Solar gain
Encyclopedia
Solar gain refers to the increase in temperature
in a space, object or structure that results from solar radiation. The amount of solar gain increases with the strength of the sun, and with the ability of any intervening material to transmit
or resist the radiation.
Objects struck by sunlight absorb the short-wave radiation from the light
and reradiate the heat at longer infrared
wavelength
s. Where there is a material or substance (such as glass) between the sun
and the objects struck that is more transparent to the shorter wavelengths than the longer, then when the sun is shining the net result is an increase in temperature - solar gain. This effect, the greenhouse effect
, so called due to the solar gain that is experienced behind the glass of a greenhouse, has since become well known in the context of global warming
.
s and door
s) and shading devices, shading coefficients are commonly mentioned properties. Shading coefficients measure the solar energy transmittance
through windows.
"G-value" is the coefficient commonly used in Europe - called a Solar Factor on some window literature (%) ie, 53% = 0.53;
"Solar Heat Gain Coefficient (SHGC)" is used in the United States;
"Shading Coefficient" is an older term that is still sometimes used in the United States - the relationship between SHGC and SC is as follows: SHGC = SC × 0.87.
G-values and SHGC values ranges from 0 to 1, a lower value representing less solar gain. Shading coefficient values are calculated using the sum of the primary solar transmittance (T-value) and the secondary transmittance. Primary transmittance is the fraction of solar radiation that directly enters a building through a window compared to the total solar insolation
, the amount of radiation that the window receives. The secondary transmittance is the fraction of inwardly flowing solar energy absorbed in the window (or shading device) again compared to the total solar insolation.
the aim of the designer is normally to maximise solar gain within the building in the winter (to reduce space heating
demand), and to control it in summer (to minimise cooling requirements). Thermal mass
may be used to even out the fluctuations during the day, and to some extent between days.
In direct solar gain systems, the composition and coating of the building glazing can also be manipulated to optimise the greenhouse effect, while its size, position and shading can be used to optimise solar gain. Solar gain can also be transferred to the building by indirect or isolated solar gain systems. For further details, see passive solar building design
.
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
in a space, object or structure that results from solar radiation. The amount of solar gain increases with the strength of the sun, and with the ability of any intervening material to transmit
Transmittance
In optics and spectroscopy, transmittance is the fraction of incident light at a specified wavelength that passes through a sample. A related term is absorptance, or absorption factor, which is the fraction of radiation absorbed by a sample at a specified wavelength...
or resist the radiation.
Objects struck by sunlight absorb the short-wave radiation from the light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
and reradiate the heat at longer infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
s. Where there is a material or substance (such as glass) between the sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
and the objects struck that is more transparent to the shorter wavelengths than the longer, then when the sun is shining the net result is an increase in temperature - solar gain. This effect, the greenhouse effect
Greenhouse effect
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere...
, so called due to the solar gain that is experienced behind the glass of a greenhouse, has since become well known in the context of global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
.
Shading coefficients
When discussing the properties of fenestration (e.g. windowWindow
A window is a transparent or translucent opening in a wall or door that allows the passage of light and, if not closed or sealed, air and sound. Windows are usually glazed or covered in some other transparent or translucent material like float glass. Windows are held in place by frames, which...
s and door
Door
A door is a movable structure used to open and close off an entrance, typically consisting of a panel that swings on hinges or that slides or rotates inside of a space....
s) and shading devices, shading coefficients are commonly mentioned properties. Shading coefficients measure the solar energy transmittance
Transmittance
In optics and spectroscopy, transmittance is the fraction of incident light at a specified wavelength that passes through a sample. A related term is absorptance, or absorption factor, which is the fraction of radiation absorbed by a sample at a specified wavelength...
through windows.
"G-value" is the coefficient commonly used in Europe - called a Solar Factor on some window literature (%) ie, 53% = 0.53;
"Solar Heat Gain Coefficient (SHGC)" is used in the United States;
"Shading Coefficient" is an older term that is still sometimes used in the United States - the relationship between SHGC and SC is as follows: SHGC = SC × 0.87.
G-values and SHGC values ranges from 0 to 1, a lower value representing less solar gain. Shading coefficient values are calculated using the sum of the primary solar transmittance (T-value) and the secondary transmittance. Primary transmittance is the fraction of solar radiation that directly enters a building through a window compared to the total solar insolation
Insolation
Insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter or kilowatt-hours per square meter per day...
, the amount of radiation that the window receives. The secondary transmittance is the fraction of inwardly flowing solar energy absorbed in the window (or shading device) again compared to the total solar insolation.
Solar gain and building design
In the context of passive solar building designPassive solar building design
In passive solar building design, windows, walls, and floors are made to collect, store, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer...
the aim of the designer is normally to maximise solar gain within the building in the winter (to reduce space heating
Space heating
A space heater is a self-contained device for heating an enclosed area. Space heating is generally employed to warm a small space, and is usually held in contrast with central heating, which warms many connected spaces at once...
demand), and to control it in summer (to minimise cooling requirements). Thermal mass
Thermal mass
Thermal mass is a concept in building design which describes how the mass of the building provides "inertia" against temperature fluctuations, sometimes known as the thermal flywheel effect...
may be used to even out the fluctuations during the day, and to some extent between days.
In direct solar gain systems, the composition and coating of the building glazing can also be manipulated to optimise the greenhouse effect, while its size, position and shading can be used to optimise solar gain. Solar gain can also be transferred to the building by indirect or isolated solar gain systems. For further details, see passive solar building design
Passive solar building design
In passive solar building design, windows, walls, and floors are made to collect, store, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer...
.
See also
- Double-skin facadeDouble-skin facadeThe Double Skin Façade is a system consisting of two skins placed in such a way that air flows in the intermediate cavity. The ventilation of the cavity can be natural, fan supported or mechanical...
- Heating degree dayHeating degree dayHeating degree day is a measurement designed to reflect the demand for energy needed to heat a home or business. It is derived from measurements of outside air temperature. The heating requirements for a given structure at a specific location are considered to be directly proportional to the...
- Insulated glazingInsulated glazingInsulated glazing also known as double glazing are double or triple glass window panes separated by an air or other gas filled space to reduce heat transfer across a part of the building envelope....
- Low-emissivity coatingsLow-emissivityLow emissivity - actually low thermal emissivity - is a quality of a surface that radiates, or emits, low levels of radiant thermal energy. All materials absorb, reflect and emit radiant energy...
- Low-emissivity coatings