Air conditioning – Introduction

Air conditioning is not a process of only heating or cooling to some desired temperature. Air conditioning is dealing with conditioning or controlling the air. The complete process of air conditioning includes the following processes.

1. Cooling or heating air
2. Addition of moisture in the air (Humidification) or removal of moisture from the air (Dehumidification)
3. Controlling movement of air
4. Purification of air
5. Addition of fresh air from outside
6. Distribution of air

Air Conditioning Definition :

Air conditioning may be defined as simultaneous control of temperature, humidity, motion, and purity of air within an enclosed space.

OR

It may also be defined as the science which deals with supply and maintaining desirable internal atmospheric condition irrespective of external condition

Principle of air conditioning

In the air conditioning system, the device or unit provides air conditioning is called an air conditioner. This device continuously draws air from an indoor space which is required to cool, it cools in the refrigeration system and discharges back into the same indoor space. This continuous cyclic process of drawing, cooling, and recirculation of the cooled air maintains indoor space cool at the required lower temperature which is required for comfort cooling.

Components of the air conditioning system

The basic components of the air conditioning system are,
1. Fans: For circulation of air
2. Filters: For cleaning air
3. Heating element: Heating of air (It may be an electric heater, steam, hot water)
4. Control system: It regulates automatically the amount of cooling or heating.
5. Grille: It adjusts the direction of conditioned air to the room.
6. Tray: It collects condensed water

Classification of Air conditioning system / Types Of Air Conditioning System :

1. According to the arrangement of equipment

a. Unitary Air Conditioning System

In this system different component of air conditioning system is manufactured and assembled as a unit in a factory. This unit is installed in or near to space to be conditioned.
Example: Window air conditioner and Split air conditioner

b. Central Air Conditioning System

In this system different components are manufactured in a factory and assembled at the site. This type of system is used for conditioning of air in theatres, cinemas, restaurants, exhibition halls, big factory space, etc.

In the central air conditioning system all the components are group together in one central room and conditioned air then distributed from the central room to the required places through the extension duct system. The main components of the central system are compressor with motor drive, condenser with cooling coil, throttling devices. This system used large capacity units. (above 25 tons).
The central air conditioning either direct or indirect type.

2. According to the purpose

a. Comfort air conditioning system
b. Industrial air conditioning system

3. According to the season of the year

a. Winter air conditioning system
b. Summer air conditioning system
c.Year-Round Air Conditioning System  

4. According to Working substance used in the system:

a. All Air system.
b. Chilled water system
c. Air-water system

Year-Round Air Conditioning System  

The arrangement of the year-round air conditioning system is as shown in fig. The amount of outdoor fresh air and recirculated air is controlled by the motor. The air conditioner designed such that when the outdoor air temperature is either above or below a certain selected value, it assumes the season as summer or winter respectively.
In the summer season, bypass damper is almost closed and most of the air passes through the cooling coil. The cooling coil may be evaporator of the refrigeration system or coil through which chilled water is passed. All air is passed through the heating coil. In the winter season, bypass damper is in an almost open position. Most of the air is directly passed to the heating coil bypassing the cooling coil.

Winter air conditioning System 

In winter air conditioning, the air is heated which is generally followed by humidification. The schematic arrangement of the system is shown in Fig. The outside air flows through a damper and mixes up with the re-circulated air (which is obtained from the conditioned space). The mixed air passes through a filter to remove dirt, dust, and other impurities. The air now passes through a preheat coil in order to prevent the possible freezing of water and to control the evaporation of water in the humidifier. After that, the air is made to pass through a reheat coil to bring the air to the designed dry bulb temperature. Now, the conditioned air is supplied to the conditioned space by a fan. From the conditioned space, a part of the used air is exhausted to the atmosphere by the exhaust fans or ventilators. The remaining part of the used air (Known as re-circulated air) is again conditioned as shown in Fig. The outside air is sucked and made to mix with re-circulated air, in order to make up for the loss of conditioned (or used) air through exhaust fans or ventilation from the conditioned space.

Summer Air conditioning System

This system is used in summer air conditioning applications. In this system air is cooled and generally dehumidified. The schematic diagram is shown in figure. The outside air flows through the damper and mixes up with recirculated air .which is obtained from air-conditioned space. The mixed air passes through a filter to remove dirt, dust, and other impurities. The air now passes through the cooling coil. The coil has a temperature much less than the required dry bulb temperature of the air in the conditioned space. The cooled air passes through a perforated membrane and loses its moisture in the condensed form which is collected in a sump. Air now passes through a heating coil which heats up
the air slightly, in order to bring air to requisite DBT and relative humidity. Now conditioned air passes to conditioned space by a fan. From the conditioned space the part of air is exhausted to atmosphere by exhaust fans or ventilators. The remaining part of the used air or recirculated air is again conditioned as shown in the figure. The outside air is sucked and made to mix with recirculated air in order to make up for the loss of conditioned or used air through exhaust fans or ventilators from conditioned space.

Room air conditioner

Room air conditioner consists of a casing which is divided into two parts by a vertical partition i.e. outdoor part and indoor part.
The indoor part fitted into the room which consists of an evaporator, motor-driven fan, expansion device, and control planet, an air filter, power connection, and tray. The condenser is connected to the evaporator by a capillary tube through a filter. The evaporator is connected to the compressor by suction pipeline and the compressor is connected to the condenser by discharge pipeline.

Window air conditioner

The window air conditioner mainly used for conditioning of air in the room. Commonly it is mounted in a window, hence it is known as a window air conditioner.

The window air conditioner unit consists of the following components as shown in fig 

Refrigeration unit
Evaporator/cooling coil, condenser, compressor, expansion device Air circulation fan

Working

The hot air coming from room is flowing on the evaporator (cooling coil), the cooling coil absorbs heat from the air. The moisture of air gets removed on the cooling coil surface by the process of condensation of air. Thus the air is cooled and dehumidified to meet the requirement of comfort air conditioning in the room. The filter cleans the air coming from the room before passes through the cooling coil. The tray is provided below the cooling coil (evaporator) to collect moisture which condenses from the recirculation of air.
The flow of hot air (from the room) and cooled air (to room) is taking place by the evaporator blower. The refrigerating unit provides a cooling effect at the evaporator. The condenser fan circulates air on the outside of condenser tubes, the refrigerant in condenser rejects heat to outside atmospheric air. Necessary fresh air is allowed to mix with the recalculated room air to meet the ventilation requirement. Ventilation air is controlled by ventilation damper. The room -temperature is controlled by a thermostat using an on-off power supply to the compressor motor.

Limitations

• It produces noise in the room because of the compressor is very near to the room.
• The evaporator and condenser are enclosed in a single unit. Therefore evaporator cannot be used as an interior of room because condenser requires outside air for cooling.
• It requires an appropriate size of window or hole in the wall to fit the conditioner.

Split air conditioner

It is a modification of the window air conditioner.

Construction

This unit differs from the window air conditioner. In terms of splits of the unit into two parts. In the split air conditioner, the window air conditioner divided (split) into two parts.

First part: Includes the evaporator, filter, evaporator fan, and grille (cooling coil). They placed inside the room.

Second part: Includes condenser, condenser fan, and compressor. This placed outside the room.

The first part (inside of the room) and the second part (outside of the room) are connected by small diameter tubes. Therefore, a small hole required in the wall for the installation of a split air conditioner.

The advantages of a split air conditioner over a window air conditioner

• The compressor is outside of the room, therefore no compressor noise in the room.
• No window opening and fixing needed.
• The compressor is outside of the room, therefore no compressor noise in the room.

Automobile air conditioning system.

Air conditioners work on the principle that “liquids absorb heat when they become a vapor (evaporate). Low-pressure R134a vapor entering the compressor is compressed to become high pressure/temperature R134a vapor. This is then circulated along with lubricant oil to the condenser. As the high pressure/temperature vapor travels through the condenser, heat is released to the cooler ambient air passing over the condenser tubes condensing the vapor into a liquid. This high pressure/temperature liquid then travels through the filter drier onto the expansion valve where a small variable orifice provides a restriction against which compressor pushes.

Suction from the compressor pulls the high pressure/temperature liquid R134a through small variable orifice of the TX valve and into the low-pressure side of the A/C system. The R134a is now under low pressure/temperature vapor where heat from the cabin being blown over the evaporator coil surface is absorbed into the colder low-pressure refrigerant The R134a is then pulled through the evaporator and into the compressor.

Difference Between Central Air conditioning and Unitary Air Conditioning : 

Applications of air conditioning system.

1.Laboratories: to make precise measurements

2. Printing Industry: Specific temperature and humidity are maintained in the printing industry. Paper becomes too dry in low humidity and improper stamping takes place. Paper swell in high humidity and ink spreads as well as taken time to dry causing non-uniform printing.

3.Textile Industry: Relative humidity and temperature are the key factors of the textile industry. Humidity has an effect on strength, quality of fabric to make them soft and reliable instead of brittle and weak.

4.Pharmaceutical: industry needs refrigeration to reduce air borne bacteria and dirt to preserve products

5. Photographic- Industry Provides accurate control of temperature, humidity for manufacturing as well as processing in photographic films.
6. Machine tools Industry –  The Same machining processes requires accurate temperature and humidity. Ex. Processing in manufacturing of bearing, scientific instruments, electronic devices test gauges, and precision gears, etc. where close tolerance of dimensions is required.
7. Farm Animals
8. Computer Rooms:

Industry Air-conditioning – Used to control the condition of the atmosphere required to carry out industrial processes most efficiently, economically with better quality. Ex-Textile mills, paper mills, printing and photo processing plants, etc.

Comfort Air-conditioning – It is provided for the ultimate comfort of human being Ex-airconditioning system at home, office, etc. In this case, the stay time of occupants is prolonged.

Commercial Air-conditioning – It is similar to comfort air-conditioning except that the stay time of occupant is short. Ex-air-conditioning system is the bank, departmental store, etc.

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