ASHRAE Journal - June 2019 - 21

TECHNICAL FEATURE

indicated that the HVAC configuration of the operating room can also affect such acceleration. When the
low wall return grilles were replaced by series of ceiling grilles the maximum centerline acceleration was
reduced by almost 30%, which was attributed to the
reduction in the thermal gradient across the supply air
jet.6
These previous CFD analyses of a hospital operating room HVAC system motivated the current study to
systematically analyze the behavior of unidirectional
airflow with a rather simple setup of a test chamber
involving a just a single ceiling-mounted diffuser panel,
a table, a heat source, and two symmetric exhaust grilles
on opposite walls. The main goal of this CFD study is to
evaluate the impact of supply air velocity on the overall
airflow patterns, temperature and velocity distribution under isothermal and non-isothermal conditions.
Additionally, the entrainment of the surrounding air is
evaluated by studying the acceleration in the centerline
velocity of the supply air jet under these conditions.
Insights gained through these analyses would help in
understanding the dynamics of unidirectional airflow
which can be valuable for the ceiling mounted design of
laminar flow HVAC systems.

FIGURE 1 Schematic of CFD models of a test chamber for various test conditions.

a) Isothermal

Virtual Set-Up of a Test Chamber
A virtual test chamber is developed for this study
using three-dimensional, steady state CFD model
(Figure 1). The chamber has 168 ft2 (15.6 m2) floor area
(14 × 12 ft [4.3 × 3.6 m]) with 10 ft (3 m) ceiling height.
Figure 1 shows three different test configurations. A
single panel laminar supply diffuser (2 × 4 ft [0.6 × 1.2
m]) is placed at the center of the ceiling at 10 ft (3 m)
elevation. A 3 ft (0.9 m) high table (5 × 3 ft [1.5 x 0.9 m])
is placed at the center of the chamber under the supply
diffuser. This table creates an obstruction to the airflow. The air is exhausted out through two long grilles
(14 × 0.5 ft [4.3 × 0.15 m]), which are placed symmetrically along the long sides of the chamber at 6 in. (15
cm) above the floor. For the two separate non-isothermal analyses, a fictitious heat source representing a
constant sensible heat load of 3,412 Btu/h (1000 W) was
placed in the room. In one case the source was placed
at the center of the table under the supply diffuser
(Figure 1b) and in the other (Figure 1c) two heat sources of
1,706 Btu/h (500 W) each were placed on either side of
the supply diffuser, which represent ambient lighting

b) Non-Isothermal Heat Source on the Table

c) Non-Isothermal Heat Sources Near Ceiling

or stratification near the ceiling. As noted the total
sensible heat load in all non-isothermal cases kept
constant.
J U N E 2 0 19

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ASHRAE Journal - June 2019

Table of Contents for the Digital Edition of ASHRAE Journal - June 2019

Contents
ASHRAE Journal - June 2019 - Intro
ASHRAE Journal - June 2019 - Cover1
ASHRAE Journal - June 2019 - Cover2
ASHRAE Journal - June 2019 - 1
ASHRAE Journal - June 2019 - Contents
ASHRAE Journal - June 2019 - 3
ASHRAE Journal - June 2019 - 4
ASHRAE Journal - June 2019 - 5
ASHRAE Journal - June 2019 - 6
ASHRAE Journal - June 2019 - 7
ASHRAE Journal - June 2019 - 8
ASHRAE Journal - June 2019 - 9
ASHRAE Journal - June 2019 - 10
ASHRAE Journal - June 2019 - 11
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ASHRAE Journal - June 2019 - 15
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ASHRAE Journal - June 2019 - 17
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ASHRAE Journal - June 2019 - 19
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ASHRAE Journal - June 2019 - 21
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ASHRAE Journal - June 2019 - Cover3
ASHRAE Journal - June 2019 - Cover4
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