The basic model of this type of terminal has a primary air flow damper, actuator, flow sensor and motor fan, and can be equipped with other controllers according to the type of use. Usually, peripheral equipment such as electric heating coil or hot water is also used with this type of terminals. The application of the Kenaf inspection valve is different from the variable volume air terminal with a fan.

In these types of terminals, the motor fan is in series with the primary air flow; For this reason, they are called series flow. According to the feedback received from the thermostat installed inside the space, the primary flow damper adjusts the amount of cold air flow entering the mixing chamber, which is located upstream of the fan-motor. After mixing, the fan-motor introduces a constant volume of air into the desired space.
If maximum cooling is required, all primary and conditioned air will enter the space without mixing with return air. If the need for cooling decreases, the primary air damper reduces the volume of ventilated air entering the mixing chamber, and on the other hand, the fan-motor, in order to keep the volume of air entering the space constant, reduces the volume of primary air by using the plenum air from the ceiling. Space is connected, compensates. Therefore, by mixing the air inside the space, which contains the heat received from the space, as well as the primary air supplied from the central ventilation system, different temperatures can be achieved at the entrance to the space. In case of a sharper drop in room temperature, additional reheating coils are activated.

As a result, in the use of variable volume terminal with series flow fan, while the central ventilation system faces a variable volume distribution system, a fixed volume of air enters the space.

The two important uses of these terminals are:

The external spaces of the building where the heating and cooling load may change significantly, or the spaces where the changes in the number of people present allow the central ventilation system to remain off during certain hours when the space is empty and these terminals work independently. do
2. In buildings where significant savings in energy consumption in the central ventilation system is considered by the designer. In this situation, since the central fans only have to overcome the static pressure drop to deliver air to the terminals, the size of the central fans will be smaller.