Application of Fuzzy Logic Control for Roof-Top Bus Multi-Circuit Air Conditioning System

[html] H. Nasution[1] [2], M. N. Musa[2], H. Abdullah[2], M. N. W. Hassan[2], M. A. Baharain[2], and M. K. Mansour[3]

[1] Department of Mechanical Engineering, Faculty of Industrial Technology Universitas Bung Hatta, Indonesia
Email: henrynasution@yahoo.com
[2] Department of Thermo-Fluids, Faculty of Mechanical Engineering
Universiti Teknologi Malaysia
Tel: +607 5534878, +607 5533333 Fax: +607 5566159

Email: mdnor@fkm.utm.my
Email: hayati@fkm.utm.my
Email: matnawi@fkm.utm.my
Email: akmal@utm.my
[3] Department of Mechanical Engineering, Faculty of Engineering
Alexandria University, Egypt
Email: mdkhamis@gmail.com



Abstract - A multi-circuit roof-top bus air-conditioning (AC) system has been developed. Depending on the cooling load, either one or more circuits may automatically be switched on. The speed of one of the running compressors may automatically be varied in order to fine-tune the response of the system to the continuous variation of the cooling load. This paper presents an algorithm developed based on fuzzy logic control (FLC) that enables selected compressors to run at the appropriate operating speed. The main objective of the experimental work is to evaluate the energy saving obtained when the fuzzy algorithm, through an inverter, continuously regulates the compressor speed. The experiments were conducted, without external load, with temperature set-points for the conditioned space of 22, 23 and 24 C. Measurements were taken at a time interval of one minute. The experimental results show that significant energy savings of approximately 51.39 to 60.62%, 42.30 to 64.35% and 39.14 to 56.91% were obtained, with respect to the three temperature set-points. Another objective of the study is to determine the amount of energy saved when a conventional thermostat control mechanism is applied to the AC system. The thermostat control imposes an on/off cycle on one selected compressor that runs at the nominal frequency of 50 Hz. Measurements were taken under the same respective condition of the three temperature set-points. Comparison between the two results shows that the use of FLC gives more energy saving than the use of the on/off control.

Conclusion - The FLC developed was able to control the motor speed in order to maintain the cabin temperature at or close to the set point temperature. The FLC controller tries to minimize the error between the set point temperature and the cabin temperature. If the cabin temperature reaches the set point, the motor speed is abruptly reduced and will fluctuate to maintain the cabin temperature. However, when the cabin is thermally loaded, the controller act in such a way that the heat recovery to the cabin is faster until the temperature set point is reached again. For the on/off control, the controller turns on (50 Hz) the motor compressor when the cabin temperature reaches the upper limit temperature setting, and turns off (0 Hz) at the lower limit temperature setting. Energy saving is obtained when the motor is not working. The longer the motor compressor is off more energy is saved. The study has shown that FLC gives a higher saving and provides a better control when compared to the on/off controller. The system’s performance in terms of COP is found to follow similar trends for all the internal heat loads for the FLC experiments. [/html]