## 2 Materials and Methods  
To carry out this study, the authors considered a cold storage placed in a Logistic Centre, with geometrical dimensions L \(\times\) I \(\times\) H = 40 \(\times\) 20 \(\times\) 12 m. The cooling reference temperatures for cold storage are given in Table 1[9]. The storage warehouse is made of sandwich panels, with a PUR insulating layer, composed of a thermal insulation core and two steel sheets. The outer layer has 0.06 mm thickness, and the inner layer is of 0.4 mm thickness, both being covered with a layer of polyester and organic protective layers. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Product** & **Cold Storage (\({}^{\circ}\)C)** & **Frozen Storage (\({}^{\circ}\)C)** \\ \hline Meat products/Fruits and vegetables & 0 \(\ldots\) 4 & \(-\)23 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Indoor temperature. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Climate Zone Number** & \
\begin{tabular}{c} **Climate Zone** \\ **Representative City** \\ \end{tabular} &
\begin{tabular}{c} **Average Summer** \\ **Temperature (\({}^{\circ}\)C)** \\ \end{tabular} \\ \hline I & Constanta & 30 \\ II & Bucharest & 31 \\ III & Cluj Napoca & 25 \\ IV & Brasov & 24 \\ V & Miercurea Ciuc & 22 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Outdoor temperature. In the case of cold storage, the role of thermal insulation is particularly important to minimize the penetration of heat from the outside, so that the energy consumption necessary to maintain a low temperature inside is minimal and as an effect, the operating costs are as low as possible. The heat transfer through building parts (wall, floor and ceiling) was evaluated with the general relation (1) [11]:  
\[\dot{\mathrm{Q}}\ =\mathrm{U}\cdot\mathrm{A}\cdot\mathrm{\Delta T}\ [\mathrm{W}] \tag{1}\]  
where:  
U--Overall heat transfer coefficient given in Equation (2) [W/m\({}^{2}\cdot\)K];  
A--Total area of storage warehouse [m\({}^{2}\)];  
\(\mathrm{\Delta T}\)--Temperature difference between the outside and inside conditions [K]  
\[\mathrm{U}=\frac{1}{\sum\mathrm{R}}\ =\frac{1}{\frac{1}{\mathrm{h_{i}}}+\sum \frac{x}{\mathrm{k}}+\frac{1}{\mathrm{h_{e}}}} \tag{2}\]  
\(\mathrm{h_{i}}\)--convection heat transfer coefficient for indoor surfaces [W/m\({}^{2}\cdot\)K];  
\(\mathrm{h_{e}}\)--convection heat transfer coefficient for outdoor surfaces [W/m\({}^{2}\cdot\)K];  
x--insulation thickness [m]; There were considered thicknesses between \(0.03\div 0.2\) m;  
k--material thermal conductivity for PUR = 0.027 W/m\(\cdot\)K [12; 13]. The heat transfer through building parts depends on the thickness of the insulating layer, indoor space temperature as well as on the climatic zone, the variation is presented below in Figure 1.  
There can be noticed a decrease in the heat transfer through building parts by about 49.12% for a thickness of the insulating layer of 200 mm when compared to 100 mm. The same trend resulted from calculations made by the authors for the heat loads at frozen storage, but the values increased with an average of 76% when compared with cold storage. By taking into account the auxiliary heat inputs due to doors opening (we considered an average of 4 h/day when products are introduced or extracted from the cold/frozen storage rooms) [14; 15; 16; 17], respiration heat [11], air change per day [16], lightning, evaporator fans, heat emissions from people performing various activities, handling equipment [18], the total cold required for each cooled space is shown in Figures 2 and 3. Figure 1: The heat transfer through building parts for cold storage. The calculated cooling load was increased by 10%, to provide a safety factor for possible discrepancies between the design criteria and actual operation [19]. By analyzing Figures 2 and 3 one could notice that the cooling load required for refrigeration is higher than in the case of frozen storage.