Passive Solar Architecture Revisited
Click image above to view the larger
How can you best incorporate solar energy into your building or remodeling project? The simplicity of established passive solar design principles may prove to be a cost-effective approach for your sustainable project.
If you are a homeowner planning an addition, a remodel or other new construction, you are likely contemplating some aspect of green building for your project. With respect to sustainable energy, current building technologies fall mostly into three categories: conservation, passive solar and active solar. Because they are generally the most cost effective, energy conservation techniques gather plenty of attention. Active solar systems (photovoltaic and hot water collector panels) are quite flashy and thus also receive due consideration. Although less trendy, passive solar architecture involves long established and common sense design principles. This approach can get taken for granted in the planning of a project and valuable opportunity can be lost.
Passive solar applications are not appropriate for every structure. These methods are only effective for space heating and are thus only a consideration in cool climates. The author’s location in Santa Fe, New Mexico is nearly ideal. A building or home which does not have a good southern exposure is of course not a candidate for passive solar design. Since passive solar architecture involves not only a physical but also a visual orientation to the south, considerations of view and privacy may prohibit a strongly passive solar plan. Passive solar heating is supplementary heat and because the sun does not always shine, a back-up heating system is always required.
But the good news is that where appropriate, passive solar technologies can provide up to 80% of a home’s heat. Central to the design of each such project is the glass wall. A vertical south-facing exterior wall is fitted with windows to maximum practical extent and the warming sunshine is admitted directly to the living space. The glass wall is the primary furnace of a passive solar structure. As a rough rule of thumb, a south wall whose surface is covered about 80% with glass will fully heat a room whose depth is about one and a half times the height of the wall on cold sunny days. Precautions must be taken to avoid overheating in summer (this is discussed below.)
Insulating low emissivity glass is pretty standard in the window industry today and this will work just fine for most passive solar applications. This type of glass will reflect much of the invisible spectrum of the sun toward the warm side, thus admitting energy when it is wanted and reflecting it when it is not. Years ago, double glazed glass units were set directly between posts or columns with silicone caulk and wood trim. These applications have come to demand considerable maintenance and current practice tends to employ manufactured window assemblies with exteriors clad in pre-finished aluminum, vinyl or other durable materials. Most of the south-facing glass can be fixed, but reasonable provision must be made for ventilation in each room. Window area on the east, west and particularly on the north walls should be kept to a minimum
The real trick of passive solar applications is to provide for abundant BTU’s from the sun and at the same time to avoid overheating when the weather is not so cold. This is where the real magic of passive solar architecture comes into play. Solar energy can be stored by day in masonry, concrete or other massive materials which will then naturally release their stored heat after the sun has set. Concrete floor slabs and masonry walls should be arranged so that as much as possible of the incoming sunlight falls upon these surfaces. Dark colors on these surfaces will absorb the energy most efficiently. Concrete floor slabs (with or with out tile or stone finishes) are somewhat ideal. Masonry interior walls are also helpful; especially “trombe” walls. These are interior walls which are located very close and parallel to the south facing glass. I like to arrange masonry trombe walls of two to three feet in height and about six inches away from the glass. This narrow space allows for cleaning with a vacuum and the “half trome” walls provide visual privacy while they collect heat. It may be difficult to provide masonry or concrete storage in rooms above the ground floor and thus a less aggressive approach to the south glazing may be appropriate for these rooms.
Perhaps the simplest and most beautiful element of passive solar construction is the overhang. The sun shines at a higher angle in the summer and at a lower angle in the winter. By arranging roof overhangs with a depth of about one quarter the height of the glass wall, the summer sun will be admitted into the living space while the winter sun will be shaded out. Passive solar architecture requires no moving parts. It is the sun itself which moves! Deciduous trees of course are another shading device which works just as naturally, admitting sun in the winter and shading the glass in the summer.
Finally, check your state and federal tax laws. Your passive solar design may help you to qualify for important tax incentives. The fundamental simplicity of passive solar architecture makes it an appealing technology for an owner-builder to incorporate into any project where it is appropriate. Remember: glass, mass and overhangs. Those who wish to further refine their design will find an abundance of software modeling tools available. But don’t forget to keep it simple, solar.
If you are a homeowner planning an addition, a remodel or other new construction, you are likely contemplating some aspect of green building for your project. With respect to sustainable energy, current building technologies fall mostly into three categories: conservation, passive solar and active solar. Because they are generally the most cost effective, energy conservation techniques gather plenty of attention. Active solar systems (photovoltaic and hot water collector panels) are quite flashy and thus also receive due consideration. Although less trendy, passive solar architecture involves long established and common sense design principles. This approach can get taken for granted in the planning of a project and valuable opportunity can be lost.
Passive solar applications are not appropriate for every structure. These methods are only effective for space heating and are thus only a consideration in cool climates. The author’s location in Santa Fe, New Mexico is nearly ideal. A building or home which does not have a good southern exposure is of course not a candidate for passive solar design. Since passive solar architecture involves not only a physical but also a visual orientation to the south, considerations of view and privacy may prohibit a strongly passive solar plan. Passive solar heating is supplementary heat and because the sun does not always shine, a back-up heating system is always required.
But the good news is that where appropriate, passive solar technologies can provide up to 80% of a home’s heat. Central to the design of each such project is the glass wall. A vertical south-facing exterior wall is fitted with windows to maximum practical extent and the warming sunshine is admitted directly to the living space. The glass wall is the primary furnace of a passive solar structure. As a rough rule of thumb, a south wall whose surface is covered about 80% with glass will fully heat a room whose depth is about one and a half times the height of the wall on cold sunny days. Precautions must be taken to avoid overheating in summer (this is discussed below.)
Insulating low emissivity glass is pretty standard in the window industry today and this will work just fine for most passive solar applications. This type of glass will reflect much of the invisible spectrum of the sun toward the warm side, thus admitting energy when it is wanted and reflecting it when it is not. Years ago, double glazed glass units were set directly between posts or columns with silicone caulk and wood trim. These applications have come to demand considerable maintenance and current practice tends to employ manufactured window assemblies with exteriors clad in pre-finished aluminum, vinyl or other durable materials. Most of the south-facing glass can be fixed, but reasonable provision must be made for ventilation in each room. Window area on the east, west and particularly on the north walls should be kept to a minimum
The real trick of passive solar applications is to provide for abundant BTU’s from the sun and at the same time to avoid overheating when the weather is not so cold. This is where the real magic of passive solar architecture comes into play. Solar energy can be stored by day in masonry, concrete or other massive materials which will then naturally release their stored heat after the sun has set. Concrete floor slabs and masonry walls should be arranged so that as much as possible of the incoming sunlight falls upon these surfaces. Dark colors on these surfaces will absorb the energy most efficiently. Concrete floor slabs (with or with out tile or stone finishes) are somewhat ideal. Masonry interior walls are also helpful; especially “trombe” walls. These are interior walls which are located very close and parallel to the south facing glass. I like to arrange masonry trombe walls of two to three feet in height and about six inches away from the glass. This narrow space allows for cleaning with a vacuum and the “half trome” walls provide visual privacy while they collect heat. It may be difficult to provide masonry or concrete storage in rooms above the ground floor and thus a less aggressive approach to the south glazing may be appropriate for these rooms.
Perhaps the simplest and most beautiful element of passive solar construction is the overhang. The sun shines at a higher angle in the summer and at a lower angle in the winter. By arranging roof overhangs with a depth of about one quarter the height of the glass wall, the summer sun will be admitted into the living space while the winter sun will be shaded out. Passive solar architecture requires no moving parts. It is the sun itself which moves! Deciduous trees of course are another shading device which works just as naturally, admitting sun in the winter and shading the glass in the summer.
Finally, check your state and federal tax laws. Your passive solar design may help you to qualify for important tax incentives. The fundamental simplicity of passive solar architecture makes it an appealing technology for an owner-builder to incorporate into any project where it is appropriate. Remember: glass, mass and overhangs. Those who wish to further refine their design will find an abundance of software modeling tools available. But don’t forget to keep it simple, solar.
Posted by : Greg Allegretti
@ Apr 09, 2011
