The purpose of HVAC equipment is to maintain indoor temperature, humidity and air quality. This is a complex task, and we often need tables and formulas to describe the processes involved. However, tables and numbers are a poor way to communicate with our customers and sell equipment. The psychrometric chart is a tool for graphing the temperature and humidity of air as it goes through HVAC processes, and this paper
is an introduction to using it as a communication and sales tool.