JOHNSON CONTROLS
83
SECTION 5 – SEQUENCE OF OPERATION
FORM 100.50-NOM12
ISSUE DATE: 04/02/2019
5
3. Ready: The HGRH status is ready when one or
more of the following requirements is met.
• The unit is running in an Active Cooling mode
• The OAT is equal to/greater than 55.0°F
• Dehumidification is required
• The supply air dewpoint active setpoint is
less than/equal to the HGRH SAT active
setpoint minus 5.0°F
• At least 3 minutes has elapsed since the
HGRH status was last active
• No Active HGRH Faults exist
4. Active: The HGRH status is active when all of the
following requirements are met.
• All requirements under Ready have been met
• At least one compressor from system 2 is
running for at least 5 minutes
• No Active HGRH Faults exist
5. Faulted: The HGRH status is faulted when the fol-
lowing requirement is met.
• The IPU board determines that a HGRH
Fault has occured
HGRH Sequence of Operation
• When there is a HGRH system is installed in a unit
and dehumidification control is User Enabled, the
IPU board monitors several different values to de-
termine when dehumidification is needed.
• The IPU board monitors the relative humidity of
the return air and the dewpoint of the supply air.
The dewpoint of the supply air is a calculated val-
ue based on the SAT and the supply air humidity.
• The active supply air dewpoint setpoint is be-
tween the supply air dewpoint high and low set-
points that are based on the return air relative
humidity for high supply air dewpoint and return
air relative humidity for low supply air dewpoint
setpoints. (
• The IPU board continuously compares the active
supply air dewpoint setpoint to the active HGRH
SAT setpoint.
• The active HGRH SAT setpoint is a calculated
value between the HGRH SAT high and low set-
points based on the current RAT and the HGRH
)
EVAP AIR TEMP
HIGH SETPOINT
Return Air-Humidity
Active
Increasing RARH
EVAP AIR TEMP
EVAP AIR TEMP
LOW SETPOINT
LOW RARH
SETPOINT
HIGH RARH
SETPOINT
Active Setpoint
LD20881
FIGURE 41 -
EVAPORATOR AIR TEMPERATURE
ACTIVE SETPOINT VS RETURN AIR HUMIDITY
HGRH SAT
LOW SETPOINT
HGRH SAT
HIGH SETPOINT
Return Air
Temperature (RAT)
HGRH SAT
Active
Setpoint
~RAT COOLING
SETPOINT-2.0°F
Increasing RAT
~RAT COOLING
SETPOINT-1.0°F
LD21611
FIGURE 42 -
HGRH SAT ACTIVE SETPOINT VS
RETURN AIR TEMPERATURE
• When the active supply air dewpoint setpoint
drops 5.0°F or more below the active HGRH SAT
setpoint, the HGRH system becomes either ready
or active depending on the HGRH status require-
ments.
• Once HGRH goes active, the HGRH 3-way step-
per valve modulates between the minimum (25%)
and maximum (95%) values, controlling the flow
of refrigerant between the HGRH coil and the
condenser coil.
• The HGRH 3-way stepper valve is controlled to
maintain the active HGRH SAT setpoint.
• The HGRH bleed solenoid is closed whenever
HGRH is active.
•
When the demand for dehumidification is satis
-
fied or the unit exits an Active Cooling mode, the
HGRH 3-way stepper valve closes off refrigerant
flow to the HGRH coil, and after a 5 minute time
delay the HGRH bleed solenoid opens.
