Air conditioning

Why ?

1. Heat or cool the air in the enclosed space to comfortable temperature.

2. Ensure comfortable humidity and air velocity.

3. Ensure required fresh air change for avoiding CO2 buildup in breathing space.

How ?

Heating is straight; by Electric heater, boiler, burner or heat pump

Cooling and humidity control are little complicated

cooling

Unlike heating, cooling is achieved by removing heat from space to outside.

Mainly done by vapour compression method.

Principle of vapour compression system.

1. Every fluid needs energy(heat) to become vapour.

2. It gives out energy(heat) when vapour is changed liquid.

Now it is simple, arrange a fluid to change from liquid to gas in the room to be cooled and get the reverse process(gas to liquid) outside the room, where heat to be thrown out.

An Air conditioner unit is just to achieve the above.

Now the task is to find a fluid which evaporates at temperature where we need cooling and liquefies at hot outside temperature.

Any common fluid which we see around us not having these temperatures for conversion.

Water is zero degree liquefying and 100 C for evaporation. Not practical!

It was found that some particular compounds can have a property of evaporation at some pressure at low temperature (say 0 C) and condensation at hot outside temperature(say 50 C) when the pressure is raised.

These Fluid material is called Refrigerant.

Eg: R22, R134a, R407C

Now the task is cut out!

An equipment with 4 components, connected in series.

1. Supplies heat at low temperature ( extracting heat from the space to be cooled) to convert the liquid to gas.
2. Raising pressure of gas.
3. Removing heat from pressurized gas( converting back to liquid)
4. Lowering the pressure of the liquid.

No 1 is called evaporator, 2 is compressor, 3 is condenser, 4 is expansion device.

Air to be cooled is passed through the evaporator coil to cool it. Compressor need to be powered by an electric motor. This is the main input to the equipment. Condenser and evaporator need fans to force air to cool it. Expansion device, in its simple form is just a narrow copper tube.

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