EFS Chapter 7 Solar Energy for Buildings: Approaching Zero Net Energy

Solar Resource

The sun's energy that can be harnessed for various purposes in buildings, such as heating, cooling, and electricity generation.

Net Zero Energy Buildings

Buildings that produce as much energy as they consume, typically achieved through energy-efficient design and the use of renewable energy sources.

Solar Angles

The altitude angle and azimuth angle of the sun, which determine its position in the sky at different times of the day and year.

Altitude Angle

The angle between the sun and the horizon, measured vertically.

Azimuth Angle

The angle between the sun and a reference direction, typically measured clockwise from north.

Solar Declination

The latitude over which the sun revolves on a particular day, varying sinusoidally between ±23.45° throughout the year.

Overhangs

Architectural features that project out from a building's facade to provide shade and control the amount of sunlight entering through windows.

Sun Path Diagrams

Graphical representations of the sun's location in the sky at different times of the day and year, useful for site analysis and determining obstructions to sunlight.

Daylighting

The use of natural sunlight to illuminate indoor spaces, reducing the need for artificial lighting.

Solar Thermal Collectors

Devices that capture the sun's heat and transfer it to a fluid, typically used for heating water or space in buildings.

Photovoltaics (PVs)

Solar panels that convert sunlight directly into electricity.

All-Electric Systems

Building systems that rely solely on electricity for heating, cooling, water heating, and cooking, often paired with rooftop PVs to offset energy demand.

Altitude

The angle of an object above the horizon, measured in degrees.

Azimuth

The angle of an object along the horizon, measured in degrees.

Sun path diagram

A diagram that shows the path of the sun throughout the year, indicating the position of the sun at different times of the day.

Shading problems

Issues caused by obstructions that cast shadows on a site, affecting the availability of sunlight.

Shadow diagrams

Diagrams that illustrate how far and in what direction an obstacle may cast shadows.

Solar access

The availability of sunlight to a specific location or unit.

Photovoltaics

Technology that converts sunlight into electricity.

Shading

The blocking of sunlight on solar collectors, which can significantly reduce their power output.

Architectural modeling

The use of physical models to represent proposed buildings and analyze their design features, including shading implications.

Heliodon

A machine used for testing physical models to observe shading implications of overhangs, neighboring buildings, or other obstacles.

Latitude

The angular distance of a location north or south of the Earth's equator, measured in degrees.

Rooftop spacing

The distance between rows of solar collectors on a rooftop to avoid shading.

Energy-Efficient Building Design Strategies

Certain fundamental building design guidelines that can make a building perform better in terms of energy bills and occupancy comfort.

Building Orientation

The orientation of a building greatly affects the balance between letting the sun get into a building in the winter and minimizing excessive solar gain in the summer.

Overhangs

Architectural elements designed to protect south-facing windows (north-facing for those in the southern hemisphere) from excessive solar gain in the summer.

Clear-Sky Irradiance

The amount of solar energy that strikes windows of different orientations, affecting the heating and cooling loads of a building.

East- and West-Facing Windows

Windows that are exposed to nearly horizontal morning and afternoon solar radiation, which can cause overheating in the summer and are not very helpful in the winter.

South-Facing Windows

Windows that provide solar gains in the winter and can act as net energy providers, but also lose energy all day and all night, all winter long.

Solar Heat Gain Coefficient (SHGC)

The measure of the fraction of solar energy that hits a window and is transmitted into the interior of the building. A high SHGC is desirable for passive solar heating, while a low value is important in commercial buildings with significant cooling loads.

Thermal Mass

The ability of a material to absorb and store heat energy. Adding extra thermal mass, such as a concrete floor, can help absorb excess heat from south-facing windows during the day and release it at night.

Cooling Loads

The calculations and considerations involved in determining the cooling needs of a building, including heat gains through the building envelope, unwanted solar gains, infiltration and ventilation air, and internal gains.

Natural Ventilation

Taking advantage of prevailing winds to provide airflow and natural cooling in a building.

Ventilation efficiency

The measure of how effectively breezes can cool a building when they approach at an angle rather than head-on.

Leeward side

The side of a house or building that is sheltered from the wind.

Heat island effect

The phenomenon where the ambient temperature of a neighborhood increases due to the presence of hot roofs and other factors.

Ridge and soffit vents

Vents located at the ridge and soffit of a roof that help reduce attic temperatures.

Radiant barriers

Shiny foil barriers placed under the roof rafters or on top of ceiling joists to reduce attic temperatures.

Solar reflectivity

The ability of a roofing material to reflect solar energy.

Net positive heat gains

The condition where a window provides more heat to a building than it loses.

U-factor

A measure of a window's insulation properties, specifically its ability to conduct heat.

SHGC (Solar Heat Gain Coefficient)

A measure of how much solar radiation a window allows to pass through.

Green roof

A rooftop garden designed to reduce rooftop temperatures and provide stormwater management services.

Roof surface emissivity

The ability of a roof surface to emit thermal radiation.

Atmospheric window

The range of wavelengths in the far-infrared region where radiation emitted from Earth's surface can easily pass through the atmosphere to outer space.

Thermal mass

The ability of a material to absorb and store heat energy.

East-west axis orientation

The alignment of a building along the east-west direction to optimize solar gains and shading.

Thermal flywheel effect

The use of thermal mass to absorb and store coolth (cooling energy) at night and release it during the day to reduce air conditioning loads.

Solar gains

The heat gain from solar radiation entering through windows.

Glazing

The glass or transparent material used in windows.

Tinted windows

Windows that have been treated with a tinted film or coating to reduce solar radiation.

Reflective windows

Windows that have a reflective coating to block solar radiation.

Natural daylight

The natural light from the sun that enters through windows, reducing the need for artificial lighting.

Spectrally selective, low-emissivity glass

Glass that controls solar gains by selectively allowing certain wavelengths of light to pass through while reflecting others.

Solar spectrum

The distribution of solar energy across different wavelengths, including ultraviolet, visible, and infrared.

Ultraviolet (UV) portion of the spectrum

The portion of the solar spectrum that contains 7% of the incoming solar irradiation and can cause skin cancer and fade materials.

Visible range

The portion of the solar spectrum that contains about 47% of the incoming solar irradiation and is responsible for allowing us to see things.

Infrared portion of the spectrum

The portion of the solar spectrum that contains 46% of the incoming solar irradiation and provides heat but no light.

Solar heat gain coefficient (SHGC)

A measure of how much solar heat is transmitted through a window or glazing system.

Visible light transmittance (VT)

A measure of how much visible light is transmitted through a window or glazing system.

Light-to-solar-gain (LSG) ratio

A metric that compares the visible light transmittance (VT) to the solar heat gain coefficient (SHGC) of a window or glazing system.

R-value

A measure of the thermal resistance of a material or assembly, indicating its ability to resist heat transfer.

Building envelope gains

Heat gains or losses through the building envelope (walls, roof, windows, etc.) due to temperature differences between the indoor and outdoor environments.

Cooling degree-days (CDD)

A measure of the cooling load required to maintain a comfortable indoor temperature, calculated based on the number of days and the magnitude of temperature differences above a base temperature.

Seasonal energy efficiency ratio (SEER)

A measure of the cooling output (in Btu) divided by the electrical energy input (in Wh) for an air conditioning system.

Distribution system efficiency

The efficiency of the ducts and other components that distribute cooled air from the air conditioner to different parts of the building.

Clear-sky irradiance

The amount of solar radiation reaching the Earth's surface under clear sky conditions.

Heat gain from windows

The amount of solar heat gained through windows, which can contribute to the cooling load of a building.

Solar gain

The amount of solar irradiance that is absorbed by a building through its windows.

SHGC

Solar Heat Gain Coefficient, a measure of how much solar heat is transmitted through a window.

Dehumidification

The process of removing moisture from the air to reduce humidity levels.

Latent heat

The heat energy required to change the state of water from liquid to vapor.

Psychrometric chart

A chart that shows the relationship between air temperature, humidity, and moisture content.

Absolute humidity

The actual amount of moisture present in the air.

Relative humidity

The ratio of the actual amount of moisture in the air to the maximum amount it can hold at a given temperature.

Cooling load

The amount of heat that needs to be removed from a space to maintain a desired temperature.

Predicted mean vote (PMV)

A metric used to assess human comfort based on various environmental factors.

Metabolic rate

A measure of the body's energy expenditure or activity level.

Clo

A measure of the insulation value of clothing.

Infiltration rate

The rate at which outside air enters a building through leaks or openings.

SEER

Seasonal Energy Efficiency Ratio, a measure of the cooling efficiency of an air conditioner.

Sensible heat transfer

The transfer of heat through conduction, convection, or radiation that affects the temperature of a space.

Air conditioning demand

The total amount of cooling required to maintain a comfortable indoor temperature.

Metabolic rate

The rate at which the body burns calories during physical activity.

Btu

British thermal unit, a unit of energy commonly used in the United States.

Passive solar heating

A method of heating buildings by utilizing sunlight to provide heat through windows and other solar apertures.

Active solar

A method of heating buildings that uses special solar thermal collectors to collect heat, which is then moved to storage and distribution systems using pumps and blowers.

Comfort zone

The range of indoor temperature and humidity conditions in which a person feels comfortable.

Passive House Institute (PHI)

An organization that promotes the construction of energy-efficient buildings with low energy demand.

Envelope efficiency

The effectiveness of a building's exterior walls, roof, and floor in preventing heat transfer.

South-facing glazing systems

Windows or other openings in a building's south-facing side that allow solar energy to enter.

Thermal mass

The ability of a material to absorb and store heat energy.

Infiltration

The unintentional leakage of air into and out of a building through cracks, gaps, and openings.

UA-value

The overall heat transfer coefficient of a building, which measures the rate of heat loss or gain through the building envelope.

Thermal index

A measure of a building's energy efficiency, calculated based on the thermal performance of its components.

Sun-Tempered House

A house design that utilizes south-facing windows to capture solar heat and regulate indoor temperature.

Solar Gain Window Area

The area of windows in a house that allows for solar heat gain.

Thermal Mass

The ability of a material to absorb and store heat energy.

(UA)-value

The measure of heat loss or gain through a building component, calculated by dividing the overall heat transfer coefficient (U-value) by the area (A) of the component.