【正文】 rollable electrical heaters locatedin the cold store, while in other tests a real cooling load hasbeen considered represented by 200 kg of fruit andvegetables for whose preservation the temperature hasbeen fixed at 5 8C in the cold store. In these last twoFig. 1. Sketch of the experimental plant.C. Aprea et al. / International Journal of Refrigeration 27 (2020) 639–648 641situations, the cold store door has been opened every 10 minto simulate a real working condition。DT222。d240。=dt222。f222。 theinference process determines the output fuzzy by means ofthe rules fixed according to the experimental reality。 1–30 bar ^。 0–16 A ^% .。 this happens when the cold store dooris open. To increase the sensitivity of the controller withrespect to the rate of the change of the derivative with timeof the temperature difference, the fuzzy subset might have asmaller definition, perhaps ranging from to .However, satisfactory results can be obtained with theprevious definition of the fuzzy subsets. The values ofthe pressor motor supply frequency considered in theoutput fuzzy subset membership function (Fig. 5), arelocated in the range 30–50 Hz. It was not possible toconsider values under 30 Hz because the pressorvibrations and the noise increase considerably togetherwith the lubrication troubles due to the splash systemincrease. The inference mechanism employed has been theproduct inferencing method whereby the minimum operatorfor the ‘a(chǎn)nd’ is replaced by the product operation [29–31].This mechanism allows a better interpolative reasoningamong the input and output variables because the effect ofthese variables on each other is obtained more effectively.The adopted defuzzification method is based on thedetermination of the mass center of a pound set。DT222。 this last value is acceptable as itcorresponds to the differential band of a thermostat.To explain the reason for the energy saving obtainablewith a fuzzy control algorithm that allows to regulatecontinuously the pressor velocity in parison with athermostatic control, an exergetic analysis of the ponents of the refrigeration plant has been realized onvarying the pressor speed. For this purpose, it resultsmore correct to realize the exergetic analysis in the steadystate conditions instead of the transient conditions, whichderive from the pressor speed fuzzy control, selectingagain the same conditions in terms of pressor refrigeration capacity. In particular, the refrigeration powercorresponding to each frequency of 30, 35, 40, 45, 50 Hzunder the transient conditions is considered again under thesteadystate conditions to allow a correct measurementprocess. This experimental analysis has been performedrelated to the summer season, with the outdoor temperatureat the condenser kept at about 32 8C, but similar results havebeen obtained also in other working conditions. Inparticular, the tests realized in the winter season verify thecorrect refrigerant lamination when, varying the pressorspeed, the pression ratio across the valve is low.The exergetic analysis allows to obtain importantinformation about the plant total irreversibility distributionamong the ponents. The overall plant exergeticefficiency has been evaluated as the ratio between theexergy output and the exergy input and can be expressed as:hex188。 1 2_ExdesP_Exin240。An accurate analysis can be realized evaluating the exergydestroyed for each single ponent of the plant. Inparticular, the exergy flow destroyed in the condenser isevaluated as:_Exdes。 _mref240。co2 exout。2_Qcotco240。and the exergy flow destroyed in the evaporator is evaluatedas:_Exdes。 _mref240。ev2 exout。2_Qevltevl 240。where the dimensionless exergetic temperature can bedefined as:t 188。air240。where T0is the environmental temperature while Tmt。cp188。exin。cp222。_Lcp240。The exergy flow destroyed in the valve is evaluated as:_Exdes。 _mref240。va2 exout。240。The efficiency defect has been evaluated for each device ofthe plant, considering the ratio between the exergy flowdestroyed in each ponent and the exergy flow requiredto sustain the process, . the electrical power supplied tothe pressor:di188。i_Lcp240。The efficiency defects of the ponents are linked to theexergetic efficiency of the whole plant by means of thefollowing relation:hex188。8222。 moreover, in Fig. 9 thevalues of the evaporation power and the trend of the electricenergy consumption are also reported. The experimentaltests have been carried out for an air temperature settled inthe cold store equal to 0 8C and for each frequency of 30, 35,Fig. 7. Electric energy consumption for R507 and R407C using boththe fuzzy control and the thermostatic control (cooling load !electric heaters).Fig. 8. Summer electric energy consumption for R507 and R407Cversus cold store air temperature using both the fuzzy control andthe thermostatic control (cooling load ! fruits and vegetables).C. Aprea et al. / International Journal of Refrigeration 27 (2020) 639–648 64540, 45, 50 Hz of the pressor electric motor supplycurrent. The exact refrigeration capacity that the pressorcan supply at the selected frequency has been considered ascooling load by means of some controllable electric heaterslocated in the cold store. The exergetic efficiency of thewhole plant is linked to the actual COP and to the reversibleCOP of the plant: hex188。 as the COPrevisfixed, referring to the temperatures shown in Fig. 9, theexergetic efficiency follows the trend of the COP. It is to benoted that when the pressor speed decreases the COPincreases. In particular, it is necessary to observe that, whenthe pressor speed decreases, the global heat transfercoefficient of the heat exchangers is practically constantbecause the