A brief discussion on the selection of fans
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I. When selecting a ventilation fan, the following factors should be taken into consideration: 1 The fan must be capable of handling the total air volume required by the system, plus the air leakage caused by the ductwork and equipment； Note: The positive pressure dust removal system does not take into account the air leakage rate of the dust collectors. 2 When using a fan with a fixed speed, the fan’s pressure should be 10%-15% higher than the pressure loss calculated for the system ； 3 When variable-frequency ventilators are used, the pressure of the ventilator should be based on the total pressure loss calculated for the system as the rated wind pressure; however, the power of the ventilator’s motor should be increased by an additional 15%-20% on top of the calculated value ； 4 The efficiency under the design operating conditions for fan selection shall not be lower than 90% of the fan’s maximum efficiency. II. For ventilation and air conditioning systems that handle air at non-standard conditions, when the system pressure loss is calculated using charts based on standard conditions and actual volumetric air flow rates, and fans are selected from standard fan performance tables, neither the air flow rate nor the air pressure needs to be adjusted; however, the shaft power of the motor must be verified. III. When the air volume or resistance of the ventilation system is high and a single ventilator is insufficient to meet the requirements, it is advisable to use two or more ventilators of the same model and with the same performance, installed in parallel or in series. However, the air volume and pressure under their combined operation should be determined based on the characteristic curves of the ventilators and the ducts. Ventilators of different models and with different performance characteristics should not be installed in series or in parallel.
1# rong10 is very useful; choosing the right fan is also key to energy savings
This seems to be part of some standard or specification; could you explain it using a practical example?
It’s very practical; I exactly needed this kind of knowledge. Thank you
The fans used in traditional boilers regulate the air volume through dampers, which causes the motor to operate at full load all the time, resulting in high power consumption. Currently, in many coal slurry-fed boilers, the fans used are regulated in terms of airflow volume through frequency converters, which makes operation simple and saves energy!
It still seems like something theoretical; it would be better if it could be analyzed in conjunction with engineering examples
For fan selection, it is first necessary to understand that fans are devices within a system. To this end, the air volume and air pressure of the fan must meet the requirements of the system. I usually use this approach to select fans. 1. Determine the air volume required by the fan through mass and heat balance calculations ； 2. Carry out plan and elevation layouts and prepare pipe layout diagrams ； 3. The resistance is calculated using the rated air volume; the resulting system pressure loss is then multiplied by a coefficient to determine the air volume required by the fan ； 4. Since the performance curves and parameters provided by our fan manufacturers are based on standard conditions, adjustments are made to account for the properties of the medium and local weather conditions, in order to determine the parameters required for the fans ； 5. Select the manufacturer from which to place the order, make a choice based on the performance curve, and ensure that the operating condition falls within the high-efficiency range. General methods for selecting ventilators: Fan selection is a highly technical task, and there are many specific methods for doing so. These include selection based on dimensionless characteristic curves, selection using logarithmic coordinate curves, selection based on dimensional characteristic curves or performance tables, variant selection, and selection based on the resistance in the piping system. Nowadays, it is also possible to use web-based selection systems and specialized selection software for this purpose. The methods are diverse and complex, and mastering some of them requires certain specialized knowledge. For general business personnel, it is sufficient to be familiar with and master both the method of selecting based on dimensionless performance tables and specialized selection software for fans. These two methods are simple and easy to operate. When selecting a fan, one first determines the model and series number of the fan based on the two basic parameters: the air volume and total pressure required. This can be done using the fan’s dimensional performance table (relevant data is provided in the product manuals of various fan manufacturers), and it is possible that more than one product meets the requirements ； At this point, taking into account factors such as the fan’s intended use, process requirements, and operating environment, the type, model, and structural material of the fan are selected to meet the required operating conditions. The goal is to ensure that the fan’s rated flow rate and pressure are as close as possible to those specified by the process requirements, so that the operating point of the fan falls within its efficient range. The specific principles are as follows: 1) Before selecting a ventilator, it is necessary to understand the production and quality of ventilators in the country, including the types and specifications of ventilators produced, the specific uses of various products, as well as the development and dissemination of new products. Environmental protection requirements should also be fully considered in order to select the most suitable ventilator. 2) Select fans with different applications based on the physical and chemical properties of the gases conveyed by the fans. If transporting explosive and flammable gases, an explosion-proof ventilator should be selected ； For dust removal or conveying coal powder, a dust removal or coal powder ventilator should be selected ； For transporting corrosive gases, corrosion-resistant ventilators should be selected ； For use in high-temperature environments or for transporting high-temperature gases, high-temperature ventilators should be selected. 3) When more than two types of fans are available for selection as indicated on the fan performance chart, priority should be given to the fan with higher efficiency, a smaller model number, and a wider range of adjustment. Of course, it is also necessary to compare them and weigh the pros and cons before making a decision. 4) If the diameter of the fan impeller selected is much larger than that of the original fan’s impeller, in order to make use of the existing motor shaft, bearings, and supports, it is necessary to evaluate the motor’s starting time, the strength of the fan’s original components, and the critical speed of the shaft. 5) When selecting a centrifugal ventilator, if the power of the motor associated with it is 75 KW or less, it is not necessary to install a valve intended solely for starting purposes. When a centrifugal boiler exhaust fan is selected for conveying hot flue gas or air, a starting valve should be installed to prevent overload during cold operation. 6) For ventilation systems with noise reduction requirements, fans with high efficiency and low impeller peripheral speed should be selected, and they should operate at their peak efficiency point ； Appropriate noise reduction and vibration damping measures should also be taken, depending on the way in which noise and vibrations generated by the ventilation system are transmitted. For vibration reduction measures of ventilators and motors, vibration-damping foundations can generally be used, such as spring dampers or rubber dampers. 7) When selecting a ventilator, parallel or series operation of ventilators should be avoided as much as possible. When it is inevitable, fans of the same model and with the same performance should be selected to operate together. When used in series, there should be a certain piping connection between the first-stage ventilator and the second-stage ventilator. 8) The selected fresh air unit should take into account issues such as making full use of existing equipment, suitability for on-site fabrication and installation, and safe operation.
I’d like to read the content of the original poster’s article, thank you