Glossary
Active
Solar System: A
system that uses mechanical devices and an external
energy source in addition to solar energy, to collect,
store, and distribute thermal (heat) energy.
Advection:
The horizontal transport of air along the earth's
surface felt as the wind. Also serves to transfer
temperature and humidity characteristics from one region to another
(e.g., the sea breeze is one form of advection).
ASHRAE:
American Society of Heating, Refrigeration
and Air Conditioning Engineers
Angle
of Incidence:
The angle created by incoming radiation and
a line perpendicular to an intercepting surface.
Bead
Wall:
A form of movable insulation using
pea-sized balls of polystyrene alternately blown into
and vacuumed out between a double-glazed panel during
the diurnal cycle.
BTU
(British Thermal Unit):
A measurement of energy representing the
amount of heat needed to raise 1 pound of water by 1
degree Fahrenheit. About the same amount of energy
released by a single lit match.
Clerestorey:
A vertical roof window placed that is used
for light, ventilation, and to collect heat.
Conduction:
The distribution of heat or coolness
through a material. The rate of conduction is dependent
on the ability of molecules to receive and pass on
energy.
Convection,
Natural: Heat transfer through a medium, such as
air or water, by currents that result from the rising of
lighter, warmed medium and the sinking of heavier, cool
medium.
Convection,
Forced:
Heat transfer through a medium, such as air
or water, by current, caused by a device powered by an
external energy source.
Cooling
Degree-Day:
Refer to "degree-day."
Degree-Day:
Term referring to the number of units
(degrees) that the average outdoor temperature falls
below or exceeds a base value (usually 65° F) in a
given period of time. Each degree that the mean daily
temperature is above the base value is called a cooling
degree day (CDD) unit. Each degree that the mean daily
temperature is below the base value is called a heating
degree-day (HDD) unit. The monthly CDD & HDD values
are simply the sum of the individual CDD and HDD units
for the days in the month. Degree-days are reasonably
good indices of the heating and cooling requirements of
buildings.
Diurnal:
Daily
Glazing:
A glass, plastic or transparent/translucent covering.
Greenhouse
Effect:
The build-up of heat in an interior space
caused by energy input through a transparent membrane
such as glass.
Heat
Capacity:
A measurement of the specific heat of a material
multiplied by its density. See "specific
heat."
Heating
Degree-Day:
Refer to "degree-day"
Heat
Sink:
A body which is capable of accepting and
storing heat or cool and, therefore, may also act as a
delayed heat source.
Hybrid
Solar System:
A system that combines passive solar
collection with active elements for transport of heat to
an isolated storage system.
Infiltration:
The uncontrolled flow of air into, and out
of, a building through cracks, openings, doors, or other
areas which allow air to move.
Insolation
(Incident Solar Radiation):
A term denoting the amount of solar
radiation (all wavelengths) which strikes the earth. The
basic unit of measurement is the Langley, a unit of heat
energy equivalent to one calorie falling on one square
centimeter of surface. One BTU per square foot is the
equivalent of 0.27125 Langley.
Inversion:
A reversal of the normal atmospheric situation where the
temperature decreases with height. Under inversion
conditions, the atmosphere actually gets warmer with
height. Atmospheric conditions associated with inversion
conditions are the absence of wind and hazy, smoggy
views associated with trapped air pollutants.
Microclimate:
The climate of a defined local area, such
as a house or building site, formed by a unique
combination of wind, topography, solar exposure, soil
and vegetation of the site.
Precipitation:
Water, in either liquid or solid form,
which falls from clouds. Includes rain, hail, sleet,
snow, etc.
Radiant
Energy:
Low temperature infrared energy emissions
from the sun.
Radiation:
Along with convection and advection, one of
the three major processes in transferring heat energy
from place to place. In the radiation process, heat is
transferred in the form of waves of energy. The sun
transfers its heat and light energy to the earth by this
process. The earth loses heat to space by this process.
Radiation
Fog:
A low-lying fog formed when the ground
loses heat to space by radiation to the point where it
becomes cooler than the air, which lies above. The
overlying air is then cooled to the dew point by contact
with the cold surface causing a dense fog to form. Tule
fogs in the Central Valley are formed by this process.
Relative
Humidity:
A measure of the ability of air to hold
gaseous water vapor. The warmer the air, the more water
it can hold. Relative humidity is usually expressed as a
percentage of saturation: 0% = totally dry air, and 100%
= fully saturated air. Relative humidity becomes
important for human comfort as at high values
perspiration is not readily evaporated and thus
discomfort is felt. Relative humidity is also important
from the standpoint of the atmosphere's ability to lose
heat to space at night (water vapor absorbs and retains
heat exceedingly well). Drier climates thus have a
greater potential for night ventilation cooling than do
more humid ones.
Roof
Ponds:
Passive heating/cooling system. Enclosed
water above and in immediate contact with ceiling
elements, with movable insulation, which expose ponds to
the winter sun for heating, and to the night sky for
summer cooling.
Solar
Constant:
The amount of heat energy delivered by
solar radiation to a square foot of material set
perpendicular to the sun's rays for one hour at the
outer edge of the earth's atmosphere.
Solar
Radiation:
See "insolation."
Specific
Heat:
The amount of heat, measured in BTU's for a
given mass. a material can hold when its temperature is
raised one degree Fahrenheit.
Thermal
Chimney:
An air heating device that provides a
constant vacuum which may be used to vent the house,
bring warm air from collectors, or pull air from cool
towers, earth tubes or rock bed coolers. This creates
what is called a "stack effect."
Thermal
Energy:
Heat energy
Thermal
Storage Mass:
A thermal element that has heat or cooling storage
capacity in a given assembly or system. Water storage
tanks. concrete floors, rocks, and masonry are examples
of thermal mass.
Trombe
Wall:
A concrete, stone or masonry wall that has
vents at regular intervals both along the floor and just
below the ceiling. The exterior. south-facing side is
dark in color and fronted with glass. Air is warmed
between the glass and wall and circulates by convection
through the vents. It is named after Dr. Felix Trombe,
one of it, developers.
Vestibule:
An enclosed, double entryway into a
structure.
Water
Walls:
A passive heating and cooling technique for
collecting and controlling solar energy, usually fronted
by glass. Water walls are usually water-filled
containers exposed to or protected from the sun
depending on mode (heating or cooling). Wintertime use
is to collect
and store heat, which is used to warm a living space.
Summer use is to absorb unwanted internal heat, thereby
cooling the interior, and dissipating the heat at a
later time.
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