Civil Engineering Reference
In-Depth Information
Fig. 9.1
Control schematics for an air handling unit
workstation if the cooling coil is proven closed and the cooling coil discharge
temperature is at least 2 °F (adjustable) below the cooling 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 hap-
pened and requires attention).
In addition to sequence of operation, a well-drawn schematic control diagram and
an Input/Output summary can help to transfer ideas of the control designer to control
installers and commissioning agents as well as building engineering personnel.
A schematic control diagram (Fig.
9.1
) depicts the physical location of different
elements in each one of the equipment in an orderly manner and shows each ele-
ment's communication with the central direct digital control system. For example a
typical schematic diagram of an air handling unit should show the path of air move-
ment through the outdoor and return air dampers, fi lter, preheat coil, cooling coil,
fan, discharge plenum, humidifi er, and space terminal units. In the path from each
element to the next a group of desired control sensors such as temperature and
humidity sensors will be shown to be installed which their main responsibility is to
sense the condition at that specifi c location and communicate that with the direct
digital control controller. Also location of the actuators which upon receiving com-
mands from the direct digital control central controller will be physically operating
