More on Daylighting for Buildings
I have run across additional information that relates to my previous entry on the use of natural daylighting for buildings. As we know, LEED credits for this application are available in four of of the six credit areas -- Indoor Environmental Quality (the main emphasis) Energy and Atmosphere, Materials and Resources, and lastly, Innovation and Design (if one goes above and beyond the minimum requirements of LEED.)
The June 2009 issue of Architectural Record has a good review of this topic, and I have picked out several points that add to and reinforce my earlier entry from the Urban Green High Performance Buildings meeting of June 11.
The article points out that merely increasing the amount of windows in a building will not produce effective use of daylighting. In many areas, the available light, as measured in foot-candles (fc) can be as much a s 10,000. This is far too much, and will result in excessive brightness and glare issues, which will only cause shades to be closed and artificial lighting to be used. It will also result in interference with computer use. A normal level of required light level in most offices is around 50 fc. Examples of this issue can be seen in many older school buildings in my area of Rockland County, which were built during the early to mid 1950's, when fuel was cheap. These schools were built with entire walls of single pane awning or double-hung windows, which let in excessive amount of sunlight and glare, especially on east and west exposures. In addition, in winter, heat loss was apparent from the outset, even at the higher thermostat settings common during that time, students that sat near these window walls often asked to move away from them. The same was true during the warmer months of the school year, with the heat gain issue. (As mentioned above, shades or blinds were often closed, resulting in the use of artficial lighting.)
In general, it is best to have most windows oriented to the north and south, as lighting is most consistent year round, and the extreme sun glare during the morning and late afternoon is minimized.
Window glazing, as mentioned in my last entry, has increased the options that a designer has available regarding daylight use. There are three options in current use that contribute to energy performance and human comfort factor:
Low-E glass involves the coating of glass surface with metallic particles that selectively reflect the solar gain or heat loss, while still letting in sufficient amounts of daylight. In addition, this option allows for adequate views to the outside. The Low-E technology is continually evolving, and we now have available glass that can filter out up to 70% of the solar radiation that would be transmitted through clear, uncoated glass.
Low-E glass is now available in two types of spectrally selective coated products: sputter coated and pyrolytic coated. As the name implies for the first type, this method involves the spraying of a metallic oxide (often optically transparent silver) film on to existing glass. Sputter process is used in a vacuum system between two or more panes of glass. The pyrolytic glass method has the metallic particles embedded during the actual manufacturing process of the glass.
It should be noted that sputter coated glass will allow for more visible light transmission, and at the same time, dramatically lower heat loss and gain. Pyroltic glass, on the other hand, will allow for more solar heat to be transmitted. Thus, pyrolytic glass can be of value in a colder climate, when use in combination with exterior shading during the warmer summer months.
The Solar Heat Gain Coefficient (SHGC) in these newer low-E products have been dramatically decreased. For example, it now possible to achieve a SHGC as low as 0.28. This can lead to as much as a $2.50 per square foot of cost savings for a building by downsizing HVAC equipment. In general, Low-E glass can block as much as 72% of the solar energy, while still letting in 54% of the natural light, which is about the right amount that is really needed for proper occupant comfort and office functions.
There is now another option in glazing, which is called Channel Glass. Channel glass is a U-shaped linear cast of glazing that is usually long and narrow. This makes it especially useful for daylight use applications, as it can be as long as 23 feet, providing for expansive vertical views. It offers a warmer, more diffuse light, and can accommodate small, tight radiuses. In addition, vertical mullions are often not needed, and it can be adapted to areas requiring seismic code compliance.
Another area covered here was the use of steel framing v.s aluminum for glazing. Steel is three times as strong as aluminum, and has a lower heat transmission (U-value) factor. This offers greater use of larger, uninterrupted areas of glass, as well as less framing sweating in colder climates.
The June 2009 issue of Architectural Record has a good review of this topic, and I have picked out several points that add to and reinforce my earlier entry from the Urban Green High Performance Buildings meeting of June 11.
The article points out that merely increasing the amount of windows in a building will not produce effective use of daylighting. In many areas, the available light, as measured in foot-candles (fc) can be as much a s 10,000. This is far too much, and will result in excessive brightness and glare issues, which will only cause shades to be closed and artificial lighting to be used. It will also result in interference with computer use. A normal level of required light level in most offices is around 50 fc. Examples of this issue can be seen in many older school buildings in my area of Rockland County, which were built during the early to mid 1950's, when fuel was cheap. These schools were built with entire walls of single pane awning or double-hung windows, which let in excessive amount of sunlight and glare, especially on east and west exposures. In addition, in winter, heat loss was apparent from the outset, even at the higher thermostat settings common during that time, students that sat near these window walls often asked to move away from them. The same was true during the warmer months of the school year, with the heat gain issue. (As mentioned above, shades or blinds were often closed, resulting in the use of artficial lighting.)
In general, it is best to have most windows oriented to the north and south, as lighting is most consistent year round, and the extreme sun glare during the morning and late afternoon is minimized.
Window glazing, as mentioned in my last entry, has increased the options that a designer has available regarding daylight use. There are three options in current use that contribute to energy performance and human comfort factor:
- Tinted Glass
- Reflective Coatings -- Low-Emittance (Low-E)
- Double or triple glazed units with films or gas fill between the panes.
Low-E glass involves the coating of glass surface with metallic particles that selectively reflect the solar gain or heat loss, while still letting in sufficient amounts of daylight. In addition, this option allows for adequate views to the outside. The Low-E technology is continually evolving, and we now have available glass that can filter out up to 70% of the solar radiation that would be transmitted through clear, uncoated glass.
Low-E glass is now available in two types of spectrally selective coated products: sputter coated and pyrolytic coated. As the name implies for the first type, this method involves the spraying of a metallic oxide (often optically transparent silver) film on to existing glass. Sputter process is used in a vacuum system between two or more panes of glass. The pyrolytic glass method has the metallic particles embedded during the actual manufacturing process of the glass.
It should be noted that sputter coated glass will allow for more visible light transmission, and at the same time, dramatically lower heat loss and gain. Pyroltic glass, on the other hand, will allow for more solar heat to be transmitted. Thus, pyrolytic glass can be of value in a colder climate, when use in combination with exterior shading during the warmer summer months.
The Solar Heat Gain Coefficient (SHGC) in these newer low-E products have been dramatically decreased. For example, it now possible to achieve a SHGC as low as 0.28. This can lead to as much as a $2.50 per square foot of cost savings for a building by downsizing HVAC equipment. In general, Low-E glass can block as much as 72% of the solar energy, while still letting in 54% of the natural light, which is about the right amount that is really needed for proper occupant comfort and office functions.
There is now another option in glazing, which is called Channel Glass. Channel glass is a U-shaped linear cast of glazing that is usually long and narrow. This makes it especially useful for daylight use applications, as it can be as long as 23 feet, providing for expansive vertical views. It offers a warmer, more diffuse light, and can accommodate small, tight radiuses. In addition, vertical mullions are often not needed, and it can be adapted to areas requiring seismic code compliance.
Another area covered here was the use of steel framing v.s aluminum for glazing. Steel is three times as strong as aluminum, and has a lower heat transmission (U-value) factor. This offers greater use of larger, uninterrupted areas of glass, as well as less framing sweating in colder climates.
Posted by Alan L. Englander at 6/27/2009 2:00 PM 
Categories: Low-E Glazing, Pyrolytic Coated, Window Design Considerations, Glare, Sputter Coated, Window Framing, Chanel Glass
Categories: Low-E Glazing, Pyrolytic Coated, Window Design Considerations, Glare, Sputter Coated, Window Framing, Chanel Glass
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