Variable air ratio 
The air conditioning system runs under partial load conditions for most of the year, that is to say, the wind turbine of the variable air volume system, the air duct and the air volume at the end are mostly between the maximum air volume and the minimum air volume.
According to experience, if there is no problem in these two extreme states, then basically the system can be guaranteed to run normally most of the time.
The ratio of the minimum design air volume to the maximum design wind is defined as the variable air volume ratio (KV). Generally, the room variable air volume ratio KV value is preferably not less than 0.4 ~ 0.5, otherwise it will easily lead to room airflow organization deterioration, noise and ventilation problems;
The KV value of the system should not be less than 0.4 ~ 0.5, otherwise it will lead to serious shortage of fresh air and unstable control.
Whether it is a room or a system, the variable air volume ratio is an important dynamic characteristic parameter for characterizing the variable air volume system; 
Fresh air problem 
In the transition season, the fresh air volume is changed to maintain a mixed air temperature by adjusting the opening of the three valves of fresh air, return air and exhaust air. This is to shorten the opening time of the cold machine, let alone talk about whether the economic cycle system can operate normally in the quantitative system.
For air-conditioning systems that use mixed air, whether it is a constant air volume system or a variable air volume system, the fresh air volume is distributed according to the load in each room. That is to say, even if the total fresh air volume meets the requirements, some rooms will have the problem of insufficient fresh air.
For the variable air volume system, since the air volume sent to the room changes, the fresh air volume of the room must also change. In order to meet the requirements of these rooms, the total fresh air volume will increase, and sometimes even exceed the required air supply volume.
To this end, the ASHRAE standard proposes that under a certain amount of fresh air, the content of carbon dioxide in the total return air may not exceed the standard, and the return air can be utilized to reduce the total fresh air volume.
The ASHRAE standard only answers how to determine the total fresh air volume problem. However, for the variable air volume system, the air volume sent to the room changes, and the fresh air volume of the room must also change, and the problem of fresh air is more prominent.
Therefore, in the case of high fresh air requirements, it may be necessary to lay a new air duct separately. In this way, the space occupied by the wind tunnel will increase.
Therefore, in the variable air volume system, there are three main problems in the new wind: the control of total fresh air volume, the determination of total fresh air volume and the distribution of fresh air. 
Noise problem 
In the variable air volume system, the relatively large noise source has a variable air volume end device in addition to the sending and returning (row) fans. The wind speed flowing through the end inlet is relatively large, because the pressure-independent variable air volume end has a wind speed measuring sensor, and these sensors generally require a wind speed higher than a certain value to ensure accurate measurement.
This is one reason why the end device produces higher noise.
The general throttling end is to change the air volume by adjusting the opening of the valve. When the valve is closed, the wind speed through the valve plate is also increased, so valve adjustment is also a source of noise. 
Airflow organization 
Generally, the air supply ports of the air conditioning system are cut off, and the angle of the guide vanes is rarely changed. Therefore, when the air volume is reduced, the airflow organization in the room will be affected. 
Small pressure between fingers 
Since the new exhaust air volume of the variable air volume system and the return air volume of the room are changed, the positive pressure of the room is also fluctuating, and it cannot be determined that the air volume system is so stable.
If this problem is not handled well, problems such as difficulty in opening the door, serious infiltration of the door joints and window seams, etc. will occur. 
End device selection 
There are many types of end devices, and the products of different manufacturers have their own characteristics. When choosing, the acoustics, control performance and room function requirements of the end device should be fully considered.
In the size selection, generally based on the design of the maximum air volume, but also to consider a certain margin to meet the needs of future development. However, the end selection should not be too large, and the selection of the assembly will reduce the adjustment range of the damper and reduce the adjustment capability, which will easily cause the end damper to oscillate when the air volume is small.
Motion Control Sensor is an original part that converts the change of non-electricity (such as speed, pressure) into electric quantity. According to the converted non-electricity, it can be divided into pressure sensor, speed sensor, temperature sensor, etc. It is a measurement, control instrument and Parts and accessories of equipment.
Encoder And Decoder,Encoder For Motor , Encoder In Communication,Encoder Communication
Changchun Guangxing Sensing Technology Co.LTD , https://www.gx-encoder.com