What are the meanings of LDG D2 19*6, LDH D2 19*6 and lqd219 * 6 in the air-conditioning plumbing diagram?

This name is given by the general cartographer himself, which is generally the abbreviation of Pinyin. For example, LDG is a chilled water supply pipe, LDH is chilled water, and return pipe LQG is a cooling water supply pipe. The back D2 19*6 is a pipe with a diameter of 2 19 and a thickness of 6mm. Generally, letters are pinyin abbreviations, but some of them are English abbreviations. For example, gas pipes are generally called gas. I drew a picture in those years, and I named it XH. Actually, pinyin should be XF, hehe.