Experimental analysis of the scroll compressor performances varying its speed

Referring to a vapour compression plant able to operate both as water chiller and heat pump, the aim of this paper is to evaluate experimentally the energy saving obtainable varying the scroll compressor speed to control the refrigeration capacity instead of the classical thermostatic control. The compressor speed is continuously controlled by means of a fuzzy algorithm regulating an inverter located on the electric line supplying the compressor motor. On the contrary the control by thermostat imposes on/off cycles on the compressor that works at the nominal frequency of 50 Hz. In particular, the performances of a vapour compression experimental plant, generally used in industrial processing or conditioning plants where a supply of refrigerated and reheated water is required, are studied. The experimental plant is made up of an hermetic scroll compressor, a plate-type water heat exchanger inserted in a water tank, a finned tube air heat exchanger, two thermostatic expansion valves that have substituted the classical capillaries not suitable for fast load variations. The use of a scroll compressor allows to have a compressor electric motor supply current frequency even of 15 Hz in comparison with the semi-hermetic reciprocating compressor that for frequency values under 30 Hz presents considerable vibrations and noise increase together with the lubrication troubles due to the splash system. For different working conditions a significant energy saving on average equal to about 20% has been obtained adopting a scroll compressor speed control algorithm, based on the fuzzy logic, in comparison with the classical thermostatic control. Moreover, in this paper the aim has been to determine also experimentally the optimum frequency, corresponding to a definite heating (cooling) load, to be imposed to a compressor electric motor by means of an inverter to obtain the highest energy saving.