Invensys  D irect D igital C ontrol

Invensys  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. 8.Communication LAN. 9.Programming Methods.

Invensys  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.

Invensys  2. Software  Hardware is the of instructions and procedures that tells the computer what computations to perform and what to do with the results.

Invensys  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)

Invensys  DDC CONTROLLERS  All DDC Systems consist of : HARDWARE SOFTWARE FIRMWARE

Invensys  4. Local DDC Controllers 1.Application Specific Controllers 2.Application Programmable Controllers 3.Flexible (Fully) Programmable Application Controllers  Local Controllers directly control HVAC equipment. They are classified in three types:

Invensys  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

Invensys  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.

Invensys  2. Application Programmable Controllers Fig. Page 77

Invensys  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.

Invensys  3.Flexible (Fully) Programmable Application Controllers Fig. Page 78

Invensys  5. Input/ Output 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…  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:

Invensys  5. Input/ Output 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.  Universal Points:

Invensys  5. Input/ Output 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.  Pulse Input Points:

Invensys  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”.

Invensys  6. Global DDC Controllers Fig 1 page 90

Invensys  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.

Invensys  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

Invensys   Controllers are connected in Series.  There is always two ends for the network. 1.Daisy Chain Fig. p93

Invensys   Controllers are connected in different ways (easier to wire).  There are more than two ends for the network. 2.Star Connection

Invensys  2.Star Connection Fig. p94

Invensys  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.

Invensys  9. Programming Methods

Invensys  9. Programming Methods

Invensys  9. Programming Methods