What is the function of fan box speed regulation? Leave air volume to actual load management

The production equipment of an electronics factory only operates during the day, and only personnel are on duty at night. The ventilation system is designed according to the maximum load during the day, and the fans run at a constant speed throughout the day. The terminal air volume at night far exceeds actual demand, and air conditioning energy consumption remains high. Later, a speed control was installed on the fan box, which automatically reduced the air volume to the duty air volume at night and restored the designed operating conditions during the day. The electricity bill dropped significantly throughout the year.

This scene illustrates a simple truth: when the demand itself is changing, the fixed speed operation method will inevitably cause waste. The role of fan box speed regulation cannot be summed up in the words 'power saving', but to allow the air supply volume to follow the actual load.

Aili Industry is discussingWhen configuring the fan box and control , we will first understand the load change pattern and time-based operation requirements of the project, and then determine whether the speed regulation plan is suitable and how to set the speed regulation range.

Only with changing needs can there be control value

The value of speed regulation comes from demand differences. If the system operates at full load 24 hours a day throughout the year, the benefits brought by speed regulation mainly come from the motor efficiency itself, rather than speed regulation. But if any of the following situations exist, the significance of speed regulation will obviously increase:

Production equipment operates in shifts, with different loads during the day and night; some areas are opened at different times, and not all air duct branches are used at the same time; seasonal load changes, the demand for fresh air is different in summer and winter; the number of equipment turned on changes, and the end resistance changes accordingly.

In these cases, the fixed speed either operates according to the maximum demand, resulting in excessive air supply during low load periods, or operates according to the average demand, but fails to meet the requirements during peak periods. Speed ​​regulation allows the fan output to follow changes in demand, helping to control the input power during the corresponding period.

Power saving is determined by the load curve, system resistance and speed regulation strategy. You cannot promise a fixed ratio just because 'the speed regulator is installed'. If the system operates at full load for a long time, the benefits brought by speed regulation will be limited; if there are obvious on-duty or partial load periods, the value of the speed regulation solution will be reflected.

The farthest end is the check point for the lower limit of speed regulation.

Reducing the RPM also changes the pressure available. The air volume is approximately proportional to the rotational speed, and the shaft power is approximately proportional to the cube of the rotational speed. The rotation speed is reduced by 20%, the air volume is reduced by approximately 20%, and the shaft power is reduced to approximately 51% of the rated value. However, the system resistance curve is not linear. After the air volume decreases, the pipeline resistance will also decrease, and the actual working point needs to be repositioned on the curve.

For multi-branch systems, the required air volume or pressure difference should be verified at the most unfavorable end. Merely seeing a drop in current does not prove that the entire system still meets usage requirements. Some branches are close to the fan, and the air volume does not drop significantly after speed adjustment; some branches are at the farthest end, and the air volume may have been lower than the requirement after speed adjustment.

The correct approach is to measure the air volume and the farthest end pressure difference of each branch at full speed, duty speed and minimum allowable speed during the commissioning phase. Only when the farthest end meets the requirements, the lower limit of speed regulation is confirmed. The minimum operating air volume should be determined by the end demand rather than the minimum speed of the drive.

Things to note when sharing across multiple areas

When one branch is closed and other branches remain open, the fan operating point will change. If the rotation speed is controlled based on only one sensor, the air volume in the remote area may be insufficient. For example, the sensor is installed on the main air duct close to the fan. When a large branch is closed, the pressure in the main air duct increases. The sensor feedback pressure is sufficient, and the driver reduces the speed, but the air volume of the remote small branch is no longer enough.

In this case, it should be confirmed that each typical combination of states can meet the minimum requirements through branch balance and reasonable sensor location. The sensor can be installed on the most unfavorable branch, or multi-point measurements can be used to take the most unfavorable value as the basis for control. No matter which method is used, the actual effect of each branch combination should be verified during the debugging stage.

If the end of the system is configuredHEPA/ULPA high-efficiency filter , the resistance of the filter will increase with dust accumulation. The speed regulation strategy should be adjusted accordingly to ensure that the terminal air volume does not decrease due to increased resistance. When the process requirements are higher, it can be evaluatedDoes the ULPA ultra-high efficiency filter meet the requirements?

How to set up the operating mode

First form the air volume requirements under working, on-duty and abnormal conditions, and then set the target and switching conditions for each state. The working mode operates according to the designed working conditions, the duty mode operates according to the minimum ventilation or pressure difference requirements, and the abnormal mode defines the action in case of disconnection, failure or fire alarm.

Each mode should be clear: target air volume or pressure difference, allowable speed range, switching conditions, sensor location, and action in case of failure. These contents should be confirmed before commissioning and reviewed during on-site joint debugging, and should not be left to the electrician's on-the-spot judgment.

If the project adopts a DC speed regulation scheme, the speed regulation range, control signal type and driver installation location must also be confirmed. It cannot be assumed that all DC fan chassis use the same analog, PWM or communication protocol. The terminal definitions of different drives may be different.

Clean room ceiling air supply is comparableFFU fan filter unit ; centralized management of multiple devices can be matchedThe FFU computer group control system realizes zone speed regulation and status monitoring. Protection of single process equipment can be consideredEquipment-side fan filter unit (EFU) . The final filtered air supply at the end of the air duct can beHigh-efficiency air supply outlet (HEPA BOX) . The division of labor and linkage relationship between these equipment and the fan box should be clear on the system flow chart.

Speed ​​regulation is not a panacea

Speed ​​regulation can solve the problem of excessive air supply caused by changes in demand, but it cannot make up for unreasonable air duct size, miscalculation of the most unfavorable end air volume, or insufficient estimation of system resistance. If the pipeline design itself is too small, the resistance will increase later, and even if the speed is adjusted to increase the speed, it may cause noise and extra power consumption.

Speed ​​regulation cannot replace system balancing. Uneven adjustment of the branch valve, long-term failure of the filter to maintain or air leakage in the air duct will affect the speed regulation effect. Only by dealing with these system losses first and then evaluating the speed adjustment plan can real energy-saving benefits be obtained.

Aili Industry isThe fan box and control configuration can be discussed in conjunction with the motor and drive matching, and the setting values ​​can be adjusted according to on-site data during debugging. Specific structure and configuration options can be found inIt is confirmed in the fan box product catalog that non-standard projects should provide equipment or machine room drawings, and then shape them based on the determined working points and on-site interfaces.