How to determine the air volume of the DC fan box in a new air conditioning system? Summary from partition requirements
Direct answer: The air volume of the DC fan box of a newly built air conditioning system cannot be inferred from the fan sample, nor can it be estimated based on only one air change number. The correct sequence is to first clarify the air supply needs of each zone, balance the air volume in the zones, then summarize the total air volume of the system, calculate the resistance of the most unfavorable path, obtain the design working point, and finally select the DC fan box. Whether the air volume is reasonably determined directly determines the air duct size, system static pressure, equipment selection and annual energy consumption.
Aili Industry is discussingWhen selecting a fan box , the project is usually required to provide a zone air volume balance table, the most unfavorable path pressure loss and operating period, and then check the fan, motor and control configuration accordingly.
Zone air volume balancing is the first step
The air volume for a new air conditioning system should be summarized starting from the needs of the room or zone. How much air supply volume is required for each zone depends on the room usage, heat and moisture load, fresh air volume, number of personnel and process requirements. List these requirements item by item to form a partition air volume balance table, and then consider the simultaneous use coefficient and pipeline air leakage margin to obtain the total air volume of the system.
The zone air volume balance table should at least include: zone name, supply air volume, return air volume, exhaust air volume, fresh air volume, simultaneous use coefficient and remarks. If multiple partitions share a fan chassis, it is also necessary to indicate which areas are running at the same time and which areas are running at a time. This information determines whether the total air volume of the system is simply added, or whether simultaneous use factors need to be considered.
System end configurationWhen using a HEPA/ULPA high-efficiency filter , the resistance of the filter will affect the air supply volume. When the process requirements are higher, it can be evaluatedDoes the ULPA ultra-high efficiency filter meet the requirements?
The number of air changes cannot replace the load calculation
The air supply volume of the air conditioning system may be constrained by heat and moisture load, fresh air volume and air distribution requirements at the same time. The calculation cannot be completed by multiplying the number of air changes by the room volume. The number of air changes is an empirical reference value, not a design basis. For rooms of the same size, the air supply volume may vary greatly due to different equipment calorific values, different numbers of personnel, and different fresh air requirements.
The correct approach is to first determine the design basis for each area from the HVAC plan, and then assign it to the system served by the fan box. If you only estimate based on the number of air changes, two problems may occur: the estimate is too large, the equipment selection is too large, and it runs at low load for a long time; the estimate is too small, the terminal air volume is insufficient, and the room temperature, humidity or cleanliness is not up to standard.
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.
The most unfavorable path determines the external static pressure
After obtaining the total air volume of the system, the next step is to calculate the system resistance. Calculate the pressure loss of the filter section, coil, air duct, elbow, reducer, valve and end along the most unfavorable path, and then consider a reasonable usage margin. The least favorable path is not necessarily the physically longest path, but the path with the greatest pressure loss. Although some branches are short, they have many elbows and valves or the resistance of the end filter is large, and the pressure loss may exceed that of a long straight pipe.
What the fan box needs to overcome is the external static pressure, that is, the pressure at the outlet of the fan box that can be used to overcome the resistance of the external pipeline. The internal losses of the unit and the outlet dynamic pressure cannot be counted as external static pressure. When enquiring, the supplier should be asked to clearly indicate the measurement boundaries and avoid using full pressure instead of external static pressure.
If the system is equipped with a high-efficiency filter, the pressure difference at the end of the filter's use should also be checked. If the model is selected only according to the clean state, the terminal air volume may not be satisfied after running for a period of time. The design working condition should use the pressure difference allowed before maintenance. Common working conditions can use clean state or typical operating state, but the conditions must be noted.
Common working conditions determine the speed adjustment range
The value of DC speed regulation often occurs during part load periods. The design document should list both peak operating conditions and common operating conditions, allowing the manufacturer to check the operating range based on the fan, motor and control configuration, rather than just delivering a peak air volume number.
Peak working conditions are used to check the air supply capacity, and common working conditions are used to judge energy consumption. If the system operates at full load for a long time, the benefits brought by speed regulation are limited; if there are obvious on-duty or partial load periods, the value of the speed regulation solution will be reflected. 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.
Common operating conditions should indicate the corresponding external static pressure and expected operating hours. If only peak operating conditions are provided, the project can only confirm the upper limit of equipment capacity and cannot evaluate long-term operating energy consumption.
Leave the partition balance table and resistance calculation to the manufacturer
Determining the air volume of a new air conditioning system is not a one-time calculation, but a process of aligning end demand, system resistance, equipment capabilities and installation conditions. The project party provides the zone air volume balance table, the most unfavorable path pressure loss and the operating period. The manufacturer can check the fan, motor and control configuration accordingly to form an executable plan.
Aili Industrial can discuss based on the design and common working conditions.DC fan box . Motor, fan and control combination for 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.
