ASHRAE Journal - November 2019 - 60

TECHNICAL FEATURE

FIGURE 5 Perspective view for the predicted (a) velocity and (b) temperature
contours for the radiant ceiling arrangement at x = 6.33 ft.

PMV

fpm
91.1503
85.4555
79.7567
74.0600
68.3634
62.6666
56.9699
51.2731
45.5765
39.8797
34.1830
28.4862
22.7896
17.0929
11.3961
5.6993
0.0026

1.495312
1.361600
1.227666
1.094176
0.960464
0.826752
0.693039
0.559327
0.425615
0.291903
0.158191
0.024479
-0.109234
-0.242946
-0.376658
-0.510370
-0.644082

12.72927
12.24619
11.76311
11.28003
10.79695
10.31387
9.830794
9.347715
8.864635
8.381556
7.898477
7.415397
6.932318
6.449238
5.966159
5.483079
5.000000

°F
84.99895
84.01696
83.03499
82.05301
81.07104
80.08907
79.10710
78.12513
77.14515
76.16118
75.17921
74.197724
73.21525
72.23328
71.25130
70.26933
69.28736

ASHRAE JOURNAL

PPD

and downwards along the walls. The mean air velocity
at the intermediate plan, x = 1.93 m (6.33 ft), is 0.038
m/s (7.48 fpm), which indicates low-velocity conditions
compared to the ASHRAE thermally acceptable velocity of 0.25 m/s (49.2 fpm) or less. The highest values of
velocity are in the updraft area above the heat source
and within the boundary layer of the ceiling, whereas
semi-stagnant conditions are experienced in the rest of
the room. The temperature contours show a uniform
temperature distribution all over the intermediate plan
with a mean value of 24.96°C (76.9°F). The PMV and PPD
contours show a uniform distribution with a mean PMV
value of 0.13 and a mean PPD value of 6.19%, indicating
ideal comfortable conditions. The ASHRAE seven-point
scale for the PMV is: -3 cold, -2 cool,-1 slightly cool,
0 neutral, +1 slightly warm, +2 warm and +3 hot. The
comfort range for the PMV is defined from -0.5 to +0.5,
while the comfort range for the PPD is defined as less
than 10%.
For the radiant walls arrangement, Figures 7 and 8 show
the velocity, temperature, and PMV and PPD contours,
respectively, at the intermediate plan x = 1.93 m (6.33 ft).
Figure 7a shows the air velocity behaves in a similar
60

FIGURE 6 Perspective view for the predicted (a) PMV and (b) PPD contours for
the radiant ceiling arrangement at x = 6.33 ft.

ashrae.org

N O V E M B E R 2 0 19

manner as in the radiant ceiling arrangement (the first
arrangement). The mean air velocity at the intermediate
plan is 0.034 m/s (6.69 fpm), indicating low velocity conditions. Unlike the first case, the highest values of velocity are only in the updraft area above the heat source,
whereas semi-stagnant conditions are experienced in
the rest of the room. The temperature contours show a
uniform temperature distribution all over the intermediate plan with a mean value of 24.84°C (76.71°F). Unlike
the first arrangement, temperature values near the floor
are found to be relatively low (around 18°C [64.4°F]),
which may lead to less comfortable conditions. The PMV
and PPD contours show a uniform distribution with a
mean PMV value of 0.11 and a mean PPD value of 8.5%.
These values indicate comfortable conditions, but less
comfortable than the first arrangement.
For the convection HVAC system, Figure 9 shows the
velocity and temperature contours and Figure 10 shows the
PMV and PPD contours at the intermediate plan x = 1.93
m (6.33 ft). Figure 9 shows the air downdraft coming from
the supply ceiling diffuser, unlike the updraft observed in
the previous arrangements. The air draft splits and circulates around the equipment and the table with higher

ASHRAE Journal - November 2019

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