【正文】 964037.Email address: (C. Renno).[1,2]. This method of refrigeration capacity control, whichconsists in varying the pressor speed to continuouslymatch the pressor refrigeration capacity to the load, hasbeen analyzed during the last years [3–10]. An inverter canbe used to regulate the pressor speed. There are differenttypes of electronic variablespeed drives, but the pulsewidth modulated source inverter (PWM) is the most suitablefor its low cost and high efficiency. The application of thistype of control of the refrigeration capacity to a mercialpressor, though presents some advantages in terms ofenergy saving, determines some disadvantages such as theinverter cost and some troubles linked to the pressorlubrication and reliability [11,12] and to the correct workingof the expansion devices. This last problem is negligiblewhen the secondary fluids at the heat exchangers are in gasphase, as in the plant examined, but it seems to beremarkable when the secondary fluids are in the liquidphase [13]. So, the primary aim of this paper is to setup acontroller capable of regulating continuously the speed of areciprocating pressor frequently used in cold stores andin other small size refrigeration systems whose this type ofpressor generally has no oil pump. This kind of controlallows us to match the pressor refrigeration capacity tothe cooling load at any time, so that the pressor can alsowork at other frequencies smaller than 50 Hz. It is to beconsidered that with the classical thermostatic controlfrequently used in the cold stores and in other small sizerefrigeration systems, the pressor works only at 50 Hz.In particular, referring to a vapor pression refrigerationplant subjected to a mercially available cold store, acontrol algorithm based on the fuzzy logic, and able to selectthe most suitable pressor speed in function of the coldstore air temperature, is presented in this paper. Apart fromthe fuzzy logic, the pressor speed control might also beobtained by means of other techniques such as thetraditional proportionalintegral and derivative control(PID) [14–18]. In particular, the fuzzy control logic,pared with PID, allows both to use better theexperimental knowledge related to the trend of the variableswhich characterize the working of the refrigeration plantand to adopt a control logic based on a nonmathematicalmodel, and hence to avoid the determination of the specificmodels of the refrigeration plant ponents [19–21].Moreover, a fuzzy controller with respect to PID controlgenerally might allow obtaining performances parableor sometimes better in terms of precision of the set pointrequired. Besides referring to a fuzzy controller theovershoot of the variables is small and the settling timefast as regards the dynamic response during the suddenvariations in the cooling load。 it is lubricated with polyester oil and its speed isregulated by means of a PWM inverter. It is formed by arectifier that converts the threephase main voltage, .380 V, 50 Hz to DC voltage and by an inverter that invertsNomenclatureCOP coefficient of performanceE_x exergy (W)ex specific exergy (J/kg)f pressor electric motor supply frequency(Hz)_Lcppressor power input (W)_m mass flow rate (kg/s)_Q thermal power (W)T temperature (8C)T0environmental temperature (8C, K)t time (s)Tair。 at the output of the inverter the voltage isadjustable in frequency and magnitude. The manifold withboth valves has been mounted to solve possible troubles,because the expansion valves behavior, when the pressor speed varies, is unknown [13]. The expansion valvesused are specifically designed for the R407C and R507. Inthe evaporation temperature range 220 to 10 8Cata308Ccondensing temperature, working with the R407C at thenominal frequency of 50 Hz, the pressor refrigerationcapacity varies in the range – kW. To fix the airtemperature on the condenser and to simulate the externalconditions, the air flows under the influence of a blower in athermally insulated channel, where some electrical resistances are located. To exactly obtain the same temperaturefixed for the air, a regulator is used to control the electricalresistances supply. In some experimental tests, the coolingload in the cold store is simulated by means of some electricheaters linked to a regulator and the electric power ismeasured by means of a Wattmeter. Table 1 lists thespecifications of the transducers used. The test apparatus isequipped with 32 bit A/D acquisition cards linked to apersonal puter allowing a high sampling rate and amonitoring of all the measures carriedout by means of thetransducers. The data acquisition software has been realizedin a Labview environment and the R407C and R507thermodynamic properties have been evaluated using adedicated software that has also been used to determine theenergy and exergy balances.3. Experimental procedure descriptionTo evaluate the plant performances when an inverteris used, it is necessary to pare the plant energyconsumption when the refrigeration capacity is regulatedby on/off cycles of the pressor that works at a supplycurrent frequency of 50 Hz, and when the refrigerationcapacity is controlled by the fuzzy algorithm. In theexperimental tests, different types of cooling loads havebeen considered. First of all some experimental tests whenthe cooling load is due both to the periodic opening of thecold store door and to the inevitable heat exchanges withoutdoor air, even when the cold store door is closed, havebeen realized. These tests have been performed at varioustemperature levels for the air in the coldstore and, precisely,at 5, 0 and 25 8C, opening the cold store door every 20 minfor about 5 min with an outdoor air temperature of about18 8C. Moreover, in some tests the cooling load has beenobtained by means of cont