|Title||Detailed Thermal Performance Data on Conventional and Highly Insulating Window Systems|
|Publication Type||Conference Paper|
|LBNL Report Number||LBL-20348|
|Year of Publication||1985|
|Authors||Arasteh, Dariush K., Stephen E. Selkowitz, and John Hartmann|
|Secondary Title||International Daylighting Conference|
|Conference Location||Clearwater Beach, FL|
Data on window heat-transfer properties (U-value and shading coefficient [SC]) are usuallyspresented only for a few window designs at specific environmental conditions. With thesintroduction of many new window glazing configurations (using low-emissivity coatings and gassfills) and the interest in their annual energy performance, it is important to understandsthe effects of window design parameters and environmental conditions on U and SC. This papersdiscusses the effects of outdoor temperature, wind speed, insulation, surface emittance, andsgap width on the thermal performance of both conventional and highly insulating windows.sSome of these data have been incorporated into the fenestration chapter of thesASHRAE Handbook - 1985 Fundamentals.
The heat-transfer properties of multiglazed insulating window designs are alsospresented. These window systems include those having (1) one or more low-emittance coatings,s(2) low-conductivity gas-fill or evacuated cavities, (3) a layer of transparent silica aerogel,sa highly insulating microporous material, or (4) combinations of the above. Using thesdetailed building energy analysis program, DOE 2.1B, we show that these systems, which allsmaintain high solar transmittance, can add more useful thermal energy to a space than theyslose, even in a northern climate. Thus, in terms of seasonal energy flows, these fenestrationssystems out-perform insulated walls or roofs.