GOAL OF HVAC
The goal of the heating, ventilating, and air
conditioning (HVAC) system is to create and
maintain a comfortable environment within a
"Conditioned" air means that air is clean and odor-
free, and the temperature, humidity, and movement
of the air are within certain comfort ranges.
Furniture and work surfaces
COMFORT REQUIREMENTS BY HVAC
Comfort requirements that are typically impacted by
the HVAC system include:
Cleanliness of the air
Some HVAC systems address these comfort
requirements better than others.
FUNCTIONS OF HVAC
Control of air temperature
Control of moisture content in the air
Proper air movement.
To hold the air contamination within acceptable
FIVE SYSTEM LOOP
The premise of this method is that any HVAC system
can be dissected into basic subsystems.
These subsystems will be referred to as "loops/"
There are five primary loops that can describe
virtually any type of HVAC system.
Airside loop (yellow)
Chilled-water loop (blue)
Refrigeration loop (green)
Heat-rejection loop (red)
Controls loop (purple)
The first two comfort requirements mentioned were
dry-bulb temperature and humidity.
In order to maintain the dry-bulb temperature in the
conditioned space, heat (referred to as sensible heat)
must be added or removed at the same rate as it
leaves or enters the space.
In order to maintain the humidity level in the space,
moisture (sometimes referred to as latent heat) must
be added or removed at the same rate as it leaves or
enters the space
COMPONENTS OF AIR LOOP
Supply fan and filter
CHILLED WATER LOOP
A chilled-water applied system uses chilled water to
transport heat energy between the airside, chillers
and the outdoors.
COMPONENTS OF CHILLED WATER
The components of the chiller
An air- or water-cooled condenser
Recall that in the chilled-water loop, the evaporator
allows heat to transfer from the water to cold liquid
liquid refrigerant at 38ºF (3.3ºC) enters the tubes of
the shell-and-tube evaporator.
As heat is transferred from the water to the
refrigerant, the liquid refrigerant boils.
The resulting refrigerant vapor is further warmed
(superheated) to 50ºF (10ºC) inside the evaporator
before being drawn to the compressor
HEAT REJCTION LOOP
The fourth loop is the heat-rejection loop.
In the refrigeration loop, the condenser transfers
heat from the hot refrigerant to air, water, or some
other fluid. In a water-cooled condenser, water flows
through the tubes while the hot refrigerant vapor
enters the shell space surrounding the tubes.
Heat is transferred from the refrigerant to the water,
warming the water.
Water enters the condenser at 85ºf (29.4ºc), absorbs
heat from the hot refrigerant, and leavesat 100ºf
HEAT REJCTION LOOP
The water flowing through the condenser must be
colder than the hot refrigerant vapor
A heat exchanger is required to cool the water that
returns from the condenser—at 100ºF (37.8ºC)—
back to the desired temperature of 85ºF (29.4ºC)
before it is pumped back to the condenser.
When a water-cooled condenser is used, this heat
exchanger is typically either a cooling tower or a fluid
cooler (also known as a dry cooler).
COMPONENTS OF HEAT REJCTION
PUMP AND CONTROL VALVE
The fifth, and final, loop of the HVAC system is the
Each of the previous four loops contains several
components. Each component must be controlled in a
particular way to ensure proper operation.
Typically, each piece of equipment (which may be
comprised of one or more components of a loop) is
equipped with a unit-level, automatic controller.
In order to provide intelligent coordinated control so that
the individual pieces of equipment operate together as an
efficient system, these individual unit-level controllers
are often connected to a central, system-level controller