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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