How to choose the fan box motor? Start with shaft power, temperature rise and control requirements
Direct answer: When selecting a fan box motor, the power cannot be determined first. Instead, the shaft power should be calculated based on the target operating point, and then the operating margin, temperature rise, power supply, and speed regulation method should be considered. The rated power of the motor is only the upper limit of the capability. What really determines the operating performance is the input power of the whole machine under the target air volume and external static pressure. For projects with continuous operation, frequent starts and stops or wide-range speed regulation, the thermal load of the motor and driver must be additionally checked.
Aili Industry is discussingWhen configuring the fan box motor and drive , it is usually required to provide the design air volume, external static pressure, operating time, power supply conditions and control requirements, and then check the motor, fan and box structure accordingly.
Calculate the shaft power first, then determine the motor power
Shaft power is the actual mechanical power consumed by the fan impeller at the target operating point. It is determined by air volume, pressure, fan efficiency and transmission efficiency. For a simple estimate, you can multiply the air volume by the pressure, and then divide it by the fan efficiency and transmission efficiency; after unit conversion, the approximate value of the shaft power is obtained.
After the shaft power is calculated, the motor rated power should be greater than the shaft power, with a reasonable margin. If the margin is too small, the motor may be overloaded if the filter accumulates dust, the air duct leaks, or the system resistance increases. If the margin is too large, the motor will run in the low load area for a long time, and the efficiency and power factor will decrease, which will increase the operating cost. A reasonable margin range is typically a 10 to 20 percent increase in shaft power, depending on how much system resistance changes can be expected.
If the end of the system is configuredFor HEPA/ULPA high-efficiency filters , the initial resistance and post-use resistance of the filter should be included in the calculation of the working point. Select the motor according to the pressure difference allowed before maintenance to ensure that the terminal air volume can still be met after the filter accumulates dust. When the process requirements are higher, it can be evaluatedDoes the ULPA ultra-high efficiency filter meet the requirements?
Continuous operation and speed adjustment must be checked separately.
Projects that require long-term continuous operation should pay attention to the temperature rise, insulation level and bearing life of the motor. When the motor is running near the rated point, the temperature rise is controllable, but if it runs at low speed for a long time, the cooling effect of the built-in fan will decrease, and the temperature rise may increase instead. When using DC speed regulation or variable frequency speed regulation, the motor needs to confirm whether it is allowed to run continuously in the low speed zone. If necessary, use an independent fan for forced cooling.
For projects with frequent starts and stops, the starting current, number of starts and stops and protection devices must be checked. Just because the rated power of the motor meets the requirements does not mean that unlimited starts and stops are allowed. The procurement documents should indicate the number of starts and stops per day, the duration of each operation and whether hot starts are allowed.
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. The electrical diagram and terminal description should be checked before on-site wiring.
Temperature rise is not just a problem with the motor itself
The temperature rise of the motor is affected by the ambient temperature, altitude, installation space and ventilation conditions. The same motor may have completely different temperature rises when installed in a well-ventilated machine room or in a closed mezzanine. As the altitude increases, the air density decreases, the cooling effect becomes worse, and the motor needs to be derated.
Drives also get hot. If the driver is installed in a box or control cabinet, insufficient heat dissipation space may cause overheating alarm or reduced frequency operation. During the selection stage, the installation location, surrounding space and protection level of the driver should be confirmed. Do not wait until the equipment arrives to discover that the control cabinet cannot be placed or the heat dissipation is insufficient.
Control needs determine the motor solution
Control requirements directly affect the selection of motors and drives. Fixed-speed operation projects can use AC fixed-speed motors, which have simple structure and easy maintenance. For projects that need to adjust the air volume in different time periods, AC variable frequency motors or EC motors can be used to adjust the speed through analog, PWM or communication signals.
The speed of the EC motor is controlled by the matching driver, and the speed control signal can be analog, PWM or communication. The terminal definitions of different drives may be different. Please check with the electrical diagram and terminal description before on-site wiring. If the project requires status reading by the building control system, it should also be clear whether the operating feedback and fault feedback are independent signals or obtained through communication.
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.
Don’t just look at motor efficiency
Even if the motor efficiency is high, if the fan operating point is far from the appropriate range for a long time, the power consumption of the whole machine may still be high. When comparing motor plans, the input power of the entire machine under the same air volume and static pressure should be used as the basis for judgment, and the noise, temperature rise, and expected number of starts and stops should be checked at the same time.
The rated power of the motor is used to define the motor's capability, and the input power of the whole machine is the actual power consumption of the fan box under specific working conditions. The two are not the same number. When comparing, the supplier should be asked to indicate the rotation speed, filter status and valve opening during the test. Power figures for test conditions are missing and cannot be used for scenario comparison.
Acceptance based on complete machine performance
Procurement documents should record the air volume, static pressure, input power and control actions of the complete machine. The motor model is only part of the configuration. These data should be measured during acceptance and the valve opening, filter status and rotation speed should be recorded. Only by checking the motor nameplate, it is impossible to determine whether the equipment meets the design requirements.
Aili Industrial DiscussionWhen configuring the fan box motor and drive , we can combine the supporting capabilities of our own motors and fans to implement a power plan from the working point. 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 finalize them based on the determined working points and on-site interfaces.
