Passive solar building design

Passive energy gain

Passive solar technologies use sunlight without active mechanical systems (as opposed to active solar ). Such technologies convert sunlight into usable heat (in water, air, and thermal mass), cause air-movement for ventilation , or future use, with little use of other energy sources. A common example is a solarium on the equator -side of a building. Passive cooling is the use of the same 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 .

Passive solar technologies live include and indirect solar gain for space heating, solar water heating systems based on the thermosiphon , use of thermal mass and Phase-change materials for Slowing indoor air temperature swings, solar cookers , the solar chimney for Enhancing natural ventilation, and earth sheltering .

More widely, passive solar technologies include the solar furnace , but this typically requires some external energy for their concentrating mirrors or receivers, and historically is not practical or effective. Low-grade energy needs, such as space and water heating, have been improved over time by solar energy.

As a science

The scientific basis for passive solar building design has-been Developed from a combination of climatology , thermodynamics (PARTICULARLY heat transfer : conduction (heat) , convection , and electromagnetic radiation ), fluid mechanics / natural convection (passive movement of air and water without the use of electricity, fans or pumps), and human thermal comfort based on heat index , psychrometrics and enthalpy control for buildings to be inhabited by humans or animals, sunrooms, solariums, and greenhouses for raising plants.

Location, location and solar orientation of the building, local sun path , the prevailing level of insolation ( latitude / sunshine / clouds / precipitation ), design and construction quality / materials, placement / size / type of windows and walls, and incorporation of solar energy-storing thermal mass with heat capacity .

While thesis considerations May be directed Toward Any building, Achieving an ideal optimized cost / performance solution requires careful, holistic , system integration engineering of These scientific principles. Modern refinements through computer modeling (such as the comprehensive US Department of Energy “Energy Plus” ^[3] building energy simulation software), and application of decades of lessons learned (since the 1970s energy crisis) can achieve significant energy savings and environmental reduction damage, without sacrificing functionality or aesthetics. ^[4] 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 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 can be used in the field of solar energy, 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 input and output.

One of The Most Useful post-construction assessment tools has-been the use of thermography using digital thermal imaging cameras for a quantitative scientific formal energy audit . 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 day or hot summer day.

The scientific lessons learned over the last three decades-have-been captured in sophisticated comprehensive building energy simulation computer software systems (like US DOE Energy Plus).

Scientific passive solar building design with quantitative cost benefit product optimization is not easy for a novice. The level of complexity has resulted in a persistent 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. ^[5]

The economic motivation for scientific design and engineering is significant. If it had been applied comprehensively to new building construction in 1980 (based on 1970s lessons learned), America could be saving over $ 250,000,000 per year on expensive energy and related pollution today. ^[5]

Since 1979, Passive Solar Building Design has been a critical element of achieving zero energy by educational institutions, and governments around the world, including the US Department of Energy, and the energy research scientists that they have supported for decades. The cost effective proof of concept Was Established decades ago, goal cultural assimilation into architecture, construction trades, and building-owner decision making has-been very slow and difficulty to change. ^[5]

The new terms “Architectural Science” and “Architectural Technology” are being added to some schools of Architecture, with a future goal of teaching the scientific and energy-engineering principles. ^{[ quote needed ]}

The solar path in passive design

The ability to achieve these goals is fundamentally dependent on the seasonal variations in the sun’s path throughout the day.

This OCCURS as a result of the inclination of the Earth’s axis of rotation in relation to ict orbit . The sun is unique for any given latitude.

Northern hemisphere non-tropical latitudes farther than 23.5 degrees from the equator:

• The sun will reach its highest point towards the south (in the direction of the equator)
• As winter solstice approaches, the angle at which the sun rises and sets progressively moves further towards the South and the daylight hours will be shorter
• The opposite is to be seen in the future and to the future of the North and the daylight hours will lengthen ^[6]

The Hemisphere, but the visions of the hemisphere are in the future.

In equatorial regions at less than 23.5 degrees, the position of the sun at solar noon will oscillate from north to south and back again During the Year. ^[7]

In regions closer than 23.5 degrees from north-west-south pole, during the summer months, it will not be possible to see more than six months later, during the height of winter. ^[8]

The 47-degree difference in the altitude of the sun at noon between winter and summer forms the basis of passive solar design. This information is combined with local climatic data ( degree day ) heating and cooling requirements to be determined at what time of the year solar gain will be beneficial for thermal comfort , and when it should be blocked with shading. By strategic positioning of items such as glazing and shading devices, the percent of solar gain can be controlled throughout the year.

One passive solar sun path is in the same relative position six weeks before, and six weeks after, the solstice, due to “thermal lag” from the thermal mass 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 complete rooms 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. ^[9] 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. ^[4]

Passive Solar Heat Transfer Principles

Personal thermal comfort is a function of personal health factors (medical, psychological, sociological and situational), ambient air temperature, mean radiant temperature , air movement ( wind chill , turbulence ) and relative humidity (Affecting human evaporative cooling). Heat transfer in buildings occurs through convection , conduction , and thermal radiation through roof, walls, floor and windows. ^[10]

Convective heat transfer

Convective heat transfer can be beneficial or detrimental. Uncontrolled air infiltration from poor weatherization / weatherstripping / draft-proofing can contribute up to 40% of heat loss during winter; ^[11] HOWEVER, strategic placement of operable windows or winds can Enhance convection, cross-ventilation and summer cooling When the outside air is of a comfortable temperature and relative humidity . ^[12] Filtered energy recovery ventilation systems may be useful in eliminating humidity, dust, pollen, and microorganisms in unfiltered ventilation air.

Natural convection causes rising warm air and falling air cooler can result in an uneven stratification of heat. This may cause uncomfortable variations in temperature and temperature, as well as in the use of hot air, or be designed in a natural convection air-flow loop for passive solar heat distribution and temperature equalization. Natural human cooling by perspiration and evaporation May be Facilitated through natural or forced convection air movement by fans, aim 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 inhibits evaporative cooling by humans.

Radiative heat transfer

The source of heat transfer is radiant energy , and the primary source is the sun. Solar radiation occurs predominantly through the roof and windows (but also through walls). Thermal radiation moves from a warmer surface to a cooler one. Roofs receive the majority of the solar radiation delivered to a house. A cool roof , or green roof in addition to a radiant barrier can help prevent your attic ^[13] (see albedo , absorptivity , emissivity , and reflectivity ).

Windows are a ready and predictable site for thermal radiation . ^[14] Energy from radiation can move into a window in the day, and out of the same window at night. Radiation uses photons to transmit electromagnetic wavesthrough 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 , shading, and orientation. Windows are particularly difficult to insulate compared to roof and walls. Convective heat transfer through and around window coverings also degrade its insulation properties. ^[14]When shading windows, external shading is more effective at reducing heat gain than internal window coverings . ^[14]

Western and eastern sun can provide warmth and light, but are not vulnerable to overeating. In contrast, the low midday sun is very low in the winter, but it may be easily shaded with the length of the leaves. The latitude , altitude , cloud cover , and seasonal / incidence angle of incidence (see Sun path and Lambert’s cosine law ).

Another passive solar design is that thermal energy can be stored in certain building materials and released again when heat gains eases to stabilize diurnal (day / night) temperature variations. The complex interaction of thermodynamic principles can be counterintuitive for first-time designers. Precise computer modeling can help you avoid costly construction experiments.

Site specific considerations during design

• Latitude , sun path , and insolation (sunshine)
• Seasonal variations in solar gain eg cooling or heating degree days , solar insolation , humidity
• Diurnal variations in temperature
• Micro-climate details related to breezes, humidity, vegetation and land outline
• 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 the equator (or a few degrees to the East to capture the morning sun) ^[9]
• Extending the building dimension along the east / west axis
• Adequately sizing in the summer, and being shaded in the summer.
• Minimizing windows on other sides, especially western windows ^[14]
• Erecting correctly sized, latitude-specific roof overhangs, ^[15] or shading elements (shrubbery, trees, trellises, fences, shutters, etc.) ^[16]
• Using the appropriate amount and type of insulation and minimizing excessive heat gain or loss
• Using thermal mass to store excess energy during the winter day (which is then re-radiated during the night) ^[17]

The precise amount of equator-facing glass and thermal mass should be based on consideration of latitude, altitude, climatic conditions, and heating / cooling degree day requirements.

Factors that can degrade thermal performance:

• Deviation from ideal orientation and north / south / west / west aspect ratio
• Excessive glass area (“over-glazing”) resulting in overheating (resulting in warming 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 can be controlled by eg West-facing, angled glazing, skylights ^[18]
• Thermal losses through non-insulated or unprotected glazing
• Lack of adequate shading during high solar gain periods (especially on the West wall)
• Incorrect application of thermal mass to moderate daily temperature variations
• Open staircases leading to a distribution of warm air between upper and lower floors as warm air rises
• High building area to volume – Too many corners
• Inadequate weatherization leading to high air infiltration
• Lack of, or incorrectly installed, radiant barriers during the hot season. (See also cool roof and green roof )
• Insulation materials that are not matched to the main mode of heat transfer (eg undesirable convective / conductive / radiant heat transfer )

Efficiency and economics of passive solar heating

Technically, PSH is highly efficient. Direct-gain systems can be used (ie, convert into “useful” heat) 65-70% of the energy of solar radiation or the aperture or collector.

Passive solar fraction (PSF) is the percentage of the required heat load and is represented by PSH. RETScreen International has reported a PSF of 20-50%. Within the field of sustainability , the energy conservation 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. ^[20]

For more information see Solar Air Heat

Key passive solar building configurations

There are three primary passive solar energy configurations: ^[21]

• direct solar system
• indirect solar system
• isolated solar system

Direct solar system

In a direct-gain passive solar system , the solar collector, heat absorber, and distribution system. South-facing glass in the northern hemisphere admits solar energy into the building where it directly heats up (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 a thermal mass are incorporated as part of the building and the heat of the day. At night, the heated thermal mass radiates heat into the indoor space. ^[21]

In cold climates, a sun-tempered buildingis the most basic type of direct passive solar gain. 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 is a new addition to the building (ie, 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. Energy savings are modest with this system, and are very low cost. ^[21]

In real 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 mass can be concrete, adobe, brick, and water. Thermal mass in floors and walls should be kept 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 ft ² of south-facing glass, about 5 to 10 ft ³ of thermal mass is required for thermal mass (1 m ³ per 5 to 10 m ² ). When accounting for a minimum-to-one wall and floor coverings and furniture, this typically equates to about 5 to 10 ft ² per ft ² (5 to 10 m ² per m ² ) of south-facing glass, depending on whether the sunlight strikes the surface directly. The simplest rule of thumb is that the thermal area should have an area of ​​5 to 10 times the surface area of ​​the direct-gain collector (glass) area. ^[21]

Solid thermal mass (eg, concrete, masonry, stone, etc.) should be relatively thin, no more than about 4 in (100 mm) thick. Thermal masses with a lot of sun in the sun (at least 2 hours) perform best. Medium-to-dark, with high absorbency, should be used on surfaces of thermal mass that will be in direct sunlight. Thermal mass is not in contact with sunlight can be any color. Lightweight elements (eg, 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 in plastics and the presence of heat in the air. The convection process also prevents the surface of the surface from becoming dark.

Depending on the 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 (eg, 10 to 20 ft ² of glass for a 100 ft ² floor area) . This should be based on the net glass or glazing area. Note that most windows have a glass / glazing area which is 75 to 85% of the overall window unit area. Above this level, problems with overheating, and fading of fabrics are likely. ^[21]

Indirect solar system

In an indirect-gain passive solar system , the thermal mass ( concrete , masonry, or water) is located directly behind the south-facing glass and in front of the heated indoor space and is not direct sunlight from entering the room and can also obstruct the view through the glass. There are two types of indirect gain systems: ^[21]

Thermal Storage (Trombe) Walls

In a thermal storage wall system, often called a Trombe Wall, 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 concrete, brick, adobe, stone, or solid concrete masonry units. Sunlight enters the glass and is immediately absorbed into the surface of the mass wall and is stored in the material mass to the inside space. The thermal mass can not 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 incorporated into the walls behind the wall by incorporating heat-distributing winds at the top of the wall. This wall system was first envisioned and patented in 1881 by its inventor, Edward Morse.

A thermal storage wall 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 in 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 and uses it for nighttime use. Unlike a direct gain system, the thermal storage system provides passive solar heating. However, the ability to take advantage of the daylighting is eliminated. The performance of Trombe walls is diminished if the wall is not open to the interior spaces. Furniture, bookshelves and wall cabinets installed on the interior of the wall will reduce its performance.

A classical trombe wall , also generically called a vented thermal storage wall , has operable winds to 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 it begins to rise. Air venting into the lower air, then into the space between the walls and the wall of the room. This allows the wall to be directly involved in air space; usually at a temperature of about 90 ° F (32 ° C).

If winds are left open at night (or on cloudy days), a reversal of convective airflow will occur, wasting heat by dissipating it outdoors. Winds must be closed at night so radiant heat from the interior surface of the storage wall heats the indoor space. Generally, winds 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 wind to the outside. Such winding makes the system act as a solar chimney driving through the building during the day.

Vented thermal storage walls have been somewhat ineffective, mostly due to 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 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 (eg, aluminum) because it will become very hot at 180 ° F (82 ° C). Heat from sunlight passing through the glass is absorbed by the dark surface, stored in the wall, and slowly conducted inward through the masonry. As an architectural detail, the pattern of glass can be seen in the exterior of the world without sacrificing solar transmissivity.

A water wall uses water containers for thermal mass instead of a solid mass wall. Water walls are more efficient than solid mass walls because they are more easily absorbed into the water. These currents cause rapid mixing and quick transfer of heat from the solid masses.

Temperature variations between the exterior and interior wall surfaces Inside the building, however, daytime heat gain is delayed, only become available at the interior surface of the thermal mass during the evening when it is needed because of the sun has set. The time lag is the time difference when the sun goes up. Time lag is contingent on 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 different daytime solar energy sources. Windows can be placed in the wall for natural lighting or aesthetic reasons,

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 the surface temperature 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 the rate of one inch per hour). A good thermal connection between the inside wall finishes (eg, 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 shoulds be limited to Approximately 0.2 to 0.3 ft ² of thermal mass wall area per ft ² of floor area being white heated (0.2 to 0.3 m ² per m ² of floor area), depending upon climate. A water wall should have about 0.15 to 0.2 ft ² of water wall area per ft ² (0.15 to 0.2 m ² per m ² ) of floor area.

Thermal balances are best-suited to sunny winter climates that have high diurnal (day-night) temperature swings (eg, southwest, mountain-west). They do not perform well in the climate or in the climate where there is a large 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 a less than a day, and then leak heat, which dramatically raises backup heating requirements. Covering the glazing with tight-fitting, moveable insulation panels during a long time cloudy periods and nighttime hours will enhance performance of a thermal storage system.

The main drawback of thermal storage 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 with 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 on the surface of the wall^[21]

Roof Pond System

A roof lays passive solar system , sometimes called Expired a solar roof, uses water stored on the roof, and 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 gold 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. These systems require good drainage systems, movable insulation, and an enhanced structural support system at 35 to 70 lb / ft ² (1.7 to 3.3 kN / m ²) dead load.

With the angles of incidence of sunlight during the day, it is only possible 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. ^[21]

Isolated solar system

In an isolated passive solar system , the components (eg, collector and thermal storage) are isolated from the indoor area of ​​the building. ^[21]

An attached sunspace , also sometimes called a solar room or solariumIt is a type of remote control that can be used to reduce the risk of damage to the environment. It functions like a combined greenhouse that makes a combination of direct-gain and indirect-gain system characteristics. A sunspace can be called and appears to be a greenhouse, but a greenhouse is designed to grow plants and 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 a room to grow plants and other vegetation. In moderate and cold climates, however, supplemental space heating is required to keep plants freezing during extremely cold weather.

An attached sunspace’s south-facing glass collects solar energy as a direct-gain system. The simplest sunspace design is to install vertical windows with no overhead glazing. Sunspaces can experience high heat gain and high heat loss through their abundance of glazing. Although horizontal and sloped in the winter, it is minimized to prevent overheating during the 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. The wind, windows, doors, or fans. In a common design, the thermal mass wall will be located in the living space of the living space. Solar energy entering the space is retained in the thermal mass.

In cold climates, double glazing should be used to reduce conductive losses through the glass to the outside. Night-time heat loss, which is important in the past, can not be excluded from 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 with open space.

A sunspace with a masonry wall will need thermal Approximately 0.3 ft ² of thermal mass wall area per ft ² of floor area being white heated (0.3 m ² per m ² 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 ft ² of thermal mass wall area per ft ² of floor area being heated (0.2 m ² per m ²of 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 be used as a heat sink and providing summer-shading systems.

The internal surfaces of the thermal mass should be dark in color. Movable insulation (eg, window coverings, shades, shutters) can be used to help the environment and the environment. When closed during extremely hot days, window coverings can help keep the sunspace from overheating.

To maximize comfort and efficiency, the non-glass roofs, ceiling and foundation should be 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).

Heat storage

The sun does not shine all the time. Heat storage, thermal mass gold , keeps the building warm when the sun can not heat it.

In diurnal solar houses, the storage is designed for one or a few days. The usual method is a custom-built thermal mass. This includes a trombe wall , a ventilated concrete floor, a cistern, a water wall or a roof pond. ^[22] It is also possible to use the thermal mass of the earth itself, either by incorporation into the structure or by using earth as a structural medium. ^[23]

In subarctic areas, or areas that have long terms without solar gain (eg 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 insulated thermosiphon 3 m under a house, and insulate the ground with a 6 m waterproof skirt. ^[24]

Insulation

Thermal insulation or superinsulation (type, placement and amount) reduces unwanted leakage of heat. ^[10] Some passive buildings are actually constructed of insulation .

Special glazing systems and window coverings

The effectiveness of direct solar gain is significantly enhanced by insulative (eg double glazing ), spectrally selective glazing ( low-e ), or movable window insulation (window quilts, interior insulation shutters, shades, etc.). ^[25]

Generally, Equator-facing windows should not employ glazing coatings that inhibit solar gain.

There is extensive use of super-insulated windows in the standard German Passive House . Selection of different spectrally selective window coating on the ratio of heating versus cooling degree days for design rental.

Glazing selection

Equator-facing glass

The requirement for vertical equator-facing glass is different from the other side 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 to reduce heat loss. Indirect-gain and isolated-gain configurations may still be able to function effectively with single-pane glazing. Nevertheless, the optimal cost-effective solution is both rental and system dependent.

Roof-angle glass and skylights

Skylights admitted harsh direct overhead sunlight and glare ^{[26] or} 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 angled glass roof (the angle of incidence is Nearly parallel to angled glass roof-morning and afternoon). When the summer 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 (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 southern hemisphere, and southern hemisphere. Some of the most important things are that of indirect illumination, except that the sun may rise on the non-equator side of the building (at some latitudes ). 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 is partially reduced during solar 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 waves).

You can partially reduce some of the roof-angled-glazing summer solar heat gain by installing a skylight in the shade of deciduous (leaf-shedding) trees, 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 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 risk of breakage.

“Sawtooth roof glazing” with vertical-glass-only can bring some of the passive solar building design benefits to 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 in the most applications. Well-insulated light tubes 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 color thermal imaging cameras (used in formal energy audits ) can Quickly thermal paper the negative impact of roof-angled glass gold skylight is a cold winter night or hot summer day.

The US Department of Energy states: “vertical glazing is the best option for sunspaces.” ^[27] Roof-angled glass and sidewall are not recommended for passive solar sunspaces.

The US DOE explains drawbacks to roof-angled glazing: When installed vertically, glass (or plastic) is subject to gravity. As the glass tilts off the vertical axis, however, an increased area of ​​the glazing has to bear the force of gravity (now the sloped cross-section). Glass is also brittle; it does not flex much before breaking. To counteract this, you should 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 in the space.

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 can cause material failure. For occupant safety, regulatory agencies usually require a laminated, or a combination thereof, which reduces solar gain potential. Most of the roof-angled glass on the Crowne Plaza Orlando Airport Hotel 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 space with sloped glazing during the summer and the middle of a mild and sunny winter day. Skylights are the antithesis of zero energy building. Passive Solar Cooling in climate with an air conditioning requirement.

Angle of incident radiation

The amount of solar energy gain is also affected by the angle of the solar radiation incident . Sunlight striking a single sheet of glass Within 45 degrees of perpendicular 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 . ^[28]

All of these factors can be modeled more precisely with a photographic light meter and a heliodon or optical bench , which can quantify the ratio of reflectivity to transmissivity , based on angle of incidence .

Alternatively, passive solar computer software can determine the impact of sun path , and cooling-and-heating degree days on energy performance.

Operable shading and insulation devices

A design with too much equator-facing glass can result in excessive winter, spring, or cold weather heating, uncomfortably bright living spaces at certain times of the year, and excessive heat transfer on winter nights.

Although the sun is at the same altitude, the heat and cooling conditions are very 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 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 requirements variations.

Home automation 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 . Using information we Color for electromagnetic radiation to determine icts thermal radiation properties of reflection or absorption can assist the choices.
See Lawrence Berkeley National Laboratory and Oak Ridge National Laboratory: “Cool Colors”

Landscaping and gardens

Energy-efficient landscaping materials for passive solar choices include hardscape building material and ” softscape ” plants . The use of landscape design principles for selection of trees , hedges , and lattice – pergola features with vines ; all can be used to create summer shading. For winter solar gain it is desirable to use deciduous plants That drop Their leaves in the autumn Gives year round passive solar benefits. Non-deciduous evergreen shrubsand trees can be windbreaks, at variable heights and distances, to create protection and shelter from winter wind chill . Xeriscaping with ‘mature size appropriate’ native species of and drought tolerant plants , drip irrigation , mulching, and organic gardening practices reduce or reduce the need for energy-and-water-intensive irrigation , gas powered garden equipment, and reduced the landfill waste footprint. Solar powered landscape lighting and fountain pumps, and covered swimming pools and plunge pools with solar water heaters can reduce the impact of such amenities.

• Sustainable gardening
• Sustainable landscaping
• Sustainable landscape architecture

Other passive solar principles

Passive solar lighting

Passive solar lighting techniques enhance the advantage of natural lighting for interiors, and so reduce reliance on artificial lighting systems.

This can be achieved by careful design, orientation, and placement of window sections to collect light. Other creative solutions involve the use of reflecting surfaces to a daylight in the interior of a building. Window sections shoulds be adequately sized, and to Avoid over-illumination can be shielded with a breeze sun , awnings , well Placed trees, glass coatings, and other passive and active devices. ^[29]

Another Major Issue for Many window systems Is That They Can Be Potentially vulnerable websites of excessive thermal gain or heat loss. High-level clerestory window and traditional skylights can be used in a small area of ​​the building. ^[30] [31] Thus, it is often more important to operate HVAC systems to maintain thermal comfort .

Various methods can be employed to address this Including but not limited to window coverings , insulated glazing and novel materials Such As airgel semi-transparent insulation, optical fiber embedded in walls or roof, or hybrid solar lighting at Oak Ridge National Laboratory .

Reflecting Elements, from active and passive daylighting collectors, Such As light shelves , lighter wall and floor colors, mirrored wall sections, interior walls with upper glass panels, and clear or translucent glassed hinged doorsand sliding glass doors take the captured light and passively Reflect it further inside. The light can be from passive windows or skylights and solar light tubes or from active daylighting sources. In traditional Japanese architecture,the Shoji sliding panel doors, with translucent Washi screens, are an original precedent.International style , Modernist and Mid-century modern architecture are the most innovative 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 to heat water for domestic use. Different active-and-passive solar hot water technologies-have different location-specific economic cost benefit analysis 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. ^[32] 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 qualified as sustainable. This is done by the use of a photovoltaic cell which uses energy from the sun to power the pumps. ^[33]

Passive House Comparison Standard in Europe

There is growing momentum in Europe for the Passive House approach ( Passivhaus in German) Institute in Germany. Rather than simply relying on passive solar thermal design, this approach seeks to make use of all sources of heat, minimizes energy use, and emphasizes the need for high levels of thermal insulation. cold air infiltration. Most of the buildings built to the standard Passive House also incorporate a heat transfer ventilation 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 PHPP2007, where 2007 is the year of issue. A building can be certified as a “Passive House” when it meets the criteria of the most important requirements of the 15kWh / m ² a.

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. ^[34] In modern times, computer programs can model this phenomenon and include local climate data (including site impacts such as overshadowing and physical obstructions) to predict the solar power gain potential for a particular building design over the course of a year. GPS -based smartphone applications can now do this inexpensively on a hand held device. These design toolsprovide the passive solar designer the ability to evaluate local conditions, design elements and orientation. 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 houses can achieve comfort, comfort or usability. ^[35] This is done using good siting and window positioning, small amounts of thermal mass, with good-but-a-standard, weatherization, and an occasional supplementary heat source, such as a central radiator connected to a (solar) water heater. Sunrays can be said to have a wall during the daytime and raise the temperature of its thermal mass . This will then radiate heat into the building in the evening. External shading, or a radiation barrier plus air gap, may be used to reduce summer solar gain.

An extension of the “passive solar” approach to solar seasonal capture and storage of heat and cooling. These designs attempt to capture warm-season solar heat, and convey it to a higher temperature (“annualized 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. The approach also can move into the warm season. examples:

• Passive Annual Heat Storage (PAHS) – by John Hait
• Annualized Geothermal Solar (AGS) – Don Stephen
• Earthed-roof

A “purely passive” solar-heated house, 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 analyze these systems is by measuring their coefficient of performance. A heat pump might be useful for the sake of the future. 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 . ^[36] [37] Although ZEB uses multiple passive solar building design concepts, ZEB is usually not purely passive, having active mechanical renewable energy generation systems such as: wind turbine , photovoltaics , micro hydro , geothermal , and other emerging alternative energy sources.

Passive Solar Design on Skyscrapers

There has been a significant increase in the use of large areas of surface area on which to improve their overall energy efficiency. Because they are more important in urban environments, they require large amounts of energy to operate, there is potential for large amounts of energy savings employing passive solar design techniques. One study, ^[38] which analyzed the proposed 22 Bishopsgateenergy efficiency in the building, energy efficiency, energy efficiency, energy efficiency using double or triple glazed low emissivity window glass for direct solar gain. Indirect solar gain techniques included moderating wall heat flow by wall thickness (from 20 to 30 cm), using window glazingon the outside space to prevent heat loss, dedicating 15-20% of floor area for thermal storage, and implementing a Trombe wallto absorb heat entering the space. Overhangs are used to block the sun, and allow it in the winter, and heat-reflecting shields are inserted between the thermal walls and the glazing to limit heat build-up in the summer months.

Another study ^[39] 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 be used as a source of income.

In more temperate climates, these strategies can be considerably reduced, in the 30% to 60% range. ^[40]

See also

Energy Rating systems

• House Energy Rating (Aust.)
• Home energy rating (USA)
• EnerGuide (Canada)
• National Home Energy Rating (UK)

References