Direct Digital Controllers (DDC) are commonly used, in intelligent building management systems which take care of monitoring, controlling, communicational and computational. DDC consist of inputs and outputs (I/O) which communicate with field mounted sensors, actuators and other field devisors. DDC allows a lot of data points to be come together in a relatively small geographical area. Commonly available numbers of datapoint pairs in a DDC are 06, 16, 20, 32, and 50. It is better to have limited number of datapoints. Advantage of such design is eventual failure only affect to a small part of a technical installation. It is better to include 20% excess capacity for I/O, memory and data collection and storage.
CHILLERS
| Inputs | I/O number | Outputs |
| Chiller system auto/manual status (binary) | 1 | Chiller system auto/manual control(binary) |
| Chiller system on/off status (binary) | 2 | Chiller system on/off control (binary) |
| Chiller system set point status (anolag) | 3 | Chiller system set point control (anolag) |
| Difference of supply and return chilled water temperature (analog) | 4 | Compressor control (analog) |
| Condenser water flow rate (analog) | 5 | Chiller on/off control(binary) |
| Common Alarm Signal & Trip Alarm (Design) | 6 | (not used) |
| Chiller system chilled water in temperature (analog) | 7 | (not used) |
| Chiller system chilled water in pressure (analog) | 8 | (not used) |
| Chiller system chilled water out temperature (analog) | 9 | (not used) |
| Chiller system chilled water out pressure (analog) | 10 | (not used) |
| Chilled Water Differential Pressure (analog) | 11 | (not used) |
| Chiller system condenser water in Temperature (analog) | 12 | (not used) |
| Chiller system condenser water in pressure (analog) | 13 | (not used) |
| Chiller system condenser water out Temperature (analog) | 14 | (not used) |
| Chiller system condenser water out pressure (analog) | 15 | (not used) |
| Condenser Water Differential Pressure (analog) | 16 | (not used) |
| Chilled Water Return Valve position (analog) | 17 | (not used) |
| Condenser Water Return Valve position (analog) | 18 | (not used) |
| Oil Temperature Sump | 19 | (not used) |
| Oil Temperature Feed | 21 | (not used) |
| Oil Pressure | 22 | (not used) |
| Compressor Motor Percent RLA | 23 | (not used) |
| Compressor Motor Current | 24 | (not used) |
One chiller unit require 24 datapoints, 20% additional datapoints also need to be provisioned.
Total datapoints required = 24 + (24/100*20)
= 28.8
Chiller need 29 datapoints, therefore it is better to allocate a 32 datapoint DDC for one chiller. All four chillers in the BOC head quarters require four numbers of DDCs with 32 datapoints each.
CHILLED WATER PUMPS
I/O objects pumps
| CHILLED PUMP | ||
| Inputs | I/O Number | Outputs |
| Pump Auto/ Manual status (Binary) | 1 | Pump Auto/ Manual control (Binary) |
| Pump On/Off status | 2 | Pump On/Off Control |
| Chilled Water Return Header Temp | 3 | (not used) |
| Chilled Water Supply Header Temp | 4 | (not used) |
| Speed Control Signal (VFD) | 5 | (not used) |
| Pump Trip Alarm | 6 | (not used) |
Each chilled water pump and condenser water pump require six datapoints. BOC headquarters consist of three chilled water pumps at each chiller room. Therefore all the chilled water pumps require 18 datapoints.
CHILLED WATER DISTRIBUTION
I/O objects CHW distribution
| Inputs | I/O Number | Outputs |
| Chilled Distribution Water System Flow Rate | 7 | (not used) |
| Chilled Distribution Water Supply Header Temperature | 8 | (not used) |
| Chilled Distribution Water Return Header Temperature | 9 | (not used) |
Chilled water distribution requires three datapoints. Therefore chilled water pumps and chilled water distribution can be connected to one DDC.
Total datapoints required = 21 + (21/100*20)
= 25.2
Pumps and chilled water distribution need 26 datapoints, therefore it is better to allocate a 32 datapoint DDC for the system for one chiller room.
COOLING TOWERS
I/O objects cooling towers
| Inputs | I/O Number | Outputs |
| Cooling Tower Auto/Manual Status (Binary) | 1 | Cooling Tower Auto/Manual Status (Binary) |
| Cooling Tower ON/OFF Status (Binary) | 2 | Cooling Tower ON/OFF Control (Binary) |
| Trip Status (Binary) | 3 | (not used) |
| Motor Frequency (Analog) | 4 | (not used) |
| Cooling Tower Basin Temperature | 5 | (not used) |
One cooling tower requires five datapoints. There three cooling towers at 3rd floor and 31st floor each. Therefore a set of cooling towers need 15 datapoints.
Total datapoints required = 15 + (15/100*20)
= 18
Cooling towers need 18 datapoints, therefore it is better to allocate a 20 datapoint two number of DDC for all cooling towers.
CONDENSER WATER PUMP
I/O objects pumps
| CONDENSER WATER PUMP | ||
| Inputs | I/O Number | Outputs |
| Pump Auto/ Manual status (Binary) | 1 | Pump Auto/ Manual control (Binary) |
| Pump On/Off status | 2 | Pump On/Off Control |
| Condenser Water Return Header Temp | 3 | (not used) |
| Condenser Water Supply Header Temp | 4 | (not used) |
| Speed Control Signal (VFD) | 5 | (not used) |
| Pump Trip Alarm | 6 | (not used) |
Each condenser water pump requires six datapoints. BOC headquarters consist of three condenser water pumps at each pump area. Therefore all the condenser water pumps require 18 datapoints.
Total datapoints required = 18 + (18/100*20)
= 21.6
Even though condenser water pumps require 22 datapoints, using 20 datapoint two DDC for all condenser water pumps is cost effective.
AIR HANDLING UNIT
I/O objects AHU
| AIR HANDLING UNIT | ||
| Inputs | I/O Number | Outputs |
| AHU Auto/Manual Status (Binary) | 1 | AHU Auto/Manual Status (Control) |
| AHU ON/OFF Status (Binary) | 2 | AHU on/off Control (Binary) |
| AHU Trip Status (Binary) | 3 | (not used) |
| AHU 1 Motor speed (Analog) | 4 | (not used) |
| AHU Discharge Air Temperature | 5 | (not used) |
| AHU mixed Air Temperature | 6 | (not used) |
| Outside Air Temperature | 7 | (not used) |
| AHU 1 Motorised Valve Position Feed Back (Analog) | 8 | (not used) |
| AHU 1 Filter Clog Status (Binary) | 9 | (Not Used) |
Each AHU requires nine datapoints. BOC headquarters consist of 70 AHUs, usually there are two AHU per floor.
Total datapoints required = 18 + (18/100*20)
= 21.6
Even though AHUs per floor require 22 datapoints, using 20 datapoint DDC is cost effective and manageable.
In BOC headquarters 29 floors are air conditioned by central air conditioning system. Whole building requires 29 DDCs with 20 datapoints each.
VARIABLE AIR VOLUME BOX
| VARIABLE AIR VOLUME BOX | ||
| Inputs | I/O Number | Outputs |
| Discharge Air Temperature (Analog) | 1 | (not used) |
| Damper Position status (Analog) | 2 | Damper Position Control (Analog) |
| Space Temperature | 3 | (not used) |
| Space Temperature Setpoint | 4 | (not used) |
| Space Relative Humidity | 5 | (not used) |
Presently there is no variable air volume (VAV) system. But to get the maximum energy saving benefit from the chillers, we propose to install VAV system to all the floors of the building except cafeteria floor, auditorium floor, and two other customer floors. According to that 25 floors need to install VAV systems. Averagely five VAV boxes need to be installed per one floor.
Total datapoints required per floor = 5*5 + (25/100*20)
= 30
In BOC headquarters 25 floors VAV system. It is better to install DDC with 32 datapoints for each floor. Whole building requires 25 DDCs with 30 datapoints each.
EXHAUST FAN
I/O objects exhaust fan
| EXHAUST FAN | ||
| Inputs | I/O Number | Outputs |
| Exhaust fan Auto/ Manual Status (Binary) | 1 | Exhaust fan Auto/ Manual Status (Binary) |
| Fan On/Off Control (Binary) | 2 | Fan On/Off Control (Binary) |
| Fan trip alarm (Binary) | 3 | (not used) |
| Space Relative Humidity | 4 | (not used) |
| By-pass Damper | 5 | (not used) |
Each exhaust fan requires five datapoints. BOC headquarters consist of seven exhaust fans but they are located at different areas. Therefore it is better to have separated DDC controllers for each.
Total datapoints required = 5 + (5/100*20)
= 6
Therefore building requires seven DDC controllers with six datapoints each.
TOTAL REQUIREMENT OF DDC
DDC requirement
| Equipment | Number of equipment | Number of DDC required | Datapoints required for each DDC |
| Chillers | 4 | 4 | 32 |
| Chilled water pumps & distribution | 6 | 2 | 32 |
| Cooling Towers | 6 | 2 | 20 |
| Condenser water pumps | 6 | 2 | 20 |
| AHU | 58 | 29 | 20 |
| VAV | 125 | 25 | 30 |
| Exhaust Fans | 7 | 7 | 6 |
| Total |
| 71 |
|
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