Part 1. Overview
12 Design Guide DCM014A51
2.5 Changeover Master and Secondary (Non-Master) Indoor Units
1. Cool and heat modes are only available for selection on the cool/heat changeover master
indoor unit. The following table indicates the available operating modes for secondary indoor
units in the system based on the selected mode of the master indoor unit.
When the master
indoor unit is set to:
Secondary indoor units in the
system can be set to:
2.6 Indoor Unit Logic
1. The indoor unit contains control logic to maintain room temperature by adjusting the
refrigerant flow and has the following data points:
a. Unit ON/OFF.
b. Operation Mode – Cool, Heat, Fan, Dry, Auto (Auto mode is not recommended as it can
create large temperature differentials between mode changes).
c. Setpoint – 60
o
F to 90
o
F, 1
o
F basis (16
o
C to 32
o
C, 0.1
o
C basis).
d. Room Temperature (read only).
e. Fan Speed – L, ML, M, MH, H, Auto (depends on indoor unit type).
f. Airflow Direction (if the indoor unit has louvers).
g. Alarm Status (read only).
h. Malfunction Code (read only).
2. Indoor Unit Sequence of Operation
a. During the cooling thermo-on (call for cooling) period, the indoor unit fan will operate based
upon the fan setting from the local controller, iTM, or BMS.
b. During the cooling thermo-off (cooling satisfied) period, the fan will continue to operate
based on the setting from the local controller, iTM, or BMS fan speed setting. However, the
fan can be turned OFF during the thermo-off period with a field setting (depends on the
indoor unit type). Also, the fan should not be OFF when an indoor unit receives outside air.
c. During the heating thermo-on (call for heating) period, the indoor unit fan will operate
based on the fan setting from the local controller, iTM, or BMS.
d. During the heating thermo-off (heating satisfied) period, the fan will continue to operate in
LL (Low Low) speed (default). The fan can be set to ON (H, MH, M, ML, L), LL or completely
OFF with a field setting (depends on the indoor unit type). However, the fan should not be
OFF when an indoor unit receives outside air.
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