## 3 Energy Consumption Tests
### Temperature Indicators  
Figure 5 shows the average values of condensing and evaporating temperatures during 24-h test for both system layouts operating with R-134a and R-507A (the figure inside the bars gives the exact value). Condensing temperature is calculated using compressor's pressure discharge measurement and a vapour title of 50%, according to Equation (1) [24], only when the compressor was in operation. The evaporating level is averaged during the 24 h using the pressure at the exit of the evaporator of the cabinet in the case of the direct expansion configuration and using compressor suction pressure measurement for the indirect layout. Evaporation temperature is computed with Equation (2) using the indicated pressure measurements and the mean enthalpy in the evaporator [24]. The thermophysical properties of the refrigerants are evaluated using Refprop 9.1 [25]. \[T_{K}=f(P_{dis},X_{v}=50\%) \tag{1}\]  
\[T_{O}=f\bigg{(}P_{O,out},h=\frac{h_{O,in}\ +\ h_{v,P_{O},out}}{2}\bigg{)} \tag{2}\]  
Regarding the condensing level, no significant differences were observed among the system layouts and both refrigerants, being the maximum difference below 0.5 K. Regarding the evaporating temperature during the tests, some differences were observed. When going from a direct system to an indirect using R-134a as refrigerant, there is a reduction in the evaporating level, only from water inlet temperatures from 32.8 \({}^{\circ}\)C on. For 32.8 \({}^{\circ}\)C, the measured reduction was by 0.6 K, and for 43.6 \({}^{\circ}\)C by 2.3 K. However, the impact of the conversion is stronger when operating with R-507A. The reduction of the evaporating level when going to an indirect system was of 2.9 K at 23.3 \({}^{\circ}\)C, similar at 32.8 \({}^{\circ}\)C and of 1.9 K at 43.6 \({}^{\circ}\)C. Additionally, it must be mentioned that this reduction in the evaporating level is weakened by the behaviour improvement of the expansion valve when it operates with the indirect layout (braged plate evaporator) instead of the direct arrangement (evaporator of the cabinet), reaching average superheat values in the evaporator during the 24 h lower (Table 3). Figure 5: Average evaporating and condensing (comp. ON) temperatures 24 h test. Referring to the working temperatures in the cabinet, Figure 6 presents average values during 24 h of average product temperature (five samples), air return temperature to the heat exchanger of the cabinet, air impulsion at the air distribution port of the cabinet, the average temperature in the cabinet's heat exchanger and the evaporating level. As can be observed, the operation, using a direct or indirect system, with both refrigerants has no influence on the air and product temperatures in the cabinet, since the product, air return and air impulsion temperatures are equivalent. The difference between the system layouts is observed in the working temperatures of the heat exchanger and the evaporating level. When using a direct expansion system, the cabinet's heat exchanger temperature corresponds to the evaporating temperature (equal in the graph); however, when using an indirect system, the average working temperature of the heat exchanger of the cabinet (SF heat exchanger) largely differs from the evaporating level. For both refrigerants, the average temperature of the secondary fluid in the cabinet heat exchanger is \(-\)2.0 \(\pm\) 0.3 \({}^{\circ}\)C. The differences between average temperature in the SF heat exchanger and the evaporating temperature are of 12.9 K, 12.8 K and 12.7 K when using R-134a, and of 21.3 K, 17.4 and 16.1 K when using R-507A.