Johnson Controls 40 25 TON, Installation Operation & Maintenance

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JOHNSON CONTROLS
5276178-JIM-C-0118
5
FlexSys
A FlexSys unit is a modified VAV system. In a FlexSys
system the supply air from the unit is distributed
through an underfloor air distribution system. In order
to temper the air a by-pass duct between the unit return
and supply duct is installed in the curb, and return air
is used to temper the supply air. A damper is installed
in the by-pass duct in order to control the amount of
by-pass return air.
There are two different occupied cooling modes when
a unit is configured for FlexSys operation, OCCUPIED
COOLING without BYPASS and OCCUPIED
COOLING with BYPASS. The Unit Control monitors
the return air temperature and compares it to the “MX
SUPPLY AIR TEMP SETPOINT” plus the “RETURN
AIR DIFF SP” . The “ RETURN AIR DIFF SP” can be
set between 2.0 and 10.0°F through the SETPOINTS
key, COOLING subsection of the User Interface. If
the return air temperature is equal to or greater than
the “RAT COOLING SETPOINT” plus 0.5°F but less
than the “MX SUPPLY AIR TEMP SETPOINT” plus
the
“RETURN AIR DIFF SP”
the unit will operate in
the COOLING without BYPASS mode. If the return
air temperature is equal to or greater than the “RAT
COOLING SET POINT” plus 0.5°F but equal to or
greater than the “MX SUPPLY AIR TEMP SETPOINT”
plus the
“RETURN AIR DIFF SP”
the unit will operate
in the COOLING with BYPASS mode.
When the unit is in the OCCUPIED COOLING without
BYPASS mode the compressors are controlled to
maintain the “MX SUPPLY AIR TEMP SETPOINT” .
When the unit is in the OCCUPIED COOLING with
BYPASS mode the compressors are controlled to
maintain the “EVAP LEAVING AIR TEMP HIGH” or
“EVAP LEAVING AIR TEMP LOW” set points. The
“EVAP LEAVING AIR TEMP HIGH” and “EVAP
LEAVING AIR TEMP LOW”
set points are set through
the SET POINT key, COOLING subsection of the User
Interface.
ACTIVE SET POINT DETERMINATION
Constant Volume
On a Constant Volume unit the Control Method (Staged
or Zone) does not have a direct effect on the control of
the compressor and heating stages. Instead the input
from the Staged (usually a thermostat) or Zone (hard
wired or communicated) is only used to determine the
“UNIT MODE”
. The staging of the compressor and
heating stages is always based on the
“SUPPLY AIR
TEMP ACTIVE SP” .
Staged Input Control
When the “CONTROL METHOD” is set to “STAGED” ,
the
“SUPPLY AIR TEMP ACTIVE SP”
is determined
by the “1ST STAGE COOLING SETPOINT”, “2ND
STAGE COOLING SETPOINT”, “1ST STAGE
HEATING SETPOINT” , and “2ND STAGE HEATING
SETPOINT” inputs. Table 60 shows what the setpoints
would be for each staged input combination.
Y1
LOW
COOL
Y2
HIGH
COOL
W1
LOW
HEAT
W2
HIGH
HEAT
OCC.
MODE
UNIT MODE ACTIVE SP
ON OFF OFF OFF OCCUPIED OCCUPIED COOLING LOW 1ST STAGE COOLING SETPOINT
ON/
OFF
ON OFF OFF OCCUPIED OCCUPIED COOLING HIGH 2ND STAGE COOLING SETPOINT
OFF OFF ON OFF OCCUPIED OCCUPIED HEATING LOW 1ST STAGE HEATING SETPOINT
OFF OFF ON/OFF ON OCCUPIED OCCUPIED HEATING HIGH 2ND STAGE HEATING SETPOINT
OFF OFF OFF OFF OCCUPIED
OCCUPIED STANDBY (SEE
ALSO COMFORT VENTILATION
OPERATION)
NONE
ON OFF OFF OFF UNOCCUPIED UNOCCUPIED COOLING LOW 1ST STAGE COOLING SETPOINT
ON/
OFF
ON OFF OFF UNOCCUPIED UNOCCUPIED COOLING HIGH 2ND STAGE COOLING SETPOINT
OFF OFF ON OFF UNOCCUPIED UNOCCUPIED HEATING LOW 1ST STAGE HEATING SETPOINT
OFF OFF ON/OFF ON UNOCCUPIED UNOCCUPIED HEATING HIGH 2ND STAGE HEATING SETPOINT
OFF OFF OFF OFF UNOCCUPIED UNOCCUPIED STANDBY NONE
TABLE 69
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ACTIVE SAT SET POINT DETERMINATION, STAGED INPUT