View
223
Download
0
Category
Preview:
DESCRIPTION
Collection Need a way to collect the suns energy One way is large windows on the south face of the building Another way is a passive solar collector on the south wall – In the collector, the heated air rises and flows into the structure, while the cool air from inside sinks and flows back into the collector. No need for fans, this air flow sets itself up naturally
Citation preview
Passive Solar
• Makes use of natural solar heating• Requires buildings be designed to maximize
the suns heating• Most important element: face south (toward
the sun)!• Requires 3 design elements: insulation,
collection, storage• Passive because it does not involve pumps,
fans, fuel, electricity etc.
Insulation
• Keep the heat in!• Walls, floors, ceilings must make use of
materials that help hold in the heat.• Doors and windows must also be designed to
maximize heat retention in the building• Most modern buildings ignore these ideas
Collection
• Need a way to collect the suns energy• One way is large windows on the south face of
the building• Another way is a passive solar collector on the
south wall– In the collector, the heated air rises and flows into
the structure, while the cool air from inside sinks and flows back into the collector. No need for fans, this air flow sets itself up naturally
Storage• Need a thermal mass inside the house• Thermal mass-any material that can absorb solar
energy then cool down later giving its energy back to its surroundings.– Example – Why is it always warmer in cities than in
the country in the summer, especially at night?– Buildings and roads act as a thermal mass, heating up
during the day and releasing that heat at night• In our building the material has to hold enough
heat to keep the temperature constant at night or over a cloudy day(s).
Storage• The heat stored in the thermal mass is not much greater than the usual
temperature of the structure, thus a lot of it is needed.• Water is an excellent thermal mass. Tanks of water could be stored just inside the
windows, but that’s not very aesthetic. Another way to use water is a roof pond (yes a pond on your roof!) or green roof (yes your garden on your roof).
• Example-Since Chicago installed a 20,000 square foot "green roof" atop City Hall five years ago(2006 report), the city has saved about $25,000 in energy costs.
• Trombe Wall: A massive concrete wall on the south side of the structure, with a space between it and the windows. The concrete wall acts as the thermal mass. Not only does the wall heat the air in the space and convection sets up a natural flow to warm the room on the other side, but the concrete itself will radiate into the room.
Chicago City Hall green roof
Storage
• Direct Gain method– South facing windows with thermal mass in the
floor and opposite wall to regulate and store heat.
Potential
• Based on sun angle, this figure shows the potential for passive solar use across the US
Solar Electric Power generation
• Two types:– Thermal -use sun’s ability to heat (usually water)
to create electricity– Photovoltaic devices- a device which directly
converts the Suns energy to electricity
Solar Thermal
• Obvious idea would be to use sunlight to boil water and provide steam to drive a turbine
• But what happens when you place a container of water in the sun-it typically does not boil!
• Need to concentrate or focus the sun’s energy to achieve this goal
• How do we focus sunlight?
Basic properties of light• To answer this question, lets look at some basic
properties of light in the wave description of light. • Refraction-light is bent at the interface between two
media.• Snell’s law relates the angle of incidence and the index
of refraction of medium 1 tothe angle of refraction and index of refraction of medium
2.
Focusing light
• If the interface is flat, the light is not focused.
• Example-pencil in a glass of water
• If it is curved in the correct fashion, i.e. the surface of a convex lens, the light can be brought to a focus
convex
concave
Fresnel Lens• For the most part, lens
are very heavy, suffer from reflection at the surfaces, and are expensive to construct to the sizes needed to achieve the desired heating.
• There is one type of lens, a Fresnel lens that can be inexpensively constructed from plastic
Fresnel Lens
• Seen in lighthouses-used to form a concentrated beam of light.
Recommended