Screw Blowers
Industrial standard ISO-1217 requires the performance of the blower to be measured at the blower outlet. This is a far more accurate indication of the performance of the blower and clearly qualifies the air volume that is available to the aeration system. That is the reason why, for instance, our company provides data for its low pressure screw blowers' in line with the ISO1217 standard, which requires the performance of the blower to be stated as FAD (Free Air Delivery) - the actual volume of air at the
blower outlet.
From an operational standpoint, it may not always be appreciated that when comparing the energy efficiency of different blower technologies the performance data may not be presented in a comparable manner. For example, lobe blower performance data is commonly offered by indicating the air intake flow volume and the energy used at lobe element shaft, not the actual volume of air the blower package delivers - the net usable air - and not the energy consumption including all the blower package power losses.
This anomaly is all the more surprising when it applies to waste water aeration process operations. In order to maintain the desired oxygen level within the aeration lanes, the precise volume of the aeration air being supplied by the blowers is a critical factor in sustaining the aerobic process. It is for this reason that the latest revision to the Water Industry Mechanical and Electrical Specifications (WIMES) for low pressure blowers has included measuring the blower performance according to the ISO 1217 standard, reflecting the evolving needs of the water industry.
From a technical perspective, the lobe blower has to work harder and therefore less efficiently because the delivered air is compressed externally and depends on back pressure from the connected pipeline (and from water resistance in the aeration tank) to maintain the required air flow and pressure. By contrast, the rotary screw type blower demands less energy because the internal compression concept offers higher efficiency. This becomes even more significant when there is a variable aeration demand; the screw blower exhibits a more consistent volumetric efficiency derived from the design of the rotor elements.
When comparing blower technologies a true package power evaluation should be made. The factors to be considered should include the pressure drops within the blower, transmission losses: belt drive compared to direct drive, motor efficiency and, of course, the air volume at the blower outlet versus the total package power input.
On face value, the lobe blower may appear to offer plant operators a simple, low cost, basic option for low pressure air applications. The reality is that in a low carbon economy many industrial applications can benefit from improved performance and significant energy savings through the replacement of conventional lobe equipment with innovative and sustainable, screw technology solutions.
The increased emphasis on the ISO 1217 standard in providing flow figures from a blower will ensure that operators are provided with a truer picture of blower efficiency and the FAD volume of air that is supplied to their processes.
Additional information can be found at the Fan and Blower company web site http://www.fanblower.com
Susann Terlitski
Air Handling Units (AHU) Engineer
Fan and Blower Co.
http://www.fanblower.com/product.htm
http://www.fanblower.com/manufacturers_centrifugal_blower.htm
blower outlet.
From an operational standpoint, it may not always be appreciated that when comparing the energy efficiency of different blower technologies the performance data may not be presented in a comparable manner. For example, lobe blower performance data is commonly offered by indicating the air intake flow volume and the energy used at lobe element shaft, not the actual volume of air the blower package delivers - the net usable air - and not the energy consumption including all the blower package power losses.
This anomaly is all the more surprising when it applies to waste water aeration process operations. In order to maintain the desired oxygen level within the aeration lanes, the precise volume of the aeration air being supplied by the blowers is a critical factor in sustaining the aerobic process. It is for this reason that the latest revision to the Water Industry Mechanical and Electrical Specifications (WIMES) for low pressure blowers has included measuring the blower performance according to the ISO 1217 standard, reflecting the evolving needs of the water industry.
From a technical perspective, the lobe blower has to work harder and therefore less efficiently because the delivered air is compressed externally and depends on back pressure from the connected pipeline (and from water resistance in the aeration tank) to maintain the required air flow and pressure. By contrast, the rotary screw type blower demands less energy because the internal compression concept offers higher efficiency. This becomes even more significant when there is a variable aeration demand; the screw blower exhibits a more consistent volumetric efficiency derived from the design of the rotor elements.
When comparing blower technologies a true package power evaluation should be made. The factors to be considered should include the pressure drops within the blower, transmission losses: belt drive compared to direct drive, motor efficiency and, of course, the air volume at the blower outlet versus the total package power input.
On face value, the lobe blower may appear to offer plant operators a simple, low cost, basic option for low pressure air applications. The reality is that in a low carbon economy many industrial applications can benefit from improved performance and significant energy savings through the replacement of conventional lobe equipment with innovative and sustainable, screw technology solutions.
The increased emphasis on the ISO 1217 standard in providing flow figures from a blower will ensure that operators are provided with a truer picture of blower efficiency and the FAD volume of air that is supplied to their processes.
Additional information can be found at the Fan and Blower company web site http://www.fanblower.com
Susann Terlitski
Air Handling Units (AHU) Engineer
Fan and Blower Co.
http://www.fanblower.com/product.htm
http://www.fanblower.com/manufacturers_centrifugal_blower.htm
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