IM 893-10 • ROOFPAK SINGLEZONE UNITS 76 www.DaikinApplied.com
u
nIT
o
PTIons
Dehumidification Initiation
An analog sensor is mounted in the return duct, the space, or
outdoors to sense Relative Humidity. The location is selected
by setting the Sensor Location value on the keypad to Return,
Space, or OAT. OAT can only be selected for units with DAT
control. Dehumidification is disabled when the unit is in either
the Heating or Minimum DAT state. When Dehumidification is
enabled, Dehumidification operation is initiated when Humidity
Control is set to either Relative Humidity or Dew Point and
that value rises above the appropriate setpoint by more than
half its deadband. Economizer operation is disabled in the
Dehumidification mode so the unit immediately transitions to
Cooling if Dehumidification is initiated in Economizer state.
Dehumidification Termination
Dehumidification is terminated if the selected variable, Relative
Humidity or Dew Point, drops below the appropriate humidity
setpoint by more than half its deadband. Dehumidification is
also terminated if cooling is disabled for any reason or the unit
enters either the Heating or Minimum DAT state. For units with
compressors, the number of cooling stages is reduced by one
and control reverts to normal control when dehumidification
is terminated in the Cooling state. Another compressor stage
change could then occur after one Cooling Stage Time has
elapsed.
Control & Arrangement
In conjunction with dehumidification, MHGRH is used to raise
the temperature of the cooled air to a desirable value. MHGRH
is comprised of a parallel coil arrangement, with both the
condenser and reheat coils of the micro channel type, dual
reheat valves (which operate in concert with one another) and
a check valve. MHGRH components will always be installed in
circuit #2.
During Dehumidification control w/ modulating Hot Gas
Reheat (MHGRH) an analog signal (0-10Vdc) is controlled as
described here.
• A PI Loop is used to control the HGRH valves to maintain
the Discharge Air Temperature from the reheat coil.
• Compressor staging during reheat (or dehumidification)
will be controlled by the Leaving DX Coil Temperature.
For increased dehumidification during reheat, the
standard default compressor staging range is 45 - 52°F.
• When dehumidification is active in the Cooling state, the
reheat set point equals the DAT Cooling Setpoint. For
DAT units, this is the normal DAT set point resulting from
any reset. For Zone Control units, this set point is the
result of a PI Loop based on the Control Temperature.
• Communication with the reheat control valves is
accomplished by providing a 0-10Vdc signal to a pair of
interface boards which in turn supply the control signal to
the reheat valves (step type).
• In the Fan Only state, no sensible cooling is required, but
the dehumidification mode will still be enabled if the dew
point or humidity sensor is not satisfied. In this case the
reheat set point varies from a maximum value (default
65°F) when the Control Temperature is at or below the
heating changeover setpoint to a minimum value (default
55°F) when the Control Temperature is at or above the
cooling changeover setpoint.
• Lead/Lag Arrangement w/ MHGRH (when applicable)
—
Alternate staging with circuit #1 as lead will be the
standard default arrangement.
—
During cooling mode, circuit #1 will lead and load up
before starting circuit #2.
—
During reheat mode, circuit #2 will lead and load up
before starting circuit #1.
—
For reheat operation, compressor(s) in circuit #2 must
be active. If the unit is operating in the cooling mode
when a call for dehumidification/reheat arises,circuit
#2 will become the lead and the controller will bring
on an additional stage of cooling for dehumidification.
If any compressors in circuit #1 are operating at this
moment they will be switched over to compressors
in circuit #2. Dehumidification operation is disabled if
circuit #2 is disabled for any reason.
• In the reheat mode, the minimum position for the reheat
valves is 10% (1.0 Vdc). The controller will modulate the
reheat valves from this starting position.
• Reheat valve(s) must be at 0% (0 Vdc) position before
starting the first compressor in the reheat circuit to
prevent pressure spikes.
• Upon termination of dehumidification (reheat), the
maximum ramp down or decay rate of the reheat control
valves shall be 1% per sec (or 0.1V per sec).
• Upon termination of dehumidification (reheat), staging
of compressor(s) is delayed for 1 minute after reheat
capacity = 0% (0Vdc).
• Every 24 hours, the reheat control valves will be driven to
their maximum position (10Vdc) and then returned to their
normal operating position (0Vdc). If unit is operating in
cooling or dehumidification (reheat) at the prescribed time
it will be deferred to the next time.
• Dehumidification status can now be found under the MTIII
main system menu. Reheat capacity (valve position)
can also be found under the main system menu, display
based on percentage (0-100%).
• A solenoid (SV6) and a check valve is provided to the
reheat refrigeration circuit. The solenoid is normally open
and removes refrigerant from the reheat portion of the
refrigerant circuit when Reheat is inactive. When Reheat
is active, the solenoid closes and isolates the reheat
portion of the refrigeration circuit. When the solenoid is in
the open position, it meters refrigerant flow and flushes
the refrigerant as it enters the suction line. This feature
reduces the amount of refrigerant needed for reheat up to
75%, compared to a flooded system arrangement.
Содержание RDT
Страница 60: ...IM 893 10 ROOFPAK SINGLEZONE UNITS 60 www DaikinApplied com Wiring Diagrams Figure 64 VFD Control SAF and RAF...
Страница 61: ...Wiring Diagrams www DaikinApplied com 61 IM 893 10 ROOFPAK SINGLEZONE UNITS Figure 65 VAV Control Inputs...
Страница 65: ...Wiring Diagrams www DaikinApplied com 65 IM 893 10 ROOFPAK SINGLEZONE UNITS Figure 67 Electric Heat Control...