Daylighting Analysis with Radiance
Building performance simulation is becoming the new norm as the tools become more common and approachable for designers and consultants. Not unlike the aircraft or automotive design industry, architecture too is utilizing computer simulation tools that allow the design team to build a virtual building that can be analyzed and tested. Computer simulations have long been utilized by aircraft design industry to test for variables like drag and air flow, a branch of analysis that is called CFD (computational fluid dynamics). This is just one of the many forms of digital modeling that is making a more common appearance in architecture. It has long been a goal of designers to create buildings that are well daylight that is to say that the buildings can operate functionally without the presence of electric lighting. Not only is this technique useful in directly lower the electric load due to decreased light it also takes some of the internal heat gain load out of the building during cooling operations. It is also important to make the distinction that good daylight is not sunlight; direct sun can create glare problems for occupants and increase internal heat gains.
To create well daylit spaces architects and consultants have turned to a software program that has been around for a relatively long time, as far as software goes. Radiance is a collection of over 50 programs for accurate calculation and rendering of (day)lighting situations and it's analysis. Radiance is a highly accurate ray-tracing software system originally developed in the mid 80’s by Greg Ward Larson with funding from the U.S. and Swiss governments. To design the new Cleveland Clinic in Abu Dhabi U.A.E., Architects HDR (based in Omaha, with offices in Boise) and consulting firm Loisos + Ubbelohde (L+U) utilized Radiance as a way of calculating lighting levels and recognizing glare conditions during schematic and design development stages of the project.
The new Cleveland Clinic was to be built with a double skin façade, which coincidentally was also analyzed with thermal computer models, however the skin of the building was to be highly glazed and had the potential to create significant glare problems. HDR and L+U analyzed a myriad of different design options including the testing of many different types of glass with a varying level of VLT(visual light transmittance) and SHGC (solar heat gain coefficient) as well as the inclusion of internal roll down shading devices. In images 3 and 4 above and 1 and 2 below you can see the dramatic effect that a semi transparent roll down shading device can have on a typical patient room.
As computer simulation rapidly becomes the norm rather than the exception designers will have the opportunity to predict with more precision the effects that there design schemes will have on the performance of buildings
SOURCES
- Journal Article:
- Fortmeyer, Russell “Transparency: Literal and Sustainable”, Architectural Record, 04, 2009 (July 2009)?
- Websites:
- Lawrence Berkley National Laboratory, Radsite. < http://radsite.lbl.gov/ >
- Loisos + Ubbelohde, Architecture and Energy. < http://www.coolshadow.com/index.html >