; Sequence Of Operation - For Head Pressure Control; Intelli-Start - York MILLENNIUM Y22 Installation Manual

102777-YIM-E-0206
NOTE: For smoke purge, etc., special connections: for
standard controls, consult a controls specialist
familiar with your local codes.
All power exhaust options require that the cus-
tomer provide tubing connections to the trans-
ducer from a representative location in the
building; modulating-vane and VFD exhausts will
open full / power on in Purge mode

HEAD PRESSURE CONTROL

DESCRIPTION

The head pressure control option controls the speed of con-
denser fan 1 for low ambient mechanical cooling operation of
systems 1 and 2. This option functions independently of the
Simplicity control.
The option includes two pressure transducers and a variable
frequency drive. The pressure transducers are connected to
the discharge line of system 1 and 2. The VFD modulates to
the higher signal; if either system 1 or 2 exceeds 280 psi, a
secondary mechanical switch close to turn on fan 2. Typically
the modulated fan will slow down; if both systems drop below
180 psi, fan 2 drops out.
System 3 on a 30 ton and system 3 and 4 on a 40 ton are
°
locked out below 45 F ambient.
NOTE: Altering the factory settings could result in poor con-
trol or operation of the system.
No special motor is required on three-phase systems; single
phase systems will use three phase motors on fan 1. The
variable Frequency Drive is pre programmed at the factory.
SEQUENCE OF OPERATION - FOR HEAD PRES-
SURE CONTROL
A call for the first stage cooling powers the 6M contactor
energizing the variable frequency drive. The drive will ramp to
the pre programmed minimum speed of 20 Hertz immediately
upon start up. As the discharge pressure on system 1 or 2
compressor rises, the transducer output signal to the variable
frequency drive rises. The drive will increase the speed of
condenser 1 fan, maintaining a setpoint of 240 PSI.
The scroll compressor produces a rapid rise in discharge
pressure upon start up. This usually will result in full speed
operation of condenser fan 1. After the discharge pressure
has settled out, the speed of condenser 1 may decrease
especially during times when the ambient temperature is
°
below 80 F. After the 1 system has stabilized and compressor
Unitary Products Group
2 is energized, the speed of condenser Fan 1 will increase to
compensate for the discharge pressure rise. Typically, since
fan 2 will run at full speed, fan 1 will slow down when fan 2
energizes.
As the ambient temperature drips below 40
denser fan will slow to the minimum speed. The circuit 2 con-
denser fan will disengage when the discharge pressure drops
below 180 PSIG as the ambient temperature falls. The dis-
charge pressure of system 1 and/or 2 will increase when con-
denser fan 2 stops, consequently causing an increase in the
speed of condenser fan 1.
The Millennium Simplicity control includes a terminal SD for
the user to wire a signal to shut down, and a Purge terminal
to signal the unit to shut off heat or mechanical cooling, open
the economizer and exhaust dampers, and run the exhaust
fan [depending on which options are installed on the unit].

INTELLI-START

If Intelli-Start is enabled the control will use that calculation to
determine when to start Morning Warm-Up. If the Intelli-Start
option is not enabled, the control will start Morning Warm-Up
one hour before Occupancy.
When Intelli-Start is enabled, the control will attempt to
recover the building to the Occupied Setpoint by the time the
Occupied period begins. On the first day when the control
has nothing stored for recovery, it will go "Occupied" two
hours before the Occupied period. The control will store the
beginning demand and track the time it takes to reach the
Occupied Setpoint. When the Occupied setpoint is reached,
the control will store how long it took, and use that warm-up
ability to calculate the period needed the next time it runs.
The control will store the recovery value separately for Heat-
ing and Cooling. Unoccupied Recovery will only run on the
first Occupied period of the day. It will always be operating on
the previous day's performance. The Economizer will be
used if free cooling is available.
Millennium Simplicity will accommodate inputs for water coil
freeze stat, SA sensor, ODA sensor, Space sensor, and
Room sensor, Building pressure sensor, Duct pressure sen-
sor, Demand ventilation, RA humidity, OD humidity, RS485
communications.

LEAD LAG

When this option is set ON, the unit will equalize run time on
compressors [except for compressor 1 if the head pressure
control option or hot gas bypass is installed].

DEVICES AND RULES

This chapter describes the many control modes of operation
for Simplicity. Because of the narrative and detailed descrip-
tions contained in this section, you should only scan this
chapter and become familiar with the primary topics. Then,
°
F the 1 con-
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