It is generally impossible to write about a college or a department. This will send the letter to the office building of the college. It's best to know his dormitory number and room number first. Students' letters are usually sent directly to the dormitory, and rarely to the office building, except for graduate students (with offices). In short, it is safest to send it to the dormitory. In addition, there are old dormitories and Bauhinia apartments in Tsinghua with the same building numbers. If it is a Bauhinia apartment, the "Bauhinia XX Building" should be added in front. If it is an apartment for the elderly, there is also the XX Building in the South District and so on.