Performance Improvement of Evaporative Cooler Equipped with a Permanent Magnet Brushless Motor Using Power Control Method

Abstract

Evaporative coolers as one of the least efficient and commonly used electrical power consumers are used in vast areas of Iran. Rrecent government agencies focus on improving this consumer by modifying motor design or replacing the single-phase induction motor with higher-efficiency motors, such as brushless motors. The control method of brushless motor used in this application is often based on the speed control, in which it works at constant speeds (for example, two speeds high and low). However, laboratory tests show that due to special characteristics of the cooler’s fan, the amount of air flow rate is not related to the fan speed alone. Commercial evaporative coolers are designed for a certain length of the channel that it is able to deliver its nominal flow. Increasing the length of channel by the owner can reduce the airflow rate and practically, despite the paid cost, no good airflow rate can be achieved. To remedy this problem, a new approach is proposed in this paper to stabilize airflow rate. For this purpose, instead of using the constant speed control approach, the motor is controlled in a constant power approach. The details of the requirement’s design and application of brushless motor in the evaporative cooler, as well as the results of the test of a 0.5 hp (horse power) brushless motor using the dynamometer are presented.  The results are compared with the results of a typical single-phase induction motor test. Afterwards, a 5000 m3/h evaporative cooler equipped with brushless motor is tested in the reference laboratory under airflow test. It is carried out both in constant speed and in constant power control approaches. The captured results indicate the absolute superiority of brushless motor rather than single phase induction motor, and also the constant power control method has better performance rather than constant speed method.