ENGINEERING MANUAL OF AUTOMATIC CONTROL
CONTROL FUNDAMENTALS
8
HVAC SYSTEM CHARACTERISTICS
Figure 2 shows how an HVAC system may be distributed in
a small commercial building. The system control panel, boilers,
motors, pumps, and chillers are often located on the lower level.
The cooling tower is typically located on the roof. Throughout
the building are ductwork, fans, dampers, coils, air filters,
heating units, and variable air volume (VAV) units and diffusers.
Larger buildings often have separate systems for groups of floors
or areas of the building.
Fig. 2. Typical HVAC System in a Small Building.
The control system for a commercial building comprises
many control loops and can be divided into central system and
local- or zone-control loops. For maximum comfort and
efficiency, all control loops should be tied together to share
information and system commands using a building
management system. Refer to the Building Management System
Fundamentals section of this manual.
The basic control loops in a central air handling system can
be classified as shown in Table 1.
Depending on the system, other controls may be required
for optimum performance. Local or zone controls depend on
the type of terminal units used.
DAMPER
AIR
FILTER
COOLING
COIL
FAN
CHILLER
PUMP
COOLING
TOWER
HEATING
UNIT
DUCTWORK
VAV BOX
DIFFUSER
BOILER
CONTROL
PANEL
M10506
GENERAL
An HVAC system is designed according to capacity
requirements, an acceptable combination of first cost and operating
costs, system reliability, and available equipment space.
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