Introduction to HVAC Systems
Presented by AirTight University
HVAC User’s Guide
Gain a better understanding of the basic concept
of air conditioning & air distribution
Review different types of units
Chilled Water Systems
VAV – Variable Air Volume
PIU – Powered Induction Unit
CRAC & CRAH – Computer Room Air Conditioners & Air Handlers
Review the common components of each unit
Review basic HVAC terms
Air Conditioners and all refrigeration systems
have Four main components:
- Metering Device
Basics of Refrigeration Cycle
Low pressure, liquid High pressure, liquid refrigerant
(gaseous mist) refrigerant from condenser coil to
from expansion valve to expansion valve
Low pressure gas taking heat
from evaporator to high pressure,
compressor Compressor gaseous refrigerant
from compressor to
Common Systems in Data Centers
Legacy Design (Raised Floor)
– Water or
Warm Return Air
Cold Supply Air
Typical Rooftop Packaged Unit
Condenser Fan Motor & Blade assembly
2. Evaporator Coil
3. Condensate Pan
4. Gas & Electrical connectors to roof
5. Control Board
6. Heat Exchanger
7. Base rail
8. Condenser fan motor
9. Belt drive blowers
10. Condenser Fan Motor & Blade
Draft Inducer Motor assembly
VAV – Variable Air Volume Box
Insulation is 1”, nylon bearings Damper design features a full
two pound density for long life and diameter contact seal that
and complies with reliable low maintains less than 1% air
UL 181 and NFPA friction operation leakage at pressures up to 4”
90A requirements water gauge
Seismic tabs are
easy installation S & Drive connection for
rapid field installation
Inlet sized to fit Shaft indicator shows damper
all standard position
Direct drive, rack & pinion
actuator maintains precise
control by eliminating
Multipoint averaging hysteresis and blade
velocity sensor vibration
amplifies airflow signal
for greater accuracy Gauge taps for Controller allows for
direct flow maximum-minimum
measurement and design settings,
field balancing pressure independent
PIU – Powered Induction Box
Internal electric, hot water or steam heat to allow for staging
of heat in conjunction with the fan running
and the cooling damper closing off.
fan to provide
as the first stage
of heat, Multipoint averaging
generally used velocity sensor
for perimeter amplifies airflow signal
zones for greater accuracy
Insulation is 1”, Direct drive, rack & pinion
two pound density actuator maintains precise
and complies with control by eliminating
UL 181 and NFPA hysteresis and blade
90A requirements vibration
Damper design features a full
diameter contact seal that Controller allows for Inlet sized to fit
maintains less than 1% air maximum-minimum all standard
leakage at pressures up to 4” design settings, round ducts
water gauge pressure independent
CRAC - Computer Room Air Conditioner
& CRAH – Computer Room Air Handler
A computer room air conditioning (CRAC or CRAH) unit is a device that monitors and maintains the
temperature, air distribution and humidity in a computer room or data center. As the I.T. industry
grows, so does the need for removing the heat from the mission critical facilities. Mainframes and
racks of servers can get as hot as a seven-foot tower of powered toaster ovens, so climate control is
important part of the data center's infrastructure.
One configuration that has been successful is the process of cooling air and having it dispensed
through an elevated floor. The air rises through the perforated sections, forming cold aisles. The cold
air flows through the racks where it picks up heat before exiting from the rear of the racks. The warm
exit air forms hot aisles behind the racks and the hot air returns to the unit intake, which are
positioned above the floor. The inverse concept can be utilized with an overhead delivery as well.
Types of Condensers
Typical Critical Systems Remote Condensers
Typical condenser– Residential of office
Condensing Unit Components
1 – Fan Blade
2 – Protective Cover
23 – Fan Motor
24 – Sheave
25 - Shaft
Filter Line Dryer
What does this “stuff” do?
• The Condensing Unit – The condensing unit is located outdoors and is
responsible for removing the heat that was captured indoors. A
compressor, located within the condensing unit, circulates the refrigerant
throughout the system.
• The Remote Condenser – The heat rejection component that dissipates
heat when the compressor is with the CRAC unit.
• The Condenser Fan – As refrigerant travels through the condenser coil it
begins to cool down. A fan blowing across this condenser coil speeds up
this process and is critical in facilitating the transfer of heat to the outside
• Filter Dryer – Removes impurities and moisture that could be in the
Types of Compressors
Reciprocating Compressor Scroll Compressor
Screw Compressor compressor
Rotary Compressor Oil-less Compressor
What does a Compressor do?
• The purpose of the compressor is to pump refrigerant
vapor/gas through the system and create a pressure
differential. A metering device creates the restriction needed
to separate the high side pressure from the low side pressure.
High pressure, hot gas is pumped out of the compressor and is
cooled into a high pressure liquid by the time it leaves the
condensing coil. This liquid is fed through a metering device
into the evaporator coil and turns into a low pressure gas by
the time it leaves. It returns to the compressor as a low
pressure gas ready to repeat the process.
Types of Air Handlers
CRAC / CRAH Air Handlers
Typical Residential / Indoor Air Handler
Components of an Air Handler
Contactors and Relay’s
Blower Pulley, Shaft and Sheave
What does the Air handler Do?
• The Air handler absorbs heat and removes humidity. It houses the filters,
blower and evaporator. The refrigerant circulating through the evaporator
coil absorbs heat as warm air travels across it. Humidity also collects on
the cold surface of the evaporator and drains down the coil and collects in
a drain pan and is disposed of down the condensate drain.
• The air handler draws filtered air over the evaporator coil.
• The cooler drier air gets pushed through the duct work by the blower and
is diffused throughout the designated space to maintain the desired
temperature and humidity levels within that designated space.
So how do these systems work
Cooling Tower Types
• Water chillers are everywhere - they are used to air condition
large industrial, commercial and institutional facilities and are
used to lower the temperatures of all kinds of equipment,
from machinery to computer parts and server racks.
• Basically, the principal is, the chiller removes heat from (cools)
a liquid, usually water, then circulates the cooled liquid
through a chilled water circuit to provide cooling to each of
the connected air handling units. CRAH units utilize this
technology in many applications.
The entire system working together
Free cooling box Outdoor type packaged A/C
Installed in Shelter
Applied in the shelter air conditioning unit
Energy saving: 15%-50%
The Reasons for Economizers are Many
• To lower the total cost of ownership – In many locations there is a
substantial opportunity for OpEx savings over the life of the equipment
operation. This is largely due to the 365x7x24 operation of the facilities
and cooling needs. When ever economizers are operating (making use of
outside air temperatures) mechanical cooling is not required.
– Makes use of the colder outside air to cool the indoor space. Bot outdoor temperature
and outdoor humidity can play a key role in when an economizer would operate.
• Reduced CapEx by increased service life of the mechanical equipment.
When economizers are in full economizer mode, compressors are not. This
reduces the amount of run hours of the equipment. Equipment life can be
doubled in some cases.
• Reduced OpEx associated with the refrigerant circuit (compressor, etc.) –
same as item 2 above.
Economizers = savings!
Definition of Common
HVAC Technical Terms
• Acid Condition in System – Condition in • Back Pressure – Pressure in low side of
which refrigerant or oil in system is refrigerating systems; also called
mixed with fluids that are acid in nature. suction pressure or low-side pressure.
• Actuator – That portion of a regulating
• Bearing – Low friction device for
valve which converts mechanical fluid,
thermal energy, or electrical energy into supporting and aligning a moving part.
mechanical motion to open or close the • Belt – a rubber-like, continuous loop
valve seats. placed between two or more pulleys to
• Air Diffuser – Air distribution outlet or transfer rotary motion.
grille designed to direct airflow into • Boiler – Closed container in which a
desired patterns. liquid may be heated and vaporized.
• Air Handler – Fan-blower, heat transfer
• Brazing – Method of joining metals
coil, filter and housing parts of a system.
with nonferrous filler (w/out iron) using
• Air Cooled Condenser – Heat of
heat between 800F (427C).
compression is transferred from
condensing coils to surrounding air. This • Btu-British Thermal Unit – Quantity of
may be done either by convention or by heat required to raise temperature of
a fan or blower. one pound of water one degree
• Capacitor – Type of electrical storage • Condensate – A fluid formed when a
device used in starting and/or running gas is cooled to its liquid state.
circuits on many electric motors.
• Condensate Pump – Device to remove
• Capacity – Refrigeration rating system. water condensate that collects
Usually measured in Btu per hour or beneath an evaporator.
• Condensation – Liquid or droplets
• Charge – Amount of refrigerant placed which from when a gas or vapor is
in a refrigerating unit. cooled below its dew point
• Circuit – Tubing, piping or electrical • Condenser, Air-Cooled – Heat
wire installation which permits flow to exchanger which transfers heat to
and from the energy source. surrounding air.
• Circuit Breaker – Safety device that • Condenser, Water – Cooled – Heat
automatically open an electrical circuit exchanger designed to transfer heat
if overloaded. from hot gaseous refrigerant to water.
• Compressor – Pump of a refrigerating • Condenser Coil – Made of copper
mechanism which draws a low tubing, this is where the hot Freon is
pressure on cooling side of refrigerant compressed to squeeze the heat out
cycle and squeezes or compresses the of it.
gas into the high-pressure or
condensing side of the cycle.
• Condenser Fan – Forced air device • Control, Low-Pressure – Cycling device
used to move air through air-cooled connected to low-pressure side of
• Condenser Fan Motor – Enables fan to • Cooling Tower – Device which cools by
blow air across the surface of the water evaporation in air. Water is
Condenser coil carrying away the heat. cooled to wet bulb temperature of
• Condensing Pressure – Pressure inside air.*****
a conde3nser at which refrigerant • Cut-In – The temperature value or the
vapor gives up its latent heat of pressure value at which the control
vaporization and becomes a liquid. circuit closes
This varies with the temperature. • Cut-Out – Temperature value or
• Condensing Temperature – pressure value at which the control
Temperature inside a condenser at circuit opens.
which refrigerant vapor gives up its • Cycle – Series of events or operations
latent heat of vaporization and which have tendency to repeat in the
becomes a liquid. This varies with same order.
• Condensing Unit – Part of a
refrigerating mechanism which pumps
vaporized refrigerant from the
evaporator, compresses it, liquefies it
in the condenser, and returns it to the
• Damper – Device for controlling airflow. • Evaporator – Part of a refrigerating
• Defrost Cycle – The process of removing ice mechanism in which the refrigerant
or frost buildup from the outdoor coil during vaporizes and absorbs heat.
the heating season. • Evaporator Coil – Typically made of
• Detector, Leak – Device used to detect and copper, carries cold gaseous Freon
that absorbs heat from air traveling
locate refrigerant leaks. over the surface of the coil.
• Drier- Substance or device used to remove • Evaporator Fan – Fan which increases
moisture from a refrigeration system. airflow over the heat exchange surface
• Drip Pan – Pan-shaped panel or trough used of evaporators.
to collect condensate from evaporator. • Expansion Valve – Device in
• Duct – Tube or channel through which air is refrigerating system which reduces the
conveyed or moved. pressure from the high side to the low
side and is operated by pressure.
• Enthalpy – Total amount of heat in one • Fan – Radial or axial flow device used
pound of a substance calculated from for moving or producing flow of gases.
accepted temperature base. Temp of 32F • Filter – Device from removing small
(0C) is accepted base for water vapor foreign particles from fluid or air.
calculation. • Flexible Duct – A duct that can be
• Evaporation – Term applied to the changing routed around obstacles by bending it
of a liquid to a gas. Heat is absorbed in this gradually.
• Float Valve – Type of valve which is • Gasket – Resilient (spongy) or flexible
operated by sphere or pan which floats material used between mating
on liquid surface and controls level of surfaces of refrigerating unit parts.
liquid. • Grille – Ornamental or louvered
• Freeze-Up – 1) Formation of ice in the opening placed in a room at the end of
refrigerant control device which may an air passageway.
stop the flow of refrigerant into the • Head Pressure – Pressure which exists
evaporator. 2) Frost formation on an in condensing side of refrigerating
evaporator which may stop the airflow system.
through the evaporator. • Head Pressure Control – Pressure
• Freon – Trade name for a family of operated control which opens
synthetic chemical refrigerants electrical circuit if high-side pressure
manufactured by the DuPont Company. becomes too high.
• Fuse – Electrical safety device • Head Pressure Safety Cut-Out Motor
consisting of strip of fusible metal in protection device wired in series with
circuit which melts when circuit is motor; will shut off the motor when
overloaded. excessive head pressures occur.
• Gas Valve – Device in a pipeline for
starting, stopping or regulating flow of
• Heat Exchanger – Device used to • Humidity – Moisture dampness of air.
transfer heat from a warm or hot
• Junction Box – Box or container housing
surface to a cold or cooler surface.
group of electrical terminals.
(Evaporators and condensers are heat
exchangers. • Liquid Line – Tube which carries liquid
refrigerant from the condenser or liquid
• Heat Load – amount of heat, measured
receiver to the refrigerant control
in Btu or watts, which is removed
during a period of 24 hours.
• Low Pressure Safety Cut-Out – Motor
• Heat Pump – Compression cycle system
protection device that senses low-side
used to supply heat to a temperature-
controlled space. Same system can also
remove heat from the same space • Moisture Indicator – Instrument used to
measure moisture content of a
• High Pressure Cut-Out – Electrical
control switch operated by the high-
side pressure which automatically • Motor – Rotating machine that transforms
opens electrical circuit if too high fluid or electric energy into a mechanical
pressure is reached. motion.
• Motor Burnout – Condition in which • Overload – Load greater than that for
the insulation of an electric motor has which system or mechanism was
• Motor Control – Device to start and/or • Overload Protector – Device, either
stop a motor at certain temperature temperature, pressure, or current
or pressure conditions. operated, which will stop operation of
• Motor Starter – high-capacity electric unit if dangerous conditions arise.
switchers usually operated by • Package Units – Complete refrigerating
electromagnets. system including compressor,
• Oil, Refrigeration – Specially prepared condenser, and evaporator located in
oil used in refrigerator mechanism the refrigerated space.
which circulates, to some extent, with • Pressure Switch – Switch operated by
refrigerant. a rise or drop in pressure.
• Open Circuit – Interrupted electrical • PSI – Symbol or initials used to
circuit which stops flow of electricity. indicate pressure measured in pounds
• Operating Pressure – Actual pressure per square inch.
at which the system works under
normal conditions. This pressure may
be positive or negative. (vacuum).
• Pulley – Flat wheel with a “V” groove. • Refrigerant Dye – Coloring agent that
When attached to a drive and drive can be added to refrigerant to help
members, the pulley provides a means locate leaks in a system.
for driving the compressor or blower
wheels. (AKA Sheave) • Refrigerant Reclaim – To reprocess
• Purging – Releasing compressed gas to refrigerant to new product
atmosphere through some part or parts specifications. This will require chemical
for the purpose of removing analysis, and usually refers to the
contaminants from that part of parts. processes available at a reprocessing or
• Refrigerant – Substance used in manufacturing facility.
refrigerating mechanism. It absorbs • Refrigerant Recovery – To remove
heat in evaporator by change of state refrigerant and place in a cylinder
from a liquid to a gas, and releases its without necessarily testing it.
heat in a condenser as the substance
returns from the gaseous. • Refrigerant Recycling – To remove
• Refrigerant Control – Device which refrigerant and place in a cylinder
measures flow of refrigerant between without necessarily testing it.
two areas of a refrigerating system. It • Refrigerant Recycling – To clean
also maintains pressure difference refrigerant fro reuse by reducing
between high-pressure and low- moisture, acidity and matter. Usually
pressure side of the mechanical applies to procedures at job site or local
refrigerating system while unit is service shop.
• Register – Combination grille and
• Reversing Valve – Device used to reverse
damper assembly covering an air direction of the refrigerant flow,
opening or the end of an air duct. depending upon whether heating or
• Relay – An electromagnetic cooling is desired.
mechanism moved by a small • Safety Control – Device to stop
electrical current in a control circuit. It refrigerating unit if unsafe pressure,
operates a valve or switch in an temperatures, and/or dangerous
operating circuit. conditions are reached.
• Relief Valve – Safety device on a • Safety Motor Control – Electrical device
used to open circuit to motor if
sealed system. It opens to release
temperature, pressure and/or current
fluids before dangerous pressure is flow exceed safe conditions.
• Safety Valve – Self-operated, quick
• Remote System – Refrigerating system opening valve used for fast relief of
in which condensing unit is away from excessive pressures.
space to be cooled. • Schrader Valve – Spring-loaded device
• Retrofit – Term used in describing which permits fluid flow in one direction
reworking an older installation to when a center pin is depressed and in
bring it up to date with modern other direction when a pressure
equipment or to meet new code
• Sensor – Material or device which
goes through physical change or • Slugging – Condition in which mass of
electronic characteristic change as liquid enters compressor causing
surrounding conditions change. hammering.
• Service Valve – Manually operated • Soldering – Joining two metals by
valve mounted on refrigerating adhesion of a metal with a melting
systems used for service operation. temperature of less than 800F. (427C)
• Short Circuit – Electrical condition • Solenoid Valve – Electromagnet with a
where part of circuit touches another
moving core. It serves as a valve or
part of circuit and causes all or part of
current take wrong path. operates a valve.
• Short Cycling – Refrigerating system • Split System – Refrigeration or air
that starts and stops more frequently conditioning installation, which places
than it should. condensing unit outside or away from
• Shroud – Housing over condenser, evaporator. Also applicable to heat
evaporator or fan. pump installations.
• Sight Glass – Glass tube or glass • Squirrel Cage – Fan which has blades
window in refrigerating mechanism. It parallel to fan axis and moves air at
shows amount of refrigerant or oil in right angles or perpendicular to fan
system and indicates presence of gas axis.
bubbles in liquid line.
• Suction Line – Tube or pipe used to • Thermocouple - Device which generates
carry refrigerant gas from evaporator electricity, using principle that if two
to compressor. unlike metals are welded together and
• Suction Pressure Control Valve – Two- junction is heated, a voltage will develop
way, manually operated valve located across the open ends.
at the inlet to compressor. It controls
suction gas flow and is used to service • Thermostat – Device which senses
unit ambient temperature conditions and, in
• Suction Side – Low-pressure side of turn, acts to control a circuit.
the system extending from the • Thermostatic Expansion Valve (TXV) –
refrigerant control through the Control valve operated by temperature
evaporator to the inlet valve of the and pressure within evaporator. It
compressor. controls flow of refrigerant. Control bulb
• Superheat – 1) Temperature of vapor is attached to outlet of evaporator.
above its boiling temperature as a
liquid at that pressure. 2) The • Transformer – Electromagnetic device
difference between the temperature which transfers electrical energy from
at the evaporator outlet and the lower primary circuit into variations of voltage
temperature of the refrigerant in secondary circuit.
evaporating in the evaporator.
• Vacuum Pump – Special high
efficiency device used for creating high • Velocity – Quickness or rapidity of
vacuums for testing or drying motion, swiftness, speed.
purposes. • Ventilation – Forced airflow, by
• Valve – Device used for controlling design, between one area to another.
• Vapor Lock – Condition where liquid
is trapped in line because of bend or
improper installation. Such vapor
prevents liquid flow.
• VAV- Variable air volume.
• V-Belt – Type of belt commonly used
in refrigeration work. Has a contact
surface with a pulley which in the
shape of a V.