JOHNSON CONTROLS
123
SECTION 5 – SEQUENCE OF OPERATION
FORM 145.05-NOM7
ISSUE DATE: 10/31/2019
5
factory set to 400 PSIG. The Unit Controller generates
a DISCHARGE PRESSURE MAXIMUM demand.
The Unit Controller uses the greater of the DIS-
CHARGE PRESSURE MINIMUM and the DIS-
CHARGE PRESSURE MAXIMUM demands for the
control of the condenser water valve.
WATERSIDE OR AIR ECONOMIZER
OPERATION
The function of the economizer is, as its name implies,
to "economize" or save on cooling costs. Obviously,
it costs money to operate the compressor. If the com-
pressor is shut down and the system can still provide
adequate cooling, energy savings occur.
The unit decides when to use the ECONOMIZER func-
tion based on parameters and setpoints entered either
through the Unit Interface or communicated through
a BAS.
The economizer is used in COOLING mode only. When
the UNIT MODE switches to OCCUPIED COOLING
or UNOCCUPIED COOLING and the conditions are
met within the programmed guidelines for economizer
operation, the Unit Controller attempts to use outdoor
air or the building's cooling water to lower the Supply
Air Temperature to the “ACTIVE SAT SETPOINT.”
When the unit has an AIR ECONOMIZER, the colder
outside air is drawn in through a factory provided set
of dampers, and the return is usually exhausted outside
since bringing more air in from the outside over pres-
surizes a building.
Operation of AIR ECONOMIZER is described in the
section Air Economizer Operation on page 130.
When the unit has a WATERSIDE ECONOMIZER,
the water that is used for the water-cooled condenser
barrel in the unit is cold enough; the condenser water
is circulated through the factory water coil for cooling,
and this cools the ducted air to the space.
Economizer
The following parameters must be programmed into
the Unit Controller through the User Interface to en-
able economizer operation:
• OPTIONS key, ECONOMIZER subsection:
“ECONO INSTALLED” and the choices are
NONE, DRYBULB, SINGLE ENTHALPY,
DUAL ENTHALPY, and WATERSIDE
• PROGRAM key, ECONOMIZER subsection:
“ECONO METHOD TO USE” and the choices are
DRYBULB, SINGLE ENTHALPY, DUAL EN-
THALPY, BEST AVAILABLE, and WATERSIDE
• SETPOINTS key, ECONOMIZER subsection “WA-
TER ECONO MIN POSITION” (default is 15%)
“WATER ECONO DELTA” (default is 5.0°F)
“OUTSIDE AIR ENTHALPY SETPOINT” for
an air economizer
Condenser and Water Economizer Valve
Under this mode of operation, the unit has an actuator
driven water valve that controls the flow of condenser
water through the water condenser and an economizer
water valve controlling a factory installed water econ-
omizer coil. The options tag on the front of the unit
shows this option if it was ordered with the unit, or
a factory order form (FOF) is obtained from the local
Johnson Controls agent or branch.
Once the “ECONO SYS STATUS” is “NORMAL -
ACTIVE,” the Unit Controller uses the “ECONOMIZ-
ER CONTROL OUTPUT” to control the return and
outdoor damper or water economizer valve to maintain
the “SUPPLY AIR TEMP ACTIVE SP.”
All waterside economizers have a fac-
tory installed freezestat that must be set
as ENABLED under the OPTIONS key,
UNIT DATA subsection. See Freezestat
Operation on page 135.
WATER-COOLED
CONDENSER
WATER
SUPPLY
WATER
RETURN
ECONOMIZER VALVE vs. COND WATER VALVE
CONDENSER
VALVE
M
ECONOMIZER
VALVE
M
WATERSIDE
ECONOMIZER
LD21635
FIGURE 77 - CONDENSER AND WATER ECONOMIZER VALVE OPERATION AND PIPING DIAGRAM
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