Glossary
heat load The total energy required for space heating. heat loss Heat flow through building envelope components (walls, windows, roof, etc.). heat pump A thermodynamic device that transfers heat from one medium to another. The first medium (the source) cools while the second (the heat sink) warms up. heating season The period of the year during which heating the building is required to maintain comfort conditions. heliodon Device that simulates solar angles and measures the number of hours of potential sunshine. hybrid solar heating system Solar heating system that combines active and passive techniques. I-V curve Plot of current versus voltage for a PV cell, module or array as a load is increased from short circuit to open circuit under fixed conditions of irradiance and cell temperature. incident angle The angle between the sun’s rays and a line perpendicular (normal) to the irradiated surface. indirect gain The indirect transfer of solar heat into the space to be heated from a collector that is coupled to the space by an uninsulated, conductive or convective medium (such as a thermal storage wall or roof pond). 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 the winter or the reverse in the summer. infrared radiation Electromagnetic radiation having wave length above the range of visible light. This is the preponderant form of radiation emitted by bodies with moderate temperatures, such as the elements of a passive solar building. insolation A contraction of ‘incoming solar radiation’ meaning the amount of solar energy incident on a given area over a certain period of time; a common unit of insolation is kW m–2 day–1, often referred to as peak hours per day. internal gains The energy dissipated inside the heated space by people (body heat) and appliances (lighting, cooker, etc.). A proportion of this energy contributes to the space heating requirements (kWh). irradiance Rate of incidence of solar energy on a flat surface at a particular angle of tilt (W m–2). isolated gain The transfer of heat into the space to be heated from a collector that is thermally isolated from the space to be heated by physical separation or insulation (such as a convective loop collector or an attached sunspace with an insulated common wall).
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