Energy Recovery - Daikin MicroTech III Operation Manuals

Energy Recovery

Energy recovery is provided by drawing outside air across half
of an enthalpy wheel and drawing exhaust air across the other
half . Latent and sensible heat is transferred from the hotter,
moister exhaust air to the colder dryer outside air in winter .
Latent and sensible heat is transferred from the hotter more
moist outside air to the cooler dryer exhaust air in summer .
Control consists of starting and stopping an exhaust fan,
modulating the speed of the exhaust fan, starting and stopping
the enthalpy wheel, and optionally controlling the speed of
the enthalpy wheel . The outdoor dampers are controlled in
the normal manner . The current statuses as well as editable
parameters associated with energy recovery are located in the
Energy Rec Setup menu .
Enthalpy Wheel
The enthalpy wheel is turned on when all of the following are
true . The speed of the enthalpy wheel is set to the maximum
speed for units with a VFD controlling the speed of the
enthalpy wheel .
• The exhaust fan is ON
• The OA Dampers are at the minimum position
• The unit is not in the Economizer operating state
• The enthalpy wheel has not been turned OFF due to frost
prevention (variable or constant speed wheels)
• The enthalpy wheel has not been turned OFF due to
defrost control (constant speed wheels only)
• The wheel has not been turned OFF due to Variable
Effectiveness Operation
The enthalpy wheel is turned OFF when any of the following is
true
• The exhaust fan is OFF
• The OA Damper Position is driven above the Minimum
OA Damper Position by more than 3% .
• Either of the frost prevention functions dictate that the
wheel be OFF .
• The constant speed wheels defrost function dictates the
wheel is to be OFF .
www .DaikinApplied .com
Enthalpy Wheel Frost Prevention
Two different frost protection methods are provided depending
on whether or not the enthalpy wheel is controlled by a VFD .
When there is a threat of frost or condensation on the enthalpy
wheel, a variable speed wheel may be first slowed down and
then stopped and a constant speed wheel may be stopped so
that less enthalpy transfer occurs and frosting or condensation
on the enthalpy wheel is avoided . In either case the frost
control is based on an Intersection Point described as follows:
Condensation and frosting can occur on the enthalpy wheel
when the exhaust air leaving the wheel is saturated . This
condition will occur when two lines intersect on a psychometric
chart, and it will not occur when these two lines do not intersect .
One of these lines is the Humidity Ratio versus the dry bulb for
saturated air . The other line is the Humidity Ratio versus the dry
bulb temperature of the exhaust air leaving the enthalpy wheel .
The two ends of this second straight line on a psychometric
chart are the OAT at 95% RH and the return air temperature
at the return air relative humidity . One line showing frosting
conditions and another line showing no frost conditions are
shown on the sketch of a psychometric chart shown .
A continuous calculation determines if and at what
temperatures these two lines intersect . If they do intersect they
intersect at two points . The higher of the two points is referred
to as the "Intersection Point" . When they do not intersect, the
enthalpy wheel runs at full speed . When they do intersect, the
variable speed enthalpy wheel may be slowed to its minimum
speed as described above to maintain the dry bulb temperature
of the exhaust air leaving the enthalpy wheel high enough
to eliminate the Intersection Point and therefore the threat of
frosting conditions . If slowing the wheel does not eliminate
the Intersection Point after a stage time period, the wheel
may be stopped . A constant speed wheel is stopped when an
Intersection Point exists .
Figure 13: Exhaust Air Psychometric Chart
99 OM 920-6 • MICROTECH UNIT CONTROLLER
o ' g
peraTor s uIde