Alternatives To Air Conditioning
A low-cost, energy-efficient alternative to traditional home air conditioning is fan-assisted natural ventilation. This alternative is less costly because air in the house is not cooled by a mechanical refrigeration system. Instead, the human body’s ability to cool itself is enhanced.
In addition, rather than being wrapped in a sealed building envelope, a person is connected with the outdoors. One can hear natural sounds such as birds singing, leaves rustling, as well as smell the scents of blooming plants. Although overhead protection is essential in Louisiana because of the strong sun and rain, wall thermal barriers are much less critical than in cold climates. The difference between indoor and outdoor temperatures is commonly twice in Louisiana. Here operable doors and windows can connect the interior with adjacent outdoor spaces.
In fact the outdoor porch and street culture of New Orleans occurred in part because people would sit outside in the pleasant nighttime air and wait for their houses to cool off so they could comfortably retire for the evening.
Human Comfort in Warm Weather
Because of the proximity of large bodies of water, the air in the warm seasons in southern Louisiana is consistently very warm and humid; but the temperature is not always blazingly hot. The high relative humidity characterizes air that already carries a great deal of water vapor and does not promote comfortable human conditions. As air temperature rises above 80 degrees, high moisture content in the air reduces the efficiency of the body’s primary cooling system. This system is evaporation of moisture from the skin, which causes bodily cooling. Because the air is already almost saturated, it cannot absorb much additional moisture. Therefore, for evaporation to occur, a large quantity of air must move across the surface of the skin. When this occurs, the comfort zone of the body is increased by up to 10 degrees, from the high 70s into the high 80s.
Fan-assisted Natural Ventilation Principles
Fans are a highly efficient way of moving air. They have been used in two primary ways in residential buildings -- fans that exhaust air to the outdoors and ceiling or portable fans that circulate airflow within a space.
Exhaust fans are necessary in residential buildings to eliminate moisture, fumes, heat and odors. In addition, fans have historically been used to exhaust heat buildup in attics or to enhance airflow through “whole house exhaust fans.” It is important to note that while these fans can reduce heat trapped inside a house, they also will draw in outside air at the ambient temperature and humidity. Therefore, by themselves they will not create conditions of interior comfort if the outside air is too warm or humid. A more-successful strategy is to prevent the heat from building up inside through site planting strategies for shade, proper orientation of building and openings, adequate insulation, radiant barriers and sun control.
In contrast to exhaust fans, ceiling fans and portable fans simply move the air within a space. The advantage of ceiling fans is that they do not obstruct the use of floor area within a room. For a fan to be effective, the air movement must interact with the person in each space; therefore, every room requires at least one ceiling fan. Fans come in different diameters, but a good rule is in areas over about 300 sq.ft., more than one fan should be considered. In rooms with high ceilings, fans should be mounted on pendants to bring airflow closer to the occupants. A good ceiling fan height is eight to nine feet above the floor. Fans are even useful outdoors on porch ceilings!
Windows That Open
Because ceiling fans do not introduce fresh air into the house, they are often used in conjunction with an open building ventilation strategy. Operable windows have been the historic means by which fresh air enters the house when mechanical systems are not activated. If windows are open on more than one wall of the house and there is a breeze, cross ventilation of the interior spaces will be induced, adding to the effectiveness of ceiling fans. In our climate, however, windows, at least on the ground floor, must be screened to prevent the intrusion of mosquitoes. This cuts the amount of airflow through the opening in half. On the second floor, some people use operable windows without screens because they are largely above the “bug line.” These open windows may be shielded from direct sun by louvered shutters.
Fan-assisted Natural Ventilation Practice
Ceiling fans are commonly available with three speeds. The middle speed is usually the best choice since it creates discernable air movement with no noise. Because the fans use so little energy, they may be left on throughout the warm seasons with virtually no cost penalty. Moving air is also useful in preventing mold. The high speed is useful for occasions when greater numbers of people occupy a space.
A hybrid system of exhaust fan and ceiling fans can be used at night or after a thunderstorm greatly lowers outdoor air temperatures. The exhaust fan can assist in more rapidly pulling the cooler air into the house while removing the warmer air from inside. A combination of fans, operable windows and louvered shutters can create a delightful interior at low cost.
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