When constructing a building energy model for the Sidwell Friends Middle school, it became obvious that certain shortcomings of DOE-2, the energy simulation engine being used to quantify energy cost savings within the LEED rating framework, were compromising the accuracy of the window shading components of the calculation. The basic problem with DOE-2 is that it does not allow for complex shading devices in its assessment of solar control, being limited to simple vertical and horizontal projections at the edge of the window areas. The shading devices at Sidwell Friends, being a series of unequally spaced angled vertical fins on both the east and west façades (figure 1) and blade style horizontal shelves on the south facade, were heavily simplified in the original model. A geometrically accurate model was analyzed in both Ecotect and Radiance was calculated, the goal being to understand the amount of radiation actually incident of the surface of the window throughout the year. One advantage of Ecotect is that it uses a normalized meteorological year (TMY2) to inform its analysis, taking into account a statistically determined hourly measure of available radiation.
KieranTimberlake Associates LLP
Kevin Pratt, AIA
When constructing a building energy model for the Sidwell Friends Middle school, it became obvious that certain shortcomings of DOE-2, the energy simulation engine being used to quantify energy cost savings within the LEED rating framework, were compromising the accuracy of the window shading components of the calculation. The basic problem with DOE-2 is that it does not allow for complex shading devices in its assessment of solar control, being limited to simple vertical and horizontal projections at the edge of the window areas. The shading devices at Sidwell Friends, being a series of unequally spaced angled vertical fins on both the east and west façades (figure 1) and blade style horizontal shelves on the south facade, were heavily simplified in the original model. A geometrically accurate model was analyzed in both Ecotect and Radiance was calculated, the goal being to understand the amount of radiation actually incident of the surface of the window throughout the year. One advantage of Ecotect is that it uses a normalized meteorological year (TMY2) to inform its analysis, taking into account a statistically determined hourly measure of available radiation.
In order to gain a better understanding of the actual effectiveness of the fins, a model was built in Ecotect and solar exposure was calculated, the goal being to understand the amount of radiation actually incident of the surface of the window throughout the year. One advantage of Ecotect is that it uses a normalized meteorological year (TMY2) to inform its analysis, taking into account a statistically determined hourly measure of available radiation.
Results indicate that the shading is highly effective. At the west façade (figure 2) average daily total insolation is reduced by 56%. Analysis of the shading devices on the south façade show it is most effective in the summer months when cooling loads are highest while still allowing significant winter sun to strike the building (figure 3).
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figure 2
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figure 3
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