Claudette Reichel | 7/22/2008 12:40:07 AM
In the Gulf Region, designing for the climate means reducing summer heat gain as first priority. Orientation (which direction your home faces) and careful planning of space are free ways to cut energy costs as well as to make your home more functional and pleasant. (Figure 1, Seasonal Sun Paths)
Helpful online tools that customize energy-saving recommendations by location are available at www.energystar.gov and
Landscaping for energy savings: Even with roof overhangs, a great deal of solar heat gain on the west, east, southwest and southeast sides of a house can occur from the rising and setting sun. Cooling demand can be greatly reduced by providing shade structures, trees and shrubs on these sides of a house. Deciduous trees (ones that lose their leaves in winter) are preferred to provide shade in the summer and let in winter sunlight. (Figure 2, Energy-saving Landscape Plan)
Pavement reflects and radiates heat that it absorbs from the sun. Avoid unshaded pavement near the house. Small shrubs, ground cover and non-reflective mulches keep the area around the house cooler and reduce reflected heat.
In winter it can be helpful to deflect cold north winds over or around the house with an evergreen barrier.
Overall house design: The more surface area the building envelope has the more heat gain and loss. The closer the plan is to a square (or circle), the less exposed surface area there is for the same living area. Space-efficient design with open planning can help save energy by reducing the overall size of a house. Open planning saves on room clearance and pathways while making areas appear and feel larger.
Kitchen and laundry room’s house heat-producing appliances so don’t place them on the west side to avoid compounding the afternoon heat buildup. Locating kitchens and living areas for northern or southern exposures can provide a lot of natural daylight without a lot of heat gain. Placing the washer, dryer and freezer outside of conditioned space can reduce cooling loads even further.
Supplement a compact house design with porches, patios or other planned outdoor areas to extend the living space outside the conditioned space. The ideal is to include a shaded area on the north side for summer use and an area on the south side for winter use.
Design to minimize solar heat gain: West- and east-facing glass can have nearly five times the solar heat gain of north-facing glass, and more than triple that of south-facing glass. Although the amount of radiant heat at west and east exposures is the same, west is most important to protect because it occurs during the hottest time of the day. Design to minimize west and east glass and wall surface, and shade it. Try to place most of the home’s glass area within 20 degrees of due south or north. (Figure 3, Solar Heat Gain) (Figure 4, Orientation of House for Solar Control)
Skylights are not generally recommended because they receive too much sun and are difficult to shade. Light tubes (domed glass roof fixtures coupled with an insulated reflective tube) are an exception. They can provide a lot of diffuse, reflected light without the heat gain, but must be correctly installed to prevent leaks and should be storm resistant.
Choosing roofing and siding colors with good solar reflectance (25% or more) can result in tangible cooling energy savings. This is particularly true for roofing materials such as light-colored tile and metal, now available with solar reflectances up to 75%. Dark colors generally absorb heat from sunlight, whereas light surfaces reflect heat and reduce cooling costs. A new option is a “cool color” metal roof coating or shingle granule technology that gives darker colors the heat reflectance of light colors.
ENERGY STAR labeled roofings have a solar reflectance of at least 25% (for sloped roofs). For optimal performance in a hot climate, choose a roofing with a high solar reflectance (> 50%) and a high emissivity (> 80%). Materials, such as painted metal, with high emissivity release heat more rapidly to the atmosphere (cool off at night) than low-e materials (like unpainted metal). (Figure 5, Light Tube)
Design for passive solar winter benefits: A passive solar home is designed to admit and store energy from the sun in winter for solar heating. To even out temperature swings, south-facing glass (with overhangs sized to admit winter sun) on the main living space should be coupled with thermal mass, such as tile or brick on a slab floor or a masonry partition wall. The best performing thermal mass is relatively thin and spread out, covering an area in the room about six times the south-facing glass area. The thermal mass must receive direct sunlight, but it is not necessary for sunshine to reach all of it. (Figure 6, Overhang for South-facing Windows) (Figure 7, Passive Solar Design With Thermal Mass).
Design for mild seasons: When the outside humidity is not high in spring and fall, a home designed with good cross ventilation can be comfortable without air conditioning. Wing walls can be designed to capture breezes from the east/southeast and deflect them into south windows. Room arrangements should allow flow through ventilation. A screened porch should be open on three sides for ventilation or in a breezeway for maximum comfort and use. (Figure 8, Cross Ventilation Aided by Wing Wall)