ASHRAE Journal - November 2019 - 59

TECHNICAL FEATURE

FIGURE 3 Perspective view for the physical model for the convection HVAC system.

TABLE 2 Number of cells of grids used in the Grid Independence Test.
GRID SIZE

X

Y

Z

Course Grid

54

54

58

Fine Grid

104

104

108

are also set to zero at the exit section. For more details
see Al Beltagy (2010).

Normalized Mean Velocity (Um/Umax)

0.25

Normalized Temperature (Tmin/Tm)

FIGURE 4 (a) Velocity results of the grid independence test and (b) temperature
results of the grid independence test.

2.00
1.80
1.60
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00

0.20
0.15
0.10
Course Grid
Fine Grid

0.05
0.00
0

10

20

30
40
50 60
70
80
Normalized Vertical Distance Z/H (%)

90

100

Course Grid
Fine Grid
0

10

20

30
40
50 60
70
80
Normalized Vertical Distance Z/H (%)

90

100

plotted along the z direction normalized using the room
height H.
The results show that the velocity results of the both
grids are nearly identical, whereas the temperature
results of the fine grid differ slightly from those of the
coarse grid. So, the fine grid is considered more accurate
and its results are regarded as the final ones.

Grid Independence Test
A moderately coarse geometrical grid is used during
the run. After reaching convergence, a grid independence test is made by repeating the calculation, and
using a finer geometrical grid as per Table 2. A comparison is made between the results obtained by the two
grids in four charts representing mean velocity Um and
mean temperature Tm values trend in multiple horizontal planes along the vertical z-axis in the center of the
room as shown in Figure 4.
The values of velocity and temperature are normalized
using the room maximum velocity Umax and the minimum air temperature Tmin, respectively. The results are

Results and Discussion
Velocity, Temperature, PMV and PPD Contours
For the radiant ceiling arrangement, Figures 5 and 6
show the velocity, temperature, and predicted mean
vote (PMV) and predicted percentage of dissatisfied
(PPD) contours, respectively, at the intermediate plan,
x = 1.93 m (6.33 ft). The velocity results show the air
updraft due the heat source, represented by the equipment on the table, up to the radiant ceiling panel. The
air draft splits in the boundary layer below the ceiling
along the positive and negative y directions into two
streams, each of which circulates around the ceiling
N O V E M B E R 2 0 19

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ASHRAE Journal - November 2019

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

Contents
ASHRAE Journal - November 2019 - Intro
ASHRAE Journal - November 2019 - Cover1
ASHRAE Journal - November 2019 - Cover2
ASHRAE Journal - November 2019 - 1
ASHRAE Journal - November 2019 - Contents
ASHRAE Journal - November 2019 - 3
ASHRAE Journal - November 2019 - 4
ASHRAE Journal - November 2019 - 5
ASHRAE Journal - November 2019 - 6
ASHRAE Journal - November 2019 - 7
ASHRAE Journal - November 2019 - 8
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