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Basic Mechanical Engineering - Air conditioning

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Information about Basic Mechanical Engineering - Air conditioning
Education

Published on March 1, 2014

Author: msstevesimon

Source: slideshare.net

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Air conditioning Prepared by M.S.Steve Assistant Professor Dept. of Mechanical Engineering Amal Jyothi College of Engineering Kanjirapally. msstevesimon@gmail.com

Definition  Process of treating the air so as to control simultaneously its temperature, humidity, purity and distribution to meet the requirements of controlled space.  Requirements of a conditioned space 1. Comfort and health of occupants 2. Needs of certain industrial processes 3. Efficient working of commercial premises/offices msstevesimon@gmail.com Page 2

Air conditioning  For human comfort ,air should have the following properties : 1. Temperature -22 °C to 27 °C 2. Humidity - 55% to 65% Relative Humidity 3. Velocity - 0.3 -0.5 m/s.  Air conditioning systems cool/heat the air, humidify/dehumidify the air to the above human comfort conditions depending on the temperature and humidity of the outside atmospheric air. msstevesimon@gmail.com Page 3

Applications  Industrial applications- To control chemical & bio chemical reactions .  Commercial applications- Theatres, hotels, banks etc.  Transport applications – automobiles, aircrafts,ships etc  Special applications – T .V centres , hospitals, computer centres etc. msstevesimon@gmail.com Page 4

Classifications  Depending up on the processes required for conditioning of outside air ,air conditioning system are classified in to : 1. Summer air conditioning- it involves Cooling & Dehumidification process. 2. Winter air conditioning – it involves Heating & Humidification process msstevesimon@gmail.com Page 5

Winter air conditioning  In winter outside temperature is low hence heating of air is needed for comfort.  Cycle of operations consists of 1. Air cleaning 2. Air heating 3. Humidification 4. Air distribution/circulation msstevesimon@gmail.com Page 6

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Winter air conditioning system  The outside air is sucked in through the damper and is filtered using an air filter.  The air is then passed through a preheat coil to heat the air to control the evaporation of water in the humidifier.  Steam is mixed with the air in required quantity to increase the humidity to 55% RH.  The air is then passed through a reheat coil to bring it to the comfort temperature of 22 °C.  The conditioned air is then supplied to the conditioned space by a blower.  Cold polluted air is discharged out and outside air is again sucked to repeat the cycle. msstevesimon@gmail.com Page 8

Winter air conditioning system These systems are used to heat the air and increase the humidity to acceptable levels. msstevesimon@gmail.com Page 9

Summer air conditioning  In summer outside temp is more and hence cooling of air is required Consists of 1. Air cleaning 2. Air cooling 3. Dehumidification 4. Air distribution/circulation msstevesimon@gmail.com Page 10

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Summer Air Conditioning  In this system air is cooled & dehumidified.  The outside air flows through the damper and is filtered using the filter.  The air is then passed through a cooling coil and the air gets cooled below the required temperature and is also dehumidified.  The cooled air is then passed through the water eliminator and water is collected in the sump.  After that air is made to pass through a heating coil to reach the desired comfort condition.  The conditioned air is now supplied to the space using the blower. msstevesimon@gmail.com Page 12

Summer Air Conditioning msstevesimon@gmail.com Page 13

Essentials of air conditioning systems Temperature control  Effective temp = 200C to 230C in summer  Effective Temp = 180C to 220C in winter  For Indian conditions 250C with 60% relative humidity to 300C with 45 % relative humidity, with air velocity not exceeding 10 m/min Page 14

 Humidity control During summer dehumidification is done so that relative humidity is 40 to 50% During winter humidification is done so that relative humidity is 50 to 60 % msstevesimon@gmail.com Page 15

Air velocity control High velocity of conditioned air may cause greater temperature difference between outside and inside. msstevesimon@gmail.com Page 16

Air quality control Air should be free from odour, toxic gases, bacteria and other micro-organisms msstevesimon@gmail.com Page 17

Essentials of air conditioning systems 1. Filtration 2. Heating (in winter) 3. Cooling (in summer) 4. Humidification 5. Dehumidification 6. Air circulation or distribution msstevesimon@gmail.com Page 18

1. Filtration  Should be capable of removing dust, ash, smoke, bacteria etc  Should be capable of holding moderate amount of dust without affecting the efficiency  Should offer low resistance to flow of air  Workable under sufficient range of velocities.  Should afford easy cleaning manually or mechanically msstevesimon@gmail.com Page 19

2. Heating (in winter)  Heating is necessary in winter so as to compensate heat loss from room.  Pre heating of incoming air may be done by passing over air furnaces or coils through which hot water is circulated msstevesimon@gmail.com Page 20

3. Cooling (in summer) Cooling of incoming air is necessary in summer. Principle of mechanical refrigeration is used. msstevesimon@gmail.com Page 21

4. Humidification Humidification or addition of water is necessary in winter because of low temp has less humidity. Incoming air is passed through pans of water or wet cloth strips msstevesimon@gmail.com Page 22

5. Dehumidification In this process certain amount of water is extracted from air. This is done in summer where incoming air is cooled. Adsorbents can be used to adsorb excess moisture from air . msstevesimon@gmail.com Page 23

Psychrometry  The properties of moist air are called as pshychrometric properties .  Although the principles of pshychrometry can be applied to any physical system consisting of gas vapour mixtures,the most common system of interest is the mixture of water vapour & air. msstevesimon@gmail.com Page 24

Terms used in psychrometry  Dry Air : Dry air is a mixture of oxygen, nitrogen, carbon dioxide, hydrogen, argon, neon ,helium etc.  Moist Air : It is an ordinary air, which is a mixture of dry air and water vapour.  Saturated Air : It is the air which contains maximum amount of water vapour which the air can hold at a given temperature and pressure.  Relative Humidity (RH) : It is the ratio of mass of water vapour in a given volume of moist air at a given temperature to the mass of water vapour contained in the same volume of moist air at the same temperature when the air is saturated.  Dry Bulb Temperature (DBT) : It is the temperature of air measured by an ordinary thermometer. msstevesimon@gmail.com Page 25

Terms used in psychrometry  Wet Bulb Temperature (WBT) : It is the temperature recorded by a thermometer, when its bulb is covered by a wet cloth and is exposed to a current of moving air.  Dew Point Temperature (DPT) : It is the temperature at which the condensation of moisture begins when the air is cooled at constant pressure.  Sensible Heat of Air : It is the enthalpy of dry air, which can be calculated by measuring its dry bulb temperature.  Total Heat : It is the sum of sensible heat of dry air and sensible plus latent heat of water vapour present in it. msstevesimon@gmail.com Page 26

Psychrometric chart Page 27

Thank You M S Steve msstevesimon@gmail.com @msstevesimon 2m.s.steve msstevesimon@gmail.com

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