Air conditioning mechanically alters the temperature of the air, by making it cooler or warmer. Control of the humidity is also possible. Air conditioning is used to provide COMFORT COOLING and CLOSE CONTROL for specific applications. The degree of Air conditioning duty required is usually referred to in either kW (Kilowatt's)
or B.T.U'S (British Thermal Units)
Air conditioning is a method of providing conditioned air to an area at the proper temperature and humidity. The term usually describes a refrigeration system designed to cool the air within a space. In the process of removing heat, the system also removes moisture, further increasing comfort levels. Auxiliary filters may also remove pollen, dust and other pollutants from the air as well. Sometimes entire buildings can be designed that air temperature, humidity and air freshness can be controlled from a central air conditioning plant. Other buildings can be temperature controlled by individual units placed at strategic points.
One type of system commonly found is the split system. Figure 1 illustrates this.
Warm humid air passes through the vanes of an evaporator coil where in, sealed tubes liquid refrigerant is "boiling off". This process absorbs heat energy from the air so that it cools down. Moisture is also removed from the air during this process and collects in a tray beneath the evaporator. The water collected is commonly referred to as "condensate" this is drained away naturally or pumped using an internal pump unit.
Fig 2, illustrates an evaporator coil, found inside most Air conditioning units. Size and shape will vary depending on the type of unit.
KEY ELEMENTS
To assist with the understanding of how an air conditioner works, lets look at an explanation using water.
If a naked flame is used to heat water it will boil at 100 0C at normal atmospheric pressure which is 14.7p.s.i (1 Bar). As we heat up the water, heat energy is absorbed from the flame. At boiling point further heat is absorbed while changing state from a liquid to a vapour (steam). All the time the water is being boiled heat energy is being absorbed.
Imagine now a fluid, flowing around a coil inside an air conditioning unit that boils at well below the normal temperature of a room. Obviously this can't be water so we use a product called refrigerant. Instead of a naked flame as the heat source, our heat source is now the air passing across the coil. As the air heats this fluid up, and boils the refrigerant, heat energy is being absorbed from the air passing through the coil. The temperature of the air is then lowered.
In principle this is how we lower the temperature of the room, by ejecting the now cooled de-humidified air from the air conditioner.
In order for this process to be continuous we need to condense the vaporised refrigerant, back in to liquid to enable the process to be re-started. To do this we need the following components.
Compressor: - This device is powered by an electric motor and sucks the refrigerant vapour that has come from inside the evaporator unit. It then compresses it and pumps it to the condenser unit.
Condenser: - The conversion from a vapour to a liquid can be easily demonstrated by removing a cold object from your refrigerator and placing it on the work surface in your kitchen. Providing the air is reasonably humid, water vapour will condense onto the surface of this cold object; this process is actually condensing water vapour back in to a liquid.
In an air conditioning system, compressing the gas will allow it to be condensed back in to a liquid even at temperatures reaching 500C. Outside air is used as the cooling medium. Outdoor air temperatures in the UK may exceed 350C or above in the summer, yet this is still cool enough to condense the refrigerant back to a liquid.
The cooled refrigerant liquid, maintains a high pressure so is passed through a small orifice which lowers its pressure restricting the flow to the indoor unit evaporator where it is boiled off again by absorbing heat from the air passing over it.
The process has then restarted.
As we have mentioned before, Air conditioning units can heat a room as well as cool it.
In fact the heating benefits of an air conditioning heat pump system is widely understood to be the most cost effective as any heating system currently available.
Fig 4. system diagram shows an air conditioning unit in Heating mode. The heat pump system has a
reversing valve which, when operated, swaps the flow of refrigerant. The indoor unit is now the condenser, warming the indoor air. The outdoor unit is now the evaporator which, while cooling the outdoor air is absorbing its heat. Outdoor air even at 0OC contains enough heat energy to be used to warm the inside air.
The reversing valve can swap the flow back and forth to cool or heat a room depending on the requirements of the occupants.
The reversing valve can swap the flow back and forth to cool or heat a room depending on the requirements of the occupants.
Air Conditioner types
Air conditioners appear in many different shapes and sizes. Some are wall mounted, see Fig 3, some are fitted through the wall and others are completely hidden from view. They all carry out the same function and cool the air in the same way.
The manufacturers web sites at the top of our home page will show you some examples.
Some Air conditioning systems use chilled water to cool the air instead of refrigerant liquid. As the chilled water cannot boil off inside the evaporator pipes but merely cool the air on contact it is not as efficient as refrigerant. The cooling coil would have to be a lot bigger to do the same cooling duty as a coil containing liquid refrigerant.
As well as altering the temperature of the air, the Air conditioner can also improve the air quality by introducing and filtering fresh air and then removing stale air. It can also remove air pollutants which can cause allergies. This means the overall benefits of Air conditioning are significant. Many trials have been done which clearly demonstrate that workers productuctivity can be maintained and even improved by controlling the air condition.
Understanding the need:-
Our offices and our homes become better insulated as they evolve. Our reliance on computers and technology also increases, your probably viewing this page on a computer right now. As each electrical device is added to the working or home environment this adds heat, sometimes due to poor air quality or noise we are unable to open windows. Even if we do, the temperarure control becomes difficult as fresh air can enter at uncontrollable rates. This can result in undesirable swings in temperature. The answer is an air conditioner which can create and control a better room environment at the touch of a button.
People are becoming increasingly aware of the benefits of air conditioning both at work and play. Most middle specification cars are now equipped with air conditioning as standard, this can be beneficial in reducing fatigue and reducing the possibility of road rage incidents during warmer weather.
As our offices and our cars become air conditioned, we inevitably become increasingly aware of the benefits of Air conditioning. Its not surprising therefore that air conditioning in the home is now becoming increasingly popular.
Find out more by returning to our home page.
To summarise.
Air conditioning units carry out an important job in maintaining air quality and in providing a comfortable environment for people to work, rest and play.