An Investigation On Climate Responsive Design Stra
An Investigation On Climate Responsive Design Stra
An Investigation On Climate Responsive Design Stra
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ABSTRACT
Energy conservation issues and environmental problems in recent years have increased interest in traditional
architecture which is well known for its energy saving designs. This paper thoroughly investigates vernacular
housing designs and evaluates on the aspect of building physics. A new research methodology which is adapted
to the natural and social context of Vietnam was proposed and applied. The process was carried out step by step,
including: climate zoning, systematic analysis, in-situ survey and building simulations. The results of this study
indicate that vernacular housing in Vietnam is creatively adapted to the local natural conditions and uses various
climate responsive strategies. Through this study, the most frequently used strategies and their effectiveness
were derived. The authors also found that under extreme weather conditions, traditional designs might not be
sufficient to maintain indoor thermal comfort.
Keywords : Vernacular housing ; Climatic design strategies ; CFD ; Solar shading ; Thermal simulation
1. Introduction
In recent years, facing the risk of global warming and of the depletion of fossil fuels, reduction in energy
consumption along with sustainable development is a priority for many countries, including Vietnam. Today, we
generally acknowledge that the building sector consumes about one-third of the total energy consumption
worldwide and this figure may vary according to building type and location. In 2010, the building sector in
Vietnam occupied between 20% and 24% of the total national energy consumption and this portion is expected
to increase significantly [1]. Reducing energy use, especially energy used by occupants of buildings, is an
important issue in Vietnam as the country is constantly in the state of energy crisis. Research to reduce energy
consumption in the building sector through climate responsive strategies without compromising human comfort
is essential. Vernacular architecture is widely recognised as a practical, effective and popular solution.
Vernacular architecture is a term used to categorise methods of construction which use locally available
resources to address the local needs [2]. Vernacular architecture results from long-term growth and is part of
traditional popular culture; therefore vernacular architecture is considered well adapted to the natural and social
conditions of a specific location in which it exists.
In Vietnam, many detailed studies have shown that Vietnamese vernacular architecture is multiform and
valuable. Unfortunately, due to many fierce wars, the impact of state policies (for example the land reform from
1953 to 1956) and natural disasters, much vernacular architecture in Vietnam has been destroyed or has
disappeared altogether. Today, those remaining are very modest in scale and form, but the architectural and
environmental lessons that they provide are still considerable.
The principal purposes of this study were to: (1) search and discover the underlying climate responsive strategies
conceived in vernacular architecture; (2) transform and recommend appropriate solutions for current design and
construction, aiming towards sustainable development and (3) assess the importance of preserving the vernacular
housing remaining in Vietnam.
Six old houses in rural and urban areas spread over the 3 regions of Vietnam, representing vernacular
architecture, traditional architecture and old architecture, were thoroughly investigated to understand the climatic
Published in: Building & Environment 46 (2011) 2088-2106
Status: Postprint (Author’s version)
design strategies employed and their effectiveness in maintaining human comfort and health.
To comprehensively and systematically review architectural strategies in Vietnam, both scientific methods and
respect for the natural and social context was essential. Various approaches were employed in the literature. Dili
et al. [3] used long-term in-situ measurement method to evaluate the thermal environment in a traditional
building in Kerala, India. Cañas and Martín [4] employed statistical method to gather data about vernacular
Spanish buildings and categorised them into different bioclimatic strategies based on their locations. By doing
so, they found the most frequently used strategies which correspondenced to the building locations and local
climate. Vissilia [5] conducted a study to evaluate a sustainable Greek vernacular settlement by using subsequent
analysis, based on two major steps: (1) a study concerning the evolution of the built environment (typological
analysis, site planning, construction materials and techniques), and (2) an evaluation of specific vernacular
dwelling types and their response to climate, based on passive design principles. She has made it clear that the
vernacular settlement demonstrates an economical use of local building resources, adapting to climatic
conditions without using much energy and providing human comfort.
Manioğlu and Yılmaz [6] studied energy saving design strategies employed in ancient housing in Mardin,
Turkey. They made a simplified thermal evaluation and comparison of a traditional house with a contemporary
house by using in-situ measurement method and questionnaires which were carried out for 100 buildings. They
found traditional houses performed better than their counterparts in providing human comfort and energy saving.
In an intensive study in Japan, Hiroshi et al. [7] researched four traditional farmhouses using both in-situ
measurement and computer simulation on a model house. Their findings revealed that cooling technologies of
traditional buildings, such as solar shading by thatched roof, earthen floor and natural ventilation et cetera are
effective for interior cooling.
The territory of Vietnam stretches from the North to the South and along the country the complex social
background differs. Based on these geographical and social characteristics and referring to all the above-
mentioned methods (in-situ measurement, statistical method, comparative study and computer simulation), this
study proposes a new approach for analysing and evaluating vernacular dwellings in Vietnam in terms of
building physics. This approach includes six subsequent steps as clearly described in Fig. 1. It is expected that
both qualitative and quantitative analysis included in this method will reinforce the findings from this study.
Fig. 1. 3ew approaches and steps proposed and applied in this research.
Published in: Building & Environment 46 (2011) 2088-2106
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Fig. 2. The map of Vietnam which shows the selected sites of the present study.
Fig. 4. Traditional life on boats affected the housing style of Viet people: (a) ancient boat and (b) ancient house
found on Dong Son bronze drum 6th century BC; (c) current Viet communal house.
Fig. 5. Architectural details of selected houses: house A; house B; house C; House D; house E; house F (from
left to right and upper to lower, respectively).
Published in: Building & Environment 46 (2011) 2088-2106
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All the climatic data used in this analysis were gathered from Vietnam Building Code 2009 [8]. Data in the Code
is based on monitoring data over several years from Meteorological stations of the Vietnam General department
of Hydrometeorology. In this analysis, three typical sites, including Hanoi (latitude: 21° N), Danang (latitude:
16° N) and Hochiminh city (latitude: 11° N), which represent the three climatic regions in the North, Centre and
South of Vietnam, were selected (see Fig. 2). Weather conditions in December and June, representing the winter
and summer periods, were chosen for analysis and comparison.
Fig. 3 shows all climatic data of three selected sites in the diagrams and charts. It is clear that the Sun mainly
moves on the South sky of the observation points; and the three sites have very high solar radiation, relative
humidity and average yearly rainfall. We also emphasise the following points on the climatic features of each
site:
- Hanoi has a short cold winter, but the lowest temperature hardly falls below 5 °C. The highest temperature can
reach 40 °C. Temperature and humidity are generally moderate. Rainfall as well as rain intensity are more
significant. Protection from the cold winds is required in winter. Generally, Hanoi is not affected by tropical
storms.
- In Danang, the climate is tropical with monsoons. The winter is not cold and the lowest temperatures are often
well above 10 °C. The highest temperatures can exceed 40 °C. Because of the impact of the sea, daily and yearly
temperature ranges are quite small. Protection from the cold is not required. Coastal parts are directly influenced
by strong tropical storms and rainfall often peaks during the month of October making appropriate roofing
essential.
- Hochiminh city has a hot and humid climate with monsoons all year round. There are only two annual
contrasting seasons; dry and wet, both consistent with two inhomogeneous monsoons in the region. Rainfall is
quite high. Air temperature and solar radiation are quite high all year which indicate that cooling is in demand.
Wind is abundant all year round and this resource can be exploited for passive cooling strategies, especially
when the hot weather is uncomfortable.
Vietnam is a country of rivers. Its origins can be traced from two big deltas established by the Hong river in the
North and the Cuu Long river in the South. In ancient times, Viet people travelled on boats, and then lived in stilt
houses which have influenced current communal houses (see Fig. 4). Today, in many parts of Vietnam, people
still live in stilt houses like their ancestors did.
Most traditional houses in Vietnam have been destroyed or have completely disappeared due to damage caused
by wars, natural disasters and even the policies of both feudalism and the government. Those remaining, among
which the most ancient house (property of the Nguyen Thac family) was built in 1734 [9], are modest in size and
age.
This study investigated six typical houses in three climatic regions mentioned in Section 3.1. Each region is
represented by two houses: one in an urban area and the other in a rural area, since many significant differences
between these two housing styles exist. Urban houses are typically large, multi-functional, and influenced by
foreign architectural styles whereas rural houses are smaller, purely vernacular and are only used for living
purposes. All six houses are typical in terms of style and size and are in good state of repair. The purpose of this
selection is to find the climate responsive designs corresponding to all climate types in Vietnam. Architectural
details of these selected houses are presented in Fig. 5 and their specific data is listed in Table 1.
It is well-known that vernacular housing all over the world makes use of materials found locally which reduces
energy consumption and environmental impact and also encourages local characteristics which is also the case of
the houses studied (see Table 2).
Among the above mentioned materials, some types were widely used in housing construction in Vietnam,
especially in rural areas, until the end of the 20th century. These materials have certain advantages and positive
characteristics as described in Table 3.
Published in: Building & Environment 46 (2011) 2088-2106
Status: Postprint (Author’s version)
Popular climatic strategies used in the built environment in hot humid regions were categorised and numbered as
17 architectural solutions as follows:
These 17 strategies applied in these selected houses were qualitatively investigated and evaluated using the
"Descripnon and Image" approach. In this approach, the criteria of assessment is that if there is at least one
climate responsive solution which corresponds to each of the local climatic features, the house is considered
completely adapted to its local climate. Conversely, if no adaptation measures are found, the house is regarded as
completely unadapted. In practice, most of the houses are neither completely adapted nor completely unadapted
and are usually within this range. Subsequently, the following points were carefully examined: the advantages
and disadvantages of local climatic features were identified; the drawings and photos of the buildings were
analysed to show climate responsive solutions and their effectiveness; qualitative assessments were then derived
based on the criteria and analysis illustrated in Table 4-6.
Detailed analysis in Table 4-6 reveals that vernacular housing in different regions of Vietnam has adapted
relatively well to the climate as well as adverse weather conditions. Though the solutions employed are
considered simple, inexpensive and easy to apply, they proved to be very effective, demonstrating a deep
understanding of the ancestors about the building and its surrounding environment.
Other findings were also obtained. All strategies used were numbered and their usages were listed in Table 4-6.
Consequently, the frequency of use of each strategy in these houses was found and illustrated in Fig. 6. This
Published in: Building & Environment 46 (2011) 2088-2106
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graph shows that in all regions natural ventilation was the most used strategy whereas earth cooling and passive
solar energy were not employed. Sophisticated technical requirements may be the main reason that passive solar
energy was not employed for heating in vernacular housing, but solar heating has a potential to be applied in
Vietnam and needs to be investigated further. Other findings are that it is suitable and effective to employ natural
ventilation, building orientation — building shape and solar shading strategies in Vietnamese climatic conditions
while earth cooling, thermal insulation and high thermal mass are inappropriate. Storm prevention was only
found in central Vietnam where tropical storms usually hit. Due to time and resource limitations, this preliminary
investigation included only six buildings. The findings can be consolidated by larger investigations.
In order to have a more accurate assessment than the qualitative one mentioned above, an in-situ survey and
measurement was carried out in Hanoi. Since investigations on all six houses would not be feasible, this study
targeted the house at N°102 Bui Thi Xuan street in Hanoi as the unique building of full-scale measurement. The
survey was continuously conducted from 8 h to 21 h on a typical summer day and winter day in Hanoi (16
December and 22 August).
All measurements were in relation to four physical climatic indexes: air temperature, relative humidity, wind
velocity and natural illuminance. The results shown here are the averaged values of 10-min measurements (for
mean wind velocity) and of 3-min measurements (forothervariables). The measuring points were distributed as
shown in Fig. 7. The indoor air temperature, humidity, wind velocity and natural illuminance were measured at
head level of a sitting person (height of 1.1 m) as recommended by ISO 7726 [15]. During measurement periods,
openings of the house were operated by the occupants, adapting to outdoor conditions. Measuring instruments
are listed in Table 7. The results for illumination were compared with requirements in the Vietnam building code
[16] as shown in Table 8.
Table 4 Qualitative investigation of bioclimatic design strategies used in traditional architecture - 3orth of
Vietnam.
Climatic Ancient house in Hanoi Traditional stilt house of small ethnic group on the mountain (house B)
features centre (house A)
Description of strategies Ca. Image Description of Ca. Image
used strategies used
High solar Openings with wooden 2 Thick thatch roof 10, 7
radiation, louvres shades the glazing (about 200 mm)
especially well provides ideal
on West and insulation (U-value
horizontal 0.25-0.35 W/m2K).
surfaces Thatch roof
absorbs moisture
which reduces
overheating by
evaporative
cooling effect
- Large, well ventilated 11 - Deep eaves shade 2
attic acts as a well short walls,
insulated roof protecting all walls
and openings from
direct sun
North cold Building orientation strategy for prevailing wind is NOT available due to its Windows are 1, 3a
wind, location in the city centre oriented to the
South-East South; cross
cool wind ventilation through
door, windows,
and openings on
the gables. When
there is no wind,
stack effect
increases airflow
Low diurnal - Light weight construction 5 Light weight 5 See Fig. 5
and (thin load bearing wall — building
seasonal 220 mm) has average time components: thatch
temperature lag (about 6-7 h) roof, bamboo
-humidity - Insulation was not used lattice enclosure
range with high porosity,
bamboo floor and
wooden column
Others Indoor lighting is fairly 4 House on stilts 14
good due to adapts well to
many large openings floods (from high
and light from the mountain) and
courtyard prevents wild
animals (snakes,
centipedes, insects
etc.) from entering
Published in: Building & Environment 46 (2011) 2088-2106
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Table 5 Qualitative investigation of bioclimatic design strategies used in traditional architecture - Centre of
Vietnam.
Climatic Traditional urban house in Traditional house
features Hoian (house C) in Quangnam
province (house D)
Description of strategies Ca. Image Description of Ca. Image
used strategies used
High solar Thick porous roofing 7 Thick and porous 7
radiation, materials absorb moisture roofing materials
especially on at night and release it absorb moisture at
West and during daytime cooling the night and release it
horizontal roof. during daytime
surfaces. cooling the roof. 1
Main building is
oriented to the
South to avoid
East-West solar
radiation.
- Many shade 2, 9
trees, fruit-trees See Fig. 5
(e.g. jackfruit,
plum...) on the
West.
- Heat absorption
of the facades is
minimised by its
light colour.
High On outdoor walls, there 3 Many large 3
average are 17 windows in total openings facing
temperature (19.7 m2) and 8 doors South include: 2
and (23.42 m2). So/ windows (1 × 1.2
humidity Sf = (19.7 + 23.42)/293.92 m), 3 grand doors
= (1.9 × 1.9 m),
14.7% effectively enhances enhancing natural
airflow ventilation.
Table 6 Qualitative investigation of bioclimatic design strategies used in traditional architecture - South of
Vietnam.
Climatic Old urban house in Hochiminh city (house E) Traditional house in Tiengiang province (house F)
features
Description of strategies Ca. Image Bioclimatic Ca. Image
used strategies used
High solar Wide corridors on the west 2 Corridor and deep 2
radiation, and south façade protect eaves around
especially the house from high solar the house protect it
on West and radiation. Room from direct
horizontal arrangement: Stair, WC sunlight.
surfaces. and store facing West. 1 Main façade is 1
Main rooms are protected oriented to the
from direct Sun. Main South.
façade is oriented to the
South to avoid East-West
solar radiation.
Fig. 7. Distribution of measuring points (1,2,..., 10 are illumination measuring points; A, B,..., E correspond
with measuring points of other variables).
Average air temperature, humidity and wind velocity at survey points were plotted on a combined diagram
shown in Fig. 8. As can be seen from Fig. 8, there are no significant disparities between indoor and outdoor
temperature as well as humidity except humidity at point E (in the kitchen) which was a little higher because of
its earthen floor. This demonstrates that good ventilation of indoor space was achieved. However, daytime
ventilation in summer was not appropriate since outdoor temperature was rather high. This corresponds to the
study carried out by Kubota et al. [17] in which they reported that in a hot humid climate, night ventilation
effectively reduces indoor operative temperature and improves thermal comfort, but the majority of occupants
tend to apply not night ventilation but daytime ventilation mainly due to insects, security risks and rain. Fig. 8
also reveals that indoor wind velocity achieved in the survey was not sufficient to remove heat and humidity in
summer, but was a little high in winter. High indoor wind velocity in winter could be easily reduced by an
appropriate openings control. Natural ventilation performance and humidity at point E was worst since this room
uses single-side ventilation.
Indoor and outdoor hourly temperature, humidity and wind velocity were also compared as shown in Fig. 9. It is
clear that indoor parameters were similar to those measured outdoors. The fluctuation of indoor humidity might
be caused by occupants' activities (cooking, washing et cetera). These confirm the "open" characteristics of this
house which are generally recommended for hot humid climates. Another finding is that the wind velocity at
point D (in the courtyard) was independent of wind conditions at point A (in front of the house). This improves
natural ventilation of the rooms facing the courtyard.
In order to evaluate indoor thermal comfort, PMV index at point C in the summer and winter day was calculated
using measured results. In this study, PMV calculation is based on PMV — calculator of professor de Dear [18]
and on the following assumptions: average occupant's height: 1.65 m, weight: 60 kg(Adubois = 1.65 m2), wearing
clothes at 0.5 clo in summer and 1.0 clo in winter at sedentary work (70 W/m2), exposure time of 60 min, mean
radiant temperature is also assumed to be equal to air temperature.
Although PMV-PPD model is the basis of comfort standards ISO 7730 [19] and ASHRAE 55 [20], it was
assumed to be inaccurate in predicting thermal sensation of the occupants in a naturally ventilated building in hot
humid climate since it neglects human physiological, behavioural and psychological adaptations [21 ]. Thus,
PMV results from the summer day are corrected by an expectancy factor e = 0.6 (for Hanoi - assumed to be
equal to Bangkok) [22].
As shown in Fig. 10, PMV of a winter day was completely in the comfort range and could be improved by an
appropriate control of openings. However, PMV of the summer day was well between slightly warm and warm
scale. This PMV analysis reveals that the house performs fairly well in winter, but it needs other strategies to
maintain human comfort in summer. Two possibilities are proposed: (1) combining better thermal insulation for
the enclosure with night ventilation or (2) employing mechanical support during extreme conditions.
Natural illuminance of the 10 survey points on the winter day (16 December, 15 h) is illustrated in Fig. 11.
During the measurement period, the sky was completely obstructed by the cloud cover and outdoor illuminance
was around 5000 lux. Although the house has many openings, it is a little surprising that some indoor points did
not have enough light according to the current Building code of Vietnam while others exceeded. This suggests
that many openings should be appropriately distributed to achieve better lighting.
Published in: Building & Environment 46 (2011) 2088-2106
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Fig. 8. Average air temperature, relative humidity and scalar wind velocity at surveyed points in a typical
summer and winter day (measurement at point E in summer was unavailable due to construction work being
done there).
Fig. 9. Change of temperature, humidity and wind velocity at some survey points during a typical summer and
winter day.
Published in: Building & Environment 46 (2011) 2088-2106
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In recent years, building simulation has become an effective method to predict building performance and save
time and resources. It also gives predictions for numerous different cases and can simulate extremely
complicated circumstances which people rarely examine by experimental methods. Nevertheless, it is
recommended that the reliability of simulation results be carefully validated before use. The present study
employs three simulation tools, including CFD tool, solar tool and thermal prediction tool which will be
presented in the following sections.
Natural ventilation of various situations of house A was examined using Computational fluid dynamics (CFD)
method. RNG k-ε turbulence model in conjunction with Phoenics code was used as it was reported to be one of
the most reliable two-equation turbulence models for indoor and outdoor airflow applications [23,24]. RNG k-ε
turbulence model was also proved to be effective in predicting cross ventilation by the authors [25]. Although
CFD simulation needs validation to verify its reliability in predicting airflow for any specific case, in preliminary
assessments it is assumed that the accuracy of this turbulence model and CFD code is acceptable. The following
boundary conditions were applied : power-law wind velocity profile with exponent α = 0.22; zero external
ambient pressure; no heat transfer; structured grid distribution: 106, 72, and 39 in the x-, y- and z-axes,
respectively; Hybrid convection schemes; equilibrium Logarithmic wall-function, SIMPLES algorithm [26],
global convergence criteria of 0.01, converged iteration of around 3500. Average wind velocity of 1 m/s at
height of 1.1 m in the in-situ measurement was adopted in all simulations. All windows were assumed to be
opened while doors were closed, reflecting normal operating conditions of the house. Urban context was
included into the model by adding neighbouring houses and creating a street canyon. Airflow field in the living
room, retail shop and courtyard in five cases as well as their simulation results were examined as shown in Table
9.
Fig. 11. Indoor illuminance compared with Building code (15 h, 16th December).
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In cases A, B, and C, ventilation flow rates were low due to the "slide-effect" caused by inertial force of the wind
and the row house (wind slides on building surface without entering the room). This detailed CFD analysis found
that in these cases, courtyard-facing windows sometimes played a more important role than street-facing
windows did. The "slide-effect" can be reduced by providing each of two front windows with vertical wing
walls. Case D and E had significantly higher flow rates since "slide-effect" did not occur. Standard deviation is
shown in Table 9 as well as that wind motion in the Living room was more homogeneous than that in the Retail
shop; and outdoor wind was generally more homogeneous than its indoor counterpart.
3.5.1.1. Effects of side corridor. Comparison between case D (side corridor open) and case E (side corridor
closed) shows that ventilation flow rate and average indoor velocity increased noticeably when the side corridor
was closed (case E). Another effect was that average velocity in the courtyard dropped significantly in this case.
These phenomena can be explained by employing the principle of static pressure drop. Fig. 12 illustrates
pressure and velocity filed in these two cases. It is clear that case E had a larger static pressure drop between the
windward and leeward wall than that of case D. According to Bernoulli's equation of flow rate (Q =
CdAuref√∆Cp; where ∆CP is mean pressure coefficient across the openings), this high pressure drop leads to
higher flow rate in case E. Average velocity in the courtyard in case D (0.324 m/s) was, in contrast, far higher
that that of case E (0.181 m/s), proving that the side corridor played the role of a wind tunnel which induced
more wind into the courtyard.
Since natural ventilation conditions in the front and back part of this house is a function of wind conditions in the
courtyard, the side corridor and the courtyard are a good way to control natural ventilation. Closing the side
corridor gives better ventilation in the front part while opening the side corridor improves wind induced
ventilation in the back part.
3.5.1.2. Comparison with standard and code. ASHRAE standard 62.1 [27] recommends that in residential
facilities Air change rates should be higher than 0.35 ACHs and 7.5 1/s. person to ensure indoor air quality. Flow
rates shown in Table 9 were far higher than these requirements (minimum air change rate occurred in case A and
was 3.01 ACHs). However, the average indoor wind velocity of case A, B and C were lower than the minimum
wind speed (0.2 m/s [20]) needed to improve human thermal sensation.
Shading effectiveness of the shading devices was examined by using the solar tool embedded in Ecotect
analysis® software [28]. Three cases are presented in Fig. 13. Case B reflects the current context in which the
house exists whereas case A and case C are the control case and comparative case, respectively.
Percentages of the shaded area on different vertical surfaces are compared in Fig. 14. It can be seen that in the
current context (case B), the house is currently suitably protected by its shading system since all walls achieved
very high shaded percentages (over 90%) in summer and much of the sunlit area in winter. In its previous
context (case C), the shading system also performed well with over 80% average shading area in summer.
Certainly, case A performed worst among these cases although north and south walls were protected well in
summer. In brief, the shading system of the house almost satisfies the shading requirement, especially in the
current context.
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Fig. 12. Distribution of static pressure and time-averaged velocity in case D with side corridor opened (above)
and case E with side corridor closed (below).
Fig. 13. Three cases in the study of solar shading effectiveness (14 h; 11th July).
This study employed COMFIE [29] thermal simulation tool developed by "Centre d'Énergétique de l'École des
Mines de Paris". This software requires information regarding global characteristics of the buildings in question:
materials, composition, building finishes, ventilation schedules, surrounding conditions and so forth. COMFIE's
performance was validated by Peuportier [30] by comparing simulation results with those of similar tools like
DOE2, TRNSYS, TAS, SIMULA, CODYBA, confirming COMFIE successfully predicted the building thermal
environment. However, the calibration procedure for this case which helps to improve the accuracy of simulation
results was overlooked due to lack of experimental details. Therefore, the following scenarios were assumed:
operating scheme reflects the activity of a typical Vietnamese family (maximum of 4 occupants during night
time); three natural ventilation strategies (night, daytime and full-day ventilation) with different flow rates were
separately applied for summer, winter and the mild season using a maximum flow rate of 0.258 m3/s obtained
from the CFD simulation; the attic was ventilated at 1 ACH during daytime and 0.5 ACH during night time; the
average internal heat gain was 25 W/m2 and varied according to the house's occupancy; the weather data was
exploited from a Typical Meteorological Year (TMY) weather file of Hanoi, then converted into Test Reference
Year (TRY) format for COMFIE. All building parameters were reproduced in the model as shown in Fig. 15 and
Appendix.
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Temperature variation during a year shown in Fig. 16 shows that indoor temperature was relatively stable,
regardless of the fluctuation of outdoor temperature. However, the house failed to protect indoor environment
from extreme outdoor conditions although these conditions did not last very long (see highlighted points in Fig.
16). For the rest of the year, the indoor environment was almost thermally acceptable.
Thermal comfort in the living room was examined by plotting hourly temperatures on an adaptive comfort model
proposed by de Dear and Brager [31]. The optimum comfort temperature underlined in this model is as follows:
where: Tcomf is comfort temperature and Ta;out is mean outdoor dry bulb temperature.
The plotting result in Fig. 17a shows that 58.21% of the total time was found to be thermally acceptable,
corresponding with 90% acceptability. About 70% of the uncomfortable period dropped into the cold zone,
showing that the house needs further thermal insulation against the cold in free running mode. Fig. 17b shows
that there was only 6% of the total time in which indoor temperature exceeded 31 °C, proving that the house
performed better in hot weather. According to ISO 7730 [19] and ASHRAE standard 55 [20], this warm
sensation (about 2 °C higher than comfort temperature) can be completely eliminated by a wind speed of 0.6
m/s, e.g. created by a ceiling fan. This finding does not coincide with that in Section 3.4, indicating that a short-
term in-situ survey cannot always provide an overview of a buildings' performance.
Fig. 14. Shading effectiveness on the hottest day - 11th July (above) and monthly average shading percentage of
the vertical façades (below).
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This study thoroughly assessed the design principles employed in simple, durable and eco-friendly vernacular
dwellings in Vietnam and their effectiveness by qualitatively and quantitatively assessing their performance. The
new approach launched in this study to evaluate vernacular architecture proves to be effective and adequate and
may be employed in the research of vernacular housing in other regions. Nevertheless, necessary modifications
would be strongly recommended due to the differences in climate, geographical features and so forth.
The results of this study clearly indicate that not all vernacular buildings have perfect building physics. Through
this study, the advantages and disadvantages of these buildings were thoroughly investigated, with the aim to
effectively exploit their positive attributes for current developments. The evaluation of a vernacular building
should employ suitable objective methods; otherwise the process leads to incorrect or inaccurate findings as
described in Section 3.5.3. Since the weather might change from day to day, in some cases short-term in-situ
measurement cannot give an accurate overview of building performance. It would be better to combine short-
term in-situ measurements with other long-term prediction tools, such as building simulation.
Fig. 16. Temperature variation in the living room over one year.
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Fig. 17. Hourly plot of air temperature on an adaptive comfort model (left) and cumulative distribution of indoor
temperature (right) in the living room over one year.
Generally, vernacular housing in Vietnam has adapted fairly well to climatic conditions in different locations by
using low-energy design principles that basically ensure human comfort and health. Natural ventilation, building
orientation - building shape and solar shading were the strategies most commonly employed whereas earth
cooling and high thermal mass seemed inappropriate. Although thermal insulation was not used in the six
investigated dwellings, but the above - mentioned analyses suggested that thermal insulation will improve indoor
thermal comfort during the cold weather in the Northern areas of Vietnam. The survey on a house in an urban
area showed that the shading devices performed quite well, but the distribution and configuration of the openings
should be adjusted to improve natural lighting and ventilation. Building courtyard played a significant role on
ventilation flow rate of the rooms facing the courtyard.
In the relatively severe climate of Vietnam, relying entirely on traditional design strategies to maintain thermal
comfort is not completely possible. Therefore, under extreme conditions the building would benefit from low-
energy mechanical systems, such as mechanically assisted ventilation, evaporative cooling, passive solar
heating... or occupants' adaptive responses such as clothing insulation, activities, opening controls and the use of
fans.
The present study has limitations as the quantitative assessment of only one house was carried out. A larger
investigation is therefore needed. Besides, further study to include comparative assessments between vernacular
and more modern architecture is necessary to better evaluate their performance and provide recommendations for
sustainable housing design in Vietnam.
In conclusion, this study has emphasised the importance of climate conscious appropriate building design for the
living environment without excessive use of natural resources. Vernacular housing in Vietnam is evidence that
humans can live in harmony with nature, confirming the need to preserve vernacular architecture there.
Acknowledgements
This study was financially supported by the Ministry of Education and Training of Vietnam (Grant N° 624/QD-
BGDDT: 9th Feb. 2010) and partly by Wallonie Bruxelles International (Grant N° 23478/AMG/BEVN/JP/jp).
We would like to thank the Centre for the Preservation and Restoration of Hoian city and the Centre for Heritage
and Tourism of Quangnam province for their support and input data. The authors also appreciate all reviewers'
comments, the initial help of Anne Françoise Marique and other friends.
Published in: Building & Environment 46 (2011) 2088-2106
Status: Postprint (Author’s version)
Appendix
Surface conditions.
Name Emissivity Absorptivity
Red Brick 0.92 0.68
Cement 0.88 0.60
Smooth white colour 0.85 0.25
White mixture of lime and water (dried) 0.80 0.3
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