Part 2. Functional Specifications
24 Design Guide DCM014A51
3. Auto-changeover
a. The iTM handles the cool/heat auto-changeover for the Changeover Group that consists of
all indoor units in Heat Pump systems, or under BS units in Heat Recovery system.
b. The Changeover Group is configured in the iTM.
c. The changeover method is configured from one of the following: Fixed, Average, Individual
and Vote which is selected in the iTM.
d. Different changeover options can be selected for each Changeover Group.
e. The Auto-changeover point (system point) allows the BMS to enable or disable all the
Changeover Groups simultaneously when the Changeover Groups are configured in the iTM.
f. The BMS Integrator should be provided with the Changeover Group configuration.
4. Scheduling
a. The iTM can accommodate daily scheduling of the indoor unit groups.
b. There are four types of schedules that can be set in the iTM 7 day, Weekday/Weekend,
Weekday/Saturday/Sunday, and Every day.
c. The BMS can use the “Enable iTM Schedule” point to enable or disable the schedule in the
iTM. Typically the BMS Master Schedule is used to control the indoor units, and iTM
Schedule is not used.
5. Forced System Shutdown
a. The “Forced System Shutdown” point can be used to turn off all indoor unit groups
connected to the iTM via the DIII-Net communication bus when an emergency signal has
been received by the BMS. Emergency Stop program should be configured and enabled in
advance.
b. Indoor unit groups cannot be restarted from the remote controller until the Forces System
Shutdown point is set to inactive.
4. VRV System Monitor/Control Objects
4.1 Member Objects
1. In BACnet®, a BACnet Object Identifier (hereinafter abbreviated as "ObjectID") is defined as
follows:
4.2 Indoor Unit Device
1. Each indoor unit monitoring/control item (called Member Object) is mapped to a BACnet object
(called indoor unit object) and to an ObjectID instance number, as indicated in the following
table.
2. Each of the object types BI, BV, MI, MO, and MV sets the text shown in the following table in
the Description Property in accordance with the value of the Present_Value.
3. The BMS cannot command an indoor unit from cool to heat (or from heat to cool) if the indoor
unit is not designated as the changeover master.
4. When more than one indoor unit is connected to a single remote controller group, the BMS
should only send commands to the indoor unit that is designated to receive the command for
the remote controller group (unit #0). The BMS should not send commands to other indoor
units in the remote control group. If commands are sent to the other indoor units in the
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