Saving energy using fuzzy control applied to a chiller: an experimental study

In this study the energy consumption of a chiller system, under different configurations and control strategies, was investigated. Two control strategies (Proportional integral—PI and fuzzy-PI) were applied to regulate the temperature of propylene glycol solution and the evaporating temperature using compressor motor supply frequency and pump rotation frequency as manipulated variables. The experiments were initiated with the system in open loop. When the steady-state condition was reached the system was submitted to a positive disturbance in its heat load and the feedback control was activated. Hence, the results were analyzed by means of integral of the time-weighted absolute error (ITAE) criterion and total energy consumption. The analysis of experimental results showed that both controllers were able to regulate the controlled variables appropriately. Also, it was verified that the use of the compressor motor supply frequency as manipulated variable can smooth out process variable oscillations. Besides, comparing the energy demands of both controllers, it was observed that the fuzzy-PI controller required 3.4% less electric energy (0.81 kWh). Considering the propylene glycol solution temperature (secondary fluid) as controlled variable and compressor motor supply frequency as manipulated variable, fuzzy-PI control achieves smaller ITAE index value, and energy consumption than the PI counterpart, consuming 0.25 kWh less energy. Thus, energy savings could be attained for control configurations that exhibit higher ITAE values. It was demonstrated that is desirable to include the energy consumption as a control performance parameter in order to increase the energetic efficiency of process.