Weak current College】 【VAV unit control classification introduction --- Power By】 【China power house network.

Room temperature control is via VAV control of air flow. This is the basic of VAV system control links. Terminal device control can be divided into three categories: with pressure (also called pressure related type); limit the air flow; not with pressure (also known as pressure-independent type).

1. with pressure of the air terminal device control

This class of the control unit end device is installed on the terminal device of Xiang tinei of an air flow control valve, it accepts the indoor temperature controller instruction while changing the aperture to adjust the air. Because the VAV system terminal units are continually adjust their respective air, thus the entire system of static pressure is constantly changing, such devices are not to compensate for the change of the static pressure in the pipeline and set of control measures, so that the amount of air transport will be directly affected by its upstream wind tube static pressure changes, which have air's so-called "overshoot" or "less stressed," causing the room to produce large temperature fluctuations. At the same time, these devices also required at the scene debugging a maximum and minimum air, but this kind of debugging only in system pressure consistent results when debug is true. Visible, to do this is very time consuming, it is very difficult. However, with pressure terminal device as long as with more sensitive indoor temperature regulator can still be in a comfortable room temperature control. Moreover such device structure is simple, inexpensive, to comfort for purposes of civil construction in VAV system, is still widely used.

2. limit the air flow of terminal device for air flow control

This type of terminal device or install the greatest amount of wind qualifier, or install a minimum air flow qualifier, or for maximum air flow restrictions, or restrictions on the minimum air flow. Air quantity qualifier in the factory to debug. If installed, the maximum air volume qualifier, minimal air is still required at the scene debugging, this is very time-consuming and difficult. Although most of the time, to avoid air more than qualified for set value, however, in practice, only a very small number of the year running hours appears maximum load status, so that the results of this control, as with pressure terminal device, will air the "overshoot" or "less stressed" phenomenon.

Air volume limit control in two ways, one is the use of mechanical (with spring) air flow regulator, is used with orifice or speed probe of differential pressure controller. The former requires a system of high static pressure values are generally higher than other system 120 ~ 130PA, available, high-voltage systems in use. While the latter requires a system of static pressure value is not high, can be used in low pressure system.

3. not with pressure of the air terminal device control

This type of terminal equipment in any condition, only according to the needs of a room load corresponding to the quantity of air transport, and air duct system is independent of the static pressure variations, from largest to smallest air within the control, only accept indoor temperature controller instruction. Maximum and minimum air are also good at manufacturing plant debugging. This eliminates air "overshoot" and "less-" phenomenon, system operation is the most stable, indoor temperature wave is very small.

This type of terminal device used by the control, and limit the air flow of terminal device similar to the use of mechanical air flow regulator set or differential pressure controller, and equipped with air valve or regulator. With mechanical air flow regulator set, to pass with the rod to regulators and control air actuator connected. Actuator receives the indoor temperature controller instruction and action, but when the system pressure is changed, the regulator will enable actuator then adjust to maintain the original need air. Obviously, this kind of control, still need system has high static pressure in order to ensure the regulator is working properly. Using differential pressure controller, its control of the process is in accordance with the indoor temperature regulator of signal changes, and then set-point adjustment controllers, flow range and pressure are determined by differential pressure controller to control, there is no need to go through with the rod to the actuator for further adjustment.