Defining and grading passive solar heating potential indicator in China: A new irradiation degree hour ratio parameter.

• Irradiance degree hour ratio in heating period to assess solar heating potential. • "Hour by hour, and then cumulative" principle proposed in potential assessment. • Solar heating grade in China obtained with direct-normal irradiance degree hour ratio. • Solar heating recommendations based on based on new indicator in solar energy rich region. The rational utilization of solar resources is essential for promoting the development of passive solar heating. Grading the solar heating potential is a prerequisite for the sensible utilization of solar resources in the winter. However, due to the lack of an accurately assessed solar heating potential grade across China, developing potential indicators that can be applied to cover the entire country is increasingly important. In particular, identifying reasonable index parameters is a critical problem when accurately determining solar heating potential indicators. In this study, meteorological data between 1988 and 2017 from 1019 stations were selected to verify the suitability of the potential indicator comprising the irradiation temperature difference ratio (ITR) in different states for developing solar heating potential indicators. The optimal value form was selected by comparing the ITR results for typical cities. The results showed that the irradiance degree hour ratio (C-IDHR hp) during the heating period was more accurate for assessing solar heating potential at the country–level in China. A C-IDHR hp indicator for irradiation based on the difference between the indoor and outdoor temperatures greater than zero corresponds to the irradiation at a specific moment based on the principle of "hour by hour and then cumulative" calculation. This direct-normal C-IDHR hp indicator delineates the distribution of the solar heating potential levels in China, and south and horizontal C-IDHR hp indicators provide guidance about solar heating measures in solar energy rich region. [ABSTRACT FROM AUTHOR]