potential of using passive/active stacks to enhance …potential of using passive/active stacks to...
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Potential of using passive/active stacks to enhance the
natural ventilation in HDB flats
This study investigates the feasibility of applying passive and active stack systems to enhance
the natural ventilation in public housing. The primary objective is to assess the status of natural
ventilation in a typical 4-room HDB flat using scaled model in the wind tunnel, and to develop an
effective passive or active stack system to enhance natural ventilation in the flat. CFD simulations
were also conducted to have a better understanding of the airflow inside the HDB unit using the
active stack systems and parametric studies were done to identify the various critical design
factors such as stack location, stack size etc.
It was observed that the active stack provides substantial increase in the internal air velocities. It
was noted that the velocities increase with the increase in fan velocities and also with the
increase in the stack size. It was also noted that, even though the enhancement in the velocity is
much higher when the doors are closed, they are more or less localized. But when the doors are
kept open, the velocity increase is more evenly distributed. Since our main concern is the
nighttime when bedroom doors are closed, more attention is given towards such situation. The
percentage increase in the velocity is up to 550% and the maximum velocity achieved was 0.67
m/s. A velocity of 0.26 m/s was achieved even with the smallest stack. For larger stacks high
velocities were achieved even when the wind tunnel was turned off. This indicates that on a calm
evening thermal comfort could be achieved. It was also observed that for larger stacks, the
increase in the fan speed has no significant effect on the air velocities. The maximum size of the
stack used is 0.4 m X 0.4 m, which is not much compared to a typical column of width 0.30 m of
an HDB flat and therefore the economic feasibility is well validated.
10.5
2
3.22
3.22
2.951.81 1.76
2.28 Bath
2.08 1.60
Service
2.28Bath
2.95
Master
3.12
1.22
Bed Room
Store
3.58
Bed Room
4.34
Living Room
Kitchen
3.68
10.55
10.55
3.00
3.00
Section A
Section B
Floor Plan
Elevation
10.20
A
BBed Room
Bed Room Living Room
Bed Room Bed Room KitchenMaster
Figure 1: Plan and sectional details of the residential unit under investigation
Figure 2: Physical model for the wind tunnel study (scale 1:5)
Figure 3: External wind velocities measured in the wind tunnel experiments
Air Velocity Increment Analysis
0%
20%
40%
60%
80%
100%
Open Close Open Close Open Close Open Close
15x15-Loc.1 40x40-Loc.1 15x15-Loc.2 40x40-Loc.2
Perc
enta
ge In
crem
ent (
%)
WT WT+IF IF
Figure 4: Comparison of the air velocity increment due to wind effect (WT), combination of wind
effect and stack fan (WT+IF) and stack fan (IF) alone
C
1Bath
B
0
A
Bed Room Master
Bed Room2
D
EBath
X
Kitchen
Store
Bed Room Living Room
Y F G H
Figure 5: Velocity vectors of Case 30: stack size 40x40, location 2-doors closed
F
Figure 6: Section of velocity vectors for Case 30: stack size 40x40, location 2-doors closed