Evaporative coolers with single-phase induction motors (SPIMs) are one of the least efficient and most commonly used electrical power consumers all over the world. Recently, it has been suggested to substitute SPIMs with higher-efficiency motors, such as permanent magnet brushless (PMBL) motors.
However, control method for brushless motors often work based on speed, while laboratory tests indicate that, due to fluid characteristics of the blower, the airflow rate is not just related to the speed, where increasing the cooler’s duct length reduces the airflow rate, thereby preventing the desired airflow rate to be reached.
To overcome this problem, in this work, a new power based control scheme has been developed to stabilize the outlet airflow rate instead of the speed control. In this approach, output power of PMBL motor is regulated around a set point power corresponding to the desired air flow rate. A 5000 m3/h evaporative cooler equipped with brushless motor was tested with both constant speed and power control strategies. Results indicated superiority of the proposed brushless motor drive and power control scheme.
- Brushless motor
- Electric drive
- Energy saving
- Evaporative cooler
- Power control
In this paper, application of a brushless motor drive for a 5000 m3/h commercial evaporative cooler to replace a conventional SPIM has been investigated. Efficiency test results indicate an improved efficiency of at least 75% compared to SPIM. This would improve the energy ranking grade of the evaporative cooler system from IE1 to IE5. Challenges involved in airflow reduction due to various pressure differences caused by restrictions in ducting systems (length, bends, etc.) were discussed.
A newly constant power control method was proposed to replace the conventional constant speed control method to overcome such challenges. Various approaches were expressed for determination of feedback power, required in the proposed power control method. For simplicity and cost efficiency, the input current of the drive, proportional to the feedback power was employed for this purpose.
Air flow rate test results confirmed that the proposed method could maintain a desired flow at longer ducting systems or operating conditions yielding higher pressure differences. Further improvements may be achieved in increasing the system reliability and cost efficiency, using sensorless control methods or employing directly coupled brushless motor assembly.
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