Siemens BACNET 125-699 - Manual (Page 18)

Siemens BACnet Heat Pump Controller - Multi-Stage Owner’s Manual
10 Siemens Building Technologies, Inc.
Power Failure Recovery
Upon return from a power failure, the heating and cooling compressors are kept off, the
electric heat (if used) is kept off and the fan is kept off. In addition to the equipment being
OFF, both cooling and heating loops are set to 0. This situation will remain in effect until the
power failure recovery period for this controller is over.
The controller returns to normal control when its power failure recovery period is over. The
power failure recovery time for a heat pump is based on the following formula:
RETURN DELAY + (CTLR ADDRESS × 10 seconds)
This lessens the demand of having all the electrical equipment starting at once.
Centralized Alarm Monitoring
DI 6 can be used to monitor an input that changes state when the heat pump is in alarm.
DI 6 can be unbundled to send alarm information to the field panel for centralized alarm
monitoring.
Overriding DOs
Heat Pump applications allow spare DOs, damper (DO1 and DO2) and electric heat stages
(DO3, DO6 and DO7 when applicable) to be commanded.
Physical points DO1 and DO2 can never be overridden when configured for motor control.
However, the position of the attached motor is always commandable via the DMPR COMD
point.
To prevent damage to the mechanical equipment, the fan, reversing valve, and
compressor(s) DOs cannot be directly commanded ON or OFF unless the point HP DO
OVRD is set to ENABLE. When HP DO OVRD is set to DISABL (default), commands to the
fan, reversing valve and compressor DO points are ignored regardless of BACnet command
priority.
CAUTION:
HP DO OVRD should be set to ENABLE only when there is a complete
understanding of the consequences. Since the direct control will override the
application minimum on/off time safeties, improper use of DO commands can
cause permanent equipment damage. Also, during normal daily operation the
override of critical DOs should only be done via a BACnet command.
Fail-safe Operation
If the RTS or the setpoint dial fails, the controller operates using the last known temperature
value.