Good Solar Design
Light and thermal energy are gained in a solar home or room through
radiation. The transfer of that energy takes the form of convection.
A properly designed space must allow the correct amount of light in
and control the amount of energy dissipated.
Insulation allows for the containment of energy taken in. Radiation
absorption can be increased passively with color. The albedo of an
object refers to how strongly it reflects light (Figure 5-14). For
example, a white surface will reflect sunlight almost nine times
more than a black surface. This means that your thermal mass, the
area that stores heat energy, should be dark in color. A
light-colored floor or wall may rise in temperature to 80 or 90°F,
but a dark-color thermal mass can rise in temperature to 130 or
140°F.
Types of Solar Gain
In indirect solar gain, heat enters the building through an aperture
and is captured and stored in a thermal mass. The mass then slowly
and indirectly heats the building through conduction and convection.
Isolated solar gain is a separate space, such as a sunroom, in which
the solar energy is captured and then passively moved as heat
through the living space by natural convection.
A third type of solar gain, concentrated solar power (CSP), was
reviewed in Chapter 3. While most applications are large commercial
structures, consumers can use CSP water heaters in their homes. CSP
is best in warm climates where sunlight is a constant and rainfall
is low.
Simple Improvements for Solar Gain
Every homeowner and renter can make simple home improvements to
increase the passive solar energy available and used in the home.
Keeping in mind the five elements required for passive solar,
consider the following. The thermal mass in most homes is already in
place and will not change. This solar storage will be a floor or
wall. The larger and more dense the mass, the more heat storage is
available. You can also change the color to absorb more heat energy.
For most homes, the aperture is in the form of windows or skylights,
and the control will be some type of shade.
Heat and Light Transfer Through Windows
The solar heat gain coefficient (SHGC), shown in Figure 5-15, refers
to the percentage of solar radiation that passes through a window
and is expressed in a value of 0 or 1. The higher the SHGC, the more
solar gain in the home.
The visible light transmission (VT), shown in Figure 5-16, refers to
the amount of light transmitted through a window and is also
measured by values between 0 and 1. A window with a VT of 1 will
allow no loss of transmission. The use of a second pane of glass or
a coating will lower the VT value.
Low-E coatings, which stands for low emissivity, refers to the
relative ability of a surface to emit energy by radiation. A Low-E
coating for windows refers to a thin metallic or metallic oxide
layer deposited on one of the glass surfaces (Figure 5-17). Heat
gained or lost through a window is due to radiation from either
outside-in or inside-out. The coating reflects a portion of the
radiation, reducing heat flow through the window. The coating is
normally invisible to the homeowner. Low-E is also rated on a scale
of 0 to 1. A black object would have an emissivity of 1, absorbing
all light, and a perfect reflector would have a value of 0.
Source: Solar Power for Your Home by David S. Findley