ArticlePDF Available

Effects of outdoor air conditions on hybrid air conditioning based on task/ambient strategy with natural and mechanical ventilation in office buildings

Authors:

Abstract and Figures

This research aims to clarify the effects and indoor environmental characteristics of natural and mechanical hybrid air-conditioning systems in office buildings during intermediate seasons and to obtain design data. Natural and mechanical hybrid air conditioning is an air-conditioning system that utilizes natural ventilation and mechanical air-conditioning systems to improve the quality of the indoor thermal and air environment, and to reduce energy consumption. This report first categorizes the available natural ventilation conditions and estimates the amount of natural ventilation available in a model building. Furthermore, based on the concept of task-ambient air conditioning, after controlling the average temperature in the task zone to a target air conditioning temperature (26°C), changes in the outdoor temperature/humidity and the inflow rate, and the indoor environment and amount of cool heat input were studied with changes in the size of the natural vent using three-dimensional Computational Fluid Dynamics (CFD) analysis. The results of these studies indicated that natural ventilation at temperatures lower than the indoor temperature effectively covered the lower indoor task zone through negative buoyancy, which enabled energy-saving air conditioning in the task zone.
Content may be subject to copyright.
Available online at www.sciencedirect.com
Building and Environment 39 (2004) 153 164
www.elsevier.com/locate/buildenv
Eects of outdoor air conditions on hybrid air conditioning based
on task/ambient strategy with natural and mechanical ventilation
in oce buildings
Hyunjae Changa;, Shinsuke Katob, Tomoyuki Chikamotoc
aDaewoo Engineering & Construction Co., Ltd, 60 Songjuk-dong Jangan-gu, Suwon, Kyungi-do 440-210, South Korea
bInstitute of Industrial Science, University of Tokyo, 6-1, Komaba 4-chome, Meguro-ku, Tokyo 153-8505, Japan
cNikken Sekkei Ltd, 2-1-2 Koraku, Bunkyo-ku, Tokyo 112-0004, Japan
Received 6 January 2003; received in revised form 26 March 2003; accepted 12 July 2003
Abstract
This research aims to clarify the eects and indoor environmental characteristics of natural and mechanical hybrid air-conditioning
systems in oce buildings during intermediate seasons and to obtain design data. Natural and mechanical hybrid air conditioning is
an air-conditioning system that utilizes natural ventilation and mechanical air-conditioning systems to improve the quality of the indoor
thermal and air environment, and to reduce energy consumption. This report rst categorizes the available natural ventilation conditions
and estimates the amount of natural ventilation available in a model building. Furthermore, based on the concept of task-ambient air
conditioning, after controlling the average temperature in the task zone to a target air conditioning temperature (26C), changes in the
outdoor temperature/humidity and the inow rate, and the indoor environment and amount of cool heat input were studied with changes in
the size of the natural vent using three-dimensional Computational Fluid Dynamics (CFD) analysis. The results of these studies indicated
that natural ventilation at temperatures lower than the indoor temperature eectively covered the lower indoor task zone through negative
buoyancy, which enabled energy-saving air conditioning in the task zone.
?2003 Elsevier Ltd. All rights reserved.
Keywords: Natural ventilation; CFD; Ventilation eciency
1. Introduction
Outdoor air cooling and natural ventilation through open
windows have both been proposed and actually used as
energy-saving cooling methods for oces. However, the for-
mer is primarily used to remove the heat load and introduce
outdoor air when the heating is turned o during interme-
diate seasons. Direct introduction of outdoor air by opening
the windows has been developed signicantly in past stud-
ies. For an example of recent accomplishments on this, Hunt
and Linden describe the uid mechanics of natural venti-
lation by the combined eects of buoyancy and wind [1].
W.Z. Lu et al. investigated the characteristics of cross ven-
tilation in a designated refuge oor in a high-rise building
[2]. Yuguo Li et al. derived analytical solutions for cal-
culating natural ventilation ow rates and air temperatures
Corresponding author. Tel.: +82-31-250-1216;
fax: +82-31-250-1131.
E-mail address: changhj@ihanyang.ac.kr (H. Chang).
in a single-zone building [3,4]. M.M. Eftekhari et al. studied
air ow distribution in and around a single-sided naturally
ventilated room [5]. However, direct introduction of outdoor
air through the windows does not necessarily guarantee con-
trol of the indoor thermal environment within a comfortable
range, because it allows air to enter, but gives no control
over the temperature of the air inow from outdoors or the
ow rate, and the period during which windows can be left
open is often limited. Thus, this research aims to develop a
new natural and mechanical hybrid air-conditioning system
that will maintain a comfortable indoor thermal environment
and maintain air quality, while achieving energy conserva-
tion by a rational use of natural ventilation, achieved by
opening natural indoor vents such as windows, and mechan-
ical cooling. For this purpose, the concept of task-ambient
air conditioning was introduced, which is founded on the
need for an even distribution of indoor temperatures and
air quality while breaking away from the conventional
fully mixed indoor air conditioning. This adopts the con-
cept illustrated in Fig. 1, where the heat and contaminants
0360-1323/$ - see front matter ?2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.buildenv.2003.07.008
154 H. Chang et al. / Building and Environment 39 (2004) 153 164
Cool fresh air
Thermal stratification
being formed
Efficient exhausting
of excess heat
Ambient zone
Task one
Exhausting
contaminants
Comfortable in terms of heat andair quality
z
Fig. 1. Concept of natural and mechanical hybrid air conditioning system.
generated in an oce indoor task zone are exhausted to
the outdoors by natural ventilation such as opening win-
dows, while using air conditioning to assist with removing
part of the heat load when this is unachievable by natural
ventilation alone. Compared to ordinary oces, which in-
troduce only a minimum amount of outdoor air as required,
those with a natural and mechanical hybrid air-conditioning
system can expect to have a tremendous increase in the
amount of outdoor air introduced, and this will signicantly
improve the indoor air quality when using natural venti-
lation. This was ascertained from eld measurements in
Liberty Tower at Meiji University, which is located in the
center of the Tokyo Metropolitan area in Japan, and which
has introduced a hybrid air-conditioning (cooling) system
[6]. The natural ventilation system in Liberty Tower is de-
signed to introduce outdoor air through an opening under
the window. The outdoor air introduced rises up through
the wind core (escalator void) by the stack eect, and is
then exhausted at the wind oor on the 18th level. From
the results of the eld measurements, however, in order to
make feasible a ventilation and air-conditioning system that
is most likely to provide these energy-conservation eects
and good air quality, it is critical to determine the mixture
and dispersion properties of natural ventilation air and in-
door air conditioning air, as well as to estimate the amount
of natural ventilation available. At present, there are almost
no estimation or evaluation methods that take these into
consideration. This research carries out a detailed study of
the following in providing oce space with natural venti-
lation by opening indoor vents in the ambient zone while
cooling the task zone:
1. Indoor micro heat/air mixture-dispersion phenomena by
Computational Fluid Dynamics (CFD).
2. The indoor thermal environment and ventilation e-
ciency.
3. Heat transfer phenomena in the task and ambient zones.
4. The energy-conservation eects (indoor load reduction
and reduction in the power of the air-conditioner fan
throughout the year).
A comprehensive examination is conducted into the eec-
tiveness of a natural and mechanical hybrid air-conditioning
system and what constitutes an ecient air-conditioning sys-
tem. This report describes the concept of task-ambient hy-
brid air conditioning, followed by the results of examining
the eects of outdoor air conditions on energy conservation.
2. Method of analysis
The analysis ow for this research is shown in Fig. 2. The
amount of natural ventilation in a single room was estimated
Macro model Micro model
The indoor air current and temperature
distribution and ventilation efficiency for
an office with a hybrid air conditioning
system were analyzed with the amount of
natural ventilation based on the results of
macro model 1. With the average
temperature in the task zone maintained at
a constant 26˚C, the following were
conducted:
- CFD analysis of the indoor air current
and thermal environment in the office
with a hybrid air conditioning system
- Analysis based on CFD results for indoor
ventilation efficiency in the office
From micro model analysis results
- Analysis of mixture rate of natural
ventilation and air conditioning air
- Analysis of the amount of heat mixed
and dispersed between the task zone
and the ambient zone
Evaluation of a hybrid air conditioning system
- Evaluation of indoor heat and air quality distribution properties in
the office
- Evaluation of indoor energy in the office
Macro model 1:
The amount of
natural ventilation
in the entire buil-
ding was comput-
ed by ventilation
circuit network
analysis.
Macro model 2:
The annual ene-
rgy simulation to-
ol based on a
block model was
made by using a
database contain-
ing the amount of
indoor heat load
removed by natu-
ral ventilation and
air conditioning.
Fig. 2. Research ow.
H. Chang et al. / Building and Environment 39 (2004) 153 164 155
Y axi s:
Assuming the reference
value of the summer cool-
ing load to be 70(W/m2),
the amount of natural
ventilation required to
remove this load
[m3/(h.m2)]
45 [m3/(h.m2)] (assumed
to be air of a volume not
exceeding a wind velo-
city of 1.5 [m/s] (assum-
ption) which may blow
papers off the desk*))
7.5 [m3/(h.m2)]
(minimum OA: Outdoor
air required per person
30 [m3/(h person)]
x Occupancy 0.25
[person/m2]) The lowest limit at which
the possibility of condensa-
tion is considered
Established temperature (the
upper limit of outdoor temp-
erature effective for remov-
ing the cooling load)
X axis:
Outdoor temperature [˚C]
Equation for volume of natural ventilation air required :
70[W/m2]
Cp.ρ: 0.34 [(W.h)/(˚C.m3)] × (Indoor Temp. 26[˚C] - Outdoor Temp. [˚C, X axis])
Conditions of excessive
natural ventilation
Natural ventilation air
volume being tighten-
ed by controlling
the ventilation
air volume
through the
opening
Portion of load removed by
air conditioning assistance
Conditions of insufficient
natural ventilation
Portion of load removed
by natural ventilation
Upper limit of ventilation
amount (in order to prevent
papers from being blown
away)
Frequency of ventilation
15 [times/h]
10 [times/h]
5 [times/h]
Amount of outdoor ai
r
introduced by ordinary ai
r
conditioning
50
40
30
20
10
014 16 18 20 22 24 26 28
Fig. 3. Concept of control by a natural and mechanical hybrid air conditioning system.
Computed as the instantaneous wind velocity on desks 1.5 m/s×wind velocity ratio on window surfaces and desks 1.2 (assumption on safety side)/G.F.2
(assumption)/oce depth 10.8 m×opening vertical width 0.5 m×ow coecient 0.3×3600.
by wind-driven ventilation macro-analysis for a model build-
ing, followed by micro-analysis of the indoor temperatures
and air quality distribution properties to control the amount
of heat transfer in the indoor task and ambient zones, based
on which macro-analyses were conducted on the air condi-
tioning energy required annually.
2.1. Conditions of available natural ventilation
The results of organized conditions for natural ventila-
tion made available by a natural and mechanical hybrid
air-conditioning system are shown in Fig. 3. Available natu-
ral ventilation is determined by the outdoor temperature and
the air volume introduced indoors. Outdoor temperatures are
shown on the horizontal axis; the amount of natural ven-
tilation per unit area [m3=(h m2)] is shown on the vertical
axis. Ventilation rates for the oce model adopted for this
research are shown at the right of the gure. The graph indi-
cates the amount of natural ventilation required to remove an
indoor cooling load—(70 W=m2) in this case. The oce in-
doors is assumed to have fully mixed air conditioning. More
outdoor air becomes necessary when the outdoor tempera-
ture becomes higher, and the cooling load can be adequately
reduced with less outdoor air when the outdoor temperature
becomes lower. When there is too much inow of outdoor
air, problems occur, such as papers being blown o desks,
and when outdoor temperatures are too low (16C or lower
for example), condensation and cold drafts occur, making
natural ventilation unusable. The area above the graph shows
excessive (adequate) natural ventilation conditions, and the
area under the graph shows conditions in which the load re-
moved by natural ventilation is insucient. This research
Targeted mid- to high-rise building:
floor height at 4m
25-story building
(100m)
VOID
Office space on each floor
(open to exterior and void sides)
Office depth: void depth:
10.8m 10.8m
2-dimensional analysis
(continuous in depth direction)
Exterior wind velocity: 3.0m/s
vertical ventilation width: 0.5m;
wind direction: 90˚ to window surface
Fig. 4. Oce building model.
was intended to show the use of mechanical cooling in as-
sisting conditions where natural ventilation is insucient.
2.2. Macro model 1
The assumed oce building model has a void (court-
yard) in the center as shown in Fig. 4, and is a mid- to
high-rise oce building with a cooling load in the interior
area throughout the year. The amount of natural ventilation
was analyzed by a ventilation network computation, taking
assumed values for the outdoor wind direction, wind velo-
city, wind pressure coecient, and opening ow coecient.
The amount of indoor natural ventilation targeted for study
was obtained through this analysis and used as the boundary
conditions for the micro model analysis.
156 H. Chang et al. / Building and Environment 39 (2004) 153 164
2.3. Micro model
Based on the amount of natural ventilation obtained, a
CFD analysis was conducted on the thermal and air quality
distribution in the oce. Based on these results, indoor
air quality was analyzed using a scale for ventilation
eciency (SVE) such as the spatial distribution of the age
of fresh outdoor air (SVE 3) and the contribution ratio of
the natural ventilation inlet (SVE 4) [7]. The thermal envi-
ronment and air quality of natural and mechanical hybrid
air conditioning based on a task-ambient air condition-
ing concept that diers from the indoor fully mixed air
conditioning method were investigated by these analyses.
CFD analyses were conducted by a steady-state compu-
tation, and time uctuations in natural ventilation were
not taken into consideration. Fluctuation components in
natural ventilation have a signicant inuence on dealing
with human comfort, aspects of which are currently being
studied [8].
2.4. Macro model 2
From the above results, the macro properties of heat and
air that transfer and disperse between the task, ambient, and
perimeter areas were analyzed and reanalyzed by annual
simulation based on a macro model. However, the results of
the macro model 2 annual simulation are not described in
this report; they will be reported subsequently.
3. Establishing the oce model
3.1. Establishing the model
The oce model established in this research is shown
in Fig. 5. It was assumed to be a 10.8 m deep continuous
oce, with a 1:8 m wide section (half of the 3:6 m space)
used for analysis. One side of one wall (the left wall sur-
face in Fig. 4) faced the exterior, with the other wall facing
the void (Fig. 3), both of which had an opening for natu-
ral ventilation above the window. Natural ventilation was
Exhaust
PC.
Pa
Human
model rtition
Wall
Ceiling
Chair
Symmetry
plane
:
Natural Ventilation
x
1
x
2
x
3
Unit
:
m
Window
glass
Lighting (0.2 × 1.2)
&
Exhaust opening (0.1 × 1.2
)
Floor supply opening
(0.2
×
0.1)
Natural Ventilation
Exhaust window opening
2.6
0
.
5
Supply
:
Mechanical Air-conditioning
Desk
Floor
Natural Ventilation
Suply window Opening
Natural ventilation
supply window opening
Natural ventilation
exhaust window opening
Mechanical air-conditioning
Natural ventilation
Fig. 5. Targeted oce (for micro analysis).
induced by negative pressure at the top of the void, allow-
ing outdoor air to ow in from the outside (the left wall
surface in Fig. 4) and pass through to the void. Air for
a hybrid air-conditioning system was supplied through air
diusers in the oor intended to provide task air condi-
tioning. Air was exhausted from the ceiling return. Also,
fresh outdoor air was introduced to the indoors only by nat-
ural ventilation, and was not introduced by air condition-
ing through air diusers. The oce was divided into 3:6m
spaces by I-form partitions perpendicular to the window
sides, and in which desks were placed. Each desk had a
surface generating heat from a PC, etc., as an indoor heat
source.
3.2. Dividing the targeted oce into domains
The oce was divided into three domains: task, ambient,
and perimeter zones, the thermal characteristics for each of
which were analyzed (see Fig. 6). The human habitation
area was the main target of control in this research, and
was named the task zone. With the task zone as a start-
ing point, the perimeter area was established as a space
up to 0:9 m from the glass surface with a solar radiation
load. The interior area was divided into task and ambient
zones; the task zone considered as a space for humans to
work while seated, with a domain extending 1:5 m above the
oor.
3.3. Establishing indoor heat loads
Heat loads in the analysis spaces were established as
shown in Table 1.
1. Lighting load: 400 W; from lighting sources on the
ceiling.
2. Solar radiation load: to be uniform on the inside surface of
the exterior window assuming the amount of south-facing
all-weather solar radiation in Tokyo at 14:00 in May
(200 W=m2) to be 0.5 = transmittance of the glass +
absorptivity (with the assumption that sunlight does not
strike the void side).
H. Chang et al. / Building and Environment 39 (2004) 153 164 157
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
EEEEE E
0 10 20 30 30 20 10 0
Exterior wind velocity
in upper air: 3m/s
Windward office
Indoor heat generated: 87W/m2
Boundary conditions for
windward opening
Opening vertical width: 0.5m
Wind pressure coefficient: 0.7
Flow rate coefficient: 0.3
25F
20F
15F
10F
1F
5F
18h-1
23h-1
26h-1
29h-1
32h-1
33h-1
8h-1
12h-1
19h-1
24h-1
29h-1
32h-1
Void top boundary conditions:
Opening size: 10.8m
Wind pressure coefficient: -0.4
Flow rate coefficient: 0.8
Void side opening boundary
conditions:
Vertical opening width: 0.5m
Flow rate coefficient: 0.1
(Obstacles such as hallways
were considered.)
Indoor air
flowing out
Leeward office
Outdoor air
flowing in Leeward opening boundary
conditions:
Vertical opening width: 0.5m
Wind pressure coefficient: -0.5
Flow rate coefficient: 0.3
Ventilation frequency (h-1)Ventilation frequency (h-1)
VOID
Fig. 6. Examples of ventilation circuit network.
Table 1
Cooling loads of domains for computationa
Heat generation Lighting Solar radiation PC Human model Floor surface Total
unit (4 units) (window surface) (4 units) (1 unit) (human)
Amount 400 225 800 55(SH) 220(SHb) 1700(SH)
of heat 28(LH) 111(LHc) 139(LH)
(W)
aSensible heat load per oor area (19:4m
2)is87:6[W=m2].
bSH: sensible heat.
cLH: latent heat.
3. Oce automation equipment load: 4 PC units per desk
(800 W total).
4. Humans: approximately 0.25 persons/m2occupancy
load; in order to evaluate the thermal environment with
respect to heat loss/gain by convection and the radiation
between humans and the surrounding environment, one
human model was placed in the space to be analyzed;
other human heat loads were uniformly positioned on
the oor (total of both sensible heat loads: 275 W); a
0:45 m ×0:33 m ×0:88 m block was used as a human
model for the convenience of the CFD analysis (see
Fig. 4).
In the CFD analysis, the distribution of the indoor cooling
load convection transfer was provided by a coupled simu-
lation of radiation/convection made using preparatory com-
putations. 1
1Boundary conditions on simulated heat ows were computed by giving
the amount of convection transmission heat obtained through preparatory
computations by a radiation and convection coupled analysis. Strictly
speaking, the distribution of the amount of convection transmission heat
diered in each case; however, identical distribution properties were
assumed because dierences in the indoor heat loads were not so great,
and the indoor environmental properties were not thought to vary so
signicantly either.
4. Computing the ventilation rate
Assuming a 25-story mid- to high-rise oce building, the
rate of ventilation from the wind pressure and buoyancy was
analyzed based on the ventilation network. The assumed
wind pressure coecient, ow coecient at the opening,
and sample results are shown in Fig. 6. The ventilation rate
was computed with the outdoor wind velocity assumed to
be 1.0–3:0m=s, the ventilation window vertical width to be
0.1–0:5 m and the wind direction to be varied at 45 –90to
the window surface. As a result, a ventilation rate of 15–30
times/h was obtained at mid-level in the oce building on
the leeward as well as windward sides due to negative pres-
sure (wind pressure coecient: 0:4) 2at the void top (ap-
proximately 30 times/h at lower level; 5–20 times/h at upper
level). Some reverse ventilation was obtained at the upper-
most level on the leeward side. Results varied depending
on dierences in the conditions noted above. In establish-
ing boundary conditions for analyzing the properties of the
indoor thermal environment distribution by micro-analysis
(CFD analysis), the use of air conditioning and a uniform
2The wind pressure coecient was assumed to be constant on the
building surface. Also, the outdoor wind velocity distribution was con-
sidered only in the vertical directions (1/4 power law).
158 H. Chang et al. / Building and Environment 39 (2004) 153 164
ventilation rate of 10 times/h for natural ventilation were
established, and further micro-analyses were conducted.
5. Micro-analysis
5.1. Method of analysis
(1) Indoor ow-eld simulation. Flow-elds were
simulated by three-dimensional CFD analysis based on
the standard kmodel [9]. The continuity equation
and the fundamental equations governing the motion of
steady, incompressible, and turbulent ows are the
averaged Navier-Stocks equations that can be expressed as
follows:
@Ui
@xi
=0;
Ui
@Ui
@xi
=1
@P
@xi
+@
@xi@Ui
@xj
+@Uj
@xiu
iu
j:(1)
The kmodel relates the turbulent kinetic energy kand the
dissipation rate of turbulence by
vt=C
k2
;
u
iu
j=vt@Ui
@xj
+@Uj
@xi+2
3kij;(2)
where ij is the Kronecker symbol.
Kand can be solved by the following transport equa-
tions:
Uj
@k
@xj
=@
@xjv+vt
k@k
@xj+Pk;
Table 2
Boundary and computation conditions
Air diuser Uin is the velocity at the natural ventilation inow and air conditioning air diuser
kin =3=2(Uin ×0:05)2
in =C×k3=2
in =lin
lin =1=7 of the air diuser width
Tin :Tsupply
AHin :AH
supply
Air return Velocity is free outow (based on the law of conservations of mass)
kout,out ,T, AH=Free slip
Velocity: wall surface is based on generalised logarithmic law; symmetry surfaces are free slip.
Wall surface Heat: the amount of convection heat transfer is xed
Absolute temperature,
human model, oor surface: the amount of heat generated is constant
Other walls: humidity gradient =0
Analysis meshes 88 (X1)×17 (X2)×15 (X3)=22;440
Note:U: Air current velocity (m=s); k: energy of turbulence (m2=s2); : dissipation rate of k(m2=s3). lin : air diuser turbulence scale (m); T:
temperature (C); AH: absolute humidity (kg=kg).
Uj
@
@xj
=@
@xjv+vt
@
@xj+C1Pk
kC2
2
k;
Pk=vt
@Ui
@xj@Ui
@xj
+@Uj
@xi:(3)
The model constants are as follows:
C=0:09;C
1=1:44;C
2=1:92;
k=1:0;and =1:3:
A CFD simulation based on the standard kmodel was
validated by comparing the results of the room airow sim-
ulation with the experimental results [10,11]. Detailed CFD
boundary conditions are shown in Table 2.
(2) Air-conditioning system control. The variable air
volume (VAV) method was assumed for controlling
oor-diused air conditioning in the task zone. The aver-
age temperature in the task zone for each CFD step was
obtained, and the dierence from the air conditioning target
(average task zone temperature: 26C) was quantitatively
computed. The air conditioning air volume was gradually
changed according to the dierence, which was computed
again by CFD. The volume of air conditioning air and
indoor input heat from air conditioning when the air con-
ditioning target was achieved were analyzed through these
convergence computations.
5.2. Analysis cases
Analysis cases are shown in Tables 3and 4. In the oce
model where the average space temperature in the task zone
is controlled by air conditioning at the target temperature
(26C), the indoor thermal and air quality environment and
the air conditioning input heat volume were analyzed for the
H. Chang et al. / Building and Environment 39 (2004) 153 164 159
Table 3
Analysis conditions and results (total of indoor heat generated targeted for computation: 1700 W; oor area = 19:4m
2)
Air conditioning system Natural ventilation Temperature
when
Cooling Imposed Diused Air Temperature/ Amount Imposed Inow Air Temperature/ Air Ar of instantaneous
load load air volume humidity of fresh load wind ow humidity inlet natural and uniform
Case (W)() velocity ()(
C)/(%) outdoor () velocity rate (C)/(%) width ventilation dissipation
(W)(
)(m
3=h) air (W) (m/s) (m3=h) (m) air inow is assumed
(m/s) introduced ()(
)
(m3=h) (C)
A 0 0 0 1700 18.8/69 4:83 28.6
B 146 0.07 25.2 1554 19.5/66 4:36 28.8
C 366 0.31 111.6 1334 0.16 10 21.0/60 3:36 28.7
D 627 0.49 176.4 1073 22.5/54 2:35 28.9
E 843 0.66 237.6 19.0 0 857 24.0/50 0.5 1:34 29.1
F 1700 882 0.64 230.4 /80 818 0.08 5 13:42 30.3
G 563 0.39 140.4 1137 0.12 7.5 5:97 30.0
H 129 0.09 32.4 1571 0.20 12.5 21.0 2:15 28.4
I 0 0 0 1700 0.23 15 /60 1:49 27.6
J 491 0.46 165.6 1209 0.39 10 0.2 0:21 27.9
K 545 0.55 198.0 1155 0.78 10 0.1 0:03 27.5
Note:(
) was obtained from results of CFD analysis.
Table 4
Analysis cases when the temperature of natural ventilation air ow varied
Cases C-1 C-2 C-3 C-4 C-5 C-6 C-7
Inow outdoor relative humidity
(%) 30405060708090
Note: Conditions other than inow outdoor relative humidity in Table 4are the same as Case C in Table 3.
following cases:
1. Inow air temperature varied assuming that the natural
ventilation inow rate (10 times/h) and absolute humidity
were xed (Cases A–E).
2. Air inow rate varied assuming the natural ventilation
temperature remained constant (21C) (Cases F–I).
3. Size of the natural ventilation inlet varied assuming that
the natural ventilation temperature and ow rate were
xed (Cases J–K).
4. Inow humidity varied assuming that the inow
temperature (21C) and natural ventilation inow
rate (10 times/h) were xed (Table 2, Cases C-1
to C-7). Case C is the reference case when the
air inow rate, size of inlet, and inow humidity
varied.
5.3. Analysis results
(1) When the inow temperature varied (Cases A–E).
Only results for Cases A, C, and E are shown.
(a) Air current distribution. The air current distribution
when the inow temperature varied is shown in Fig. 7. The
ow patterns of the natural ventilation inow jets indicated a
decrease in the Ar number 3with an increase in the outdoor
temperature, and the jets penetrated deeper into the interior.
Because the dierence between the outdoor and indoor tem-
peratures was great in Case A (Ar number = 4:83), the
inow air fell along the walls on the window side due to the
strong negative buoyancy, and owed towards the inside at
a slow speed. Air that reached the wall surface on the other
side rose along the wall surface, and was discharged from
the natural ventilation outlet. Because the target air condi-
tioning temperature (26C) was achieved only by natural
ventilation in Case A, the wind velocity at the air condi-
tioning air diusers became zero. The natural ventilation in-
ow jets penetrated deeper into the interior and mixed bet-
ter with the indoor air in Case C (Ar = 3:36) and Case E
(Ar = 1:34) than in Case A.
(b) Temperature distribution. The temperature distribu-
tion when the inow temperature varied is shown in Fig. 8.
Because inow air at a relatively low temperature (18:8C)
owed into the interior without mixing very well with the
indoor air in Case A, temperature stratications were formed
3Ar = g L=U 2; where g: gravitational acceleration [m=s2]; : ex-
pansion coecient [C1]; : temperature dierence between the natural
ventilation inlet and the average task zone [C]; L: natural ventilation
inlet height [m]; U: natural ventilation inow velocity [m/s].
160 H. Chang et al. / Building and Environment 39 (2004) 153 164
(b) Case C (Ar number of inflow outdoor air = -3.36; T = 5.0°C)
Ceiling return
21.0°C
24.0°C
(c) Case E (Ar number of inflow outdoor air = -1.34; T = 2.0°C)
1 m/s
Natural ventilation inlet
0.16m/s, 18.8°C
Perimeter zone
Human model Ambient zone
Tas k zone
(a) Case A (Ar number of inflow outdoor air = -4.83; T = 7.2°C)
Natural venti-
lation outlet
(T: (Average task zone temperature (26°C)) - (Outdoor temperature))
Fig. 7. Air current distribution (center sections including human models;
air diusers installed in the oor).
in the general space. Also, the air conditioning ow rate
(temperature at air diuser: 19C) increased with an increase
in the natural ventilation inow temperature to maintain the
average temperature (26C) in the task zone, and the tem-
perature gradient near the oor became great.
(2) When the inow rate varied (Cases F–I)
(a) Air current distribution. Figures for air current dis-
tribution when the natural ventilation inow rate varied are
omitted because of their similarity with Fig. 6. The ow pat-
terns of the natural ventilation inow jets varied intricately
with the increase in the outdoor air inow rate. Natural ven-
tilation vents were continuous in a slot diuser congura-
tion, and the jets exhibited a two-dimensional aspect when
the natural ventilation ow rate was high; however, they did
not necessarily become two-dimensional when the ow rate
was low, and exhibited a three-dimensional aspect when in-
uenced by air currents from the indoor air conditioning air
diusers. The natural ventilation jets varied in a complex re-
lationship to many factors, such as negative buoyancy acting
on the surface of the ceiling, the walls and jets themselves,
the fact that the air conditioning diuser jets decrease the
air ow rate in inverse proportion to an increase in the nat-
ural ventilation ow rate, and the indoor circulating ow
properties.
(b) Temperature distribution. Figures for the temper-
ature distribution when the natural ventilation inow rate
varied are excluded because of their similarity with Fig. 7.
(a) Case A (a : 26.2°C, b : 26.0°C)
26
26
27
25
27
28
Natural ventilation inlet
0.16m/s, 18.8°C
Perimeter zone Human model Ambient zone
Task zone
Natural venti-
lation outlet
a: Average indoor temperature
b: Average task zone temperature
(b) Case C (a : 26.6°C, b : 26.0°C)
Ceiling return
21.0°C
26
26 25
27
27
26
27 25
24.0°C
(c) Case E (a : 26.9°C, b : 26.0°C)
26
26
26
27
25
24
27
27
28
23
27
Fig. 8. Temperature distribution (center sections including human models;
air diusers installed in the oor).
Relatively stable temperature stratications were formed in
task-ambient zones that the natural ventilation jets did not
reach. The high/low temperature gradient became smaller
with the increase in the natural ventilation air inow rate,
reducing the relative high temperature zone near the ceiling.
This was thought to be because a large quantity of natural
ventilation air, hotter than the current from the air condi-
tioning air diusers, owed into the task zone and mixed
well with the surrounding air.
(3) When the inlet size varied
(a) Air current distribution. Figures for air current dis-
tribution when the air inlet size varied are omitted because
of their similarity with Fig. 6. As the inow velocity of
the natural ventilation air became greater with a decrease in
the height of the natural ventilation inlet (with temperature
and ow rate constant), the natural ventilation inow jets
penetrated deeper into the interior. The natural ventilation
inow jets owed into the interior along the ceiling sur-
face, and fell where the human model was located in Case
J (Opening height: 0:2 m; Ar number at natural ventilation
inlet: 0:21). The natural ventilation inow jets passed the
human model in Case K (Opening height: 0:1 m; Ar num-
ber: 0:03). The velocity of the natural ventilation inow
in Cases J and K exceeded 0:5m=s immediately after the
natural ventilation inlet; however, it reduced to a low speed
of 0:25 m=s or slower near the human model in each case.
H. Chang et al. / Building and Environment 39 (2004) 153 164 161
Fig. 9. Relative humidity distribution (center sections including human
models; air diusers installed in the oor).
(b) Temperature distribution. Figures for the tempera-
ture distribution when the air inlet size varied are excluded
because of their similarity with Fig. 7. No outstanding tem-
perature stratication was observed in the general space in
any case. However, as the inow velocity of the natural ven-
tilation air became greater with a decrease in the height of
the natural ventilation inlet and the natural ventilation inow
air penetrated deeper into the interior, mixing well with the
indoor air, the temperature gradient became small near the
oor on the right side of the room across from the air inlet.
Also, the isotherms became parallel and indicated a slight
tendency to form stratications on the left side of the room.
(4) When the inow humidity varied. Only the results for
Cases C-1, C-3, C-5, and C-7 are shown.
(a) Relative humidity distribution. The indoor relative
humidity distribution when the natural ventilation humidity
varied is shown in Fig 9. As the ow rate of the natural ven-
tilation inow air was higher than that at the air conditioning
Fig. 10. PMV distribution (center sections including human models; air
diusers installed in the oor).
air diusers, the indoor relative humidity was inuenced by
the outdoor temperature. Also, the indoor distribution was
signicantly inuenced by the temperature distribution ((b)
in Fig. 7). Cases with the natural ventilation inow at a 50%
or lower relative humidity (Cases C-1, C-2, and C-3), gen-
erally indicated a humidity of 50% or lower. Cases with the
inow at a 70% or higher relative humidity (Cases C-5, C-6,
and C-7), generally exceeded a relative humidity of 50%.
(b) PMV distribution. The PMV distribution 4when the
inow outdoor humidity varied is shown in Fig. 10. The
indoor PMV distribution properties were signicantly inu-
enced by the temperature distribution ((b) in Fig. 7). The
average PMV values in the task zone were 1.4–1.7 in all
analysis cases, which felt warm. Also, the PPD then was
46 62%. This is thought to have been primarily due to great
4The fundamental heat resistance value of clothing was assumed to be
0.6 (clo), and the amount of metabolism to be 1.2 (met). The wall surface
temperature was obtained from the temperature near the wall surface and
the amount of convection heat transfer, assuming the convection heat
transfer to be 4 (W=m2C), from which the average radiation temperature
was computed.
162 H. Chang et al. / Building and Environment 39 (2004) 153 164
1
0.8
0.8
1
(a) Case A (τn =360sec)
Natural ventilation inlet
0.16m/s, 18.8°C
Perimeter zone
Human model Ambient zone
Tas k zone
Natural venti-
lation outlet
Ceiling return
(b) Case C (τn =360sec)
21.0°C
1
0.8
0.8
0.6
0.4
0.2
(c) Case E (τn =360sec)
1
1
1.2
1
0.8
0.6
0.6
0.8
0.4
24.0°C
Fig. 11. Non-dimensional age of air distribution (center sections including
human models; air diusers installed in the oor).
interior heat generation and a high average radiation tem-
perature. The PMV became greater with an increase in the
natural ventilation inow humidity; however, while the in-
owing outdoor air relative humidity varied from 30% (Case
A) to 90% (Case G), the average PMV value was more than
0.3, from 1.4–1.7, which was conrmed comparatively in-
sensitive to the relative humidity.
(5) Age of air and contribution ratio
(a) Age of air (SVE3). The age of the natural ventila-
tion inow was computed based on the ow-eld analysis
results. For cases in which the inow temperature varied,
only the results for Cases A, C, and E are shown in Fig. 11.
The computation results were rendered non-dimensional by
the ventilation time n(reciprocal of the ventilation rate).
The indoor air age distribution responded well to ow elds.
As the inow air owed into the task zone without mixing
well with the indoor air in Case A, the age of air in the task
zone became relatively low. As the inow air mixed well
with the indoor air near the perimeter zone and owed into
the interior in Case C, the farther it owed into the interior,
the higher the age of the air became. As the inowing out-
door air owed into the interior in jets, mixing well with the
indoor air and owing deeper into the interior in Case E, a
long and narrow domain of air aged 1 or lower extended hor-
izontally to the right on the right side of the human model.
(b) Contribution ratio of the natural ventilation inlet
(SVE4). For cases in which the inow temperature varied,
only the results for Cases C–E are shown in Fig. 12. All do-
mains had 1.0 in Case A, where only natural ventilation was
0.9
>0.9
0.9 0.80.7
(a) Case C (Ar number of inflow outdoor air: -3.36)
Natural ventilation inlet
0.16m/s, 21.0°C
Perimeter zone
Ambient zone
Tas k zone
Natural venti-
lation outlet
Ceiling return
(b) Case D (Ar number of inflow outdoor air: -2.35)
22.5°C
0.8
0.9
0.8 0.8 0.7
0.7 0.6
>0.8
0.7
0.8 0.7
0.7
0.6 0.6
(c) Case E (Ar number of inflow outdoor air: -1.34)
24.0°C
Fig. 12. Range of natural ventilation inuences (vertical sections including
air conditioning air diusers).
used for the conditioning air. As the air conditioning ow
rate increased with the rise in the inow temperature, the
contribution ratio of the natural ventilation inlet decreased.
The contribution ratio of the natural ventilation inlet in the
task zone became approximately 0.7 in Case E, where the
air conditioning ow rate was the greatest.
(6) Amount of air conditioning input heat. The amounts
of air conditioning input heat when the average task zone
temperature was controlled at a constant 26C were obtained
as a result of micro-analysis.
(a) When the inow temperature varied. The amounts
of air conditioning input heat when the inow temperature
varied are shown in Fig. 13. The amount of air condition-
ing input heat is proportional to the natural ventilation in-
ow temperature. Each case indicated a value approximately
460 W lower than the amount of air conditioning input heat
required when an instantaneous and uniform dissipation was
assumed. This is thought to be because the natural ventila-
tion inow at a relatively low temperature did not mix well
with the indoor air, which contributed to the average tem-
perature in the task zone becoming lower than that indoors.
When the natural ventilation inow temperature was 18:8C
(Case A), the target air conditioning temperature in the task
zone was achieved only by natural ventilation.
(b) When the inow rate varied. The amounts of air
conditioning input heat when the inow rate varied are
shown in Fig. 14. The amount of air conditioning input heat
H. Chang et al. / Building and Environment 39 (2004) 153 164 163
0
200
400
600
800
1000
1200
1400
1600
17 19 21 23 25
Case A
Case A
Case B
Case C
Case D
Case E
Case B
Case C Case D
Case E
Instantaneous
and uniform dis-
sipation assumed
Task zone constant
temperature contro-
lled air conditioning
Natural ventilation inflow temperature [°C]
Amount of air conditioning
input heat [W]
Fig. 13. Natural ventilation inow temperature and amount of air condi-
tioning input heat.
Natural ventilation inflow rate (h-1)
Case F
Case G
Case C
Case H Case I
Case F
Case
Case G
Case C
Case D
Case D
Case H
Case I
1400
1200
1000
800
600
400
200
00 5 10 15 20
Amount of air conditioning
input heat [W]
Instantaneous and
uniform dissipat-
ion assumed
Task zone constant
temperature contro-
lled air conditioning
Fig. 14. Natural ventilation inow rate and amount of air conditioning
input heat.
decreased with an increase in the natural ventilation inow
rate. It indicated a value approximately 450 W lower than
the amount of air conditioning input heat when an instanta-
neous and uniform dissipation was assumed. This is thought
to be because the natural ventilation inow at temperatures
relatively lower than that indoors owed into and cooled the
task zone without mixing well with the indoor air.
(c) When the size of the inlet varied. The amounts of air
conditioning input heat when the size of the inlet varied are
shown in Fig. 15. The amount of air conditioning input heat
was inversely proportional to the height of the natural venti-
lation inlet. This is thought to be because the natural ventila-
tion inow velocity decreased with an increase in the height
of the natural ventilation inlet, causing air to enter the task
zone without mixing well with the indoor air. The amount of
air conditioning input heat in Case K became 290 W lower
than when complete indoor mixing was assumed (1/3 of the
input heat of 840 W assuming an instantaneous and uniform
dissipation; 1/6 of the total cooling load of 1700 W). Case
Amount of air conditioning
input heat [W]
Width of natural ventilation inlet [m]
Case C
Case JCase K Case C
Case J
Case K
1000
800
600
400
200
00 0.1 0.2 0.3 0.4 0.5 0.6
Instantaneous and uniform
dissipation assumed
Task zone constant
temperature controlled
air conditioning
Fig. 15. Width of natural ventilation inlet and amount of air conditioning
input heat.
30
Case C-1
Case C-2
Case C-3
Case C-4
Case C-5
Case C-6
Case C-7
Case C-2
Case C-3
Case C-1
Case C-4
Case C-5
Case C-6
Case C-7
40 50 60 70 80 90
0
500
1500
2000
2500
1000
Mechanical air conditioning only
Hybrid air conditioning
Outdoor inflow relative humidity [%]
Amount of air conditioning
input heat [W]
Fig. 16. Relationship of outdoor inow humidity and amount of air
conditioning input heat.
C indicated a value 470 W lower (1/2 of the input heat as-
suming an instantaneous and uniform dissipation; 1/4 of the
total cooling load). The height of the natural ventilation in-
let in Case C (0:5 m wide) was 5 times that of Case K, and
the amount of air conditioning input heat was as low at 2/3
that of Case K.
(d) When the inow humidity varied. The amounts of air
conditioning input heat with only mechanical air condition-
ing 5and with hybrid air conditioning 6when the natural
ventilation inow humidity varied are shown in Fig. 16. The
dehumidifying load was imposed in both cases when the in-
ow outdoor relative humidity exceeded 70%, and increased
5The amount of air conditioning input heat was assumed to be fully
mixed, and was the sum of the outdoor latent heat loads when the indoor
cooling load (1700 W + 139 W: see Table 1) and the amount of outdoor
air introduced per person in the room was 30 m3=h.
6The amount of air conditioning input heat is the sum of the amount
of sensible heat removed by the air conditioning and the amount of latent
heat obtained from the dierence in the enthalpy of the water vapour at
the air conditioning inlets and diusers.
164 H. Chang et al. / Building and Environment 39 (2004) 153 164
20% and 40%, respectively in Cases C-6 and C-7 with hy-
brid air conditioning compared to Cases C-1 to C-5. How-
ever, these were considerably small compared to the cases
with only mechanical air conditioning. In other words, in
these cases where the outdoor temperature was 21C, using
the hybrid air conditioning conserved more energy regard-
less of the outdoor humidity except for when the ventilation
openings could not be opened, such as when it was raining.
6. Summary
The eects of outdoor air conditions on hybrid air condi-
tioning utilizing natural ventilation in oce buildings were
investigated in this study. The results of this study were
derived from CFD simulation with simple geometry, there-
fore dierent results may be reached when the geometrical
layout is asymmetrical, or when the desk arrangements are
changed. The following conclusions can be drawn:
1. The higher the outdoor temperature (closer to the indoor
temperature), the lower the absolute value of the Ar num-
ber of the outdoor inow became; the natural ventilation
inow mixed better with the surrounding air, reaching
deeper into the interior, while the temperature gradient
near the oor increased.
2. The ow patterns of the natural ventilation jets varied
intricately with an increase in the inow rate, and the
high/low temperature gradient in the task-ambient zones
decreased.
3. The absolute value of the Ar number decreased with a de-
crease in the size of the natural ventilation inlet, and the
natural ventilation inow jets penetrated deep into the in-
terior while the high/low temperature gradient decreased
on the right side of the room across from the inlet.
4. Because the inow rate of the natural ventilation was
higher than that of the air conditioning air diusers, the
indoor relative humidity was inuenced by the outdoor
humidity.
5. The distribution properties of the indoor temperature and
PMV were signicantly inuenced by the temperature.
6. The indoor air age distribution properties responded well
to ow elds.
7. The contribution ratio of the natural ventilation inlet,
when the natural ventilation inow temperature varied,
decreased with the rise in the inow temperature.
8. The amount of air conditioning input heat increased with
a rise in the natural ventilation inow temperature, with
a decrease in the ow rate, and with a decrease in the
height of the natural ventilation inlet.
References
[1] Hunt GR, Linden PF. The uid mechanics of natural
ventilation-displacement ventilation by buoyancy-driven ows assisted
by wind. Building and Environment 1999;34:707–20.
[2] Lu WZ, Lo SM, Fang Z, Yuen KK. A preliminary investigation of
airow eld in designated refuge oor. Building and Environment
2001;36:219–30.
[3] Li Y, Delsante A. Natural ventilation induced by combined wind and
thermal forces. Building and Environment 2001;36:59–71.
[4] Chen ZD, Li Y. Buoyancy-driven displacement natural ventilation
in a single-zone building with three-level openings. Building and
Environment 2002;37:295–303.
[5] Eftekhari MM, Marjanovic LD, Pinnock DJ. Air ow distribution
in and around a single-sided naturally ventilated room. Building and
Environment 2003;38:389–97.
[6] Chikamoto T, Kato S, Ikaga T. Hybrid air-conditioning system in
Liberty Tower at Meiji University. Hybvent Forum 1999;99:123–7.
[7] Kato S, Murakami S, Kobayashi H. New scale for evaluating
ventilation eciency as aected by supply and exhaust openings based
on spatial distribution of contaminants. ISRACVE (Tokyo) 1992;
321–32.
[8] Song D, Kato S, Murakami S, Shiraishi Y, Chikamoto T, Nakano A.
Study on adaptive control systems under hot and humid climates—
Part 3: continuous measurement of thermal environment around a
moving person and his thermal adaptation. Summaries of Technical
Papers of the Annual Meeting of the Architectural Institute of Japan
2001;35960 [in Japanese].
[9] Launder BE, Spalding DB. The numerical computation of turbulent
ows. Computer Methods in Applied Mechanics and Engineering
1974;3:269–89.
... Few works have explored the envelope design optimization of MMV buildings, as it can be seen in the comprehensive literature review conducted by Salcido et al. (2016), which evaluated the potential of MMV systems in office buildings. For instance, the main methodologies adopted in previous studies consisted on either case studies, performed through field monitoring and questionnaires (Deuble and de Dear, 2012;Healey, 2014;Luo et al., 2015;Rowe and Dinh, 2001;Aggerholm, 2003;Blondeau et al., 1997;Brohus et al., 2003;Principi et al., 2003;Wei et al., 2013) and/or modelling, based on simplified representations of reality by using software tools such as EnergyPlus (Wang and Greenberg, 2015;Roetzel et al., 2014;Wang and Chen, 2013;De Wilde and Tian, 2010b;Ben-David and Waring, 2016;Ezzeldin and Rees, 2013;Olsen and Chen, 2003;Pfafferott et al., 2005;Wang et al., 2017), TRNSYS (Blondeau et al., 1997;Engelmann et al., 2014) or computer fluid dynamics (Malkawi et al., 2016;Chang et al., 2004;Gritzki et al., 2003). The areas of uncertainty and future research subjects reported in previous studies include, mainly, the applicability of thermal comfort models (static or adaptive) in MMV buildings (Deuble and de Dear, 2012;Ezzeldin and Rees, 2013), occupant behaviour and occupants' thermal response (Luo et al., 2015;Wang and Chen, 2013), optimal control strategies and control algorithms (Hu and Karava, 2014;Ezzeldin and Rees, 2013), the lack of specific standards or guidelines (Deuble and de Dear, 2012;Emmerich, 2006) and the lack of field studies and/or façade design strategies in accordance to local climates (Deuble and de Dear, 2012;Wang and Greenberg, 2015;Roetzel et al., 2014), which is the focus of the present study. ...
... Pesquisa imobi, 2016), based on the following criteria: cellular office buildings operating through a concurrent mixed-mode ventilation system, built over a twenty-year period (between 1995 and 2016) (Neves et al., 2017). Then, we selected 30 scientific publications with research topics related to thermal and energy performance analysis of mixed-mode office buildings (Deuble and de Dear, 2012;Healey, 2014;Luo et al., 2015;Rowe and Dinh, 2001;Hu and Karava, 2014;May-Ostendorp et al., 2011;Malkawi et al., 2016;Wang and Greenberg, 2015;Roetzel et al., 2014;Wang and Chen, 2013 Tian, 2010b;Aggerholm, 2003;Artmann et al., 2008;Bajenaru et al., 2016;Ben-David and Waring, 2016;Blondeau et al., 1997;Brohus et al., 2003;Chang et al., 2004;Corgnati and Kindinis, 2007;Emmerich, 2006;Engelmann et al., 2014;Ezzeldin and Rees, 2013;Gritzki et al., 2003;Olsen and Chen, 2003;Principi et al., 2003;Pfafferott et al., 2005;Rupp and Ghisi, 2013;Wang et al., 2017;Wei et al., 2013;Zhou et al., 2011), from peer reviewed literature search engines, published within the same period from the buildings sample. Envelope design parameters used either in the real buildings sample and/or the referenced literature were then compared, enabling the selection of architectural design variables that could affect the energy performance of MMV office buildings. ...
... The first research step consisted in gathering envelope and natural ventilation design solutions of 153 mixed-mode office buildings from the city of Sao Paulo, Brazil, built over a twenty-year period, and compare it with the technical literature, published within the same period, in order to understand how far research has come in addressing this topic. The selected papers (Deuble and de Dear, 2012;Healey, 2014;Luo et al., 2015;Rowe and Dinh, 2001;Hu and Karava, 2014;May-Ostendorp et al., 2011;Malkawi et al., 2016;Wang and Greenberg, 2015;Roetzel et al., 2014;Wang and Chen, 2013;De Wilde and Tian, 2010b;Aggerholm, 2003;Artmann et al., 2008;Bajenaru et al., 2016;Ben-David and Waring, 2016;Blondeau et al., 1997;Brohus et al., 2003;Chang et al., 2004;Corgnati and Kindinis, 2007;Emmerich, 2006;Engelmann et al., 2014;Ezzeldin and Rees, 2013;Gritzki et al., 2003;Olsen and Chen, 2003;Principi et al., 2003;Pfafferott et al., 2005;Rupp and Ghisi, 2013;Wang et al., 2017;Wei et al., 2013;Zhou et al., 2011) analysed thermal comfort, energy efficiency and/or air quality of mixed-mode office buildings located worldwide (Europe, China, USA, Canada, Australia, Brazil, India, Japan, South Korea, Egypt, and Saudi Arabia), through building energy simulation, field monitoring and/or survey. Table 7 presents a summary of the gathered information. ...
Article
Studies have demonstrated the energy savings potential of mixed-mode ventilated office buildings. Yet, it is important to widen the knowledge about how those buildings have been designed and built in practice, and which design parameters have greater influence on its energy performance. The aim of this paper was to evaluate how building envelope design parameters influence the energy performance of cellular mixed-mode office buildings, in order to identify key design variables. The analysis presents a comparison among literature research studies and typical construction practices from a sample of buildings located in the city of Sao Paulo, Brazil. According to a base case model, established based on the real buildings sample, three sensitivity analysis techniques were performed to obtain relative parameter sensitivity to thermal loads: OFAT, Morris and Monte Carlo. Results showed the importance of the window opening effective area and the reduced impact of the window-to-wall ratio on the energy performance of mixed-mode office buildings. By applying a multivariate regression model, it showed significant in predicting 78.1% of the variance in annual thermal loads. The accurate determination of annual thermal loads into mixed-mode office buildings can be used to optimize the envelope characteristics based on a combination of input data and the building geometry. Findings from this study could also be applied to other locations, provided that similar climatic environment and urban context are taken into account.
... They also conducted an analysis on the influence of ventilation rates and filter efficiency on the indoor PM 2.5 and ozone concentrations in office buildings. Despite the diverse range of studies on pollutant control via mechanical ventilation, most have focused on ventilation devices in office spaces [25,26], while studies analyzing the effects of ventilation systems in actual residential houses are limited. In the case of offices, the frequent influx and outflow of people through entry points make it challenging to predict changes over time. ...
Article
Full-text available
The mechanical ventilation systems used in houses are designed to reduce carbon dioxide emissions while minimizing the energy loss resulting from ventilation. However, the increase in indoor fine particulate (PM2.5) concentration because of external PM2.5 influx through the ventilation system poses a problem. Here, we analyzed the changes in indoor PM2.5 concentration, distinguishing between cases of high and low outdoor PM2.5 concentrations and considering the efficiency of the filters used in residential mechanical ventilation systems. When using filters with the minimum efficiency reporting value (MERV) of 10 in the ventilation system, the outdoor PM2.5 concentration was 5 μg/m³; compared to the initial concentration, the indoor PM2.5 concentration after 60 min decreased to 73%. When the outdoor PM2.5 concentration was 30–40 μg/m³, the indoor PM2.5 concentration reached 91%. However, when MERV 13 filters were used, the indoor PM2.5 concentration consistently dropped to 73–76%, regardless of the outdoor PM2.5 concentration. Furthermore, by comparing the established equation with the mass balance model, the error was confirmed to be within 5%, indicating a good fit. This allows for the prediction of indoor PM2.5 under various conditions when using mechanical ventilation systems, enabling the formulation of strategies for maintaining indoor PM2.5, as recommended by the World Health Organization.
... The authors have also conducted investigation on various performances of the TAC for developing the new systems and effective control methods, e.g. TAC system which provide 100 % fresh and conditioned air to the individual space from the task unit on the desk in naturally ventilated room (hybrid ventilation) with low energy consumption and high productivity (Chikamoto 2001 [1], Chang et al. 2004 []), TAC system which is a desktop packaged air conditioning unit and supplies both direct air flow against human and wide covered air flow around human [3]), TAC system which uses multi-flow ceiling cassette type packaged air-conditioner which is widely used in office and is not likely to be detached at the layout change, though it is likely detached at the layout change when applying it to furniture (Ishiguro et al. 2011 [4]) and TAC system on the ceiling which can supply directional or diffusible airflow selected by each office worker using his or her PC (Lee et al. 2016 [5]). * Corresponding author: tomoyuki@se.ritsumei.ac.jp ...
Article
Full-text available
A personal air conditioning system using vortex rings, which are characterized by their linearity and low diffusivity, is developed in this study. The authors have clarified the characteristics of the vortex ring airflow by LES (unsteady CFD) and full‐scale experiments. However, the airflow type and worker's comfort using vortex rings as an air conditioning system has not been clarified yet. As a result of the subject experiments, it became clear that air conditioning with vortex rings cooled the subjects better than conventional air conditioning and improved their sense of comfort with respect to the airflow. In addition, it was found that airflow to the neck was more effective since the subjects were less likely to feel the airflow at the top of the head due to the resistance of the hair on the head. The effectiveness of the vortex ring as a personal air conditioning system was clarified, enabling relaxation of the room temperature setting. The comfortability of the airflow sensation provided by the vortex ring was also examined when further airflow was given.
... IAQ problems are caused by indoor air pollutant that comes from the outdoors, mechanical ventilation and air-conditioning (MVAC), building equipment as well as human activities [6]. The most common indoor air pollutant is Carbon dioxide (CO2) as it is being emitted by human beings where the level of CO2 in an area is dependent to the number of people around and the degree of metabolic activity which is carried out within the area. ...
Article
Full-text available
Indoor Air Quality (IAQ) is an important element for a healthy working environment. Working in poor IAQ can lead to sick building syndrome (SBS) with symptoms and troublesome to concentrate in delivering the task. In this study, a preliminary IAQ investigation was carried out at a teaching foundry facility of a higher learning institution in Malaysia. The foundry processes are known to discharge pollutants and gasses. Therefore, this assessment was used to investigate the existence of harmful gasses including Carbon Dioxide (CO 2 ), Carbon Monoxide (CO), particulate matter (PM), and Volatile Organic Compound (VOC) throughout the complete foundry process cycle. An advanced environmental monitor kit was used to monitor the air quality at three different locations within the foundry space to get a good distribution of data. The results reveal that only CO 2 and PM10 traces were detected with the reading is still within the allowable range based on guidelines from the Department of Occupational Safety and Health (DOSH), Malaysia. As for thermal comfort result, the Temperature and Relative Humidity (RH) was found to exceeds the benchmark value. Therefore, a more comprehensive and detail thermal comfort study should be conducted to validate the current finding and an appropriate mitigation strategy must be put in place to ensure the thermal comfort of the occupants during the teaching and learning process in the foundry can be improved.
... Figure 6 presents the geometry and Table 1 presents the model's input fixed parameters and values. Ten variable parameters were chosen based on their influence over the annual energy demand of a mixed-mode office building (Bajenaru et al, 2016;Engelmann et al, 2014;Corgnati and Kindinis, 2007;Chang et al, 2004). Ranges of variation were set based on feasible values from the building industry. ...
Conference Paper
Full-text available
Building Energy Simulation (BES) tools have an important role in early design stages, since they include energy performance parameters in the decision-making process. However, processing a large number of simulations can be unfeasible, costly and time-consuming, especially when architectural conceptual design phase is considered. Therefore, the development of computer codes can facilitate this process. The aim of this work was to develop a code in Python language, which could perform parametric analyses of a mixed-mode office building in EnergyPlus, considering random variables related to its design process. Ten parameters were chosen, including materials properties, envelope dimensions and geometry related variables. Ranges of variation for each variable were settled according to practical restrictions resultant from the building industry. Results showed that the code operates properly and can easily be used to create a set of design scenarios, proving to be a useful tool to architectural designers. A specific case study is presented, in order to illustrate the application of the method and its potential benefits in an integrated design process.
... For these reasons, it is the most widely used ventilation method at present. Many studies have been conducted on hybrid ventilation performance in office [13][14][15][16] and school building [17][18][19] settings. Turner [20] experimental proved that hybrid ventilation systems can effectively improve thermal environments. ...
Article
Full-text available
An industrial building may have several heat sources which together create a high-temperature working environment that puts the health of workers at risk. Ventilation is an effective way to remove heat, but improperly designed systems may fail to create a healthy thermal environment. The performance of buoyancy-driven hybrid ventilation in a multi-heat-source industrial plant was investigated in this study. The effects of the height of the inlet above the floor and exhaust velocity on the hybrid ventilation performance were studied; properly increasing the above-floor inlet height appears to improve the thermal environment while excessive mechanical exhaust velocity leads to increased energy consumption with a negative impact on ventilation efficiency. The optimum parameters of the improved ventilation system were determined and compared against existing ventilation systems. In summer, the improved ventilation system shows an average temperature of 34.61 °C, which is 3.40 °C lower than the existing system. The allowed exposure time (AET) is 52 minutes, which is 18 minutes longer than the existing system. In winter, the improved ventilation system shows an average temperature of 18.68 °C, which meets the design requirements for industrial buildings. The improved ventilation system can provide thermally comfortable conditions in both summer and winter.
... It was found that NV openings under the ceiling can supply higher fresh air velocity to occupancy areas than openings at lower positions. Chang, Kato, and Chikamoto (2004) assessed the energy savings of a natural and mechanical hybrid air-conditioning system based on the concept of a task-ambient air conditioning strategy. The concept of task-ambient air conditioning divides the whole office into two zones: a task zone where people stay while working, and an ambient zone which is outside of the task zone. ...
Article
With rapid economic growth, the number of high-rise buildings increases significantly due to land shortage in highly populated cities. Compared with other types of buildings, high-rise buildings have a higher cooling load and are more energy intensive, leading to huge cooling energy consumption and peak electricity demand. Ventilation has proved to be an effective approach to reduce cooling load and thereby save cooling-related energy and reduce peak electricity demand for high-rise buildings, which is important for achieving sustainable development of cities and society. Building safety is a challenge in high-rise ventilation. Fires and the resultant air pollution in high-rise buildings are often disastrous and cause huge losses if the high-rise ventilation system is not designed and operated well. This paper presents a review of previous studies on energy efficiency and building safety for high-rise ventilation, including natural ventilation, mechanical ventilation and hybrid ventilation. Statistical analysis was conducted on the research methods, number of literature review sources, and topics. The research gap was also discussed. Through the review, it was found that increasing research has been conducted on high-rise ventilation, especially on the topic of building safety. It was also recommended to consider both safety and energy simultaneously, in order to achieve energy efficiency and safety in high-rise ventilation and therefore to promote the application of ventilation in high-rise buildings.
... In other words, in hybrid ventilation, the active mode (mechanical ventilation) reflects the outdoor environment and benefits from ambient condition by a passive system (natural ventilation). For instance, in intermediate season natural ventilation can provide acceptable IAQ and thermal comfort when outdoor temperature is lower than room temperature and in the rest of the year combination of natural and mechanical ventilation provides comfort condition [94]. ...
Article
Hybrid ventilation is an effective means of minimizing ventilation energy and improving indoor environment. A scale experimental model with a heat source was created for hybrid buoyancy-driven natural ventilation with a mechanical exhaust system. The aim of this study is to examine the performance of hybrid ventilation in an industrial building. The temperature distributions and hybrid ventilation efficiencies with different mechanical exhaust velocities were analyzed. Results showed that the hybrid ventilation efficiency first increased and then decreased with the mechanical exhaust velocity. A critical mechanical exhaust velocity was identified and the hybrid ventilation efficiency reached maximum at the critical mechanical exhaust velocity. The critical mechanical exhaust velocity was 1.4 m/s at the heat flux of the heat source q = 200 W and 1.0 m/s at q = 500 W, and the corresponding ventilation efficiencies were 24.4 and 6.69, respectively. Four modes of hybrid ventilation were investigated, and ventilation strategies of different modes of hybrid ventilation were given. An excessive mechanical ventilation rate will cause consumption of ventilation energy to increase and may lead to short circuiting of airflow and a bad thermal environment. These results should prove helpful in designing of hybrid ventilation systems for industrial buildings.
Article
Full-text available
Refuge ¯oor is specially designed in high-rise buildings for the purpose of supplying a temporarily safe place for evacuees under emergency situations. The provision of such designated refuge ¯oor is a prescriptive requirement in the ®re code of Hong Kong. Such a provision appears to be desirable by the regulators as it relates to simple rules and has administrative convenience. In order to ful®ll its function, the refuge ¯oor should be a safe place for the evacuees. The safeness of refuge ¯oors under ®re situations may be impaired if the ¯oor is a€ected by smoke from lower levels. The code prescribes that cross-ventilation should be provided in refuge ¯oor so as to prevent smoke logging. However, the adequacy of such a measure and the in¯uence of such an open ¯oor on the rest of building have not been analytically studied. An investigation on the air¯ow around and inside the refuge ¯oor is required and will provide preliminary insight on the air¯ow and the smoke movement patterns. In this paper, the Computational Fluid Dynamics method is employed to analyze the air¯ow ®eld around and inside a refuge ¯oor. The aim of this paper is to describe the air¯ow ®eld in and around a designated refuge ¯oor, which is the ®rst step to explore the wind e€ect on the safeness of refuge ¯oors. The study shows that air¯ow could be a factor a€ecting the smoke ¯ow pattern. 7
Article
Full-text available
The paper reviews the problem of making numerical predictions of turbulent flow. It advocates that computational economy, range of applicability and physical realism are best served at present by turbulence models in which the magnitudes of two turbulence quantities, the turbulence kinetic energy k and its dissipation rate ϵ, are calculated from transport equations solved simultaneously with those governing the mean flow behaviour. The width of applicability of the model is demonstrated by reference to numerical computations of nine substantially different kinds of turbulent flow.
Article
Theoretical solutions for thermal stratification and airflow rates are obtained for buoyancy-driven displacement ventilation in a single-zone building with three-level openings. Three displacement natural ventilation modes are identified: (I) the middle opening (MO) is below the stratification interface; (II) MO is above the stratification interface with inflow through MO; (III) MO is above the stratification interface with outflow through MO. It was found that for a wide range of building geometries, the ventilation mode is uniquely determined by the building geometry and the type of buoyancy sources. However, there are certain ranges of building geometry for which displacement ventilation may occur with either mode (I) or mode (II) depending on initial conditions. The significance of this finding is that numerical simulation packages for predicting displacement natural ventilation of buildings need to have the ability to cope with multiple solutions.It was also found that for a given ventilation mode, the location of the stratification interface is a function of the geometrical parameters only and independent of the strength of buoyancy sources. Some general guidelines for optimising natural ventilation in a building with three-level openings are provided.
Article
The objective of this research is to compare calculated and measured air flow distributions inside a test room which is naturally ventilated. The test room is situated in a relatively sheltered location and to visualise the resultant local wind pattern around the room for all prevailing wind directions wind tunnel trials were carried out. Both the wind tunnel and full-scale measurements show that the wind direction at the test cell was generally restricted to either a westerly or an easterly direction. To investigate air flow inside the room, the air pressures and velocities across the openings together with indoor air temperature and velocity at four locations and six different levels are measured. The experimental results demonstrate that for both winter and summer the air was entering the test room at bottom and leaving at the top louvre. Separate air flow and thermal modelling programs are used to predict the spatial distribution of the air flow and thermal comfort. The air flow distribution was predicted using a network air flow program. The predicted flow showed similar trends and the simulation results were in an agreement with the measured data. An explicit finite-difference thermal modelling simulation package was used to predict the thermal comfort indices.
Article
Analytical solutions are derived for calculating natural ventilation flow rates and air temperatures in a single-zone building with two openings when no thermal mass is present. In these solutions, the independent variables are the heat source strength and wind speed, rather than given indoor air temperatures. Three air change rate parameters α, β and γ are introduced to characterise, respectively, the effects of the thermal buoyancy force, the envelope heat loss and the wind force. Non-dimensional graphs are presented for calculating ventilation flow rates and air temperatures, and for sizing ventilation openings. The wind can either assist the buoyancy force or oppose the airflow. For assisting winds, the flow is always upwards and the solutions are straightforward. For opposing winds, the flow can be either upwards or downwards depending on the relative strengths of the two forces. In this case, the solution for the flow rate as a function of the heat source strength presents some complex features. A simple dynamical analysis is carried out to identify the stable solutions.
Article
This paper describes the fluid mechanics of natural ventilation by the combined effects of buoyancy and wind. Attention is restricted to transient draining flows in a space containing buoyant fluid, when the wind and buoyancy forces reinforce one another. The flows have been studied theoretically and the results compared with small-scale laboratory experiments. Connections between the enclosure and the surrounding fluid are with high-level and low-level openings on both windward and leeward faces. Dense fluid enters through windward openings at low levels and displaces the lighter fluid within the enclosure through high-level, leeward openings. A strong, stable stratification develops in this case and a displacement flow is maintained for a range of Froude numbers. The rate at which the enclosure drains increases as the wind-induced pressure drop between the inlet and outlet is increased and as the density difference between the exterior and interior environment is increased. A major result of this work is the identification of the form of the nonlinear relationship between the buoyancy and wind effects. It is shown that there is a Pythagorean relationship between the combined buoyancy and wind-driven velocity and the velocities which are produced by buoyancy and wind forces acting in isolation. This study has particular relevance to understanding and predicting the air flow in a building which is night cooled by natural ventilation, and to the flushing of gas from a building after a leak.
Study on adaptive control systems under hot and humid climates-Part 3: continuous measurement of thermal environment around a moving person and his thermal adaptation
  • D Song
  • S Kato
  • S Murakami
  • Y Shiraishi
  • T Chikamoto
  • A Nakano
Song D, Kato S, Murakami S, Shiraishi Y, Chikamoto T, Nakano A. Study on adaptive control systems under hot and humid climates-Part 3: continuous measurement of thermal environment around a moving person and his thermal adaptation. Summaries of Technical Papers of the Annual Meeting of the Architectural Institute of Japan 2001;359 -60 [in Japanese].
Hybrid air-conditioning system in Liberty Tower at Meiji University
  • T Chikamoto
  • S Kato
  • T Ikaga
Chikamoto T, Kato S, Ikaga T. Hybrid air-conditioning system in Liberty Tower at Meiji University. Hybvent Forum 1999;99:123-7.
New scale for evaluating ventilation efficiency as affected by supply and exhaust openings based on spatial distribution of contaminants
  • S Kato
  • S Murakami
  • H Kobayashi
Kato S, Murakami S, Kobayashi H. New scale for evaluating ventilation e ciency as a ected by supply and exhaust openings based on spatial distribution of contaminants. ISRACVE (Tokyo) 1992; 321-32.