ASHRAE Journal - November 2019 - 61

TECHNICAL FEATURE

FIGURE 7 Perspective view for the predicted (a) velocity and (b) temperature
contours for the radiant walls arrangement at x = 6.33 ft.

fpm
87.6898
82.2095
76.7290
71.2487
65.7682
60.2879
54.8076
49.3271
43.8468
38.3666
32.8861
27.4058
21.9253
16.4450
10.9647
5.4842
0.0039

FIGURE 8 Perspective view for the predicted (a) PMV and (b) PPD contours for
the radiant walls arrangement at x = 6.33 ft.

PMV

3.000000
2.757904
2.515808
2.273712
2.031616
1.789520
1.547424
1.305328
1.063232
0.821136
0.579040
0.336944
0.094849
-0.147247
-0.389343
-0.631439
-0.873535

°F

PPD

94.42002
92.54745
90.67485
88.80228
86.92968
85.05711
83.18451
81.31194
79.43934
77.56677
75.69417
73.82160
71.94900
70.07643
68.20383
66.33126
64.45866

29.34720
27.82550
26.30380
24.78210
23.26040
21.73870
20.21700
18.69530
17.17360
15.65190
14.13020
12.60850
11.08680
9.565101
8.043400
6.521700
5.000000

velocities until it reaches the low-level return air grills
at the bottom of the opposed 3.86 × 2.25 m (12.7 × 7.38 ft)
walls. The mean air velocity at the intermediate plan is
0.084 m/s (16.53 fpm), which indicates relatively higher
velocity conditions. The highest values of velocity are
ahead of the supply ceiling diffuser and return air grills,
compared to values reached in the rest of the domain,
whereas slower velocities are experienced in the rest of
the room. The temperature contours show a uniform
temperature distribution all over the intermediate plan,
except for the area under the supply ceiling diffuser with
a mean temperature of 22.9°C (73.2°F). The temperature
under the ceiling diffuser is close to the supply temperature, 14°C (57.2°F), which is a low temperature resulting
in uncomfortable conditions. The PMV and PPD contours
show a uniform distribution with a mean PMV value of
-0.29 and a mean PPD value of 9.37%, indicating slightly
cold conditions as compared to the radiant cases.

Mean Velocity, Temperature, PMV, and PPD Plots
Plots are made to compare the results of all the three
proposed arrangements. Figure 11 shows the vertical
variation of the mean temperature Tm and the mean

velocity Um in a none dimensional form. The mean temperature and velocity are normalized using the minimum air temperature Tmin and maximum velocity Umax
respectively. The vertical distance z is normalized using
the room height H. Finally, Figure 12 depicts the vertical
variation of the PMV and mean PPD indices. The radiant
cooling case, Figure 11a shows the temperature gradually
increases in the vertical direction until it reaches a maximum above the table position where the heat loads are
located. From this point upward, the ﬂow behaves like a
plume of hot air rising in a stratiﬁed environment. The
plume temperature decreases and progressively loses
buoyancy. At some level, it will lose all buoyancy and will
begin to spread horizontally, causing an increase in the
average temperature. This increase in average temperature is caused by the horizontal spreading of the hot air,
as shown in Figure 5b. However, for the convection HVAC
system, the air inside the room is well mixed. As a result,
there are no temperature variations in the regions below
and above the table. However, the temperature will
increase across the table due to the equipment load.
Figure 11b shows that for the two radiant arrangements,
the velocity variation with a normalized vertical distance
N O V E M B E R 2 0 19

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ASHRAE Journal - November 2019

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