How to select the air volume of the DC fan box of a new air conditioning system? Use two sets of peak and common working conditions
When selecting a DC fan case for many new air conditioning projects, only a design air volume and a design static pressure are given. The manufacturer selects a piece of equipment according to this point. If the air volume and static pressure are sufficient, it is done. After installing it, I found that the system did not operate at the design point most of the time, the actual energy consumption was much higher than expected, and the speed adjustment range did not cover commonly used partial load conditions.
The problem is that only peak operating condition selection is used. The value of the DC fan box lies in speed regulation. Whether the speed regulation range can cover the actual operating range throughout the year determines whether it can truly supply air on demand. Therefore, at least two sets of working conditions are required for model selection: a set of peak values to ensure capacity; a set of common conditions to check speed regulation and energy consumption.
Direct answer: When choosing a DC fan chassis for a new air conditioning system, first consider the design peak air volume and corresponding external static pressure as the first set of working conditions, and confirm on the fan performance curve that the equipment can meet the air supply requirements under the most unfavorable conditions. Then use the part-load air volume and corresponding static pressure that the system often operates as the second set of working conditions to check the stability, efficiency and noise of the motor, driver and fan in this range. The selection is complete only if both groups are covered.
Group 1: Guaranteed design capabilities under peak operating conditions
Peak operating conditions come from HVAC design. After the total air volume of the system is determined, the pressure losses of the filter section, coil, damper, muffler, elbow and straight section of the air duct are calculated along the most unfavorable path, and the total external static pressure is obtained. The design air volume and external static pressure form the peak operating point, and find the corresponding position on the fan performance curve.
This point should fall near the high efficiency area of the fan, and the motor and driver should have the ability to cover it. The peak operating condition is not necessarily the longest operating condition throughout the year, but it determines the lower limit of equipment capacity. If the peak working conditions cannot be met, it will be useless no matter how good the speed adjustment is later.
When selecting, confirm the shaft power at the peak point, the input power of the whole machine and the noise. The shaft power determines the motor capacity, the input power of the whole machine is used for energy consumption calculation, and the noise determines whether additional noise reduction measures are needed. Just look at whether the air volume is sufficient without looking at the other three items, and the selection is incomplete.
If the system is configuredFor HEPA/ULPA high-efficiency filters , peak operating conditions should be calculated based on the final resistance of the filter, not the initial resistance. The final resistance may be two to three times the initial resistance. If the model is selected based on the initial resistance, the air volume may not be enough after a few months of operation. When the process requirements are higher, it can be evaluatedDoes the ULPA ultra-high efficiency filter meet the requirements?
Group 2: Common working conditions determine the speed range and energy consumption
Common operating conditions are the points where the system actually operates most of the time and the corresponding external static pressure. It may be lower than the peak air volume, or it may be a change in resistance due to part of the branch being closed. This working condition determines whether the speed regulation range of the DC fan box covers the actual operating range, and also determines the annual energy consumption level.
Mark the common air volume and the corresponding external static pressure on the performance curve, and confirm that this point falls within the range where the fan and driver can operate stably. If the speed drops too low, the fan may enter an unstable zone or be unable to overcome the resistance of the filter section. Whether the driver output torque is sufficient at low speed and whether the motor temperature rise is controllable, these must be checked.
The input power of the whole machine under common working conditions is the basis for calculating the annual power consumption. Multiply the power under common operating conditions by the corresponding operating hours, and then add it to the power under peak operating conditions multiplied by the peak hours to get the estimated annual electricity consumption. If you only multiply the peak power by the number of hours throughout the year, you will overestimate energy consumption; if you only calculate it based on common operating conditions, you will miss the peak hours.
From the fan law, the air volume is proportional to the rotational speed, and the shaft power is 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. This is the fundamental reason for speed regulation and energy saving. However, the actual energy saving depends on the load curve, system resistance characteristics and speed regulation strategy. Whether the commonly used operating point falls in the high-efficiency zone directly determines whether the energy-saving effect can be realized.
Filter segments and control boundaries should be included simultaneously
The resistance of the filter section is a factor that must be considered in both groups of working conditions. Peak operating conditions are calculated based on final resistance, and common operating conditions can be calculated based on typical operating conditions, such as filter mid-section resistance or average resistance. If the system has pressure difference control, the control target should match the resistance change range of the filter section to avoid frequent adjustment of the rotation speed.
The control boundaries should also be confirmed during model selection. What is the speed command corresponding to common working conditions, the minimum operating air volume is determined by the end demand, and how the equipment will act when a fault occurs. These should be stated in the control point table. Just writing 'adjustable speed' is not enough. Specific signal types, terminal definitions and action logic are required during on-site debugging.
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 devices and the DC fan chassis should be clearly stated on the system flow chart.
How to implement two groups of working conditions in model selection
During actual selection, two sets of working conditions can be written into a table: peak air volume, peak external static pressure, corresponding shaft power, complete machine input power, noise; common air volume, common external static pressure, corresponding rotation speed, complete machine input power, and expected annual operating hours. This form is given to the manufacturer as a basis for selection and acceptance.
If the two groups of working conditions differ greatly, it means that the system load has changed significantly, and the value of DC speed regulation is higher. If the two groups of working conditions are close, the system is basically running at full load, and the benefits brought by speed regulation mainly come from the motor efficiency itself. In either case, the two sets of working conditions can help determine whether the equipment capacity and speed range match.
Aili Industry has independent supporting capabilities in fans, motors, controls and sheet metal structures. It can check the impeller, motor, driver and box under two sets of peak and common working conditions to confirm the efficiency, noise and stability of the complete machine under common working conditions. It also checks whether the speed regulation range can cover the range from the peak to the lowest operating air volume. This kind of internal collaboration from the power end to the entire machine structure can reduce the common problems of low efficiency under common working conditions and insufficient coverage of the speed regulation range that are common in outsourced assembly solutions. The project provides two sets of working conditions and on-site interface conditions, and the complete machine configuration and test conditions can be confirmed before leaving the factory.
The technical conditions must clearly state two sets of working conditions.
In the procurement technical conditions, in addition to the design air volume and external static pressure, the air volume, static pressure and expected operating hours under common working conditions should also be stated. During acceptance, the air volume, static pressure, input power and noise of the whole machine were measured under two sets of working conditions, and the rotation speed and filter status were recorded. Without the acceptance of common working condition data, it is impossible to judge the performance of the equipment in actual operation.
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.
