JOHNSON CONTROLS
132
FORM 145.05-NOM7
ISSUE DATE: 10/31/2019
SECTION 5 – SEQUENCE OF OPERATION
No Compressors ON When Economizer
Becomes Active
Compressors are turned ON based on the “NEXT
STAGE TO ENABLE” when all the following are sat-
isfied:
• 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 Interstage Delay Timer has expired
Compressors are turned OFF based on the “NEXT
STAGE TO DISABLE” when all the following are sat-
isfied:
• 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 Interstage Delay Timer has expired
Compressor ON When Economizer
Becomes Active
One compressor is staged OFF and the sequence out-
lined in the section
mizer Becomes Active on page 132
ia followed.
Supply Air Tempering
This operation only comes into act in the VENTILA-
TION mode if the unit has a factory installed Airside
Economizer installed with outside air connected to it.
In some installations, the ventilation requirements
combined with low outdoor temperature can result in
the Supply Air Temperature dropping below the “SUP-
PLY AIR TEMP ACTIVE SP,” resulting in an over
cooling of the space. Supply Air Tempering uses the
unit's heating source to raise the Supply Air Tempera-
ture to an acceptable level.
For Supply Air Tempering to be active, the following
items must be programmed into the Unit Controller.
Under the PROGRAM key, HEATING subsection,
“HEATING SYSTEM” must be set to USER EN-
ABLE. Under the PROGRAM key, COOLING subsec-
tion, “SUP AIR TEMPERING” must be set to USER
ENABLE.
The Supply Air Tempering logic varies depending on
the type of heat installed in the unit. A description of
each of the operating logics follows.
Operation In Supply Air Tempering with
Hot Water and Steam Heat
To enable Supply Air Tempering, the following condi-
tions must be met:
Operating Conditions
• For CV and VAV units, the SUPPLY AIR TEMP
must be less than or equal to the “SUPPLY AIR
TEMP ACTIVE SP” minus 2.5°F for 5 minutes
FlexSys operation is mentioned below,
but for further examples go to FlexSys
• For FlexSys without Bypass, the MX SUPPLY
AIR TEMP must be less than or equal to the “MX
SUPPLY AIR TEMP SETPOINT” minus 2.5°F
for 5 minutes
• For FlexSys with Bypass, the RETURN AIR BY-
PASS CURRENT must be greater than or equal to
the MAXIMUM BYPASS minus 5%
• Economizer Output must be less than or equal to
5%
• Compressor operation must have been OFF for 10
minutes
On modulating hot water and steam, the following cri-
teria must be met to terminate the Supply Air Temper-
ing:
Operating Conditions
• For CV and VAV units, the SUPPLY AIR TEMP
must be greater than or equal to the “SUPPLY
AIR TEMP ACTIVE SP” for 5 minutes
• For FlexSys with or without Bypass, the SUPPLY
AIR TEMP must be greater than or equal to the
MX SUPPLY AIR TEMP for 5 minutes
• The “HW / STEAM – VALVE POS” must be less
than or equal to 2%
