Trane TRG-TRC014-EN manual System-LevelControl Modes, System Configurations, period three

period three

System Configurations

notes

Any unneeded air is diverted to the return air stream, allowing individual comfort control of the spaces.

At part-load conditions, when more of the primary air bypasses the space, the mixture of previously conditioned primary air and recirculated return air cuts energy use at the cooling and heating equipment. This explains the use of the term “bypass” in the name of this system. However, due to the fan providing a constant airflow, no fan energy savings is realized at part-load conditions.

The term “changeover” refers to how this system handles the cooling and heating requirements of the building. The central air handler can provide either cooled or heated primary air to the space terminal units, and it makes this decision by periodically “polling” the spaces. Because it can only provide heating or cooling at a given time, this system is most appropriately used for smaller buildings that have a minimal number of incidences where heating is required in some spaces and cooling is simultaneously required in others.

System-Level Control Modes

▲Occupied mode

▲Unoccupied mode

▲Morning warm-up/cool-down mode

Figure 67

System-Level Control Modes

When designing a VAV system for a commercial application, three system-level control modes need to be addressed:

nOccupied mode

nUnoccupied mode

nMorning warm-up/cool-down mode

48 TRG-TRC014-EN