Air Conditioning

Index

  • Homes in temperate climatic zones don't have severe air conditioning requirements, but there is little doubt that many homes in such zones require cooling systems. One way to deal with overheating problems in temperate zones is mechanical air conditioning such as heat pumps. Such systems cost thousands of dollars, require a lot of maintenance and energy, i.e., $$$. They also make noise.

    Passive systems are usually less expensive to install, require little maintenance and very little energy. Passive systems use shading and natural venting to keep homes cool. Such systems were used by the Anasazi and Ancient Egyptians. And passive cooling is the normal way to keep homes cool around the Mediterranean and many other parts of the world. Passive cooling systems are not magic but they do require some careful design. Such systems may also require some assistance from the inhabitants of the home. They are quiet and they work very well!

    Location and exposure play a large part in overheating problems. For example, homes with an unobstructed southern exposure will be heated by the sun more than those in a shaded area or those with a northeaster exposure. This may save in winter heating costs but it may also require some summer cooling systems. The design of the home is often a major contributing factor in such cases. Yet, relatively simple design modifications are almost always possible solutions to such overheating problems. And energy consuming air conditioning systems are rarely required nor are they the most desirable method to keep homes cool in temperate zones.

  • The best way to shade the house is by stopping the rays of the sun from hitting the house surface, especially glass surfaces. Exterior shades are the answer. Interior shades are not very effective because they do not stop the conversion of light energy into heat energy, a process which occurs when light hits solid surfaces e.g. glass. Shading along the South side of a building can be in the form of an awning since the angle of the sun is relatively high when the sun is located in the Southern horizon. Exterior shades are required at east and west facing windows. Awnings do not work as well at East and West facing windows due to the very low morning and afternoon sun angles.

  • Deciduous trees located along the side of the house which require shading, (that is the South, East and West sides of the house), make for an ideal natural shading system. They provide maximum shading during the hottest times of the year, and allow for solar heating during the winter months. The ideal deciduous tree selection would be one which can be pruned into the desired configuration, i.e., a shape which maximizes the desired shading.

    The disadvantages of using natural shading have to do with the time that it takes to grow the trees, and the need for maintenance and gardening work and the additional gutters and roof cleaning. The impact on views must also be considered.

  • The least expensive and most versatile shading system is an exterior roll up shade such as a bamboo shade mounted under the eve of the house.

    In condominiums, permission from the condominium home owners association may be required to mount an exterior shading system. Where exterior shades are not possible, an interior shading system is an alternative but second best choice.

    exterior shutters

    Windows in Venice and in most other parts of the Mediterranean have exterior shutters. Its part of the local "air-conditioning" system.

    The building in back (top right side) has adjustable canvas awnings. The stores and some of the windows have roller shutters, used for shading and security. The most traditional style can be seen at the windows in the center - louvered shutters.

    (Note the local window delivery system.)

    On South facing windows, large overhangs, trellises, awnings and similar devices work well to block the high sun angles in the Southern sky. Shades are required to block the low morning sun angels on west and east facing windows. Retractable systems will also allow for some solar gain in the winter time, and additional light when desired.

    The important factor to keep in mind is that sunlight is converted to heat energy when it strikes the glass (and other objects). Exterior shades and awnings work best because such systems block the sunlight before it's conversion to heat.

  • Convection ventilation example drawing

    The fact that warm air rises can be used to develop a non-mechanical cooling system. The ideal self cooling home has a high operable window, skylight or vent which allows the rising warm air to escape from the house and to "pull" cooler air behind it. This cooler air comes from a low operable window or vent located in a shaded part of the house, for example, a north wall.

    This system works particularly well in tall, narrow houses, and is hardest to accomplish in wide, flatter houses such as ramblers. The shape and design of a house will dictate the best location and numbers of operable windows and skylights.

    Source: Passive Solar Energy in Washington: results of the Washington Passive Solar Design/Build Competition, Washington State Energy Office, March 1982, Van and Van Horne Architects and George Guttmann, General Contractor.

  • Good quality operable skylights are one of the best ways to keep homes cool. They allow warm air to escape from high ceiling locations and that in turn can pull cool air from shaded and cool areas into the house. Such convection action work like a fan but better:

    • They don't require a motor.
    • They don't use electricity.
    • They don't make noise.
    • They can add light to a dark area of the house.
    • And most homes can be retrofit with an operable skylight for less cost than an air conditioning unit for a single room.

    I have them in my home, I use them all the time, I love them and I love to recommend them to people who's homes need cooling systems!

    Here are a few tips:

    • The best location for such skylights is on the side opposite of the prevailing winds. This helps draw air out of the house.
    • A single skylight in the middle of the house can help cool the whole house.
    • If the house has two floors and an open staircase then a centrally located skylight in the 2nd floor hallway will work very well.
    • A home on a single story may require more than one operable skylight. It may not have less vertical space to create a good convection current.
    • An operable skylight in a bathroom can double as a moisture venting system. It is more tolerant of rain entry if the skylight is left wide open during a rain storm.
    • Size is not as important as location.
    • The best time to add an operable a skylight is when new roofing is installed or when the roofing is relatively new and flexible.
    • Most operable skylights are designed not to allow for rain entry when left partially open. We have an operable skylight at our cabin and leave it partially open from May till October - no problem.
    • Some manufacturers of operable skylights provide optional shading and screening systems.
    • Some fancy models open and close with small motors and can be programed with thermostats, rain detectors and all sorts of fancy equipment. (I prefer the long pole or crank.)
    • See the consult question and answers on Windows and Skylights.

    and a note from a satisfied customer...

    George -

    Thank you so much for the suggestion of putting in operable skylights in our town home. They have absolutely saved us through the hot summer with the increased ventilation. With our tower of a house it really helps regulate the temperature. We end up having the bathroom skylight open almost all the time.

    Thanks again for all the great advice! Shannon H