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8.2 Reducing Cooling Load: Opaque Surfaces & Overall

This part of the Energy Efficiency Manual lowers the cost of air conditioning by limiting the entry of unwanted solar heat through the opaque surfaces of the building structure, especially through roofs and large walls. In buildings such as warehouses, supermarkets, and department stores, this path for unwanted solar heat is more important than the cooling load caused by windows.

The heat of sunlight passes through opaque surfaces in a sequence of steps. First, sunlight is absorbed in the outer skin, raising its temperature. Then, the absorbed heat is driven through the structure by the temperature difference between the outer and inner surfaces. Once inside the envelope, the heat is transferred to the interior space by radiation, conduction, and convection.

Correspondingly, you can reduce air conditioning energy cost at each of these stages by using these methods:

• Prevent sunlight from reaching the outside surface by shading.
• Reflect the sunlight from the outside surface.
• Cool the exterior surface.
• Minimize the conduction of heat through the structure by effective insulation.
• Vent heat from the inside of the structure, especially from attics.

Here you will learn the details of the techniques that are economical and reliable. Insulation is the primary method of keeping heat from passing through the building structure. The appropriate insulation methods for roofs and walls are explained.

To reflect heat from surfaces, you can apply inexpensive reflective coatings. This can be tricky, and you will learn to do it correctly.

Effective ventilation of attic spaces is important, but it is rarely done well. Here you will learn how to ventilate attics to maintain the lowest possible temperatures, using ventilation fans, roof vents, turbine ventilators, and other methods.

For exterior shading, you will learn to shade buildings by planting trees, which is not as simple as it seems. You will learn to select the best species and locate them properly.