134
JOHNSON CONTROLS
5276178-JIM-C-0118
Sequence of Operation
“FLEX EVAP TEMP CURRENT”
to the
“FLEX EVAP
TEMP ACTIVE SP”
plus or minus the
“COOLING
CONTROL OFFSET”.
If the
“FLEX EVAP TEMP
CURRENT”
temperature is greater than the
“FLEX
EVAP TEMP ACTIVE SP”
plus the
“COOLING
CONTROL OFFSET”
and all the compressors are not
ON the Unit Controller will initiate a call for compressor
or additional compressor operation based on the
“NEXT
STAGE TO ENABLE”
.
If the
“FLEX EVAP TEMP CURRENT”
temperature
is less than the
“FLEX EVAP TEMP ACTIVE SP”
minus the
“COOLING CONTROL OFFSET”
and all
the compressors are not OFF the Unit Controller will
turn a compressor OFF based on the
“NEXT STAGE
TO DISABLE”
.
When the Unit Controller turns a compressor ON or
OFF, it records the SAT temperature just prior to the
time the compressor is started or stopped. After the
3-1/2 minute Interstage Delay Timer has expired the
Unit Controller records the SAT temperature again.
The Unit Controller then calculates the change in the
SAT temperature SAT
(CH).
The Unit Controller uses the
SAT
(CH)
and FORMUA 1 to calculate a new
“COOLING
CONTROL OFFSET”
if either of the following
conditions are met:
•
When a compressor is turned OFF and 3-1/2
minutes later the SAT temperature is greater than
the
“ACTIVE SAT SETPOINT”
plus the current
“COOLING CONTROL OFFSET”.
•
When a compressor is turned on and 3-1/2 min-
utes later the SAT temperature is less than the
“ACTIVE SAT SETPOINT”
minus the current
“COOLING CONTROL OFFSET”.
“
COOLING CONTROL OFFSET”
=
SAT (change) + 1°F
2
FORMULA 1
If a new
“COOLING CONTROL OFFSET”
is
calculated, it is rounded up to the next half degree.
After a
“COOLING CONTROL OFFSET”
calculation is
made the Unit Controller initiates a 45 minute Cooling
Control Offset Timer. If no compressor is turned ON
or OFF before the Cooling Control Offset Timer has
expired, the
“COOLING CONTROL OFFSET”
will
be reset to 2.0°F
.
COMPRESSOR OPERATION WITH
ECONOMIZER
If the economizer is suitable, the Unit Controller will set
the
“COOLING CONTROL OFFSET”
to 4.5°F. As long
as the economizer remains active, the Unit Controller
will not recalculate the
“COOLING CONTROL
OFFSET”
and it will remain at the 4.5°F setting.
No Compressors On When Economizer
Becomes Active
Compressors will be turned ON, based on the
“NEXT
STAGE TO ENABLE”
, when all the following are
satisfied:
•
The
“ECONOMIZER CONTROL OUTPUT”
to the economizer must be greater than 95% for
30 seconds. This value can be viewed under the
ECONOMIZER key of the User Interface.
•
The
“SUPPLY AIR TEMP CURRENT”
must be
greater than or equal to the
“SUPPLY AIR TEMP
ACTIVE SP”
plus the
“COOLING CONTROL
OFFSET”
(4.5°F).
•
The Inter-Staged Delay Timer has expired.
Compressors will be turned OFF, based on the
“NEXT
STAGE TO DISABLE”,
when all the following are
satisfied:
•
The
“ECONOMIZER CONTROL OUTPUT”
to
the economizer is less than 5% for 30 seconds.
•
The
“SUPPLY AIR TEMP CURRENT”
must be
less than or equal to the
“SUPPLY AIR TEMP
ACTIVE SP”
minus the
“COOLING CONTROL
OFFSET”
(4.5°F).
•
The Inter-Staged Delay Timer has expired.
Compressor On When Economizer Becomes
Active
One compressor will be staged OFF and then the
sequenced outlined above will be followed.
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