n this paper, referring to a vapour compression plant able to operate both as refrigeration system and heat pump, the performances of the classical thermostatic
Electric energy consumption (kWh)
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control, that imposes on/off cycles at the compressor working at the nominal frequency of 50 Hz, are com- pared with that of a control algorithm based on the fuzzy logic and built in Labview environment; this algo- rithm is able to select the most suitable scroll compres- sor speed in function of the water temperature requested. In particular, the use of a scroll compressor offers advantages in comparison with the semi-hermetic reciprocating compressor both in reducing noise and vibration levels and in terms of energetic performances, because it allows to have a compressor electric motor supply current frequency also of 15 Hz. Referring to the water chiller, working for different set-point temper- atures (7, 11 and 15 °C) of the water cooled at the evap- orator and for different water pump velocities, a significant energy saving on average equal to about 20% has been obtained using the scroll compressor speed control algorithm in comparison with the thermo- static control. Similar results have been obtained related to the heat pump working. In particular, the best ener- getic performance when the scroll compressor speed var- ies is due above all to the greater global efficiency due also to its smaller compression ratio when the compres- sor speed decreases. Moreover, in this paper the aim has been to determine also experimentally the optimum fre- quency, 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. This aspect is important because it is not sure that the compressor velocity decrease determines any energy sav- ing in comparison with the thermostatic control.