The Cellular Method for Optimal Shading
Master Thesis. Author: Eran Kaftan
Committee Members: Chalfoun N. (chair), Yoklic M., Matter F., Medlin L., & Sobin H.
The University of Arizona, College of Architecture, 2001.
Abstract
The cellular method is an innovative approach to design an optimal shading. The method offers calculating an optimal shading form, accounting for both needs of summer solar protection and winter solar gain. As a result, it provides better thermal comfort and maximum annual energy conservation in cooling and heating. The method can generate Mapping of Shading Importance for any location in the world, any opening configurations, and any preferred period (such as year, season, month, etc.). The mapping indicates, for these particular settings, the optimal form of shading-means (such as shading device, overhang, etc.). Since architectural and environmental settings are varied, the calculated optimal shading forms usually have unique forms, often complex and intriguing. Such forms are not only enriching the building façade, but also correspond best to the specific environmental conditions.
The method was developed by architect Dr. Eran Kaftan, in the framework of a M.Arch thesis at the University of Arizona (2001). It was presented at several international conferences and at leading international architectural and engineering offices, such as Frank Gehry & Associates; ARUP; and Foster and Partners. In addition, it was integrated in several simulation programs, Autodesk Ecotect and SHADERADE of Harvard University.
Optimal Shading
The design of shading-means which provides optimal shading (establishing maximum reduction in the building energy consumption) is rather complex, requiring solving the fundamental “Shading Dilemma”. On the one hand, shading intercepts summer direct solar radiation, thus, reducing the cooling loads during the summer (positive effect); however, on the other hand, shading also reduces desirable winter solar gain and daylight, thus, increasing the heating and artificial lighting loads (negative effect). Therefore, an optimal form of a shading device or overhang should provide an optimal balance among the necessity for solar obstruction, solar gain, and daylight. Since solar radiation varies according to different sun angles, and the sun appears in the sky in curved pathways, even a rectangular window will not have a simple optimal shading form. In addition, since windows or walls are varied in configurations, orientations, and locations around the world, it is natural, that each one requires a unique shading form. An optimal shading form can help in optimizing annual building energy conservation, reducing the cost in operating mechanical systems of cooling and heating; thus supporting the world energy conservation and sustainability.
The Cellular Method
The Cellular Method for Optimal Shading evaluates numerous theoretical-cells of proposed shading-means (such as shading device, overhang, etc.) for their degree of importance to provide shade or solar penetration. Then, this information can be utilized to modify the proposed shading-means. The method can also be used to determine new shading-means, by evaluating numerous theoretical-cells of space adjacent to a proposed shaded space (such as window, courtyard, etc.). Calculations of the optimal shading form takes into consideration the window configuration, orientation, and geographical location, as well as hourly solar radiation and hourly thermal comfort conditions at the space needed to be shaded. This process can be applied to a particular preferred period, in order to design fixed or seasonal shading-means (such as shading devices, overhangs, shading membranes, etc). In addition, it can be applied to a sequence of short time-segments, in order to design dynamic shading systems.
Applications
[reduced width] The Cellular Method for Optimal Shading was implemented in several state-of-the-art simulation programs. [/reduced width]
Excel Tool (2001)
An excel tool, OPTIMAL-SHADING, uses the Cellular Method for Optimal Shading, through about 800,000 calculations, to determine the optimal shape of shading-means. The tool is limited to simple forms of windows, and requires an external thermal analysis.
Ecotect’s Cellular Method Plugin (2005)
Collaboration between Research & EcoDesign and Ecotect developer (SQUARE ONE research) has produced an external Plug-In for Ecotect software. The plug-in uses the Cellular Method for Optimal Shading to determine for outdoor locations the degree of importance to provide either shading or solar penetration during a period. The process is carried out in the following steps:
 1. Setting a shading grid; |
 2. Calculating annual solar potential (solar radiation admitted or eliminated through selected windows); |
 3. Calculating annual shading needs (the requirements for either shading or solar gain, according to thermal comfort, zone temperatures, or heat gain and losses); |
 4. Conducting hourly shading projection and a data accumulation process (at all cells); |
 5. Reciving a map of final degrees of importance at different regions of a proposed shading; device, to provide either solar shading (blue scale) or solar penetration (red scale) during a period (such as the entire year); |
 6. Optimizing the shading form acording to the shading importance map. |
Autodesk Ecotect (2008)
Another result of the collaboration with Ecotect developer is that major parts of the Cellular Method for Optimal Shading can be used directly within the Autodesk Ecotect software. The tool can be launched through a “shading potential” calculation option. The tool calculates the relevant accumulation of radiation data on an analysis grid for a selected period, but in contrast to the plug-in, it does do not account for both summer needs for shading and winter needs for solar penetration. Additional information may be found in Ecotect’s help files.
SHADERADE (Harvard University; 2011)
The tool uses a modified version of the Cellular Method for Optimal Shading to generate optimal shading using Rhinoceros® and EnergyPlus programs (it is scheduled to be released as an addition to the DIVA-for-Rhino plug-in).
Relevant Publications
Kaftan, Eran. (2001). The Cellular Method to Design Energy Efficient Shading Form to Accommodate the Dynamic Characteristics of Climate. Master Thesis (Architecture). The University of Arizona. 183p.
Kaftan, E. (2001). The Cellular Method to Design Energy Efficient Shading Form to Accommodate the Dynamic Characteristics of Climate. Conference proceedings. PLEA 2001 – The 18th Conference on Passive and Low Energy Architecture. Florianopolis, Brazil. Volume 2. pp 829-833.
Kaftan, E. (2002). Cellular Method for Optimal Solar Shading. US Patent Application. 46p.
Kaftan E. & Marsh A. (2005). Integrating the Cellular Method for Shading Design with a Thermal Simulation. The International Conference on Passive and Low Energy Cooling for the Build Environment (PALENC 2005), Santorini, Greece.
Kaftan, E. and Ben-Aharon R. (2005). Passive – Yet Not Indifferent: Cellular Shading Method. Architecture of Israel (Architectural Quarterly). No. 62, pp 51-55.
Sargent, Jon, Niemasz Jeffrey, & ReinhartChristophF. (2011). SHADERADE: combining rhinoceros and energyplus for the design of static exterior shading devices. Building Simulation 2011. Sydney, Australia.
Kaftan Eran, 2015. Urban Shade: Thermal and Visual Experience. Urban Shading In Israel. Editor: Martin Weyl. Israel.
