A raised-floor plenum is often used to distribute cooling airflow in data centers. Traditional Computational Fluid Dynamics (CFD) can accurately model airflow distribution in plenums, but it is expensive (computationally and financially) and is, therefore, often not accessible to designer or operator. This paper presents an alternative CFD methodology based on Fast Fluid Dynamics (FFD), which is faster, more parallelizable, and simpler to program. The improvement in computational speed afforded by FFD is particularly important for multiple-iteration optimization simulations, or applications for which near-real-time performance is required. The potential speed improvements of FFD have been widely do however, it has been generally accepted that this benefit is accompanied by a modest loss of accuracy relative to traditional CFD. We show here not necessarily true. Plenum airflow predictions by our FFD implementation, which utilises a first-order upwind rather than Semi-Lagrangian advection scheme of previous research, are extremely close to those predicted by traditional CFD - provided the same turbulence model and computational grid are used consistently.