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Title: Calculating the Effect of External Shading on the Solar Heat Gain Coefficient of Windows

Abstract

Current prescriptive building codes have limited ways to account for the effect of solar shading, such as overhangs and awnings, on window solar heat gains. We propose two new indicators, the adjusted Solar Heat Gain Coefficient (aSHGC) which accounts for external shading while calculating the SHGC of a window, and a weighted SHGC (SHGCw) which provides a seasonal SHGC weighted by solar intensity. We demonstrate a method to calculate these indices using existing tools combined with additional calculations. The method is demonstrated by calculating the effect of an awning on a clear double glazing in New Delhi.

Authors:
 [1];  [2];  [2]
  1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  2. CEPT Univ., Ahmedabad (India)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Building Technologies Office (EE-5B)
OSTI Identifier:
1398508
Report Number(s):
LBNL-20011057
ark:/13030/qt2769w7wr
DOE Contract Number:
AC02-05CH11231
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION

Citation Formats

Kohler, Christian, Shukla, Yash, and Rawal, Rajan. Calculating the Effect of External Shading on the Solar Heat Gain Coefficient of Windows. United States: N. p., 2017. Web. doi:10.2172/1398508.
Kohler, Christian, Shukla, Yash, & Rawal, Rajan. Calculating the Effect of External Shading on the Solar Heat Gain Coefficient of Windows. United States. doi:10.2172/1398508.
Kohler, Christian, Shukla, Yash, and Rawal, Rajan. 2017. "Calculating the Effect of External Shading on the Solar Heat Gain Coefficient of Windows". United States. doi:10.2172/1398508. https://www.osti.gov/servlets/purl/1398508.
@article{osti_1398508,
title = {Calculating the Effect of External Shading on the Solar Heat Gain Coefficient of Windows},
author = {Kohler, Christian and Shukla, Yash and Rawal, Rajan},
abstractNote = {Current prescriptive building codes have limited ways to account for the effect of solar shading, such as overhangs and awnings, on window solar heat gains. We propose two new indicators, the adjusted Solar Heat Gain Coefficient (aSHGC) which accounts for external shading while calculating the SHGC of a window, and a weighted SHGC (SHGCw) which provides a seasonal SHGC weighted by solar intensity. We demonstrate a method to calculate these indices using existing tools combined with additional calculations. The method is demonstrated by calculating the effect of an awning on a clear double glazing in New Delhi.},
doi = {10.2172/1398508},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2017,
month = 8
}

Technical Report:

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  • The computational methods for calculating the properties of glazing systems containing shading from the properties of their components have been developed, but the measurement standards and property data bases necessary to apply them have not. It is shown that with a drastic simplifying assumption these methods can be used to calculate system solar-optical properties and solar heat gain coefficients for arbitrary glazing systems, while requiring limited data about the shading. Detailed formulas are presented, and performance multipliers are defined for the approximate treatment of simple glazings with shading. As higher accuracy is demanded, the formulas become very complicated.
  • Ordinary fenestration may be modified at low cost using various combinations of windows, duotone venetian blinds, and drapes to control the solar heat gain. In the winter, solar radiation may be absorbed by dark blinds and transferred to the air, minimizing fading of furnishings while collecting useful energy. In the summer, more than 90 percent of the total potential window heat gain may be rejected by exhausting evaporatively cooled air over the blinds. The performance of several window configurations has been theoretically analyzed, modeled on a computer, and verified experimentally.
  • The Bonneville Power Administration has occupied the building located at 1002 N.E. Holladay since 1952. During this time the occupants of the offices on the south side of the building have suffered due to solar heat gain through approximately 4200 square feet of windows. These windows have overhangs which protect them from direct solar gain during the months of May, June, July, and most of August. The overhangs do not eliminate the effects of indirect radiation during these months, however, and from the period of late August to late April do not block all the direct radiation either. For thesemore » reasons a study was undertaken to determine what factors contributed most to the problem, and to decide what product should be installed on the windows to block the solar heat gain. An investigation of the heating and cooling requirements of the building showed that the cooling load was consistently greater (with the exception of one month) than the heating load. For this reason the building was determined to be cooling dominated and it was decided that the final product purchased need not have insulating qualities. This study showed the least expensive and most efficient means of blocking solar heat gain to the building to be solar control films. Besides increasing the comfort of the occupants and being attractive in appearance a cooling load calculation indicates that a savings of approximately 156 MBtu/year could be expected with the films installed. This represents a cooling energy decrease of 43%.« less
  • The determination of solar heat gain coefficient (SHGC) values for complex fenestration systems is required to evaluate building energy performance, to estimate peak electrical loads, and to ensure occupant comfort. In the past, simplified techniques have been used to calculate the values of SHGC for fenestration systems. As glazing systems that incorporate complex geometries become more common, test methods are required to evaluate these products and to aid in the development of new computational tools. Recently, a unique facility and test method for the experimental determination of SHGC values were developed and demonstrated for simple fenestration systems. The study describedmore » in this paper further applies this method to a variety of commercially available glazing and shading systems (e.g., heat-absorbing insulated glazing units (IGUs), reflective film and suspended film IGUs), and shading devices (i.e., slat blinds and shades). Testing was conducted in a solar simulator facility using a specially designed window calorimeter. The results of this study demonstrate the feasibility of the solar simulator-based test method for the evaluation of SHGC values for solar-control glazings and shading devices.« less
  • Energy ratings are currently being used in a number of countries to assist in the selection of windows and doors based on energy performance. Developed for simple comparison purposes, these rating numbers do not take into account window removable attachments such as insect screens that are, nevertheless, widely used. Research was carried out to assess the effect of insect screens on the heat gains and losses of windows. The work reported in this paper deals with the effect of one screen type on the performance of a base-case, double-glazed window. Using an indoor solar simulator facility, measurements of the windowmore » solar heat gain coefficient (SHGC) and U value were made for different screen attachment configurations and climatic conditions. Results with the sample window tested indicate that insect screens placed on the outdoor side can reduce its SHGC by 46% with only a 7% reduction in its U value (0.19 W/m{sup 2}{center_dot}C), and that insect screens placed on the indoor side can reduce its SHGC by 15% while reducing its U value by 14% (0.38 W/m{sup 2}{center_dot}C).« less