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Direct Digital Control
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Direct Digital Control :
1. Hardware.
8. Communication LAN.
2. Software.
9. Programming Methods.
3. Firmware.
4. Local DDC Controllers.
5. Types of I/O Points.
6. Global DDC Controllers.
7. Peripheral Equipment.
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1. Hardware
 Hardware is the physical machinery consisting of :
1. Microprocessor(s)
2. Memory
3. 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 :
SOFTWARE
HARDWARE
FIRMWARE
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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.
1. Daisy chain, Bus or Trunk.
2. 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:
1.
Line By Line Programming: It is sort of a Basic Language program
2.
Block Programming (Object Oriented): It uses predefined objects of
all pieces of HVAC equipment, Links between objects is made to
create the program.
3.
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