A team of Berkeley Lab programmers and experts in
building technology and 3-D imaging are taking the science of building design into the
twenty-first century with a new tool: the Virtual Building Laboratory (VBL).
"We want to create a simulation-based tool that lets one explore the complex
energy interactions of a building," said Steve Selkowitz, co-leader of the project
and head of the Lab's Building Technologies Department. The project combines the efforts
of the Environmental Energy Technologies Division (EETD), the Information and Computing
Sciences Division (ICSD), and the National Energy Research Scientific Computing Center
(NERSC).
The aim of the VBL project is to use energy simulations and 3-D visualization
technology to allow scientists to test building performance and to explore, analyze and
alter materials and designs in virtual real-time, bypassing expensive laboratory
experiments. As the project progresses, better tools will be developed to allow more
architects and engineers to test building designs on personal computers.
The first step in this collaboration is to upgrade RADIANCE, a desktop lighting
simulation program, in order to create an interactive simulation of actual lighting
effects in virtual buildings. Unlike other virtual 3-D environments, such as video games,
in which lighting is not accurate or realistic, RADIANCE takes into account a room's
geometry, its actual lighting sources, the visual properties of surfaces, and weather to
simulate the light the human eye would see at each point in a room. Even glare can be
simulated and quantified.
"It's a what-you-see-is-what-you-get tool," says Selkowitz. "If you
can't see it in the simulation, you shouldn't see it in the real space."
To accomplish all this in a single frame, a computer must calculate the path of
millions of light rays bouncing off each surface of the room, something which demands
massive computational firepower. Developers in ICDC's Visualization Group face a difficult
task: they must use the RADIANCE simulation to capture detailed lighting images while
delivering pictures quickly enough to allow users to explore the virtual building in real
time. Given the millions of light interactions in a room, a typical PC can take up to 10
hours to compute a single image. To simulate motion, the new program must create 10 to 30
detailed pictures per second.
The task requires the deployment of the Lab's most powerful computer -- NERSC's Cray
T3E. Even so, calculating the path of every ray is a computational nightmare.
"You never have enough computer power -- even with the Cray -- so you limit the
number of rays you're calculating," said Nancy Johnston, head of the Visualization
Group. A classic solution is called ray tracking -- calculating only the rays that reach
the human eye instead of every light beam in the room. Another trick, known as eye
tracking, assigns less detail to the areas of the room on which the eye does not focus as
much. Even with these methods, over 24 million rays must be calculated per picture.
Currently programmers can run a small image at 10 frames per second, although a
full-screen picture at 20 frames per second is expected to be available in the fall, said
Stephen Lau, project manager for RADIANCE. Other goals are to control simulations over the
Internet, so that they can be viewed at remote locations, and to adapt the program to work
on office computer networks, allowing architects in small offices to use it. In the
future, as VBL is further developed, Selkowitz's team will try to display non-visible
aspects of buildings, such as heat movement, pollutant flows and comfort levels. As the
program begins to simulate more aspects of buildings, the results will be verified with
laboratory tests.
By using computer simulations to devise creative efficiency solutions, engineers can
often surpass energy requirements without following specific building code guidelines.
Better building models can help improve indoor air quality and prevent the "sick
building" syndrome, in which design flaws require costly post-construction changes.
Energy experts estimate that over half of the $200 billion spent annually in building
energy consumption could be saved with more efficient materials and building schemes.
As a leader in the building energy performance field, Selkowitz coordinates a variety
of projects to improve building efficiency. Under his direction, researchers in the
Building Technologies Department study and design better light bulbs, window glazings and
building control systems. Computer programs that Selkowitz's department has developed,
such as DOE-2, RADIANCE and WINDOW 4.0, have become industry benchmarks, used by
architects and engineers worldwide to increase building energy efficiency. These tools may
be seen on the web at http://eetd.lbl.gov/software.html.
Selkowitz believes that the EETD and ICSD partnership will help maintain Berkeley Lab's
leadership in the energy simulation field in the years to come.
Eli Kintisch is a summer intern from Yale University currently working for the
Public Information Department.
