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In passive solar building design, windows, walls, and floors are made to collect, store, reflect, and distribute
solar energy Solar energy is radiant light and heat from the Sun that is harnessed using a range of technologies such as solar power to generate electricity, solar thermal energy (including solar water heating), and solar architecture. It is an essen ...
, in the form of heat in the winter and reject solar heat in the summer. This is called passive solar design because, unlike active
solar heating A solar thermal collector collects heat by absorbing sunlight. The term "solar collector" commonly refers to a device for solar hot water heating, but may refer to large power generating installations such as solar parabolic troughs and sola ...
systems, it does not involve the use of mechanical and electrical devices. The key to designing a passive solar building is to best take advantage of the local
climate Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologi ...
performing an accurate
site analysis Site analysis is a preliminary phase of architectural and urban design processes dedicated to the study of the climatic, geographical, historical, legal, and infrastructural context of a specific site. The result of this analytic process is a sum ...
. Elements to be considered include window placement and size, and glazing type,
thermal insulation Thermal insulation is the reduction of heat transfer (i.e., the transfer of thermal energy between objects of differing temperature) between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with ...
,
thermal mass In building design, thermal mass is a property of the mass of a building that enables it to store heat and provide inertia against temperature fluctuations. It is sometimes known as the thermal flywheel effect. The thermal mass of heavy structura ...
, and shading. Passive solar design techniques can be applied most easily to new buildings, but existing buildings can be adapted or "retrofitted".


Passive energy gain

''Passive solar'' technologies use
sunlight Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when ...
without active mechanical systems (as contrasted to ''active solar'', which uses thermal collectors). Such technologies convert sunlight into usable heat (in water, air, and thermal mass), cause air-movement for ventilating, or future use, with little use of other energy sources. A common example is a solarium on the
equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can also ...
-side of a building.
Passive cooling Passive cooling is a building design approach that focuses on heat gain control and heat dissipation in a building in order to improve the indoor thermal comfort with low or no energy consumption. This approach works either by preventing heat from ...
is the use of similar design principles to reduce summer cooling requirements. Some passive systems use a small amount of conventional energy to control dampers, shutters, night insulation, and other devices that enhance solar energy collection, storage, and use, and reduce undesirable
heat transfer Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy ( heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conducti ...
. Passive solar technologies include direct and indirect
solar gain Solar gain (also known as solar heat gain or passive solar gain) is the increase in thermal energy of a space, object or structure as it absorbs incident solar radiation. The amount of solar gain a space experiences is a function of the total in ...
for space heating,
solar water heating Solar water heating (SWH) is heating water by sunlight, using a solar thermal collector. A variety of configurations are available at varying cost to provide solutions in different climates and latitudes. SWHs are widely used for residential ...
systems based on the
thermosiphon Thermosiphon (or thermosyphon) is a method of passive heat exchange, based on natural convection, which circulates a fluid without the necessity of a mechanical pump. Thermosiphoning is used for circulation of liquids and volatile gases in heat ...
, use of
thermal mass In building design, thermal mass is a property of the mass of a building that enables it to store heat and provide inertia against temperature fluctuations. It is sometimes known as the thermal flywheel effect. The thermal mass of heavy structura ...
and phase-change materials for slowing indoor air temperature swings,
solar cooker A solar cooker is a device which uses the energy of direct sunlight to heat, cook or pasteurize drink and other food materials. Many solar cookers currently in use are relatively inexpensive, low-tech devices, although some are as powerful or as ...
s, the
solar chimney :''This article refers to a device for ventilation. For the power generation technology, see Solar updraft tower.'' A solar chimney often referred to as a thermal chimney is a way of improving the natural ventilation of buildings by using convect ...
for enhancing natural ventilation, and
earth sheltering An earth shelter, also called an earth house, earth bermed house, or underground house, is a structure (usually a house) with earth (soil) against the walls, on the roof, or that is entirely buried underground. Earth acts as thermal mass, making ...
. More widely, solar technologies include the solar furnace, but this typically requires some external energy for aligning their concentrating mirrors or receivers, and historically have not proven to be practical or cost effective for widespread use. 'Low-grade' energy needs, such as space and water heating, have proven over time to be better applications for passive use of solar energy.


As a science

The
scientific Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earliest archeological evidence for ...
basis for passive solar building design has been developed from a combination of
climatology Climatology (from Greek , ''klima'', "place, zone"; and , '' -logia'') or climate science is the scientific study of Earth's climate, typically defined as weather conditions averaged over a period of at least 30 years. This modern field of stu ...
,
thermodynamics Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws ...
(particularly
heat transfer Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy ( heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conducti ...
:
conduction (heat) Conduction is the process by which heat is transferred from the hotter end to the colder end of an object. The ability of the object to conduct heat is known as its ''thermal conductivity'', and is denoted . Heat spontaneously flows along a tem ...
,
convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the c ...
, and
electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visib ...
),
fluid mechanics Fluid mechanics is the branch of physics concerned with the mechanics of fluids ( liquids, gases, and plasmas) and the forces on them. It has applications in a wide range of disciplines, including mechanical, aerospace, civil, chemical and ...
/
natural convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...
(passive movement of air and water without the use of electricity, fans or pumps), and human
thermal comfort Thermal comfort is the condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation ( ANSI/ASHRAE Standard 55).ANSI/ASHRAE Standard 55-2017, Thermal Environmental Conditions for Human Occupan ...
based on
heat index The heat index (HI) is an index that combines air temperature and relative humidity, in shaded areas, to posit a human-perceived equivalent temperature, as how hot it would feel if the humidity were some other value in the shade. The result is al ...
,
psychrometrics Psychrometrics (or psychrometry, ; also called hygrometry) is the field of engineering concerned with the physical and thermodynamic properties of gas-vapor mixtures. Common applications Although the principles of psychrometry apply to any ph ...
and
enthalpy Enthalpy , a property of a thermodynamic system, is the sum of the system's internal energy and the product of its pressure and volume. It is a state function used in many measurements in chemical, biological, and physical systems at a constant ...
control for buildings to be inhabited by humans or animals,
sunroom A sunroom, also frequently called a solarium (and sometimes a "Florida room", "garden conservatory", "garden room", " patio room", "sun parlor", "sun porch", "three season room" or "winter garden"), is a room that permits abundant daylight and ...
s, solariums, and
greenhouse A greenhouse (also called a glasshouse, or, if with sufficient heating, a hothouse) is a structure with walls and roof made chiefly of transparent material, such as glass, in which plants requiring regulated climatic conditions are grown.These ...
s for raising plants. Specific attention is divided into: the site, location and solar orientation of the building, local sun path, the prevailing level of
insolation Solar irradiance is the power per unit area ( surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre ...
(
latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north ...
/sunshine/clouds/
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
), design and construction quality/materials, placement/size/type of windows and walls, and incorporation of solar-energy-storing
thermal mass In building design, thermal mass is a property of the mass of a building that enables it to store heat and provide inertia against temperature fluctuations. It is sometimes known as the thermal flywheel effect. The thermal mass of heavy structura ...
with
heat capacity Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to an object to produce a unit change in its temperature. The SI unit of heat capacity is joule per kelvin (J/K). Heat cap ...
. While these considerations may be directed toward any building, achieving an ideal optimized cost/performance solution requires careful,
holistic Holism () is the idea that various systems (e.g. physical, biological, social) should be viewed as wholes, not merely as a collection of parts. The term "holism" was coined by Jan Smuts in his 1926 book '' Holism and Evolution''."holism, n." OED On ...
,
system integration System integration is defined in engineering as the process of bringing together the component sub- systems into one system (an aggregation of subsystems cooperating so that the system is able to deliver the overarching functionality) and ensurin ...
engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad range of more speciali ...
of these scientific principles. Modern refinements through computer modeling (such as the comprehensive U.S. Department of Energy "Energy Plus"
building energy simulation Building performance simulation (BPS) is the replication of aspects of building performance using a computer-based, mathematical model created on the basis of fundamental physical principles and sound engineering practice. The objective of buildin ...
software), and application of decades of lessons learned (since the
1970s energy crisis The 1970s energy crisis occurred when the Western world, particularly the United States, Canada, Western Europe, Australia, and New Zealand, faced substantial petroleum shortages as well as elevated prices. The two worst crises of this period wer ...
) can achieve significant energy savings and reduction of environmental damage, without sacrificing functionality or aesthetics. In fact, passive-solar design features such as a greenhouse/sunroom/solarium can greatly enhance the livability, daylight, views, and value of a home, at a low cost per unit of space. Much has been learned about passive solar building design since the 1970s energy crisis. Many unscientific, intuition-based expensive construction experiments have attempted and failed to achieve zero energy – the total elimination of heating-and-cooling energy bills. Passive solar building construction may not be difficult or expensive (using off-the-shelf existing materials and technology), but the scientific passive solar building design is a non-trivial engineering effort that requires significant study of previous counter-intuitive lessons learned, and time to enter, evaluate, and iteratively refine the
simulation A simulation is the imitation of the operation of a real-world process or system over time. Simulations require the use of Conceptual model, models; the model represents the key characteristics or behaviors of the selected system or proc ...
input and output. One of the most useful post-construction evaluation tools has been the use of
thermography Infrared thermography (IRT), thermal video and/or thermal imaging, is a process where a thermal camera captures and creates an image of an object by using infrared radiation emitted from the object in a process, which are examples of infrared i ...
using digital thermal imaging cameras for a formal quantitative scientific
energy audit An energy audit is an inspection survey and an analysis of energy flows for energy conservation in a building. It may include a process or system to reduce the amount of energy input into the system without negatively affecting the output. In co ...
. Thermal imaging can be used to document areas of poor thermal performance such as the negative thermal impact of roof-angled glass or a skylight on a cold winter night or hot summer day. The scientific lessons learned over the last three decades have been captured in sophisticated comprehensive
building energy simulation Building performance simulation (BPS) is the replication of aspects of building performance using a computer-based, mathematical model created on the basis of fundamental physical principles and sound engineering practice. The objective of buildin ...
computer software systems (like U.S. DOE Energy Plus). Scientific passive solar building design with quantitative cost benefit
product optimization Production optimization is the practice of making changes or adjustments to a product to make it more desirable. Description A product has a number of attributes. For example, a soda bottle can have different packaging variations, flavors, nutrit ...
is not easy for a novice. The level of complexity has resulted in ongoing bad-architecture, and many intuition-based, unscientific construction experiments that disappoint their designers and waste a significant portion of their construction budget on inappropriate ideas. The economic motivation for scientific design and engineering is significant. If it had been applied comprehensively to new building construction beginning in 1980 (based on 1970s lessons learned), The United States could be saving over $250,000,000 per year on expensive energy and related pollution today. Since 1979, Passive Solar Building Design has been a critical element of achieving zero energy by educational institution experiments, and governments around the world, including the U.S. Department of Energy, and the energy research scientists that they have supported for decades. The
cost effective Cost-effectiveness analysis (CEA) is a form of economic analysis that compares the relative costs and outcomes (effects) of different courses of action. Cost-effectiveness analysis is distinct from cost–benefit analysis, which assigns a moneta ...
proof of concept Proof of concept (POC or PoC), also known as proof of principle, is a realization of a certain method or idea in order to demonstrate its feasibility, or a demonstration in principle with the aim of verifying that some concept or theory has prac ...
was established decades ago, but
cultural change Culture change is a term used in public policy making that emphasizes the influence of cultural capital on individual and community behavior. It has been sometimes called repositioning of culture, which means the reconstruction of the cultural conce ...
in architecture, the construction trades, and building-owner
decision making In psychology, decision-making (also spelled decision making and decisionmaking) is regarded as the cognitive process resulting in the selection of a belief or a course of action among several possible alternative options. It could be either ra ...
has been very slow and difficult. The new subjects such as ''architectural science'' and ''architectural technology'' are being added to some schools of architecture, with a future goal of teaching the above scientific and energy-engineering principles.


The solar path in passive design

The ability to achieve these goals simultaneously is fundamentally dependent on the seasonal variations in the sun's path throughout the day. This occurs as a result of the
inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Ea ...
of the Earth's axis of rotation in relation to its
orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...
. The sun path is unique for any given latitude. In Northern Hemisphere non-tropical latitudes farther than 23.5 degrees from the equator: * The sun will reach its
highest point A list of highest points typically contains the name, elevation, and location of the highest point in each of a set of geographical regions. Such a list is important in the sport of highpointing. A partial list of highpoint lists is below: World ...
toward the south (in the direction of the equator) * As winter
solstice A solstice is an event that occurs when the Sun appears to reach its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. Two solstices occur annually, around June 21 and December 21. In many count ...
approaches, the
angle In Euclidean geometry, an angle is the figure formed by two rays, called the '' sides'' of the angle, sharing a common endpoint, called the ''vertex'' of the angle. Angles formed by two rays lie in the plane that contains the rays. Angles ...
at which the sun rises and sets progressively moves further toward the south and the daylight hours will become shorter * The opposite is noted in summer where the sun will rise and set further toward the north and the daylight hours will lengthen The converse is observed in the Southern Hemisphere, but the sun rises to the east and sets toward the west regardless of which hemisphere you are in. In equatorial regions at less than 23.5 degrees, the position of the sun at
solar noon Noon (or midday) is 12 o'clock in the daytime. It is written as 12 noon, 12:00 m. (for meridiem, literally 12:00 noon), 12 p.m. (for post meridiem, literally "after noon"), 12 pm, or 12:00 (using a 24-hour clock) or 1200 ( military time). Sola ...
will oscillate from north to south and back again during the year. In regions closer than 23.5 degrees from either north-or-south pole, during summer the sun will trace a complete circle in the sky without setting whilst it will never appear above the horizon six months later, during the height of winter. The 47-degree difference in the altitude of the sun at
solar noon Noon (or midday) is 12 o'clock in the daytime. It is written as 12 noon, 12:00 m. (for meridiem, literally 12:00 noon), 12 p.m. (for post meridiem, literally "after noon"), 12 pm, or 12:00 (using a 24-hour clock) or 1200 ( military time). Sola ...
between winter and summer forms the basis of passive solar design. This information is combined with local climatic data (
degree day A degree day is a measure of heating or cooling. Total degree days from an appropriate starting date are used to plan the planting of crops and management of pests and pest control timing. Weekly or monthly degree-day figures may also be used wi ...
) heating and cooling requirements to determine at what time of the year solar gain will be beneficial for
thermal comfort Thermal comfort is the condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation ( ANSI/ASHRAE Standard 55).ANSI/ASHRAE Standard 55-2017, Thermal Environmental Conditions for Human Occupan ...
, and when it should be blocked with shading. By strategic placement of items such as glazing and shading devices, the percent of solar gain entering a building can be controlled throughout the year. One
passive solar In passive solar building design, windows, walls, and floors are made to collect, store, reflect, and distribute solar energy, in the form of heat in the winter and reject solar heat in the summer. This is called passive solar design because, unli ...
sun path design problem is that although the sun is in the same relative position six weeks before, and six weeks after, the solstice, due to "thermal lag" from the
thermal mass In building design, thermal mass is a property of the mass of a building that enables it to store heat and provide inertia against temperature fluctuations. It is sometimes known as the thermal flywheel effect. The thermal mass of heavy structura ...
of the Earth, the temperature and solar gain requirements are quite different before and after the summer or winter solstice. Movable shutters, shades, shade screens, or window quilts can accommodate day-to-day and hour-to-hour solar gain and insulation requirements. Careful arrangement of rooms completes the passive solar design. A common recommendation for residential dwellings is to place living areas facing solar noon and sleeping quarters on the opposite side. A heliodon is a traditional movable light device used by architects and designers to help model sun path effects. In modern times, 3D computer graphics can visually simulate this data, and calculate performance predictions.


Passive solar heat transfer principles

Personal
thermal comfort Thermal comfort is the condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation ( ANSI/ASHRAE Standard 55).ANSI/ASHRAE Standard 55-2017, Thermal Environmental Conditions for Human Occupan ...
is a function of personal health factors (medical, psychological, sociological and situational), ambient air temperature,
mean radiant temperature __NOTOC__ The concept of mean radiant temperature (MRT) is used to quantify the exchange of radiant heat between a human and their surrounding environment, with a view to understanding the influence of surface temperatures on personal comfort. Mean ...
, air movement (
wind chill Wind chill or windchill (popularly wind chill factor) is the lowering of body temperature due to the passing-flow of lower-temperature air. Wind chill numbers are always lower than the air temperature for values where the formula is valid. When ...
,
turbulence In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...
) and
relative humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity dep ...
(affecting human evaporative cooling).
Heat transfer Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy ( heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conducti ...
in buildings occurs through
convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the c ...
,
conduction Conductor or conduction may refer to: Music * Conductor (music), a person who leads a musical ensemble, such as an orchestra. * ''Conductor'' (album), an album by indie rock band The Comas * Conduction, a type of structured free improvisation ...
, and
thermal radiation Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) i ...
through roof, walls, floor and windows.


Convective heat transfer

Convective heat transfer Convection (or convective heat transfer) is the transfer of heat from one place to another due to the movement of fluid. Although often discussed as a distinct method of heat transfer, convective heat transfer involves the combined processes o ...
can be beneficial or detrimental. Uncontrolled air infiltration from poor
weatherization Weatherization (American English) or weatherproofing (British English) is the practice of protecting a building and its interior from the elements, particularly from sunlight, precipitation, and wind, and of modifying a building to reduce ...
/ weatherstripping / draft-proofing can contribute up to 40% of heat loss during winter; however, strategic placement of operable windows or vents can enhance convection, cross-ventilation, and summer cooling when the outside air is of a comfortable temperature and
relative humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity dep ...
. Filtered energy recovery ventilation systems may be useful to eliminate undesirable humidity, dust, pollen, and microorganisms in unfiltered ventilation air. Natural convection causing
rising Rising may refer to: * Rising, a stage in baking - see Proofing (baking technique) *Elevation * Short for Uprising, a rebellion Film and TV * "Rising" (''Stargate Atlantis''), the series premiere of the science fiction television program ''Starg ...
warm air and falling cooler air can result in an uneven stratification of heat. This may cause uncomfortable variations in temperature in the upper and lower conditioned space, serve as a method of venting hot air, or be designed in as a natural-convection air-flow loop for
passive solar In passive solar building design, windows, walls, and floors are made to collect, store, reflect, and distribute solar energy, in the form of heat in the winter and reject solar heat in the summer. This is called passive solar design because, unli ...
heat distribution and temperature equalization. Natural human cooling by
perspiration Perspiration, also known as sweating, is the production of fluids secreted by the sweat glands in the skin of mammals. Two types of sweat glands can be found in humans: eccrine glands and apocrine glands. The eccrine sweat glands are distr ...
and
evaporation Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when h ...
may be facilitated through natural or forced convective air movement by fans, but ceiling fans can disturb the stratified insulating air layers at the top of a room, and accelerate heat transfer from a hot attic, or through nearby windows. In addition, high
relative humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity dep ...
inhibits evaporative cooling by humans.


Radiative heat transfer

The main source of
heat transfer Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy ( heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conducti ...
is
radiant energy Radiant may refer to: Computers, software, and video games * Radiant (software), a content management system * GtkRadiant, a level editor created by id Software for their games * Radiant AI, a technology developed by Bethesda Softworks for ''Th ...
, and the primary source is the sun. Solar radiation occurs predominantly through the roof and windows (but also through walls).
Thermal radiation Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) i ...
moves from a warmer surface to a cooler one. Roofs receive the majority of the solar radiation delivered to a house. A
cool roof Reflective surfaces or ground-based albedo modification (GBAM) is a solar radiation management method of enhancing the Earth's albedo (the ability to reflect the visible, infrared and ultraviolet wavelengths of the sun, reducing heat transfer to ...
, or
green roof A green roof or living roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and draina ...
in addition to a
radiant barrier A radiant barrier is a type of building material that reflects thermal radiation and reduces heat transfer. Because thermal energy is also transferred by conduction and convection, in addition radiation, radiant barriers are often supplemented wit ...
can help prevent your attic from becoming hotter than the peak summer outdoor air temperature (see
albedo Albedo (; ) is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that refle ...
, absorptivity,
emissivity The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation. Thermal radiation is electromagnetic radiation that most commonly includes both visible radiation (light) and infrared radiation, which is n ...
, and
reflectivity The reflectance of the surface of a material is its effectiveness in reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the response of the electronic ...
). Windows are a ready and predictable site for
thermal radiation Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) i ...
. Energy from radiation can move into a window in the day time, and out of the same window at night. Radiation uses
photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they alwa ...
s to transmit
electromagnetic waves In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) ...
through a vacuum, or translucent medium. Solar heat gain can be significant even on cold clear days. Solar heat gain through windows can be reduced by
insulated glazing Insulating glass (IG) consists of two or more glass window panes separated by a space to reduce heat transfer across a part of the building envelope. A window with insulating glass is commonly known as double glazing or a double-paned window, ...
, shading, and orientation. Windows are particularly difficult to insulate compared to roof and walls.
Convective heat transfer Convection (or convective heat transfer) is the transfer of heat from one place to another due to the movement of fluid. Although often discussed as a distinct method of heat transfer, convective heat transfer involves the combined processes o ...
through and around
window covering Window coverings are considered any type of materials used to cover a window to manage sunlight, privacy, additional weatherproofing or for purely decorative purposes. Window coverings are typically used on the interior side of windows, but exte ...
s also degrade its insulation properties. When shading windows, external shading is more effective at reducing heat gain than internal
window covering Window coverings are considered any type of materials used to cover a window to manage sunlight, privacy, additional weatherproofing or for purely decorative purposes. Window coverings are typically used on the interior side of windows, but exte ...
s. Western and eastern sun can provide warmth and lighting, but are vulnerable to overheating in summer if not shaded. In contrast, the low midday sun readily admits light and warmth during the winter, but can be easily shaded with appropriate length overhangs or angled louvres during summer and leaf bearing summer shade trees which shed their leaves in the fall. The amount of radiant heat received is related to the location
latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north ...
,
altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...
,
cloud cover Cloud cover (also known as cloudiness, cloudage, or cloud amount) refers to the fraction of the sky obscured by clouds on average when observed from a particular location. Okta is the usual unit for measurement of the cloud cover. The cloud c ...
, and seasonal / hourly angle of incidence (see Sun path and
Lambert's cosine law In optics, Lambert's cosine law says that the radiant intensity or luminous intensity observed from an ideal diffusely reflecting surface or ideal diffuse radiator is directly proportional to the cosine of the angle ''θ'' between the directi ...
). Another passive solar design principle is that thermal energy can be stored in certain building materials and released again when heat gain eases to stabilize diurnal (day/night) temperature variations. The complex interaction of
thermodynamic Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of ...
principles can be
counterintuitive A paradox is a logically self-contradictory statement or a statement that runs contrary to one's expectation. It is a statement that, despite apparently valid reasoning from true premises, leads to a seemingly self-contradictory or a logically u ...
for first-time designers. Precise
computer modeling Computer simulation is the process of mathematical modelling, performed on a computer, which is designed to predict the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be dete ...
can help avoid costly construction experiments.


Site specific considerations during design

*
Latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north ...
, sun path, and
insolation Solar irradiance is the power per unit area ( surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre ...
(sunshine) * Seasonal variations in solar gain e.g. cooling or heating degree days, solar
insolation Solar irradiance is the power per unit area ( surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre ...
,
humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity dep ...
* Diurnal variations in temperature *
Micro-climate A microclimate (or micro-climate) is a local set of atmospheric conditions that differ from those in the surrounding areas, often with a slight difference but sometimes with a substantial one. The term may refer to areas as small as a few squ ...
details related to breezes, humidity, vegetation and land contour * Obstructions / Over-shadowing – to solar gain or local cross-winds


Design elements for residential buildings in temperate climates

* Placement of room-types, internal doors and walls, and equipment in the house. * Orienting the building to face the equator (or a few degrees to the East to capture the morning sun) * Extending the building dimension along the east–west axis * Adequately sizing windows to face the midday sun in the winter, and be shaded in the summer. * Minimising windows on other sides, especially western windows * Erecting correctly sized, latitude-specific roof overhangs, or shading elements (shrubbery, trees, trellises, fences, shutters, etc.) * Using the appropriate amount and type of insulation including radiant barriers and bulk insulation to minimise seasonal excessive heat gain or loss * Using
thermal mass In building design, thermal mass is a property of the mass of a building that enables it to store heat and provide inertia against temperature fluctuations. It is sometimes known as the thermal flywheel effect. The thermal mass of heavy structura ...
to store excess solar energy during the winter day (which is then re-radiated during the night) The precise amount of equator-facing glass and thermal mass should be based on careful consideration of latitude, altitude, climatic conditions, and heating/cooling
degree day A degree day is a measure of heating or cooling. Total degree days from an appropriate starting date are used to plan the planting of crops and management of pests and pest control timing. Weekly or monthly degree-day figures may also be used wi ...
requirements. Factors that can degrade thermal performance: * Deviation from ideal orientation and north–south/east/west aspect ratio * Excessive glass area ("over-glazing") resulting in overheating (also resulting in glare and fading of soft furnishings) and heat loss when ambient air temperatures fall * Installing glazing where solar gain during the day and thermal losses during the night cannot be controlled easily e.g. West-facing, angled glazing, skylights * Thermal losses through non-insulated or unprotected glazing * Lack of adequate shading during seasonal periods of high solar gain (especially on the West wall) * Incorrect application of
thermal mass In building design, thermal mass is a property of the mass of a building that enables it to store heat and provide inertia against temperature fluctuations. It is sometimes known as the thermal flywheel effect. The thermal mass of heavy structura ...
to modulate daily temperature variations * Open staircases leading to unequal distribution of warm air between upper and lower floors as warm air rises * High building surface area to volume – Too many corners * Inadequate
weatherization Weatherization (American English) or weatherproofing (British English) is the practice of protecting a building and its interior from the elements, particularly from sunlight, precipitation, and wind, and of modifying a building to reduce ...
leading to high air infiltration * Lack of, or incorrectly installed,
radiant barrier A radiant barrier is a type of building material that reflects thermal radiation and reduces heat transfer. Because thermal energy is also transferred by conduction and convection, in addition radiation, radiant barriers are often supplemented wit ...
s during the hot season. (See also
cool roof Reflective surfaces or ground-based albedo modification (GBAM) is a solar radiation management method of enhancing the Earth's albedo (the ability to reflect the visible, infrared and ultraviolet wavelengths of the sun, reducing heat transfer to ...
and
green roof A green roof or living roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and draina ...
) * Insulation materials that are not matched to the main mode of heat transfer (e.g. undesirable convective/conductive/radiant
heat transfer Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy ( heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conducti ...
)


Efficiency and economics of passive solar heating

Technically, PSH is highly efficient. Direct-gain systems can utilize (i.e. convert into "useful" heat) 65–70% of the energy of solar radiation that strikes the aperture or collector. Passive solar fraction (PSF) is the percentage of the required heat load met by PSH and hence represents potential reduction in heating costs. RETScreen International has reported a PSF of 20–50%. Within the field of
sustainability Specific definitions of sustainability are difficult to agree on and have varied in the literature and over time. The concept of sustainability can be used to guide decisions at the global, national, and individual levels (e.g. sustainable livi ...
, energy conservation even of the order of 15% is considered substantial. Other sources report the following PSFs: *5–25% for modest systems *40% for "highly optimized" systems *Up to 75% for "very intense" systems In favorable climates such as the southwest United States, highly optimized systems can exceed 75% PSF. For more information see Solar Air Heat


Key passive solar building configurations

There are three distinct passive solar energy configurations, and at least one noteworthy hybrid of these basic configurations: *direct
solar system The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...
s *indirect solar systems *hybrid direct/indirect solar systems *isolated solar systems


Direct solar system

In a ''direct-gain passive solar system'', the indoor space acts as a solar collector, heat absorber, and distribution system. South-facing glass in the northern hemisphere(north-facing in the southern hemisphere) admits solar energy into the building interior where it directly heats (radiant energy absorption) or indirectly heats (through convection) thermal mass in the building such as concrete or masonry floors and walls. The floors and walls acting as thermal mass are incorporated as functional parts of the building and temper the intensity of heating during the day. At night, the heated thermal mass radiates heat into the indoor space. In cold climates, a ''sun-tempered building'' is the most basic type of direct gain passive solar configuration that simply involves increasing (slightly) the south-facing glazing area, without adding additional thermal mass. It is a type of direct-gain system in which the building envelope is well insulated, is elongated in an east–west direction, and has a large fraction (~80% or more) of the windows on the south side. It has little added thermal mass beyond what is already in the building (i.e., just framing, wall board, and so forth). In a sun-tempered building, the south-facing window area should be limited to about 5 to 7% of the total floor area, less in a sunny climate, to prevent overheating. Additional south-facing glazing can be included only if more thermal mass is added. Energy savings are modest with this system, and sun tempering is very low cost. In genuine ''direct gain passive solar systems'', sufficient thermal mass is required to prevent large temperature fluctuations in indoor air; more thermal mass is required than in a sun tempered building. Overheating of the building interior can result with insufficient or poorly designed thermal mass. About one-half to two-thirds of the interior surface area of the floors, walls and ceilings must be constructed of thermal storage materials. Thermal storage materials can be concrete, adobe, brick, and water. Thermal mass in floors and walls should be kept as bare as is functionally and aesthetically possible; thermal mass needs to be exposed to direct sunlight. Wall-to-wall carpeting, large throw rugs, expansive furniture, and large wall hangings should be avoided. Typically, for about every 1 ft2 of south-facing glass, about 5 to 10 ft3 of thermal mass is required for thermal mass (1 m3 per 5 to 10 m2). When accounting for minimal-to-average wall and floor coverings and furniture, this typically equates to about 5 to 10 ft2 per ft2 (5 to 10 m2 per m2) of south-facing glass, depending upon whether the sunlight strikes the surface directly. The simplest rule of thumb is that thermal mass area should have an area of 5 to 10 times the surface area of the direct-gain collector (glass) area. Solid thermal mass (e.g., concrete, masonry, stone, etc.) should be relatively thin, no more than about 4 in (100 mm) thick. Thermal masses with large exposed areas and those in direct sunlight for at least part of the day (2 hour minimum) perform best. Medium-to-dark, colors with high absorptivity, should be used on surfaces of thermal mass elements that will be in direct sunlight. Thermal mass that is not in contact with sunlight can be any color. Lightweight elements (e.g., drywall walls and ceilings) can be any color. Covering the glazing with tight-fitting, moveable insulation panels during dark, cloudy periods and nighttime hours will greatly enhance performance of a direct-gain system. Water contained within plastic or metal containment and placed in direct sunlight heats more rapidly and more evenly than solid mass due to natural convection heat transfer. The convection process also prevents surface temperatures from becoming too extreme as they sometimes do when dark colored solid mass surfaces receive direct sunlight. Depending on climate and with adequate thermal mass, south-facing glass area in a direct gain system should be limited to about 10 to 20% of the floor area (e.g., 10 to 20 ft2 of glass for a 100 ft2 floor area). This should be based on the net glass or glazing area. Note that most windows have a net glass/glazing area that is 75 to 85% of the overall window unit area. Above this level, problems with overheating, glare and fading of fabrics are likely.


Indirect solar system

In an ''indirect-gain passive solar system'', the thermal mass (
concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wid ...
, masonry, or water) is located directly behind the south-facing glass and in front of the heated indoor space and so there is no direct heating The position of the mass prevents sunlight from entering the indoor space and can also obstruct the view through the glass. There are two types of indirect gain systems: thermal storage wall systems and roof pond systems.


Thermal Storage (Trombe) Walls

In a ''thermal storage wall'' system, often called a ''
Trombe wall A Trombe wall is a massive equator-facing wall that is painted a dark color in order to absorb thermal energy from incident sunlight and covered with a glass on the outside with an insulating air-gap between the wall and the glaze. A Trombe wall is ...
'', a massive wall is located directly behind south-facing glass, which absorbs solar energy and releases it selectively towards the building interior at night. The wall can be constructed of cast-in-place concrete, brick, adobe, stone, or solid (or filled) concrete masonry units. Sunlight enters through the glass and is immediately absorbed at the surface of the mass wall and either stored or conducted through the material mass to the inside space. The thermal mass cannot absorb solar energy as fast as it enters the space between the mass and the window area. Temperatures of the air in this space can easily exceed 120 °F (49 °C). This hot air can be introduced into interior spaces behind the wall by incorporating heat-distributing vents at the top of the wall. This wall system was first envisioned and patented in 1881 by its inventor, Edward Morse. Felix Trombe, for whom this system is sometimes named, was a French engineer who built several homes using this design in the French Pyrenees in the 1960s. A thermal storage wall typically consists of a 4 to 16 in (100 to 400 mm) thick masonry wall coated with a dark, heat-absorbing finish (or a selective surface) and covered with a single or double layer of high transmissivity glass. The glass is typically placed from ¾ in to 2 in from the wall to create a small airspace. In some designs, the mass is located 1 to 2 ft (0.6 m) away from the glass, but the space is still not usable. The surface of the thermal mass absorbs the solar radiation that strikes it and stores it for nighttime use. Unlike a direct gain system, the thermal storage wall system provides passive solar heating without excessive window area and glare in interior spaces. However, the ability to take advantage of views and daylighting are eliminated. The performance of Trombe walls is diminished if the wall interior is not open to the interior spaces. Furniture, bookshelves and wall cabinets installed on the interior surface of the wall will reduce its performance. A classical ''Trombe wall'', also generically called a ''vented thermal storage wall'', has operable vents near the ceiling and floor levels of the mass wall that allow indoor air to flow through them by natural convection. As solar radiation heats the air trapped between the glass and wall and it begins to rise. Air is drawn into the lower vent, then into the space between the glass and wall to get heated by solar radiation, increasing its temperature and causing it to rise, and then exit through the top (ceiling) vent back into the indoor space. This allows the wall to directly introduce heated air into the space; usually at a temperature of about 90 °F (32 °C). If vents are left open at night (or on cloudy days), a reversal of convective airflow will occur, wasting heat by dissipating it outdoors. Vents must be closed at night so radiant heat from the interior surface of the storage wall heats the indoor space. Generally, vents are also closed during summer months when heat gain is not needed. During the summer, an exterior exhaust vent installed at the top of the wall can be opened to vent to the outside. Such venting makes the system act as a solar chimney driving air through the building during the day. Vented thermal storage walls vented to the interior have proven somewhat ineffective, mostly because they deliver too much heat during the day in mild weather and during summer months; they simply overheat and create comfort issues. Most solar experts recommended that thermal storage walls should not be vented to the interior. There are many variations of the Trombe wall system. An ''unvented thermal storage wall'' (technically not a Trombe wall) captures solar energy on the exterior surface, heats up, and conducts heat to the interior surface, where it radiates from the interior wall surface to the indoor space later in the day. A ''water wall'' uses a type of thermal mass that consists of tanks or tubes of water used as thermal mass. A typical unvented thermal storage wall consists of a south facing masonry or concrete wall with a dark, heat-absorbing material on the exterior surface and faced with a single or double layer of glass. High transmission glass maximizes solar gains to the mass wall. The glass is placed from ¾ to 6 in. (20 to 150 mm) from the wall to create a small airspace. Glass framing is typically metal (e.g., aluminum) because vinyl will soften and wood will become super dried at the 180 °F (82 °C) temperature that can exist behind the glass in the wall. Heat from sunlight passing through the glass is absorbed by the dark surface, stored in the wall, and conducted slowly inward through the masonry. As an architectural detail, patterned glass can limit the exterior visibility of the wall without sacrificing solar transmissivity. A water wall uses containers of water for thermal mass instead of a solid mass wall. Water walls are typically slightly more efficient than solid mass walls because they absorb heat more efficiently due to the development of convective currents in the liquid water as it is heated. These currents cause rapid mixing and quicker transfer of heat into the building than can be provided by the solid mass walls. Temperature variations between the exterior and interior wall surfaces drive heat through the mass wall. Inside the building, however, daytime heat gain is delayed, only becoming available at the interior surface of the thermal mass during the evening when it is needed because the sun has set. The time lag is the time difference between when sunlight first strikes the wall and when the heat enters the building interior. Time lag is contingent upon the type of material used in the wall and the wall thickness; a greater thickness yields a greater time lag. The time lag characteristic of thermal mass, combined with dampening of temperature fluctuations, allows the use of varying daytime solar energy as a more uniform night-time heat source. Windows can be placed in the wall for natural lighting or aesthetic reasons, but this tends to lower the efficiency somewhat. The thickness of a thermal storage wall should be approximately 10 to 14 in (250 to 350 mm) for brick, 12 to 18 in (300 to 450 mm) for concrete, 8 to 12 in (200 to 300 mm) for earth/adobe, and at least 6 in (150 mm) for water. These thicknesses delay movement of heat such that indoor surface temperatures peak during late evening hours. Heat will take about 8 to 10 hours to reach the interior of the building (heat travels through a concrete wall at rate of about one inch per hour). A good thermal connection between the inside wall finishes (e.g., drywall) and the thermal mass wall is necessary to maximize heat transfer to the interior space. Although the position of a thermal storage wall minimizes daytime overheating of the indoor space, a well-insulated building should be limited to approximately 0.2 to 0.3 ft2 of thermal mass wall surface per ft2 of floor area being heated (0.2 to 0.3 m2 per m2 of floor area), depending upon climate. A water wall should have about 0.15 to 0.2 ft2 of water wall surface per ft2 (0.15 to 0.2 m2 per m2) of floor area. Thermal mass walls are best-suited to sunny winter climates that have high diurnal (day-night) temperature swings (e.g., southwest, mountain-west). They do not perform as well in cloudy or extremely cold climates or in climates where there is not a large diurnal temperature swing. Nighttime thermal losses through the thermal mass of the wall can still be significant in cloudy and cold climates; the wall loses stored heat in less than a day, and then leak heat, which dramatically raises backup heating requirements. Covering the glazing with tight-fitting, moveable insulation panels during lengthy cloudy periods and nighttime hours will enhance performance of a thermal storage system. The main drawback of thermal storage walls is their heat loss to the outside. Double glass (glass or any of the plastics) is necessary for reducing heat loss in most climates. In mild climates, single glass is acceptable. A selective surface (high-absorbing/low-emitting surface) applied to the exterior surface of the thermal storage wall improves performance by reducing the amount of infrared energy radiated back through the glass; typically, it achieves a similar improvement in performance without the need for daily installation and removal of insulating panels. A selective surface consists of a sheet of metal foil glued to the outside surface of the wall. It absorbs almost all the radiation in the visible portion of the solar spectrum and emits very little in the infrared range. High absorbency turns the light into heat at the wall's surface, and low emittance prevents the heat from radiating back towards the glass.


Roof Pond System

A ''roof pond'' ''passive solar system'', sometimes called a ''solar roof'', uses water stored on the roof to temper hot and cold internal temperatures, usually in desert environments. It typically is constructed of containers holding 6 to 12 in (150 to 300 mm) of water on a flat roof. Water is stored in large plastic bags or fiberglass containers to maximize radiant emissions and minimize evaporation. It can be left unglazed or can be covered by glazing. Solar radiation heats the water, which acts as a thermal storage medium. At night or during cloudy weather, the containers can be covered with insulating panels. The indoor space below the roof pond is heated by thermal energy emitted by the roof pond storage above. These systems require good drainage systems, movable insulation, and an enhanced structural system to support a 35 to 70 lb/ft2 (1.7 to 3.3 kN/m2) dead load. With the angles of incidence of sunlight during the day, roof ponds are only effective for heating at lower and mid-latitudes, in hot to temperate climates. Roof pond systems perform better for cooling in hot, low humidity climates. Not many solar roofs have been built, and there is limited information on the design, cost, performance, and construction details of thermal storage roofs.


Hybrid direct/indirect solar system

Kachadorian demonstrated that the drawbacks of thermal storage walls can be overcome by orienting the Trombe wall horizontally instead of vertically. If the thermal storage mass is constructed as a ventilated concrete slab floor instead of as a wall, it does not block sunlight from entering the home (the Trombe wall's most obvious disadvantage) but it can still be exposed to direct sunlight through double-glazed equator-facing windows, which can be further insulated by thermal shutters or shades at night. The Trombe wall's problematic delay in daytime heat capture is eliminated, because heat does not have to be driven through the wall to reach the interior air space: some of it reflects or re-radiates immediately from the floor. Provided the slab has air channels like the Trombe wall, which run through it in the north-south direction and are vented to the interior air space through the concrete slab floor just inside the north and south walls, vigorous air thermosiphoning through the slab still occurs as in the vertical Trombe wall, distributing the impounded heat throughout the house (and cooling the house in summer by the reverse process). The ventilated horizontal slab is less expensive to construct than vertical Trombe walls, as it forms the foundation of the house which is a necessary expense in any building. Slab-on-grade foundations are a common, well-understood and cost-effective building component (modified only slightly by the inclusion of a layer of concrete-brick air channels), rather than an exotic Trombe wall construct. The only remaining drawback to this kind of thermal mass solar architecture is the absence of a basement, as in any slab-on grade design. The ''Kachadorian floor'' design is a ''direct-gain'' passive solar system, but its thermal mass also acts as an ''indirect'' heating (or cooling) element, giving up its heat at night. It is an alternating cycle hybrid energy system, like a
hybrid electric vehicle A hybrid electric vehicle (HEV) is a type of hybrid vehicle that combines a conventional internal combustion engine (ICE) system with an Electric motor, electric propulsion system (hybrid vehicle drivetrain). The presence of the electric powertr ...
.


Isolated solar system

In an ''isolated gain passive solar system,'' the components (e.g., collector and thermal storage) are isolated from the indoor area of the building. An ''attached sunspace'', also sometimes called a ''solar room'' or ''solarium'', is a type of isolated gain solar system with a glazed interior space or room that is part of or attached to a building but which can be completely closed off from the main occupied areas. It functions like an attached greenhouse that makes use of a combination of direct-gain and indirect-gain system characteristics. A sunspace may be called and appear like a greenhouse, but a greenhouse is designed to grow plants whereas a sunspace is designed to provide heat and aesthetics to a building. Sunspaces are very popular passive design elements because they expand the living areas of a building and offer a room to grow plants and other vegetation. In moderate and cold climates, however, supplemental space heating is required to keep plants from freezing during extremely cold weather. An attached sunspace's south-facing glass collects solar energy as in a direct-gain system. The simplest sunspace design is to install vertical windows with no overhead glazing. Sunspaces may experience high heat gain and high heat loss through their abundance of glazing. Although horizontal and sloped glazing collects more heat in the winter, it is minimized to prevent overheating during summer months. Although overhead glazing can be aesthetically pleasing, an insulated roof provides better thermal performance. Skylights can be used to provide some daylighting potential. Vertical glazing can maximize gain in winter, when the angle of the sun is low, and yield less heat gain during the summer. Vertical glass is less expensive, easier to install and insulate, and not as prone to leaking, fogging, breaking, and other glass failures. A combination of vertical glazing and some sloped glazing is acceptable if summer shading is provided. A well-designed overhang may be all that is necessary to shade the glazing in the summer. The temperature variations caused by the heat losses and gains can be moderated by thermal mass and low-emissivity windows. Thermal mass can include a masonry floor, a masonry wall bordering the house, or water containers. Distribution of heat to the building can be accomplished through ceiling and floor level vents, windows, doors, or fans. In a common design, thermal mass wall situated on the back of the sunspace adjacent to the living space will function like an indirect-gain thermal mass wall. Solar energy entering the sunspace is retained in the thermal mass. Solar heat is conveyed into the building by conduction through the shared mass wall in the rear of the sunspace and by vents (like an unvented thermal storage wall) or through openings in the wall that permit airflow from the sunspace to the indoor space by convection (like a vented thermal storage wall). In cold climates, double glazing should be used to reduce conductive losses through the glass to the outside. Night-time heat loss, although significant during winter months, is not as essential in the sunspace as with direct gain systems since the sunspace can be closed off from the rest of the building. In temperate and cold climates, thermally isolating the sunspace from the building at night is important. Large glass panels, French doors, or sliding glass doors between the building and attached sunspace will maintain an open feeling without the heat loss associated with an open space. A sunspace with a masonry thermal wall will need approximately 0.3 ft2 of thermal mass wall surface per ft2 of floor area being heated (0.3 m2 per m2 of floor area), depending on climate. Wall thicknesses should be similar to a thermal storage wall. If a water wall is used between the sunspace and living space, about 0.20 ft2 of thermal mass wall surface per ft2 of floor area being heated (0.2 m2 per m2 of floor area) is appropriate. In most climates, a ventilation system is required in summer months to prevent overheating. Generally, vast overhead (horizontal) and east- and west-facing glass areas should not be used in a sunspace without special precautions for summer overheating such as using heat-reflecting glass and providing summer-shading systems areas. The internal surfaces of the thermal mass should be dark in color. Movable insulation (e.g., window coverings, shades, shutters) can be used help trap the warm air in the sunspace both after the sun has set and during cloudy weather. When closed during extremely hot days, window coverings can help keep the sunspace from overheating. To maximize comfort and efficiency, the non-glass sunspace walls, ceiling and foundation should be well insulated. The perimeter of the foundation wall or slab should be insulated to the frost line or around the slab perimeter. In a temperate or cold climate, the east and west walls of the sunspace should be insulated (no glass).


Additional measures

Measures should be taken to reduce heat loss at night e.g. window coverings or movable window insulation.


Heat storage

The sun doesn't shine all the time. Heat storage, or
thermal mass In building design, thermal mass is a property of the mass of a building that enables it to store heat and provide inertia against temperature fluctuations. It is sometimes known as the thermal flywheel effect. The thermal mass of heavy structura ...
, keeps the building warm when the sun can't heat it. In diurnal solar houses, the storage is designed for one or a few days. The usual method is a custom-constructed thermal mass. This includes a
Trombe wall A Trombe wall is a massive equator-facing wall that is painted a dark color in order to absorb thermal energy from incident sunlight and covered with a glass on the outside with an insulating air-gap between the wall and the glaze. A Trombe wall is ...
, a ventilated concrete floor, a cistern, water wall or roof pond. It is also feasible to use the thermal mass of the earth itself, either as-is or by incorporation into the structure by banking or using rammed earth as a structural medium. In subarctic areas, or areas that have long terms without solar gain (e.g. weeks of freezing fog), purpose-built thermal mass is very expensive. Don Stephens pioneered an experimental technique to use the ground as thermal mass large enough for annualized heat storage. His designs run an isolated thermosiphon 3 m under a house, and insulate the ground with a 6 m waterproof skirt.


Insulation

Thermal insulation Thermal insulation is the reduction of heat transfer (i.e., the transfer of thermal energy between objects of differing temperature) between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with ...
or
superinsulation Superinsulation is an approach to building design, construction, and retrofitting that dramatically reduces heat loss (and gain) by using much higher levels of insulation and airtightness than normal. Superinsulation is one of the ancestors of t ...
(type, placement and amount) reduces unwanted leakage of heat. Some passive buildings are actually constructed of insulation.


Special glazing systems and window coverings

The effectiveness of direct
solar gain Solar gain (also known as solar heat gain or passive solar gain) is the increase in thermal energy of a space, object or structure as it absorbs incident solar radiation. The amount of solar gain a space experiences is a function of the total in ...
systems is significantly enhanced by insulative (e.g.
double glazing Insulating glass (IG) consists of two or more glass window panes separated by a space to reduce heat transfer across a part of the building envelope. A window with insulating glass is commonly known as double glazing or a double-paned windo ...
), spectrally selective glazing ( low-e), or movable window insulation (window quilts, bifold interior insulation shutters, shades, etc.). Generally, Equator-facing windows should not employ glazing coatings that inhibit solar gain. There is extensive use of super-insulated windows in the
German German(s) may refer to: * Germany (of or related to) **Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ge ...
Passive House "Passive house" (german: Passivhaus) is a voluntary standard for energy efficiency in a building, which reduces the building's ecological footprint. It results in ultra-low energy buildings that require little energy for space heating or coo ...
standard. Selection of different spectrally selective window coating depends on the ratio of heating versus cooling
degree day A degree day is a measure of heating or cooling. Total degree days from an appropriate starting date are used to plan the planting of crops and management of pests and pest control timing. Weekly or monthly degree-day figures may also be used wi ...
s for the design location.


Glazing selection


Equator-facing glass

The requirement for vertical equator-facing glass is different from the other three sides of a building. Reflective window coatings and multiple panes of glass can reduce useful solar gain. However, direct-gain systems are more dependent on double or triple glazing or even quadruple glazing in higher geographic latitudes to reduce heat loss. Indirect-gain and isolated-gain configurations may still be able to function effectively with only single-pane glazing. Nevertheless, the optimal cost-effective solution is both location and system dependent.


Roof-angle glass and skylights

Skylights admit harsh direct overhead sunlight and glare either horizontally (a flat roof) or pitched at the same angle as the roof slope. In some cases, horizontal skylights are used with reflectors to increase the intensity of solar radiation (and harsh glare), depending on the roof angle of incidence. When the winter sun is low on the horizon, most solar radiation reflects off of roof angled glass ( the angle of incidence is nearly parallel to roof-angled glass morning and afternoon ). When the summer sun is high, it is nearly perpendicular to roof-angled glass, which maximizes solar gain at the wrong time of year, and acts like a solar furnace. Skylights should be covered and well-insulated to reduce
natural convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...
( warm air rising ) heat loss on cold winter nights, and intense solar heat gain during hot spring/summer/fall days. The equator-facing side of a building is south in the northern hemisphere, and north in the southern hemisphere. Skylights on roofs that face away from the equator provide mostly indirect illumination, except for summer days when the sun may rise on the non-equator side of the building (at some
latitudes In geography, latitude is a coordinate that specifies the north–south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pole ...
). Skylights on east-facing roofs provide maximum direct light and solar heat gain in the summer morning. West-facing skylights provide afternoon sunlight and heat gain during the hottest part of the day. Some skylights have expensive glazing that partially reduces summer solar heat gain, while still allowing some visible light transmission. However, if visible light can pass through it, so can some radiant heat gain (they are both
electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visib ...
waves). You can partially reduce some of the unwanted roof-angled-glazing summer solar heat gain by installing a skylight in the shade of
deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, ...
(leaf-shedding) trees, or by adding a movable insulated opaque window covering on the inside or outside of the skylight. This would eliminate the daylight benefit in the summer. If tree limbs hang over a roof, they will increase problems with leaves in rain gutters, possibly cause roof-damaging ice dams, shorten roof life, and provide an easier path for pests to enter your attic. Leaves and twigs on skylights are unappealing, difficult to clean, and can increase the glazing breakage risk in wind storms. "Sawtooth roof glazing" with vertical-glass-only can bring some of the passive solar building design benefits into the core of a commercial or industrial building, without the need for any roof-angled glass or skylights. Skylights provide daylight. The only view they provide is essentially straight up in most applications. Well-insulated
light tube Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 terah ...
s can bring daylight into northern rooms, without using a skylight. A passive-solar greenhouse provides abundant daylight for the equator-side of the building. Infrared
thermography Infrared thermography (IRT), thermal video and/or thermal imaging, is a process where a thermal camera captures and creates an image of an object by using infrared radiation emitted from the object in a process, which are examples of infrared i ...
color thermal imaging cameras ( used in formal
energy audit An energy audit is an inspection survey and an analysis of energy flows for energy conservation in a building. It may include a process or system to reduce the amount of energy input into the system without negatively affecting the output. In co ...
s ) can quickly document the negative thermal impact of roof-angled glass or a skylight on a cold winter night or hot summer day. The U.S. Department of Energy states: "vertical glazing is the overall best option for sunspaces." Roof-angled glass and sidewall glass are not recommended for passive solar sunspaces. The U.S. DOE explains drawbacks to roof-angled glazing: Glass and plastic have little structural strength. When installed vertically, glass (or plastic) bears its own weight because only a small area (the top edge of the glazing) is subject to gravity. As the glass tilts off the vertical axis, however, an increased area (now the sloped cross-section) of the glazing has to bear the force of gravity. Glass is also brittle; it does not flex much before breaking. To counteract this, you usually must increase the thickness of the glazing or increase the number of structural supports to hold the glazing. Both increase overall cost, and the latter will reduce the amount of solar gain into the sunspace. Another common problem with sloped glazing is its increased exposure to the weather. It is difficult to maintain a good seal on roof-angled glass in intense sunlight. Hail, sleet, snow, and wind may cause material failure. For occupant safety, regulatory agencies usually require sloped glass to be made of safety glass, laminated, or a combination thereof, which reduce solar gain potential. Most of the roof-angled glass on the Crowne Plaza Hotel Orlando Airport sunspace was destroyed in a single windstorm. Roof-angled glass increases construction cost, and can increase insurance premiums. Vertical glass is less susceptible to weather damage than roof-angled glass. It is difficult to control solar heat gain in a sunspace with sloped glazing during the summer and even during the middle of a mild and sunny winter day. Skylights are the antithesis of
zero energy building A Zero Energy Building (ZEB), also known as a Net Zero Energy (NZE) building, is a building with net zero energy consumption, meaning the total amount of energy used by the building on an annual basis is equal to the amount of renewable energy c ...
Passive Solar Cooling in climates with an air conditioning requirement.


Angle of incident radiation

The amount of solar gain transmitted through glass is also affected by the angle of the incident
solar radiation Solar irradiance is the power per unit area ( surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre ...
.
Sunlight Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when ...
striking a single sheet of glass within 45 degrees of
perpendicular In elementary geometry, two geometric objects are perpendicular if they intersect at a right angle (90 degrees or π/2 radians). The condition of perpendicularity may be represented graphically using the '' perpendicular symbol'', ⟂. It c ...
is mostly transmitted (less than 10% is reflected), whereas for sunlight striking at 70 degrees from perpendicular over 20% of light is reflected, and above 70 degrees this percentage reflected rises sharply. All of these factors can be modeled more precisely with a photographic
light meter A light meter is a device used to measure the amount of light. In photography, a light meter (more correctly an exposure meter) is used to determine the proper exposure (photography), exposure for a photograph. The meter will include either a Di ...
and a heliodon or optical bench, which can quantify the ratio of
reflectivity The reflectance of the surface of a material is its effectiveness in reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the response of the electronic ...
to transmissivity, based on angle of incidence. Alternatively, passive solar computer software can determine the impact of sun path, and cooling-and-heating
degree day A degree day is a measure of heating or cooling. Total degree days from an appropriate starting date are used to plan the planting of crops and management of pests and pest control timing. Weekly or monthly degree-day figures may also be used wi ...
s on
energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of ...
performance.


Operable shading and insulation devices

A design with too much equator-facing glass can result in excessive winter, spring, or fall day heating, uncomfortably bright living spaces at certain times of the year, and excessive heat transfer on winter nights and summer days. Although the sun is at the same altitude 6-weeks before and after the solstice, the heating and cooling requirements before and after the solstice are significantly different. Heat storage on the Earth's surface causes "thermal lag." Variable cloud cover influences solar gain potential. This means that latitude-specific fixed window overhangs, while important, are not a complete seasonal solar gain control solution. Control mechanisms (such as manual-or-motorized interior insulated drapes, shutters, exterior roll-down shade screens, or retractable awnings) can compensate for differences caused by thermal lag or cloud cover, and help control daily / hourly solar gain requirement variations.
Home automation Home automation or domotics is building automation for a home, called a smart home or smart house. A home automation system will monitor and/or control home attributes such as lighting, climate, entertainment systems, and appliances. It m ...
systems that monitor temperature, sunlight, time of day, and room occupancy can precisely control motorized window-shading-and-insulation devices.


Exterior colors reflecting – absorbing

Materials and colors can be chosen to reflect or absorb
solar thermal energy Solar thermal energy (STE) is a form of energy and a technology for harnessing solar energy to generate thermal energy for use in industry, and in the residential and commercial sectors. Solar thermal collectors are classified by the United St ...
. Using information on a
Color Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...
for
electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visib ...
to determine its
thermal radiation Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) i ...
properties of reflection or absorption can assist the choices.
Se
Lawrence Berkeley National Laboratory and Oak Ridge National Laboratory: "Cool Colors"
In cold climates with short winter days direct-gain systems utilizing equator-facing windows may actually perform better when snow covers the ground, since reflected as well as direct sunlight will enter the house and be captured as heat.


Landscaping and gardens

Energy-efficient landscaping Energy-efficient landscaping is a type of landscaping designed for the purpose of conserving energy. There is a distinction between the embedded energy of materials and constructing the landscape, and the energy consumed by the maintenance and ope ...
materials for careful passive solar choices include
hardscape Hardscape refers to hard landscape materials in the built environment structures that are incorporated into a landscape. This can include paved areas, driveways, retaining walls, sleeper walls, stairs, walkways, and any other landscaping mad ...
building material and "
softscape Softscape refers to the live horticultural elements of a landscape. Softscaping can include flowers, plants, shrubs, trees, flower beds, and duties like weed/nuisance management, grading, planting, mowing, trimming, aerating, spraying, and digging ...
"
plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae excl ...
s. The use of
landscape design Landscape design is an independent profession and a design and art tradition, practiced by landscape designers, combining nature and culture. In contemporary practice, landscape design bridges the space between landscape architecture and ga ...
principles for selection of
trees In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are u ...
,
hedge A hedge or hedgerow is a line of closely spaced shrubs and sometimes trees, planted and trained to form a barrier or to mark the boundary of an area, such as between neighbouring properties. Hedges that are used to separate a road from adjoi ...
s, and trellis-
pergola A pergola is most commonly an outdoor garden feature forming a shaded walkway, passageway, or sitting area of vertical posts or pillars that usually support cross-beams and a sturdy open lattice, often upon which woody vines are trained. T ...
features with
vine A vine (Latin ''vīnea'' "grapevine", "vineyard", from ''vīnum'' "wine") is any plant with a growth habit of trailing or scandent (that is, climbing) stems, lianas or runners. The word ''vine'' can also refer to such stems or runners themsel ...
s; all can be used to create summer shading. For winter solar gain it is desirable to use
deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, ...
plants that drop their leaves in the autumn gives year round passive solar benefits. Non-deciduous
evergreen In botany, an evergreen is a plant which has foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with deciduous plants, whic ...
shrub A shrub (often also called a bush) is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from tree ...
s and trees can be
windbreak A windbreak (shelterbelt) is a planting usually made up of one or more rows of trees or shrubs planted in such a manner as to provide shelter from the wind and to protect soil from erosion. They are commonly planted in hedgerows around the edges ...
s, at variable heights and distances, to create protection and shelter from winter
wind chill Wind chill or windchill (popularly wind chill factor) is the lowering of body temperature due to the passing-flow of lower-temperature air. Wind chill numbers are always lower than the air temperature for values where the formula is valid. When ...
.
Xeriscaping Xeriscaping is the process of Garden design, landscaping, or gardening, that reduces or eliminates the need for irrigation. It is promoted in regions that do not have accessible, plentiful, or reliable supplies of fresh water and has gained accep ...
with 'mature size appropriate'
native species In biogeography, a native species is indigenous to a given region or ecosystem if its presence in that region is the result of only local natural evolution (though often popularised as "with no human intervention") during history. The term is e ...
of-and drought tolerant plants,
drip irrigation Drip irrigation or trickle irrigation is a type of micro-irrigation system that has the potential to save water and nutrients by allowing water to drip slowly to the roots of plants, either from above the soil surface or buried below the surface. ...
, mulching, and
organic gardening Organic horticulture is the science and art of growing fruits, vegetables, flowers, or ornamental plants by following the essential principles of organic agriculture in soil building and conservation, pest management, and heirloom variety prese ...
practices reduce or eliminate the need for energy-and-water-intensive
irrigation Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow crops, landscape plants, and lawns. Irrigation has been a key aspect of agriculture for over 5,000 years and has been devel ...
, gas powered garden equipment, and reduces the landfill waste footprint. Solar powered
landscape lighting Landscape lighting or garden lighting refers to the use of outdoor illumination of private gardens and public landscapes; for the enhancement and purposes of safety, nighttime aesthetics, accessibility, security, recreation and sports, and s ...
and fountain pumps, and covered
swimming pool A swimming pool, swimming bath, wading pool, paddling pool, or simply pool, is a structure designed to hold water to enable Human swimming, swimming or other leisure activities. Pools can be built into the ground (in-ground pools) or built ...
s and
plunge pool A plunge pool (or plunge basin or waterfall lake) is a deep depression in a stream bed at the base of a waterfall or shut-in. It is created by the erosional forces of cascading water on the rocks at formation's base where the water impacts.Mars ...
s with solar water heaters can reduce the impact of such amenities. *
Sustainable gardening Sustainable gardening includes the more specific sustainable landscapes, sustainable landscape design, sustainable landscaping, sustainable landscape architecture, resulting in sustainable sites. It comprises a disparate group of horticultural i ...
* Sustainable landscaping * Sustainable landscape architecture


Other passive solar principles


Passive solar lighting

Passive solar lighting techniques enhance taking advantage of
natural Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans ar ...
illumination for interiors, and so reduce reliance on artificial lighting systems. This can be achieved by careful building design, orientation, and placement of window sections to collect light. Other creative solutions involve the use of reflecting surfaces to admit daylight into the interior of a building. Window sections should be adequately sized, and to avoid
over-illumination Overillumination is the presence of lighting intensity higher than that which is appropriate for a specific activity. Overillumination was commonly ignored between 1950 and 1995, especially in office and retail environments.M.D. Simpson, ''A fl ...
can be shielded with a
Brise soleil ''Brise soleil'', sometimes ''brise-soleil'' (; ), is an architectural feature of a building that reduces heat gain within that building by deflecting sunlight. More recently, vertical Brise soleil have become popular. Both systems allow low- ...
,
awning An awning or overhang is a secondary covering attached to the exterior wall of a building. It is typically composed of canvas woven of acrylic, cotton or polyester yarn, or vinyl laminated to polyester fabric that is stretched tightly over a li ...
s, well placed trees, glass coatings, and other passive and active devices.Chiras, D. The Solar House: Passive Heating and Cooling. Chelsea Green Publishing Company; 2002. Another major issue for many
window A window is an opening in a wall, door, roof, or vehicle that allows the exchange of light and may also allow the passage of sound and sometimes air. Modern windows are usually glazed or covered in some other transparent or translucent mat ...
systems is that they can be potentially vulnerable sites of excessive thermal gain or heat loss. Whilst high mounted
clerestory In architecture, a clerestory ( ; , also clearstory, clearstorey, or overstorey) is a high section of wall that contains windows above eye level. Its purpose is to admit light, fresh air, or both. Historically, ''clerestory'' denoted an upper l ...
window and traditional
skylight A skylight (sometimes called a rooflight) is a light-permitting structure or window, usually made of transparent or translucent glass, that forms all or part of the roof space of a building for daylighting and ventilation purposes. History Open ...
s can introduce daylight in poorly oriented sections of a building, unwanted heat transfer may be hard to control. Thus, energy that is saved by reducing artificial lighting is often more than offset by the energy required for operating
HVAC Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. ...
systems to maintain
thermal comfort Thermal comfort is the condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation ( ANSI/ASHRAE Standard 55).ANSI/ASHRAE Standard 55-2017, Thermal Environmental Conditions for Human Occupan ...
. Various methods can be employed to address this including but not limited to
window covering Window coverings are considered any type of materials used to cover a window to manage sunlight, privacy, additional weatherproofing or for purely decorative purposes. Window coverings are typically used on the interior side of windows, but exte ...
s,
insulated glazing Insulating glass (IG) consists of two or more glass window panes separated by a space to reduce heat transfer across a part of the building envelope. A window with insulating glass is commonly known as double glazing or a double-paned window, ...
and novel materials such as
aerogel Aerogels are a class of synthetic porous ultralight material derived from a gel, in which the liquid component for the gel has been replaced with a gas, without significant collapse of the gel structure. The result is a solid with extremely low ...
semi-transparent insulation,
optical fiber An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass ( silica) or plastic to a diameter slightly thicker than that of a human hair Hair is a protein filament that grows ...
embedded in walls or roof, o
hybrid solar lighting at Oak Ridge National Laboratory
Reflecting elements, from active and
passive daylighting Passive may refer to: * Passive voice, a grammatical voice common in many languages, see also Pseudopassive * Passive language, a language from which an interpreter works * Passivity (behavior), the condition of submitting to the influence of o ...
collectors, such as
light shelves A light shelf is a horizontal surface that reflects daylight deep into a building. Light shelves are placed above eye-level and have high-reflectance upper surfaces, which reflect daylight onto the ceiling and deeper into the space. Light shelve ...
, lighter wall and floor colors,
mirror A mirror or looking glass is an object that reflects an image. Light that bounces off a mirror will show an image of whatever is in front of it, when focused through the lens of the eye or a camera. Mirrors reverse the direction of the im ...
ed wall sections, interior walls with upper glass panels, and clear or translucent glassed hinged
door A door is a hinged or otherwise movable barrier that allows ingress (entry) into and egress (exit) from an enclosure. The created opening in the wall is a ''doorway'' or ''portal''. A door's essential and primary purpose is to provide security b ...
s and
sliding glass door A sliding glass door, patio door, or doorwall A sliding glass door, patio door, or doorwall is a type of predominantly glass sliding door, in architecture and construction, that is situated in an external wall to provide egress from a room a ...
s take the captured light and passively reflect it further inside. The light can be from passive windows or skylights and solar
light tube Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 terah ...
s or from
active daylighting Daylighting is the practice of placing windows, skylights, other openings, and reflective surfaces so that sunlight (direct or indirect) can provide effective internal lighting. Particular attention is given to daylighting while designing a bui ...
sources. In traditional
Japanese architecture has been typified by wooden structures, elevated slightly off the ground, with tiled or thatched roofs. Sliding doors (''fusuma'') and other traditional partitions were used in place of walls, allowing the internal configuration of a space to ...
the
Shōji A is a door, window or room divider used in traditional Japanese architecture, consisting of translucent (or transparent) sheets on a lattice frame. Where light transmission is not needed, the similar but opaque ''fusuma'' is used (oshiire/ ...
sliding panel doors, with translucent
Washi is traditional Japanese paper. The term is used to describe paper that uses local fiber, processed by hand and made in the traditional manner. ''Washi'' is made using fibers from the inner bark of the gampi tree, the mitsumata shrub (''E ...
screens, are an original precedent. International style,
Modernist Modernism is both a philosophy, philosophical and arts movement that arose from broad transformations in Western world, Western society during the late 19th and early 20th centuries. The movement reflected a desire for the creation of new fo ...
and Mid-century modern
architecture Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and constructing buildings ...
were earlier innovators of this passive penetration and reflection in industrial, commercial, and residential applications.


Passive solar water heating

There are many ways to use
solar thermal energy Solar thermal energy (STE) is a form of energy and a technology for harnessing solar energy to generate thermal energy for use in industry, and in the residential and commercial sectors. Solar thermal collectors are classified by the United St ...
to heat water for domestic use. Different active-and-passive
solar hot water Solar water heating (SWH) is heating water by sunlight, using a solar thermal collector. A variety of configurations are available at varying cost to provide solutions in different climates and latitudes. SWHs are widely used for residential an ...
technologies have different location-specific economic
cost benefit analysis In production, research, retail, and accounting, a cost is the value of money that has been used up to produce something or deliver a service, and hence is not available for use anymore. In business, the cost may be one of acquisition, in which ...
implications. Fundamental passive solar hot water heating involves no pumps or anything electrical. It is very cost effective in climates that do not have lengthy sub-freezing, or very-cloudy, weather conditions. Other active solar water heating technologies, etc. may be more appropriate for some locations. It is possible to have active solar hot water which is also capable of being "off grid" and qualifies as sustainable. This is done by the use of a photovoltaic cell which uses energy from the sun to power the pumps.


Comparison to the Passive House standard in Europe

There is growing momentum in Europe for the approach espoused by the
Passive House "Passive house" (german: Passivhaus) is a voluntary standard for energy efficiency in a building, which reduces the building's ecological footprint. It results in ultra-low energy buildings that require little energy for space heating or coo ...
(''Passivhaus'' in German) Institute in Germany. Rather than relying solely on traditional passive solar design techniques, this approach seeks to make use of all passive sources of heat, minimises energy usage, and emphasises the need for high levels of insulation reinforced by meticulous attention to detail in order to address thermal bridging and cold air infiltration. Most of the buildings built to the Passive House standard also incorporate an active
heat recovery ventilation Heat recovery ventilation (HRV), also known as mechanical ventilation heat recovery (MVHR), is an energy recovery ventilation system which works between two air sources at different temperatures. Heat recovery is a method which is used to reduce ...
unit with or without a small (typically 1 kW) incorporated heating component. The energy design of Passive House buildings is developed using a spreadsheet-based modeling tool called the Passive House Planning Package (PHPP) which is updated periodically. The current version is PHPP 9.6 (2018). A building may be certified as a "Passive House" when it can be shown that it meets certain criteria, the most important being that the annual specific heat demand for the house should not exceed 15kWh/m2a.


Comparison to the Zero heating building

With advances in ultra low U-value glazing a Passive House-based (nearly)
zero heating building Zero-heating building or nearly zero-heating building (nZHB) is a building having essentially zero heating demand, defined as having heating demand, Q’NH, less than 3 kWh/(m2a). The zero-heating building is intended for use in heating-dominated ar ...
is proposed to supersede the apparently failed nearly-zero energy buildings in EU. The zero heating building reduces on the passive solar design and makes the building more opened to conventional architectural design. The annual specific heat demand for the zero-heating house should not exceed 3 kWh/m2a. Zero heating building is simpler to design and to operate. For example: there is no need for modulated sun shading in zero-heating houses.


Design tools

Traditionally a heliodon was used to simulate the altitude and azimuth of the sun shining on a model building at any time of any day of the year. In modern times, computer programs can model this phenomenon and integrate local climate data (including site impacts such as overshadowing and physical obstructions) to predict the solar gain potential for a particular building design over the course of a year. GPS-based
smartphone A smartphone is a portable computer device that combines mobile telephone and computing functions into one unit. They are distinguished from feature phones by their stronger hardware capabilities and extensive mobile operating systems, whi ...
applications can now do this inexpensively on a hand held device. These design tools provide the passive solar designer the ability to evaluate local conditions, design elements and orientation prior to construction. Energy performance optimization normally requires an iterative-refinement design-and-evaluate process. There is no such thing as a "one-size-fits-all" universal passive solar building design that would work well in all locations.


Levels of application

Many detached suburban houses can achieve reductions in heating expense without obvious changes to their appearance, comfort or usability. This is done using good siting and window positioning, small amounts of thermal mass, with good-but-conventional insulation, weatherization, and an occasional supplementary heat source, such as a central radiator connected to a (solar) water heater. Sunrays may fall on a wall during the daytime and raise the temperature of its
thermal mass In building design, thermal mass is a property of the mass of a building that enables it to store heat and provide inertia against temperature fluctuations. It is sometimes known as the thermal flywheel effect. The thermal mass of heavy structura ...
. This will then radiate heat into the building in the evening. External shading, or a radiant barrier plus air gap, may be used to reduce undesirable summer solar gain. An extension of the "passive solar" approach to seasonal solar capture and storage of heat and cooling. These designs attempt to capture warm-season solar heat, and convey it to a seasonal thermal store for use months later during the cold season ("annualised passive solar.") Increased storage is achieved by employing large amounts of thermal mass or earth coupling. Anecdotal reports suggest they can be effective but no formal study has been conducted to demonstrate their superiority. The approach also can move cooling into the warm season. Examples: * Passive Annual Heat Storage (PAHS) – by John Hait *
Annualized Geothermal Solar Seasonal thermal energy storage (STES), also known as inter-seasonal thermal energy storage, is the storage of heat or cold for periods of up to several months. The thermal energy can be collected whenever it is available and be used whenever nee ...
(AGS) heating – by Don Stephen * Earthed-roof A "purely passive" solar-heated house would have no mechanical furnace unit, relying instead on energy captured from sunshine, only supplemented by "incidental" heat energy given off by lights, computers, and other task-specific appliances (such as those for cooking, entertainment, etc.), showering, people and pets. The use of natural convection air currents (rather than mechanical devices such as fans) to circulate air is related, though not strictly solar design. Passive solar building design sometimes uses limited electrical and mechanical controls to operate dampers, insulating shutters, shades, awnings, or reflectors. Some systems enlist small fans or solar-heated chimneys to improve convective air-flow. A reasonable way to analyse these systems is by measuring their
coefficient of performance The coefficient of performance or COP (sometimes CP or CoP) of a heat pump, refrigerator or air conditioning system is a ratio of useful heating or cooling provided to work (energy) required. Higher COPs equate to higher efficiency, lower energy ( ...
. A heat pump might use 1 J for every 4 J it delivers giving a COP of 4. A system that only uses a 30 W fan to more-evenly distribute 10 kW of solar heat through an entire house would have a COP of 300. Passive solar building design is often a foundational element of a cost-effective
zero energy building A Zero Energy Building (ZEB), also known as a Net Zero Energy (NZE) building, is a building with net zero energy consumption, meaning the total amount of energy used by the building on an annual basis is equal to the amount of renewable energy c ...
. Although a ZEB uses multiple passive solar building design concepts, a ZEB is usually not purely passive, having active mechanical renewable energy generation systems such as:
wind turbine A wind turbine is a device that converts the kinetic energy of wind into electrical energy. Hundreds of thousands of large turbines, in installations known as wind farms, now generate over 650 gigawatts of power, with 60 GW added each year. ...
,
photovoltaics Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially ...
,
micro hydro Micro hydro is a type of hydroelectric power that typically produces from 5 kW to 100 kW of electricity using the natural flow of water. Installations below 5 kW are called pico hydro. These installations can provide power to an i ...
, geothermal, and other emerging alternative energy sources. Passive solar is also a core building design strategy for passive survivability, along with other passive strategies.


Passive solar design on skyscrapers

There has been recent interest in the utilization of the large amounts of surface area on skyscrapers to improve their overall energy efficiency. Because skyscrapers are increasingly ubiquitous in urban environments, yet require large amounts of energy to operate, there is potential for large amounts of energy savings employing passive solar design techniques. One study, which analyzed the proposed
22 Bishopsgate 22 Bishopsgate, also known as Twentytwo, is a commercial skyscraper in London, England. Completed in 2020, it occupies a prominent site in Bishopsgate, in the City of London financial district, and stands at tall with 62 storeys. The project ...
tower in London, found that a 35% energy decrease in demand can theoretically be achieved through indirect solar gains, by rotating the building to achieve optimum ventilation and daylight penetration, usage of high thermal mass flooring material to decrease temperature fluctuation inside the building, and using double or triple glazed low emissivity window glass for direct solar gain. Indirect solar gain techniques included moderating wall heat flow by variations of wall thickness (from 20 to 30 cm), using window glazing on the outdoor space to prevent heat loss, dedicating 15–20% of floor area for thermal storage, and implementing a
Trombe wall A Trombe wall is a massive equator-facing wall that is painted a dark color in order to absorb thermal energy from incident sunlight and covered with a glass on the outside with an insulating air-gap between the wall and the glaze. A Trombe wall is ...
to absorb heat entering the space. Overhangs are used to block direct sunlight in the summer, and allow it in the winter, and heat reflecting blinds are inserted between the thermal wall and the glazing to limit heat build-up in the summer months. Another study analyzed double-green skin facade (DGSF) on the outside of high rise buildings in Hong Kong. Such a green facade, or vegetation covering the outer walls, can combat the usage of air conditioning greatly - as much as 80%, as discovered by the researchers. In more temperate climates, strategies such as glazing, adjustment of window-to-wall ratio, sun shading and roof strategies can offer considerable energy savings, in the 30% to 60% range.


See also

*
Site Analysis Site analysis is a preliminary phase of architectural and urban design processes dedicated to the study of the climatic, geographical, historical, legal, and infrastructural context of a specific site. The result of this analytic process is a sum ...
*
Daylighting Daylighting is the practice of placing windows, skylights, other openings, and reflective surfaces so that sunlight (direct or indirect) can provide effective internal lighting. Particular attention is given to daylighting while designing a b ...
*
Energy-plus-house An energy-plus building (also called: plus-energy house, efficiency-plus house) produces more energy from renewable energy sources, over the course of a year, than it imports from external sources. This is achieved using a combination of micro ...
*
List of low-energy building techniques Low-energy buildings, which include zero-energy buildings, passive houses and green buildings, may use any of a large number of techniques to lower energy use. The following are some of the techniques used to achieve low-energy buildings, which ...
* List of pioneering solar buildings *
Low energy building Low-energy buildings, which include zero-energy buildings, passive houses and green buildings, may use any of a large number of techniques to lower energy use. The following are some of the techniques used to achieve low-energy buildings, which ...
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Low-energy house A low-energy house is characterized by an energy-efficient design and technical features which enable it to provide high living standards and comfort with low energy consumption and carbon emissions. Traditional heating and active cooling systems ...
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Earthship An Earthship is a style of architecture developed in the late 20th century to early 21st century by architect Michael Reynolds. Earthships are designed to behave as passive solar earth shelters made of both natural and upcycled materials suc ...
* PlusEnergy *
Solar architecture Solar architecture is an architectural approach that takes in account the Sun to harness clean and renewable solar power. It is related to the fields of optics, thermics, electronics and materials science. Both active and passive solar housing ...
* Quadruple glazing * Energy Rating systems **
House Energy Rating The Nationwide House Energy Rating Scheme (NatHERS) is a national scheme to measure the energy efficiency of a residential dwelling in Australia. An accredited software tool assesses the home based on a variety of criteria and produces an energ ...
(Aust.) ** Home energy rating (USA) **
EnerGuide EnerGuide is the official Government of Canada mark associated with the labelling and rating of the energy consumption or energy efficiency of specific products. The EnerGuide's efficiency percent is calculated by dividing the power output by power ...
(Canada) **
National Home Energy Rating The National Home Energy Rating Scheme (NHER) is both a UK accreditation scheme for energy assessors and a rating scale for the energy efficiency of housing. The NHER was owned and operated by National Energy Services (NES). Until 2011, NES was ...
(UK)


References


Bibliography

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External links


www.solarbuildings.ca
– Canadian Solar Buildings Research Network

– US Department of Energy (DOE) Guidelines *
www.climatechange.gov.au
– Australian Dept of Climate Change and Energy Efficiency
www.ornl.gov
– Oak Ridge National Laboratory (ORNL) Building Technology
www.FSEC.UCF.edu
– Florida Solar Energy Center


www.PassiveSolarEnergy.info
– Passive Solar Energy Technology Overview

– Your Home Technical Manual developed by the Commonwealth of Australia to provide information about how to design, build and live in environmentally sustainable homes.

Energy in Architecture, The European Passive Solar Handbook, Goulding J.R, Owen Lewis J, Steemers Theo C, Sponsored by the European Commission, published by Batsford 1986, reprinted 1993 {{Design Energy-saving lighting Heating, ventilation, and air conditioning Low-energy building Sustainable urban planning Renewable energy Solar architecture es:Casa pasiva