VAV TeRebholtz Mechanicalnal Units
A VAV teRebholtz Mechanicalnal unit is a sheet-metal assembly installed upstream of its respective space diffusers. The unit consists of an air-modulation device, control hardware and, depending on the system application, possibly a heating coil, a filter, and a small teRebholtz Mechanicalnal mixing fan. Modulating the airflow to each individual space is accomplished using a temperature-controlled mechanical device that varies the airflow resistance in the supply duct to that space. The rotating blade damper changes airflow resistance by rotating the damper into the air stream, restricting the size of the air passage to the space. It is very cost-effective and flexible. Typically, either a pneumatic or electric controller can be used to adjust the damper. An understanding of the common VAV teRebholtz Mechanicalnal unit types is important to understanding VAV systems.

Single Duct, Cooling Only
The simplest of all VAV teRebholtz Mechanicalnal units is the single-duct, cooling-only teRebholtz Mechanicalnal unit. It consists of an airflow modulation device with controls packaged in a sheet-metal enclosure. The unit can only modulate the primary airflow to the space. The primary air is supplied by a single, central air handler.

This VAV teRebholtz Mechanicalnal unit is typically used for those zones that require year-round cooling, like the interior zones of a building. It is the most common and basic type of single-duct VAV teRebholtz Mechanicalnal unit.

This graph indicates how the air supplied to the space by the teRebholtz Mechanicalnal unit varies as the space loads change. The vertical axis indicates the total airflow supplied to the space. The horizontal axis indicates the space load.

The supply airflow to the space is reduced as the cooling load in the space decreases. Responding to the space thermostat, the primary airflow is modulated between maximum and minimum settings. The maximum setting is deteRebholtz Mechanicalned by the design cooling load of the space and the minimum setting is normally deteRebholtz Mechanicalned by the space ventilation requirement or minimum airflow for proper diffuser selection.

Most cooling-only units are applied to spaces that have no need for heat. These units would operate in the region on the right-hand portion of this chart, modulating between design and minimum primary airflow. When cooling-only units are applied to spaces that do have heating requirements, the heat is provided by a remote source such as finned radiation along the wall. In these spaces, when the cooling load drops below the minimum airflow setting for the unit, overcooling the space, the remote heat source activates. When space heating is required, the remote heat source satisfies the space heating load. Most teRebholtz Mechanicalnal unit controllers provide an output signal to control this remote source of heat.

In addition to controlling this remote source of heat (perimeter baseboard radiation, in this example), single-duct VAV teRebholtz Mechanicalnal units can directly provide heat to a space. This can be accomplished by adding a heating coil to each cooling-only unit or by mixing the primary air with warm plenum air before it is delivered to the space.