Photos courtesy Draper Inc.
The case for solar control
There can be some negatives when more windows are incorporated into building design. Glare, solar heat gain, and direct sun on workers’ eyes or workspaces can make it harder to perform basic work functions and can actually lower productivity.
WBDG states:
The science of daylighting design is not just how to provide enough daylight to an occupied space, but how to do so without any undesirable side effects. Solar control solutions, including both exterior and interior shading systems, are thus an important part of designing a productive building.
(For more, visit the website wbdg.org/resources/daylighting.php?r=productive.)
In 2006, Heifer International opened its new headquarters in Little Rock, Ark. The building was designed with sustainability and natural light in mind. It included energy-efficient plate-glass windows for passive solar heat and indirect light, as well as a curved shape to capture the maximum amount of sunlight. These and other sustainable construction practices helped the building earn Platinum under U.S. Green Building Council’s (USGBC’s) Leadership in Energy and Environmental Design (LEED) program. However, when the facility opened, a glaring problem emerged: workers could not use their computer stations on the south side of the building due to the sun load coming through the extra-large windows. While fixed sun shades were in place to help with passive solar control and glare, workers were getting additional glare from the water surrounding part of the building. The problem was resolved by adding interior window shades, with a five per cent openness factor to still allow views through to the outside.
Thermal comfort
In addition to glare, solar heat gain can also be a problem. Thermal comfort contributes to job performance and productivity, and WBDG recommends a holistic design approach to deal with this, including use of solar-shading products. (More information is available at wbdg.org/design/provide_comfort.php.) Resolving this issue gives an exterior system the advantage, because it prevents a large part of the sun’s energy from reaching the glazing and entering the building.
Energy from the sun is short-wave (i.e. visible, ultraviolet [UV] light) and carries little heat. Reflected solar energy is also not an issue—it remains short-wave, and does not cause any heat gain. Heat is only produced when solar energy is absorbed by a surface (e.g. carpeting, furniture, clothing, or skin) and radiated as long-wave infrared (IR) energy. Transmitted energy (i.e. that absorbed by surfaces in the building and radiated as heat) is then mostly trapped inside the building, particularly if low-emissivity (low-e) glazing is used. (For more information, visit wbdg.org/resources/suncontrol.php?r=provide_comfort.) If the solar energy does not get into the building, however, it does not have to be dealt with.
