Heating and Cooling Systems - Air Conditioning

2023/2024
 1. Introduction

-Air Conditioning:
Is the process of treating air to control simultaneously its temperature,
humidity, cleanliness and distribution to meet the comfort requirements of
the occupants of the conditioned space. The goal is to create an environment
that is conducive to human comfort by addressing four crucial weather
conditions:

1. Temperature of the Space air: This aspect involves adjusting the

temperature of the indoor air to a level that is comfortable for the people. In
warm climates, the focus is often on cooling the air, while in colder climates,
heating may be required.

2. Humidity or moisture content of indoor air: Controlling the humidity

level is essential for comfort. High humidity can make a space feel warmer,
while low humidity can lead to discomfort and health issues. Air
conditioning systems often include dehumidification processes to maintain an
optimal humidity level.

3. Purity and quality of indoor air: Ensuring that the air is free from
pollutants, dust, and contaminants is crucial for creating a healthy indoor
environment. Air conditioning systems incorporate filters and purification
methods to improve the quality of indoor air.

4. Air velocity and air circulation within the space: Proper air
circulation helps distribute conditioned air evenly throughout the space. This
involves managing the speed and direction of air movement to avoid
stagnation and ensure a consistent level of comfort for all occupants.

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 The historical context of air conditioning primarily associated it with
cooling during warm months. However, in modern times, the definition has
expanded beyond seasonal cooling to encompass year-round environmental
control. This broader interpretation reflects the comprehensive nature of air
conditioning, which now includes the control of temperature, moisture
content, cleanliness, air quality, and air circulation as required by the
occupants, a specific process, or a product within the space.

The definition mentioned was first proposed by "Willis Carrier," an

early pioneer in the field of air conditioning. His work laid the foundation for
understanding and implementing systems that go beyond simple temperature
control, addressing the holistic comfort needs of individuals in various
environmental conditions. As a result, air conditioning has become a critical
aspect of building design and occupant well-being, impacting both residential
and commercial spaces.

-Applications of air conditioning and Refrigeration systems:

1. Residential Air Conditioning:

 Comfort Cooling: Keeping homes cool and comfortable during hot weather.

 Humidity Control: Maintaining optimal humidity levels for indoor comfort.

 Air Quality: Filtering and circulating air to improve indoor air quality.

2. Industrial Air Conditioning:

 Process Cooling: Cooling industrial processes and machinery to ensure

optimal functioning.

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  Comfort in Workspaces: Providing a comfortable working environment for
industrial personnel.

 Data Centers: Cooling critical electronic equipment in industrial settings,

ensuring stable operation.

3. Air Conditioning of Vehicles:

 Automobiles: Cooling the interior of cars, trucks, buses, and other vehicles
for the comfort of passengers and drivers.

 Aircraft: Regulating temperature and air quality in the cabins of airplanes for
passenger comfort.

4. Food Storage and Distribution:

 Refrigerated Trucks: Transporting perishable goods, ensuring they remain at

the required temperatures during distribution.

 Cold Storage Warehouses: Preserving and storing food products at controlled

temperatures.

5. Food Processing:

 Temperature Control: Regulating temperatures during various stages of food

processing to maintain quality and safety.

 Cleanroom Environments: Creating controlled environments for certain food

processing operations.

6. Chemical and Process Industries:

 Temperature Control in Manufacturing: Maintaining specific temperatures

for chemical reactions and manufacturing processes.

 Industrial Refrigeration: Cooling processes in industries such as

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 petrochemical, pharmaceuticals, and more.

7. Special Applications of Refrigeration:

 Cryogenics: Using extremely low temperatures for applications like medical

treatments and freezing biological materials.

 Horticulture: Providing controlled environments for the growth of plants and

crops.

 Space Exploration: Cooling systems in spacecraft to regulate temperatures

and preserve equipment.

These applications demonstrate the versatility of air conditioning and refrigeration

technologies across different sectors, contributing to comfort, efficiency, and the
preservation of various goods and processes.

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 -Fundamental Concepts:

Understanding fundamental concepts in thermodynamics, fluid

mechanics, and heat transfer is crucial for studying and designing air
conditioning systems. Here's a brief overview of the key concepts mentioned:
1. First Law of Thermodynamics:
 This law states that energy cannot be created or destroyed but can
only change forms. It introduces the concept of energy balance, which
is crucial in air conditioning systems to account for the transfer of
energy in and out of the system.
2. Energy Balance:
 In the context of air conditioning, the energy balance involves
accounting for the various forms of energy involved in the system,
including heat transfer, work done, and changes in internal energy. It's
essential for understanding how energy is utilized and transferred
within the system.
3. Fluid Mechanics:
 Flow of Liquids and Gases: Understanding how liquids and gases
move in pipes and ducts is vital for designing efficient air
conditioning systems. Concepts such as Bernoulli's equation and the
continuity equation are often applied to analyze fluid flow.
 Relationship Between Flow and Pressure Loss: The relationship
between fluid flow rate and pressure loss (pressure drop) is crucial for
determining the performance of pipes, ducts, and components in the
system.

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4. Heat Transfer:
 Conduction: The transfer of heat through a material without any
movement of the material itself. In air conditioning, understanding the
thermal conductivity of materials is important.
 Convection: The transfer of heat through the movement of fluids
(liquids or gases). This is essential in designing heat exchangers and
understanding how air or water absorbs and releases heat.
 Radiation: The transfer of heat through electromagnetic waves. While
not as dominant in HVAC systems as conduction and convection,
radiation may be considered in certain scenarios, especially in heat
transfer between surfaces.
5. Thermodynamics Concepts:
 Cycles: Understanding thermodynamic cycles, such as the
refrigeration cycle, is essential for designing and analyzing air
conditioning systems.
 Properties of Materials: Knowing thermodynamic properties of
substances, including pressure, temperature, and specific heat, is
crucial for system design and analysis.
These fundamental concepts provide the groundwork for engineers and
designers working on air conditioning systems. Applying thermodynamics,
fluid mechanics, and heat transfer principles allows for the efficient and
effective design of systems that meet comfort, efficiency, and safety
requirements.

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 -Definition of some of the more important processes required to air
conditioning:
1. Heating:
 Definition: Heating in air conditioning refers to the process of transferring
energy into a space or the air within a space to raise its temperature.
 Explanation: This can be achieved through various methods, including direct
radiation, where heat is emitted from a warm surface, and free convection,
where heated air rises naturally. The goal is to provide a comfortable and
warm environment, especially during colder seasons.
2. Cooling:
 Definition: Cooling involves the transfer of energy from a space or the air
supplied to a space to lower its temperature.
 Explanation: Commonly, air conditioning systems cool indoor spaces by
circulating air over a surface maintained at a lower temperature, often
achieved through the use of refrigeration cycles. This process is crucial for
maintaining comfort during hot weather.
3. Humidification:
 Definition: Humidification is the process of adding water vapor to
atmospheric air.
 Explanation: In certain climates or indoor environments where the air is too
dry, humidification is necessary to increase the moisture content in the air.
This is often done by introducing water vapor through various methods,
improving comfort and preventing issues associated with dry air.
4. Dehumidification:
 Definition: Dehumidification involves removing water vapor from
atmospheric air.
 Explanation: In environments with excessive humidity, such as in hot and

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 humid climates, air conditioning systems may need to dehumidify the air. This
is often achieved by cooling the air, causing condensation and extracting
moisture, or by other methods like using desiccants.
5. Cleaning:
 Definition: Cleaning in air conditioning involves the removal of contaminants,
typically through air filtration.
 Explanation: Air filters capture solid particles, dust, pollen, and other
impurities from the air, improving indoor air quality. In some cases, additional
processes may be required to remove contaminant gases.
6. Air Motion:
 Definition: Air motion refers to the movement of air in the proximity of
occupants.
 Explanation: Proper air motion is crucial for maintaining uniform comfort
conditions in a space. It helps distribute conditioned air evenly, preventing
temperature variations and ensuring a pleasant environment. However, the
motion should be gentle enough not to cause discomfort.
7. -ASHRAE:

American Society for Heating, Refrigeration & Air conditioning Engineers.

Overall, ASHRAE plays a crucial role in shaping the Air Conditioning
industry by providing leadership, fostering innovation, and disseminating
knowledge to promote sustainable and efficient practices in the design and
operation of building systems.
ASHRAE's headquarters are located in Atlanta, Georgia, USA.
8. -HVAC:

Heating, Ventilating, and Air Conditioning.

It is an acronym that encompasses the technologies, systems, and processes
involved in controlling the environmental conditions within buildings.

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-Measuring units:
-Heat: Energy & power
Heat is a form of energy that transfers between objects due to a temperature difference.

Energy
Definition:
Energy is a scalar quantity representing the ability to do work or cause a change. It exists
in various forms, including kinetic, potential, thermal, and more.
Units:
1 BTU = 1055.06 J =1.055 KJ
BTU: British thermal unit
J: Joule
KJ: kilojoule
Power
Definition: Power is the rate at which energy is transferred, converted, or used. It is the
amount of energy transferred or converted per unit time.
Units:
1 KW= 3413 Btu/hr
KW: Kilowatt
1 KW= 1000 J/s
1 KW= 0.2844 TR
TR: Ton of refrigeration
TR= 12000 Btu/hr =210 KJ/min= 3.5168 KW

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-Temperature:

Temperature is essentially a gauge of how hot or cold something is. It serves as a

measurement unit that allows us to make comparisons between different objects. For
instance, when we describe a body as hotter or colder, we are essentially referring to its
temperature. For instance, one body having a temperature of 80 is considered hotter than
another with a temperature of 60. In essence, temperature provides us with a means to
compare and understand how warm or cool a particular object or environment is.

T°F = 1.8 T°C + 32 (1)

1.8
T°C = T°F - 32 (2)

(°C): Celsius
(°F): Fahrenheit

-Absolute temperature:

Absolute temperature is a fundamental concept in gas laws and related calculations,

particularly those involving ideal gases.

TK= T°C + 273 (3)

TR= T°F + 460 (4)

(K) : Kelvin

(R) : Rankine

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Question 1
A heating system is rated at 8000 Btu/hr. Convert this heat output to kilowatts (KW).

Question 2
Calculate the Celsius temperatures that correspond to the following:
(a) Absolute temperatures of 312 K and 265 K (degrees Kelvin).
(b) Fahrenheit temperature of 95 °F.
(c) Absolute temperature 555 R (degrees Rankine).

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Solution 1:

Given conversion factors:

1 BTU = 1055.06 J = 1.055 KJ

1 KW = 3413 Btu/hr

1 KW = 0.2844 TR

1 TR = 12000 Btu/hr = 3.5168 KW

1 KW
8000 Btu/hr× 3413 Btu /hr ≈ 2.34 KW

So, the heating system is rated at approximately 2.34 kilowatts

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Solution 2:

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