Absorber
The blackened surface in a collector that absorbs the solar
radiation and converts it to heat energy.
Absorptions The ratio of solar energy absorbed by a surface
to the solar energy striking it.
Active System A solar heating or cooling system that
requires external mechanical power to move the collected heat.
Air System Solar domestic hot water systems employing
air-type collectors are available. Hot air generated by these
collectors is fan forced through an air-to-liquid heat exchanger
with the potable water being pumped through the liquid section of
the exchanger. The heated water is then circulated through the
storage tank in a similar fashion to the liquid collector system.
Air does not need to be protected from freezing or boiling, is
non-corrosive, and is free. However, air ducts and air handling
units require greater space than piping, and air leaks are
difficult to detect.
Air-Type Collector A
collector that uses air as the heat transfer fluid.
Altitude The angular distance from the horizon to the sun.
Ambient Temperature The temperature of the surrounding air.
Auxiliary Heat The extra heat provided by a conventional
heating system for periods of
cloudiness or intense cold when a solar heating system cannot
provide enough.
Azimuth The angular distance between true south and the
point on the horizon directly below the sun.
British Thermal Unit (BTU)
The quantity of heat needed to raise the temperature of one pound
of water one degree Fahrenheit.
Calorie The
quantity of heat needed to raise the temperature of one gram of
water one degree Celsius.
Coefficient of Heat Transmission The rate of heat loss in
BTU per hour through a square foot wall or other building surface
when the difference between indoor and outdoor air temperatures is
one degree Fahrenheit.
Collector A device that collects solar radiation and
converts it to heat.
Collector Efficiency The ratio of usable heat energy
extracted from a collector to the solar energy striking the cover.
Concentrating Collector A device which concentrates the
sun's rays on an absorber surface which is significantly smaller
than the overall collector area.
Conductance The rate of heat flow (in BTUs per hour)
through an object when a 1° F. temperature difference is
maintained between the sides of the object.
Conduction The flow of heat due to temperature variations
within a material.
Conductivity A measure of the ability of a material to
permit conduction of heat flow through it.
Convection The motion of fluid such as gas or liquid by
which heat may be transported.
Cover Plate A sheet of glass or transparent plastic placed
above the absorber in a flat plate collector.
Degree Day A
unit that represents a 1 degree F. deviation from some fixed
reference point (usually 65°F.) in the mean daily outdoor
temperature.
Design Heat Load The total heat loss from a house under the
most severe winter conditions likely to occur.
Design Temperature The temperature close to the lowest
expected for a location, used to determine the design heat load.
Diffuse Radiation Indirect sunlight that is scattered from
air molecules, dust and water vapour.
Direct Radiation Solar radiation that comes straight from
the sun, casting shadows on a clear day.
Drain down System Potable water is circulated from the
storage tank through the collector loop. Freeze protection is
provided by solenoid valves opening and dumping the water at a
preset low temperature. Collectors and piping must be pitched so
that the system can drain down, and must be assembled carefully to
withstand 100 psi. city water line pressures. Pressure reducing
valves are recommended when city water pressure is greater than
the working pressure of the system.
Drain back System The solar heat transfer fluid
automatically drains into a tank by gravity. Drain back systems
are available in one or two tank configurations. A heat exchanger
is necessary, because the city inlet pressure would prevent
draining. The heat transfer fluid in the collector loop may be
distilled or city water if the loop plumbing is copper. If the
plumbing is threaded galvanized pipe, inhibitors may be added to
prevent corrosion. Most inhibitors are non-potable and require a
double wall heat exchanger. The pump used must be sized to
overcome static head.
Emittance A
measure of the propensity of a material to emit thermal radiation.
Eutectic Salts A group of materials that melt at low
temperatures, absorbing large quantities of heat.
Evacuated tube collector A high efficient solar collector,
converts
direct and diffused solar radiation through a special collector
plate and a rapid heat transfer channel the heat pipe in an evacuated
glass tube.
Flat Plate Collector A
solar collection device in which sunlight is converted into heat
on a plane surface without the aid of reflecting surfaces to
concentrate the rays.
Forced Convection The transfer of heat by the flow of
fluids (such as air or water) driven by fans, blowers or pumps.
Galvanic Corrosion A
condition caused as a result of a conducting liquid making contact
with two different metal which are not properly isolated
physically and/or electrically.
Getters A column or cartridge containing an active metal
which will be sacrificed to protect some other metal in the system
against galvanic corrosion.
Gravity Convection The natural movement of heat that occurs
when a warm fluid rises and a cool fluid sinks under the influence
of gravity.
Headers
The pipe that runs across the edge of an array of solar
collectors, gathering or distributing the heat transfer fluid
from, or to the risers in the individual collectors. This insures
that equal flow rates and pressure are maintained.
Heat Capacity
A property of a material denoting its ability to absorb heat.
Heat Exchanger A device, such as a coiled copper tube
immersed in a tank of water, that is used to transfer heat from
one fluid to another through a separating wall.
Heat Storage A device or medium that absorbs collected
solar heat and stores it for use during periods of inclement or
cold weather.
Heat Storage Capacity The amount of heat which can be
stored by a material.
Heating Season The period from early fall to late spring
(in the northern hemisphere) during which additional heat is
needed to keep a house comfortable for its occupants.
Heat Pump A mechanical device that transfers heat from one
medium to another, thereby cooling the first and warming the
second.
Heat Sink A medium or container to which heat flows.
Heat Source A medium or container from which heat flows.
Hybrid Solar Energy System A system that uses both active
and passive methods in its operation.
Indirect System A
solar heating or cooling system in which the solar heat is
collected exterior to the building and transferred inside using
ducts or piping and, usually fans or ducts.
Infrared Radiation Electromagnetic radiation from the sun
that has wavelengths slightly longer than visible light.
Irradiation The total amount of solar radiation direct,
diffused and reflected-striking a surface exposed to the sky.
Insulation A material with high resistance (R-value) to
heat flow.
Langley A
measure of solar radiation; equal to one calorie per square centimetre.
Liquid Type Collector A collector using a liquid as the
heat transfer fluid.
Natural Convection See
Gravity Convection.
Nocturnal Cooling The cooling of a building or heat storage
device by the radiation of excess heat into the night sky.
One-Tank Closed-Loop System
A conventional D.H.W. tank, usually electrically heated, is
converted to a solar D.H.W. storage tank by installing an external
heat exchanger coil. The lower electrical element is removed,
leaving the uppermost of the usual two elements to provide
auxiliary water heating and to achieve good stratification
(layering of hotter water over progressively colder water).
Open System Some part of the System is open to the
atmosphere, or system contains fresh or changeable water.
Passive System A
solar heating or cooling system that uses no external mechanical
power to move the collected solar heat.
Percentage of Possible Sunshine The percentage of daytime
hours during which there is enough direct solar radiation to cast
a shadow.
Photosynthesis The conversion of solar energy to chemical
energy, by the action of chlorophyll in plants and algae.
Photovoltaic Cells Semi conductor devices that convert
solar energy into electricity.
Pyranometer An instrument for measuring solar radiation.
Radiant Panels
Panels with integral passages for the flow of warm fluids, either
air or liquids. Heat from the fluid is conducted through the metal
and transferred to the rooms by thermal radiation.
Radiation The flow of energy through open space via
electromagnetic waves, such as visible light.
Reflected Radiation Sunlight that is reflected from
surrounding trees, terrain or buildings onto a surface exposed to
the sky.
Refrigerant A liquid such as Freon that is use in cooling
devices to absorb heat from surrounding air or liquids as it
evaporates.
Resistance, or R Value The tendency of a material to retard
the flow of heat.
Retrofitting The application of a solar heating or cooling
system to an existing building.
Risers The
flow channels or pipes that distribute the heat transfer liquid
across the face of an absorber.
Seasonal Efficiency The
ratio, over an entire heating season, of solar energy collected
and used to the solar energy striking the collector.
Selective Surface A surface that absorbs radiation of one
wavelength (for example, sunlight) but emits little radiation of
another wavelength (for example, infrared); used as a coating for
absorber plates.
Shading Coefficient The ratio of the solar heat gain
through a specific glazing system to the total solar heat gain
through a single layer of clear double-strength glass.
Solar Constant The average intensity of solar radiation
reaching the earth outside the atmosphere; accounting to two
langleys or 1.94 gram-calories per square centimetre, equal to
442.4 BTU/hr/ft.², or 1395 watts/m².
Solar Radiation (Solar Energy) Electromagnetic radiation
emitted by the sun.
Specific Heat The quantity of heat, in BTU, needed to raise
the temperature of one pound of a material 1°F.
Standby Heat Loss Heat lost though storage tank and piping
walls.
Sun Path Diagram A circular projection of the sky vault,
similar to a map, that can be used to determine solar positions
and to calculate shading.
Thermal Capacity
The quantity of heat needed to warm a collector up to its
operating temperature.
Thermal Mass or Thermal Inertia The tendency of a building
with large quantities of heavy materials to remain at the same
temperature or to fluctuate only very slowly; also the overall
heat storage capacity of the building.
Thermal Radiation Electromagnetic radiation emitted by a
warm body.
Thermistor Sensing device which changes its electrical
resistance according to temperature. Used in the control system to
generate input data on collector and storage temperatures.
Thermosyphoning The process that makes water circulate
automatically between a warm collector and a cooler storage tank
above it. (See Gravity Convection).
Tilt Angle The angle that a flat plate collector surface
forms with the horizontal plane.
Trickle Type Collector A collector in which the heat
transfer liquid flows through metal tubes which are fastened to
the absorber plate by solder, clamps or other means. (See
Collector).
Tube-in-Plate-Absorber A metal absorber plate in which the
heat transfer fluid flows through passages formed in the plate
itself.
Tube-Type Collector A collector in which the heat transfer
fluid flows through metal tubes that are fastened to the absorber
plate with solder, clamps or other means. (See Collector).
Ultraviolet Radiation Electromagnetic
radiation with wavelengths slightly shorter than visible light.
