ASHRAE Journal - November 2019 - 64

TECHNICAL FEATURE

comparison is performed numerically using the commercial CFD code. Mesh sensitivity runs are performed
and the code is also validated by comparing the code
results against experimental and numerical data available in the literature for a convection cooling test case
and a radiant cooling test case. The comparison shows
that numerical predictions are in good agreement with
the experimental results.
The numerical predictions show conventional convection HVAC systems produce dynamically and thermally
un-uniform environments. As a result, convection HVAC
systems can cause local discomfort to individuals that
may be located in the path of the supply airstream. On
the other hand, the predictions show that radiant cooling
techniques are capable of achieving the required indoor
temperature with draft-free conditions. Also, radiant
cooling can provide a uniform temperature distribution
for the air-conditioned space. The PMV and PPD comfort
indices show that radiant cooling techniques are capable
of providing comfortable environments for individuals. It is also noted that temperature variations along the

vertical axis in the radiant ceiling arrangement are very
small (about 3°C [5.4°F]) unlike the radiant walls arrangement, in which the temperature difference between the
head and the feet in the occupied zone is considered relatively high (about 7°C [12.6°F]).
Cleanrooms are usually air-conditioned via a large
number of air changes, which are normally about 15 ach
to ensure a predefined degree of filtration that satisfies
hygienic requirements. Psychometrically, the supply
air temperature is around 14°C (57.2°F) for most load
profiles. Such a low temperature draft would cause local
discomfort because of local overcooling for people subjected directly to the airstream. An example of that case
is surgeons and patients inside operating rooms. For
unidirectional flow regimes, especially for those with
low-air velocities (laminar flow), an un-uniform temperature distribution is experienced. Another example
is un-uniform temperature inside sterile areas of high
clean classes (A and B), especially near load sources such
as production machines or laboratory equipment. The
use of radiant cooling techniques in the preceding cases

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ASHRAE JOURNAL

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ASHRAE Journal - November 2019

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