Measurements on
Confluent Jets Ventilation
System
Professor Bahram Moshfegh
Tech. lic Ulf Larsson
Master students Julio J. Peña Malo and Igor Panjkov
bahram.moshfegh@hig.se
Layout of the room
Cyan zone is the studied zone divided in 6 subzones. The representative points of each subzone
are shown with a small circle. In purple, the equipment inside the room. In red and blue, flow
air directions. Yellow point is the temperature measure points at two different positions. The
temperatures have been measured starting at 0.1 m from the floor. After the first point, each 20
cm for 10 times.
Case studies
Case
Confluent Jets
Ventilation
Displacement
Ventilation
Mixing
Ventilation
1
2
3
4
5
6
7
8
9
10
11
12
13
Temp cooling
ceiling
20
20
15
22.5
20
20
20
22.5
20
20
22.5
20
Cooling water
flow
3
0.25
0.5
T supply
14
14
16
16
0.25
0.25
3
0.5
0.25
3
0.5
0.25
18
18
14
16
18
14
16
18
Air flow (m3/s)
0.02
0.025
0.02
0.025
0.25
0.3
0.02
0.025
0.03
0.02
0.025
0.03
Local mean age and Air change efficiency
Confluent jets ventilation system (device at 2.2 m height)
Confluent ventilation
(2.2m)
Case 4
0.1m
Case 1
Case 4
1.2m
Case 1
Case 4
1.7m
Case 1
Case 4
Outlet
Case 1
C0
407.94
252.89
394.66
264.29
360.44
225.38
411.85
302.75
Mean age air
(min)
19.51
24.6
20.08
24.62
19.40
24.12
20.37
24.19
Local air change
index
104.41%
98.33%
101.44 %
98.25%
105%
100.29%
52.31%
50.07%
Air Change
efficiency
Local mean age and Air change efficiency
Confluent jets ventilation system (device at 1.7 m height)
Confluent ventilation
(1.7m)
Case 4
0.1m
Case 1
Case 4
1.2m
Case 1
Case 4
1.7m
Case 1
Case 4
Outlet
Case 1
C0
204
202.88
249.2
237.75
214.95
233.01
216.26
225.73
Mean age air
(min)
18.33
24.38
17.42
25.34
17.63
23.54
18
25.18
Local air change
index
98.2 %
103.3%
103.3%
99.37%
102.1%
106.9%
47%
47.5%
Air Change
efficiency
Local mean age and Air change efficiency
Displacement ventilation system
Displacement ventilation
Case 9
0.1m
Case 8
Case 9
1.2m
Case 8
Case 9
1.7m
Case 8
Case 9
Outlet
Case 8
C0
249.55
189.88
258.02
260.87
237.71
243.98
235.09
239.11
Mean age air
(min)
14.62
8.34
16.38
19.36
15.79
17.13
15.81
16.17
Local air change
index
108.14%
193.88%
108.14%
83.52%
100.12%
94.39%
49.6%
50.5%
Air Change
efficiency
Local mean age and Air change efficiency
Mixing ventilation system
Mixing ventilation
Case 12
0.1m
Case 11
Case 12
1.2m
Case 11
Case 12
1.7m
Case 11
Case 12
Outlet
Case 11
C0
314.39
294.18
262.01
253.51
215.63
281.36
263.97
272.85
Mean age air
(min)
28.01
34.23
27.97
33.21
30.65
32.36
28.48
34.24
Local air change
index
101.67%
100%
101.82%
103.10%
92.92%
105.81%
47.6%
47.6%
Air Change
efficiency
Analysis of the local mean age and
air change efficiency
Air change efficiency: Confluent jets ventilation system with the device at 2.2 m gets the
best results (50-52%) followed by displacement (50%) and the last one mixing ventilation
system (47%). Confluent system with the device at 1.7 m obtains similar results than mixing
ventilation system in terms of air change efficiency.
Local mean age:
the system which more approximate to the theory values are confluent
ventilation in any of the two heights (better at 2.2 m height). After confluent, the second best
results come from displacement, and mixing is the system which obtains the farthest results in
comparison with the theory results.
Temperature gradient
Confluent jets ventilation system
Device at 1.7 m height
Device at 2.2 m height
Temperature gradient
Displacement and Mixing ventilation system
Displacement
Mixing
Analysis of the temperature gradient
Mixing ventilation system: the temperature diagram looks like a vertical
line. This is due to the homogeneous mix that are inside the office room for
the mixing ventilation system.
Displacement ventilation system: at the low level the temperature is
lower than in the middle and in the top level. This is due to the
displacement ventilation system performance which makes supply air pass
through the floor firstly and then the air goes up towards the top part of the
room.
Confluent jets ventilation system: with the device at 1.7 m and 2.2 m, the
temperature gradient is like a mix between displacement ventilation and
mixing ventilation.
Temperature gradient
Comparison between CJV, DV and MV
Case
CJV Case 1
DV Case 8
MV Case 11
CJV Case 4
DV Case 9
MV Case 12
CJV Case 7
DV Case 10
MV Case 13
T supply
14
14
14
16
16
16
18
18
18
T mean in the occupied
zone
23.9
24.1
24.4
24.3
24.5
25.6
24.0
24.2
26.4
Temperature difference
compared to the CJV
+0.2
+0.5
+0.2
+1.3
+0,2
+2.4
Average air temperature in the occupied zone: Table above shows the influence
of the supply air device on the mean air temperature in the occupied zone. Confluent jets
ventilation system provides 0.2oC lower air temperature in the occupied zone compared to the
displacement ventilation. Comparison between confluent jets ventilation system and the mixing
ventilation shows quite considerable difference. The differences varies between 0.5oC to 2.4oC.
Thus, the Confluent jets ventilation systems provides better cooling in the room at the same
supply air temperature and flow rate.
Cooling Performance
Comparison between CJV and MV
Ventilation system
CJV
CJV
CJV
MV
MV
MV
Case
1
4
7
11
12
13
Tsupply
(C)
14
16
18
14
16
18
Texhaust
(C)
24.4
24.5
24.2
24.9
26.1
26.8
DT
(C)
10.4
8.5
6.2
10.9
10.1
8.8
Pcooling
(W)
249
255
224
261
303
318
CP
(-)
105 %
119 %
142 %
-
Texhaust = Measured exhaust temperature (C)
DT = Texhaust – Tsupply
Pcooling = Measured exhaust temperature (C)
Cooling Performance: CF = (Pcooling)MV/(Pcooling)CVJ
Cooling Performance (CP):
Table above shows the cooling performance of the
Confluent jets ventilation system (CJV) and the Mixing ventilation (MV). The results reveal that
for the studied cases the CJV has a higher cooling performance which varies between 105% to
142%. In other words the CJV has a higher cooling capacity compared to the MV.
Thermal comfort (PMV)
Confluent jets ventilation system (device at 1.7 m height)
Case 1
Case 4
Case 7
Thermal comfort (PMV)
Confluent jets ventilation system (device at 1.7 m height)
Height 0.1 m
Height 1.1 m
Height 1.7 m
Thermal comfort (PPD)
Confluent jets ventilation system (device at 1.7 m height)
Case 1
Case 4
Case 7
Thermal comfort (PPD)
Confluent jets ventilation system (device at 1.7 m height)
Height 0.1 m
Height 1.1 m
Height 1.7 m
Thermal comfort (PMV)
Confluent jets ventilation system (device at 2.2 m height)
Case 1
Case 2
Case 3
Thermal comfort (PMV)
Confluent jets ventilation system (device at 2.2 m height)
Case 4
Case 6
Case 7
Thermal comfort (PMV)
Confluent jets ventilation system (device at 2.2 m height)
Height 0.1 m
Height 1.1 m
Height 1.7 m
Thermal comfort (PPD)
Confluent jets ventilation system (device at 2.2 m height)
Case 1
Case 2
Case 3
Thermal comfort (PPD)
Confluent jets ventilation system (device at 2.2 m height)
Case 4
Case 6
Case 7
Thermal comfort (PPD)
Confluent jets ventilation system (device at 2.2 m height)
Height 0.1 m
Height 1.1 m
Height 1.7 m
Thermal comfort (PMV)
Displacement ventilation system
Case 8
Case 9
Case 10
Thermal comfort (PMV)
Displacement ventilation system
Height 0.1 m
Height 1.1 m
Height 1.7 m
Thermal comfort (PPD)
Displacement ventilation system
Case 8
Case 9
Case 10
Thermal comfort (PPD)
Displacement ventilation system
Height 0.1 m
Height 1.1 m
Height 1.7 m
Thermal comfort (PMV)
Mixing ventilation system
Case 11
Case 12
Case 13
Thermal comfort (PMV)
Mixing ventilation system
Height 0.1 m
Height 1.1 m
Height 1.7 m
Thermal comfort (PPD)
Mixing ventilation system
Case 11
Case 12
Case 13
Thermal comfort (PPD)
Mixing ventilation system
Height 0.1 m
Height 1.1 m
Height 1.7 m
Analysis of the thermal comfort PMV and PPD
 Confluent jets ventilation system with the device at 2.2 m gets better PMV value for Case 1
and Case 4 compared with the device at 1.7 m.
 However, for the Case 7 the device at 1.7 m has better PMC value compared to the device at
2.2 m.
 Confluent jets ventilation system has better PMV value for the studied cases followed by
displacement and the last one is the mixing ventilation system. People would be more
satisfied with the Confluent jets ventilation system
 Confluent jets ventilation system with the device at 2.2 m has better PMV value with the
height 0.1 m from the floor compared with the device at 1.7 m. For the other heights the
results are quite similar.
 Confluent jets ventilation system has better PMV value for all heights i.e. 0.1 m, 1.1 m and
1.7 m followed by the displacement and the last one is the mixing ventilation system.
 The same conclusions could be drawn for the PPD value. Confluent jets ventilation system
has the best values for the PPD value for all cases as well as at the different heights.
Final Conclusions
 CJV provides the most comfortable air temperature in the occupied zone compared to the
DV and MV.
 CJV has a higher cooling performance compared to the MV, which varies between 105% to
142% for the studied cases.
 CJV gets the best air change efficiency (52%) followed by the DV (50%) and the last one
MV (47%).
 CJV has better PMV and PPD values for the studied cases followed by the DV and the last
one is the MV system. People would be more satisfied with the CJV.
 CJV has better PMV and PPD values for all heights i.e. 0.1 m, 1.1 m and 1.7 m followed by
the DV and the last one is the MV.