Optimization of the variable speed compressor performances

In the last years referring to the vapour compression plants the substitution of refrigerant fluids damaging the environment and the necessity of energy saving have mainly caused the products and production process changes. The principal vapour compression plant component is the compressor which has recently been object of changes and optimizations. Generally the refrigeration and heat pump systems are designed for working under conditions of maximum load, but actually these plants work above all at partial load with compressor on/off cycles regulated by a classical thermostat. On the contrary the compressor speed continuous control allows to match opportunely the compressor capacity to the load at any time and to obtain so energy savings in comparison with the thermostat. Referring to the small size plants the aim of this paper is to study, when both the compressor speed and the working conditions vary, the compressor performances not often given by the manufacturers, and to determine the optimum compressor motor supply current frequency able to obtain the highest energy saving in comparison with the working at basic frequency. So referring to reciprocating and scroll compressors high energy savings have been obtained. The optimum frequency determination for each working condition is fundamental to carry out a control algorithm which regulates continuously the compressor speed by means of an inverter.