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Class:DDC 101 Instructor : Jack Floyd Fall 2012. Objectives. The purpose of this class Define what a DDC Control System is Define the two types of DDC Control Systems Give you the basic structure of a DDC Controls System Determine the difference between DDC System Applications

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Class ddc 101 instructor jack floyd fall 2012

Class:DDC 101

Instructor: Jack Floyd

Fall 2012


  • The purpose of this class

    • Define what a DDC Control System is

    • Define the two types of DDC Control Systems

    • Give you the basic structure of a DDC Controls System

    • Determine the difference between DDC System Applications

    • Provide you with the confidence to approach a DDC Controls System of any kind

What does ddc stand for
What does DDC stand for?

  • DDC stands for Direct Digital Controls

    • Definition: the automated control of a condition or process by a digital device (computer)

  • Key word AUTOMATED

  • What makes a DDC system automated?

  • Algorithms

    • Definition: a set of rules that precisely defines a

    • sequence of operation (the brains)

Ddc types
DDC Types



  • Canned or Configurable DDC controllers have predefined programs that can be configured to match different applications.

  • Pros are they are easy to install and setup

  • Cons are they are limited in their capabilities

  • Universal or Programable DDC controllers do not have predefined programs and require custom programming

  • Pros are they are only limited by the hardware (inputs/outputs)

  • Cons are they can be complex and difficult to setup or troubleshoot

Canned controllers
Canned Controllers

Easy to install/Easy to Configure

Must match the controller to your application when selecting


VAV application

VVT application

RTU application

Must configure controller properties to match the type of controller


a VAV application may have Fan Powered Boxes as well as VAV boxes the configuration

must be specific to the type of equipment

Why is this important from a service view?

What if a point is miss configured?

Programmable controllers
Programmable Controllers

Can be applied to virtually any application

Make sure you match the hardware inputs and outputs to the application (use expansion modules if necessary)


RTU application

AHU application

WSHP application

Must match the controller hardware to the equipment hardware


be sure you have an output that is 0-10vdc going to a 0-10vdc device input

Tstat vs ddc

TSTAT control

DDC Control

  • A thermostat can be programmable or non programmable

  • A thermostat uses inputs and outputs to control a process based on a set of rules

  • Sound familiar, TSTATs use Algorithms!

  • DDC control uses the same architecture as a Programmable TSTAT.

  • The only real difference is you have more features and you are placing the controllers on a network for accessibility

Basic structure of a ddc system
Basic Structure of a DDC System

The Daisy Chain

The DDC System in made

Up of three basic items







The equipment or process

being controlled

The DDC controller







The Communications



Daisy Chain Network: The daisy chain is the most common type of

Communications network wiring. There is only one start and one

End to a daisy chain network wiring.

Ddc network
DDC Network

  • There are several different types of Protocol (languages) that manufacturers use today

  • One thing they all have in common is they all use a network

  • Some networks may be 2 wire, some 3 wire, some are CAT5/6 or wireless

  • The network wiring will vary depending on the protocol and the manufacturer

  • Be aware of the maximum lengths of a network

  • Be aware of the maximum number of devices on a network (memory and network traffic)

  • Shielded cable – to reduce interference from EMF (Electromagnetic Field)

  • How do you properly ground the shield?

Properly grounded
Properly Grounded

Having the Network properly grounded can keep from having unwanted communication errors.

Proper grounding of the network
Proper Grounding of the network

Will this work in all applications? Why or Why not?

Ddc applications
DDC Applications

  • There are two main types of DDC Applications

  • Variable Air Volume (VAV)

    • VAV applications will maintain a static pressure set point, usually with a Variable Frequency Drive (VFD) while maintaining a supply air temperature of 55 DF. The individual zones are used to heat as needed. The air handler typically only runs the heat during a morning warm up period. This is called Pressure Independent.

  • Variable Volume and Temperature (VVT)

    • VVT applications will maintain a static pressure set point, usually with a bypass damper while modulating between heating and cooling modes depending on the demand of the system. This is called Pressure Dependant.

Which is better
Which is better?

VAV Application

VVT Application

  • Provides better comfort control of the space

  • Does not have a changeover period

  • Allows for different heating applications to be installed at the local box level

  • Less cost up front

  • Has a changeover period between modes which can cause comfort issue in the space

  • Relies on the Air handler for its heating

Bms or bas or ems

  • There a couple of common terms that come into play when talking about a DDC system.

  • Building Management System (BMS)

  • Building Automation System (BAS)

  • Energy Management System (EMS)

  • DDC control system

  • Is there any difference between them?

    • We know that a programmable or network thermostat by definition is a DDC control system

    • We know that automation is a key word in a DDC control system

Bas vs ems



  • A BAS/BMS is one or more DDC control systems that is on a network used to manage and control a process or condition of the networked devices

  • An EMS is a BAS/BMS that is also used to conserve energy by data collection and analysis of the process or conditions being controlled

Common issues
Common Issues

  • Communications

    • Improper installation and grounding of the network

    • Broken communication lines

    • Duplicate Addressing of devices

    • Failure of a device on the network

      • Sensor failures in a VVT application

      • Failed Communication chip bringing down the voltage on the network

      • Troubleshooting a Network

        • Use a Network monitoring tool if available from the manufacturer

        • Segregate the network for easier troubleshooting

Common issues cont
Common Issues Cont.

  • Power

    • Power loss can cause controllers on the network to fail, or not restart properly

    • Brown outs can cause controllers on the network to fail, or be scrambled

      • A communications network is a series of digital pulses (electricity). A drop in the power supply of a controller can cause a drop in voltage on the network sending false signals. Controllers don’t speak Chinese!

      • Electromagnetic Force (EMF) can cause disruptions in the network digital pulse as well. An induced voltage can cause the signal to be altered and provide false readings

      • Polarity reversal can cause the communications chip to burn up leaving controllers with no means of communication

Most common issue
Most Common Issue

  • The most common issue people have with a DDC control system is themselves.

  • Remember the differences between a DDC system and a Thermostat? They are virtually the same thing just on a larger scale.

  • The approach of a DDC system is actually easier because you have more information at your finger tips to help you troubleshoot and manage your processes and conditions.

  • No system is too complicated if you are willing to simply use the information it is providing for you

The end ddc 101 2012
The End!DDC 101 - 2012