Can the fan box be adjusted according to load? There should be boundaries between work and duty patterns
The fan box can be adjusted according to load, but the word 'according to load' must first clarify what load it is. Is it a signal to start and stop production equipment, or is it the occupancy status of the air-conditioned area, or is it a change in air duct pressure difference? Different signals correspond to completely different control logic. More importantly, each operating mode must have a clear minimum air supply boundary, and the speed cannot be reduced to the end because the load is low. The working mode and the duty mode are not simply 'high speed' and 'low speed', but two sets of working points that meet the usage requirements.
First define what the load signal is
There are many sources of load signals. Production equipment operation signals, area occupancy sensors, temperature and humidity controller output, air valve switch status, and pressure difference transmitter readings can all be used as the basis for adjustment. The air supply logic corresponding to different signals is different.
If the load signal comes from the start and stop of production equipment, the fan box must adjust the air volume according to the equipment switch, and the start and stop timing and delay need to be confirmed. If the signal comes from area occupancy, such as a conference room that is opened only when no one is there and closed when no one is around, the fan box may need to maintain a minimum air exchange when no one is around, rather than shutting down completely. If the signal comes from the pressure difference, the control goal is to maintain a certain pressure difference range, and the rotational speed is adjusted with the pressure difference deviation.
'Adjust according to load' cannot be simplified to 'turn the fan to the minimum when the equipment is shut down'. Some process areas need to maintain positive pressure or a minimum number of air changes even if the equipment is shut down, otherwise external contamination may enter. These boundary conditions must be clearly written in the control plan.
Multi-device linkage should avoid frequent speed up and down
There are often multiple production equipments in a workshop, which are switched on and off in sequence. If each piece of equipment starts and stops and the fan box rises and falls accordingly, the driver may operate dozens of times a day, and the lifespan of the motor and contactor will be affected.
A reasonable approach is to set the delay and minimum operating air volume. After the equipment is started, the fan box will delay for a period of time before increasing the speed, and then make adjustments after confirming that the equipment is running stably. After the equipment is turned off, delay for a period of time before slowing down to avoid frequent changes in speed caused by repeated switching on and off in a short period of time. The delay time is set according to the process characteristics. It is necessary to avoid malfunctions and not delay too long to cause insufficient air supply.
Multiple load levels can also be set. For example, the operation of a single device, the operation of two devices, and the operation of three or more devices correspond to different rotation speeds. Set switching thresholds and hysteresis between gears to avoid jumping back and forth at critical points. These logics should be made clear in the control scheme and verified by simulating various combined states during debugging.
Work mode and duty mode should have their own goals
The working mode operates according to the designed working conditions, and the goal is to meet the air supply volume and pressure difference requirements during the production period. The duty mode operates according to the minimum air exchange or pressure difference requirements, with the goal of maintaining basic environmental conditions while reducing energy consumption. The goals of the two modes are different and the setting values are also different.
The minimum air volume in duty mode cannot be set arbitrarily. It should be determined by the end demand, such as the minimum air supply volume required to maintain positive pressure in the clean room, or the air volume corresponding to the minimum number of air changes in the room. During debugging, the air volume and pressure difference at the most unfavorable end should be measured in this mode, and then the lower speed limit should be locked after confirming that the requirements are met.
There must be clear switching conditions between working mode and duty mode. It can be time switching, such as day shift and night shift; it can be signal switching, such as delaying entry into duty mode after all production equipment stops; or it can be manual switching, selected by the operator according to production arrangements. The switching conditions should be stated in the control point table to avoid temporary decisions on site.
What should you pay attention to when sharing a fan box in multiple areas?
When multiple areas share a fan box, closing a branch will change the pressure and air volume of other branches. If the rotation speed is controlled based on only one sensor, the air volume in the remote area may be insufficient.
For example: a fan chassis serves three areas, and the sensor is installed on the main air duct close to the fan. When a large branch is closed, the main air pipe pressure increases, the sensor feedback pressure is sufficient, and the driver reduces the speed. However, the air volume of the small branch at the far end is no longer enough, because although the total air volume has not dropped much, the distribution has changed.
There are two solutions. One is to install the sensor in the most representative position, such as the most unfavorable branch road, or take the most unfavorable value among multiple measuring points as the control basis. The second is to complete the branch balance debugging first, verify the key terminal air volume under each typical combination state, and confirm that the control strategy can cover these states. No matter which method is used, the branch switch combination must be simulated during debugging, and cannot only be tested in the fully open state.
Switching oscillations and fault actions must be dealt with in advance
When switching between modes, if the control parameters are not set appropriately, oscillation may occur. For example, when switching from working mode to duty mode, the pressure difference is low after the speed drops, the controller increases the speed, and then decreases the speed after the pressure difference is high, causing repeated fluctuations. This is usually because the control parameters are too aggressive, or the switching threshold is set unreasonably.
During debugging, changes in rotation speed, air volume and pressure difference should be observed during the switching process, and then put into automatic operation after confirming that they are stable. If necessary, increase the switching delay or set a transition interval to allow the system to transition smoothly.
When control signals are lost, sensors fail, or communications are interrupted, how the equipment should act must also be agreed in advance. Systems with minimum air supply requirements should generally not be shut down, but should return to the preset safe speed and sound an alarm. Systems with upper pressure differential requirements should be slowed down or shut down. These logics should be written in the control plan and simulated and verified during debugging.
Looking at the implementation of load adjustment from the perspective of whole machine matching
Adjustment according to load ultimately comes down to matching the entire machine. Whether the driver can receive multiple load signals, whether the control parameters can cover the operating points of each gear, and whether the fan curve and pipeline characteristics allow sufficient speed adjustment range, all need to be confirmed during the selection stage. Aili Industry has independent matching capabilities in fans, motors, controls and sheet metal structures. It can put the driver, motor, impeller and box at the same working point for verification, and match the speed regulation range and feedback method according to the load signal type and operation mode of the project. This kind of internal collaboration from the power end to the control end can reduce the common problems of signal incompatibility, gear switching oscillation and insufficient speed range coverage in outsourced assembly solutions. The project only needs to provide the equipment operation table, key measuring points and the minimum air volume requirements of each mode. The control scheme and driver parameters can be set according to the point table before leaving the factory.
System end configurationFor HEPA/ULPA high-efficiency filters , the initial resistance of the filter and the resistance at the end of use will affect the working point. The load adjustment plan should calculate the margin based on the pressure difference allowed before maintenance. When the process requirements are higher, it can be evaluatedDoes the ULPA ultra-high efficiency filter meet the requirements? 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)。
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.
