Civil Engineering Reference
In-Depth Information
Analog outputs:
•
Economizer damper command (% of full open)
•
Relief damper command (% of full open)
•
Face and bypass damper command (% of full open)
•
Chilled water valve command (% of full open)
•
Humidifi er valve command (% of full open)
•
Variable frequency drive speed command (% of full speed)
•
Preheat hot water valve command (% of full open)
Digital outputs:
•
Supply fan start/stop (on-off)
•
Variable frequency drive enable/disable (on-off)
•
Humidifi er shutdown (on-off)
•
Preheat hot water pump command (on-off)
•
Power status (on-off)
In addition to these inputs and outputs, the direct digital control system will gen-
erate required software alarms and displays them in the operator's workstation.
Similar sequence of operations and input/output summaries need to be generated
for all other equipment in the system such as chilled water and hot water plants,
exhaust air system, etc.
9.6
Advanced Control Strategies for Energy Saving
9.6.1
Demand Ventilation Control
This control allows the system to be capable of operating with a level of outside air
even less than minimum outdoor air required calculated by governing standards. In
this design CO
2
sensors that are located strategically throughout the building to
sense and measure the real time part per million (ppm) of CO
2
, specifi cally in
crowded spaces of the building, and if this value is below an acceptable threshold,
allows the direct digital control system to decrease the minimum outdoor air level.
This strategy is a very effective measure for saving energy.
9.6.2
Optimum System Start or Stop
It is a common practice to set the controls of the building to switch the air condition-
ing system from unoccupied mode to occupied mode earlier than expected occu-
pancy time, in order to provide a comfortable condition for the occupants as they
arrive to the building early in the morning, or early Monday mornings. Based on
time of early occupancy of the building, outdoor conditions, and the thermal
