Why does the fan box need to match the motor and fan? Working point determines combination
Direct answer: The available working range of the fan box is determined by the impeller, motor and driver. When selecting a model, you cannot determine the motor power first and then look for the fan; nor can you just look at the fan sample curve and ignore the box structure and system resistance. The correct sequence is to first determine the target air volume and system static pressure, find the operating point on the fan performance curve, and then check whether the motor and driver can cover this operating point. The operating point determines the combination, not the motor power.
Aili Industry is discussingWhen configuring the complete fan box , it is usually required to provide the design air volume, external static pressure and operating conditions, and then check the matching relationship between the fan, motor and control scheme based on this.
Let’s talk about the fan curve first, and then talk about the motor size.
The air volume, pressure and shaft power of the impeller are different at different speeds. The fan curve describes the ability of the impeller itself: at a certain rotation speed, as the air volume increases, the pressure that can be provided gradually decreases; the shaft power increases as the air volume increases. The system resistance curve describes the pressure required by the pipeline at different air volumes. The intersection point of the two curves is the actual operating point.
A motor with a larger power rating does not guarantee more power consumption or quietness at the target operating point. If the motor operates in a low load area for a long time, the efficiency may actually decrease. If the rated power is insufficient, overload may occur under high resistance conditions. The fan curve, system resistance and motor available torque should be checked together.
Shaft power is determined by both air volume and pressure. In simple estimation, the shaft power is proportional to the product of air volume and pressure, and then divided by the fan efficiency. The motor power must be greater than the shaft power with a margin, but too much margin will cause the motor to run in the low-efficiency zone for a long time. A reasonable approach is to make the working point fall near the high-efficiency area of the motor, while leaving a margin to deal with increased resistance such as dust accumulation on the filter.
The relationship between impeller, drive and box
The performance of the fan under open test conditions is not necessarily the same as the performance after being installed in the box. If the air inlet side is close to an obstacle, or the air outlet turns sharply immediately, local losses will increase. The brackets, turns and cross-sectional changes inside the box will also consume the pressure provided by the fan. The engineering verification should be based on the test results of the final complete machine structure as much as possible, and it should be clear how much external static pressure the customer needs to reserve after the air duct is connected.
If the project adopts a DC speed regulation solution, the driver will also participate in the matching. The speed of the EC motor is controlled by the matching driver, and the speed adjustment range is limited by the driver. The fan, motor and driver need to be matched as a system: the driver receives power supply and control instructions, the motor runs at the set speed, and the final output still depends on the fan curve and air duct resistance. 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.
Box structure also affects results
The air inlet conditions in front of the fan, the turns in the box, the size of the air outlet and the layout of the bracket will all cause additional losses. Therefore, it is not enough to look at the sample curve of a single fan. The performance and test conditions of the complete machine under the corresponding box structure should be checked.
In some projects, the cabinet is reduced in order to save space. As a result, the pressure loss increases, the air volume decreases, and the noise increases. There are also projects where the access door is opened in the mainstream direction of the air flow, which facilitates maintenance but increases the disturbance inside the box. These details are easily overlooked in the selection stage, but they will affect the final operating effect. Aili Industry can coordinate around self-developed fans, motors and control solutionsComplete configuration of the fan box , and check the working point according to the box size and interface conditions.
Four common misunderstandings when matching
Misunderstanding 1: Only look at the motor power. The motor power is the upper limit of the capability and is not equal to the actual operating energy consumption. A high-power motor operating in a low-load area may consume more power than a small-power motor operating in a high-efficiency area.
Misunderstanding 2: Use the fan sample curve to replace the overall machine performance. After the fan is installed in the box, the performance may be lower than the sample data due to air inlet conditions and internal losses. The test results of the complete machine should prevail, or sufficient performance margin should be reserved.
Misunderstanding 3: Ignoring changes in filter resistance. System end configurationWhen using HEPA/ULPA high-efficiency filters , the initial resistance of the filter and the resistance at the end of use should be included in the calculation of the working point. If you select based on cleaning status only, the air volume may be insufficient after running for a period of time. When the process requirements are higher, it can be evaluatedDoes the ULPA ultra-high efficiency filter meet the requirements?
Misunderstanding 4: There is no agreement on acceptance conditions. During acceptance, only the air volume is measured, and the external static pressure and complete machine power are not measured. It is impossible to judge whether the equipment meets the design requirements. The measurement position, rotation speed, filter status and valve opening should be agreed upon.
Division of labor in different equipment forms
The fan box is responsible for providing power, and it does not have high-efficiency filtration capabilities just because the name has 'box'. When cleanliness is required, the filtration level, mounting location and sealing requirements should be determined individually.
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 between these equipment and the fan box should be clearly stated on the system flow chart.
Acceptance conditions should be written as measurable items
Project acceptance should still agree on the measurement conditions of air volume, external static pressure, power and noise, and avoid using the rated parameters of a certain component to replace the performance of the entire machine. It is recommended to state in the technical conditions:
Design air volume and common air volume
Corresponding external static pressure
Machine input power
Noise measurement distance and rotational speed
Filter status and valve opening
Speed adjustment range and control actions
Response after fault alarm and disconnection
Aili Industrial has the supporting capabilities of fans, motors and control systems, and can be discussed based on the project.The complete configuration of the fan 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.
