## 4 Discussion  
The application of passive heating of an attached sunspace plays an important role in carbon reduction of the rural building, particularly in the development of China's 'carbon peaking and carbon neutralization'. When solar radiation is intensive, the attached sunspace has an excellent heat collection and heating effect. It can create a satisfying indoor thermal environment under the zero-state response control strategy during the daytime. Due to the excellent insulating properties, the indoor temperature can be maintained for a portion of the time when solar radiation is weak. Such excellent passive heating performance can effectively reduce winter heating energy consumption after a large-scale promotion, and reduce carbon dioxide emissions and environmental pollution caused by heating [27].  
In conventional ASPSHS, the attached sunspace serves as a well-performing heat collection component during daytime, and most of the heat is transferred to the interior of the envelope to reduce heat loss at night. However, this inappropriate control logic affects the heat utilization. The optimum zero-state response control strategy for controlling the interior active window opening time increases the heat transfer impact of the attached sunspace to the room and raises the average indoor temperature above the external temperature of 25.45 \({}^{\circ}\)C during the daytime. Furthermore, the influence of the pressure differential between attached sunspace and room encourages natural convection heat exchange, and the average interior temperature difference unevenness is only 23%, indicating a uniform thermal environment.  
The test of the thermal environment, which immediately reflects the distribution of temperature in the attached sunspace and room, is a unique element of this experiment. According to the air temperature distribution inside the attached sunspace, the optimum place for the interior active window is in the top middle of the west-facing wall. According to the distribution of indoor temperature, the indoor thermal environment is closely related to the position of the interior active window at a distance.  
The natural ventilation model with the attached sunspace and room can only more correctly mimic the average temperature, as the distribution of the temperature field is difficult to simulate. The temperature and velocity fields can be further simulated using ANSYS [29] and other tools in the following study to enable better control and design optimization of the ASPSHS.  
Passive heating is challenging to achieve most of the night and exceptionally difficult during daytimes. The room's heating needs can only be satisfied by auxiliary heat sources or other forms of active heating in these hostile climates. Furthermore, due to the attached sunspace's great heat collecting ability when the solar radiation is intensive, it may bring an excessively high temperature to the inside thermal environment. If some heat storage structures can store the excess heat at this time and are paired with a wider range of control mechanisms, the attached sunspace's passive heating time can be extended, the solar heating guarantee rate can be increased, and the peaks and valleys can be retarded, resulting in a more stable indoor thermal environment.