 |
 The
text and illustrations from this page have been reprinted
from Passive Solar Energy.
Every material and principle incorporated into passive solar
design is common and in everyday use. The melting of an ice
cube or the ability of a stone to stay warm long after sunset—these
are the kind of considerations on which all passive design
is based.
The trick is to learn the labels so that it is easier to understand
and discuss. Then you can say "thermal mass" instead
of having to say (each time you discuss the phenomenon) "the
ability of a stone to stay warm long after sunset".
Air stratification |
Air
stratification
Then tendency of heated air to rise and to arrange itself
in layers with the warmest air at the top.
British thermal unit (Btu)
A measure of energy. It is the amount of heat necessary to
raise one pound of water one degree Fahrenheit. Heat loss
and gain can be measured in Btus per hour and BTUs per year.
Conduction |
Conduction
The transfer of heat between objects by direct contact.
Degree Day
A unit used to measure the intensity of winter. The more degree
days there are in total for the season, the cooler the climate.
Evaporative Cooling |
Evaporative
Cooling
Natural cooling caused by water's ability to absorb heat as
it vaporizes.
Glazing |
Glazing
Layers of glass or plastic, used in windows and other solar
devices for admitting light and trapping heat.
Insulation
Materials that conduct heat poorly and thereby slow down heat
loss from an object or space.
Insulation |
Mean
Radiant Temperature
The average temperature you experience from the combination
of all the various surface temperatures in a room: walls,
floors,
Mean Radiant Temp. |
ceilings,
furniture, and people.
Movable insulation
Insulating curtains, shutters, and shades that cover windows
and other glazing at night to reduce heat loss.
Convection |
Natural
convection
The movement of heat through the movement of air or water.
Phase Change |
Phase-change storage materials
Meltable materials store heat when they change phase from
solid to liquid form, and release that heat when they solidify.
The heat released is called the "heat of fusion."
These
materials require less mass (and volume) to store the same
amount of thermal energy than more conventional heat-storage
materials. Only small changes in temperature are necessary
to induce the phase change.
Reflectors |
Reflectors
Shiny surfaces for bouncing sunlight or heat to where it's
needed.
R-Value |
R-Value
A measure of the insulating ability of any material or group
of materials such as make up a wall or ceiling. The higher
the R-value the better the insulation and the slower the heat
loss.
Shading |
Shading
Measures for blocking out unwanted sunlight that can overheat
the house.
Thermal
mass |
Thermal
mass
Materials
that store heat. Heavy dense materials—concrete, stone,
and even water—store a lot of heat in a small volume
(compared with most lightweight materials) and release it
when needed.
Thermal radiation
The transfer of heat between objects by electromagnetic radiation.
Thermal
Radiation |
U-Value
A measure of the rate of heat loss through a wall or other
part of a building. It is the reciprocal of the total R-values
present. The lower the U-Value, the slower the heat loss.
Windows
Windows let light (and heat) in (and out).
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Copyright © 2002 Wendy M. Mathias
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