## 3 Model Development  
### Development of the Baseline Rural House Model  
Based on the Heating Degree Days (HDD18) and Cooling Degree Days (CDD26) criteria set forth by the XJ1001-2021 \"Energy Efficiency Design Standards for Residential Buildings in Severe Cold and Cold Regions\", the Wusu area falls within the severe cold zone 1C. Field surveys were carried out in Dongliang Village, with their specific locations depicted in Figure 1, to collect fundamental data on typical rural houses.  
Field research indicates that the primary structural form of rural houses in the Wusu area is brick-concrete construction. The main structures typically feature 490 mm brick walls with roofs made of cast-in-place concrete sloping roofs. Interior floors are compacted  
Figure 1: (**a**) Scope of the Wusu area; (**b**) overview of Dongliang Village (“SITE” represents the location of the benchmark rural homesetad).  
earth with a layer of cement mortar or concrete padding before tiling. Windows are generally made of single-layer plastic steel, but due to the construction quality in rural areas, the sealing performance of some windows may not be guaranteed. To combat the cold winter, rural houses tend to minimize their external surface area. A smaller form factor means that the building's external surface area is relatively small compared to its volume, which helps maintain indoor temperature by reducing heat loss through external walls during winter, thereby reducing heating demands and saving energy. The research shows that the thermal transmittance coefficients of the existing rural residential envelope structures in the Wusu area are all higher than the requirements of energy-saving design standards, and the window-to-wall ratio of the south wall is lower than the specified value of the design standards. A single-story brick-concrete rural house in Dongliang Village was selected as the subject for constructing the baseline rural house model, with model information and construction practices as shown in Figure 2 and Table 1.  
by building insulation initially increases and then decreases, whereas the proportion of building energy consumption and cost borne by the solar energy system first decreases and then increases [83].  
Using Ladybug to analyze solar radiation and the performance of solar photovoltaic (PV) panels in the Wusu area (latitude: 44.43, longitude: 84.67), it was found that the optimal annual tilt angle for installing PV panels in the Wusu area is 35.0\({}^{\circ}\), as shown in Figure 3, with the highest radiation reaching 1490 kWh/m\({}^{2}\). However, due to the significant difference in solar radiation between summer and winter, the optimal tilt angles for summer and winter are notably different. The optimal tilt angle for PV panels in summer is 22\({}^{\circ}\), while in winter, due to the lower solar altitude angle, the optimal tilt angle is 54\({}^{\circ}\). It is important to note that when the tilt angle exceeds the optimal value, the amount of radiation received by the PV cells decreases with the increase in tilt angle. Frequently adjusting the tilt angle of the PV panels would increase the cost and maintenance workload. Therefore, to achieve a higher energy collection efficiency throughout the year, this paper selects the annual optimal tilt angle for simulation calculations.