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Energy Saver: Air Conditioning
(continued ...) draw the surrounding outside air through the condenser coil. Like most things in nature, systems always try to get to equilibrium or a lower energy state. Heat transfer happens when there is a difference in temperature. Heat always flows from higher temperature to lower temperature. Even though the outside air may be 100 F (38 C), it is still much colder than the liquid refrigerant. The 'colder' air is drawn through the condenser coil and heat is removed from the liquid refrigerant. The condenser fan then ejects the warm air, usually straight up. This is no coincidence because the warmer air is less dense and so it 'wants' to rise. The density difference assists to a small degree with the condenser fan performance.
The now 'cooler' liquid refrigerant travels through a copper tube with brazed joints inside your house to the evaporator coil. Somewhere along the journey, an expansion valve or fixed orifice regulates the flow of liquid refrigerant. A very important change happens at the orifice or valve. The liquid refrigerant changes state from liquid to gaseous vapor. This phase change draws in heat from the surroundings; a lot of heat. The evaporator coil is the receiving device for this cold gaseous refrigerant. You'll notice this same effect with an aerosol spray paint can. As you press the can's valve to release the paint, the liquid paint mixture inside flashes to vapor and comes out the valve's nozzle. If held open for a minute or so, the paint can becomes cold. Warm inside air is blown across the evaporator coil cooled by the expanding gaseous refrigerant thereby transferring heat to the refrigerant. Heat always moves from a higher energy state to a lower energy state. The now 'warm' gaseous refrigerant returns back to the outside equipment and the whole process starts over. When started, the process described is actually continuous.