Assessing thermal comfort near glass facades with new tools

Assessing thermal comfort near glass facades with new tools Sabine Hoffmann, Christoph Jedek, Edward Arens Center for the Built Environment, University of California at Berkeley ABSTRACT Transparent facades impact the thermal comfort of occupants in multiple ways. This pa- per addresses such impacts both for generic glazing and for complex fenestration sys- tems such as shades and blinds. The first step in the process of evaluating comfort for a specific facade is to calculate the solar radiation load on the occupant. The second step is to assess the person’s physiological reaction to the radiation and how this reaction influences thermal sensation and perception of thermal comfort. A newly developed tool (SoLoCalc) uses bi-directional scattering functions to character- ize the radiant transmission of complex fenestration systems. The output is then linked to an advanced physiology and comfort model. Although this paper describes its use in evaluating glass facades, the tool applies equally to buildings with smaller window-to- wall ratios, or to skylights. A case study of a real construction project shows how the tool enables a new and comprehensive approach to assessing the impact of the build- ing envelope on user comfort. INTRODUCTION Using glass as a dominant material for the building envelope offers great design oppor- tunities for architects. In recent years the possibilities have been extended through the use of structural glazing, spandrel panels and a huge variety of coatings, films and frits. For the beholder from outside, successful glass architecture demonstrates transparency while for the occupant inside, the large transparent area may provide generous daylight and views. However, less successful designs can be seen to have shades and blinds closing off most of the window area, sacrificing view and daylight to avoid visual glare and occupant discomfort. In addition, large glazed areas often lead to excessive energy use compared to more traditional constructions with smaller window-to-wall ratios. While a number of measures have been introduced to keep the energy consumption of glass architecture reasonable, the thermal comfort in the space behind the glass facade has typically not been thoroughly addressed. It is often considered to be the duty of the HVAC-system to provide comfortable indoor conditions – a task that may require great energy use to fulfill. With the attempt to build “greener” buildings, engineers aim more and more for low-energy technologies such as radiant cooling, natural ventilation, and personal environmental control [Zhang et al., 2009], and move away from uniformly air- conditioned spaces. It is within this trend that more attention is being paid to the influ- ence of the facade on the comfort of occupants. Center for the Built Environment, UC Berkley, April, 2012 https://escholarship.org/uc/item/0t68701n