Civil Engineering Reference
In-Depth Information
• Typical sequence of operation for series fan powered terminal units: The direct
digital control shall start the fan and shall modulate the primary air valve of each
series fan powered variable volume air terminal between its designated minimum
and maximum quantities to maintain space temperature. When the space tem-
perature drops below a set point the direct digital control system shall modulate
the primary air valve down to its minimum setting, and modulate the hot water
control valve to maintain space temperature 72 °F (adjustable) (this control
allows a constant airfl ow with proper air temperature delivery to each individual
space. This system is usually used for high occupancy spaces such as conference
rooms in offi ce buildings).
• Typical sequence of operation for smoke detectors: If smoke detectors in the sup-
ply and return air ducts sense the heat or smoke presence the direct digital control
system shall automatically shut down the air handling unit fan (this control pre-
vents the spread of smoke to the different spaces through air handling unit fan).
• Typical sequence of operation for fan alarm: The direct digital control system
shall generate an alarm and display a warning message in operator's workstation
if the fan is commanded to operate and status is not proven after more than 15 s
(this control sends an alarm to warn the operator that a malfunction in the system
has happened and requires attention).
• Typical sequence of operation for supply air temperature alarm: The direct digi-
tal control system shall generate an alarm and display a warning message in
operator's workstation if the supply fan is proven running and supply air tem-
perature is 6 °F (adjustable) above or below its set point for at least 15 min (this
control sends an alarm to warn the operator that a malfunction in the system has
happened and requires attention).
• Typical sequence of operation for heating coil discharge temperature alarm: The
direct digital control system shall generate an alarm and display a warning mes-
sage in operator's workstation if the heating coil discharge air temperature is 6 °F
(adjustable) below its set point for a continuous period of 15 min (this control
sends an alarm to warn the operator that a malfunction in the system has hap-
pened and requires attention).
• Typical sequence of operation for heating valve leak alarm: The direct digital
control system shall generate an alarm and display a warning message in opera-
tor's workstation if the heating coil valve is proven closed and the heating coil
discharge temperature is at least 2 °F (adjustable) above the heating coil intake
temperature for a period of time of at least 30 min (adjustable) continuously (this
control sends an alarm to warn the operator that a malfunction in the system has
happened and requires attention).
• Typical sequence of operation for cooling capacity shortage alarm: The direct
digital control system shall generate an alarm and display a warning message in
operator's workstation if the cooling coil valve is in fully open condition continu-
ously for at least 1 h (adjustable) (this control sends an alarm to warn the opera-
tor that a malfunction in the system has happened and requires attention).
• Typical sequence of operation for cooling valve leak alarm: The direct digital
control system shall generate an alarm and display a warning message in operator's
