First Principles - Sustainable Design: The Science of Sustainability and Green Engineering - page 51

the temperature in urban areas by more than 10 ◦ F compared to surrounding
undeveloped areas. Strategies against the effect include the use of shade and
high-albedo (i.e., highly reflective) materials. It is also preferable that these
materials, especially on roofs, have a relatively high emissivity value (i.e., the
rate at which absorbed energy is radiated away from an object (see Table S2.1).
Thus, the choice of building materials, roofing materials, ground cover, urban
forests, planted medians, and other strategies can reduce the heat island effect
and reduce the number of cooling degree-days, which translates to less energy
use required to maintain thermal comfort inside buildings. It can also flatten
the peak demand for electricity, so that power plants can run more efficiently.

Table S2.1 Albedo and Emissivity of Various Building Materials

Material Albedo Emissivity

Concrete 0.3 0.94

Tar paper 0.05 0.93

Bright galvanized iron 0.35 0.13

Bright aluminum 0.85 0.04

Aluminum paint 0.80 0.27-0.67

White single-ply roofing 0.78 0.90

Black EPDM roofing 0.045 0.88

Gravel 0.72 0.28

Source : James I. Seeley, “The protocols of white roofing,” The Concrete
Specifier , November 1997.

LIGHT POLLUTION AND TRESPASS

Light pollution and light trespassing is another EMR factor important to
the consideration of development and site selection because of their negative
impact on nocturnal life. Urban, suburban, and even rural areas are not nearly
as dark as decades ago, due to the diffusion of light. Poor choices of lighting
systems include those that distribute light waves upwardly. Better choices are
those that target more intensely areas needing light (e.g., safe corridors in
parking lots, parks, other public places).
Electromagnetic radiation is discussed further in Chapter 7.

Returning to potential energy and kinetic energy, potential energy is lost
when the elevation of a body is decreased. The lost potential energy is usually
converted to kinetic energy. If friction and other nonconservative forces are
absent, the change in potential energy of a body is equal to the work needed to