Building Better for Solar Heating and Cooling
As a source of constant solar radiation, the sun can be a warming presence, a source of energy, or an annoying heater depending on the albedo of materials and type of construction used.
Ah, the sun. Much graceful, illuminating prose has been dedicated to its appearance, benefits, and even harmful effects. But since this is a technical article there won’t be any of that here. Instead this will be a rather dry, straightforward review of some of the ways to either use or mitigate its ever present energies in building construction.
All that energy starts at the source, the sun, which is more that just a glowing ball in the daytime. It’s a roiling mass of superheated elements undergoing energetic subatomic reactions which gives off copious amounts of electromagnetic solar radiation. And after traveling through space for around 8 minutes, this radiation winds up in our back yards and on our roofs. Depending on the albedo (the ratio of solar radiation absorbed and emitted over time) of the materials and their incorporation into the building construction, this may cause the occupants to sit down and write graceful, illuminating prose, or to turn on an air conditioner and write dark, not so graceful prose.
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Building Construction Using Solar Heating And Cooling Techniques
How can building construction help reduce the amount of dark, not so graceful prose? Living plants like trees can evapo-transpirate, animals like dogs can sweat. It’s a great way to moderate temperature in the presence of excessive heat, like being in the sun on a hot, dry day. Dousing a building with water would also have a great cooling effect, but would not be very efficient use of a precious natural resource. Instead several forms of construction, some old and some new, can be incorporated in the presence of the sun to great advantage. These include:
○ Shade: An obvious choice for millennia. Works by blocking solar radiation, preventing absorption by the building surfaces. Landscaping, awnings, porch roofs, and facades can provide strategic amounts of shade. Planning the orientation of new construction can also optimize the amount of shade a building receives by taking advantage of topography and existing greenery. Solar panels and passive solar hot water systems can do double duty by providing shade while absorbing radiation and converting its energy to another useful form. The “building within a building" technique uses a shading façade or shell to create a livable sunspace envelope while maintaining a cooler interior space.
○ Insulation: Works by limiting heat transfer from warm objects to cooler objects, as from a hot, sun exposed roof or wall to cooler interior spaces. Can be a discrete building material applied to attic, floor, and wall cavities or be integrated into structural building components. Planted roofs are an increasingly popular insulation choice, as are earth berm walls. Another popular construction option is to super insulate the outer shell of a building to minimize heat transfer, accomplished by controlling vented spaces like attics and crawl spaces, sealing all penetrations, incorporating large R-value insulating materials, and insulating slabs and ground contact walls.
○ Coatings: Works by controlling the amount of solar radiation absorbed and converted into heat. Low emissivity windows, paints which reflect the infrared and UV portions of solar spectrum, and reflective foils are all effective in limiting absorbed radiation, thereby increasing albedo. Some coatings can actively cool at night be emitting long infrared radiation back into the night sky, which acts as an almost infinite radiative heat sink.
○ Thermal Mass: Works by absorbing the sun’s energy during the heat of the day and releasing it at night when it is cooler. This may be as simple as using high mass materials such as log walls and concrete floors at strategic locations in the building. Exposure to the sun, either directly in a passive system or as part of an active heat pump system, slowly increases the temperature of the massive material. At night, if outside temperatures fall below interior temperatures, the warm mass of the walls or floors maintains the interior temperatures at comfortable levels.
These are just a few of the construction techniques available to better utilize the readily available energy from the sun. Changes in the world climate, increasing costs of other energy sources, and just plain innovative curiosity are driving development of more ideas and technology to keep the sun off our shoulders and doing useful work.