The HVAC system not only makes the building comfortable, healthful, and
livable for its occupants, it manages a substantial portion of energy usage and
related costs for the building. In maintaining the building’s air quality, the
HVAC system must respond to a variety of conditions inside and outside the
building (including weather, time of day, different types of spaces within a
building and building occupancy), while simultaneously optimizing its opera-
tions and related energy usage. The HVAC system is also critical in controlling
smoke in the event of a fire.
HVAC systems in commercial and institutional buildings are very different
from those used in typical residential housing. Larger buildings have a greater
density of people, lighting and other equipment, all of which generates more
heat. The result is that air conditioning, or the recirculation of air, becomes
more important than providing heat, depending on the local climate. Although
there may be a centralized HVAC system in commercial and institutional
buildings, sections of large buildings have different HVAC needs or thermal
loads depending on how the space is utilized.
An HVAC system having a single control thermostat serves one zone of a
“thermal load.” Most large buildings have multiple zone systems, with air sup-
plied to each zone specifically addressing its needs and thermal load. For com-
parison on a smaller scale, a two-story home may have two zones, one for the
lower floor and one for the upper floor, with one heating and cooling unit for
each floor. The upper floor may have a higher thermal load and may require
more cooling than the lower floor.
Components
HVAC systems can be very complex, consisting of many components. The
major components include boilers, chillers, air-handling units (AHUs), air
terminal units (ATUs), and variable air volume equipment (VAV).
Boilers
Boilers are used to heat air (Fig. 3.1). However, because of the general increase
in the efficiency of HVAC systems, many simply “recover” wasted heat pro-
duced from the chiller, another major component in an HVAC system, or
use smaller-scale versions of traditional boilers to generate heat.
Boilers heat air in the following manner: a fuel (typically propane or natural
gas) is combusted, and the resulting heat is used to heat water. The hot water
or steam is piped through the building to radiator units where air is forced
over them, moving heated air through the ducts and into the rooms.
32 Smart Building Systems for Architects, Owners, and Builders