D irect D igital C ontrol

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Direct Digital Control

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Direct Digital Control : 1.1. Hardware.Hardware.

2.2. Software.Software.

3.3. Firmware.Firmware.

4.4. Local DDC Controllers.Local DDC Controllers.

5.5. Types of I/O Points.Types of I/O Points.

6.6. Global DDC Controllers.Global DDC Controllers.

7.7. Peripheral Equipment.Peripheral Equipment.

8.8. Communication LAN.Communication LAN.

9.9. Programming Methods.Programming Methods.

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1. Hardware

Hardware is the physical machinery consisting of :Hardware is the physical machinery consisting of :

1.1. Microprocessor(s)Microprocessor(s)

2.2. MemoryMemory

3.3. Peripheral devices such as the sensor/actuator interfaces, Peripheral devices such as the sensor/actuator interfaces, serial and parallel communication ports and operator serial and parallel communication ports and operator interfaces.interfaces.

Peripherals communicate with the HVAC sensors, actuators, Peripherals communicate with the HVAC sensors, actuators, other computers and humans.other computers and humans.

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2. Software

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

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3. Firmware

Firmware refers to software instructions that are stored in Firmware refers to software instructions that are stored in silicon, on hardware memory chips.silicon, on hardware memory chips.

Firmware has some of the attributes of both hardware and Firmware has some of the attributes of both hardware and software. It is a set of software instructions that can be software. It is a set of software instructions that can be plugged into an integrated circuit socket. (EEPROM) plugged into an integrated circuit socket. (EEPROM)

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DDC CONTROLLERS

All DDC Systems consist of :All DDC Systems consist of :

HARDWAREHARDWARE

SOFTWARESOFTWARE

FIRMWAREFIRMWARE

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4. Local DDC Controllers

1.1. Application Specific ControllersApplication Specific Controllers

2.2. Application Programmable ControllersApplication Programmable Controllers

3.3. Flexible (Fully) Programmable Application Flexible (Fully) Programmable Application ControllersControllers

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

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1.1. Application Specific ControllersApplication Specific Controllers

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

Fig. Page 76Fig. Page 76

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

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These controllers are very flexible and freely These controllers are very flexible and freely programmable.programmable.

They can be used for most of HVAC applications, such as They can be used for most of HVAC applications, such as Boilers Control, Chillers Sequencing, Full Air Handling Units Boilers Control, Chillers Sequencing, Full Air Handling Units Control, Pumps Sequencing,…etc.Control, Pumps Sequencing,…etc.

Its main application is for Main Plants and Equipment.Its main application is for Main Plants and Equipment.

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5. Input/ Output Points

1.1. Digital Inputs (DI): Fan Status, Pump Pressure…(VFC)Digital Inputs (DI): Fan Status, Pump Pressure…(VFC)

2.2. Digital Outputs (DO): Fan/Pump/Humidifier/Electric Heater Digital Outputs (DO): Fan/Pump/Humidifier/Electric Heater Command…Command…

3.3. Analogue Inputs (DI): Sensors, Transducers, Transmitters…Analogue Inputs (DI): Sensors, Transducers, Transmitters…

4.4. Analogue Outputs (AO): Actuators, VFD Speed Control… Analogue Outputs (AO): Actuators, VFD Speed Control…

Input/ Output (I/O) Points are the physical connections from a Input/ Output (I/O) Points are the physical connections from a DDC Controller to sensors and controlled devices.DDC Controller to sensors and controlled devices.

There are 4 different types of points: There are 4 different types of points:

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Some controllers provide the ability for any Input to be Some controllers provide the ability for any Input to be configured in the field as Analogue or Digital. configured in the field as Analogue or Digital.

The same applies to Output Points. The same applies to Output Points.

Universal Points:Universal Points:

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

Pulse Input Points:Pulse Input Points:

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6. Global DDC Controllers

Global controllers are not directly connected to HVAC Global controllers are not directly connected to HVAC equipment, but are wired to a group of local controllerequipment, but are wired to a group of local controller

The global controllers major function is group local controllers The global controllers major function is group local controllers together, and share information between the local controllers together, and share information between the local controllers and with other Global controllers.and with other Global controllers.

The sharing of information is referred as “NETWORKING” or The sharing of information is referred as “NETWORKING” or “Peer-to-Peer”. “Peer-to-Peer”.

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6. Global DDC Controllers

Fig 1 Fig 1 page 90page 90

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7. Peripheral Equipment

Peripheral equipment are connected directly to global Peripheral equipment are connected directly to global controllers such as a printer or a modem.controllers such as a printer or a modem.

Each device attached to a Global Controller has a Each device attached to a Global Controller has a communication speed or baud rate. communication speed or baud rate.

The baud rate of the global controller must much the 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 for the peripheral equipment for both devices to be able to communicate. communicate.

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8. Communication LAN

When controllers are connected together, there are at least When controllers are connected together, there are at least two different physical arrangements.two different physical arrangements.

1.1. Daisy chain, Bus or Trunk.Daisy chain, Bus or Trunk.

2.2. Star ConnectionStar Connection

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Controllers are connected in Series.Controllers are connected in Series.

There is always two ends for the network.There is always two ends for the network.

1.1. Daisy ChainDaisy Chain

Fig. p93Fig. p93

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Controllers are connected in different ways (easier to wire) .Controllers are connected in different ways (easier to wire) .

There are more than two ends for the network.There are more than two ends for the network.


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Fig. p94Fig. p94

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9. Programming Methods

There are three different approaches to writing the software There are three different approaches to writing the software programs in DDC controllers:programs in DDC controllers:

1.1. Line By Line Programming:Line By Line Programming: It is sort of a Basic Language program It is sort of a Basic Language program

2.2. Block Programming (Object Oriented):Block Programming (Object Oriented): It uses predefined objects of It uses predefined objects of all pieces of HVAC equipment, Links between objects is made to all pieces of HVAC equipment, Links between objects is made to create the program.create the program.

3.3. Application Programming:Application Programming: It is a computer program that asks the It is a computer program that asks the programmer questions concerning a particular application and programmer questions concerning a particular application and creates the controller program accordingly.creates the controller program accordingly.

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9. Programming Methods

D irect D igital C ontrol

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