Direct Digital Control

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Direct Digital Control
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Direct Digital Control

1. Hardware.
2. Software.
3. Firmware.
4. Local DDC Controllers.
5. Types of I/O Points.
6. Global DDC Controllers.
7. Peripheral Equipment.

1. Communication LAN.
2. Programming Methods.

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1. Hardware

• Hardware is the physical machinery consisting of
  
• Microprocessor(s)
• Memory
• Peripheral devices such as the sensor/actuator
  interfaces, serial and parallel communication
  ports and operator interfaces.
• Peripherals communicate with the HVAC sensors,
  actuators, other computers and humans.

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2. Software

• Hardware is the of instructions and procedures
  that tells the computer what computations to
  perform and what to do with the results.

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3. Firmware

• Firmware refers to software instructions that are
  stored in silicon, on hardware memory chips.
• Firmware has some of the attributes of both
  hardware and software. It is a set of software
  instructions that can be plugged into an
  integrated circuit socket. (EEPROM)

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DDC CONTROLLERS

• All DDC Systems consist of

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4. Local DDC Controllers

• Local Controllers directly control HVAC
  equipment. They are classified in three types

1. Application Specific Controllers
2. Application Programmable Controllers
3. Flexible (Fully) Programmable Application
   Controllers

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1. Application Specific Controllers

• These controllers are specifically designed for
  some terminal units, such as Variable Air Volume
  (VAV) boxes, Fan Coil Units (FCU)

Fig. Page 76
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2. Application Programmable Controllers

• These controllers are designed for very specific
  types of equipment terminal units, such as
  Variable Air Volume (VAV) boxes, Fan Coil Units
  (FCU), Heat Pumps, RoofTop Units and Unit
  Ventilators.

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2. Application Programmable Controllers
Fig. Page 77
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3. Flexible (Fully) Programmable Application
Controllers

• These controllers are very flexible and freely
  programmable.
• They can be used for most of HVAC applications,
  such as Boilers Control, Chillers Sequencing,
  Full Air Handling Units Control, Pumps
  Sequencing,etc.
• Its main application is for Main Plants and
  Equipment.

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3. Flexible (Fully) Programmable Application
Controllers
Fig. Page 78
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5. Input/ Output Points

• Input/ Output (I/O) Points are the physical
  connections from a DDC Controller to sensors and
  controlled devices.
• There are 4 different types of points

1. Digital Inputs (DI) Fan Status, Pump
   Pressure(VFC)
2. Digital Outputs (DO) Fan/Pump/Humidifier/Electric
   Heater Command
3. Analogue Inputs (DI) Sensors, Transducers,
   Transmitters
4. Analogue Outputs (AO) Actuators, VFD Speed
   Control

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5. Input/ Output Points

• Universal Points

• Some controllers provide the ability for any
  Input to be configured in the field as Analogue
  or Digital.
• The same applies to Output Points.

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5. Input/ Output Points

• Pulse Input Points

• In some applications it is required to monitor
  and count the pulses of an energy meter or a KWH
  meter. It is necessary to make sure that the
  Digital Input can sense the number of pulses per
  second.

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6. Global DDC Controllers

• Global controllers are not directly connected to
  HVAC equipment, but are wired to a group of local
  controller
• The global controllers major function is group
  local controllers together, and share information
  between the local controllers and with other
  Global controllers.
• The sharing of information is referred as
  NETWORKING or Peer-to-Peer.

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6. Global DDC Controllers
Fig 1 page 90
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7. Peripheral Equipment

• Peripheral equipment are connected directly to
  global controllers such as a printer or a modem.
• Each device attached to a Global Controller has
  a communication speed or baud rate.
• The baud rate of the global controller must much
  the baud rate for the peripheral equipment for
  both devices to be able to communicate.

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8. Communication LAN

• When controllers are connected together, there
  are at least two different physical arrangements.
• Daisy chain, Bus or Trunk.
• Star Connection

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1. Daisy Chain

• Controllers are connected in Series.
• There is always two ends for the network.

Fig. p93
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2. Star Connection

• Controllers are connected in different ways
  (easier to wire) .
• There are more than two ends for the network.

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2. Star Connection
Fig. p94
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9. Programming Methods

• There are three different approaches to writing
  the software programs in DDC controllers
• Line By Line Programming It is sort of a Basic
  Language program
• Block Programming (Object Oriented) It uses
  predefined objects of all pieces of HVAC
  equipment, Links between objects is made to
  create the program.
• Application Programming It is a computer program
  that asks the programmer questions concerning a
  particular application and creates the controller
  program accordingly.

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9. Programming Methods
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9. Programming Methods
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9. Programming Methods