measurements on confluent jets v entilation system professor bahram moshfegh

Measurements on Measurements on Confluent Jets Confluent Jets

Ventilation SystemVentilation System

Professor Bahram MoshfeghTech. lic Ulf Larsson

Master students Julio J. Peña Malo and Igor Panjkov

[email protected]

Layout of the roomLayout 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 studiesCase studies

CaseTemp cooling ceiling

Cooling water flow T supply Air flow (m3/s)

Confluent JetsVentilation

1 20 3 14 0.022 20 14 0.0253 15 0.25 16 0.024 22.5 0.5 16 0.0255 6 20 0.25 18 0.257 20 0.25 18 0.3

DisplacementVentilation

8 20 3 14 0.029 22.5 0.5 16 0.025

10 20 0.25 18 0.03

MixingVentilation

11 20 3 14 0.0212 22.5 0.5 16 0.02513 20 0.25 18 0.03

Local mean age and Air change Local mean age and Air change efficiencyefficiency

Confluent jets ventilation system (device at 2.2 m height)

Confluent ventilation(2.2m) C0

Mean age air (min)

Local air change index

0.1m Case 4 407.94 19.51 104.41%Case 1 252.89 24.6 98.33%

1.2m Case 4 394.66 20.08 101.44 %Case 1 264.29 24.62 98.25%

1.7m Case 4 360.44 19.40 105%Case 1 225.38 24.12 100.29%

Outlet Case 4 411.85 20.37 52.31%Case 1 302.75 24.19 50.07%

Air Change efficiency


Confluent jets ventilation system (device at 1.7 m height)

Confluent ventilation(1.7m) C0

Mean age air (min)


0.1m Case 4 204 18.33 98.2 %Case 1 202.88 24.38 103.3%

1.2m Case 4 249.2 17.42 103.3%Case 1 237.75 25.34 99.37%

1.7m Case 4 214.95 17.63 102.1%Case 1 233.01 23.54 106.9%

Outlet Case 4 216.26 18 47%Case 1 225.73 25.18 47.5%



Displacement ventilation system

Displacement ventilation C0

Mean age air (min)


0.1m Case 9 249.55 14.62 108.14%Case 8 189.88 8.34 193.88%

1.2m Case 9 258.02 16.38 108.14%Case 8 260.87 19.36 83.52%

1.7m Case 9 237.71 15.79 100.12%Case 8 243.98 17.13 94.39%

Outlet Case 9 235.09 15.81 49.6%Case 8 239.11 16.17 50.5%



Mixing ventilation system

Mixing ventilation C0

Mean age air (min)


0.1m Case 12 314.39 28.01 101.67%Case 11 294.18 34.23 100%

1.2m Case 12 262.01 27.97 101.82%Case 11 253.51 33.21 103.10%

1.7m Case 12 215.63 30.65 92.92%Case 11 281.36 32.36 105.81%

Outlet Case 12 263.97 28.48 47.6%Case 11 272.85 34.24 47.6%


Analysis of the local mean Analysis of the local mean age and air change age and air change

efficiencyefficiencyAir 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: 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 Temperature gradient Confluent jets ventilation system

Device at 2.2 m heightDevice at 1.7 m height

Temperature gradient Temperature gradient Displacement and Mixing ventilation system

MixingDisplacement

Analysis of the temperature Analysis of the temperature gradient gradient

Mixing ventilation system: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: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: 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 Temperature gradient Comparison between CJV, DV and MVComparison between CJV, DV and MV

Case T supplyT mean in the occupied

zoneTemperature difference

compared to the CJVCJV Case 1 14 23.9 -DV Case 8 14 24.1 +0.2

MV Case 11 14 24.4 +0.5CJV Case 4 16 24.3 -DV Case 9 16 24.5 +0.2

MV Case 12 16 25.6 +1.3CJV Case 7 18 24.0 -DV Case 10 18 24.2 +0,2MV Case 13 18 26.4 +2.4

Average air temperature in the occupied zone: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 PerformanceCooling PerformanceComparison between CJV and MVComparison between CJV and MV

Cooling Performance (CP):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.

Ventilation system

Case Tsupply

(C)

Texhaus

t

(C)

T(C)

Pcooling

(W)

CP(-)

CJV 1 14 24.4 10.4 249 105 %CJV 4 16 24.5 8.5 255 119 %CJV 7 18 24.2 6.2 224 142 %MV 11 14 24.9 10.9 261 -MV 12 16 26.1 10.1 303 -MV 13 18 26.8 8.8 318 -

Texhaust = Measured exhaust temperature (C)T = Texhaust – Tsupply

Pcooling = Measured exhaust temperature (C)Cooling Performance: CF = (Pcooling)MV/(Pcooling)CVJ

Thermal comfort (PMV)Thermal comfort (PMV)Confluent jets ventilation system (device at 1.7 m

height)

Case 1Case 1 Case 4Case 4

Case 7Case 7


height)

Height 0.1 mHeight 0.1 m Height 1.1 mHeight 1.1 m

Height 1.7 mHeight 1.7 m

Thermal comfort (PPD)Thermal comfort (PPD)Confluent jets ventilation system (device at 1.7 m

height)


Case 7Case 7


height)




height)


Case 3Case 3


height)


Case 7Case 7


height)




height)


Case 3Case 3


height)


Case 7Case 7


height)



Thermal comfort (PMV)Thermal comfort (PMV)Displacement ventilation system


Case 10Case 10

Thermal comfort (PMV)Thermal comfort (PMV)Displacement ventilation system



Thermal comfort (PPD)Thermal comfort (PPD)Displacement ventilation system


Case 10Case 10

Thermal comfort (PPD)Thermal comfort (PPD)Displacement ventilation system



Thermal comfort (PMV)Thermal comfort (PMV)Mixing ventilation system


Case 13Case 13

Thermal comfort (PMV)Thermal comfort (PMV)Mixing ventilation system



Thermal comfort (PPD)Thermal comfort (PPD)Mixing ventilation system


Case 13Case 13

Thermal comfort (PPD)Thermal comfort (PPD)Mixing ventilation system



Analysis of the thermal comfort Analysis of the thermal comfort PMVPMV and and PPDPPD

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 ConclusionsFinal 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.

measurements on confluent jets v entilation system professor bahram moshfegh

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