Civil Engineering Reference
In-Depth Information
to change the fl ow of the medium in elements such as chilled water coil control
valve, and fan variable frequency drive will be specifi ed.
Depending on the type and direction of communication with the central direct
digital control system each element is marked with input and output and types of
input and output designations such as Analog Input (AI) or Digital Output (DO).
Any signal entering the direct digital control system controller is an input, and any
signal that leaves the direct digital control system controller is an output.
For a typical variable volume air handling unit with hot water preheat coil and
chilled water cooling coil a typical list and type of the input and output points (I/O
Summary) can be described as follows:
Analog inputs:
•
Air handling unit discharge temperature (temperature; °F)
•
Cooling coil entering air temperature (temperature; °F)
•
Cooling coil leaving air temperature (temperature; °F)
•
Space temperature (temperature; °F)
•
Space humidity (humidity)
•
Supply duct static pressure (pressure; inch of water gauge)
•
Outdoor temperature (temperature; °F)
•
Outdoor humidity (humidity)
•
Return air CO
2
level (part per million)
•
Critical space CO
2
level (part per million)
•
Chilled water valve actuator position (% of full open)
•
Preheat hot water valve actuator position (% of full open)
•
Minimum outside air damper actuator position (% of full open)
•
Maximum outside air damper actuator position (% of full open)
•
Relief damper actuator position (% of full open)
•
Fan variable frequency drive speed (speed; rounds per minute)
•
System supply airfl ow rate (fl ow; cubic feet per minute)
•
Terminal unit fl ow rate (fl ow; cubic feet per minute)
•
Minimum outdoor airfl ow (fl ow; cubic feet per minute)
Digital Inputs:
•
Supply fan proof of operation (on-off)
•
Filter status (clean-dirty)
•
Humidifi er proof of operation (on-off)
•
Selector switch status (on-off)
•
Override switch status (on-off)
•
Low temperature limit status (yes-no)
•
Mixing box static safety status (on-off)
•
Discharge static safety status (on-off)
•
Return static safety status (on-off)
•
Power status (on-off)
•
Preheat hot water pump proof of operation (on-off)
•
Smoke damper actuator position (on-off)
