HEATING AND AIR CONDITIONING PRINCIPLES

PURPOSE AND FUNCTION

An automobile’s heating, ventilation, and  air conditioning (HVAC) system keeps the driver and passengers comfortable. Its purpose is to keep the temperature and humidity in the vehicle at a suitable range for the occupants while also providing fresh, clean air. The air conditioning system transports heat from the inside of the car to the outside of the vehicle. In frigid climates, a heater is required to avoid freezing or death.

PRINCIPLES INVOLVED In Air Conditioning

 On earth, the matter is found in one of three different phases or states:

1. Solid
2. Liquid
3. Vapor (gas)

The condition is determined by the nature of the substance, its temperature, and the force or pressure applied to it. Depending on the temperature and pressure, water exists in all three states: solid ice, liquid water, and water vapor.

CHANGES OF STATE IN AIR CONDITIONING SYSTEM

A strong substance can’t be compressed and has robust resistance to flow. The molecules of a strong entice every different strongly and face up to adjustments in extent and shape.

• A substance is strong at any temperature under its melting factor. The melting factor is a feature of the substance and is associated with the temperature at which a strong turns
• into liquid. The melting factor is 32°F (0°C) for water, which means adjustments may be found between liquid water and ice beneath regular climate conditions.
• A liquid is a substance that can’t be compressed. 
• The boiling factor is the temperature when a liquid substance turns to vapor. For water at regular sea stage conditions, the boiling factor is 212°F (100°C). A vapor is a substance that may be compressed without difficulty, has no resistance to flow, and has no constant extent. Since a vapor flows, its miles consider a fluid similar to drinks.

HEAT AND TEMPERATURE 

Molecules in a substance generally tend to vibrate swiftly in all directions, and this disorganized electricity is known as heat. The depth of vibration relies upon how plenty kinetic electricity, or electricity of motion, the atom or molecule contains. Heat and temperature aren’t the same.

Heat is measured withinside the metric unit known as calorie and expresses the quantity of warmth had to enhance the temperature of 1 gram of water one diploma Celsius. It is likewise measured in British Thermal Units (BTU). One BTU is the warmth required to elevate the temperature of 1 pound of water to 1°F at sea level. One BTU equals 252 calories.

SENSIBLE HEAT 

It can be felt and measured with a thermometer makes sense. If there is 1 lb. of water at 40°F and 1 BTU of heat is added, the temperature will rise to 41°F. Adding another BTU of heat raises the temperature to 42°F, and another 170 BTU (212–42) raises the temperature to 212°F, which is the boiling point.

LATENT HEAT

Latent warmth is the “extra” warmth. This is had to remodel a substance from one kingdom to another. Imagine that a stable or a liquid is being heated on a range. When the stable reaches its melting point, or the liquid reaches its boiling point, its temperatures prevent rising. The stable starts offevolved to melt, and the liquid starts offevolved to boil. This takes place with no realistic alternate temperature, even though warmth remains carried out from the burner. The water withinside the field at the range boils at a temperature of 212°F (100°C) at sea level for as long as any liquid water remains. As warmth is similarly delivered to the water, warmth could be utilized to convert the liquid’s kingdom to a vapor. This extra, hidden quantity of power essential to alternate the kingdom of a substance is referred to as latent warmth. 

TEMPERATURE, VOLUME, AND PRESSURE OF A VAPOR

 Unlike a solid, vapor has no constant quantity. Increasing the vapor temperature, even as retaining the quantity constrained within the identical space, will increase the stress. This occurs because the vibrating vapor molecules collide increasingly more energetically with the container’s partitions. Conversely, reducing the temperature decreases the stress. This dating among temperature and stress in the vapor is why a can of nonflammable refrigerant can explode while heated via a flame—the stress buildup in the can will subsequently exceed the can’s cap potential to incorporate the stress. Increasing the stress via way of means of compressing vapor will increase the temperature. Decreasing the stress via way of means of allowing the vapor to extend decreases the temperature.

HEAT INTENSITY 

Heat intensity is vital because people are uncomfortable when it is too cold, measured in degrees. Extremely cold temperatures can induce frostbite and hypothermia. The other end of the spectrum can be equally unpleasant, resulting in heat stress and dehydration. Humans have a comfortable temperature range of 68°F to 78°F (20°C to 26°C). Individuals have different comfort zones.

RULES OF HEAT TRANSFER 

Heating and aircon should observe the simple policies of warmth transfer. The expertise of those policies enables significantly in expertise the systems.

• Heat continually flows from warm to cold. (From the better stage of power to the decreased stage of power.) 
•  To heat someone or an item, warmness should be added.
• To cool someone or an item, warmness should be removed.
• A big quantity of warmth is absorbed while a liquid adjustments kingdom to vapor

HUMIDITY

Humidity refers to water vapor gift withinside the air. The humidity stage relies upon the quantity of water vapor gift and the temperature of the air. The quantity of water vapor within the air tends to be better close to lakes or the ocean because greater water must evaporate from their surfaces. In desolate tract regions with little open water, the quantity of water vapor withinside the air tends to be below.

• Absolute humidity is the degree of the quantity of moisture (water vapor) withinside the air irrespective of the temperature.
• Relative humidity (RH) is the proportion of how a lot of moisture is gifted withinside the air compared to how much moisture the air can preserve at that temperature. The relative humidity is normally measured with a hygrometer or a psychrometer. A hygrometer relies upon sensitivity.

HEATING LOAD

Heating load is the period used while extra warmness is needed. The real load is the range of BTUs or energy of warmth power that ought to be added. In a domestic or office, burning gas is the standard way to generate warmness using coal, gas, or oil as a gas. In maximum vehicles, the warmth is furnished using the heated coolant from the engine cooling system. This coolant is usually at a temperature of 190°F to 205°F (88°C to 98°C) while the engine reaches its everyday running temperature. In maximum vehicles, heated coolant is circulated thru a warmness exchanger, known as a heater center. Air is circulated thru the heater center, in which it absorbs warmness. Then it’s far blown into the passenger compartment, in which the warmth travels directly to heat the auto indoors and occupants. 

COOLING WITH ICE

One manner to transport warmness, referred to as a cooling load, is with a block of ice. A sizeable quantity of latent warmness is needed to extrude the kingdom of the strong ice right into a liquid:

• One hundred forty-four BTU according to lb. (eighty energy according to gram).
• A 50-lb. block of ice represents 50 × one hundred forty-four, or 7, two hundred BTU, of cooling strength while it adjustments from 50 lb. of strong at 32°F to 50 lb. of liquid at 32°F. In the early days of the aircon, the period ton changed into typically used. A ton of aircon changed into the quantity of warmth it took to soften a ton of ice: 2,000 × one hundred forty-four, or 288,000 BTU.

EVAPORATIVE COOLING 

An approach of cooling that works properly in low humidity regions is water evaporation, typically referred to as evaporative cooling. If water is unfolded thinly over the extraordinarily big vicinity of a meshed cooler pad and the air is blown throughout it, the water evaporates. For every pound of water that evaporates, 970 BTU (540 energy according to gram) of warmth is absorbed. This is the latent warmness of evaporation, simply as while it’s far boiled. This is a herbal procedure and uses the most effective electricity required via way of the blower to flow into the air through the cooler pads and directly to the gap to be cooled. Disadvantages of evaporative coolers, regularly referred to as “swamp coolers,” include:

• Will increase the relative humidity.
• Now no longer powerful in regions of excessive humidity because the water does no longer evaporate unexpectedly sufficient to be efficient.

At one time, window-hooked-up evaporative coolers had been utilized in cars. They had been no longer very famous because they had been unattractive and labored properly, most effective in dry regions.

MECHANICAL COOLING IN AIR CONDITIONING SYSTEM

Mechanical refrigeration, sometimes known as air conditioning, is a third approach to handling a cooling load. Evaporation of a liquid and the high quantity of heat necessary for evaporation is also used in this system. The refrigerant boils, changing from liquid to gas. Still, it is condensed back to gas with the help of an engine or an electrically powered compressor that moves the refrigerant and increases its pressure in the system.

CONDUCTION

The best warmness motion technique is conduction, via way of means by which warmness travels thru a medium, including a strong or liquid, transferring from one molecule of the fabric to the subsequent. For instance, if one quit of twine is heated, the warmth will journey through the fabric itself and might be transferred to the alternative quit of the twine. A few materials (maximum of the metals) are exact warmness conductors. Copper and aluminum are satisfactory for the typically used metals, so maximum warmness exchangers (radiators, evaporators, and condensers) use copper or aluminum.

• A few materials, including wood, are bad warm conductors.
• A few materials, including styrofoam, behave warmness so poorly that they’re known as insulators. Most exact insulators comprise quite a few air or gaseous fabric of their shape because air is a bad conductor of warmness.

CONVECTION

 Convection is shifting warmness by transferring the heated medium, commonly air or a liquid. An instance of convection is the engine cooling system. Coolant is heated withinside the water jackets after the cylinders and combustion chambers. Then the coolant is pumped to the radiator, in which the warmth is transferred to the air visiting thru the radiator. Convection additionally happens withinside the indoors of the automobile. At the same time, the air is circulated beyond the motive force, and the passenger chooses up warmness and moves to the evaporator, in which the warmth is transferred to the evaporator fins. The evaporator fins are cooler, so warmness is transferred easily.

RADIATION IN AIR CONDITIONING SYSTEM

Heat can journey through warm rays and skip from one area to another without warming the air through which it passes. The satisfactory instance of that is the sun’s warmth, which passes through the bloodless areas and warms our planet and the entirety it shines on. The radiant warmness can be skipped from any hotter item thru the air to any cooler item. It is tormented by the sedation and texture of the warmth emitter, in which the warmth leaves, and the collector, in which the warmth is absorbed. Dark, hard surfaces make higher warmness emitters and creditors than light-colored, clean surfaces. Are in flip made of electrons, neutrons, and protons. The protons are within the atom’s center, or nucleus, and the electrons journey in orbit around them.

Approximately one hundred primary factors or atoms, each with a unique atomic range, integrate with different factors to make numerous molecules. The atomic range of detail is primarily based on the range of electrons and protons in that detail. The periodic desk of factors visible in maximum chemistry laboratories suggests the connection of those factors. Water molecules, for instance, are known as H 2O. This is a mixture of an unmarried oxygen atom and hydrogen atoms. Hydrogen has an atomic range of 1 (1 proton and 1 electron), and oxygen has an atomic range of eight (eight electrons and eight protons). The 3 states of water are widely recognized and include:

1.  Solid ice
2.  Liquid water
3.  Vapor (gaseous)

SOLID

The solid count has an exact form and substance. Solids exert stress in the simplest direction, which is down due to gravity. For instance, ice is the stable shape of water, can maintain its form, and is bloodless.

LIQUID 

Adding warmth to maximum solids reasons them to attain their melting point. It is an identical material. However, warmth power has damaged the molecular bond, and the problem turns fluid. Has no form, and it takes the form of its container. Liquids can waft through a pipe or hose and be pumped, including via the air-conditioning compressor. Water is commonly a liquid between 32°F and 212°F (0°C and 100°C). The molecules are identical to ice. However, warmth power has improved the movement of the electrons.

GAS

When warmth is brought to maximum beverages, it produces a fuel line because the beverages boil. It is an identical material. However, the warmth power has damaged the molecular bonds similarly so that the molecules haven’t any form in any respect and feature elevated a lot that they have got little or no weight. A fuel line molecule exerts stress in each direction. Gasses can also be pumped through hoses and pipes, making them smooth to transport through the air-conditioning (A/C) device. At temperatures above 212°F (100°C), water commonly boils to become a fuel line, known as steam. Again, the molecules are similar to water or ice. However, warmth power has significantly improved molecular motion.

CONTROL OF HUMIDITY 

Humid bloodless air feels lots less warm than dry air at an identical temperature. Humid, warm air slows down our herbal frame cooling device (evaporation of sweat), so it can make an afternoon experience lots hotter.

• Air this is too dry additionally tends to make human beings’ experience uncomfortable.
• As with temperature, a variety of humidity that maximum human beings experience snug in a relative humidity of approximately 45% to 55%.

As the air-conditioning device operates, it dehumidifies (gets rid of moisture) from the air. Water vapor condenses at the bloodless evaporator fins simply as it might on a pitcher preserving a chilly drink. This condensed water drops off the evaporator and runs out the drain at the lowest of the evaporator case. In-automobile humidity decreases to approximately 40% to 45% on even

the maximum humid days if the A/C is long enough.  It normally takes a quick time to dry the air and do away with the fog from the home windows.

CLEANLINESS 

A facet impact of air con is the cleansing of the air entering the automobile because it passes thru the cooling ductwork. The act of cooling and dehumidifying air on the A/C evaporator reasons water droplets to shape at the evaporator fins. Dust and different contaminants within the air that come into touch with those droplets become trapped and flushed out of the device because the water drops drain from the evaporator. Most latest motors use a cabin clear outside the A/C and heating structures to smooth the air via trapping dirt and pollen debris earlier than input into the passenger compartment.

HVAC Training – (Heating Ventilation & Air Conditioning)

FAQ

THE AIR CONDITIONER SYSTEM