Siemens BACNET 125-699 - Manual (Page 17)

Applications
Siemens Building Technologies, Inc. 9
Heating and Cooling Switchover
The heating/cooling switchover determines whether the controller is in heating or cooling
mode by monitoring the room temperature and the demand for heating and cooling (as
determined by the temperature control loops).
Electric Reheat
CAUTION:
Verify that the equipment is supplied with safeties by others to ensure that there is
airflow across the heating coils when they are to be energized.
The heating loop controls up to three stages of electric reheat (Application 2583) or one
stage (Application 2584) to warm up the room. The electric reheat is cycled on and off based
on heating demand that is determined by the room temperature heating loop. When the
controller is in cooling mode, the electric heat is OFF at all times.
Compressor Operation
When in cooling mode, the output of the cooling loop controls the staging of the compressors
and enabling/disabling the mixed air control (used as a source of cooling when the outside air
temperature is cool enough.
When in heating mode, the output of the heating loop controls the staging of the compressors
or electric heat.
NOTE: Application 2583 only. When cooling or heating mode is opposite the reversing
valve control, the compressors are turned off.
Fan Operation
Day Mode – The fan can be set to run all the time or the same as night mode.
Night Mode – The fan is controlled as follows:
The fan will turn ON when at least one of the following two conditions has been met:
• Free cooling is provided by the mixed air control loop.
• At least one compressor or stage of electric heat is ON.
The fan will turn OFF only after the following two conditions have been met:
• Free cooling is not provided by the mixed air control loop.
• All compressors and stages of electric heat have been OFF for at least 30 seconds.