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How does Air Conditioning work?

Lets first look some principles of operation.

 Latent Heat

When a liquid boils (converts to gas) it absorbs heat without raising the temperature of the resulting gas. When the gas condenses (converts back to a liquid), it gives off heat without lowering the temperature of the resulting liquid. This is called Latent Heat.

Relative Humidity

The amount of moisture (water vapour content) that the air can hold is directly related to the air temperature. The more heat there is in the air, the more moisture the air can hold. The lower the moisture content in the air, the more comfortable you feel. Removing the moisture from the air lowers its relative humidity and improves personal comfort.

Effects of Pressure on Boiling or Condensation As the pressure is increased on a liquid, the temperature at which the liquid boils (converts to gas) also increases. Conversely, when the pressure on a liquid is reduced, its boiling point is also reduced. When in the gas state, an increase in pressure causes an increase in temperature, while a decrease in pressure will decrease the temperature of the gas. 


Air conditioning is the process by which air is cooled and dehumidified. The air conditioning in your car, your home and your office all work the same way. Even your refrigerator is, in effect, an air conditioner. While there are many physical principles that relate to air conditioning, this article sticks to the basics. It explains the general concepts of automotive air conditioning, the components used and what you need to know to keep your car's A/C system working properly. Basically, air conditioning systems operate on the principles of evaporation and condensation.

Here's a simple example of evaporation. Imagine that you're swimming around in your neighbour's backyard pool on a summer day. As soon as you get out, you start to feel cooler. Why? The water on your body starts to evaporate and turns into water vapour. And as it evaporates, it draws heat away from your body, and you get goose bumps. Brrr! Now let's say your neighbour hands you a big glass of ice-cold lemonade. You take a sip and set it down on a table. After a minute or two, you notice that water has collected on the outside of the glass. This is condensation. The air surrounding the glass becomes cooler when it encounters the cold glass, and the water vapour the air is carrying condenses into water. Both of these examples occur at normal atmospheric pressure. But higher pressures can also change a vapour (or a gas) into a liquid. For example, if you look at a typical butane cigarette lighter, you can see liquid inside it. But as soon as you push down on the button, butane gas comes out. Why? The butane is under high pressure inside the cigarette lighter. This high pressure causes the butane to take liquid form. As soon as the butane is released and it encounters normal atmospheric pressure, it turns back into a gas. Now hold the lighter as you release the gas and feel it get cold - that is because as the liquid turns to gas it requires latent heat and it draws this heat out of you hand and the environment making it feel cold.

The reverse is true too - latent heat is given up when gas is compressed into a liquid.. Hold a bicycle pump in your hands after inflating a tyre an feel how hot it is. Although you can not compress the air enough to become a liquid you can feel the released latent heat being given up into your hand. OK, those are the basic ideas. But how do they apply to making your car's vents blow cool air? The principles of evaporation and condensation are utilized in your car's A/C system by a series of components that are connected by tubing and hoses. There are six basic components: the compressor, condenser, receiver-drier, thermostatic expansion valve, the evaporator and the life-blood of the A/C system, the refrigerant. Refrigerant is a liquid capable of vaporizing at a low temperature. In the past, R-12 refrigerant was used in cars. But this chlorofluorocarbon (CFC) is said to be harmful to the earth's ozone layer. Consequently, all vehicles built after 1996 use R-134A, a more environmentally friendly refrigerant. In the case of the Scorpio all the new range had R134a from the start. The refrigerant differs from R12 in that it is about 10% less efficient in cooling and has smaller molecules.

Here's how an air conditioning system and its components work. Step One: The compressor is the power unit of the A/C system. It is powered by a drive belt connected to the engine's crankshaft. On the Scorpio you can see it on the right hand side of the engine bay and although the drive belt is permanently rotating the front pulley, the pulley is connected to the compressor by a magnetic clutch. So it spins freely with the clutch disengaged and drives the compressor when engaged. When the A/C system is turned on, the compressor 'compresses' the refrigerant vapour heating it up and pumps it under high pressure to the condenser.

Step Two: The condenser is a device used to change the high-pressure refrigerant vapour to a liquid. It is mounted ahead of the engine's radiator, and it looks very similar to a radiator with its parallel tubing and tiny cooling fins. If you look through the grille of a car and see what you think is a radiator, it is most likely the condenser. The hot vapour from the compressor arrives and the fins help the air flowing through the condenser remove heat from the refrigerant, changing it to a much cooler liquid state. When the car is stationary the radiator cooling fans perform the task of moving air through the condenser.

Step Three: Refrigerant moves to the receiver-drier. This is the storage tank for the liquid refrigerant. It also removes moisture from the refrigerant. Moisture in the system can freeze and then act similarly to cholesterol in the human blood stream, causing blockage. The receiver-drier is used on the high side of the Scorpio system and uses a thermal expansion valve. This type of metering valve requires liquid refrigerant. To ensure that the valve gets liquid refrigerant, a receiver is used. The primary function of the receiver-drier is to separate gas and liquid. The secondary purpose is to remove moisture and filter out dirt. 

Step Four: As the compressor continues to pressurize the system, cool liquid refrigerant under high pressure is circulated from the receiver-drier to the thermostatic expansion valve. The valve relieves pressure from the liquid refrigerant so that it can expand and become refrigerant vapour in the evaporator. Remember that when a liquid becomes a gas it needs latent heat and so it extracts this from its surroundings cooling them down. The expansion valve is the "brain" of the system. By sensing the temperature of the evaporator, or cooling coil, it allows liquid to pass through a very small orifice, which causes the refrigerant to expand to a low-pressure, low-temperature gas. This "cold" refrigerant flows to the evaporator

Step Five: The evaporator is very similar to the condenser. It consists of tubes and fins and is mounted inside the passenger compartment. As the cold low-pressure refrigerant is released into the evaporator, it vaporizes and absorbs heat from the air in the passenger compartment. As the heat is absorbed, cool air will be available for the occupants of the vehicle. A blower fan inside the passenger compartment helps to distribute the cooler air. The evaporator serves as the heat absorption component. The evaporator provides several functions. Its primary duty is to remove heat from the inside of your vehicle. A secondary benefit is dehumidification. As warmer air travels through the aluminium fins of the cooler evaporator coil, the moisture contained in the air condenses on its surface. Dust and pollen passing through stick to its wet surfaces and drain off to the outside. On humid days you may have seen this as water dripping from the bottom of your vehicle. Rest assured this is perfectly normal.

The ideal temperature of the evaporator is 32 Fahrenheit or 0 Celsius. Refrigerant enters the bottom of the evaporator as a low pressure liquid. The reducing pressure and the warm air passing through the evaporator fins causes the refrigerant to boil (refrigerants have very low boiling points). As the refrigerant begins to boil, it absorbs large amounts of heat from the air entering the passenger compartment and this heat is then carried away with the refrigerant. Several other components work in conjunction with the evaporator. As mentioned above, the ideal temperature for an evaporator coil is 0 centigrade. Temperature and pressure regulating devices must be used to control its temperature. In the de-ice switch has a temperature probe mounted on the evaporator and cycles the compressor off when near to freezing to prevent the evaporator from freezing up. A frozen evaporator coil will not absorb as much heat.

Step Six: The heat-laden, low-pressure refrigerant vapour is then drawn into the compressor to start another refrigeration cycle.

As you can see, the process is pretty simple. Just about every vehicle's A/C system works this way, though certain vehicles might vary by the exact type of components they have.

The best thing about air conditioning is that all you have to do is press a button to make it work. Air conditioning systems are pretty reliable. On a modern and relatively new vehicle, it is rare to have problems. And if there are problems, they are pretty much one of two things: No cool air or insufficient cool air. If you own an older car and its A/C system doesn't seem to be working properly, here are some general troubleshooting tips:


Most A/C repairs are best left to a specialist repairer or garage. Recharging the refrigerant, in particular, requires special equipment that most people don't own. There are a couple things you can do, however.
First, make sure to have the system checked regularly according to your vehicle's owner's manual - in the Scorpios case that's every 10,000 miles.
Second, if you live in a place with a cold climate, it might not make much sense to run the A/C during the winter months, but many A/C technicians recommend running your A/C system regularly, because it contains a light mineral oil in the refrigerant to keep the compressor properly lubricated. The general rule of thumb is 10 minutes per month. The Scorpio heating, ventilation and air conditioning systems also engage the A/C compressor when the distribution control is in defrost mode.
So those are the basics behind air conditioning. The next time you're riding along in your car and you hit the A/C button, you can say, Boy, those evaporator tubes sure are cold. It's all thanks to R-134A!

An air conditioner is basically a refrigerator without the insulated box. It uses the evaporation of a refrigerant, like Freon, to provide cooling. The mechanics of the Freon evaporation cycle are the same in a refrigerator as in an air conditioner. According to the dictionary, the term Freon is generically "used for any of various nonflammable fluorocarbons used as refrigerants and as propellants for aerosols."

This is how the evaporation cycle in an air conditioner works The compressor compresses cool Freon gas, causing it to become hot, high-pressure Freon gas. This hot gas runs through a set of coils so it can dissipate its heat, and it condenses into a liquid. The Freon liquid runs through an expansion valve, and in the process it evaporates to become cold, low-pressure Freon gas. This cold gas runs through a set of coils that allow the gas to absorb heat and cool down the air inside the building. Mixed in with the Freon is a small amount of a lightweight oil. This oil lubricates the compressor.

Taken literally, air conditioning includes the cooling and heating of air, cleaning it and controlling its moisture level: conditioning it to provide maximum indoor comfort. An air conditioner transfers heat from the inside of a building, where it is not wanted, to the outside. Refrigerant in the system absorbs the excess heat and is pumped through a closed system of piping to an outside coil. A fan blows outside air over the hot coil, transferring heat from the refrigerant to the outdoor air. Because the heat is removed from the indoor air, the indoor area is cooled. An air conditioning system generally consists of five mechanical components:1. A compressor, 2. A fan, 3. A condenser coil (hot), 4. An evaporator coil (cool), 5. A chemical refrigerant.

Most central air conditioning systems include of a "hot" side, outside your home, and a "cold" side, inside your home. The "hot" side generally consists of a condensing coil, a compressor and a fan. The "cold" side is usually located within your furnace. The furnace blows air through an evaporator coil, which cools the air, and routes this cool air throughout your home using a series of air ducts. The cleaning function of air conditioners is performed by filters, which remove dust from the air.


The demand for air conditioning continues to grow. We all demand higher levels of comfort in our work places, hotels, restaurants and other public places. Air conditioning in cars has become a standard feature - no longer restricted to luxury models. Despite our unpredictable climate the UK enjoys Europe's 4th largest market for air conditioning and yet only some 15% of commercial buildings are air conditioned and the residential market is only just beginning to develop.

WHY DO WE NEED AIR CONDITIONING: To offset unwanted energy (heat) in an occupied space (due to lighting, computers, people, heat gains from outside etc). To offset cold conditions (due to winter climate) i.e. to add heat. To provide clean, healthy conditions. To improve productivity by providing comfortable conditions. To improve living conditions (comfort). To increase the value of property.

WHERE DO WE NEED AIR CONDITIONING: Air conditioning is used in virtually all walks of life, as it is no longer considered a luxury, especially with the lifestyle we have today and the amount of pollution that exists. Also, with the advancement of electronics and manufacturing processes, manufacturers are capable of producing highly flexible, simple, energy efficient and low cost equipment compared to our present standards of living.

There are many types of air conditioning systems available and therefore there are factors to take into consideration when choosing a suitable system:

Capital Cost: Includes not only the cost of equipment and its installation, but also all ancillary requirements such as build work, plant location and size, electrical work, progress time, administration, etc. Whole life costs also consist of maintenance, energy efficiency and life expectancy.

Energy Efficiency (Running Cost): Energy efficiency of air conditioning systems is becoming increasingly important as it can account for the largest single element of the energy requirement of a building. Also, in the near future, energy tax might be introduced. It may be more cost effective to install a system with higher initial cost but which provides greater energy efficiency.

Maintenance Cost: Maintenance cost is often over looked in any calculation and can be very costly dependent on the complexity of the system and the availability of professional service companies.

Flexibility: Flexibility of the system should be assessed in terms of installation, operation, future expansion and changes, operation, maintenance and controls.

User friendliness: This needs to be assessed in relation to the occupier or user, the operator and/or the maintenance personnel. Many systems have standard controls, which are simple in concept yet sophisticated in nature and can combine user friendliness with full technical diagnostics.

Environmental Issues: These need to be checked, such as equipment compliance with current and future legislation in terms of CO2 emissions, Ozone Depletion & Health & Safety.

Common terms :

ABSOLUTE ZERO: Absolute zero is that temperature at which molecular motion stops. It is the lowest temperature possible. There is no more heat in the substance at this point.

AIR CONDITIONER: Device used to control temperature, humidity, cleanliness, and movement of air in conditioned space.

BOILING TEMPERATURE: Temperature at which a fluid changes from a liquid to a gas/vapour. At atmospheric pressure water boils at 100C, refrigerant (R22) at -40.8 C.

BRINE: Water saturated with chemical such as salt.

CAPACITOR: Type of electrical storage device used in starting and/or running circuits on many electric motors.

CARBON FILTER: Air filter using activated carbon as air cleansing agent.

CHLOROFLUOROCARBON (CFC): A compound containing chlorine, with high risk of damaging the ozone layer.

COEFFICIENT OF PERFORMANCE (COP): The ratio of work or energy applied as compared to the energy used.

COMPRESSOR: The pump of a refrigerating mechanism which draws a vacuum or low pressure on cooling side of refrigerant cycle and squeezes or compresses the gas into the high pressure or condensing side of the cycle.

COMPRESSOR, HERMETIC: Compressor in which driving motor is sealed in the same dome or housing that contains the compressor.

COMPRESSOR, OPEN-TYPE: Compressor in which the crankshaft extends through the crankcase and is driven by an outside motor.

COMPRESSOR, RECIPROCATING Compressor, which uses a piston and cylinder mechanism to provide pumping action.

COMPRESSOR, ROTARY: A compressor, which uses vanes, eccentric mechanisms, or other, rotating devices to provide pumping action.

COMPRESSOR, SCROLL: A compressor which uses two scrolls, one is fixed while the other revolves in orbit to provide pumping action.

COMPRESSOR, SCREW: A compressor which consist of rotors having male and female gears and compresses by engaging one screw rotor and two gate rotors to provide pumping action. COMPRESSOR, CENTRIFUGAL: A compressor, which consists of impeller and volute. The impeller rotates at aprox. 10,000 rpm. Such force changes the gaseous refrigerant into speed energy, which is converted into pressure energy for compression.

CONDENSING TEMPERATURE: Temperature at which a gas changes from a gas to a liquid.

CONDENSER: The part of refrigeration mechanism which receives hot, high pressure refrigerant gas from compressor and cools gaseous refrigerant until it returns to liquid state.

CONDENSING UNIT: That part of refrigerating mechanism which pumps vaporised refrigerant from evaporator, compresses it, liquefies it in the condenser and returns the liquid refrigerant to refrigerant control.

COOLING TOWER: Device, which cools water by water evaporation in air. Water is cooled to wet bulb temperature of air.

CRYOGENICS: Refrigeration which deals with producing temperatures of 250F below zero (- 157C) and lower.

D-BACS (Daikin Building Air Conditioning Control System): Computer operated control/management system utilising information generated by Daikin and other equipment.

DEFROST CYCLE: Refrigerating cycle in which evaporator frost and ice accumulation is melted. 

DEHUMIDIFIER: Device used to remove moisture from air in enclosed space.

DRY BULB: An instrument with sensitive element, which measures ambient (moving) air temperature.

DRY BULB TEMPERATURE: Air temperature as indicated by ordinary thermometer.

ELECTROSTATIC FILTER: Type of filter, which gives particles of dust electric charge. This causes particles to be attracted to a plate so they can be removed from air stream or atmosphere.

ENERGY: Energy is the capacity or ability to do work.

EVAPORATION: A term applied to the changing of a liquid to a gas. Heat is absorbed in this process.

EVAPORATOR: Part of a refrigerating mechanism in which the refrigerant vaporises and absorbs heat.

EXPANSION VALVE: A device in refrigerating system which maintains a pressure difference between the high side and low side and is operated by pressure.

FREEZING POINT: The temperatures at which a liquid will solidify upon removal of heat. The freezing temperature for water is 32F (0C). at atmospheric pressure. 

GRAIN: A unit of weight and equal to one 7000th of a pound (0.064 grams). It is used to indicate the amount of moisture in the air.

HEAT RECLAIM VENTILATION (HRV): Ventilation system operates on the principle of reclaiming energy from exhaust air.

HEAT: Heat is a form of energy. It is related to the molecular motion or vibration. HEAT EXCHANGER: Device used to transfer heat from a warm or hot surface to a cold or cooler surface. Evaporators and condensers are heat exchangers.

 HEAT LOAD: Amount of heat, measured in Btu, which is removed during a period of 24 hours.

HEAT PUMP: A compression cycle system used to supply heat to a temperature controlled space, which can also remove heat from the same space.

HEAT TRANSFER: Movement of heat from one body or substance to another. Heat may be transferred by radiation, conduction, convection or a combination of these three methods.

HORSEPOWER: A unit of power equal to 33,000 foot pounds of work per minute. One electrical horsepower equals 746 watts.

HUMIDIFIERS: Device used to add to and control the humidity in a confined space.

HYDROCHLOROFLUOROCARBON (HCFC): A compound containing chlorine but since hydrogen is present, the risk of damaging the ozone layer is low.

HYDROFLUOROCARBON (HFC): A compound which does not contain chlorine and does not damage the ozone layer.

HUMIDITY: Moisture; dampness. Relative humidity is ratio of quantity of vapour present in air to greatest amount possible at given temperature.

LATENT HEAT: Heat energy absorbed in process of changing form of substance (melting, vaporisation, fusion) without change in temperature or pressure.

POWER: Power is the time rate of doing work.

PSYCHROMETER OR WET BULB HYGROMETER: An instrument for measuring the relative humidity of atmospheric air.

PSYCHROMETRIC CHART: A chart that shows the relationship between the temperature, pressure and moisture content of the air.

REFRIGERANT: Substance used in refrigerating mechanism to absorb heat in evaporator coil by change of state from a liquid to a gas, and to release its heat in a condenser as the substance returns from the gaseous state back to a liquid state. 

RELATIVE HUMIDITY: Ratio of amount of water vapour present in air to greatest amount possible at same temperature.

REVERSING VALVE: Device used to reverse direction of the refrigerant flow depending upon whether heating or cooling is desired.

SENSIBLE HEAT: Heat, which causes a change in temperature of a substance.

SHELL_AND_TUBE FLOODED EVAPORATOR: Device, which flows water through tubes, built into cylindrical evaporator or vice-versa.

SHELL TYPE CONDENSER: Cylinder or receiver, which contains condensing, waters coils or tubes.

SKYAIR: Skyair is a trade name of Daikin middle range split systems. SOLAR HEAT: Heat from visible and invisible energy waves from the sun.

SPECIFIC GRAVITY: Weight of a liquid compared to water, which is assigned value of 1.0.

SPECIFIC HEAT: Ratio of quantity of heat required to raise temperature of a body one-degree to that required to raise temperature of equal mass of water one degree.

SPECIFIC VOLUME: Volume per unit mass of a substance. 

SPLIT SYSTEM: Refrigeration or air conditioning installation, which places condensing unit outside or remote from evaporator. Also applicable to heat pump installations.

SUBCOOLING: Cooling of liquid refrigerant below its condensing temperature. SUCTION LINE: Tube or pipe use to carry refrigerant gas from evaporator to compressor.

SUPERHEAT: Temperature of vapour above boiling temperature of its liquid at that pressure.

TEMPERATURE: Degree of hotness or coldness as measured by a thermometer; measurement of speed of motion of molecules.

THERM: Quantity of heat equivalent to 100,000Btu (105,500 kJ).

THERMOSTAT: Device responsive to ambient temperature conditions.

VACUUM PUMP: Special high efficiency compressor used for creating high vacuums for testing or drying purposes. VAV (Variable Air Volume): A central air conditioning system which works on the principle of supplying constant temperature air volume to a space, and by varying the volume, controls room temperature. 

VRF (Variable Refrigerant Flow): A direct expansion, modular central air conditioning system providing heating and cooling. Operates on the principle of varying the flow of refrigerant to a room terminal unit to achieve desired temperature.

VRV (Variable Refrigerant Volume): Trade mark for Daikin VRF systems:

VVT (Variable Volume Variable Temperature): Same principle as VAV, except two ducts are required, one for heating, one for cooling, with variable control dampers.

VWT (Variable Water Temperature): Same as VWV but changing both the volume and the temperature of the water to achieve room  temperature.

VWV (Variable Water Volume): A central water based system operating on the principle of supplying constant temperature of chilled/hot water to room terminals and varying the flow to achieve room temperature.

WET BULB: Device used in measurement of relative humidity. Evaporation of moisture lowers temperature of wet bulb compared to dry bulb temperature in same area.

WORK: Work is force multiplied by the distance through which it travels.

Refrigeration and Air Conditioning Kettering was founded in 1970's and has now become one of the most respected names in the UK air conditioning industry, distributing air conditioner products.

Philosophy : To sell the best and widest range of available products. To offer the best engineering solutions.To provide a complete service from training to delivery, seminars to design assistance and a complete range of complementary accessories. RACe's long term strategy has always been to develop the UK market from a position of strength via technical knowledge, experience and sound financial management supported by technical expertise and long term vision. RAC has high service standards and is committed to customer satisfaction, ensuring the customer receives the right system to suit their requirements and budget, perfectly, right from the very beginning.

Air conditioning in a motor vehicle is a combination of the car heater and a refrigerant circuit. This allows the desired climatic conditions to be maintained regardless of the outdoor conditions. This makes air conditioning a significant factor for safety and driving comfort. The refrigerant circuit. The individual components in the refrigerant circuit are connected with one another by hoses forming a closed system. The refrigerant circulates in the system driven by the compressor. The circuit is divided up into two sections: The section between the compressor and expansion valve is called the high-pressure side (yellow/red). Between the expansion valve and compressor we speak of the low-pressure side (blue). In the compressor the gaseous refrigerant is compressed and thereby heated highly. Under high pressure it is pressed through the condenser. Here heat is removed from the highly heated refrigerant causing to condense and thereby changing its state from gaseous to liquid. The drier, the next station, separates impurities and air inclusions from the now liquid refrigerant. This ensures the effectivity of the system and protects the components from damage resulting from contamination. Then it passes from the drier to the expansion valve. This valve is similar to a dam. In front of the dam it maintains a uniform pressure, and in back of the dam this pressure is relieved due to the increase in volume. Since the expansion valve is located directly in front of the evaporator, the refrigerant expands into the evaporator. During evaporation, a change in the state from liquid to gaseous, heat is absorbed from the surroundings. The evaporator is a heat exchanger similar to the condenser. It has an enormously large surface, over which it can absorb heat from the surroundings for evaporation. This cold air is then blown into the vehicle passenger compartment by the ventilation system where it ensures the comfort of the passengers. On the low pressure side the refrigerant is again gaseous flows to the compressor where the circuit starts over again.


Air Conditioning Systems Unrivalled standards of experience, professionalism and customer care have combined to establish Icecape Ltd t/a RAC Kettering as one of the UK's leading distributors of Daikin Air Conditioning Products and Systems. RAC Kettering has chosen Daikin in 1977 as its first UK supplier and has since grown steadily to become a major UK Distributor of Air Conditioning Equipment with special expertise in VRV and Chiller Systems. In addition to just supplying Daikin Air Conditioning Products, we also operate a highly professional distribution service and demonstrate our ommitment to fully back-up our clients by maintaining a well-stocked spare parts department. Similarly high standards apply to the full pre and after sales support services provided by RAC Kettering. Clients throughout the UK depend on the expertise of RAC Kettering whose Sales Engineers operate nation-wide to give a comprehensive design and support service. This is reinforced with a programme of specialised product training for client's design and engineering personnel. An experienced Technical Department assists with any engineering issue and can provide on-site commissioning and troubleshooting.

What is air conditioning? Throughout the ages, we have sought to improve the level of comfort offered by our surroundings. In colder regions, we have tried to heat our dwellings and in warmer climes, to cool them down because if we are not comfortable, we can neither work nor relax. But thermal comfort vital to our well being, is subject to three basic influences:

Among these influences, the human factor is somewhat unpredictable. The others can be controlled in order to provide that much sought after feeling of well being. Changing patterns in construction, working practises and internal occupancy levels have created new parameters within which designers must operate. Modern buildings for instance, generate far more heat than their predecessors of say, 50 years ago and there are several reasons for this:

Solar Infiltration Developments in building technology have also given rise to an increased use of glass - even when solar protective glazing is fitted, solar gains can be considerable.
Occupants Increasing numbers of occupants, each generating some 120W/h of heat, are routinely crammed into office areas.
Electrical Appliances Computers, printers and photo copiers, all part of the modern offices scenario, also generate substantial heat loads.
Ventilation Introducing the outside air into a building also introduces its temperature something of a problem if it's 30ºC outside!
All these heat gains must be removed if a comfortable living or working environment is to be attained and the only genuinely effective way of achieving this is via air conditioning. The principles of air conditioning are based around the transportation of heat from one place to another and the medium generally used to effect transportation is refrigerant.

The principles of air conditioning are based around the transportation of heat from one place to another and the medium generally used to effect transportation is refrigerant. Refrigerant is used because it evaporates at very low temperature. Physics shows that the evaporation of a substance (change of phase) requires considerable energy.
The low boiling point inherent in refrigerant enables it to be used at relatively low temperature, such as room temperature. When a liquid refrigerant evaporates it absorbs heat from its surroundings which therefore, cool down. Evaporation causes the refrigerant to change from liquid to gas (phase change), at which point it contains considerably more energy (heat) than in its liquid state the maximum amount possible, in fact. If the refrigerant is to be reused, this heat must be released, preferably at a point where it is no longer required. Once again, physics shows that when a substance condenses, it releases much of the energy it carries thus the refrigerant must be condensed. This requires its pressure to be increased in order to raise the condensation temperature above that of the heat exhaust point. This operation is carried out by a compressor. Once returned to its fluid state, the refrigerant can absorb heat again. But its pressure is now too high, as is its condensation point and also its evaporation temperature. The problem is overcome by use of an expansion valve which allows the pressure to fall, thereby reducing the evaporation temperature to its original level. At this point the cycle can recommence. Manipulation of the refrigerant pressure enables heat to be absorbed from an area of lower temperature and released to an area of higher temperature with the corresponding result of cooling or heating.

Air conditioners are part of our lives and we enjoy their comfort everywhere. In shops, restaurants, offices, hotels it's hard to imagine life without them. Air conditioning provides you with pure cool air when it's hot outside. But what about winter, and those cooler periods during spring and autumn? This is when we need heating. Not cooling. ...heating in the winter  The ideal solution to this problem is the Heat pump. It cools when it's hot, and warms when it's cold. The choice is yours, at the push of a button. Comfort and well being all year round. A simple principle developed to perfection Air conditioning works like your refrigerator, which removes heat continuously from the cabinet and discharges it into the kitchen. You can feel this 'free' heat by touching the coil on the back of your refrigerator. In summer, the heat pump extracts heat from the warm air in your home and pumps it outside. Your home stays comfortable and cool. In winter, it's the reverse. Natural heat in the outdoor air - even when it's freezing - is extracted and moved indoors. Wonderful warmth when you need it. Comfort that costs less Three kilowatts of heat for each kilowatt of electricity used. Heat pumps are up to three times more economical than conventional gas fired or electric heating systems. Installation costs are lower too. With just one system for cooling in summer and heating in winter, you save on equipment outlay.

If we look for AIR CONDITIONING in Collins English Dictionary it states:

"A system or process for Controlling the Temperature and sometimes the Humidity and Purity of the air"

Controlling the Temperature is being able to Heat and Cool. Not only cool. The air that we breathe is made up of 3 major components all capable of carrying energy (heat):

1) The component molecular constituents of air: Oxygen (23%), Nitrogen (76%), Carbon Dioxide (< 1%) and Inert Gases (< 1%).

2) Moisture or Water Vapour: Water vapour is present in the air at all times, the quantity present being dependent upon the air temperature. The higher the air temperature the higher the water vapour (quantity).

3) Airborne Particulate: These are the suspended impurities within the air from either industrial or natural pollution such as Pollen, Dust, Smoke, Germs etc.

As air is the only media that encompasses the whole of our body, we need to condition this air to provide comfort.

The action we need to take is:

1) Control Temperature (Heating & cooling) which entails adding energy (heating) or removing unwanted energy (cooling). General comfort conditions range between 20 - 25 C in the UK.

2) Control Humidity (moisture content in the air), either Humidify (add moisture) when dry, which can result in dryness of skin, dry throat and encourages static built-up) or de-humidify (remove moisture) when the amount of moisture in the air is high, which can result in breathing discomfort. Comfort humidity is generally between 30-70 % RH (Relative Humidity) for the UK.

3) Provide Ventilation to provide the necessary Oxygen for breathing and dispelling carbon dioxide, Odour,dust, smoke etc. General Ventilation requirement ranges between 5 - 18 litres per second per person.

4) Provide Filtration to clean outside and inside air by removing dust, pollen, etc. Dust in dry air combined with dryness (lack of moisture in the air) is the main cause of static shocks. Lack of ventilation and filtration combined with the lack of maintenance is the main causes of Sick Building Syndrome (SBS). Therefore air conditioning encompasses HEATING, COOLING, HUMIDITY CONTROL, VENTILATION, FILTRATION.

There are many different methods of achieving comfort conditions (Heating, Cooling, Humidity Control, Ventilation & Filtration).

1) Heating and Cooling (which should be treated as one entity) are the most important parts of the Air conditioning system. Heating (adding energy): Is achieved through electrical energy input, Natural Gas Boilers, Oil Boilers and Reverse Cycle Refrigerant Heat Pump. Transfer of this energy from source to the air-conditioned space can be via air circulation (Air systems), via water circulation (Water systems) or via refrigerant (Extended Direct Expansion systems). Cooling (absorbing/removing heat): This is the reverse of heating i.e. transferring unwanted energy/heat (generated by lights, computers, people, solar heat gains through glass, structure heat gains, ventilation heat gains, etc.) from inside to outside. The transfer method is via the same media as heating transfer: Air systems, Water systems or Extended Direct expansion systems. Statement: 95% of cooling systems (air, water or Extended Direct Expansion (EDX)) use Refrigerant (vapour compression cycle or VCC) in the heat rejection process, as Refrigerant is the most efficient media and has the advantage of having a boiling temperature of -40C (water =+100C) and an energy carrying capacity 10 times more efficient than water and 50 times more efficient than air.

2) Ventilation which can be: A part of the whole air conditioning system, (in the case of Air Systems) where Air is also used to transfer energy.  Or an independent system mainly to provide ventilation (in the case of Water Systems and EDX). However, outside air needs to be treated (heated and/or cooled and filtered) to meet indoor temperature conditions, especially in extreme winter conditions and not so extreme summer conditions. Statement: Utilising ventilation in mid season to control temperature can also provide an acceptable energy efficient solution. This is more the case in outer city areas and areas of low level, internal energy gain. Ventilation can represent a high percentage of building energy consumption, especially in centralised systems. Modular systems are more controllable, run only where needed and easily added to when requirements change.

3) Filtration is an integral part of any air movement device; the level of it depends on the type of equipment selected to provide the other parts of the air conditioning system. It can also be added to an existing system or stand-alone (e.g. electrostatic) Dependent on the application (Public Houses, etc) and special requirements (Hospitals, etc). Statement: There may be applications where due to capital cost implication, excessive ventilation (oversized) is applied to overcome the above special requirements at the expense of running cost. Localised filtration is more possible these days at low cost rather than over sizing the ventilation system

Air conditioning is to control the temperature in the main, control the humidity and clean the atmosphere that we live in. To control the temperature we have to add heat (energy) when cold and remove heat (energy) when warm. This energy has to be transported from outside to inside (Heating) and from inside to outside (Cooling). There are three main methods to transfer this energy: Air Systems, Water Systems and Refrigerant Systems. Air Systems: This where we use the air to carry the energy from inside to outside and vice versa. The use of Air Handling Units (AHU) or Roof Top Packages (RTP) to condition the air (Temperature, humidity sometimes), filter and refresh the air and send it through ductwork to the occupied space where the conditioned air will heat or cool the space as required and return via return air ducts back to the AHU or RTP. Air Handling Units contain a cooling coil (connected to a chiller or condensing unit) a heating coil (connected to boilers or electric heaters) filters and circulating fan(s). Roof Top Packages contain refrigerant cooling cycle, heating coils (connected to boilers or electric heaters), filters and circulating fan(s).

Water Systems: In these systems water is used to carry the energy from inside to outside and vice versa. The use of a chiller (on roofs or plant rooms) to cool the water which would be circulated via circulating pumps to the occupied space where it will be passed through fan coils (terminal units) which circulate room air over the coil, hence absorbing unwanted heat. The use of boilers (in plant rooms) to heat the water (separate circuit from cooling) which would be circulated via circulating pumps to and back from the occupied space where it will be passed through the same fan coil which circulate room air hence adding heat to the space. Water Systems only control the temperature. Filtering of the air is normally carried out through the indoor fan coils (terminal units). Ventilation is normally carried out through a separate system with a range of AHU and ductwork distribution system (smaller than air systems) which can be localised to the air-conditioned space.

Refrigerant Systems (Known as Extended Direct Expansion or DX Systems): In these systems refrigerant is used to carry the energy from inside to outside or vice versa. The use of outdoor condensing units (can be reverse cycle heat pump for heating) cool the refrigerant and sends it through refrigeration small bore pipe work to indoor fan coils (terminal units) where it will expand to lower the temperature of the refrigerant in the pipe, hence room air when circulated over the coil will lose its unwanted heat. Heating is achieved via the same outdoor unit by reversing the cycle or utilising a third pipe to carry hot refrigerant to the indoor unit to provide heating. Filtering of the air is normally carried out through the indoor fan coils (terminal units). Ventilation is normally carried out through a separate system with a range of AHU and ductwork distribution system (smaller than air systems) which can be localised to the air-conditioned space.

The basis of most (more than 95%) air conditioning systems is the ' vapour compression cycle". The media (vapour) is Refrigerant (hydrochlorofluorocarbons - HCFC or hydrofluorocarbons - HFC) which is non-toxic, non-explosive and non-corrosive. These Refrigerants have a boiling point of aprox. Minus 40C which means that even if the air (outside or inside) temperature is as low as minus 39C it still has heat to be absorbed by refrigerants.

The vapour compression cycle requires four components:

1) The compressor: To raise the pressure of low-pressure low temperature gas to high-pressure high temperature gas. There are many types of compressors; the most common are Reciprocating, Rotary, Scroll, Screw and Centrifugal.

2) The Condenser: To change the state of high-pressure, high temperature gas to high-pressure, high temperature LIQUID. This is achieved by passing ambient air (known as air-cooled) or water (known as water-cooled) over the condenser tubes.

3) The Expansion Device: The purpose of the device is to change the state of the refrigerant from high-pressure, high temperature liquid to low pressure low temperature saturated liquid. This is achieved by passing the liquid through an orifice.

4) The Evaporator: To absorb the heat from room air or water, which in the case of a chiller is circulated around the evaporator coil. This will change the state of low-pressure, low temperature saturated liquid to low pressure, low/medium temperature gas. These components are common to the vast majority of domestic refrigerators and appear in slightly different forms in 95% of air conditioning and refrigeration systems, Domestic, commercial or industrial. This vapour compression cycle if reversed (condenser becomes evaporator and visa versa) can now absorb heat from outside and transfer it to inside, hence saving energy. This is called Reverse Cycle Heat Pump. Energy savings can be as high as 4 to 1 (for every kW input we get 4 kW output).


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