JOHNSON CONTROLS
29
SECTION 11 - SERIES 100: FLEXSYS OPERATION
FORM 100.50-SU8
ISSUE DATE:1/28/2016
11
The following sections deal with the operation of a Se-
ries 100 unit configured for Flexsys operation. Flexsys
operation is the use of an underfloor plenum to provide
conditioned air to a building. Since the conditioned
air is delivered up from the floor, the operation differs
from that of a typical VAV system. Please review these
sections thoroughly before proceeding with unit set-
up, start-up, and operation.
The design of a Flexsys system is very critical to the
proper operation of the Series 100 unit. Please review
the following areas that create issues with the proper
operation of a Flexsys system/unit.
1. Plenum Integrity: “If you make a hole, seal a
hole.”Theunderoorplenummustbecompletely
sealed from air leaking out.
2. Open plenum returns: It is highly recommended
that returns be ducted to every room. This allows
the warmer return air to properly mix and be at the
proper temperature returning to the unit.
3. Six foot cooling zone: When designing a Flexsys
system,onlytherst6feetfromtheoorupisto
be conditioned. Above 6 feet, the air needs to be
mixed with heat loads. This will ensure that the
R/A is at least 78.0 °F. It is has been determined
that RATs cooler than 78.0 °F cannot properly
raise the temperature of the air leaving the evap
coil to the recommended Mixed SAT (MX SAT) of
62.0–64.0 °F. It has been determined than MX
SAT’s lower than 62.0 °F are uncomfortable to
occupants of a space.
4. Multiple Plenums/One Unit: When designing
a system that will serve multiple plenums, it is
highly recommended that each plenum have its
own volume damper controlled by an actuator.
Each plenum should also have its own pressure
transducer that controls the actuator driven vol-
ume damper. Each plenum should be maintained
at 0.05 ”WC.
The above issues should have been taken into consid-
eration during the design and engineering phase of the
project.
Since a Flexsys unit delivers air through an underfloor
plenum, some of the SPs differ from a typical VAV
unit. Below are recommended SP’s provided by the
engineering team. There has been a lot of testing and
research done on these systems to arrive at these SPs.
Please be advised that these are recommendations only,
and job specific SPs could be different. We recommend
using these SPs at least as a starting point.
Factory Recommended Setpoints:
• RAT Cooling SP: 78.0 °F
• MX SAT SP: 62.0–64.0 °F (see note)
• Evap Leaving Air Temp High SP: 58.0 °F
• Evap Leaving Air Temp Low SP: 55.0 °F
• Duct Static SP: 0.05 ”WC
• Heating SAT SP: 80.0 °F
• Max Bypass: 40%
On a Flexsys unit, the MX SAT is the tem-
perature of the supply air off the evapora-
tor coil mixed with the warmer return air
that is bypassed around the evaporator
coil. The bypassed return air is introduced
directly under the supply air fan.
FLEXSYS: CURRENT OPERATING MODE
(OCCUPIED)
The current operating mode for a Flexsys configured
unit will be decided the same as for a VAV configured
unit by the Return Air temperature (RAT).
• IftheRATis≥theCoolingRATSPby0.5°F, the
unit will enter the Cooling mode.
• IftheRAT≤theHeatingRATSPby0.5°F, the
unit will enter the Heating mode.
• If the RAT is between the Cooling RAT SP and
the Heating RAT SP, the unit will remain in the
Standby mode.
FLEXSYS: FAN OPERATION
The same as a VAV configured unit, the supply fan
will be controlled by a VFD. The VFD will control the
speed of the supply fan up/down to achieve and main-
tain the Active Duct Static SP.
The same as a VAV configured unit, the supply fan will
be on whenever the unit is in the Occupied Mode and
will cycle on/off in the Unoccupied Mode with a de-
mand for heating or cooling.
SECTION 11 - SERIES 100: FLEXSYS OPERATION
To Next Page
Loading...
Need help?
General
