Basics for Air Conditioning


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HISTORIC DEVELOPMENT SOME OF THE PRINCIPLES OF REFRIGERATION WERE KNOWN AS LONG AS THOUSAND YEARS BEFORE CHRIST Air-conditioning is as old as man himself. The primitive man, wore skins of animals, and thus combated with the auguries of nature. This was the first form of Conditioning. As time progressed the Egyptian ruling class used slaves, equipped with palm branches to fan their masters. Thus, the evaporative cooling provided some relief from the desert heat. The Romans brought ice from mountains to chill wine, and possibly also to chill water for bathing.   However, Willis H Carrier (1876-1950) was the man who opened humanity to this interesting area of Air Conditioning. He is rightly called the “Father of Air Conditioning”. His contribution to the advancement of the developing industry has been really remarkable.

Environmental & safety aspects in HVAC : 

Environmental & safety aspects in HVAC Environmental aspect Ozone depletion Ozone layer protect the life damaging from ultraviolet rays of sun. Use of refrigerants like R-12 is damaging the layer . Ozone Ozone is a molecular form of oxygen but different chemical properties Large concentration of ozone is poisonous It has irritating pungent odor In high concentration it has a pale blue color

Ozone hole : 

Ozone hole Ozone hole refers to the loss of the blocking effect of ozone to UV radiation. With the depletion of the ozone barrier a hole has been created, which allows much of UV radiation to penetrate to the earth. Reaching of UV radiations creates hazard to human being as many of skin deceases may attack. Global warming is again a huge threat result from greenhouse effect as depletion of ozone layer.

Destruction of ozone : 

Destruction of ozone Chlorine (CL) is the major gas causing the destruction of ozone Chlorine starts chain reactions in which a single molecule of chlorine can destroy hundred thousand ozone molecules. The main sources of chlorine are chlorofluorocarbons(CFCs), also referred to as Freons. CFCs are artificially man made chemicals comprised chlorine(CL), fluorine(F), carbon ( C ), Hydrogen (H). CFCs are very stable chemicals & are nonflammable, nonirritating, nonexplosive, noncorrosive, odorless & low in toxicity They vaporize at very low temperature, which make them very suitable for use as a coolant in refrigerators & A.C. But the concern is that the current hole & depletion have resulted from chlorine released by the CFCs.

Safety aspects : 

Safety aspects As per this topic is concerned we have to think environment safety & personal safety. Environment safety is mainly related to restricted escape of CFCs to atmosphere while deals with HVAC system, either by using substitute coolant in the system or recover these chemicals instead released to open. Personal safety are the basic precautions to almost any type of automotive service. *Use safety glasses or goggles. *Ensure ignition switch is in off position & usage of parking brakes. *Operate the engine in well ventilated area. *Remove ring, watches, & loose hanging jewelry. *Avoid loose clothing. *Keep hands, clothing, tools etc. from radiator fan & condenser fan. *Avoid contact with hot parts such as radiator,exhaust manifold etc. *Follow the procedures outlined in service manuals

Comfort : 

Comfort Human comfort control A human being is sensitive to impurities such as dust, smoke, & pollen that cause irritation to the nose, lungs, & eyes, Thus the need for clean air. A human also require fresh air to renew oxygen supply as well as to dilute undesirable odors. With this some properties of the air must essential to provide provide a comfortable & healthful environment. Temperature, by cooling or heating. Moisture content by humidifying or dehumidifying. Movement by circulation Cleanliness by filtration Ventilation by recalculating fresh air to replace stale air.

Comfortable environment for humans : 

Comfortable environment for humans Human body adjusts to the temperature changes of its surrounding Inside temperature of human body, known as subsurface temperature is 37 degree c.(98.6 F) Temperature at the skin surface is about 21 degree c.(70 F.) If surrounding temperature adjacent to skin, Is more than skin surface temperature we fill hot, If less we fill cold. When cold, nerve send the signal to brain to close the pores tightly, When hot, nerve send the signal to brain to open the pores causing to released the liquid from skin, which in turn maintained the temperature of skin surface by evaporation, to fill comfortable. A balance is thus maintained so that deep tissue heat should not deviates more than one degree Fahrenheit, However this does not means one is always comfortable, as out side tissues always come across these variable conditions which results in discomfort able fillings to human being.

Comfort zone : 

Comfort zone The comfort zone that feels comfortable for most of us covers a range of few degrees below & above the skin surface temperature of about 21 degree cel. However the relative humidity, temperature & surrounding air movement are the important factors for producing comfort or discomfort There is no specific set of temperature & humidity conditions or comfort zone that is comfortable for every one. So some range is fixed by of combined temperature,humidity, & air movement is fixed by ASHRAE ( The American society of Heating, Refrigerating, and Air-conditioning Engineers.) that provides more comfort for the most peoples is known as Comfort Zone Each combination combination of temperature, humidity & air velocity is called an effective temperature.

Typical comfort zone for the average person : 

Typical comfort zone for the average person

Air movement : 

Air movement Air movement or velocity is very important as human comfort is concerned. Comfortable air movement is different for different air temp, It is recommended that both heating & cooling air velocity be 70ft/min. max. Warm heating is more subject to draft, as the human body react more quickly to warm air current than to cold air current. Air flow for automotive air-conditioning is not a big problem, as variable speed blowers can regulate the air velocity as required to generate good comfort.

Wind chill factor : 

Wind chill factor Combination of temperature & wind speed to measure the relative personal discomfort. The wind chill factor is a measure of how rapidly heat is being removed from human body. However the actual effect of wind chill, depend on several factors, such as the nature of clothing, health, age, gender, & body weight of the individuals.

Effect of humidity : 

Effect of humidity Humidity The weight of the water contained in a volume of air is the absolute humidity and usually expressed as a percentage of vapor by weight. The ratio of water vapor that exist in the air and amount needed to produce saturation is called relative humidity. Water is required inside body for survival. When one is deprived of water, becomes dehydrated, & this is very dangerous situation. When moisture contained in air is low the one may feel dryness, And when is high feel sticky.

Odor problem : 

Odor problem Under some climatic & operating conditions, a musty odor is detected from the A.C. system. This is generally due to growth of mold on evaporator core, as climatic conditions change I,will disappear on its own. Some time problem can be eliminated by spraying air fresheners, deodorizers, or antibacterial product into the A.C. system However odor is exist we have the clean the core with appropriate cleaners. Use proper tools & procedure as given by manufacturer for cleaning of evaporators core.

Heat transfer fundamentals : 

Heat transfer fundamentals Heat Heat is a form of kinetic energy. Heat contained in matter is often express in British thermal unit (But). Heat may be measure on thermometer. Heat can be transfer from one place to another. Heat usually transfer from high temperature to low temperature. Heat transfer take place four natural processes. Convection Forced convection Natural convection Radiation Evaporation Conduction

Convection : 

Convection Transfer of heat through the actual movement of the molecules of the medium is termed as convection. Generally convection takes place in fluids substances. e.g. Smoke from chimney, Water placed on fire. Phenomena applied to body The body gives off heat to the surrounding air, which has a lower temperature ( can say less heat ) The surrounding air becomes warmer & move upward. As the warmer air moves upward, air containing less heat takes its place. Thus convection help to maintained body surface temperature In a comfortable zone.

Types of convection : 

Types of convection Force convection When the process of convection is being taking place forcibly by some external means will termed as Force convection. e.g. Vehicle cooling system ( air cooling or water cooling of engine) Natural convection When the process of convection is being taking place naturally without any external force termed as Natural convection. e,.g. Warming of water on stove.

Radiation : 

Radiation Transfer of heat by a heat source to an object by means of heat rays is termed as radiation. Radiation take place independently of convection. Radiation does not require any medium to transfer of heat. Although heat is being transmitted without heating the medium. Heat transfer in this manner diminishes by the square of the distance. e.g. Heat transfer of sun to the earth. Heat transfer from red hot metal.

Conduction : 

Conduction Transfer of heat through a solid by mean of molecular agitation within material without any motion of the materials as a whole. Any material that is a poor conductor of electricity is also a poor conductor of Heat. An excellent conductor of electricity is also a excellent conductor of Heat. e.g. Copper is a good conductor of electricity & heat Wood is a bad conductor of electricity & heat

Temperature : 

Temperature Temperature is a measure of the degree of hotness of any material. If temperature is more we fill hot. If temperature is less we fill cold. Unit for the measurement of temperature is degree celcious or degree Fahrenheit. Temperature can be measure with the help of Thermometers of different kinds, Relationship between degree celcious & Fahrenheit C/5 = ( F – 32 )/ 9 Ergonomically controlling the temperature with in comfort zone is a prime requirement for the human comfort.

Pressure : 

Pressure Pressure is defined as a force exerted per unit of surface area. Atmospheric pressure: Pressure exerted by the surrounding of air around the earth. Gauge pressure: Pressure above atmospheric pressure is referred as gauge pressure. Vacuum pressure: Pressure below atmospheric pressure is referred as vacuum pressure. Pressure measurement is done by barometer or pressure gauge. Unit of pressure is pound per square inch (psi), kg/cm2, Pascal

Relations between Temperature & Pressure : 

Relations between Temperature & Pressure Temperature rises with rise in pressure & vice a versa. Pressure rises with rise in temperature & vice a versa. Due to these variable pressure & temperature condition, The state of some matter may change. Air conditioning cycle is totally based on these principles. Specially formulated chemical termed as a refrigerant is undergo different pressure & temperature conditions, in turn change of state. Which make it possible to remove the heat from vehicle inside & control the temperature with in a comfort zone.

Refrigerants & Lubricants : 

Refrigerants & Lubricants The fluid use in the air conditioning system is termed as a Refrigerant. Nature has not provided a perfect refrigerant to fulfill our requirements. It is necessary to devise a compound suitable for this purpose. Requirement of refrigerants: Should very safe for human. Should be non poisonous & nontoxic. Should withstanding high pressure & temperature without deteriorating or decomposing. Should not spoiled the components of the system. Should undergo the system requirements as temperature & pressure change is concerned.

Refrigerant commonly used : 

Refrigerant commonly used There is no any refrigerant naturally available, which is having the properties to fulfill the design requirements of the system to produce desire effect. Refrigerant commonly used are. R-12 R-134a Out of these R-12 has banned because of it’s tendency to damaged Ozone layer. Now R-134 a is commonly use for automobile application.