351579-YTS-B-0608
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Johnson Controls Unitary Products
Single Enthalpy:
the control will consider, along with
outside temperature, outside air humidity [OAH sensor;
parameter must be set to ON] in enabling free cooling.
The outside air enthalpy setpoint parameter [BTU per
pound] must also be set.
Dual Enthalpy (Comparative/Differential Enthalpy):
Both the Outdoor Air Enthalpy and the Return Air
Enthalpy [RAH sensor, option parameter must be set to
ON] are connected to the control. The setpoint when the
outdoor air enthalpy is less than the return air enthalpy,
free cooling is available. The rules in the control will lock
out free cooling and force mechanical cooling when the
outside air temperature exceeds setpoints.
19.
Power Exhaust Option with Modulating Dampers:
The
power exhaust controls are enabled in Occupied mode. The
building pressure sensor [BSP] provides a signal to the con-
trol. The exhaust dampers are modulated by a 2-10VDC sig-
nal from the control, proportional to the pressure sensed, to
the damper actuator. When the actuator opens the damper
more than the parameter “Exhaust Damper Position for
Exhaust Fan to Turn ON” setting, the
Simplicity
®
control
powers the 10M starter to engage the power exhaust fan
motor. When the dampers reach the ”Exhaust Damper Posi-
tion for Exhaust Fan to Turn OFF” setting, the control turns
the motor off. When the power exhaust is disabled, the con-
trol closes the exhaust dampers.
20.
Non-Modulating Power Exhaust Option:
The power
exhaust controls are enabled by the
Simplicity
®
control.
The control powers the exhaust fan motor by monitoring
the position of the economizer damper vanes [“Economizer
Damper Setting for Exhaust Fan to Turn ON [OFF]”]. The
outlet pressure of the power exhaust fan forces the baro-
metric relief dampers open. Exhaust Fan operation is con-
tinued until the economizer reaches the % set in the
parameter Gravity closes the barometric relief dampers
when the exhaust fans are off.
21.
Power Exhaust Option with Variable Frequency Drive
(VFD):
The power exhaust controls are enabled through
the
Simplicity
®
control. The variable frequency drive is con-
trolled by a signal from the control, based on the Building
Pressure sensor (BPS), located in the control box, which
translates the building pressure signal to a VDC signal.
Fine tuning is accomplished by setting parameters in the
VFD [ref: separate instruction].
NOTE:
Modulated exhaust: Pressure-tap tubing must be run
from an appropriate location in the building to the
"high" port on the BPS transducer. Dampers on the
VFD power exhaust are gravity-closed and are not
modulated. The BPS signal is proportional with the dif-
ference between outside ambient pressure and build-
ing pressure. The VFD is set for a minimum speed of
33% and a maximum of 100%. The VFD parameters
are factory set, specific for each control system, and
are detailed on a sticker by the drive. The drive man-
ual is shipped with the unit.
NOTE:
For smoke purge, etc., special connections: for stan-
dard controls, consult a controls specialist familiar with
your local codes.
HEAD PRESSURE CONTROL, R22 (R410A)
DESCRIPTION
The head pressure control option controls the speed of
condenser 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 R22 (360
psi for R410a), 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 R22 and system 3 and 4 on a 40 ton R22
(and all R410a units) are locked out below 45°F ambient.
NOTE:
Altering the factory settings could result in poor control
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 PRESSURE
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 R22 (325 psi
R410a).
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 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.
All power exhaust options require that the customer
provide tubing connections to the transducer from a
representative location in the building; modulating-
vane and VFD exhausts will open full / power on in
Purge mode.
