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138
JOHNSON CONTROLS
5276178-JIM-C-0118
Sequence of Operation
CONDENSER FAN OPERATION
On the 25, 30, and 40 ton units as soon as compressor
1 or 2 come ON condenser contactor 6M is energized
and condenser fan number 1 is turned ON. The circuit
to condenser fan number 2 is also energized but the
operation of the condenser fan is controlled through
pressure switches PS5 in the compressor 1 discharge
line and PS6 in the compressor 2 discharge line. If the
high side pressure for ether compressor 1 or compressor
2 gets above 295 PSIG condenser contactor 7M is
energized and condenser fan number 2 is turned ON.
On the 25 and 30 ton unit as soon as compressor number
3 or 4 is turned ON, condenser fan contactors 8M and
9M are energized and condenser fans number 3 and 4
are turned ON.
On the 40 ton unit, as compressor 3 or 4 come on
condenser contactor 8M is energized and condenser
fan number 3 is turned ON. The circuit to condenser
fan number 4 is also energized but the operation of the
condenser fan is controlled through pressure switches,
PS7 in the compressor 3 discharge line, and PS8 in the
compressor 4 discharge line. If the high side pressure
for either compressor 3 or compressor 4 gets above
295 PSIG, condenser contactor 9M is energized and
condenser fan number 4 is turned ON.
LOW AMBEINT CONDENSER FAN
OPERATION
The standard condenser fan arrangement will operate
down to an ambient temperature of 50°F. If mechanical
cooling is required below 50°F, the unit must be ordered
with the pressure transducer option as well as a VFD
(Variable Frequency Drive) for each refrigerant system
that is required to operate below 50°F. The speed of the
primary condenser fan will be controlled to maintain a
minimum discharge pressure of 270 PSIG.
ECONOMIZER
Economizer is used in cooling mode only. As soon as the
UNIT MODE switches to
“OCCUPIED COOLING”
or
“UNOCCUPIED COOLING”
and the conditions
are within the programmed guidelines for economizer
operation the Unit Controller will attempt to use outdoor
air to lower the supply air temperature to the
“ACTIVE
SAT SETPOINT”
. The following parameters must be
programmed into the Unit Controller through the User
Interface to enable economizer operation:
•
“ECONO METHOD TO USE”
–
OPTIONS key
/ ECONOMIZER subsection.
The choices are
“DRY BULB”
,
“SINGLE
ENTHALPY”
,
“DUAL ENTHALPY”
,
“BEST
AVAILABLE”
.
•
“OUTSIDE AIR ENTHALPY SETPOINT” –
SETPOINTS key / ECONOMIZER subsection.
•
“ECONO INSTALLED” –
OPTIONS key /
ECONOMIZER subsection.
The choices are
“NONE”
,
“DRYBULB”
,
“SIN-
GLE ENTHALPY”
,
“DUAL ENTHALPY”
.
Dry Bulb
When the
“ECONO METHOD TO USE”
is set to
“DRY BULB”
, the Unit Controller will reference
the
“OUTSIDE AIR TEMP”
only to determine the
“ECONO SYS STATUS”
.
The
“ECONO SYS STATUS”
will be NORMAL -
ACTIVE if all of the following conditions are met:
•
The
“OUTSIDE AIR TEMP”
is less than or equal
to the
“SUPPLY AIR TEMP ACTIVE SP”
plus
8°F.
•
The current
“UNIT MODE”
is OCC COOLING
or UNOC COOLING.
Once the
“ECONO SYS STATUS”
is NORMAL
–
ACTIVE, the
“ECONO SYS STATUS”
is set to
NORMAL - INACTIVE if any of the following are
met:
•
The
“OUTSIDE AIR TEMP”
is greater than or
equal to the
“SUPPLY AIR TEMP ACTIVE SP”
plus10°F.
•
The current
“UNIT MODE”
is not OCC COOL-
ING or UNOCC COOLING.
Single Enthalpy
When the
“ECONO METHOD TO USE”
is set to
“SINGLE ENTHALPY”
, the controller will reference
the
“OUTSIDE AIR TEMP”
and
“OUTSIDE AIR
ENTHALPY”
(derived from the
“OUTSIDE AIR TEMP”
and
“OUTSIDE AIR HUMIDITY”
) to determine the
“ECONO SYS STATUS”.
The
“ECONO SYS STATUS”
will be NORMAL
–
ACTIVE if all of the following conditions are met:
•
The
“OUTSIDE AIR TEMP”
is less than or equal
to the
“SUPPLY AIR TEMP ACTIVE SP”
plus
8°F.
Содержание 40 25 TON
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