airflow characteristics and ventilation effectiveness in
TRANSCRIPT
Airflow Characteristics and Ventilation Effectiveness in the Office Room
with Task and Ambient Air-Conditioning System using Personalized
Selective Task Diffusers
Toshio Yamanaka1, Kazunobu Sagara
1, Hisashi Kotani
1, Masashi Yamagiwa
2,
Susumu Horikawa3, Tatsuya Yamashita
4, Eunsu Lim
1
1 Osaka University, Japan
2 THE KANSAI ELECTRIC POWER CO., INC, Japan
3 NIKKEN SEKKEI LTD., Japan
4 SANKI ENGINEERING CO., LTD., Japan
Corresponding email: [email protected]
SUMMARY
“Task and ambient air conditioning system” for the large office room is a very comfortable
and energy saving system with an ambient temperature maintained at a little higher than the
that of the zone in the vicinity of seated occupants so long as the occupants can control the
thermal environment freely as a personal zone. A new selective floor diffuser for task zone
(occupancy zone) has been developed in order to improve the personal controllability. This
diffuser can provide two different airflows ; one is swirling diffusive flow (“swirl flow”) and
the other is directional jet (“directional flow”). One can change the flow type easily by turning
the switch on the floor diffuser. This selection can give the comfortable environment for any
occupants with different thermal tastes.
In this study, the temperature distributions, airflow characteristics and ventilation
effectiveness were measured in a large office room with this floor diffusers and grille type
ceiling outlets for ambient zone. The tracer gas pulse method was adopted to measure the
local mean age of air and SVE4 (scale for ventilation efficiency No.4) which presents the
contribution ratio of each supply outlet. In addition to the measurements, the CFD analysis
was conducted to investigate the detail of the air distributions in the room.
As a result of these investigations, the attainment of “task zone” around the occupants and
negligible effect of the task diffusers other than the closest task diffuser were confirmed.
INTRODUCTION
The measurement of the temperature, air velocity and ventilation indices were conducted in
an large office room with task and ambient air-conditioning system using personalized
selective task diffusers. This office room is located in the 30th
floor of a high-rise office
building in Osaka, Japan. As presented in previous papers [1][2], this building was designed
to utilize wind-forced ventilation for the environment control of ambient zone of he room in
intermediate seasons. In summer and winter seasons, the openings for wind-forced ventilation
are all closed, and so-called “task and ambient air conditioning system” control the indoor
environment. The purpose of this measurement is to examine the effect of the change of the
flow type of floor diffuser on the flow characteristics and thermal environment around a
sitting occupant. In fact, a simple thermal mannequin and black lamps were used instead of
real persons. Two indices, local mean age of air [3][4] for specific supply opening and SVE4
[5] (scale for ventilation efficiency No.4) were used, and tracer gas pulse method was applied
to measure these indices. In addition to the measurement, CFD analysis by standard k- model
was conducted to clarify the effect of the flow rate ratio of floor diffuser and ceiling grille on
the temperature distribution in the room.
The results of the measurement and CFD analysis under the hybrid air conditioning system of
floor supply and natural ventilation will be presented in another paper [6] printed in
proceedings of ROOMVENT 2007.
MEASUREMENT
Outline of measured building and air conditioning system
The measurement was conducted in an office room on
the 30th
floor of the high rise office building shown in
Fig.1. The outline of the building is shown in Table 1.
Table 1. Outline of the measured building. Location Osaka city, Japan
Building use Office, Substation, District heating
and cooling, Parking
Total floor area 5 stories in underground and 41
stories on the ground (GL+195m)
As many openings for wind-forced ventilation were
closed, and conditioned air is supplied from ceiling
grille for ambient zone and floor diffusers for the task
zone around occupants. Fig.2 shows the duct system,
and the supply flow rates are shown in Table 2, flow
rate of return air in Table 3. As is shown in Fig. 2, the
ambient zone temperature is set to 28 ºC and task zone
26ºC. Outside fresh air is introduced into AHU for
ambient zone and supplied from the ceiling sully grille.
As for AHU for task zone, only the return air is
circulated. The flow rate of outside air is 6,600 m3/h. The supply flow rate is 21,000 m
3/h for
floor diffuser, 18,000 m3/h for ceiling grille.
VAV
MD
Outside air
ceiling slit for return air
Ambient zone (28 degC) Ceiling supply grille
Floor diffuser
AHU for ambient zone
AHU for tast zone
Task zone (26 degC)
Opening for wind-forved ventilation
MD
MD
Relief air toEV hallCeiling plenum chamber
Figure 2. Duct and AHU system in section.
Measured floor
27-34F : floors with openings for wind-forced ventilation
14-17F : floors with openings for wind-forced ventilation
Office
Office
Entrance hall
GL+195m
GL
Figure 1. Section of
measured building.
Table 2. Supply air conditions.
Supply
opening Control
Supply air
temperature
Maximum airflow
rate of each
supply
Number
of supply
unit
Floor
diffuser (for
task zone)
Person sensor or manual
switch
Flow rate : (Large, Small,
Close)
Flow direction :
(Directional, Swirl flow)
21~22 degC
(during
measurement)
110 m3/h 254
Ceiling grille
(for ambient
zone)
VAV
21.5~22 degC
(during
measurement)
Perimeter zone:
110 m3/h
Interior zone: 100
m3/h
143
Table 3 Airflow rate of return, relief and exhaust air
Airflow rate
Return through ceiling chamber 39,000 m3/h
Relief air 6,600 m3/h
Exhaust from the smoking room 800 m3/h
57,600
36,0
00
NArea showed in Fig.7
Measured occupant area with a mannequin generating 60W
Measured room
Outside of measurement area
Floor difuser Ceiling grille
Open ceiling(30-32F)
Smoking room
Figure 3. Plan of measured 30th floor.
The plan of the measured floor is shown in Fig. 3.
Fig. 4 shows the picture of floor diffuser. The flow type of
this diffuser can be changed by shutting the directional
outlet at the center of this diffuser. One is called
“directional flow”, and the other “swirl flow”. Fig.5 shows
the schematic airflow from the floor diffuser to an
occupant for each flow setting of the diffuser. One floor
diffuser is prepared for one sitting occupant in principle.
Fig.6 shows the picture of ceiling grille.
φ200mm φ200mm
φ100mm φ100mm
Swirl diffuserSwitch of flowrate
Directional diffuser Shutter switch
Figure 4. Face of floor diffuser.
Method of measurement
The measurement was carried out from 16 July,
2005 to 18 July, 2005. A mannequin wrapped with
heating tape was seated in the area of dotted line
in Fig.3. Air velocity, temperature and tracer gas
concentration were measured around the
mannequin. SF6 was used as tracer gas, and the
balloons filled with SF6 set in the ten floor diffuser and three ceiling grille were divided by a
needle one by one, and the concentration response of SF6 was measured at many points. The
positions of the diffusers and grilles where a balloon was divided are shown in Fig. 7.
Measurement points of tracer gas concentration are shown in Fig.8. As the flow from ceiling
grilles is directed to the left (west) direction in Fig.7, three ceiling grilles in the right (east)
side of the mannequin were selected as a pulse source of tracer gas. The floor diffuser “T-3”
is the closest one to the heated mannequin.
T-1
T-3
T-4
T-5
T-7
T-6
T-8
T-9
T-10
T-2A-1
A-3A-A-2
Area of dotted line in Fig.3
Measured occupant zone
Floor diffuserFloor diffuser with tracer gas injection (T-1~10)Ceiling grille with tracer gas injection (A-1~3)
L L'
C C'
C10
C11
C12
1600
1100
100
500
500
500
500 500
C1
C2
C4
C5
C7
C8
C9
C-C' section
R R'T-4
T-3
Directional airflow
Directional airflow
Mouse of mannequin
M
C3 C6
plan
Measurement point of tracer gas concentration (36 points)
Measured occupant area
Figure 7. Plan of measured area. Figure 8. Measurement points of SF6 concentration
Because measurement period was holidays, there were no working occupants in the office. A
hundred and ten black lamps of 60 W were set at all chairs to simulate the heat emission from
persons. As other heat source, all the illuminators on the ceiling were lit and all notebook
computers on the desk were set to standby mode.
Measurement was carried out under two conditions of the floor diffuser ; diffusive flow
setting and swirl flow setting. The flow rate of floor diffusers was set to the maximum (110
m3/h). Under the directional flow setting, only the ten diffusers were directed to the each
occupant seat closest to each diffuser. The flow the directional diffuser was set to the
direction with 45 degrees to each occupant horizontally because flow from the diffuser will
change its direction due to the swirling flow around the directional diffuser.
Section Plan
Section Plan
(1) Directional flow setting
(2) Swirl flow setting
Direction change due to swirl flow
Swirl flow
Figure 5. Schematic flow from floor
diffuser.
200mm
200mm
Figure 6. Face of ceiling grille.
Time mean values of air velocity and temperature were calculated, and the local mean age of
air for specific supply opening ip and SVE4 (Scale for Ventilation Efficiency No.4) were
calculated from the measured concentration response of SF6 according to the method
presented by Lim et al. [6]. Here, it is important to note “local mean age of air for specific
opening” is different from the normal local mean age in the respect that only the air supplied
to the specific supply opening is accounted for.
MEASUREMENT RESULTS
Temperature distribution in task zone around mannequin
The temperature distributions in the case of two flow settings of floor diffusers are shown in
Figure 9. It can be seen that the positions of area with the lowest temperature is different. In
both cases, ambient zone with rather uniform temperature is maintained in the upper zone of
the room.
2525
24
24
24
24
24.5
24.5
24.75
23.75 23.7524.25
25.25
25
25
24.5
24.5
24.75
24.25
25.25
00
500500
10001000
15001500
20002000
25002500
28002800
2500250020002000150015001000100050050000 2500250020002000150015001000100050050000
T-3 T-3
Unit : [degC] Unit : [degC]
[mm] [mm]
[mm] Ceiling grille Ceiling grille
MannequinMannequin
Desk Desk
Directional flow setting Swirl flow setting Figure 9. Temperature distribution in task zone around mannequin.
Vertical distribution of air velocity at the back of mannequin
Fig.10 shows vertical distribution of air velocity at the back
of mannequin (point : C7, C8, C9) under the condition of
directional flow, swirl flow and closed case (no supply air).
From this figure, the maximum velocity is seen at the height
of 60 cm above floor on both flow settings, but the velocity of
directional flow is much higher than the swirl flow. This
indicates the supplied air from floor diffuser reaches the
occupant under directional flow setting.
Distribution of “local mean age of air for specific
opening” ip
Based on the integration of Sf6 concentration response on
time series, local mean age of air for specific opening ip was
calculated. Fig. 13 shows the horizontal distributions of
ip around mannequin at the height of FL+1600, FL+1100
and FL+100. The left row is the cases of directional flow and the right row is the cases of
swirl flow. Mean age ranges from 60 to 90 seconds around the mannequin in the case of swirl
0
200
400
600
800
1000
1200
1400
1600
1800
0 0.1 0.2 0.3air velocity [m/s]
Hei
ght a
bove
flo
or [
mm
]
Directionalflow setting
Closed
Swirl flowsetting
Figure 10. Vertical
temperature distribution
at the back of mannequin.
flow supply, but mean age of directional
flow is shorter than that of swirl flow
supply, which ranges from 40 to 60
seconds. ip at higher level is larger than
ip at lower level.
The vertical distributions of ip in the
section passing the centerline of the
mannequin are shown in Figure 12. The
shape of these distributions resemble the
temperature distribution shown in Fig.9.
This tendency suggest that the convection
and diffusive transfer of heat is similar to
the convection and diffusive transfer of
supplied air.
Figure 13 shows the local mean age of air
for 10 floor diffusers (T-1~10) and three
ceiling grilles (A-1~3) at the front of the
occupant (C4, C5, C6). In the case of
directional flow setting, mean age of T-3
(nearest diffuser) is the smallest at
FL+100 and FL+1100, but the effect of
the floor diffusers in the opposite row
across the desks (T-6~10) is rather strong
at FL+1600. This shows the arrival of the
air supplied over the desks from the
opposite row of floor diffusers. The mean
age from the ceiling grilles is
comparatively small.
In the case of swirl flow settings of floor
diffusers, mean age of T-6~10 is not so
small as mean age of the diffusers on the
same row as the mannequin.
The mean age of ceiling grilles
is lager than most of mean age
of floor diffusers. From the
above, it is said that the
diffusers on the other side of
desks have less effect than the
diffusers on the same side as
the mannequin if the floor
diffusers are set to swirl flow.
The index of mean age,
however, indicates only the
time of arrival and does not
evaluate the amount of air
which arrived there.
0
200
400
600
800
1000
1200
1400
1600
0
200
400
600
800
1000
1200
1400
1600
0
200
400
600
800
1000
1200
1400
1600
0 200 400 600 800 100012000
0 200 400 600 80010001200
FL+1600
FL+1100
FL+100
FL+1600
FL+1100
FL+100
50
60
60
60
5040
5060
60
60
60
7070
70
70
70
80
8080 90
60 70
70 8080
90
8090
90
90
100
100
100
110
120
80
20
30
4050
50
6060
70 80
40
60
80
100 100
Swirl flowDirectional flow
Swirl flowDirectional flow
Swirl flowDirectional flow
[mm]
[mm]
[mm]
[mm] [mm]
T-3 T-3
T-3 T-3
T-3T-3
Unit : [s] Unit : [s]
Unit : [s] Unit : [s]
unit : [s] unit : [s]
GasEmission
GasEmission
GasEmission
Gasemission
Gasemission
Gasemission
Desk Desk
Desk Desk
Figure 11. Horizontal distribution of local
mean age of air for specific opening.
Directional flow setting Swirl flow setting
Gas emission Gas emission20
30
40
40
5050
5050
50
60
60
70
40
60
60
8080
80
100
100120
Unit : [s] Unit : [s]
30T-3 T-3
Figure 12. Vertical distribution of local mean age of air
for specific opening.
SVE4 of each supply openings at the front of
Figure 14 shows the ratio of SVE4 at three points in front of the mannequin (C4, C5, C6) for
both cases of directional flow setting and swirl flow setting. SVE4 is an index to evaluate the
relative strength of each supply opening at a certain point in the room. From this figure, the
floor diffuser T-3 has the largest ratio at FL+100 and FL+1100 when the floor diffuser is set
to directional flow. This corresponds to the result of local mean age of air seen in Fig.15. On
the other hand, SVE4 of ceiling grilles are quite small in the lower level. At FL+1600, the
values of the diffusers on the other side of desks T-6~10 are several times as large as the
diffusers on the mannequin side (T-1~5). Therefore, it is said that task zone will be formed
around sitting occupant by supplied air from the nearest diffuser (T-3) of directional flow
setting.
In the case of swirl flow setting, SVE4 of T-3 have larger values at any height, which means
the volume of task zone is a little larger than that of directional flow case. Anyway, in both
cases of directional flow case and swirl flow case, task zone is formed clearly around the
sitting occupants. In other word, task and ambient air conditioning system is maintained
regardless of occupant’s selection of flow type of floor diffusers.
0
20
40
60
80
100
120
140
160
Loc
al m
ean
age
for
spec
ific
ope
ning
[s]
Loc
al m
ean
age
for
spec
ific
ope
ning
[s]
Loc
al m
ean
age
for
spec
ific
ope
ning
[s]
0
20
40
60
80
100
120
140
160
0
20
40
60
80
100
120
140
160
T-1 T-2 T-3 T-4 T-5 T-6 T-7 T-8 T-9 T-10 A-1 A-2
Floor diffuser (T)Ceilinggrille(A)
Mannequin row Opposite rowFloor diffuser (T)
Ceilinggrille(A)
Mannequin row Opposite row
Floor diffuser (T)Ceilinggrille(A)
Mannequin row Opposite rowFloor diffuser (T)
Ceilinggrille(A)
Mannequin row Opposite row
Floor diffuser (T)Ceilinggriller(A)
Mannequin row Opposite rowFloor diffuser (T)
Ceilinggrille(A)
Mannequin row Opposite row
T-1 T-2 T-3 T-4 T-5 T-6 T-7 T-8 T-9 T-10 A-1 A-2
T-1 T-2 T-3 T-4 T-5 T-6 T-7 T-8 T-9 T-10 A-1 A-2
C4 (FL+1600mm)
C5 (FL+1100mm)
C6 (FL+100mm)
T-1 T-2 T-3 T-4 T-5 T-6 T-7 T-8 T-9 T-10 A-1 A-2 A-3
T-1 T-2 T-3 T-4 T-5 T-6 T-7 T-8 T-9 T-10 A-1 A-2 A-3
T-1 T-2 T-3 T-4 T-5 T-6 T-7 T-8 T-9 T-10 A-1 A-2 A-3
C4 (FL+1600mm)
C5 (FL+1100mm)
C6 (FL+100mm)
Directional flow
FL+1.6m
FL+1.1m
FL+0.1m
Swirl flow
Figure 13. Comparison of local mean age of air for different supply openings.
CFD ANALYSIS
CFD simulation was carried out with
standard k- model. Fluent ver.6.2 was
used for CFD code. Analyzed volume is
14,400 2,800 7,200mm3 as shown
in Fig.15. This space consists of eight
modules. The area of one module is
3,600 14,400 m2, and one module contains 4 desks, 2 illuminators and return slits, 4 person
simulators and 3.5 floor diffusers on average. As it is quite difficult to make the complex
shape of floor diffusers in CFD field, the boundary model of the velocity vector, k and were
input at the height of 350 mm above the floor (see Fig.16) based on the velocity measurement
using a hot-wire anemometer [7]. Instead of the floor diffusers, simple square openings were
installed on the floor. Velocity vector of ceiling grille is inclined to the left side by 45 degrees.
Three conditions were assumed. These are ambient (ceiling grilles) only, task and ambient
(the same as measurement), task (floor diffuser with diffusive flow) only. The flow rate of
each opening was decided so as to keep the room temperature 23.3 ºC if the room air is
T-1T-2
T-3T-4
T-5
A-1A-2
T-10
T-6
T-7
T-8
T-9
Opposite row (T6~10)
Mannequin row (T-1~5)
Ceiling grille
(A)
C4 (FL+1600)
FL+1.6m
T3
T-1
T-4T-5
T-6
T-7
T-8
T-9
T-10A-1 A-2
T-2Ceiling grille (A)
M
annequin nrow (T-1~5)
Opposite row (T6~10)
C5 (FL+1100)
FL+1.1m
Mannequin row (T-1~5)
Ceiling grille
(A)
C4 (FL+1600)
FL+1.6m
T-1T-2
T-3
T-4T-5T-6
T-7
T-8
T-9
T-10
A-1A-2
A-3
Opposite row (T6~10)
T-4
C5 (FL+1100)
Mannequin row (T-1~5)
Ceiling grille (A)
T-6~10
FL+1.1m
T-2
T-3
A-1~3T-1
T-5
C6 (FL+100)
Mannequin row (T1~5)
Floor diffuser (A)T-6~10
Ceil
ing grill
e (T-6~10)
T-1
T-2
T-3
T-4
T-5
A-1 A-2
FL+0.1m
Directional flow
C6 (FL+100)
Oppo
site row
(T) A-1~3
T-6~
10
FL+0.1m
T-2
T-3
T-1
T-5T-4
Mannequin row (T1~5)
Ceiling grille (A)
Swirl flow
Figure 14. Ratio of SVE4 in front of
the mannequin.
100
600
600
400
400
Square suppy opening
300
Blocks for virtual boundary
Figure 16. Boundary model for floor diffuser.
Swirl flow model Square supply opening
Illuminator Ceiling slit for return air
Notebook computer
Person simulator
Figure 15. Analyzed space by CFD.
Figure 17. Temperature distributions in the case
of ambient only, task and ambient, task only.
(1) Only ceiling grilles (260m3/h per one grille)
(3) Only floor diffusers (170m3/h per one diffuser)
(2) Task and ambient (110m3/h per one floor diffuser and 90 m3/h per one ceiling grille)
15
25
161718192021222324
[ºC]
perfectly mixed. Here, supply
temperature of floor diffuses is 21 ºC,
and the supply temperature of ceiling
grilles is 18 ºC.
Figure 17 shows the temperature
distributions in section under three
conditions. In the case of ceiling
diffusers only, there can be seen rather
large temperature decline from the right
to the left. This horizontal distribution is
caused by the inclined flow direction of
ceiling grilles. The temperature
distribution of task and ambient is so
similar to the case of floor diffusers
only, and there is a clear task zone
around each occupant. From Figure 18, there is large velocity at the back of all occupants,
which may cause draught to occupants and bring thermal discomfort. Therefore, it is said that
the task and ambient air conditioning system is the most comfortable and energy saving
system among three in respect of the environment around occupants.
DISCUSSION
As a result of the measurement in a real office room with task and ambient air conditioning
system, the existence of task zone around the occupants were confirmed by the distribution of
temperature, local mean age of air for specific opening and SVE4. The flow selection of floor
diffusers turned out to be effective in order to control the personal thermal sensation of each
occupant. From the CFD analysis, the priority of this system to ceiling supply and floor
supply system was made clear.
The assessment from the view point of energy consumption will be needed, and the boundary
model for the floor diffuser used for CFD should be verified and improved for wider
application of this method to the design process of this kind of air conditioning system.
ACKNOWLEDGEMENT
The authors would like to thank Ms. Machiko Kuise and Mr. Shogo Takeda for helping us
with the experiment and analyzing the data.
REFERENCES
1. Ushio, T, Sagara, K, Yamanaka, T, Kotani, H, et al. 2006. Task Ambient Air Conditioning
System with Natural Ventilation for High Rise Office Building (Part 1: Outline of System and
Thermal Environment in Working Zone). 2006. Proceedings of Healthy Buildings 2006, Vol.4,
pp.269-274.
2. Kotani, H, Sagara, K, Yamanaka, T, Kuise, M, et al. 2006. Task Ambient Air Conditioning
System with Natural Ventilation for High Rise Office Building (Part 2: Measurement of Natural
Ventilation Rate and CFD Analysis using Measured Data). Proceedings of Healthy Buildings
2006, Vol.5, pp.135-140.
3. Sandberg, M. 1983. Ventilation Efficiency as a Guide to Design, ASHRAE Transactions, Part
2B, pp.455-477.
(1) Only ceiling grilles (260m3/h per one grille)
(3) Only floor diffusers (170m3/h per one diffuser)
(2) Task and ambient (110m3/h per one floor diffuser and 90 m3/h per one ceiling grille)
0
1.0
0.10.20.30.40.50.60.70.80.9
[m/s]
Figure 18. Velocity distributions in the case of
ambient only, task and ambient, task only.
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John Wiley & Sons.
5. Kato, S, Murakami, S, Kobayashi H. 1992. Preprints of International Symposium on Room Air
Convection and Ventilation Effectiveness (ISRACVE), pp.321-322
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Hybrid Air-conditioning System of Task Air Supply and Natural Ventilation, ROOMVENT
2007
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Environment in Room with Task Ambient Air Conditioning System with Natural Ventilation
(Part 3. Airflow Modeling of Under-floor Air Supply Opening for CFD Simulation). Technical
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