Control Temperature - Daikin MicroTech III Operation Manuals

Illustrative Heat/Cool Changeover Sequence
The following is an illustration of the heat/cool changeover
function .
When the control temperature is below the occupied or
unoccupied heating setpoint by more than ½ the deadband
(point A), heating operation is enabled . Heating operation then
remains enabled until the control temperature begins to rise
and rises above the occupied or unoccupied heating setpoint
by more than ½ the deadband (point B), at which point heating
operation is disabled and the unit enters the fan only (or Min
DAT) operating state . If the control temperature rises above
the occupied or unoccupied cooling setpoint by more than ½
the deadband (point C) cooling operation is enabled . Cooling
operation remains enabled until the control temperature begins
to fall below the occupied or unoccupied cooling setpoint by
more than ½ the deadband (point D), at which point the unit
returns or fan only (or Min DAT) operating state .
Figure 12: Heat/Cool Changeover

Control Temperature

The "Control Temperature" is defined as the unit temperature
input used to make the heat/cool changeover decision . This
determines whether or not cooling or heating is enabled .
The user may select Space Temperature, Return
Temperature, Outdoor Air Temperature or None for DAT units .
Normally either the Return or Space Temperature is selected
as the control temperature . Outdoor Air Temperature may
be used as the control temperature for DAT units, but not for
Zone Control units .
When the Control Temperature Source is set to None, the unit
no longer "changes over" between heating and cooling in the
normal manner . Instead it acts as if it is always in the "cooling"
mode of operation controlling to the discharge air cooling set
point . In this case the unit operating state will vary between
Cooling, Fan Only and Min DAT (heating) in order to maintain
the discharge air cooling set point . The unit will only enter the
Heating operating state and control to the discharge heating
set point for morning warm up purposes .
www .DaikinApplied .com
The Control Temperature Source automatically reverts from
Return to Space if both of the following are true:
• The Return Air Sensor is not present and reliable
• A network or local Space Sensor is present and reliable
The Control Temperature Source automatically reverts from
Space to Return if both of the following are true:
• The space sensor is not reliable (a valid space
temperature value is not provided via the network and
the space temperature sensor is either in alarm or not
present)
• The return air sensor is reliable (present and not in alarm)
The Control Temperature Source automatically reverts
from either Outdoor Air or Mixed Air to Return if the Control
Type is Zone (Not DAT) . If the return air temperature is not
reliable, the control temperature may then revert to space as
described above .
The Control Temperature Source automatically reverts from
Mixed Air to Outdoor Air if Unit Type is not SCU .
A Control Temperature Fault that shuts down the unit is
initiated if any of the following is true .
• The return air sensor is not present and reliable and
Return Air is selected as the control temperature and a
space sensor is not available .
• A network or local space sensor is not present and
reliable and Space is selected as the control temperature
and a return temperature sensor is not available .
• The OAT Sensor is not present and reliable and Outdoor
Air is selected as the control temperature
• The mixed air temperature sensor is not present
or reliable and Mixed Air is selected as the control
temperature
Occupied Temperature Set Points
When the Use Tstat set point parameter is set to No, the
Occupied Cooling Set Point and the Occupied Heating Set
Point may be set through the keypad or via a network signal .
In this case these set points are changed whenever the
network or keypad value changes . When the Use Tstat set
point parameter is set to Yes these set points can only be
adjusted through the zone thermostat. Heating and cooling set
points must not overlap . The Occupied Heating Set Point must
be equal to or less than the Occupied Cooling Set Point . If a
conflict occurs from values entered via the keypad or network,
the Occupied Heating Set Point is automatically adjusted down
to eliminate the conflict. When the Occupied Cooling Set point
is changed by more than 0 .5 degrees through the wall mounted
sensor, the Occupied Heating Set Point is raised or lowered
the same amount so that the difference between the Cooling
and Heating set points does not change .
95 OM 920-6 • MICROTECH UNIT CONTROLLER
o ' g
peraTor s uIde