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A Closer Look

Passive Solar Design
assive solar application is an economi- lator, so windows must have curtains or can place carpets and furniture as they wish.
Pcally justifiable use of solar energy movable insulation panels to slow energy Controls to prevent energy loss at night are
today. Passive solar design uses a structure’s loss at night. This requires the daily activ- still necessary with this design.
construction to heat a living space with ity of closing curtains or moving insulation An isolated solar gain home uses a
solar energy. There are few electric fans, panels at night and then opening curtains structure that is separated from the liv-
motors, or other energy sources used. The and moving panels in the morning. Passive ing space to collect and store solar energy.
passive solar design takes advantage of free solar homes, therefore, require a high level Examples of an isolated gain design are
solar energy; it stores and then distributes of personal involvement by the occupants. an attached greenhouse or sunporch (Box
this energy through natural conduction, There are three basic categories of Figure 4.3). Energy flow between the
convection, and radiation. passive solar design: (1) direct solar gain, attached structure and the living space
In general, a passive solar home makes (2) indirect solar gain, and (3) isolated can be by conduction, convection, and
use of the materials from which it is con- solar gain. radiation, which can be controlled by
structed to capture, store, and distribute A direct solar gain home is one in which opening or closing off the attached struc-
solar energy to its occupants. Sunlight solar energy is collected in the actual living ture. This design provides the best controls,
enters the house through large windows space of the home (Box Figure 4.1). The since it can be completely isolated, opened
facing south and warms a thick layer of advantage of this design is the large, open to the living space as needed, or directly
concrete, brick, or stone. This energy window space with a calculated overhang, used as living space when the conditions
“storage mass” then releases energy dur- which admits maximum solar energy in the are right. Additional insulation is needed
ing the day and, more importantly, during winter but prevents solar gain in the sum- for the glass at night, however, and for sun-
the night. This release of energy can be by mer. The disadvantage is that the occupants less winter days.
direct radiation to occupants, by conduc- are living in the collection and storage com- It has been estimated that building
tion to adjacent air, or by convection of ponents of the design and can place nothing a passive solar home would cost about
air across the surface of the storage mass. (such as carpets and furniture) that would 10 percent more than building a traditional
The living space is thus heated without interfere with warming the storage mass in home of the same size. Considering the
special plumbing or forced air circulation. the floors and walls. possible energy savings, you might believe
As you can imagine, the key to a success- An indirect solar gain home uses a that most homes would now have a passive
ful passive solar home is to consider every massive wall inside a window that serves solar design. They do not, however, as most
detail of natural energy flow, including as a storage mass. Such a wall, called a new buildings require technology and large
the materials of which floors and walls Trombe wall, is shown in Box Figure 4.2. amounts of energy to maximize comfort.
are constructed, convective air circula- The Trombe wall collects and stores solar Yet, it would not require too much effort to
tion patterns, and the size and placement energy, then warms the living space with consider where to place windows in relation
of windows. In addition, a passive solar radiant energy and convection currents. to the directional and seasonal intensity of
home requires a different lifestyle and liv- The disadvantage to the indirect solar gain the sun and where to plant trees. Perhaps
ing patterns. Carpets, for example, would design is that large windows are blocked by in the future you will have an opportunity
defeat the purpose of a storage-mass floor, the Trombe wall. The advantage is that the to consider using the environment to your
since they would insulate the storage mass occupants are not in direct contact with the benefit through the natural processes of
from sunlight. Glass is not a good insu- solar collection and storage area, so they conduction, convection, and radiation.

Sunlight
Sunlight
Convection
Convection
Trombe
Sunlight wall
Reradiated energy

Storage mass
BOX FIGURE 4.1 The direct solar gain BOX FIGURE 4.2 The indirect solar BOX FIGURE 4.3 The isolated solar
design collects and stores solar energy in the gain design uses a Trombe wall to collect, gain design uses a separate structure to
living space. store, and distribute solar energy. collect and store solar energy.

4-17 CHAPTER 4 Heat and Temperature 101