This document discusses drafting mechanical layout and details. It provides definitions for terms related to heating, ventilating, and air conditioning (HVAC) systems. It explains how air conditioners work and the functions of air conditioning systems, which include cooling, dehumidifying, heating, humidifying, and cleaning air. It also outlines circulation standards for heating and humidifying, cooling and dehumidifying, and air motion. The overall document provides information to familiarize readers on drafting the layout of HVAC systems and their components.