www . refrigerationandaircon . co . za RACA Journal I January 2024 11
Associations
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HOW EC MOTORS DIFFER FROM AC MOTORS EC is an abbreviation for electronically commutated , which means that these motors deliver higher efficiencies than the conventional AC type . Refer to Graph :
DC motors are easier to speed control by fluctuating the voltage , and they are more efficient than AC motors in terms of electrical input power versus shaft output power . AC motors were the most common type of motors that we used , and they work by supplying alternating current to the windings that create an electromagnetic field . This field induces a secondary magnetic field within the rotor , and the relative movement of these fields causes the rotor to spin . The frequency of the AC power determines the speed of rotation . To use a DC motor , one needs to convert the AC power into DC power , which is all integrated within our EC motors . There are also other advantages of EC motors ,
such as Modbus communications and built-in protection devices .
FAN AERODYNAMICS Each one of the individual components has a role to play in the overall performance of the fan . If we look at only the motors , we would have heard about IE ratings . The conventional AC motors used in the past were IE1 or IE2 . Nowadays , we can go up to IE4 and higher . The efficiency of a fan is the ratio of what we get out vs what we put in . We put in electrical power and we get out air movement . The air movement can be measured in kilowatts if we use the formula : volume ( in cubic meters per second ) x pressure ( in Pascals ). This is the ideal power required to move air , without considering any losses . But in reality , the fan has
“ If we assume that the fan and
the motor are both 86 % efficient based on the catalogue data , we are totally wrong .” many individual components that contribute to such losses , such as the motor windings , belt drives , bearings and overall aerodynamics of the impeller itself . For example , if we put one kilowatt of electrical power into the motor , we don ’ t get one kilowatt of shaft power out of it . The motor has an efficiency rating that tells us how much power it can deliver to the shaft . As an example , if we buy a standard 3kW IE2 motor , it has an efficiency of ± 86 %. If we buy a premium IE4 motor , it has an efficiency of ± 88 %. This means that for every kilowatt of electrical power we put in , we get 0.86 or 0.88kW of shaft power out . The same principle applies to the other components of the fan . So , to calculate the overall efficiency of the fan , we need to consider all such factors and losses .
To accurately calculate the overall efficiency of a fan , we cannot simply use the catalogue data of maximum efficiency for individual components . We need to adjust the efficiency of the various components according to the actual performance of such , within the duty point .
This is done by applying the correction factors from ISO 12759 . For example , if we assume that the fan and the motor are both 86 % efficient based on the catalogue data , we are totally wrong . The actual overall efficiency of the fan is only 58 %. So , if I want to sell you a fan that is 2 % more efficient , but you have to pay 10 % more , how can I ever convince you ? The best and most accurate way to determine the fan efficiency is to measure it physically . We need to measure the electrical input power and the air output power and divide them by each other . However , this is not always easy in the installations or design phase . That ’ s why we use these calculations to obtain accurate results .
Globally and locally , ebmpapst can assist with selecting the most efficient fans , as well as providing detailed Life Cycle Cost calculations .
Please contact your nearest office for any further assistance . RACA
Supplied by ebm-papst
www . refrigerationandaircon . co . za RACA Journal I January 2024 11