REPUBLIC OF IRAQ Ministry of Higher Education & Scientific Research University of Babylon College of Engineering Mechanical Engineering Department Basic Principals of Air conditioning By Dr. Esam Mejbil Abed
Definition Air conditioning is the controlling of air temp., its humidity, its purity and its flow rate at a certain place to produce a comfort zone Ventilation is refreshing the air in a crowded place by feeding the place with a mount of air at a certain time and draw the same a mount of air to obtain an healthy environment empty of dust, gases and bad smell.
Importance of air The human need to 1.2 kg. of water, 2.7 kg. of food and 16 kg. of air per day. The healthy requirements is : Moving the air by 2.5 L/s A third of the feeding air must be fresh air and the 2 thirds is return air after purifying the entire air in the air conditioned areas must be moved at a velocity between 0.15 to 0.25 M/S. This velocity doesn t cause a noise
Human s comfort The human needs to a comfort medium and we can do that by the next 5 properties treatment : 1. Dry bulb temp.(d.b.t) : It is needed to cool or heat the air before flowing 2. The humidity ratio (H) : The air must be humidified or dehumidified before flowing. 3. The air movement : the flow rate of air and its distribution must be changed to be homogeneous at the conditioned areas to make everyone feel the same conditions (the static air cause a temp.diff. between the breath level and the ceiling level about 8-16 c 0.) 4. Air purifying : By using filters to prevent dust and killing the bacteria 5. Ventilation : It is required to use fresh air to provide the needed oxygen for the conditioned areas
AIR PROPERTIES 1. DRY BULB TEMP.(d.b.t):It is the temp. which the thermometer can measure 2. WET BULB TEMP.(w.b.t): If a moist wick is placed over a thermometer bulb, the evaporation of moisture from the wick will lower the thermometer reading.this temp. is known as the w.b.t. 3. DEW POINT (d.p): is the temp.below which water vapor in the air start to condense. 4. HUMIDITY (H): Is the presence of moisture or water vapor in the air.the amount of humidity in the air affects the rate of evaporation of perspiration from the body.dry air causes rapid evaporation. 5. RELATIVE HUMIDITY(rh): Is a term used to express the amount of moisture in a given sample of air. It is stated in a percentage
PSYCHROMETRIC CHART 30 70 80 90 25 100 30 28 26 24 22 20 20 30 5 40 10 50 60 15 20 18 16 14 12 10 8 6 4 2 0 10 20 Dry bulb temp. 30 40 50
PSYCHROMETRIC CHART APPLICATION EXAMPLE : ( 1 ) Moist air exists at 40 o c dry- bulb temperature and 20 o c thermodynamic wetbulb temperature, and 101.325 kpa pressure. Determine the humidity ratio, enthalpy, dew-point temperature, relative humidity, and volume.
PSYCHROMETRIC CHART APPLICATION 30 70 80 90 25 100 30 28 26 24 22 20 20 30 5 40 10 50 60 15 Dew point = 7 o c 20 18 16 14 12 10 8 6 4 2 0 10 20 Dry bulb temp. 30 40 50
PSYCHROMETRIC CHART Process 12 represents cooling and APPLICATION dehumidification Process 13 dehumidify-process 32 cooling 90 Cooling capacity = m air ( h 1 h 2 ) 80 70 25 60 50 20 40 15 30 2 20 10 5 100 30 1 3 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 10 20 Dry bulb temp. 30 40 50
Alcohol on ones hand evaporates and cools
Sensible Heat Heat which causes a change in temperature of a substance
Sensible Heat Heat which causes a change in temperature of a substance is called sensible heat. If a substance is heated and the temperature rises as the heat is added, the increase in heat is called sensible heat. Likewise, heat may be removed from a substance. If the temperature falls, the heat removed is, again, sensible heat. Sensible heat can be measured in degree of temperature.
Latent Heat Heat energy absorbed in the process of changing form of a substance without a change in temperature or pressure. Heat energy that cannot be measured with a thermometer. 32 o
Latent Heat Heat which brings a change in state with no change in temperature. When we think about change of state conditions we are considering Solids to Liquids and Liquids to Vapours.
Latent or Sensible? What changed from previous slide What type of heat was involved 32 o
Latent Heat 32 o 32 o
Saturated Vapor Vapor and liquid are in contact with one another.
Subcooling Cooling the refrigerant below its condensing temperature. A refrigerant must be in a complete liquid state before it can be subcooled.
Superheat To raise the temperature of a vapor beyond its boiling point. No liquid can remain when a refrigerant is superheated.
Pressure / Temp. Charts Boiling points at atmospheric pressure (14.7PSIA) R-11 = + 75 o R-123 = + 82 o R-12 = - 21 o R-134a = - 15 o R-22 = - 41 o
Vapor Pressure 80 F (Saturated state) 1.5 PSIG 86.4 PSIG 143.6 PSIG R-11 R-134a R-22
Terminology Saturation Point: - The boiling temperature of a substance at a given pressure. Saturation: - A mixture of liquid and vapour at its saturation temperature and pressure. Superheat: - Vapour at a temperature above its saturation temperature, measured in degrees of superheat. Subcooled: - Liquid below its saturation temperature, measured in degrees of subcooling.
Vapor Compression Cooling Tower Condenser Motor Compressor Expansion Valve Evaporator
Vapor Compression Cooling Tower Condenser Motor Compressor Expansion Valve Evaporator
Optimum Chilled Water Circuit for wax pack. unit Condenser Motor Compressor CHILLER 165 T.O.R Expansion Valve Evaporator Hot water tank OVER FLOW 90M 3 /Hr WAX PAC. UNIT 90M3 /Hr CHILLED WATER STORAGE TANK PREPARED BY: ENG. MOSTAFA FADEL
What is Refrigeration? The low pressure, low temperature vapour is then sucked into the compressor where it is compressed into high pressure, high temperature vapour.
Vapor Compression Cooling Tower Condenser Motor Compressor Expansion Valve Evaporator
More Terminology Evaporator split: - The temperature difference between the evaporator saturation temperature and the leaving process temperature. Evaporator range: - The temperature difference between the entering and leaving process temperature. Condenser split: - The temperature difference between the condenser saturation temperature and the leaving condenser water temperature. Condenser range: - The temperature difference between the entering and leaving condenser temperature.
System analysis Look at the following exercises and see if you can analyze the system operation
R22 System operating logs analysis Look at the following operating logs of a R22 water chiller and evaluate the system operation based on the actual readings compared to design conditions.
Cooling load calculations 1. Sensible heat : causes increase in temperature. Heat transfers from walls,windows, roofs,and floors according to the temp. Difference between outdoor and indoor Heat from outside walls which supposed to the sun. Heat from interior source like lights, motors, heaters, and other heating equipments.
Cooling load calculations 1. Latent heat : causes increase in humidity Water vapor from humans breath. Humidity from air leakages from outside. Humidity from process inside the building.
Cooling load calculations COOLING LOAD (Q) = Q SENSIBLE + Q LATENT KW 1 TON OF REFREGIRATION(T.O.R) = 3.5 KW
THE END THANK YOU FOR YOUR TIME.