# Investigation on an Improved Household Refrigerator for Energy Saving of Residential Buildings
## 5 Results and Discussion
### Performances at Different Temperature Gears  
When the ambient temperatures, \(A_{eu}\) and \(X_{int}\), are fixed to 25.0 \({}^{\circ}\)C, 0.146 m\({}^{2}\), and 16%, respectively, and the temperature gears are given as A-D, the measured boundary conditions are utilized to further compare the performances of original and improved refrigerators. The representative heat transfer parameters of original and improved side freezer walls are shown in Figure 8. As the temperature gear is adjusted from A to D, the inside convective heat transfer coefficient for the original side wall (\(\alpha^{\prime}s_{in}\)) remains close to 3.34 W\(\cdot\)m\({}^{-2}\).K\({}^{-1}\), whereas that for the modified one (\(\alpha^{\prime}s_{in}\)) remains at about 3.59 W\(\cdot\)m\({}^{-2}\).K\({}^{-1}\). The inside surface temperature for the modified side wall (\(T_{s,in}\)) raises from \(-\)12.1 \({}^{\circ}\)C to \(-\)9.6 \({}^{\circ}\)C; and the inside surface temperature for the original side wall (\(T^{\prime}s_{in}\)) raises from \(-\)13.9 \({}^{\circ}\)C to \(-\)11.8 \({}^{\circ}\)C. When the temperature gear changes from A to D, \(T_{s,in}\) remains higher than \(T^{\prime}s_{in}\), and their difference slightly enlarges from 1.8 \({}^{\circ}\)C to 2.1 \({}^{\circ}\)C. The enhancement on the inside heat transfer of the modified side freezer wall intensifies as the inside temperatures of the refrigerator raise. The topside freezer wall of the improved refrigerator is with boundary condition 1, and thus the bilateral heat transfer characteristics are affected by the heat pipe. Figure 9 shows the surface temperature comparison between the original and the modified topside freezer walls under different temperature gears. Take temperature gear B for example, the outside surface temperature increases from 20.2 \({}^{\circ}\)C to 20.8 \({}^{\circ}\)C after adding the heat pipe, and the inside surface temperature correspondingly  
Figure 8: Inside heat transfer characteristics of the topside freezer wall at various temperature gears. Figure 7: Cold loss recovery performances of modified freezer at various ambient temperatures. increases from \(-\)11.6 \({}^{\circ}\)C to \(-\)9.9 \({}^{\circ}\)C. The existence of the heat pipes changes the temperature distribution in the topside freezer wall and reduces the temperature gap between its outside surface and ambient air. The phenomenon indicates that a considerable heat energy is transported from the fresh food compartment and flow into the freezer along with the outside heat leakage. Besides, the inside surface temperature for the modified topside freezer wall (\(T_{t,in}\)) raises from \(-\)10.3 \({}^{\circ}\)C to \(-\)7.9 \({}^{\circ}\)C, and the outside surface temperature for the original topside freezer wall (\(T^{\prime}{}_{t,out}\)) slightly increases from 19.4 \({}^{\circ}\)C to 20.3 \({}^{\circ}\)C. The inside surface temperature for the original topside freezer wall (\(T^{\prime}{}_{t,in}\)) and the outside surface temperature for the modified topside freezer wall (\(T_{t,out}\)) remain close to \(-\)11.5 \({}^{\circ}\)C and 20.8 \({}^{\circ}\)C, respectively. Results confirm that the influence of heat pipes intensifies as the inside temperatures of the refrigerator raise. The heat transfer behaviors of the heat pipes are further studied to support the above analyses. As shown in Figure 10, the temperature of the heat pipes (\(T_{HP}\)) raises from \(-\)2.8 \({}^{\circ}\)C to \(-\)0.4 \({}^{\circ}\)C as the temperature gear is varied from A to D, and the difference between the air temperature at the fresh food compartment and \(T_{HP}\) enlarges from 4.9 \({}^{\circ}\)C to 5.4 \({}^{\circ}\)C. Correspondingly, the heat transfer capability of heat pipes enhances and its heat flux (\(Q_{HP}\)) increases from 3.0 W to 3.5 W. Heat pipes provide a cold loss recovery function for the freezer, and the heat shunt amount is closely affected by the temperature gear of the refrigerator.