Refrigeration and air conditioning

introduction about Refrigeration and air conditioning

1. BASIC CIVIL AND MECHANICAL ENGINEERING REFRIGERATION AND AIR CONDITIONING

2. REFRIGERATION It is the process of removing heat continuously from a body/object, to reduce its temperature lower than that of its surrounding atmospheric and maintaining it by continuously absorbing the heat

3. REFRIGERATOR It is an equipment used for producing and maintaining the temperature in a closed space below the surrounding atmospheric temperature

4. REFRIGERANT Refrigerant is a fluid which absorbs the heat from the body and rejects the heat at high temperature Properties of refrigerant : It should have low freezing and low boiling point It should have high co-efficient of performance It should be non-Explosive It should have low specific heat of liquid It should be non flammable It should be non corrosive to metal

5. APPLICATIONS OF REFRIGERATION For preserving the food, fruits, and drinks for a long duration For preserving the flowers, medicines and medical drugs Refrigeration is used in refineries for removing wax

6. TERMINOLOGY OF REFRIGERATION Refrigeration Effect : R efrigeration effect is defined as the quantity of heat extracted from a cold body or space to be cooled in a given time N = Heat extracted from the cold space Time taken

7. Capacity of refrigeration unit The capacity of refrigerating machines are expressed by their cooling capacity The standard unit used for expressing the capacity of refrigerating machines is tonne of refrigeration One tonne of refrigeration is defined as the quantity of heat abstracted ( refrigerating effect ) to freeze ( into ice ) one tonne of water in a duration of 24 hours at 0 o C

8. 1 tonne of refrigeration = 210 KJ/Min = 3.5 KJ/s = 3.5 KW

9. Co- Efficient of Performance (COP) Performance of a refrigeration system is measured by Co-efficient of performance (COP) It is defined as the ratio of heat extracted in a given time ( refrigerating Effect ) to the work input COP = Heat Extracted / work done

10. Classifications of refrigerants Primary refrigerants Secondary refrigerants

11. Primary refrigerants These are refrigerants that directly take part in the refrigeration system R-12 - Dichloro difluoro methane - CCl 2 F 2 R-22 - Monochloro difluoro methane - CHClF 2 R-717 - Ammonia - NH 3 R-744 - Carbon dioxide - CO 2

12. Secondary refrigerants These are the refrigerants which are first cooled by primary refrigerants and then used for cooling purpose Calcium chloride - CaCl 2 Sodium chloride - NaCl Glycols

13. Types of refrigerators Vapour compression refrigerators Vapour absorption refrigerators

14. Vapour compression refrigerators Main Parts : Compressor Condenser Receiver Expansion Valve Evaporator

15. Vapour compression refrigerators High T, Low P, Vapour High T, High P, Vapour Low T, High P, Liquid Low T, Low P, Liquid Heat absorbs Heat rejects

16. Vapour absorption refrigerators Main Parts : Absorber Pump Heat Exchanger Generator Condenser Expansion valve Evaporator

17. Vapour absorption refrigerators H.E

18. Layout of typical domestic refrigerator

19. Comparison between Vapour compression & Vapour Absorption refrigeration systems S.No Vapour Compression System Vapour Absorption System 1 The system has more wear and tear and produces noise due to the moving parts in the compressor The only moving part is the pump. The system is quiet in operation and is subjected to very little wear 2 A compressor ( Mechanical energy ) is used to change the condition of the refrigerant from the evaporator Heat energy is used to change the condition of the refrigerant from the evaporator 3 The refrigerant capacity for a compressor unit is less than 1000 tonnes Refrigerants with more than 1000 tonnes capacity can be built 4 Electric power is needed to drive the system . i.e to run the compressor Heating coils or gas flame or even waste exhaust steam can be used to heat the generator. Thus this system can run even without electricity 5 Capacity of the system drops rapidly with lowered evaporator pressure Capacity of the system decreases very little with lowered evaporator pressure 6 Energy supplied is ¼ to ½ of refrigerating effect Energy supplied is about 1 ½ times the refrigerating effect 7 Refrigerant refilling is simple Refrigerating refilling is hard 8 At partial loads, the performance is poor At partial loads, the performance is not affected

20. AIR CONDITIONING

21. AIR CONDITIONING Air conditioning is the process of conditioning the air according to the human comfort, irrespective of external conditions

22. PSYCHROMETRY Science which is the study about the behaviour of moisture air.

23. PROPERTIES OF PYSCHROMETRIC Atmospheric air: Air in the atmosphere is referred to as atmospheric air. Dry air: The normal atmospheric air with out the presence of water vapour is called dry air. Water vapour: It is the moisture present in the dry air.

24. Moisture: It is the water vapour present in dry air. Moisture air: It is the mixture of dry air and water vapour. Saturated air: When the mixture of air and water vapour at a given temperature contains the maximum amount of water vapour that it hold then it is known as saturated air. Humidity: It is the mass of water vapour present in 1 Kg of dry air and is generally expressed in terms of gm per kg of dry air.

25. Absolute Humidity: It is the mass of water vapour present in 1m cube of dry air and is generally expressed in terms of gm per cubic meter of dry air. Relative humidity: It is the ratio of actual mass of water vapour in a given volume of moisture air to the mass of water vapour in the same volume of saturated air. at the same temperature and pressure.

26. Degree of saturation: It is the ratio of actual mass of water vapour in unit mass of dry air to mass water vapour in the same volume of saturated air at the same temperature. Dry Bulb Temperature (DBT): The temperature which is measured by an ordinary thermometer is known as dry bulb temperature.

27. Wet bulb temperature (WBT): It is the temperature of air measured by a thermometer when its bulb is covered with wet cloth and is exposed to a current rapidly moving air. Wet bulb depression (WBD): It is the difference between dry bulb temperature and wet bulb temperature. Dew point temperature (DPT): It is temperature at which the water vapour present in the air begins to condense when the air is cooled.

28. Dew point Depression (DPD): It is the difference between dry bulb temperature and dew point temperature. Psychrometer: It is a device which is used for measuring dry bulb and wet bulb temperature simultaneously.

29. PSYCHROMETRIC PROCESS Sensible heating process Sensible cooling process Humidification process Dehumidification process

30. Sensible heating process: The heating of air with out addition of moisture is known as sensible heating. The heating is done by passing the air over heating coil of tubes. Sensible cooling process: The cooling of air with out removal of moisture is known as sensible cooling. The cooling is done by passing the air over cooling coil of tubes.

31. Humidification process: The addition of water vapour to the air is known as humidification. Humidification is done by spraying water over air stream at constant dry bulb temperature of air. Dehumidification process: The removal of water vapour from the air is known as dehumidification. The water vapour from the air can be removed chemically, physically or thermodynamically.

32. Requirements of comfort air conditioning The following factors are affecting the human comfort in air conditioning Temperature of air Humidity of air Air motion Air purity noise

33. Classifications of Air conditioning According to the purpose Comfort air conditioning Industrial air conditioning According to season of the year Summer air conditioning Winter air conditioning Year round air conditioning

34. Types of air conditioning Room air conditioning Window air conditioning Central air conditioning

35. Functions of air conditioning Cleaning air Controlling the temperature of air Controlling the moisture content Circulating the air

36. Window air conditioner Or Room air conditioner Refrigerant used : R-12 or R-22 It consists of : Compressor Air cooled condensor Capillary tube Evaporator

37. Condensor Refrigerant vapour ----- liquid Refrigerant ( High P, High T ) ( High P, Low T ) Capillary tube : Liquid Refrigerant------ Liquid Refrigerant ( High P, low T ) ( Low P, Low T ) Evaporator : Liquid Refrigerant ------ vapour Refrigerant ( Low P, low T ) ( Low P, Low T) Compressor: Refrigerant vapour - ----- Refrigerant vapour ( low P, Low T ) ( High P, High T )

38. Split type room air conditioner They are used for small rooms and halls, usually in places where window air conditioners cannot be installed. It can be classified into two parts : The outdoor unit The indoor unit

39. Outdoor unit The outdoor unit, fitted outside the room, houses components like the compressor , condenser, and expansion valve

40. It consists of : Compressor : main component of the system used to compress the refrigerant Condenser coil : used to reject the heat from the refrigerant to the outside air Condenser fan : rejecting the heat from the indoor unit to the space outside the building Condenser motor : usually has two to three speeds. Smaller unit may only have 1 speed of control and turns on/off simultaneously with the compressor

41. Indoor unit The indoor unit comprises the evaporator or cooling coil and the cooling fan. The spilt air conditioner can be used to cool one or two rooms

42. It consists of Evaporator coil Control panel Air filter Supply and return Air Grills Fan Blower Capillary tube

43. Multispilt Air conditioner In units for one outdoor unit there are two indoor units which can be placed in two different rooms or at two different locations inside a large room