Passive solar building design
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.
Specific attention is divided into: the site, 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 these considerations may be directed toward any building, achieving an ideal optimized cost/performance solution requires careful, holistic, system integration engineering of these scientific principles.
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.
The cost effective proof of concept was established decades ago, but cultural change in architecture, the construction trades, and building-owner decision making has been very slow and difficult.
[7] 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.
This information is combined with local climatic data (degree day) heating and cooling requirements to determine at what time of the year solar gain will be beneficial for thermal comfort, and when it should be blocked with shading.
The amount of radiant heat received is related to the location latitude, altitude, cloud cover, and seasonal / hourly angle of incidence (see Sun path and Lambert's cosine law).
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 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 requirements.
[20] 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.
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.
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.
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 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.
Covering the glazing with tight-fitting, moveable insulation panels during lengthy cloudy periods and nighttime hours will enhance performance of a thermal storage system.
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.
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.
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).
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.
[29] 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.
Home automation systems that monitor temperature, sunlight, time of day, and room occupancy can precisely control motorized window-shading-and-insulation devices.
[30] 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.
Non-deciduous evergreen shrubs and trees can be windbreaks, at variable heights and distances, to create protection and shelter from winter wind chill.
Window sections should be adequately sized, and to avoid over-illumination can be shielded with a Brise soleil, awnings, well placed trees, glass coatings, and other passive and active devices.
Whilst high mounted clerestory window and traditional skylights can introduce daylight in poorly oriented sections of a building, unwanted heat transfer may be hard to control.
International style, Modernist and Mid-century modern architecture were earlier innovators of this passive penetration and reflection in industrial, commercial, and residential applications.
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.
[37] 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.
Passive solar building design sometimes uses limited electrical and mechanical controls to operate dampers, insulating shutters, shades, awnings, or reflectors.
One study,[41] which analyzed the proposed 22 Bishopsgate 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.
