Useful Energy Glossary

If you’re looking for a list of energy related terms, look no further. Here you will find anything from air changes per hour to weatherstripping. This is a very handy list..


Above Grade – The portions of a foundation wall above ground level.

Absorber – The surface in a collector that absorbs solar radiation and converts it to heat energy. Generally, matte black surfaces are good absorbers and emitters of thermal radiation while white and metallic surfaces are not.

Absorption – The ratio of solar radiation absorbed by a surface to the amount that strikes it.

Active Solar Energy System – A system in which the collector and thermal storage components are separated and require a pump or fan to circulate the solar-heated fluid between them. The choice of location for active collectors is flexible; rooftops are commonly used.

Air Changes Per Hour (ACH) – The rate at which the volume of air in a home changes; the number of air changes per hour can vary from as low as .35 to as high as 5.

Airlock Entry – A vestibule enclosed with two relatively airtight doors that permits entry without extensive air or heat exchange.

Air Tube – The part of an oil furnace into which atomized oil and air are forced and mixed together, prior to entry into the combustion chamber.

Air-Type Collector – A collector that uses air as the heat transfer fluid.

Air Valve – A device used on one and two pipe steam distribution systems which allows trapped air to be vented from the system.

Altitude – One of two angles used to specify the sun’s position at any given time; altitude is the angle from the horizon to the sun.

Ambient Temperature – Temperature of the surrounding outside air.

Amperes – Standard units for measureing the rate at which electric current moves which determines the strength of the current.

Angle of Incidence – The angle at which direct sunlight strikes a surface. The angle of incidence affects the amount of energy absorbed by a solar collector. Sunlight with an incident angle close to 90 degrees perpendicular to the surface tends to be absorbed, while lower angles tend to reflect light.

Attached Ceiling – A type of ceiling which is attached directly to the joists. It is usually made form the same material as the interior wall surface.

Awning Window – A window which has one or more sashes that are hinged at the top and swing out at the bottom.

Azimuth – One of two angles used to specify the sun’s position at any given time; azimuth is the angle between south and the point on the horizon directly below the sun. South is 0 degrees and angles to the east and west are described as 0 to 180 E or 0 to 180 W.

Backflow Preventer – A device or other means to prevent reverse flow of a heat transfer fluid; a one-way valve often suffices.

Backup Heating System – A constantly available source of heat energy that is brought into operation when the solar system storage has been exhausted and the need for heat exists.

Balloon Construction – A type of wood from construction which uses a one-member sill platform, and a ribband to support floor joists, rather than individual platforms for each floor.

Band Joist – A board which rests on the sill and covers the outside surface of the joists, and the space between them. It is usually the same size as the joist, and is installed completely around the house.

Base Plate – The base for the wall in platform construction. It sits on the subflooring, and is also called the sole, or sole plate.

Bedding Strip – A strip of material between the sill and the foundation, used to compensate for the irregularities in the surface of the foundation, and hence to make a tight seal.

Betz Limit – The theoretical limit of 59.3% of the energy in a windstream that can be captured by a SWECS; this does not include the losses in conversion from mechanical to electrical energy.

British Thermal Unit – The amount of heat necessary to raise the temperature of one pound of water one degree Fahrenheit; a unit of heat reoughly equal to the amount of heat given off by burning a kitchen match.

Building Orientation – The relationship of a building to south. A building’s orientation is specified by the direction of its longest axis.

Bypass Loop – A piping arrangement that bypasses or circles the flow of a heat absorbing medium around rather than through a piece of mechanical equipment.

Casement Window – A window in which the sash is hinged on one side, and opens on the other by means of a crank or push rod.

Carbon Monoxide – A colorless, odorless, highly poisonous gas, produced by incomplete combustion of carbonaceous material

Caulking – Pliable materials used to reduce the passage of air and moisture by filling small gaps including at fixed joints of the building, underneath bareboards in a building, in exterior walls and electric outlets, around pipes and wires entering a building, and around dryer vents and exhaust fans in exterior walls. Caulking includes, but is not limited to, materials commonly known as sealants, putty, and glazing compounds.

Cavity Walls, Ceilings, and Floors – Walls, ceilings, and floors that contain tunnel-like cavities through which a transport medium can travel.

Ceiling Insulation – A material primarily designed to resist hat flow which is installed between the conditioned area of a building and an unconditioned attic. Where the conditioned area of a building extends to the roofs, the term ceiling insulation also applies to such material used between the underside and upperside of the roof.

CFM – An abbreviation for cubic feet per minute.

Chimney Effect – The tendency of air or gas in a duct or other vertical passage to rise when heated displacement of internal heated air by unheated outside air occurs because of the difference in their densities caused by temperature differences.

Clerestory – Window placed high in wall near eaves; used for light, heat gain, and ventilation.

Closed Loop – Any loop in the system that is not exposed to the atmosphere.

Collector – Any device or area that captures the sun’s energy to heat domestic water or to heat, cool, or light a living space. This broad definition includes not only familiear space and domestic water heating system collectors but also collectors for space cooling.

Collector Aperture – The glazed opening being used for admitting solar radiation.

Collector Efficiency – The ratio of usable heat energy extracted from a collector to the solar energy striking the cover.

Collector Tilt – The angle between the horizontal plane and the solar collector plane.

Cold-air Return Duct – A duct located at floor level in a conditioned space which allows air to return to the furnace.

Combustion – The act or process of buring, rapid oxidation, accompanied by hat and usually light.

Combustion Efficiency – The ratio of the amount of heat available as a result of the combustion process, compared to the amount of heat potentially available from that fuel in an ideal process; it is expressed as a percentage.

Combustion System – A system in which fossil fuels are mixed with air and ignited to produce combustion, in order to obtain heat; the heat is then transferred to a distribution system, while the by-products of the combustion process are expelled through the vent pipe.

Components – Any identifiable elements of a heating or cooling system, such as valves, piping, controls, and containers.

Concentrating Collector – A device that concentrates the sun’s rays on an absorber surface the is significantly smaller than the overall collector area.

Condensation – The process of changing a vapor to a liquid by extracting heat from the vapor.

Conditioned Environment – Any space in a residential building which is served by a heating or cooling system.

Conductance – The rate of heat flow through an object when a temperature difference of one degree F is maintained between the sides of the object.

Conduction – A process of heat transfer whereby heat moves through a material; the flow of heat due to temperature variations within a material.

Conductivity – A measure of the ability of a material to permit conductive heat flow through it.

Control Subsystem – The assembly of devices and their electrical, pneumatic, or hydraulic auxiliaries that regulate the processes of collecting, transporting, storing, and utilizing energy in response to the thermal, safety, and health requirements of the building occupants.

Convection – Transfer of heat by movement of a fluid or gas.

Convective Cooling – Cooling at night or when outside temperatures are low; using ventilation or prevailing breezes.

Convective Loop – Subsystem of passive solar systems that utilizes natural convection to transport heat. Heated air or liquid from collectors rises, and cooler air or liquid replaces it from below. The air or liquid travels within an enclosed loop; cooler air/liquid continually moving into the low collectors and warmer air/liquid rising.

Crawl Space – The space between the foundation and the rest of the home, a non-basement foundation

Daylighting – The amount of visible light transmitted through a window configuration divided by the amount of visible light incident on the outside surface.

Degree-Day – The degree day is a unit of heat measurement equal to one degree variation from a standard temperature to the average temperature of one day. If the standard is 65 degrees F and the average outside temperature is 50 degrees for two days then the number of degree days is 30.

Demand Load – Domestic water heating needs that solar or conventional energy supplies must meet.

DHW Tank – Abbreviation for Domestic Hot Water Tank.

Diffuse Sunlight – Sunlight that reaches the earth after being reflected off atmospheric particles. On a cloudy day, diffuse sunlight may account for all the sunlight received at the surface. Diffuse sunlight comes along no set path; it generally comes from the entire skyvault, with most coming from the area of the sky near the sun.

Direct Gain – When solar energy enters a building, usually through glazing, and is absorbed and stored inside by thermal mass in the building.

Direct Radiation – Sunlight that comes straight from the sun. Skyspace angles and most solar planning guidelines are based on direct sunlight. Direct sunlight has higher intensity than diffuse sunlight.

Discharge – Removing heat from storage by radiative or convective heat transfer.

Domestic Water Pressure – The pressure of potable water within the building from sources not related to the solar domestic hot water system.

Double-Glazed – A frame with two panes of transparent glazing with space between the panes.

Double Hung Window – A type of window in which the panels or sashes slide vertically along grooves in side jambs.

Double wall Seperation – Heat exchangers utilizing nonpotable heat transfer fluids are separated from potable water system by use of two walls between the fluids.

Down Wind Machine – The wind generation design in which the blades intercept the wind downstream of the tower; a tail is not needed, since the blade configuration acts to orient the machine.

Draft – The movement of hot toxic gases up the venting system, caused by the lightness of the gases in relation to the air in the venting system and the air outside. The upward movement of the gases creates a partial vacuum which draws new air necessary for combustion into the combustion chamber.

Draft Regulator – A component of gas-fired furnaces or boilers which mixes secondary air with the combustion gases leaving the unit thus enabling a smooth, continuous relief of exhaust gases up the vent pipe.

Drum Wall – A type of thermal storage wall in which the thermal mass is large metal drums filled with a storage medium, usually water.

Duct Insulation – A material primarily designed to resist heat flow which is installed on a heating or cooling duct in an unconditioned area of a building.

Efficiency – The ability to produce a desired effect, product, etc. with a minimum of waste, expense or effort. The efficiency of a system is the ratio of the amount of useable energy produced to the amount of potential energy put into it.

Emission – A measure of the propensity of a material to radiate heat to its surroundings in the form of longwave radiation.

Energy – The capacity for doing work – taking a number of forms, which may be transformed from one into another, such as thermal, mechanical, electrical, and chemical.

Energy Efficiency Ratio – The ratio of useable output to input of energy; in the case of cooling units, since the input is usually electrical power; and the amount of heat removed is measureable in BTUs, the EER is the ratio of the number of BTUs per hour to the number of watts used.

Energy Transport Subsystem – The portion of the heating system that contains the heat transfer medium and provides the means to transport energy throughout the system.

Envelope – The protective shell of a building that separates the outside environment from the inside environment.

Eutectic Salts – Chemical compounds that melt at relatively low temperatures and absorb high quantities of heat as they melt. The salts are sometimes used as storage medium in solar heating and cooling systems.

Evaporative Cooling – Cooling provided by the evaporation of water. Evaporative cooling uses water’s ability to absorb and store heat in the evaporative process, cooling itself and the environment in contact with it. This process is most effective during daytime hours; therefore most systems using this principle require integral shading devices.

Expansion Tank – A tank that allows for the increase or decrease of water volume in a hot water distribution system due to temperature differences.

Fixed Window – A type of window that does not open.

Flat-Plate Collector – A solar collector composed oof sheet materials for the glazing and absorber plate in which sunlight is converted into heat on a plane surface without the aid of reflecting surfaces to concentrate the rays.

Floor Insulation – A material primarly designed to resist heat flow which is installed between the first level conditioned area of a building and an unconditioned basement, a crawl space, or the outside beneath it. Where the first level conditioned area of a building is on a ground level concrete slab, the term floor insulation also means such material installed around the perimeter of the slab.

Flue – A tube, pipe, or shaft which allows for the passage of exhaust gases to the outside environment.

Forced Circulation – A heat distribution system that utilizes a pump to circulate hot water through a boiler and pipes to a conditioned space.

Gasket – Any piece of rubber, metal, paper, vinyl etc. placed around a joint to make it leakproof.

Header – The pipe that runs across the edge of an array of solar collectors, gathering the heat transfer fluid from the risers in the individual collectors. This ensures that equal flow rates and pressures are maintained.

Heat – A form of energy that is transferred by virtue of a temperature difference.

Heat Absorbing Glass – A type of glass that absorbs selected wavelengths of light, and thus absorbs more solar heat than conventional glass; it reduces the amount of summer solar heat gain and retains heat in the winter.

Heating Capacity of Air – The amount of heat required to raise the temperature of one cubic foot of air one degree F.

Heat Capacity – A property of a material denoting its ability to absorb heat; the quantity of heat needed to raise the temperature of one cubic foot of the material one degree F.

Heat Exchanger – A device, such as 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 Gain – An increase in the amount of heat contained in a space, resulting from direct solar radiation and the heat given off by people, lights, equipment, machinery and other surfaces.

Heating Load – The amount of energy required to perform the task of water and/or space heating.

Heating Season – The period from early fall to late spring during which additional heat is needed to keep a house comfortable for its occupants.

Heat Loss – A decrease in the amount of heat contained in a space, resulting from heat flow through walls, windows, roof, and other building envelope components.

Heat Sink – A massive body that can serve to absorb and store solar heat.

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 that can be stored by a material.

HEUR Heat Energy Use Rate – The amount of energy used in a residence, per hour, per degree F, to maintain the desired temperature.

Hopper Window – A window which has a sash that is hinged along the bottom and swings inward.

Hybrid Solar Energy System – A system that can be classified as either active or passive.

Infiltration – The uncontrolled flow of air into and out of a building through cracks, openings, doors, or other areas that allow air to penetrate.

Inlet Vent – An opening in the exterior surface of a building that allows air to enter an area that requires ventilation.

Jalousie Window – A variety of awning window made up of several slats of glass which open simultaneously by means of a crank.

Killowatt – A measure of power equal to one thousand Watts, approximately 1 1/3 Horsepower, usually applied to electricity.

Kilowatt-Hour – The amount of energy equivalent to 1 kilowatt of power being used for one hour.

Kinetic Energy – Energy in motion. Actual energy, in the process of overcoming resistance.

Law of Conservation of Energy – In a physical process the total energy present at the end of a transfer or transformation must equal the total energy in all forms at the beginning of the transfer or transformation process.

Life-cycle Cost – The total cost of a system calculated over its anticipated operational life span.

Masonry – Stone, brick, rammed earth, adobe, ceramic, hollow tile, concrete block, gypsum block, or other similar building materials bonded together with mortar to form a wall, pier, floor, roof, or similar form.

Main Gas Value – The device in a agas furnace which regulates the flow of gas to the combustion chamber and to the pilot light area; it is attached to the room thermostat.

Microclimate – The climate of a specific site or portion of a site. Microclimates result form the overall regional climate as it is affected by local site conditions. These microclimatic influences affect both the heating and cooling requirements of the house.

Movable Insulation – Insulation such as shutters, panels, curtains, or reflective foil draperies that can be moved manually or by mechanical means.

Natural Cooling – Space cooling alternatives to energy-consumptive central air-conditioning systems. The five principal means of natural cooling are shading, ventilation, conduction control, radiation, and evaporation.

Outlet vent – An opening in the exterior surface of a building that allows air to exit an area that requires ventilation.

Passive Solar Energy System – A system where the collector and thermal storage components are integrated, requiring no transfer device for solar heated fluid. A passive system tends to have less hardware than an active system; it is usually built as an essential component of the building rather than as an addition.

Pipe Insulation – A material primarily designed to resist heat flow which is installed on a heating or cooling pipe in an unconditioned area of a building.

Plenum – A cavity, or air space, through which air is moved. In some passive solar designs, a plenum may be used to evenly distribute heat that otherwise would collect at a single point.

Potential Energy – Energy in the inactive form. Energy which is present in a system or precess relative to the position or struction of the system or process.

Radiative Cooling – Cooling that occurs when warm surfaces radiate excess heat to cool surfaces. Water bodies like roof ponds and massive construction materials absorb heat from interior spaces during daytime hours and radiate it at night.

Recessed Light Fixture – A light fixture set into the ceiling so that the surface of the fixture is flush with the ceiling.

Relative Humidity – The ratio of the amount of water vapor in the air to the amount it could potentially hold at the same temperature.

Retrofit – the process of increasing the energy efficiency of a building.

Resistance Heat Unit – A form of electric generation of heat which uses a metal element as the primary conversion unit; when the element, which has a high resistance to electricity, I sforced to conduct electricity, it heats up and thus generates heat.

R-Value – A measure of a material’s resistance to heat flow. The unit of time for a unit area of a particular body or assembly having defined surfaces with a a unit average temperature difference established between two surfaces per unit of thermal tansmission. It is the reciprocal of U-value.

Ridge Vent – A type of vent that replaces a portion of the peak of the roof of a building to provide ventilation

Rolled Vinyl Gaskets – A gasket type weatherstripping which is used to seal the crack between the stop and the moving part of the window or door. Often called “tubular gasket” weatherstripping.

Safety Control Valve – A valve attached to a gas burner, which shuts down gas flow if the pilot light is extinguished.

Seasonal Efficiency – The ratio, over an entire heating season, of the solar energy collected and used to the solar energy strikng the collector.

Soffit – The board connecting the end of the overhang of the roof to the edge of the home.

Soffit Vent – A type of vent that replaces a portion of the soffit of a building to provide ventilation.

Solar Angles – Angles used to specify the sun’s position at a given time.

Solar Energy – The photon energy originating from the sun’s radiation in wavelengths from .3 to 2.4 micrometers; the radiant energy from the sun, whether it be direct, diffuse, or reflected radiation.

Solar Heating System – The complete assembly of subsystems and components necessary to convert solar energy into useful thermal energy or to use climate resources appropriately.

Spring Metal Weatherstripping – A jamb type weatherstripping which sits inside the jamb and creates a V shaped spring seal. May be comprised of bronze, brass, aluminum, or other lightweight alloys.

Stack Effect – The ability to set up a large enough temperature difference to effect the displacement of warm air by cooler air in a thermal chimney, such that the lighter warm air rises through a distribution space.

Standby Heat Loss – Heat loss through storage tank and piping walls.

Temperature – Measurement of the level of motion or agitation of molecules and atoms; with reference to the tendency to communicate heat to matter in contact with them.

Thermal Conduction – The movement of heat from molecule to adjacent molecule, through a substance or from one substance to another in contact with it.

Thermal Convection – The circulation of heat within a gas or liquid due to the differences in density resulting from temperature changes.

Thermal Envelope – The enclosure of a building that resists thermal loss.

Thermal Resistance – The capacity of a material to resist heat flow.

Thermal Window – A window system with an improved thermal performance through the use of multiple panes, and more airtight construction. Some thermal windows also provide an insulating frame and sash to provide greater thermal efficiency.

Threshold – A wood or metal member, beveled or tapered on each side, used to close the space between the bottom of the door and the sill or floor underneath.

Trombe Wall – A massive wall that absorbs collected solar heat and holds it until it is needed to heat the house interior.

Upwind Machine – A wind generator design in which the rotor blades intercept the wind prior to the tower; a tail is used to orient the blades into the wind.

U-Value – The capability of a substance to transfer heat. Used to describe the conductance of a material, or a composite of materials, in construction.

Unconditioned Environment – Any space, out of doors or in a residential building which is not served by a heating or cooling system.

Vapor Barrier – A moisture impervious layer appied to the surface enclosing a humid space to prevent moisture penetration.

Vapor Compression Refrigeration – A cooling system which vaporizes the heat energy from the conditioned space by sending it into a cold refrigerant in evaporative tubes which has been compressed and heated, changed to a liquid and experienced a decrease in temperature in order to accept the heat energy from the conditioned space.

Ventilation – The process of supplying or removing air by natural or mechanical means to or from any space.

Vent Pipe – An exhaust pipe which carries the products of combustion from furnaces, boilers or water heaters to the outside environment.

Vertical Axis Machine – A wind generator design whose rotor axis is perpendicular to the ground; the egg beater type of machine is an example.

Wall Insulation – A material primarily designed to resist heat flow which is installed within or on the walls between conditioned areas of a building and unconditioned areas of a building, or the outside.

Water Heater Damper – A device which automatically closes vents on oil and gas fired water haters to prevent the escape of heat through the vent pipe when the main burner is not being fired.

Water Heater Insulation – A material primarily designed to resist heat flow which is suitable for wrapping around the exterior surface of a water heater casing.

Weatherstripping – Narrow strips of material placed over or in movable joints of windows and doors to reduce the


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