Chapter 9 - Control Diagrams and Sequences

Abstract

This chapter introduces how control systems are designed and how the design intent is conveyed using control diagrams (schematics), damper and valve schedules, parts lists, and written control sequences. Designing heating, ventilation, and air conditioning (HVAC) control systems is a science but allows for different approaches. The critical first step towards success is to be absolutely clear about the objective. Many organizations have developed their own library of graphic symbols and it is wise to include on the controls drawings a key to their meaning to avoid any misunderstandings. The symbols cover four sections: air handling, piping, controls, and equipment. The graphic symbol may have two types of information added about particular variations of device and detail about the device function. The graphic symbols are mostly generic; as they do not define the type of controls hardware and lines are used to indicate an interconnection between devices without defining whether they represent wiring or tubing. Generic control diagrams are generally acceptable for most HVAC designs for bidding purposes because they, along with the written sequence of controls described in the next section, should sufficiently define the requirements of the control system.