Advanced Building Simulation

156 Addington
Figure 6.4 Velocity profiles comparing micro-source placement for directly controlling the location of
air mixing and/or separation. (See Plate VI.)
The primary concern of the researchers was that the heat pump profile was too small
physically to overcome the viscous effects of air in order to provide homogeneous
conditions in large volumes. In essence, the hegemony of the HVAC system is such
that even radically different technologies are still expected to perform in the same
manner.
By characterizing the boundary layer behavior through micro-scale modeling, one
could begin to explore the true potential of new technologies. Whereas, the microand
meso-devices may be impractical as straightforward replacements for the standard
components used for conventional HVAC systems, they offer unexploited potential to
significantly impact local heat transfer in interior environments. At the scale of the
boundary layer, these devices have commensurate length-scales, and as such, are
capable of intervening in the layer to effect either a regime change or a shift in
the flow phenomenon. The heat transfer rate from any surface or object could then
be directly modified without necessitating changes in materials or construction. If the
concept is pushed even further, these types of tiny interventions could be effective
at forcing particular behaviors in specific locations. For example, a major concern of
air quality monitoring is the determination of the proper location for sensors so that
they can pick up minute quantities of contaminants. Currently the best method is
through increased mixing which has the disadvantage of increasing the contaminant
residence time and exposure. One could place the sensor almost anywhere and then,
through the judicious placement of tiny heat sources and sinks, establish a specific
buoyant plume with thermal qualities designed to manipulate the density of the contaminant
to ensure that the sensor sees the contaminant first (Figure 6.4). But these
types of solutions, experiments, or just even ideas can only be explored through CFD
simulation.
CFD simulation has been a boon to building system designers, and its impact in
improving both the efficiency and efficacy of conventional systems cannot be discounted.
Nevertheless, building modelers need to begin to consider small-scale behaviors
so as to expand the application of CFD from the prediction of the known to the
exploration of the unknown.