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Chapter 5: Automated Control Systems
Electrical Theory & Applications for HVACR
SYSTEM PROTOCOLS
Most companies have their own proprietary controllers for specific applicaƟons. Some controls are
designed with limited funcƟonality, such as starƟng or stopping an HVAC system. Others are more
flexible, allowing temperature adjustments and more. Most have proprietary soŌware that works
with ASHRAE's open protocol BACnet or open protocol LonTalk.
CommunicaƟon standards are being developed that will allow all controls regardless of manufacturer
to interface with each other. This will make it possible to improve funcƟonality at a future Ɵme,
without replacing enƟre control systems. The following is a list of the various networks and
communicaƟon protocols in use today.
Consumer Electronic Bus (CEBus):
A protocol designed to be used over the power lines by uƟlity
companies. This system was intended for use with smart type electrical meters to monitor energy
use.
LonTalk:
Competed with CEBus by using power line technology. It is well established in the industrial
space in parts of Europe and Asia.
Universal Plug and Play:
MicrosoŌ worked with the Home AutomaƟon & Security commiƩee on this
project. It is used for connecƟng Web‐enabled devices to computer systems.
Simple Control Protocol:
Was developed by GE, CEBus and MicrosoŌ. This protocol automaƟcally
allowed a computer to recognize the enabled device when plugged into the power outlet.
ZigBee:
Uses Web Service Device (WSD) a protocol, which interfaces with a device, allowing it to be
seen and controlled using third‐party soŌware.
BACnet:
A data communicaƟon protocol for building automaƟon and control networks. BACnet was
developed by a commiƩee formed by the American Society of HeaƟng, RefrigeraƟng and Air‐
CondiƟoning Engineers (ASHRAE). The main set of rules govern the exchange of data over a computer
network. It covers the type of cable used and how to form a parƟcular request or command from the
communicaƟons equipment.
Climate Talk Alliance:
An organizaƟon of companies commiƩed to developing a common
communicaƟon infrastructure for HVAC and Smart Grid devices. Their goal is to enable diverse
systems and organizaƟons to work together.
BASIC OPERATING STRUCTURE
The operaƟng technology of automated controls uses analog and digital signals. Analog signals are
used as input or output for variable measurements or control of temperatures, motor speeds, and
pressures.
Digital signals are used to turn things on or off and to indicate “on” or “off.” In either case, the
control signal is normally low‐voltage and, depending on the control, AC or DC.