Passive cooling uses design and technology to cool a building without energy. Techniques range from shading to strategic building design, insulation, and convection. Passive cooling reduces or eliminates the need for powered cooling, resulting in cost savings and minimal environmental impact.
Passive cooling is a method that incorporates design and technology to cool a building without the use of energy. Traditional cooling techniques, such as air conditioning or evaporative cooling, rely on power to drive compressors and fans that forcefully cool a space. This energy is generally purchased from a local utility company and is generated from the combustion of fossil fuels which can have degrading effects on the environment. Passive cooling techniques require no power and range from simple, such as building shading, to more complex, such as strategic building design. The use of such techniques can reduce or eliminate the need for powered cooling.
In hotter climates, particularly arid regions, cooling is the biggest environmental problem for buildings. There are two primary sources of unwanted heat that must be addressed to keep the building interior comfortable for the occupants. Direct sunlight on a building, especially windows, is a major source of heat gain for most buildings. The infiltration of warm air through cracks and crevices and the transfer of heat through building materials also affect the internal temperature.
Typically, the easiest way to cool a building is to prevent it from being heated in the first place. Strategic orientation of a building to minimize direct solar exposure, especially during the hottest part of the day, can significantly reduce its heat load. Once a structure has been built, the use of sunscreens or awnings and strategic landscaping can help avoid direct sun exposure. Where direct exposure cannot be avoided, such as on a roof, reflective techniques may be employed to prevent unwanted heating. For example, a roof may be coated with a white reflective coating to reduce heating over a large, unprotected area.
Passive cooling techniques can also prevent overheating by reducing heat infiltration into the structure. Heat flows naturally from hotter-temperature areas, such as outdoors in the summer, to cooler-temperature areas, such as a comfortable home interior. Caulking and adding gaskets around windows and doors, for example, reduces the area through which unwanted warm air can enter a structure. Insulation is a material with a high resistance to heat flow. Adding insulation to a building prevents the unwanted transfer of heat from the hotter outside environment to the inside space which is kept cool.
While much heat can be prevented, it is often not possible to keep a structure at a comfortable temperature with prevention alone. Another passive cooling strategy involves cooling the structure by convection. Convection is a process in which heat is transferred from one place to another by the movement of molecules of a gas or liquid.
Vents and windows strategically integrated into a building’s design, for example, can draw warm air out of the house while drawing in cool air to replace it. Warmer air is more buoyant than cooler air and rises naturally on its own. Vents placed near the ceiling on the side of the house away from the prevailing winds can help this warmer air escape the structure. To replace it with fresh air, vents and windows can be placed low on the side of the house in the path of the prevailing wind. It is therefore a question of opening vents and windows to favor natural convection to cool the structure.
More complex passive cooling methods can also be incorporated into a building’s design, such as ground cooling pipes. Earth cooling pipes harness the cooler temperatures below the surface of the earth to cool a structure. Buried underground as they lead into a structure, ground cooling pipes draw outside air into the building via an underground path. As it passes through these tubes, the air gives off heat to the much cooler ground through which it travels to enter the structure. Other passive cooling techniques are typically used in conjunction with earth pipes to create natural convection through the structure and push the hotter air out.
While not suitable for use in all locations, passive cooling is employed in many areas for energy efficiency resulting in cost savings and minimal environmental impact. It is generally best suited for hotter climates and arid regions. Passive cooling can avoid some or all of the cost of cooling techniques that are driven by powered devices such as fans and compressors. This energy saving strategy can also benefit the environment by reducing the need to burn non-renewable fuels that emit environmentally harmful waste by-products.
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