Fundamentals of HVAC Controls

HVAC systems are classified as either self-contained unit packages or as central systems. Unit package describes a single unit that converts a primary energy source (electricity or gas) and provides final heating and cooling to the space to be conditioned. Examples of self-contained unit packages are rooftop HVAC systems, air conditioning units for rooms, and air to-air heat pumps.

With central systems, the primary conversion from fuel such as gas or electricity takes place in a central location, with some form of thermal energy distributed throughout the building or facility. Central systems are a combination of central supply subsystem and multiple end use subsystems.

There are many variations of combined central supply and end use zone systems. The most frequently used combination is central hot and chilled water distributed to multiple fan systems. The fan systems use water-to-air heat exchangers called coils to provide hot and/or cold air for the controlled spaces. End-use subsystems can be fan systems or terminal units. If the end use
subsystems are fan systems, they can be single or multiple zone type. The multiple end use zone systems are mixing boxes, usually called VAV boxes.

Contents
Why Automatic Controls?
HVAC systems
How does central air-conditioning system work?
What Parameters are controlled?
Control Strategies
Where are HVAC controls required?
Benefits of a Control System
Control Basics
What is Control?
Elements of a Control System
Theory of Controls
Type of Control Systems
SENSORS
Type of Sensors
Classification of Sensors
Temperature Sensors
Electronic Sensors
Relative Humidity Sensors
Pressure Sensors
Flow Sensors
Air Flow Measurements
Dew Point Measurements
Liquid Level Measurements
CONTROLLERS
Controller Action
Identifying Reverse or Direct Action
CONTROLLER TYPES
RESET
CONTROLLED DEVICES
Control Valves
Coil Characteristics
Valve Characteristics
Sizing Control Valves
Dampers
Damper Applications
Actuators
Pumps & Fans Control
CONTROLLER RESPONSES
Two-Position Control
Floating DDC Control
Proportional Control
Proportional plus Integral (PI) Control
Proportional plus Integral plus Derivative (PID) Control
Stability of the System
DDC HVAC Systems
What is DDC?
DDC Terminology & Theory of Operation
DDC Hardware
The Control Network
Advantages of Using DDC
ENERGY SAVING FEATURES
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