ASHRAE Journal - May 2020 - 17

TECHNICAL FEATURE

FIGURE 3 Selected mesh for CFD calculations.

X

1

3

3.00

2.50

2.50

2.00

2.00

1.50

1

2

3

1.50

1.00

1.00

0.50

0.50

0.00
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Velocity (m/s)

0.00
15 17 19 21 23
Temperature (°C)

25

FIGURE 5 Results of total outdoor airflow and door sealing.

2,500
Total Outdoor Airflow (cfm)

using CFD studies in the conceptual analysis at the early
design phase. Figure 3 depicts the selected mesh.
A much finer mesh is necessary for a complete description of the flow field. However, given the objective of
the study to show the applicability of the CONTAM-CFD
software in a conceptual analysis at the early design
phase, the study focused on providing a mesh that is
suitable enough to represent the general flow features
of the studied solution. This strategy enables the design
team to study several basic strategies with the same
computational time that would be involved in a detailed
calculation, trimming down the candidate solutions for
a more detailed CFD analysis in a future design phase.
To ensure that the selected mesh is suitable for this preliminary simulation, the following method was used:
1. A grid refinement study was conducted using the
CONTAM-CFD option to select a sufficiently fine mesh
for a complete description of the flow field. The MV
(mixed ventilation) case was selected for evaluation. The
resultant profile from one of the tested positions is presented in Figure 4. It was estimated that a mesh with 1.5
million elements would be suitable.
2. Supplementary simulations were conducted with
a commercial CFD software that has already been used
in similar studies. A mesh with 2,431,276 elements was
built and taken as acceptable, given the results of the
grid refinement studies. The MV and UD scenarios were
also simulated with this commercial software, using
this mesh. The resultant flow fields were compared with
the results of the basic CONTAM-CFD simulations, performed with the 256,932 elements mesh. CFD validation
for this application was performed in a previous study.17

2

3.00

h (m)

h (m)

Y

FIGURE 4 Resultant profiles for one of the tested positions located at the middle
plane, 0.7 m from the operation table. Mesh sizes: #1: 195,426; #2: 415,296; #3:
1,491,441.

2,000

760
15

1,500

300

1,000
1,550

1,550

1,550

Tight

Base

Loose

500
0

a

Additional Airflowa
Ventilation Requirementsb

To comply with the relative pressurization criteria

b To

comply with room ventilation criteria

Parametric Test of the Supply Air Velocity on the Contaminant Purging
Performance for the UD Design
Previous studies11,18 have demonstrated that the flow
patterns in an OR with unidirectional flow diffusers
(UD) are dependent on the supply air velocity for a
given thermal load. Therefore, this test was set to compare the performance of different supply air velocities
on contaminant purge for the UD design. The tested
supply velocities comprised 0.06 m/s (12 fpm), 0.13
m/s (25 fpm), 0.18 m/s (35 fpm), 0.26 m/s (51 fpm) and
0.32 m/s (62 fpm). These values were selected since
the recommended supply velocities are in the range of
0.13 m/s to 0.18 m/s (25 fpm to 35 fpm).11 For this analysis, the coupled simulation was used (CONTAM -> CFD
M AY 2020

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ASHRAE JOURNAL

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ASHRAE Journal - May 2020

Table of Contents for the Digital Edition of ASHRAE Journal - May 2020

Contents
ASHRAE Journal - May 2020 - Intro
ASHRAE Journal - May 2020 - Cover1
ASHRAE Journal - May 2020 - Cover2
ASHRAE Journal - May 2020 - 1
ASHRAE Journal - May 2020 - Contents
ASHRAE Journal - May 2020 - 3
ASHRAE Journal - May 2020 - 4
ASHRAE Journal - May 2020 - 5
ASHRAE Journal - May 2020 - 6
ASHRAE Journal - May 2020 - 7
ASHRAE Journal - May 2020 - 8
ASHRAE Journal - May 2020 - 9
ASHRAE Journal - May 2020 - 10
ASHRAE Journal - May 2020 - 11
ASHRAE Journal - May 2020 - 12
ASHRAE Journal - May 2020 - 13
ASHRAE Journal - May 2020 - 14
ASHRAE Journal - May 2020 - 15
ASHRAE Journal - May 2020 - 16
ASHRAE Journal - May 2020 - 17
ASHRAE Journal - May 2020 - 18
ASHRAE Journal - May 2020 - 19
ASHRAE Journal - May 2020 - 20
ASHRAE Journal - May 2020 - 21
ASHRAE Journal - May 2020 - 22
ASHRAE Journal - May 2020 - 23
ASHRAE Journal - May 2020 - 24
ASHRAE Journal - May 2020 - 25
ASHRAE Journal - May 2020 - 26
ASHRAE Journal - May 2020 - 27
ASHRAE Journal - May 2020 - 28
ASHRAE Journal - May 2020 - 29
ASHRAE Journal - May 2020 - 30
ASHRAE Journal - May 2020 - 31
ASHRAE Journal - May 2020 - 32
ASHRAE Journal - May 2020 - 33
ASHRAE Journal - May 2020 - 34
ASHRAE Journal - May 2020 - 35
ASHRAE Journal - May 2020 - 36
ASHRAE Journal - May 2020 - 37
ASHRAE Journal - May 2020 - 38
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ASHRAE Journal - May 2020 - 40
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ASHRAE Journal - May 2020 - 42
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ASHRAE Journal - May 2020 - Cover4
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