Group 1 - The article discusses ancient methods of cooling in the Forbidden City, including ice cellars and mechanical fans invented by emperors [1][14] - Ice cellars were used to store ice blocks harvested in winter for use in summer, with a historical record indicating that the Forbidden City had five ice cellars capable of holding 25,000 ice blocks [3][5] - The construction of ice cellars included thick walls and special materials to maintain a constant temperature of 16-17°C, regardless of outside conditions [4] Group 2 - The article details the design and function of the ice box, known as "ice jian," which was used to preserve food and provide cooling effects [8][10] - The ice box was made of wood with a lead lining, allowing it to maintain low temperatures and prevent water leakage [9][10] - Various ice-based delicacies were enjoyed in the Forbidden City, supported by the ice stored in the ice cellars, including ice drinks and desserts [12][13] Group 3 - The article highlights the innovation of mechanical fans during the reigns of Emperors Yongzheng and Qianlong, who sought to improve cooling methods in the palace [14][15] - The mechanical fan designed by Yongzheng utilized a wooden frame and multiple small fans to enhance airflow, while Qianlong's version was integrated into a self-winding clock [15]