ASHRAE Journal - April 2009 - 27

or it could be used in a heat exchanger. The air can also be used for drying a desiccant wheel if temperatures are high enough for sufficient frequency and duration. In the winter it can serve to prewarm incoming air. Closing Remarks DSF Thickness Solar Heat Gain Coefficient U-Value Solar Transmissivity Solar Reflectivity inch (m) Inner Skin Outer Btu/h · ft2/°F (W/m2 · K) 1/2 (0.013) 0.73 0.98 (5.59) 0.64 0.06 Skin The selection of the building envelope is one of the most critical aspects of building Single Façade 0.34 0.22 (1.25) 0.28 0.32 1 5/8 (0.042) (Triple Pane) design. This selection will dictate how occupants will behave in the building (e.g., Table 2: Glazing properties for Beijing building. lighting, natural ventilation), Poirazis, H. 2004. “Double Skin Façades for Offices Buildings: the energy demand to manage the external climate, and the appearance of the building. The range of design options of a Literature Review.” Division of Energy and Buildings Design, Lund building envelope can lead to a dramatic difference in the siz- Institute of Technology, Lund University. Report EBD-R-04/3. ing of building ventilation and cooling systems. If the building www.ecbcs.org/docs/Annex_43_Task34-Double_Skin_Facades_A_ Literature_Review.pdf. skin is not done well, then occupant behavior to moderate their Straube, J.F., R.V Straaten. 2002. “The Technical Merit of Double . environment (e.g., drawing blinds and closing windows) can Skin Façades for Office Buildings in Cool Humid Climates.” School dramatically affect the energy use and change the basis of design of Architecture, University of Waterloo, Waterloo, ON, Canada. www. of the building. In this case, at best, this means the building uses civil.uwaterloo.ca/beg/Downloads/DoubleFacadesPaper.pdf. more energy. At worst, the systems are undersized and building occupants will be uncomfortable. Optimal energy savings requires an appropriate balance of opaque walls and glazing. A double skin façade is one means to manage the interaction between the outdoors and the internal spaces. It also provides some architectural flexibility to the design. Energy efficiency and thermal comfort adjacent to the façade requires careful configuration of glass, solar control devices (both for thermal and visual effects), and ventilation of the DSF cavity. A responsive control system for the solar control devices and the ventilation of the DSF is required. The examples presented here show how different operating practices (e.g., flow rates), or design decisions (glazing choices) can affect the ultimate performance of the DSF. Decisions on these elements should be based on analysis that accounts for the detailed physics and inclusion of site climatic data as illustrated in this article. 1 (0.025) 0.38 0.28 (1.57) 0.33 0.31 Bibliography Blomsterberg, Å. et al. 2007. “BESTFAÇADE: Best Practice for Double Skin Façades—Literature.” EIE/04/135/S07.38652. www. bestfacade.com. Lee, E., et al. 2002. “High Performance Commercial Building Façades.” Building Technologies Program, Environmental Energy Technologies Division, Ernest Orlando Lawrence Berkeley National Laboratory, Report No: LBNL-50502. http://gaia.lbl.gov/hpbf/ documents/LBNL50502.pdf. Oesterle, E. et al. 2001. Double-Skin Façades: Integrated Planning: Building Physics, Construction, Aerophysics, Air-Conditioning, Economic Viability. Munich: Prestel Publishing. www.info.hotims.com/23934-30 April 2009 ASHRAE Journal 27

ASHRAE Journal - April 2009

Table of Contents for the Digital Edition of ASHRAE Journal - April 2009