Cooling systems are a vital part of many aspects of modern society, including cars, computers and buildings. Cooling systems are generally divided into two types: active and passive. Active cooling is a type of heat transfer that uses powered devices such as fans or pumps. Passive cooling transfers heat without using any additional energy.
Active cooling solutions are commonplace in contemporary society. These systems work by using energy to affect some kind of heat transfer, usually by conduction or convection. Conduction occurs when heat energy is equalized between atoms of different energy levels. Bringing water to a boil over an electric eye is a common example of conduction. Convection takes place when warmer matter is forced away from a heat source, as when hot air rises above a heater.
One everyday use of active cooling is the system that keeps an automobile engine running. Internal combustion generates a great deal of heat and, without cooling, a car engine would quickly seize up. To keep the engine cool, water mixed with coolant is pumped through the engine compartment, where it absorbs heat by conduction. The superheated water is then pumped to the radiator to be cooled by airflow. This is an active cooling solution because of the energy used by the water pump.
Another example of active cooling is the air conditioner system (AC) in a home or office. While these systems may use different basic designs, most AC cooling works by chilling the air and using fans to force it through the building. This process of forced convection is one of the most commonly used active cooling methods.
Many active cooling systems work in tandem with passive cooling elements to function more effectively. For example, a passive heat sink is used to transfer heat away from a computer processor. As heat radiates through the heat sink, a fan blows air around the sink to keep it cooler. Additional fans typically cycle air through the computer case so the heated air is pushed outside of the system. This type of cooling is used in many consumer electronics devices and is one reason why these devices are often so loud.
New technology places an emphasis on passive cooling solutions, because these systems generally use less energy. Many new buildings have design features that allow heat transfer to occur naturally instead of using fans or AC. A good example of this is ridge vents versus attic fans in a home. Ridge vents allow heat to escape the attic space without using extra energy to power a fan blade. Passive systems can often save on both money and energy when compared to active cooling systems.