351579-YTS-B-0608
Johnson Controls Unitary Products
27
As the ambient temperature dips below 40 °F the 1 condenser fan
will slow to the minimum speed. The circuit 2 condenser fan will
disengage when the discharge pressure drops below 180 psi R22
(300 psi R410a) as the ambient temperature falls. The discharge
pressure of system 1 and/or 2 will increase when condenser 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 Heating 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 sensor,
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 descriptions
contained in this section, you should only scan this chapter and
become familiar with the primary topics. Then, use this chapter
as a reference whenever a more detailed understanding of a
particular mode is needed.
You should keep in mind that, especially with digital controls,
interlocking between control modes is common and easily
achieved. Also, by the very nature of digital control
programming, many simultaneous rules can be implemented
because they generally require only software programming and
very little peripheral hardware. This reduces the costs
associated with manufacturing and servicing equipment with
this level of interacting features - but you can’t see the status of
interlocked rules as you can with discreet relays.
Several control modes will override other modes of operation.
For example, The Demand Ventilation (or, Indoor Air Quality)
control may override Comfort Ventilation / Economizer control
and drive the OA dampers above the established minimum
position. The Excessive SAT control will override all
temperature control modes, Economizer mode, and
compressor operation as well. If you suspect that a problem
exists with the economizer, or the compressors are locked out
when no alarms are set, verify that one of the control modes is
not overriding the normal mode of operation or the operation
you might expect to see. Another important example is the Air
Proving Switch interlocking mode. If the Air Proving Switch
alarms on a VAV unit, the unit will refer to the duct pressure
sensor; if duct pressure is present, the control will assume the
fan is working even though the APS is not.
If the fan status [APS] fails, and the duct pressure switch of a
VAV unit sees no duct pressure, all controlling algorithms and
operations, and outputs (except hydronic heat) will cease and
the control will shut down all outputs.
AIR PROVING SWITCH
When the control starts the supply fan, it waits 90 seconds to
check for closure of the Air Proving Switch (APS). If the APS
does not close, the control will turn off all outputs except Fan
and the VFD speed signal, flag an alarm, and flash an alarm on
the display. If it is a VAV unit, the control will look to the duct
pressure signal; if it is above .05”, the control will flag a bad
APS and continue operation.
It will retry the Fan output every 30 minutes for three retries. If
after three retries it still cannot qualify the Fan, it will Alarm and
lock all heating and cooling operation out. If the switch closes
after an alarm has been flagged, the control will resume normal
operation and clear the active alarm.
After the control has turned off the fan, it will wait 90 seconds
and verify that the switch opens. If the switch does not open
after 90 seconds, the control will flag a failed switch and flash
the alarm. On the next startup, the control will stage up
equipment normally.
This switch-closed failure mode of the Air Proving Switch can
only be detected with the Supply Fan off. It is important to
detect because it effectively disables the fan failure alarm
checking while fan is running, described in the paragraphs
above. Those checks would always pass as the switch would
remain closed. In networked applications, the error flag is
readable by the network. The alarm will automatically reset after
the problem that caused it has been corrected.
When the control is running the fan and the APS has already
been proven, and then it opens, the control will wait 2 seconds
before shutting down heating, cooling, and locking out. It will
alarm and retry as if it happened during start-up.
