# Investigation on an Improved Household Refrigerator for Energy Saving of Residential Buildings
## 1 Introduction  
Worldwide demands for living quality grow rapidly with social and economic development [1], which leads to a considerable increase in domestic appliances in buildings [2]. As a representative, the popularity of household refrigerators prevents the reduction of the world's energy demand and CO2 emissions, and its energy consumption is accounting for more than a quarter of the global residential electricity demand [3]. Thus, promoting new and efficient technologies for the efficiency advance in household refrigerators is extremely urgent. Great efforts have been made to enhance the performances of the key components, such as the compressor [4], the condenser, and the evaporator [5], to optimize the refrigeration cycle [6], to modify internal and external structural design [7], and to improve the thermal insulated behaviors [8]. However, there still exists a balance between cost and performance in the research field of household refrigerators [9]. Recently, an increasing number of new technologies have been applied for breaking this chain. [PERSON] et al. designed a heat storage evaporator and cold storage condenser for a household refrigerator, and its energy saving ratio was 32% [10]. [PERSON] et al. enhanced the heat dissipation of a household refrigerator. The surface temperature close to the compressor was reduced by 11 \({}^{\circ}\)C [11]. [PERSON] et al. proposed to adopt a diffuser pipe to enhance the behavior of a normal refrigerator, which leads to a 3.36-4.09% reduction in power consumption [12]. [PERSON] et al. conducted a preliminarily experimental study on a cool-storage refrigerator for the use ofpeak load shifting [13]; the follow-up research focused on the temperature management enhancement of household refrigerator [14]. [PERSON] et al. used a hybrid cooling system to reduce cooling times and improve temperature stability of a household refrigerator [15]. [PERSON] et al. suggested utilizing a ternary hydrocarbon mixture for household refrigerators and analyzed its energy and exergy behaviors in details [16]. Certain achievements have been made by the above attempts; however, the potential of a household refrigerator in its cold loss recovery did not arouse enough attention [17]. In a conventional household refrigerator, the temperature of the freezer is much lower than that of the fresh food compartment, and the only evaporating temperature of its cooling cycle is determined by the former. If the wasted cold energy of the freezer can be partly reused by the fresh food compartment, the overall energy consuming amount of the refrigerator is reduced while no additional exergy loss is generated. In our last study, this basic ideal was performed by utilizing the efficient heat transfer capability of two-phase loop thermosyphons to separate cold loss from the interlayer of the isolation wall of the freezer to the fresh food compartment [18]. In comparison to increasing the wall thickness, there was no reduction in the usable space of freezer by adopting this novel cold loss reduction method, and the cost increment of the improved refrigerator was relatively low, since the main structure of two-phase loop thermosyphons is made by low-cost aluminum alloy. Preliminary numerical research on the cold loss reduction behaviors of the modified freezer walls was performed in fixed operating conditions of an imaginary refrigerator, and results proved the effectiveness of heat pipes in the energy saving of household refrigerators. However, the overall energy saving capability is unknown, and the accuracy of quantitative analysis is still insufficient. Derived research focused on radical structural change of a household refrigerator, which deviates from the original intention of saving energy through simple structural improvement [19].