Saturday, October 10, 2015

How ddc works: HVAC Furnace direct digital control


CENTRAL WORKSTATION (control, monitor, manage)
-         talks to global controllers/building controllers
-         send, receive, process, store, print the data
-         check component and system status
-         check trends and monitor performance of equipment
-         change set points, schedules and settings
-         ASCENT COMPASS - Alerton

GLOBAL CONTROLLERS (integrate devices)
-         talks to field controllers/zone controllers
-         connects/provides gateway to allow communication
with devices made by different manufacturers
-          integrates different devices
-         ACM, BCM, VLX - Alerton

FIELD CONTROLLERS (control terminal units)
-         operates actuators, fans, blowers, pumps
-         field controller for VAV, AHU, Fan coil unit, chiller
cooling tower, boiler, terminal unit
-         VLC, VAV - Alerton

-         provide input, send signal to controllers
-         display room setpoints and fan status
-         display room temperature, outside air temperature, relative humidity
-         MICROSET - Alerton

Receive Input Information From Sensors
Process Input Information
Respond with an Output Action
Receive Feedback when set point is met
Respond with another Output Action

Example:  How a Furnace DDC works?

1.      Thermostat (Sensor) calls for heat
2.      Thermostat switch is closed, sends voltage signal to control board
3.      Control board (“Brain”) receives and processes input signal from thermostat
4.      Control board closes contactor, inducer fan motor starts
5.      Air flow switch/Sail switch closes to confirm air flow supplied by fan
6.      Control board will activate the Spark Igniter
7.      Control board activates Gas Valve
8.      Burner ignites
9.      Flame Sensor detects flame
10.   Spark Igniter deactivates
11.   Control board energizes Indoor Fan Blower motor
12.   Furnace supplies heat to the structure (room, home, building, etc.)
13.   Thermostat temperature set point is met
14.   Thermostat opens switch, sends feedback signal voltage to control board
15.  Control board shuts off the Gas Valve and Induced draft fan
BAS uses an integrated network of Workstations, Global Controllers, Field Controllers, Sensors, Gateways, Routers, Repeaters, Cables and other associated components that are designed and programmed to provide the following building services:

  1. Networking
  2. Control, Monitoring and Alarms
  3. Data collection
  4. HVAC – Heating, Ventilation, Air-Conditioning
  5. Real-time Adjustments of Setpoints, Percent valve openings, etc
  6. Scheduling, Remote Operation and Remote Access
  7. Changing Modes, e.g. Economizer mode (to save on energy costs)
  8. Load and Demand Control
  9. Fire Protection
  10. Security
  11. Lighting management
  12. Energy Management



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