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44 TRG-TRC014-EN
notes
period three
System Configurations
When overhead heating is acceptable, VAV reheat, fan-powered, or dual-duct
terminal units can be used to provide both perimeter cooling and heating.
In cooling mode, the VAV reheat terminal unit modulates in response to the
changing space cooling load, always maintaining a minimum airflow to serve
ventilation requirements. For space loads below this minimum airflow, the unit
maintains this constant minimum airflow and modulates the reheat coil
capacity to satisfy the space tempering or heating requirements.
Reheating previously-cooled primary air is not energy efficient. However,
because the VAV system has already reduced the supply airflow, it must reheat
only a limited amount of air. The VAV reheat system is far more energy efficient
than a similarly-applied, constant-volume reheat system.
VAV reheat
VAV reheat
terminal unit
terminal unit
VAV Reheat
heat loss < 250 Btu/hr/ft
heat loss < 250 Btu/hr/ft
[240 W/m][240 W/m]
[240 W/m]
Figure 60