The potential of a variable speed compressor running with a controller to provide enhanced load-matching capability, energy saving and thermal comfort for application in roof-top bus air conditioning system is demonstrated. This paper presents an algorithm developed based on fuzzy logic control (FLC) and programmable logic control (PLC), which allows 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 FLC and PLC algorithm, through an inverter, continuously regulates the compressor speed. It demonstrates better control of the compressor operation in terms of energy consumption as compared to the control by using a thermostat imposing on/off cycles on the compressor at the nominal frequency of 50 Hz. The experimental set-up consists of original components from the air conditioning system of a compact passenger vehicle. The experiments were conducted with temperature set-points for the conditioned space of 22oC. Measurements were taken at a time interval of one minute. The experimental results indicate that the proposed technique can save energy and improve indoor
comfort significantly for roof-top bus air conditioning systems compared to the conventional (on/off) control
technique. The experimental results also showed that more energy saving can be obtained through the use of FLC when compared to the PLC and on/off control.