Unit 7

Basics of Air Conditioning

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Air conditioning
• Air-conditioning is that process used to create and maintain
certain temperature, relative humidity and air purity
conditions in indoor spaces. This process is typically applied to
maintain a level of personal comfort.
• It can also be defined as the branch of applied science which deals
with the conditioning of air i.e supplying and maintaining
desirable internal atmospheric condition for human comfort,
irrespective of external condition.
• Also it may be referred as the treatment of air so as to
simultaneously control its temperature, moisture content ,
cleanliness, odour and circulation as required by the occupants, a
product or process in the space.

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Air conditioning
In 1908, the ‘father of air conditioning’, G. B. Wilson defined air
conditioning as being able to:
• Maintaining a suitable humidity in all parts of a building.
• During certain seasons, freeing the air from excessive humidity.
• Being able to provide a constant and adequate supply of
ventilation.
• Removing from the air, any micro-organisms, soot, dust and other
‘foreign bodies’.
• During warmer seasons, efficiently keep the indoor air cool.
• Have the potential to at least partially warm rooms in the winter.
• Air conditioning should not be too expensive to buy or maintain.

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Need and Importance of Air conditioning
1. It’s literally a life saver

• An Environmental Protection Agency study of heat-related deaths found that more than 9,000
Americans died from the heat between 1979 and 2013, a figure which does not even fully capture the
magnitude of the problem. Many more deaths have heat as a contributing factor but not the main
cause. Keeping cool with an efficient air conditioner is the best means of preventing heat-related
deaths and illnesses, according to the Centers for Disease Control and Prevention.

2. Better air quality

• Air conditioners circulate and filter air, removing pollutants and mold from the air. This is especially
important for people who suffer from allergies and asthma because it minimizes the irritants that
trigger an attack. This only holds true, however, if your system is kept clean and filters are regularly
changed. Otherwise, the AC can actually contribute to indoor air pollution.

3. Fewer insects and parasites

• The filters also keep out insects and are far more effective than a screen in an open window. Insects are
annoying but they can also be dangerous to people with allergies. One of the benefits of good air
conditioning system is that it will helps keep indoor pets flea and tick free, as well.

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Need and Importance of Air conditioning
5. Cooler tempers

• It’s not just our brains that suffer from the heat either. When the mercury rises so do tempers. while
our brains are slowing down, our bodies are speeding up with increased heart rates and higher blood
pressure. All this leads to more aggressive behavior making a cool environment key to maintaining
peace at home, work, and in public places.

6. Easier sleep

• Those same physical changes – higher heart rate and blood pressure – that make us angry can also
make it next to impossible to get a good night’s sleep. One’s core body temperature is also a critical
factor in getting to and staying asleep. A too hot (or too cold) room interferes with natural temperature
regulation which doctors say functions best at between 65 and 75 degrees.

7. Protects furniture

• Heat, and especially the humidity that often accompanies it, can wreak havoc on furniture of all kinds.
Wood gains and loses moisture with the air around it which over time leads to warping. Leather also
absorbs moisture which could eventually cause that stylish couch to rot. And any fabric is susceptible
to the mold that breeds rampantly in damp environments.

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Need and Importance of Air conditioning
8. Prevents electronic devices from overheating

• Almost as scary as the effects of heat and humidity on our bodies is the damage they can do to our
electronics. The phones and computers we depend on daily can suffer serious meltdowns when the
temperature goes up leading to loss of data and an overall shorter lifespan. If your place of work
includes computer servers, they can be completely destroyed or at least suffer major damage if not kept
cool enough.

9. Better security

• We’ve already discussed how open windows, even with screens, are limited when it comes to keeping
bugs out. They’re even worse at keeping out unwanted people. Depending on where you live or work,
an unsecured window or door simply isn’t safe. You want to keep your loved ones and valuables
protected from both the elements and the unpleasant side of humankind.

10. Fewer sweat stains

• This pales in comparison to many of the other issues, but the heat can be murder on your
clothes. Unsightly discoloration from sweat can cause serious embarrassment and send a favorite shirt
to the rag bag. Keeping cool with a central air conditioning system can help preserve your wardrobe
and your budget.
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Factor Affecting Air Conditioning

The four important factors for comfort

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Factor Affecting Air Conditioning
(a) Temperature:
 The control of temperature is necessary in air conditioning. Even
though the outdoor temperature is varying, the indoor temperature is
maintained to be constant which is the desired condition.
 The heat may be either removed or added to the conditioned space
depending upon the surrounding conditions.
 The person may feel comfortable when the temperature is 20°C and
relative humidity is 60%.

(b) Humidity:
 Humidity control means an increase or a decrease in moisture
content inside the space to be air-conditioned.
 It is necessary not only for human comfort but also to increase the
working capability. In summer, the relative humidity should be 60%
and in winter it should it should be 40%.
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Factor Affecting Air Conditioning
(c) Purity/Cleanliness:
It is one of the most important factors which affect the air
conditioning. In addition to the control of temperature and
humidity for human comfort, it is necessary to clean air, i.e., to
make the indoor air free from dust, dirt, and odor. It is necessary
that proper filtration and purification of air should be done and
the supply of air free from dust and dirt should be made in air-
conditioned space.
(d) Air Motion:
Air motion or proper circulation of air is also a factor affecting
the human comfort. In order to maintain constant temperature
throughout the conditioned space, it is necessary that there
should be equal distribution of conditioned air in the space. The
air movement is maintained at the desirable velocity of about 8
m/min using appropriate distribution system, grills, etc.
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Factor Affecting Air Conditioning
(e) Other factors which also affect the air conditioning are:
- Hot and cold Surface
- Heat Produced and regulation in human body
- Moisture losses from the human body
- Air stratification

So, Air conditioning is the simultaneous control of temperature

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Human Comfort
Human thermal comfort is defined as a condition of mind, which
expresses satisfaction with the surrounding environment. High
temperatures and humidity provide discomfort sensations and
sometimes heat stress (i.e., reducing the body's ability to cool
itself).

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Factor affecting Human Comfort
1. Environmental factors
a. Air temperature
This is the temperature of the air surrounding the body. It is usually
given in degrees Celsius (°C).
b. Radiant temperature
 Thermal radiation is the heat that radiates from a warm object.
Radiant heat may be present if there are heat sources in an
environment.
 Radiant temperature has a greater influence than air temperature on
how we lose or gain heat to the environment.
 Examples of radiant heat sources include: the sun; fire; electric fires;
ovens; kiln walls; cookers; dryers; hot surfaces and machinery,
molten metals etc.

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Environmental factors
c. Air velocity
 This describes the speed of air moving across the employee and may help
cool them if the air is cooler than the environment.
 Air velocity is an important factor in thermal comfort for example:
 still or stagnant air in indoor environments that are artificially heated may
cause people to feel stuffy. It may also lead to a build-up in odour
 moving air in warm or humid conditions can increase heat loss through
convection without any change in air temperature
 physical activity also increases air movement, so air velocity may be
corrected to account for a person's level of physical activity
 small air movements in cool or cold environments may be perceived as a
draught as people are particularly sensitive to these movements

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Environmental factors
d. Humidity
 If water is heated and it evaporates to the surrounding environment, the resulting
amount of water in the air will provide humidity.
 Relative humidity is the ratio between the actual amount of water vapour in the air
and the maximum amount of water vapour that the air can hold at that air
temperature.
 Relative humidity between 40% and 70% does not have a major impact on thermal
comfort. In workplaces which are not air conditioned, or where the weather
conditions outdoors may influence the indoor thermal environment, relative
humidity may be higher than 70%. Humidity in indoor environments can vary
greatly, and may be dependent on whether there are drying processes (paper mills,
laundry etc) where steam is given off.
 High humidity environments have a lot of vapour in the air, which prevents the
evaporation of sweat from the skin. In hot environments, humidity is important
because less sweat evaporates when humidity is high (80%+). The evaporation of
sweat is the main method of heat reduction.
 When non-breathable vapour-impermeable personal protective equipment (PPE) is
worn, the humidity inside the garment increases as the wearer sweats because the
sweat cannot evaporate. If an employee is wearing this type of PPE (eg asbestos or
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chemical protection suits etc) the humidity within the PPE will be high
2. Personal factors
a) Clothing insulation
 Thermal comfort is very much dependent on the insulating effect of clothing on the
wearer.
 Wearing too much clothing or PPE may be a primary cause of heat stress even if
the environment is not considered warm or hot.
 If clothing does not provide enough insulation, the wearer may be at risk from cold
injuries such as frostbite or hypothermia in cold conditions.
 Clothing is both a potential cause of thermal discomfort as well as a control for it as
we adapt to the climate in which we work. You may add layers of clothing if you
feel cold, or remove layers of clothing if you feel warm. Many companies inhibit
this ability for employees to make reasonable adaptations to their clothing as they
require them to wear a specific uniform or PPE.
 It is important to identify how the clothing contributes to thermal comfort or
discomfort. By periodically evaluating the level of protection provided by existing
PPE and evaluating newer types of PPE you may be able to improve the level of
thermal comfort.

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2. Personal factors
b) Work rate/metabolic heat
 The more physical work we do, the more heat we produce. The more
heat we produce, the more heat needs to be lost so we don't overheat.
The impact of metabolic rate on thermal comfort is critical.
 A person's physical characteristics should always be borne in mind
when considering their thermal comfort, as factors such as their size
and weight, age, fitness level and sex can all have an impact on how
they feel, even if other factors such as air temperature, humidity and
air velocity are all constant.

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Thank You

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