Heating, ventilation,

and air conditioning

Heating, ventilation, and air conditioning

(HVAC)[1] is the use of various
technologies to control the temperature,
humidity, and purity of the air in an
enclosed space. Its goal is to provide
thermal comfort and acceptable indoor air
quality. HVAC system design is a
subdiscipline of mechanical engineering,
based on the principles of
thermodynamics, fluid mechanics, and
heat transfer. "Refrigeration" is sometimes
added to the field's abbreviation as
HVAC&R or HVACR, or "ventilation" is
dropped, as in HACR (as in the designation
of HACR-rated circuit breakers).

Rooftop HVAC unit with view of fresh-

air intake vent

Ventilation duct with outlet diffuser

vent. These are installed throughout a
building to move air in or out of
rooms. In the middle is a damper to
open and close the vent to allow more
or less air to enter the space.
 The control circuit in a household
HVAC installation. The wires
connecting to the blue terminal block
on the upper-right of the board lead to
the thermostat. The fan enclosure is
directly behind the board, and the
filters can be seen at the top. The
safety interlock switch is at the
bottom left. In the lower middle is the
capacitor.

HVAC is an important part of residential

structures such as single family homes,
apartment buildings, hotels, and senior
living facilities; medium to large industrial
and office buildings such as skyscrapers
and hospitals; vehicles such as cars,
trains, airplanes, ships and submarines;
and in marine environments, where safe
and healthy building conditions are
regulated with respect to temperature and
humidity, using fresh air from outdoors.

Ventilating or ventilation (the "V" in HVAC)

is the process of exchanging or replacing
air in any space to provide high indoor air
quality which involves temperature control,
oxygen replenishment, and removal of
moisture, odors, smoke, heat, dust,
airborne bacteria, carbon dioxide, and
other gases. Ventilation removes
unpleasant smells and excessive moisture,
introduces outside air, keeps interior
building air circulating, and prevents
stagnation of the interior air. Methods for
ventilating a building are divided into
mechanical/forced and natural types.[2]

Overview
The three major functions of heating,
ventilation, and air conditioning are
interrelated, especially with the need to
provide thermal comfort and acceptable
indoor air quality within reasonable
installation, operation, and maintenance
costs. HVAC systems can be used in both
domestic and commercial environments.
HVAC systems can provide ventilation, and
maintain pressure relationships between
spaces. The means of air delivery and
removal from spaces is known as room air
distribution.[3]

Individual systems

In modern buildings, the design,

installation, and control systems of these
functions are integrated into one or more
HVAC systems. For very small buildings,
contractors normally estimate the capacity
and type of system needed and then
design the system, selecting the
appropriate refrigerant and various
components needed. For larger buildings,
building service designers, mechanical
engineers, or building services engineers
analyze, design, and specify the HVAC
systems. Specialty mechanical
contractors and suppliers then fabricate,
install and commission the systems.
Building permits and code-compliance
inspections of the installations are
normally required for all sizes of buildings.

District networks

Although HVAC is executed in individual

buildings or other enclosed spaces (like
NORAD's underground headquarters), the
equipment involved is in some cases an
extension of a larger district heating (DH)
or district cooling (DC) network, or a
combined DHC network. In such cases, the
operating and maintenance aspects are
simplified and metering becomes
necessary to bill for the energy that is
consumed, and in some cases energy that
is returned to the larger system. For
example, at a given time one building may
be utilizing chilled water for air
conditioning and the warm water it returns
may be used in another building for
heating, or for the overall heating-portion
of the DHC network (likely with energy
added to boost the temperature).[4][5][6]

Basing HVAC on a larger network helps

provide an economy of scale that is often
not possible for individual buildings, for
utilizing renewable energy sources such as
solar heat,[7][8][9] winter's cold,[10][11] the
cooling potential in some places of lakes
or seawater for free cooling, and the
enabling function of seasonal thermal
energy storage. By utilizing natural
sources that can be used for HVAC
systems it can make a huge difference for
the environment and help expand the
knowledge of using different methods.

History
HVAC is based on inventions and
discoveries made by Nikolay Lvov, Michael
Faraday, Rolla C. Carpenter, Willis Carrier,
Edwin Ruud, Reuben Trane, James Joule,
William Rankine, Sadi Carnot, Alice Parker
and many others.[12]

Multiple inventions within this time frame

preceded the beginnings of the first
comfort air conditioning system, which
was designed in 1902 by Alfred Wolff
(Cooper, 2003) for the New York Stock
Exchange, while Willis Carrier equipped the
Sacketts-Wilhems Printing Company with
the process AC unit the same year. Coyne
College was the first school to offer HVAC
training in 1899.[13] The first residential AC
was installed by 1914, and by the 1950s
there was "widespread adoption of
residential AC".[14]

The invention of the components of HVAC

systems went hand-in-hand with the
industrial revolution, and new methods of
modernization, higher efficiency, and
system control are constantly being
introduced by companies and inventors
worldwide.

Heating
Heaters are appliances whose purpose is
to generate heat (i.e. warmth) for the
building. This can be done via central
heating. Such a system contains a boiler,
furnace, or heat pump to heat water,
steam, or air in a central location such as a
furnace room in a home, or a mechanical
room in a large building. The heat can be
transferred by convection, conduction, or
radiation. Space heaters are used to heat
single rooms and only consist of a single
unit.
Generation

Central heating unit

Heaters exist for various types of fuel,

including solid fuels, liquids, and gases.
Another type of heat source is electricity,
normally heating ribbons composed of
high resistance wire (see Nichrome). This
principle is also used for baseboard
heaters and portable heaters. Electrical
heaters are often used as backup or
supplemental heat for heat pump
systems.

The heat pump gained popularity in the

1950s in Japan and the United States.[15]
Heat pumps can extract heat from various
sources, such as environmental air,
exhaust air from a building, or from the
ground. Heat pumps transfer heat from
outside the structure into the air inside.
Initially, heat pump HVAC systems were
only used in moderate climates, but with
improvements in low temperature
operation and reduced loads due to more
efficient homes, they are increasing in
popularity in cooler climates, they can also
operate in reverse by cooling an interior.

Distribution

Water/steam

In the case of heated water or steam,

piping is used to transport the heat to the
rooms. Most modern hot water boiler
heating systems have a circulator, which is
a pump, to move hot water through the
distribution system (as opposed to older
gravity-fed systems). The heat can be
transferred to the surrounding air using
radiators, hot water coils (hydro-air), or
other heat exchangers. The radiators may
be mounted on walls or installed within the
floor to produce floor heat.

The use of water as the heat transfer

medium is known as hydronics. The
heated water can also supply an auxiliary
heat exchanger to supply hot water for
bathing and washing.

Air

Warm air systems distribute the heated air

through ductwork systems of supply and
return air through metal or fiberglass
ducts. Many systems use the same ducts
to distribute air cooled by an evaporator
coil for air conditioning. The air supply is
normally filtered through air filters to
remove dust and pollen particles.[16]

Dangers

The use of furnaces, space heaters, and

boilers as a method of indoor heating
could result in incomplete combustion and
the emission of carbon monoxide, nitrogen
oxides, formaldehyde, volatile organic
compounds, and other combustion
byproducts. Incomplete combustion
occurs when there is insufficient oxygen;
the inputs are fuels containing various
contaminants and the outputs are harmful
byproducts, most dangerously carbon
monoxide, which is a tasteless and
odorless gas with serious adverse health
effects.[17]

Without proper ventilation, carbon

monoxide can be lethal at concentrations
of 1000 ppm (0.1%). However, at several
hundred ppm, carbon monoxide exposure
induces headaches, fatigue, nausea, and
vomiting. Carbon monoxide binds with
hemoglobin in the blood, forming
carboxyhemoglobin, reducing the blood's
ability to transport oxygen. The primary
health concerns associated with carbon
monoxide exposure are its cardiovascular
and neurobehavioral effects. Carbon
monoxide can cause atherosclerosis (the
hardening of arteries) and can also trigger
heart attacks. Neurologically, carbon
monoxide exposure reduces hand to eye
coordination, vigilance, and continuous
performance. It can also affect time
discrimination.[18]

Ventilation
Ventilation is the process of changing or
replacing air in any space to control the
temperature or remove any combination of
moisture, odors, smoke, heat, dust,
airborne bacteria, or carbon dioxide, and to
replenish oxygen. Ventilation often refers
to the intentional delivery of the outside air
to the building indoor space. It is one of
the most important factors for maintaining
acceptable indoor air quality in buildings.
Methods for ventilating a building may be
divided into mechanical/forced and natural
types.[19]

Mechanical or forced

HVAC ventilation exhaust for a 12-

story building

Mechanical, or forced, ventilation is

provided by an air handler (AHU) and used
to control indoor air quality. Excess
humidity, odors, and contaminants can
often be controlled via dilution or
replacement with outside air. However, in
humid climates more energy is required to
remove excess moisture from ventilation
air.

Kitchens and bathrooms typically have

mechanical exhausts to control odors and
sometimes humidity. Factors in the design
of such systems include the flow rate
(which is a function of the fan speed and
exhaust vent size) and noise level. Direct
drive fans are available for many
applications and can reduce maintenance
needs.

In summer, ceiling fans and table/floor

fans circulate air within a room for the
purpose of reducing the perceived
temperature by increasing evaporation of
perspiration on the skin of the occupants.
Because hot air rises, ceiling fans may be
used to keep a room warmer in the winter
by circulating the warm stratified air from
the ceiling to the floor.
Passive

Ventilation on the downdraught

system, by impulsion, or the 'plenum'
principle, applied to schoolrooms
(1899)

Natural ventilation is the ventilation of a

building with outside air without using
fans or other mechanical systems. It can
be via operable windows, louvers, or trickle
vents when spaces are small and the
architecture permits. ASHRAE defined
Natural ventilation as the flow of air
through open windows, doors, grilles, and
other planned building envelope
penetrations, and as being driven by
natural and/or artificially produced
pressure differentials.[2]

In more complex schemes, warm air is

allowed to rise and flow out high building
openings to the outside (stack effect),
causing cool outside air to be drawn into
low building openings. Natural ventilation
schemes can use very little energy, but
care must be taken to ensure comfort. In
warm or humid climates, maintaining
thermal comfort solely via natural
ventilation might not be possible. Air
conditioning systems are used, either as
backups or supplements. Air-side
economizers also use outside air to
condition spaces, but do so using fans,
ducts, dampers, and control systems to
introduce and distribute cool outdoor air
when appropriate.

An important component of natural

ventilation is air change rate or air
changes per hour: the hourly rate of
ventilation divided by the volume of the
space. For example, six air changes per
hour means an amount of new air, equal to
the volume of the space, is added every
ten minutes. For human comfort, a
minimum of four air changes per hour is
typical, though warehouses might have
only two. Too high of an air change rate
may be uncomfortable, akin to a wind
tunnel which has thousands of changes
per hour. The highest air change rates are
for crowded spaces, bars, night clubs,
commercial kitchens at around 30 to 50 air
changes per hour.[20]

Room pressure can be either positive or

negative with respect to outside the room.
Positive pressure occurs when there is
more air being supplied than exhausted,
and is common to reduce the infiltration of
outside contaminants.[21]
Airborne diseases

Natural ventilation [22] is a key factor in

reducing the spread of airborne illnesses
such as tuberculosis, the common cold,
influenza, meningitis or COVID-19.
Opening doors and windows are good
ways to maximize natural ventilation,
which would make the risk of airborne
contagion much lower than with costly
and maintenance-requiring mechanical
systems. Old-fashioned clinical areas with
high ceilings and large windows provide
the greatest protection. Natural ventilation
costs little and is maintenance free, and is
particularly suited to limited-resource
settings and tropical climates, where the
burden of TB and institutional TB
transmission is highest. In settings where
respiratory isolation is difficult and climate
permits, windows and doors should be
opened to reduce the risk of airborne
contagion. Natural ventilation requires
little maintenance and is inexpensive.[23]

Air conditioning
An air conditioning system, or a
standalone air conditioner, provides
cooling and/or humidity control for all or
part of a building. Air conditioned
buildings often have sealed windows,
because open windows would work
against the system intended to maintain
constant indoor air conditions. Outside,
fresh air is generally drawn into the system
by a vent into a mix air chamber for mixing
with the space return air. Then the mixture
air enters an indoor or outdoor heat
exchanger section where the air is to be
cooled down, then be guided to the space
creating positive air pressure. The
percentage of return air made up of fresh
air can usually be manipulated by
adjusting the opening of this vent. Typical
fresh air intake is about 10% of the total
supply air.
Air conditioning and refrigeration are
provided through the removal of heat. Heat
can be removed through radiation,
convection, or conduction. The heat
transfer medium is a refrigeration system,
such as water, air, ice, and chemicals are
referred to as refrigerants. A refrigerant is
employed either in a heat pump system in
which a compressor is used to drive
thermodynamic refrigeration cycle, or in a
free cooling system that uses pumps to
circulate a cool refrigerant (typically water
or a glycol mix).

It is imperative that the air conditioning

horsepower is sufficient for the area being
cooled. Underpowered air conditioning
systems will lead to power wastage and
inefficient usage. Adequate horsepower is
required for any air conditioner installed.

Refrigeration cycle

A simple stylized diagram of the

refrigeration cycle: 1) condensing coil,
2) expansion valve, 3) evaporating
coil, 4) compressor

The refrigeration cycle uses four essential

elements to cool, which are compressor,
condenser, metering device, and
evaporator.
At the inlet of a compressor, the
refrigerant inside the system is in a low
pressure, low temperature, gaseous
state. The compressor pumps the
refrigerant gas up to high pressure and
temperature.
From there it enters a heat exchanger
(sometimes called a condensing coil or
condenser) where it loses heat to the
outside, cools, and condenses into its
liquid phase.
An expansion valve (also called
metering device) regulates the
refrigerant liquid to flow at the proper
rate.
 The liquid refrigerant is returned to
another heat exchanger where it is
allowed to evaporate, hence the heat
exchanger is often called an
evaporating coil or evaporator. As the
liquid refrigerant evaporates it absorbs
heat from the inside air, returns to the
compressor, and repeats the cycle. In
the process, heat is absorbed from
indoors and transferred outdoors,
resulting in cooling of the building.

In variable climates, the system may

include a reversing valve that switches
from heating in winter to cooling in
summer. By reversing the flow of
refrigerant, the heat pump refrigeration
cycle is changed from cooling to heating
or vice versa. This allows a facility to be
heated and cooled by a single piece of
equipment by the same means, and with
the same hardware.

Free cooling

Free cooling systems can have very high

efficiencies, and are sometimes combined
with seasonal thermal energy storage so
that the cold of winter can be used for
summer air conditioning. Common
storage mediums are deep aquifers or a
natural underground rock mass accessed
via a cluster of small-diameter, heat-
exchanger-equipped boreholes. Some
systems with small storages are hybrids,
using free cooling early in the cooling
season, and later employing a heat pump
to chill the circulation coming from the
storage. The heat pump is added-in
because the storage acts as a heat sink
when the system is in cooling (as opposed
to charging) mode, causing the
temperature to gradually increase during
the cooling season.

Some systems include an "economizer

mode", which is sometimes called a "free-
cooling mode". When economizing, the
control system will open (fully or partially)
the outside air damper and close (fully or
partially) the return air damper. This will
cause fresh, outside air to be supplied to
the system. When the outside air is cooler
than the demanded cool air, this will allow
the demand to be met without using the
mechanical supply of cooling (typically
chilled water or a direct expansion "DX"
unit), thus saving energy. The control
system can compare the temperature of
the outside air vs. return air, or it can
compare the enthalpy of the air, as is
frequently done in climates where
humidity is more of an issue. In both
cases, the outside air must be less
energetic than the return air for the system
to enter the economizer mode.

Packaged split system

Central, "all-air" air-conditioning systems

(or package systems) with a combined
outdoor condenser/evaporator unit are
often installed in North American
residences, offices, and public buildings,
but are difficult to retrofit (install in a
building that was not designed to receive
it) because of the bulky air ducts
required.[24] (Minisplit ductless systems
are used in these situations.) Outside of
North America, packaged systems are
only used in limited applications involving
large indoor space such as stadiums,
theatres or exhibition halls.

An alternative to packaged systems is the

use of separate indoor and outdoor coils
in split systems. Split systems are
preferred and widely used worldwide
except in North America. In North America,
split systems are most often seen in
residential applications, but they are
gaining popularity in small commercial
buildings. Split systems are used where
ductwork is not feasible or where the
space conditioning efficiency is of prime
concern.[25] The benefits of ductless air
conditioning systems include easy
installation, no ductwork, greater zonal
control, flexibility of control, and quiet
operation.[26] In space conditioning, the
duct losses can account for 30% of energy
consumption.[27] The use of minisplits can
result in energy savings in space
conditioning as there are no losses
associated with ducting.

With the split system, the evaporator coil is

connected to a remote condenser unit
using refrigerant piping between an indoor
and outdoor unit instead of ducting air
directly from the outdoor unit. Indoor units
with directional vents mount onto walls,
suspended from ceilings, or fit into the
ceiling. Other indoor units mount inside
the ceiling cavity so that short lengths of
duct handle air from the indoor unit to
vents or diffusers around the rooms.

Split systems are more efficient and the

footprint is typically smaller than the
package systems. On the other hand,
package systems tend to have a slightly
lower indoor noise level compared to split
systems since the fan motor is located
outside.
Dehumidification

Dehumidification (air drying) in an air

conditioning system is provided by the
evaporator. Since the evaporator operates
at a temperature below the dew point,
moisture in the air condenses on the
evaporator coil tubes. This moisture is
collected at the bottom of the evaporator
in a pan and removed by piping to a central
drain or onto the ground outside.

A dehumidifier is an air-conditioner-like
device that controls the humidity of a
room or building. It is often employed in
basements that have a higher relative
humidity because of their lower
temperature (and propensity for damp
floors and walls). In food retailing
establishments, large open chiller cabinets
are highly effective at dehumidifying the
internal air. Conversely, a humidifier
increases the humidity of a building.

The HVAC components that dehumidify

the ventilation air deserve careful attention
because outdoor air constitutes most of
the annual humidity load for nearly all
buildings.[28]
Humidification

Maintenance

All modern air conditioning systems, even

small window package units, are equipped
with internal air filters. These are generally
of a lightweight gauze-like material, and
must be replaced or washed as conditions
warrant. For example, a building in a high
dust environment, or a home with furry
pets, will need to have the filters changed
more often than buildings without these
dirt loads. Failure to replace these filters
as needed will contribute to a lower heat
exchange rate, resulting in wasted energy,
shortened equipment life, and higher
energy bills; low air flow can result in iced-
over evaporator coils, which can
completely stop airflow. Additionally, very
dirty or plugged filters can cause
overheating during a heating cycle, which
can result in damage to the system or
even fire.

Because an air conditioner moves heat

between the indoor coil and the outdoor
coil, both must be kept clean. This means
that, in addition to replacing the air filter at
the evaporator coil, it is also necessary to
regularly clean the condenser coil. Failure
to keep the condenser clean will eventually
result in harm to the compressor because
the condenser coil is responsible for
discharging both the indoor heat (as
picked up by the evaporator) and the heat
generated by the electric motor driving the
compressor.

Energy efficiency
HVAC is significantly responsible for
promoting energy efficiency of buildings
as the building sector consumes the
largest percentage of global energy.[29]
Since the 1980s, manufacturers of HVAC
equipment have been making an effort to
make the systems they manufacture more
efficient. This was originally driven by
rising energy costs, and has more recently
been driven by increased awareness of
environmental issues. Additionally,
improvements to the HVAC system
efficiency can also help increase occupant
health and productivity.[30] In the US, the
EPA has imposed tighter restrictions over
the years. There are several methods for
making HVAC systems more efficient.

Heating energy

In the past, water heating was more

efficient for heating buildings and was the
standard in the United States. Today,
forced air systems can double for air
conditioning and are more popular.

Some benefits of forced air systems,

which are now widely used in churches,
schools, and high-end residences, are

Better air conditioning effects

Energy savings of up to 15–20%
Even conditioning

A drawback is the installation cost, which

can be slightly higher than traditional
HVAC systems.

Energy efficiency can be improved even

more in central heating systems by
introducing zoned heating. This allows a
more granular application of heat, similar
to non-central heating systems. Zones are
controlled by multiple thermostats. In
water heating systems the thermostats
control zone valves, and in forced air
systems they control zone dampers inside
the vents which selectively block the flow
of air. In this case, the control system is
very critical to maintaining a proper
temperature.

Forecasting is another method of

controlling building heating by calculating
the demand for heating energy that should
be supplied to the building in each time
unit.

Ground source heat pump

Ground source, or geothermal, heat pumps

are similar to ordinary heat pumps, but
instead of transferring heat to or from
outside air, they rely on the stable, even
temperature of the earth to provide
heating and air conditioning. Many regions
experience seasonal temperature
extremes, which would require large-
capacity heating and cooling equipment to
heat or cool buildings. For example, a
conventional heat pump system used to
heat a building in Montana's −57 °C
(−70 °F) low temperature or cool a building
in the highest temperature ever recorded
in the US—57 °C (134 °F) in Death Valley,
California, in 1913 would require a large
amount of energy due to the extreme
difference between inside and outside air
temperatures. A metre below the earth's
surface, however, the ground remains at a
relatively constant temperature. Utilizing
this large source of relatively moderate
temperature earth, a heating or cooling
system's capacity can often be
significantly reduced. Although ground
temperatures vary according to latitude, at
1.8 metres (6 ft) underground,
temperatures generally only range from 7
to 24 °C (45 to 75 °F).

Solar air conditioning

Photovoltaic solar panels offer a new way

to potentially decrease the operating cost
of air conditioning. Traditional air
conditioners run using alternating current,
and hence, any direct-current solar power
needs to be inverted to be compatible with
these units. New variable-speed DC-motor
units allow solar power to more easily run
them since this conversion is unnecessary,
and since the motors are tolerant of
voltage fluctuations associated with
variance in supplied solar power (e.g., due
to cloud cover).

Ventilation energy recovery

Energy recovery systems sometimes

utilize heat recovery ventilation or energy
recovery ventilation systems that employ
heat exchangers or enthalpy wheels to
recover sensible or latent heat from
exhausted air. This is done by transfer of
energy from the stale air inside the home
to the incoming fresh air from outside.
Air conditioning energy

The performance of vapor compression

refrigeration cycles is limited by
thermodynamics.[31] These air
conditioning and heat pump devices move
heat rather than convert it from one form
to another, so thermal efficiencies do not
appropriately describe the performance of
these devices. The Coefficient of
performance (COP) measures
performance, but this dimensionless
measure has not been adopted. Instead,
the Energy Efficiency Ratio (EER) has
traditionally been used to characterize the
performance of many HVAC systems. EER
is the Energy Efficiency Ratio based on a
35 °C (95 °F) outdoor temperature. To
more accurately describe the performance
of air conditioning equipment over a
typical cooling season a modified version
of the EER, the Seasonal Energy Efficiency
Ratio (SEER), or in Europe the ESEER, is
used. SEER ratings are based on seasonal
temperature averages instead of a
constant 35 °C (95 °F) outdoor
temperature. The current industry
minimum SEER rating is 14 SEER.
Engineers have pointed out some areas
where efficiency of the existing hardware
could be improved. For example, the fan
blades used to move the air are usually
stamped from sheet metal, an economical
method of manufacture, but as a result
they are not aerodynamically efficient. A
well-designed blade could reduce the
electrical power required to move the air
by a third.[32]

Demand-controlled kitchen
ventilation

Demand-controlled kitchen ventilation

(DCKV) is a building controls approach to
controlling the volume of kitchen exhaust
and supply air in response to the actual
cooking loads in a commercial kitchen.
Traditional commercial kitchen ventilation
systems operate at 100% fan speed
independent of the volume of cooking
activity and DCKV technology changes
that to provide significant fan energy and
conditioned air savings. By deploying
smart sensing technology, both the
exhaust and supply fans can be controlled
to capitalize on the affinity laws for motor
energy savings, reduce makeup air heating
and cooling energy, increasing safety, and
reducing ambient kitchen noise levels.[33]
Air filtration and cleaning

Air handling unit, used for heating,

cooling, and filtering the air

Air cleaning and filtration removes

particles, contaminants, vapors and gases
from the air. The filtered and cleaned air
then is used in heating, ventilation, and air
conditioning. Air cleaning and filtration
should be taken in account when
protecting our building environments.[34]

Clean air delivery rate (CADR) is the

amount of clean air an air cleaner provides
to a room or space. When determining
CADR, the amount of airflow in a space is
taken into account. For example, an air
cleaner with a flow rate of 30 cubic metres
(1,000 cu ft) per minute and an efficiency
of 50% has a CADR of 15 cubic metres
(500 cu ft) per minute. Along with CADR,
filtration performance is very important
when it comes to the air in our indoor
environment. This depends on the size of
the particle or fiber, the filter packing
density and depth, and the airflow rate.[34]

Industry and standards

The HVAC industry is a worldwide
enterprise, with roles including operation
and maintenance, system design and
construction, equipment manufacturing
and sales, and in education and research.
The HVAC industry was historically
regulated by the manufacturers of HVAC
equipment, but regulating and standards
organizations such as HARDI (Heating, Air-
conditioning and Refrigeration Distributors
International), ASHRAE, SMACNA, ACCA
(Air Conditioning Contractors of America),
Uniform Mechanical Code, International
Mechanical Code, and AMCA have been
established to support the industry and
encourage high standards and
achievement. (UL as an omnibus agency is
not specific to the HVAC industry.)
The starting point in carrying out an
estimate both for cooling and heating
depends on the exterior climate and
interior specified conditions. However,
before taking up the heat load calculation,
it is necessary to find fresh air
requirements for each area in detail, as
pressurization is an important
consideration.

International

ISO 16813:2006 is one of the ISO building

environment standards.[35] It establishes
the general principles of building
environment design. It takes into account
the need to provide a healthy indoor
environment for the occupants as well as
the need to protect the environment for
future generations and promote
collaboration among the various parties
involved in building environmental design
for sustainability. ISO16813 is applicable
to new construction and the retrofit of
existing buildings.[36]

The building environmental design

standard aims to:[36]

provide the constraints concerning

sustainability issues from the initial
stage of the design process, with
building and plant life cycle to be
considered together with owning and
operating costs from the beginning of
the design process;
assess the proposed design with
rational criteria for indoor air quality,
thermal comfort, acoustical comfort,
visual comfort, energy efficiency, and
HVAC system controls at every stage of
the design process;
iterate decisions and evaluations of the
design throughout the design process.
United States

Licensing

In the United States, federal licensure is

generally handled by EPA certified (for
installation and service of HVAC devices).

Many U.S. states have licensing for boiler

operation. Some of these are listed as
follows:

Arkansas [37]
Georgia [38]
Michigan [39]
Minnesota [40]
 Montana [41]
New Jersey [42]
North Dakota [43]
Ohio [44]
Oklahoma [45]
Oregon [46]

Finally, some U.S. cities may have

additional labor laws that apply to HVAC
professionals.

Societies

Many HVAC engineers are members of the

American Society of Heating,
Refrigerating, and Air-Conditioning
Engineers (ASHRAE). ASHRAE regularly
organizes two annual technical
committees and publishes recognized
standards for HVAC design, which are
updated every four years.[47]

Another popular society is AHRI, which

provides regular information on new
refrigeration technology, and publishes
relevant standards and codes.

Codes

Codes such as the UMC and IMC do

include much detail on installation
requirements, however. Other useful
reference materials include items from
SMACNA, ACGIH, and technical trade
journals.

American design standards are legislated

in the Uniform Mechanical Code or
International Mechanical Code. In certain
states, counties, or cities, either of these
codes may be adopted and amended via
various legislative processes. These codes
are updated and published by the
International Association of Plumbing and
Mechanical Officials (IAPMO) or the
International Code Council (ICC)
respectively, on a 3-year code
development cycle. Typically, local building
permit departments are charged with
enforcement of these standards on private
and certain public properties.

Technicians

HVAC Technician
Occupation

Occupation type Vocational

Activity sectors Construction

Description

Education required Apprenticeship

Related jobs Carpenter, electrician,

plumber, welder
An HVAC technician is a tradesman who
specializes in heating, ventilation, air
conditioning, and refrigeration. HVAC
technicians in the US can receive training
through formal training institutions, where
most earn associate degrees. Training for
HVAC technicians includes classroom
lectures and hands-on tasks, and can be
followed by an apprenticeship wherein the
recent graduate works alongside a
professional HVAC technician for a
temporary period.[48] HVAC techs who
have been trained can also be certified in
areas such as air conditioning, heat
pumps, gas heating, and commercial
refrigeration.
United Kingdom

The Chartered Institution of Building

Services Engineers is a body that covers
the essential Service (systems
architecture) that allow buildings to
operate. It includes the electrotechnical,
heating, ventilating, air conditioning,
refrigeration and plumbing industries. To
train as a building services engineer, the
academic requirements are GCSEs (A-C) /
Standard Grades (1-3) in Maths and
Science, which are important in
measurements, planning and theory.
Employers will often want a degree in a
branch of engineering, such as building
environment engineering, electrical
engineering or mechanical engineering. To
become a full member of CIBSE, and so
also to be registered by the Engineering
Council UK as a chartered engineer,
engineers must also attain an Honours
Degree and a master's degree in a relevant
engineering subject. CIBSE publishes
several guides to HVAC design relevant to
the UK market, and also the Republic of
Ireland, Australia, New Zealand and Hong
Kong. These guides include various
recommended design criteria and
standards, some of which are cited within
the UK building regulations, and therefore
form a legislative requirement for major
building services works. The main guides
are:

Guide A: Environmental Design

Guide B: Heating, Ventilating, Air
Conditioning and Refrigeration
Guide C: Reference Data
Guide D: Transportation systems in
Buildings
Guide E: Fire Safety Engineering
Guide F: Energy Efficiency in Buildings
Guide G: Public Health Engineering
Guide H: Building Control Systems
Guide J: Weather, Solar and Illuminance
Data
 Guide K: Electricity in Buildings
Guide L: Sustainability
Guide M: Maintenance Engineering and
Management

Within the construction sector, it is the job

of the building services engineer to design
and oversee the installation and
maintenance of the essential services
such as gas, electricity, water, heating and
lighting, as well as many others. These all
help to make buildings comfortable and
healthy places to live and work in. Building
Services is part of a sector that has over
51,000 businesses and employs
represents 2–3% of the GDP.
Australia

The Air Conditioning and Mechanical

Contractors Association of Australia
(AMCA), Australian Institute of
Refrigeration, Air Conditioning and Heating
(AIRAH), Australian Refrigeration
Mechanical Association and CIBSE are
responsible.

Asia

Asian architectural temperature-control

have different priorities than European
methods. For example, Asian heating
traditionally focuses on maintaining
temperatures of objects such as the floor
or furnishings such as Kotatsu tables and
directly warming people, as opposed to
the Western focus, in modern periods, on
designing air systems.

Philippines

The Philippine Society of Ventilating, Air

Conditioning and Refrigerating Engineers
(PSVARE) along with Philippine Society of
Mechanical Engineers (PSME) govern on
the codes and standards for HVAC /
MVAC (MVAC means "mechanical
ventilation and air conditioning") in the
Philippines.
India

The Indian Society of Heating,

Refrigerating and Air Conditioning
Engineers (ISHRAE) was established to
promote the HVAC industry in India.
ISHRAE is an associate of ASHRAE.
ISHRAE was founded at New Delhi[49] in
1981 and a chapter was started in
Bangalore in 1989. Between 1989 & 1993,
ISHRAE chapters were formed in all major
cities in India.

See also
Air speed (HVAC)
Architectural engineering
ASHRAE Handbook
Auxiliary power unit
Cleanroom
Electric heating
Fan coil unit
Glossary of HVAC terms
Head-end power
Hotel electric power
Mechanical engineering
Outdoor wood-fired boiler
Radiant cooling
Sick building syndrome
Uniform Codes
 Uniform Mechanical Code
Ventilation (architecture)
World Refrigeration Day
Wrightsoft

References
1. "HVAC". HVAC Tools (https://www.eds.tec
h/) .
2. Ventilation and Infiltration chapter (https://
www.ashrae.org/advertising/handbook-adv
ertising/fundamentals/ventilation-and-infiltr
ation) , Fundamentals volume of the
ASHRAE Handbook, ASHRAE, Inc., Atlanta,
GA, 2005
3. Designer's Guide to Ceiling-Based Air
Diffusion, Rock and Zhu, ASHRAE, Inc., New
York, 2002
4. Rezaie, Behnaz; Rosen, Marc A. (2012).
"District heating and cooling: Review of
technology and potential enhancements".
Applied Energy. 93: 2–10.
doi:10.1016/j.apenergy.2011.04.020 (http
s://doi.org/10.1016%2Fj.apenergy.2011.04.
020) .
5. Werner S. (2006). ECOHEATCOOL (WP4)
Possibilities with more district heating in
Europe. Euroheat & Power, Brussels. (http
s://web.archive.org/web/2015092400343
4/http://www.euroheat.org/files/filer/ecohe
atcool/project_4.htm) Archived (https://we
b.archive.org/web/20150924003434/http://
www.euroheat.org/files/filer/ecoheatcool/p
roject_4.htm) 2015-09-24 at the Wayback
Machine
6. Dalin P., Rubenhag A. (2006).
ECOHEATCOOL (WP5) Possibilities with
more district cooling in Europe, final report
from the project. Final Rep. Brussels:
Euroheat & Power. (http://www.euroheat.or
g/files/filer/ecoheatcool/project_5.htm)
Archived (https://web.archive.org/web/201
21015001418/http://www.euroheat.org/file
s/filer/ecoheatcool/project_5.htm) 2012-
10-15 at the Wayback Machine
7. Nielsen, Jan Erik (2014). Solar District
Heating Experiences from Denmark. Energy
Systems in the Alps - storage and
distribution … Energy Platform Workshop 3,
Zurich - 13/2 2014 (https://web.archive.or
g/web/20171215232127/http://www.alpco
nv.org/en/organization/groups/past/WGEn
ergy/Documents/WS3/3.Nielsen_PlanEnerg
i_Solar_Di)
8. Wong B., Thornton J. (2013). Integrating
Solar & Heat Pumps (https://web.archive.or
g/web/20131015092834/http://www.geo-e
xchange.ca/en/UserAttachments/flex1304_
5-%20SAIC-%20Bill%20Wong%202013%20-
%20Integrating%20Solar%20and%20Heat%
20Pumps.pdf) . Renewable Heat
Workshop.
 9. Pauschinger T. (2012). Solar District
Heating with Seasonal Thermal Energy
Storage in Germany (http://www.solar-distri
ct-heating.eu/LinkClick.aspx?fileticket=4Ve
N0WSc5Pk%3d&portalid=0) Archived (http
s://web.archive.org/web/2016101807354
4/http://solar-district-heating.eu/LinkClick.a
spx?fileticket=4VeN0WSc5Pk%3d&portalid
=0) 2016-10-18 at the Wayback Machine.
European Sustainable Energy Week,
Brussels. 18–22 June 2012.
10. "How Renewable Energy Is Redefining
HVAC | AltEnergyMag" (https://www.altener
gymag.com/article/2018/06/how-renewabl
e-energy-is-redefining-hvac/28700/) .
www.altenergymag.com. Retrieved
2020-09-29.
11. " "Lake Source" Heat Pump System" (http
s://hvac-talk.com/vbb/showthread.php?69
732-quot-Lake-Source-quot-Heat-Pump-Sys
tem) . HVAC-Talk: Heating, Air &
Refrigeration Discussion. Retrieved
2020-09-29.
12. Swenson, S. Don (1995). HVAC: heating,
ventilating, and air conditioning (https://ww
w.abebooks.com/9780826906755/HVAC-H
eating-Ventilating-Air-Conditioning-0826906
753/plp) . Homewood, Illinois: American
Technical Publishers. ISBN 978-0-8269-
0675-5.
13. "History of Heating, Air Conditioning &
Refrigeration" (https://web.archive.org/we
b/20160828060622/https://www.coynecoll
ege.edu/programs/hvac) . Coyne College.
Archived from the original (https://www.coy
necollege.edu/programs/hvac) on August
28, 2016.
14. "What is HVAC? A Comprehensive Guide" (h
ttps://www.hvac.com/expert-advice/what-i
s-hvac/) .
15. Iain Staffell, Dan Brett, Nigel Brandon and
Adam Hawkes (30 May 2014). "A review of
domestic heat pumps" (https://www.resear
chgate.net/publication/255759857) .
16. (Alta.), Edmonton. Edmonton's green home
guide : you're gonna love green (http://worl
dcat.org/oclc/884861834) .
OCLC 884861834 (https://www.worldcat.or
g/oclc/884861834) .
17. Bearg, David W. (1993). Indoor Air Quality
and HVAC Systems. New York: Lewis
Publishers. pp. 107–112.
18. Dianat, Nazari, I,I. "Characteristic of
unintentional carbon monoxide poisoning in
Northwest Iran- Tabriz" (https://www.ncbi.nl
m.nih.gov/pubmed/) . International Journal
of Injury Control and Promotion. Retrieved
2011-11-15.
19. Ventilation and Infiltration chapter,
Fundamentals volume of the ASHRAE
Handbook, ASHRAE, Inc., Atlanta, Georgia,
2005
20. "Air Change Rates for typical Rooms and
Buildings" (http://www.engineeringtoolbox.
com/air-change-rate-room-d_867.html) .
The Engineering ToolBox. Retrieved
2012-12-12.
21. Bell, Geoffrey. "Room Air Change Rate" (http
s://web.archive.org/web/2011111702302
9/http://ateam.lbl.gov/Design-Guide/DGHt
m/roomairchangerates.htm) . A Design
Guide for Energy-Efficient Research
Laboratories. Archived from the original (htt
p://ateam.lbl.gov/Design-Guide/DGHtm/roo
mairchangerates.htm) on 2011-11-17.
Retrieved 2011-11-15.
22. "Natural Ventilation for Infection Control in
Health-Care Settings" (https://www.ncbi.nl
m.nih.gov/books/NBK143284/pdf/Bookshe
lf_NBK143284.pdf) (PDF). World Health
Organization (WHO), 2009. Retrieved
2021-07-05.
23. Escombe, A. R.; Oeser, C. C.; Gilman, R. H.;
et al. (2007). "Natural ventilation for the
prevention of airborne contagion" (https://w
ww.ncbi.nlm.nih.gov/pmc/articles/PMC180
8096) . PLOS Med. 4 (68): e68.
doi:10.1371/journal.pmed.0040068 (http
s://doi.org/10.1371%2Fjournal.pmed.00400
68) . PMC 1808096 (https://www.ncbi.nlm.
nih.gov/pmc/articles/PMC1808096) .
PMID 17326709 (https://pubmed.ncbi.nlm.
nih.gov/17326709) .
24. "What are Air Ducts? The Homeowner's
Guide to HVAC Ductwork" (https://www.sup
ertechhvac.com/air-ducts-guide-hvac-duct
work/) . Super Tech. Retrieved 2018-05-14.
25. "Ductless Mini-Split Heat Pumps" (https://w
ww.energy.gov/energysaver/heat-pump-sys
tems/ductless-mini-split-heat-pumps) . U.S.
Department of Energy.
26. "The Pros and Cons of Ductless Mini Split
Air Conditioners" (https://homereference.ne
t/ductless-mini-split-pros-cons/) . Home
Reference. 28 July 2018. Retrieved
9 September 2020.
27. "Ductless Mini-Split Air Conditioners" (http
s://www.energy.gov/energysaver/ductless-
mini-split-air-conditioners) . ENERGY
SAVER. Retrieved 29 November 2019.
28. Moisture Control Guidance for Building
Design, Construction and Maintenance.
December 2013.
29. Chenari, B., Dias Carrilho, J. and Gameiro
da Silva, M., 2016. Towards sustainable,
energy-efficient and healthy ventilation
strategies in buildings: A review. Renewable
and Sustainable Energy Reviews, 59,
pp.1426-1447.
30. "Sustainable Facilities Tool: HVAC System
Overview" (https://sftool.gov/explore/green
-building/section/9/hvac/system-overvie
w) . sftool.gov. Retrieved 2 July 2014.
31. "Heating and Air Conditioning" (https://ww
w.nuclear-power.net/nuclear-engineering/th
ermodynamics/thermodynamic-cycles/heat
ing-and-air-conditioning/#Vapor-compressi
on_Cycle_8211_Vapor-compression_Refrige
ration) . www.nuclear-power.net. Retrieved
2018-02-10.
32. Keeping cool and green (https://www.econ
omist.com/science-and-technology/2010/0
7/15/keeping-cool-and-green) , The
Economist 17 July 2010, p. 83
33. "Technology Profile: Demand Control
Kitchen Ventilation (DCKV)" (https://www.e
nergystar.gov/sites/default/files/dckv_tech
nology_profile.pdf) (PDF). Retrieved
2018-12-04.
34. Howard, J (2003), Guidance for Filtration
and Air-Cleaning Systems to Protect
Building Environments from Airborne
Chemical, Biological, or Radiological
Attacks (https://www.cdc.gov/niosh/docs/
2003-136/) , National Institute for
Occupational Safety and Health,
doi:10.26616/NIOSHPUB2003136 (https://
doi.org/10.26616%2FNIOSHPUB2003136) ,
2003-136
35. ISO. "Building environment standards" (htt
p://www.iso.org/iso/iso_catalogue/catalog
ue_tc/catalogue_tc_browse.htm?commid=
54740) . www.iso.org. Retrieved
2011-05-14.
36. ISO. "Building environment design—Indoor
environment—General principles" (http://ww
w.iso.org/iso/iso_catalogue/catalogue_tc/c
atalogue_detail.htm?csnumber=41300) .
Retrieved 14 May 2011.
37. "010.01.02 Ark. Code R. § 002 - Chapter 13
- Restricted Lifetime License" (https://www.
law.cornell.edu/regulations/arkansas/010-0
1-02-Ark-Code-R-SS-002) .
38. "Boiler Professionals Training and
Licensing" (https://oci.georgia.gov/inspecti
ons-permits-plans/boilers-pressure-vessel
s/boiler-professionals-training-and-licensin
g) .
39. "Michigan Boiler Rules" (https://www.law.co
rnell.edu/regulations/michigan/department
-licensing-and-regulatory-affairs/bureau-of-
construction-codes/board-of-boiler-rules/m
ichigan-boiler-rules) .
40. "Minn. R. 5225.0550 - EXPERIENCE
REQUIREMENTS AND DOCUMENTATION
FOR LICENSURE AS AN OPERATING
ENGINEER" (https://www.law.cornell.edu/re
gulations/minnesota/Minn-R-5225-0550) .
41. "Subchapter 24.122.5 - Licensing" (https://
www.law.cornell.edu/regulations/montana/
department-24/chapter-24.122/subchapter-
24.122.5) .
42. "Chapter 90 - BOILERS, PRESSURE
VESSELS, AND REFRIGERATION" (https://w
ww.law.cornell.edu/regulations/new-jersey/
title-12/chapter-90) .
43. "Article 33.1-14 - North Dakota Boiler Rules"
(https://www.law.cornell.edu/regulations/n
orth-dakota/title-33.1/article-33.1-14) .
44. "Ohio Admin. Code 1301:3-5-10 - Boiler
operator and steam engineer experience
requirements" (https://www.law.cornell.ed
u/regulations/ohio/Ohio-Admin-Code-1301-
3-5-10) .
45. "Subchapter 13 - Licensing of Boiler and
Pressure Vessel Service, Repair and/or
Installers" (https://www.law.cornell.edu/reg
ulations/oklahoma/title-380/chapter-25/su
bchapter-13) .
46. "Or. Admin. R. 918-225-0691 - Boiler,
Pressure Vessel and Pressure Piping
Installation, Alteration or Repair Licensing
Requirements" (https://www.law.cornell.ed
u/regulations/oregon/OAR-918-225-0691) .
47. "ASHRAE Handbook Online" (https://www.a
shrae.org/technical-resources/ashrae-hand
book/ashrae-handbook-online) .
www.ashrae.org. Retrieved 2020-06-17.
48. "Heating, Air Conditioning, and Refrigeration
Mechanics and Installers : Occupational
Outlook Handbook: : U.S. Bureau of Labor
Statistics" (https://www.bls.gov/ooh/install
ation-maintenance-and-repair/heating-air-c
onditioning-and-refrigeration-mechanics-an
d-installers.htm#tab-4) . www.bls.gov.
Retrieved 2023-06-22.
49. "About ISHRAE" (https://ishrae.in/Home/ab
out_ishrae) . ISHRAE. Retrieved
2021-10-11.

Further reading
International Mechanical Code (https://w
eb.archive.org/web/20150308003244/htt
p://publicecodes.cyberregs.com/icod/im
c/2012/index.htm) (2012 (Second
Printing)) by the International Code
Council, Thomson Delmar Learning.
Modern Refrigeration and Air
Conditioning (https://archive.org/details/
ModernRefrigerationAndAirConditioning)
(August 2003) by Althouse, Turnquist,
 and Bracciano, Goodheart-Wilcox
Publisher; 18th edition.
The Cost of Cool. (https://www.nytimes.c
om/2012/08/19/sunday-review/air-condit
ioning-is-an-environmental-quandary.htm
l?_r=0)
Whai is LEV? (https://www.youtube.com/
watch?v=Ky8y2jDk6i8&list=RDCMUCRPc
R5JV-lRttH-b6iSgjNA&start_radio=1&rv=K
y8y2jDk6i8&t=0)

External links
Media related to Climate control at
Wikimedia Commons
Retrieved from
"https://en.wikipedia.org/w/index.php?
title=Heating,_ventilation,_and_air_conditioning&old
id=1177609432"

This page was last edited on 28 September 2023,

at 12:59 (UTC). •
Content is available under CC BY-SA 4.0 unless
otherwise noted.