Daikin MicroTech III Operation Manuals page 100

Constant Speed Wheel Frost Prevention Control
The enthalpy wheel is stopped when both of the following are
true:
• The enthalpy wheel has been ON for longer than the
edited Wheel Stage Time
• The exhaust air temperature leaving the enthalpy wheel
is below the Intersection Point plus an edited minimum
temperature difference .
• Defrost Method=ExhAir
• Enthalpy wheel is constant speed
The enthalpy wheel is turned back ON when the wheel has
been OFF due to Frosting/Condensation for longer than an
edited Minimum Off Time and the exhaust air temperature
leaving the enthalpy wheel is above the Intersection Point plus
an edited Maximum Temperature Difference .
Variable Speed Wheel Frost Prevention Control
The enthalpy wheel VFD speed is set to a minimum wheel
speed (default 5%) value when all of the following are true:
• The enthalpy wheel has been operating at maximum
speed for longer than the edited Wheel Stage Time
• The exhaust air temperature leaving the enthalpy wheel
is below the Intersection Point plus an edited Minimum
Temperature Difference .
• Enthalpy wheel is variable speed
To prevent Frosting/Condensation ON the enthalpy wheel, the
enthalpy wheel is turned OFF when both of the following are
true:
• The exhaust air temperature leaving the enthalpy wheel
is below the Intersection Point plus an edited Minimum
Temperature Difference .
• The wheel has been operating at the minimum wheel
speed for longer than an edited Wheel Stage Time
The enthalpy wheel is turned ON at minimum speed when both
of the following are true:
• The enthalpy wheel has been OFF due to Frosting/
Condensation for longer than an edited Minimum Off Time
• The exhaust air temperature leaving the enthalpy wheel
is above the Intersection Point plus an edited Maximum
Temperature Difference .
The Enthalpy Wheel speed will be increased to its maximum
speed when both of the following are true:
• The exhaust air temperature leaving the enthalpy wheel
is above the Intersection Point plus an edited Maximum
Temperature Difference (MaxExhTDiff)
• The wheel has been operating at the minimum speed for
longer than the edited Wheel Stage Time
OM 920-6 • MICROTECH UNIT CONTROLLER
Enthalpy Wheel Defrost Control (Constant Speed
Wheels Only)
In lieu of the frost prevention method described above, a
constant speed enthalpy wheel can be set for a simpler
timed defrost method of frost management . With this method
the enthalpy wheel is stopped periodically for a defrost time
duration when the outdoor air temperature is below an outdoor
frost temperature threshold setpoint .
Defrost operation becomes enabled when all of the following
are true:
• Defrost Method = Timed
• Energy wheel is constant speed
• OAT is less than the OA frost temperature setpoint .
• Normal wheel operation has the enthalpy wheel ON
When defrost operation is enabled, the wheel is stopped for the
Defrost Time (default 5 minutes) every Defrost Period (default
60 minutes) .
When the wheel is stopped due to defrost operation the wheel
must be slowly rotated so that both halves of the wheel are
allowed to be defrosted by the relative warm exhaust air
leaving the wheel . This is accomplished by alternately turning
the wheel off for the editable Defrost Off Time (default 24
seconds) and on for the editable Defrost On time (default 1
second) during defrost operation .
Enthalpy Wheel Capacity Limiting
Enthalpy wheel capacity limiting control is a means to limit
the capacity of an energy wheel during part load conditions .
Normally wheels are sized for worst case winter/summer
load and, therefore, at part load the wheel may be oversized .
Capacity limiting control is allowed when the energy recovery
wheel leaving air temperature (ERDAT) sensor is present and
reliable and the outdoor air temperature (OAT) is colder than
the returning air temperature .
Capacity limiting control is not allowed during dehumidification
operation or when either the wheel frost prevention or defrost
operation are active .
Capacity limiting operation differs depending on whether the
energy recovery wheel is constant or variable speed .
Constant Speed Wheel
The conditions that cause the energy recovery wheel to turn
due to capacity limiting are different depending on the unit
operation state as follows:
Fan Only
When the unit is operating in the Fan Only state, the energy
recovery wheel is stopped due to capacity limiting whenever
the discharge air temperature (DAT) is above the MinDATLimit
setpoint by more than ½ the discharge air heating deadband .
The wheel is re-started when the DAT falls back to or below
the MinDATLimit setpoint plus ½ the discharge air heating
deadband .
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