Trane TRG-TRC014-EN manual Glossary

Glossary

changeover/bypass VAV system A system that allows variable supply air to the spaces but uses a constant-volume central supply fan. This is accomplished by using a large damper to bypass the excess air. This is common in smaller buildings requiring individual space comfort control.

Coanda effect Concept behind the operation of a linear slot diffuser. Air is discharged at a relatively high velocity along the surface of the ceiling, creating an area of low pressure that causes the supply air to hug the ceiling. As it travels along the ceiling, air from the space is drawn into, and mixed with, the supply airstream. When the air settles to the occupied levels of the space, it has reached an average temperature.

constant-volume system temperature of a constant conditions of the space.

Type of air-conditioning system that varies the volume of air supplied to meet the changing load

cooling-only terminal unit Simplest type of single-duct VAV terminal unit. It has the capability of varying the airflow, but has no method for space heating.

diffuser Device connected to the end of the supply duct system, used to distribute the supply air effectively to the conditioned space.

direct digital control (DDC) Method of terminal-unit control using an electric motor to operate the airflow modulation-device activator. It uses a microprocessor that enables digital communication between the unit controller and a central building automation system.

discharge dampers Method of supply fan modulation that matches the static pressure supplied by the fan with the static pressure required by the system. This is accomplished by using a modulating damper a little bit downstream of the fan to create a static-pressure drop in the system.

dual-duct terminal unit VAV terminal unit consisting of two primary airflow modulation devices, one for cool primary air and one for warm primary air. These units can be controlled to provide either a constant volume or a variable volume of supply air to the space.

electronic control Method of terminal unit control using an electric motor to operate the airflow modulation-device actuator. The motor can drive the modulation device open or closed.

equal friction duct design method Method of designing an air duct system that results in an equal static-pressure drop per foot of duct. Equal-friction duct systems can be easily designed by hand.

fan modulation curve Curve that illustrates the static pressure requirement of the VAV system fan over the range of airflows.

fan outlet static-pressure control Method of VAV system static-pressure control that mounts the static-pressure sensor near the outlet of the main supply fan and maintains a constant static pressure at the sensor.

fan performance curve Plot of the airflow capacity of a specific fan at a given speed (rpm) versus the static pressure it generates.

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