JOHNSON CONTROLS
140
FORM 145.05-NOM7
ISSUE DATE: 10/31/2019
SECTION 5 – SEQUENCE OF OPERATION
Occ Cooling w/ Bypass
If the RAT ≥ RAT SP plus 0.5°F, AND, RAT > MX
SAT SP + the RA Diff SP (user adjustable between
2.0–10.0°F)
The unit controller cycles the compressors to maintain
either the EVAP LEAVING AIR TEMP HIGH SP or
the EVAP LEAVING AIR TEMP LOW SP.
The unit controller modulates the FlexSys Bypass
Damper open/closed to achieve and maintain the MX
SAT SP.
Evap Leaving Air Temp High SP:
• R/A Humidity sensor is not reliable
OR
• R/A Enthalpy < the RESET ENTHALPY SP
Evap Leaving Air Temp Low SP:
•
R/A Enthalpy is ≥ RESET ENTHALPY SP
OR
•
Underfloor Slab Dewpoint is ≥ Underfloor Slab
Temp – 2.0°F for 120 seconds (only if Dew Point
Reset is USER ENABLED)
Return Air Bypass
Current %:
This is the amount of air the unit thinks
it is bypassing due to the fact that the MX SAT is not
increasing. The unit controller utilizes the current RAT,
the Current Evap Leaving Air Temp, and the MX SAT
to perform a calculation to arrive at the Current %.
Active SP %:
This is how much of the return air the
unit thinks it needs to bypass to warm the MX SAT
from its current value to the MX SAT SP. The unit con-
troller utilizes the current RAT, the current Evap Leav-
ing Air Temp, and the current MX SAT to perform a
calculation to arrive at the Active SP %.
Both of the above numbers are based on internal algo-
rithms and logic built into the Unit Controller. These
algorithms and internal logic are not user adjustable.
Bypass Damper Position:
This is the actual position
of the bypass damper. The bypass damper should be
able to drive between 0% and 100%.
Bypass Damper Operation:
The operation of the by-
pass damper is slow, and the logic that drives the damp-
er is quite complicated. When the unit is in normal op-
eration, it could take up to 40 minutes for the bypass
damper to go from 0% to 100%. If the unit is operating
properly and the temperatures are in the proper range,
the damper probably never drives to 100%.
Unoccupied
UNOCCUPIED COOLING mode is initiated by the
Current Zone Temp being higher than the UNOCCU-
PIED ZONE COOLING SP by 0.5°F. The “NIGHT
SET BACK” feature must be USER ENABLED.
“NIGHT SET BACK” can be found under the HEAT-
ING menu.
1. Supply fan starts. Supply fan VFD is controlled to
the ACTIVE DUCT STATIC SP
2. O/A damper is modulated open/closed to achieve
and maintain the MX SAT SP
AND/OR
3. Compressors are cycled on/off to achieve and
maintain the MX SAT SP
a. Bypass damper remains closed
b. Cooling operation continues until the Current
Zone Temp is less than the UNOCC ZONE
COOLING SP by 0.5°F
FlexSys: Compressor Control
Occupied Cooling w/o Bypass
1. Unit enters an active COOLING mode
2. Unit Controller sets the “COOLING CONTROL
OFFSET” to 2.0°F
3. Unit Controller compares the current MX SAT to
the MX SAT SP plus or minus the “COOLING
CONTROL OFFSET”
4. If MX SAT is greater than the MX SAT SP plus
the “COOLING CONTROL OFFSET,” the Unit
Controller:
a. Starts a compressor
OR
b. Commences an additional stage of cooling
based on the “NEXT STAGE TO ENABLE”