Advanced Building Simulation

Chapter 6
New perspectives on Computational
Fluid Dynamics simulation
D. Michelle Addington
6.1 Introduction
Simulation modeling, particularly Computational Fluid Dynamics (CFD), has opened
an unprecedented window into understanding the behavior of building environments.
The late entry of these tools into the building arena—more than 20 years after their
initial application in the aerospace industry—is indicative of the complexity of building
air behavior. Unlike many applications, such as turbomachinery or nuclear power
cooling, in which one or two mechanisms may dominate, building air flow is a true
mixing pot of behaviors: wideranging velocities, temperature/density stratifications,
transient indoor and outdoor conditions, laminar and turbulent flows, conductive,
convective and radiant transfer, and random heat and/or mass generating sources. As
impossible to visualize as it was to determine, building air behavior represented one
of the last problems in classical physics to be understood. CFD offers system designers
as well as architects and building owners a “picture” of the complex flow patterns,
finally enabling an escape from the all too often generically designed system.
Nevertheless, the true potentials of CFD and simulation modeling have yet to be
exploited for building applications. In most other fields, including automotive design,
aeronautics, and electronics packaging, CFD has been used for much more than just
a test and visualization tool for evaluating a specific installation or technology.
Rather, many consider CFD to be a fundamental means of describing the basic
physics, and, as such, its numerical description completes the triad with analytical
and empirical descriptions. Given that the major technology for heating and cooling
buildings (the HVAC system) has been in place for nearly a century with only minor
changes, a large opportunity could be explored if CFD were used to characterize and
understand the physical phenomena taking place in a building, possibly even leading
to a challenge of the accepted standard of the HVAC system.
This chapter will address the differences between building system modeling and
phenomenological modeling: the relative scales, the different modeling requirements,
the boundaries, and modes of evaluation. In particular, the chapter will examine the
fundamental issues raised when density-driven convection is treated as the primary
mode of heat transfer occurring in buildings. This is in contrast to the more normative
privileging of the pressure-driven or forced convection produced from HVAC
systems that is more often the focus of CFD simulations in building. The chapter will
then conclude with a discussion of how the exploration of phenomenological behaviors
could potentially lead to the development of unprecedented technological
responses.