Earth-air heat exchangers – a strategy of pre-tempering fresh air for ventilation, and in some cases, providing building cooling by passing incoming air through buried ducts.

Earth contact – the strategy of placing building surfaces in contact with the ground to reduce the temperature difference between inside and outside, reduce infiltration, and/or use the subsurface soil temperature to cool the building.

Emissivity – the property of emitting heat by radiation, possessed by all materials to a varying extent. “Emittance” is the numerical value of this property.

Envelope heat gain or loss – heat transferred through the skin of a building or via infiltration/ventilation.

Equinox – meaning equal light. The dates during the year when the hours of daylight are equal to the hours of darkness. On the equinox, the sun rises from the horizon at due east and sets due west. The equinoxes fall on March 21 and September 21.

Evaporation – phase change of a material from liquid to vapour at a temperature below the boiling point of the liquid. Cooling occurs during the process of evaporation.

Evaporative cooling – a heat removal process in which water vapour is added to air, increasing its humidity while lowering its temperature. The total amount of heat in the air stays constant, but is transferred from sensible heat in the air to latent heat in the moisture. In the process of changing from liquid to vapour (evaporating), the water must absorb large amount of heat.

Evaporative cooling, Direct – a cooling process where the warm and dry air moves through a wetted medium to evaporate moisture in the air. The cool humid air is then used to cool a place.

Evaporative cooling, Indirect – a cooling process where the evaporative process is remote from the conditioned space. The cooled air is then used to lower the temperature of the building surface, such as in a roof spray, or is passed through a heat exchanger to cool indoor air. The indirect process has the advantage of lowering temperatures without adding humidity to the air, thus extending the climate conditions and regions in which evaporate cooling is effective.

Glare – the perception caused by a very bright light or a high contrast of light, making it uncomfortable or difficult to see.

Glazing – transparent or translucent materials, usually glass or plastic, used to cover an opening without impeding (relative to opaque materials) the admission of solar radiation and light.

Greenhouse effect – refers to the characteristic tendency of some transparent materials such as glass to transmit shortwave radiation and block radiation of longer wavelengths.

Heat exchanger – a device usually consisting of a coiled arrangement of metal tubing used to transfer heat through the tube walls from one fluid to another.

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 sources.

Heat island – the increased temperatures, relative to surrounding open load, found in the centre cities and areas of high development density. Heat islands are caused by concentrations of heat sources, decreased vegetation cover, increased massive and dark surfaces, decreased wind flows, and narrow sky view angles.

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 pump – a thermodynamic device that transfers heat from one medium to another; the first medium cools while the second warms up.

Humidity – water vapour within a given space.

HVAC – mechanical system for heating, ventilating and air-conditioning that controls temperature, humidity, and air quality.

Hybrid system – a solar heating or cooling system that combines active and passive elements.

Hygroscopic – absorptive of moisture, readily absorbs and retains moisture.

Illuminance – the measure of light intensity striking a surface. Specifically, the concentration of incident luminous flux, measured in foot-candle (I-P) or Lux (SI).

Illumination – lighting of the surface by daylight or electric light.

Index of refraction – a property of glazing materials that determines the reflection/refraction characteristics of the glazing.

Infiltration – the uncontrolled movement of outdoor air into the interior of a building through cracks around windows and doors or in walls, roofs and floors. This may work by cold air leaking in during winters, or the reverse in summers.

Infrared radiation – electromagnetic radiation having wavelength above the wavelength range of visible light. This is the predominant form of radiation emitted by bodies with moderate temperatures such as the elements of a passive building.

Internal gains – the energy dissipated inside the heated space by people and appliances. A portion of this energy contributes to the space heating requirement.

Isothermal – an adjective used to indicate a change taking place at constant temperature.

Jalousie (jali) – an exterior fixed element made up of a perforated frame which covers the whole window. It allows natural ventilation and protects against direct solar radiation and view from the exterior.

Latitude – the angular distance north(+) or south (-) of the equator, measured in degrees of arc.

Latent heat – change of enthalpy during a change of state, usually expressed in J/kg (Btu per lb). With pure substances, latent heat is absorbed or rejected at constant temperature at any pressure.

Lighting, diffused – lighting in which the light on a working plane or on an object is not incident predominantly from a particular direction.

Longwave radiation – radiation emitted between roughly 5 and 30 m wavelength, as in thermal radiation from the surface of a room, or from the outside surface of the roof.

Longitude – the arc of the equator between the meridian of a place and Greenwich meridian measured in degrees east or west.

Louvre – an assembly of sloping vanes intended to permit air to pass through and to inhibit transfer of water droplets.

Lumen – SI unit of luminous flux; it is the luminous flux emitted in unit solid angle by a uniform point source having a luminous intensity of 1 candela.

Lux – SI unit of illuminance; it is the illuminance produced on a surface of unit area (square metre) by a luminous flux of 1 lumen uniformly distributed over that surface.

Masonry – concrete, concrete block, brick, adobe, stone, and similar other building materials.

Negative pressure – a pressure below the atmospheric. In residential construction, negative pressure refers to pressure inside the house envelope that is less than the outside pressure. Negative pressure will encourage infiltration.

Night insulation – movable insulation that covers a glazing at night and is removed during the day.

Night ventilation of mass – a cooling process whereby a building is closed during the hot daytime hours. Its heat gains are stored during that time in the building’s structure or other thermal mass. At night, the building is opened and cooler outdoor air is used to flush heat from the mass, lowering its temperature, to prepare for another cycle.

Night sky radiation – a reversal of the day time insolation principle. Just as the sun radiates energy during the day through the void of space, so also heat energy can travel unhindered at night from the earth’s surface back into space. On a clear night, any warm object can cool itself by radiating longwave heat energy to the cooler sky. On a cloudy night, the cloud cover acts as an insulator and prevents the heat from travelling to the cooler sky.

Opaque – not able to transmit light; for example, unglazed walls.

Passive system – a system that uses non-mechanical and non-electrical means to satisfy heating, lighting, or cooling loads. Purely passive systems use radiation, conduction, and natural convection to distribute heat, and daylight for lighting.

Pond, spray – arrangement for lowering the temperature of water in contact with outside air by evaporative cooling of the water. The water to be cooled is sprayed by nozzles into the space above a body of previously cooled water and allowed to fall into it by gravity.

Positive pressure – a pressure above atmospheric. In residential construction, this refers to pressure inside the house envelope that is greater than the outside pressure; a positive pressure difference will encourage exfiltration.

Pressure – the normal force exerted by a homogenous liquid or gas, per unit area, on the wall of container.

Pressure difference – the difference in pressure between the volume of air enclosed by the building envelope and the air surrounding the envelope.

Pressure, vapour – the pressure exerted by the molecules of a given vapour.

Go to terms A-D  ;  Go to terms Q-Z