Daikin DPS Installation And Maintenance Manual page 102

Constant Speed Wheel
The enthalpy wheel is stopped to prevent frosting whenever
an Intersection Point exists and the exhaust air leaving the
enthalpy wheel (ER EAT) is below the Intersection Point by
more than an editable minimum temperature difference (Min
ExhT Diff=) and the wheel has been running for a minimum
time period (ER Whl Stg Tm=) .
The enthalpy wheel is turned back on when the exhaust
air leaving the enthalpy wheel (ER EAT) rises above the
Intersection Point by more than an editable maximum
temperature difference (Max ExhT Diff=) and the wheel has
been off for a minimum time period (ER Whl Off Tm=) .
Variable Speed Wheel
The enthalpy wheel is first slowed to an editable minimum
speed (Default 5%) to prevent frosting whenever an
Intersection Point exists and the exhaust air leaving the
enthalpy wheel (ER EAT) is below the Intersection Point by
more than an editable minimum temperature difference (Min
ExhT Diff=) and the wheel has been running at maximum
speed for a minimum time period (ER Whl Stg Tm=) .
The wheel is stopped if it has been operating at minimum
speed for the ER Whl Stg Tm=period and the exhaust air
leaving the enthalpy wheel (ER EAT) is below the Intersection
Point by more than the Min ExhT Diff= value .
The enthalpy wheel is turned back on when the exhaust
air leaving the enthalpy wheel (ER EAT) rises above the
Intersection Point by more than an editable maximum
temperature difference (Max ExhT Diff=) and the wheel has
been off for a minimum time period (ER Whl Off Tm=) .
The enthalpy wheel speed is increased back to maximum
speed after is has been operating at minimum speed for the
Whl Stg Tm= and the exhaust air leaving the enthalpy wheel
(ER EAT) is above the Intersection Point by more than the Max
ExhT Diff= value .
Enthalpy Wheel Defrost Control
(Constant Speed Wheels Only)
A unit equipped with a constant speed wheel includes a wheel
defrost function that can be enabled in lieu of frost prevention
by setting the Fst Mgmt Meth= parameter to Timed .
With this method there is nothing that prevents frost from
forming on the wheel but the wheel is periodically stopped
to allow the wheel to defrost . When this function is enabled,
the wheel is stopped for a defrost time period Defrost Time=
(Default=5 minutes) every defrost period Defrst Period=
(Default=60 minutes) .
OM 1141-3 • MICROTECH UNIT CONTROLLER
When the wheel is stopped due to defrost operation, it must
be slowly rotated so that both halve of the wheel are allowed
to defrost by the relatively warm exhaust air leaving the wheel .
This is accomplished by alternately turning the wheel control
output off for and editable defrost off time Defrst Off Tm=
(Default=24 seconds) and on for an editable defrost on time
Defrst On Tm= (Default=1 second) during the Defrost Time
period .
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 .
Heating
When the unit is operating in the Heating state, the energy
recovery wheel is stopped due to capacity limiting whenever all
heating is off and the discharge air temperature (DAT) is above
the discharge heating setpoint by more than ½ the discharge
air heating deadband . The wheel is re-started when the DAT
falls back to or below the discharge heating setpoint plus ½ the
discharge air heating deadband .
Cooling
When the unit is operating in the Cooling state, the energy
recovery wheel is stopped due to capacity limiting whenever
the energy recovery wheel leaving air temperature (ER LAT)
is above the discharge cooling setpoint by more than ½ the
discharge air cooling deadband . The wheel is re-started
when the ER LAT falls back to or below the discharge cooling
setpoint plus ½ the discharge air cooling deadband .
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