Energy-efficient interior design

This traditional-style house in Illinois uses 50 percent less energy for heating and cooling than comparable homes. It is part of the Department of Energy's Energy Star Program, which emphasizes high efficiency appliances, electronics and building materials. -- DOE Photo.

Energy-conscious interior design is the designing and planning of rooms and specification of materials with the goal of reducing energy consumption in a home. Energy-conscious occupants focus on ways to make their homes thermally comfortable while reducing energy consumption.

Energy-conscious design combines conservation methods, such as insulation and thermostat set-back, with passive solar heating. This design approach can be applied to both newly built homes and older homes. It involves first making the home as energy conserving as possible, then supplying the remaining heating needs with solar heat by increasing the number of windows on the south side to collect heat (and possibly reducing the number of windows on the north and west sides), using thermal mass to store heat, and properly designing and placing walls and furnishings to allow distribution of heat.

Storage of solar heat occurs in a dense mass material such as concrete, brick or water. Most mass materials are hard surfaces that reflect sound. Combining the hard thermal mass with a large expanse of window glass gives you many sound-reflecting surfaces. Therefore, if not absorbed by proper materials, noise can become a problem. Furniture design should enhance air circulation, and furniture placement should allow maximum exposure of the thermal mass to the sun.

Color

The lightness or darkness of a color affects whether it can absorb or reflect heat and light. Generally, light values---tints of a hue such as beige, pink or cream--- are used to reflect heat from a lightweight thermal mass, such as furniture or ceilings, to a more efficient mass that stores the heat, such as a brick wall. The use of light values to reflect heat can be balanced by dark value colors on the thermal mass.

The color used in a room can make you feel warmer or cooler. Generally, reds, oranges and yellows are considered warm colors. These would be used where the actual room temperature is cooler, such as on the north side of the house where there is no direct sunlight. The cool greens, blues and violets should be used in rooms with southern or even western exposure.

Photo: Paint Quality Institute

Thermal Mass

The thermal mass added to a house enables the solar heating system to work properly. Mass, in the form of a dense material, absorbs heat during the daytime to prevent overheating. lt then stores the heat until the air temperature of the room drops when the sun goes down. Then the heat is naturally released from the mass material, warming the interior throughout the cool night. This same natural process occurs in the passive solar home, except that the heat is trapped by the walls or floors of the house and used to warm its occupants. (Insulation is closed across the windows at night to keep the heat inside.)

A mass material's effectiveness is measured by its ability to absorb sunlight, conduct surface heat into its mass and hold the resulting heat. Mass materials vary greatly in the amount of heat they retain. Frequently, older structures are not designed to support the weight of additional thermal mass. Lightweight, efficient mass is suggested for many installations.

The percentage absorption varies according to material, color, and finish or texture. The best thermal mass materials would seem to have a dark-colored, rough, matte surface.

Of equal importance is the need to place furniture so that it shades the mass floor or wall as little as possible. The general rule of thumb is to shade less than 30 percent. This will still allow maximum effectiveness for heat absorption and release. The furniture also should be raised off the floor slightly so air can circulate. This means no wall-to-wall carpeting; no large sectional sofa; no skirted sofas that shade mass floors; no bookcases on mass walls; and no secretaries or armoires on mass walls.

Conclusion

Fine tuning your energy-conscious interior design will take some effort, but it will allow you to reduce energy consumption without losing design quality. Here is a list of additional energy conservation measures that are possible through appropriate interior design:

1. Covering walls with fabric, gathered on a rod top and bottom (be sure to flame-proof the fabric).
2. Using closets as buffers on north or west walls.
3. Adding a heat lamp to a bathroom to take the chill off on cold mornings.
4. Using thermal wallpaper to insulate, foil wallpaper to reflect heat back into the interior.
5. Using filled bookcases on outside, non-mass walls to act as insulation.
6. Using large decorative area rugs, tapestries or fabric wall hangings on outside, non-mass walls to add insulation.
7. Using carpet and a good pad to reduce heat transfer through floors, in addition to keeping bare feet warm.
8. Using high-back, overstuffed furniture in northern rooms to reduce drafts and allow one to become engulfed (snuggle) in the chair.
9. Using furniture with skirts where drafts need to be avoided.
10. Using a reversible ceiling fan to pull the air up in the winter to circulate the warm ceiling-level air without any draft on the occupant (particularly those fans placed directly over a seating area). Then reverse it for summer so the air flows across an occupant, cooling by evaporation.

Here is a list of products and where to find them to help conserve energy:

1. Movable insulation: designed to cover and insulate windows on the interior; can be found at fabric stores, energy stores, drapery shops and some lumber yards.
2. Mini-blinds: used to reflect sunlight and focus daylight; can be found in most department or drapery stores.
3. lnsulated decorative ceiling tiles: added to the ceilings as insulation; can be found in lumber yards and energy stores.
4. Thermal wallpaper: used to add insulation to outside walls; can be found in energy stores, lumber yards and some wallpaper stores.
5. Vinyl wallpaper: used as a vapor barrier on outside walls; found in wallpaper stores.
6. Patterned and dyed concrete floors: used as a thermal mass, cheaper than tile floor and aesthetically pleasing; inquire of local contractors.
7. Area rugs: used on north walls to insulate, in buffer areas to insulate or add psychological warmth; can be found in department and carpet stores.
8. Quarry tile, ceramic tile, brick veneer or paving brick: used as a decorative treatment and additional mass over the thermal mass floor or wall; can be found at building supply firms and some lumber yards.
9. Fluorescent lighting fixtures: used to replace some incandescent fixtures, especially in bathrooms, kitchens and utility rooms; can be found in electrical and lighting supply stores. Pictured above in an outdoor lighting fixture with fluorescent bulb.
10. Other energy-conscious design products can be found in energy stores or order the Solar Age Resource Book, Everest House, 1133 Avenue of the Americas, New York, NY 10019.

This information comes from Michigan State University Extension bulletin E-1771, Energy-Conscious Interior Design.