Introduction
Global environmental issues and the sustainability movement
In response to the severe environmental depression and energy crisis of recent decades, significant changes in human behavior towards nature have become essential The concept of "sustainable development" was introduced in 1980 in the "World Conservation Strategy" by the International Union for Conservation of Nature and Natural Resources (IUCN) This report emphasizes that sustainable development should not only prioritize economic growth but also address vital social needs and consider the ecological impact.
The term "sustainable development" has evolved from local ecosystem management to encompass global ecological considerations Its usage has expanded across various scientific fields, including economics, tourism, architecture, construction, and urbanism.
The Brundtland Report, also known as "Our Common Future" (1987), popularized the term "sustainable development," defining it as development that fulfills present needs without compromising future generations' ability to meet their own Sustainable development is a dynamic process that requires aligning resource exploitation, investment direction, technological advancement, and institutional changes with both current and future needs It aims to balance economic growth, social equity, and environmental protection, necessitating collaboration across all sectors, including governments and social organizations.
The concept of balancing the economy, society, and environment is crucial, as highlighted during the United Nations Conference on Environment and Development (UNCED) in Rio de Janeiro in 1992 The Rio Declaration emphasized the need for harmony among these three dimensions to ensure sustainable development.
- Environmental (protection of ecosystems and biodiversity, wise use of natural resources, fight against pollution, etc),
- Social (fight against exclusion and poverty, social equity, quality of life, public health, etc),
- Economic (cost-effective use of resources, etc)
Building construction and operational activities account for around 30% of global energy consumption, with the residential sector playing a significant role Additionally, buildings utilize vast natural resources and contribute to environmental strain throughout their life cycle.
Architects and engineers face the urgent challenge of addressing the pressing issues of energy efficiency and resource conservation while maintaining occupant comfort and affordability Immediate action is crucial to mitigate climate change and environmental impacts Sustainability has become a primary focus for architects, necessitating its integration into their professional practices The concept of "sustainable architecture" emerges as a vital response from the building research and design community, aiming to incorporate sustainable development principles into architectural design.
Figure 1-1: The three pillars of sustainable development (Liébard & de Herde, 2005)
Final energy consumption (%) Commercial Residential Total
Sustainable architecture, a vital aspect of sustainable development, integrates environmental, socio-cultural, and economic considerations to meet present needs without compromising future generations It encompasses a wide range of factors, including political, scientific, technical, financial, and human resources Often mistakenly viewed as merely environmentally-conscious design, sustainable architecture seeks holistic solutions to minimize environmental impacts through thoughtful design strategies, material selection, energy efficiency, and occupancy considerations.
In 1993, the World Congress of Architects in Chicago, organized by the Union of International Architects, officially recognized "sustainable architecture" as a key agenda item, emphasizing the significant responsibility architects have toward sustainability This marked one of the earliest efforts to implement sustainable practices in architecture.
The UK introduced BREEAM assessment criteria for green buildings in 1990, paving the way for various countries to develop their own standards, including LEED in the U.S., GBTool in Canada, EcoProfile in Norway, and Environmental Status in Sweden In Vietnam, the inaugural version of its Green Building assessment criteria, known as "LOTUS," was published in 2011.
In recent years, the rise of eco-friendly architectural trends has highlighted the design community's commitment to sustainability, making sustainable architecture an essential movement rather than just a passing trend This approach fosters collaboration across various disciplines, requiring the involvement of architects, engineers, economists, sociologists, and psychologists to create effective sustainable projects.
Table 1-1: Percentage of the final energy consumption used in commercial and residential buildings in 2004 (Pérez-Lombarda, et al., 2008)
Sustainable architecture encompasses various dimensions, each with specific targets and design solutions Figure 1-2 highlights these key aspects, with the bolded elements representing the focus of this thesis.
Figure 1-2: The hierarchy of sustainability in architecture
Many architects view sustainable architecture primarily through the lens of energy performance and building technologies, often underestimating their significance and relegating them to the realm of engineering skills (McMinn & Polo, 2005) This perception stems from a lack of knowledge in architectural and environmental sciences among architects, creating a disconnect between sustainability and the building design community, particularly in residential projects As a result, architects frequently struggle to integrate sustainability requirements with various design constraints To address this issue, this thesis aims to develop comprehensive design solutions for sustainable housing in Vietnam.
This research aims to enhance living environments and occupant comfort while maintaining cost-effectiveness, reducing energy consumption, and minimizing the environmental impact of buildings through advanced building science applications It specifically addresses climate-responsive design strategies for human thermal comfort and energy savings, which are critical challenges for architects and engineers in Vietnam Additionally, a study of vernacular and traditional housing will enrich the socio-cultural perspective, while life-cycle cost optimization will offer strategies for achieving affordable and comfortable housing in the country.
Since the 1950s, climate responsive design has been extensively studied, notably by Victor Olgyay in his 1963 book While numerous studies in developed countries have greatly advanced building science knowledge, similar research in Vietnam remains scarce and practical This thesis aims to leverage modern building science advancements and analytical methods to offer Vietnamese designers enhanced opportunities for achieving sustainable housing goals.
Research on building science in Vietnam is relatively common; however, most studies yield qualitative results rather than employing advanced analytical methods Consequently, these studies are often deemed inadequate and lacking in quality.
Housing issues in Vietnam - Identifying problems
Vietnam, located in the heart of Southeast Asia, spans from 9° to 23°20’ North latitude and 102° to 110° East longitude, covering an area of 331,212 km² with a coastline of 3,200 km The country is divided into 64 provinces, 609 districts, and 10,554 communes, and is home to 54 ethnic minorities, with the Viet (or Kinh) group making up 87% of the population Despite their diverse languages and cultures, these groups coexist harmoniously According to a national survey conducted by the Government and General Statistics Office in April 2009, Vietnam's population reached 85.8 million, ranking third in Southeast Asia and 13th globally, with a sex ratio of 98.1 men for every 100 women Notably, around 70.4% of the population resides in rural areas.
2009, average population growth-rate was 1.2% per year while urban growth was 3.4% per year and 0.4% per year in rural areas (CPHSC, 2010)
The poverty rate in Vietnam has gradually decreased since 1986 when the
The Vietnamese government's liberalization process has led to significant economic achievements, though it's crucial to recognize that the country started from a low baseline According to the World Bank, in 2008, Vietnam's GDP per capita was $2,787 (using the PPP method), ranking 118th out of 168 countries globally This figure highlights the low income levels and substantial disparities between urban and rural areas, emphasizing the need for continued economic development.
Recent economic advancements have elevated the country to lower-middle-income status, with GDP per capita rising from approximately 1,024 USD in 2008 to 1,411 USD in 2011 Despite this progress, a significant number of families still live below or just above the poverty line In 2008, the monthly income per capita in Vietnam was only 995,200 VND (around 58.5 USD), with even lower figures reported in rural areas.
3 Data available at http://data.worldbank.org/indicator/NY.GDP.PCAP.CD [Last accessed 11 Oct
In 2008, the average living space per Vietnamese individual was 16.3 m², significantly lower than the global average and the living standards of several other countries, such as urban China at 30.0 m² per person, Sweden at 43.6 m², Belgium at 33.7 m², Germany at 41.3 m², Russia at 22.4 m², and Ukraine at 22.5 m² Despite this disparity, the living area in Vietnam has been steadily improving, increasing by over 0.5 m² annually in recent years.
Total Permanent house Semi- Permanent house
For many Vietnamese families, a permanent house represents their most significant investment, necessitating extensive savings and considerable effort Unlike in many developed countries, it is common for Vietnamese homeowners to avoid bank loans for construction Instead, when faced with financial shortfalls, they often turn to relatives for assistance or resort to high-interest informal lending services.
The total construction costs in urban and rural areas in Vietnam differ significantly
It was estimated that a 120 m 2 private house in urban areas with acceptable quality might costs averagely 18000 USD (150 USD/m 2 ) 6 while in rural areas, people usually build their
4 Data available at http://wenku.baidu.com/view/58a1768302d276a200292e91.html [Last accessed 11 Oct 2012]
5 Data available at http://www.statinfo.biz/Geomap.aspx?act62&lang=2 [Last accessed 11 Oct
6 Value estimated by the author
Table 1-2: Monthly income per capita by urban and rural region - unit: 1000 VND (At exchange rate of 1USD ≈ 17.000 VND) (CPHSC, 2010)
Table 1-3: Living area per capita by type of house, urban-rural region (Unit: m 2 )
In rural Vietnam, houses can be built for between $5,000 and $7,000 (approximately $40 to $58 per square meter) using a variety of local materials Residents often create their own cement blocks and clay bricks from local clay soil, and utilize thatch for roofing However, essential materials like cement, steel, roofing sheets, tiles, doors, and windows must be purchased from commercial markets.
Housing quality and durability in Vietnam, particularly in rural areas, is a significant concern As of 2008, nearly 80% of rural homes were classified as semi-permanent or temporary, making them highly susceptible to frequent natural disasters such as storms, typhoons, and floods An international workshop revealed that approximately 70% of houses in coastal central Vietnam have been replaced or renovated in the last 15 years; however, a similar proportion still falls into the ‘semi-solid’ or ‘weak’ category, rendering them vulnerable to damage.
Type of house in percentage Total Permanent house Semi- Permanent house Temporary and other house
In Vietnam, small residential buildings are often constructed with minimal investment and without professional guidance, leading to larger housing projects that prioritize investor profit over occupant comfort This approach results in inadequate indoor comfort due to poor design In many developing countries, having a reliable shelter is a significant aspiration, causing residents to voice concerns about building services and quality, while their assessments of thermal comfort and indoor environments are frequently overlooked.
7 Value estimated by the author
Table 1-4: Percentage of house by housing condition, urban - rural area (CPHSC, 2010)
As living standards improve, housing and indoor comfort will become primary concerns for occupants, particularly in Vietnam's hot and humid climate With short, warm winters and long, challenging summers, most residential buildings rely on natural ventilation, leading to indoor environments that closely mimic outdoor conditions This situation raises important questions and challenges regarding the quality of indoor living spaces.
(1) whether the current design of residential buildings can provide indoor comfort;
(2) which design strategies can improve thermal comfort;
(3) about the efficiency and applicability of these solutions
Research on housing issues, particularly those affecting the poor—who are the most vulnerable group—holds practical significance and the potential for substantial social impact in Vietnam This study aims to address the challenges of human thermal comfort within this context.
NV dwellings serve as primary housing for many low-income families in Vietnam This article examines not only the initial construction costs associated with these homes but also their energy consumption and the overall life cycle operating costs of air-conditioned residential buildings.
Research objectives
This thesis aims to create design strategies for comfortable, eco-friendly, and energy-efficient buildings that remain within a reasonable budget The proposed solutions will be tailored to Vietnam's context by effectively utilizing building materials, focusing on climate-responsive design, and intelligently integrating various design elements All solutions will align with the principles of sustainable development.
To obtain this target, the following specific aims need to be achieved:
- Good understanding of the thermal comfort condition of Vietnamese, corresponding to each climatic region, by using both predictive models and field surveys on thermal comfort;
- Identifying strengths and weaknesses of the current housing design in Vietnam through an investigation on thermal performance of the current housing stock;
- Discovering our ancestors’ wisdom underlining the design principles of traditional and vernacular architecture and their applicability in modern housing development;
- Developing passive solutions to improve thermal performance of the current design, based on required thermal conditions for Vietnamese; and quantifying the effectiveness of these solutions;
- Successfully providing general guidelines and recommendations for housing design towards comfortable and sustainable architecture
This work aims to deliver valuable academic materials and offers refined guidelines for practical applications in building design The author envisions integrating the analytical approach of this thesis with creative design elements to create aesthetic, comfortable, affordable, energy-efficient, secure, and healthy built environments.
Research hypotheses
The primary objective of this research is to enhance common housing design in Vietnam to achieve improved thermal comfort and reduced energy consumption The proposed solutions aim to contribute significantly to sustainable housing practices in the region Additional research hypotheses are also presented for further exploration.
The 1 st hypothesis: Many studies have pointed out that thermal conditions required for human comfort in NV buildings are not quite similar to those in climate-controlled environment On the other hand, people in developing countries in hot and warm climates are believed to be acquainted with long-term warm conditions and may have lower comfort expectation As a result, their preferred thermal conditions might differ considerably from what have been prescribed by international standards of thermal comfort This research therefore hypothesizes that Vietnamese people living in NV buildings have specific thermal preferences and thermal comfort conditions These conditions need to be defined
The 2 nd hypothesis: This research hypothesizes that common design of residential buildings in Vietnam have failed to provide appropriate indoor thermal conditions so that a major part of occupants would be thermally satisfied It means that the thermal performance of the current housing stock needs to be improved and housing design methods should be subject to modifications and supplementations
The 3 rd hypothesis: Architectural design and occupancy strategies play an important role in protecting building occupants from disadvantageous effects of the climate and
Creating a favorable indoor environment in Vietnam can be achieved through strategies such as natural ventilation, optimal building shape and orientation, sun shading, humidity control, thermal insulation, and effective thermal mass and ventilation management These climate-responsive solutions are hypothesized to significantly enhance the thermal performance of the existing housing stock in the country.
The 4 th hypothesis: Traditional - vernacular architecture has been developed over the centuries and is the result of much trial and error It is generally true to say that traditional - vernacular architecture underlines many effective passive design principles, reflecting excellent knowledge of our ancestors about the climate, natural environment and local cultural institution This thesis hypothesizes that traditional - vernacular architecture, in general, or specifically vernacular housing in Vietnam is also able to provide valuable lessons for current development and therefore needs to be considered
The 5 th hypothesis: The basic characteristic of the climate of Vietnam is hot and humid The weather often reaches extreme conditions, e.g very hot and humid (over 35°C and RH of 75% - 90%) Such a climate type requires indoor environment to be sometimes fully controlled by mechanical systems to ensure thermal comfort It is hypothesized that design and occupancy strategies derived by using the optimization method are capable to minimize building energy consumption and thus environmental impacts, to maximize thermal comfort and to minimize the construction and operation costs The optimization method is able to shift the optimal houses into some sustainable building categories, e.g net-zero energy houses or passive houses, defined in some guidelines and standards.
Limits of the research
Sustainability and sustainable housing represent a significant area of research To maintain the quality and clarity of this study, the thesis will focus on specific objectives and hypotheses Additionally, certain aspects will be intentionally excluded from the research domain of this thesis.
This research focuses primarily on indoor thermal comfort, deliberately excluding other occupant comfort issues such as indoor air quality (IAQ), visual comfort, and acoustic comfort, which are considered independent from thermal comfort.
This thesis concentrates exclusively on passive design strategies that architects can implement during the design phase and that building occupants can manage during occupancy Active methods, such as HVAC system design and operation, are beyond the scope of this research and will not be examined in detail.
This research focuses exclusively on residential buildings, specifically low-rise apartment complexes, low-income housing, and private dwellings, while excluding other types of structures such as commercial, office, industrial, and educational buildings.
This research focuses exclusively on building-scale aspects, including building design, operation, and indoor micro-climate, while intentionally excluding broader urban-scale issues such as urban morphology, arrangement, and landscape design.
In Vietnam, residential facilities predominantly utilize natural ventilation (NV) to leverage the benefits of the tropical climate This research will primarily focus on NV buildings, which are the most prevalent type for low-income residents, while also briefly addressing air-conditioned (AC) buildings, albeit with less emphasis.
Structure and methodologies of the thesis
The workflow of the research is depicted in Figure 1-3, highlighting the key steps, methods, objectives, and outcomes, all anchored in the author's peer-reviewed publications This figure emphasizes a consistent research focus on thermal comfort and the thermal performance of buildings Utilizing the inductive scientific method, the study begins with extensive observations of various case-study dwellings, including vernacular and contemporary homes, as well as a generic single-zone housing model, all examined under typical climate patterns in Vietnam The aim is to derive impactful insights and general design principles from these findings.
13 recommendations are derived It is therefore essential to note that more observations from other variants will further consolidate the findings of this work
Figure 1-3: The workflow of the thesis
This thesis is constituted by 9 chapters Summary of the content of the remaining chapters are described as follows:
Chapter 2: This chapter reports the state of the art of sustainable housing, climate responsive architecture, its applications in housing design and human thermal comfort This chapter gives an idea of the general development and latest advancements in this research domain based on which the research methodology of the thesis is established
Chapter 3: This chapter develops a thermal comfort model applicable for Vietnamese people The model is based on the adaptive theory in thermal comfort, which is usually used to explain the deviation between predicted thermal sensation votes by analytical theories and actual thermal sensation votes in NV buildings The choice and implementation of comfort models for two building types, namely NV and AC buildings, are defined Many other comfort related issues are also discussed
Chapter 4: In this chapter, the climates of Vietnam are first described and categorized into three major climatic regions A new simple climate analysis tool is developed in order to analyze the climate of these 3 regions and to draw preliminary design guidelines This tool is also applied in CHAPTER 6 to evaluate thermal comfort of some indoor conditions The “performance of the climate” is also presented and its application is explained
Chapter 5: Three most common housing prototypes are indentified and case-study houses are selected Afterward this chapter presents a comprehensive framework through which thermal performances of 3 typical housing types are derived Various techniques, including in situ monitoring, building thermal simulation, CFD and airflow network model, numerical model calibration are employed to obtain the results Results of these studies provide the reference thermal performances for further improvements
Chapter 6: This chapter presents a comprehensive investigation on climate responsive design strategies applied in vernacular housing in Vietnam The investigation employs both qualitative and quantitative assessment methods The study to some extend reveals the remaining value of vernacular housing and provides valuable lessons for modern applications
Chapter 7: Based on the thermal models and CFD models of the case-study houses, this chapter uses the parametric simulation method to improve the thermal performances of these houses and thermal comfort by natural ventilation Performances of the improved
15 cases are compared with the reference performances obtained in CHAPTER 5 The efficiency of the parametric simulation method is also defined
Chapter 8: This chapter is divided into two parts In the first part, the Monte Carlo- based sensitivity analysis method is used to quantify the impact (sensitivity) of design parameters on the thermal performance of the houses Parameters that have highest impact on the building performance are selected for the next step In the remaining part, the thermal performances of the reference cases are optimized using the simulation-based optimization method Optimization results show the best design for each climatic region The performances of the optimal solutions are compared with the references, providing an insight of the efficiency of the optimization approach in building design The chapter also gives many discussions on the results obtained and compares them with the results found in the literature
Chapter 9: This chapter summarizes the different objectives yielded in this thesis and provides general design recommendations for different climate regions in Vietnam It also outlines limitations and possible future extensions of this thesis through new researches.
Literature review
Literature review on the bioclimatic approach in architecture
Since the first appearance of the term “bioclimatic approach” in architecture
The bioclimatic approach to architectural regionalism, as defined by Olgyay (1963), highlights the significance of the relationship between living organisms and the local climate in building design, promoting sustainable development This approach requires a multidisciplinary effort to effectively address climate control, beginning with identifying comfort conditions for occupants, which is rooted in biology Next, climatology provides essential insights into local climate conditions Ultimately, an architectural solution is developed through engineering sciences, ensuring that buildings harmonize with their environment while enhancing sustainability.
Climate responsive design strategies embody the bioclimatic approach in building design, playing a crucial role in creating sustainable structures Today, these principles are essential for achieving environmentally friendly architecture.
17 therefore necessary for building design practice as a starting point for architectural conceptions with the climate in mind
In recent years, sustainability has become a significant focus for the building research community and design professionals, leading to the emergence of passive low energy architecture globally The PLEA conference series serves as clear evidence of this trend (Hyde, 2008) New terminologies such as “eco house,” “passive house,” “energy-efficient building,” “carbon neutral building,” “zero energy building,” and “green building” have been introduced to describe innovative sustainable building concepts While the design of these structures involves various integrated design tools and methods, such as building simulation, it is crucial to recognize that they primarily depend on passive design features of the building's form and fabric to achieve sustainability goals Thus, the bioclimatic approach remains vital in architectural design practice.
2.1.2 Bioclimatic architecture - conventional methods and novel approaches
The bioclimatic approach originates from the design principles found in vernacular and traditional architecture worldwide These architectural styles have evolved to embody the environmental, cultural, technological, and historical contexts of their specific locations Consequently, vernacular architecture has accumulated valuable knowledge in climate-responsive design over time.
In the 1930s, renowned American architect Frank Lloyd Wright established the concept of "organic architecture," which emphasizes designing structures that harmonize with both humanity and the environment Wright's work served as a bold challenge to the prevailing modernist architectural trends of the time.
It seems that the first academic publication on the issue of climate responsive architecture was published by Aronin (1953) Nevertheless, the first work that had strong
8 See http://plea-arch.org for further information
In 1963, Olgyay published a seminal work that laid the groundwork for the bioclimatic approach, utilizing a bioclimatic chart specifically designed for inhabitants of the U.S moderate zone This chart served as a valuable tool for analyzing various regional climates across the U.S., translating findings into architectural design principles and applications Olgyay's book also introduced design principles and examples tailored to four distinct climatic regions in the U.S His most significant contribution was pioneering the integration of human thermal comfort into climate assessment and building design.
Givoni (1969) significantly advanced the bioclimatic design method by introducing the building bioclimatic chart based on the psychrometric chart, which became a key tool in building research This chart effectively illustrated all thermodynamic processes of moist air, enabling the identification of control zones for various passive design strategies Additionally, Givoni provided a thorough review of architectural sciences and offered design guidelines tailored to three major climatic types worldwide Together, the contributions of Olgyay and Givoni established essential frameworks for future studies in climate-responsive architecture.
Several authors, including Koenigsberger et al (1973), O'Cofaigh et al (1996), Givoni (1998), Roaf et al (2001), Szokolay (2004), and Liébard & de Herde (2005), have conducted comprehensive reviews of recent advancements in architectural science, contributing significantly to the field.
Figure 2-1: The building bioclimatic chart of Olgyay (left) and Givoni (right)
19 their design guides for different climatic regions based on their experience and the abundant available literature
During the design process of a 'high performance' building, critical questions arise regarding comfort levels without HVAC systems, peak overheating durations, heating and cooling loads, and annual electricity consumption Traditional methods only provide qualitative answers, but the strict design requirements of these buildings necessitate precise and detailed responses Numerical modeling and simulation have emerged as effective bioclimatic approaches to address these challenges efficiently Building simulation accounts for local weather variations and different occupancy scenarios, serving multiple purposes such as design advice, testing, fine-tuning, verification, and diagnostics.
The simulation method plays a crucial role in advancing research and design practices in architecture, particularly in the context of bioclimatic housing Hyde (2008) introduces innovative applications of simulation in building design, emphasizing energy efficiency as a key focus, rather than solely on thermal comfort and passive building elements This shift reflects a broader trend towards climate-responsive architecture, which is essential for achieving zero carbon targets and creating energy-efficient buildings Hyde's work exemplifies the evolution of design practices in the computer-based era.
Since 2000, researchers have increasingly focused on sustainability in the built environment, highlighting the importance of passive design principles in innovative building solutions This shift has sparked interest across various research communities, as evidenced by the works of Smith (2005), Bay & Ong (2006), Glicksman & Lin (2006), and Santamouris (2006).
2.1.3 Classification of bioclimatic research methodologies
The evolution of the bioclimatic approach in building design can be categorized into three distinct periods, each representing a unique design method As summarized in Table 2-1, these three major bioclimatic approaches exhibit specific characteristics Notably, the numerical modeling and simulation approach offers enhanced capabilities, leading to wider applications compared to earlier methods.
Empirical approach Analytical approach Numerical modeling and simulation approach Estimated effective period
Until the year 1950s 1930 - present 1990 - present
Rules of thumb Building bioclimatic chart
Standards and codes (thermal comfort model, natural lighting code, IAQ code)
Observation Discrete statistical weather data
Design objectives Human comfort and health
Human comfort and health Energy consumption Environmental impact Performance verification method
Trial and error Monitoring and comparison
Diagnostic method Trial and error Trial and error, monitoring and analysis
Comfortable building Energy-efficient building
Zero energy building Green building Comfortable NV building
Recent advancements in computer science have significantly accelerated research on climate-responsive architecture, particularly through a third approach that continues to influence contemporary studies (Wang & Wong, 2007; Singh, 2010; Nguyen et al., 2011; Nguyen & Reiter, 2012c; Nguyen & Reiter, 2013) This numerical modeling approach demonstrates substantial potential for enhancing both research and design practices in the field.
As many other countries, vernacular housing in Vietnam has illustrated valuable examples of the harmony between the nature and manmade structures (Nguyen, et al.,
Table 2-1: Three major bioclimatic approaches in the evolutional order
Research on building physics in Vietnam has been ongoing since 1960, focusing on the interplay between architecture and climate The first comprehensive academic work on this topic, "Building Physics" by Pham et al (1980), addressed fundamental issues in building design specific to Vietnam Subsequent studies by scholars like Pham (2002) and Hoang (2002) explored the climate's impact on architecture, with Pham introducing a bioclimatic approach and a building bioclimatic chart tailored for Vietnam's diverse climates While these studies drew on methodologies from international authors, they have yet to fully address the evolving demands of contemporary building standards, such as the "Lotus 2011" green building rating tool.
To enhance climate-responsive design principles in Vietnam, it is crucial to adopt a more robust and comprehensive approach This methodology not only improves building design practices but also significantly contributes to the architectural theory in Vietnam, aligning with global objectives outlined in this thesis.
Literature review on human thermal comfort in built environments
2.2.1 Thermal comfort and its role in built environments
Comfort refers to a state of physical ease free from pain or constraints, influenced by environmental factors According to ASHRAE (2004), thermal comfort is defined as a mental state where satisfaction with the thermal environment is expressed through subjective evaluation This highlights that the perception of comfort is a cognitive process shaped by various inputs, including physical, physiological, and psychological factors.
9 Oxford online dictionary: http://oxforddictionaries.com (Last accessed Feb 2013)
Thermal comfort is a crucial aspect of building science that significantly impacts building design, energy efficiency, and environmental quality (Brager & de Dear, 1998) Due to individual physiological and psychological differences, achieving universal thermal satisfaction in a space is challenging However, research indicates that it is possible to create conditions that meet the comfort needs of a majority of occupants (ASHRAE, 2004) Six primary factors influence an occupant's thermal sensation: dry-bulb air temperature, radiant temperature of surrounding surfaces, air humidity, air velocity, metabolic heat production, and clothing insulation Additionally, subjective thermal perception can vary based on factors such as sex, age, adaptation, and circadian rhythms.
Thermal comfort has become a key focus for building scientists, as it plays a crucial role in ensuring that a majority of occupants find indoor environments comfortable This concept is directly linked to occupant satisfaction, health, and productivity Additionally, thermal comfort standards are essential for setting HVAC thermostats in air-conditioned buildings, which in turn affects energy consumption and the environmental impact of building systems.
The human body's core temperature is tightly regulated around 37°C, with even minor fluctuations triggering significant physiological responses At rest, the brain's temperature averages 36.8°C, increasing to approximately 37.4°C during walking and reaching nearly 37.9°C while jogging (ASHRAE, 2009).
The hypothalamus, situated in the brain, serves as the primary regulator of body temperature It contains sensors for both hot and cold temperatures and is fully integrated with arterial blood This vital brain region primarily gathers thermal information from the bloodstream, enabling it to maintain the body’s thermal balance.
The body regulates temperature primarily through skin blood flow, adjusting circulation to either release or conserve heat based on internal temperature changes When temperatures exceed a setpoint, increased blood flow to the skin facilitates heat dissipation, while reduced flow helps retain warmth during extreme cold In response to significant heat loss, muscle tensing and shivering generate additional metabolic heat, potentially reaching up to 260 W/m², compared to 60 W/m² for a resting individual As internal temperatures rise, sweating becomes a critical cooling mechanism, with rates of up to 1 liter per hour in moderate heat and 2.5 liters per hour in extreme conditions This sweating process can dissipate heat at a rate of approximately 0.63 kW, based on the latent heat of water evaporation.
The means by which a human body exchanges heat with surrounding environment consist of: evaporation, radiation, convection and conduction The heat production and heat exchange processes are illustrated in Figure 2-2
1 Heat produce by: a) Basal processes b) Activity c) Digestive process d) Muscle tensing and shivering in response to cold
2 Absorption of thermal radiation: a) From the Sun b) From glowing radiators c) From non-glowing hot objects
3 Heat conduction toward the body: a) From the air above skin temperature b) By contact with hotter objects
4 Outward radiation: a) To sky b) To colder surroundings
5 Heat conduction away from the body by contact with colder objects
6 To air below skin temperature (hastened by air movement – convection)
7 Evaporation: a) From respiratory tract b) From skin
Heat production in the body arises from metabolism, where the components of digested food are oxidized in cells to generate the energy necessary for various organ functions, including muscle contraction, involuntary internal activities like heart function, respiration, and digestion, while also maintaining stable body temperature Typically, only 5-10% of this energy production is utilized for mechanical work performed by the muscles (Nishi, 1981).
Figure 2-2: Heat exchange between man and his environment
The human body continuously produces heat through various activities, necessitating effective heat dissipation to maintain normal body temperatures (ASHRAE, 2009) Even at rest in warm environments, the body's heat production remains at a baseline level known as basal metabolism, typically around 85W for an average individual This heat output increases to 117W during sedentary activities, 223W while walking at 3.22 km/h, 323W at 6.4 km/h, and can reach between 880 to 1400W during maximum exertion.
The mechanism of heat balance between a human body and the environment can be expressed in a mathematical equation as shown in Figure 2-3 sk res
M = rate of metabolic heat production, W/m2;
W = rate of mechanical work accomplished, W/m2; q sk = total rate of heat loss from skin, W/m2; q res = total rate of heat loss from respiration, W/m2;
In thermal comfort calculations, W is often assumed to be zero, as noted by ASHRAE (2009) Typically, human thermoregulation maintains a balance that allows individuals to feel comfortable within a temperature range of approximately ±1.7°C to ±2.5°C around the optimal comfort temperature However, under unfavorable conditions, this balance can be disrupted, leading to excessive heat gain or loss and resulting in uncomfortable thermal sensations Therefore, key questions regarding thermal comfort in built environments include identifying the optimal conditions for occupant comfort and predicting thermal sensations in the event of thermal imbalance.
2.2.3 Comfort temperature in climate-controlled environments
Rohles and Nevins (1971) carried out a comprehensive thermal comfort survey on
A study involving 1,600 college-age students in the U.S examined their comfort levels in a climatic chamber over three hours while engaged in sedentary tasks and dressed in 0.6 clo clothing The ambient humidity was maintained at approximately 50%, revealing that both male and female participants preferred a temperature of 25.6°C for optimal comfort.
Figure 2-3: Heat balance mechanism and body temperature
Fanger investigated the effects of cold climates on various Danish subjects, including college students, winter swimmers, and meat packers from a refrigerated environment Conducted in the 1970s under consistent experimental conditions—sedentary activity, 0.6 clo clothing, and 3 hours of exposure—his findings revealed that all three groups exhibited a similar preferred temperature range of approximately 25.0°C to 25.7°C (Brager & de Dear, 1998).
A study by Fanger (1970) assessed the impact of acclimatization on thermal preference, involving 16 long-term tropical residents immediately after their arrival in Copenhagen The results indicated a preferred temperature of 26.2°C, which is slightly higher than the 25.5°C benchmark Similarly, de Dear et al (1991) conducted research with 32 Singaporean students in the hot and humid climate of Singapore, revealing that the upper limit of the acceptable comfort zone at 70% humidity was 27.6°C.
Chung and Tong (1990) studied the thermal comfort of 134 college-age Chinese individuals in Hong Kong's warm, humid climate During a 3-hour sedentary activity, participants wore standard clothing with a clo value of 0.6 and were exposed to various thermal conditions The research found that the neutral temperature was 24.9°C, with a neutral zone ranging from 22.2°C to 25.2°C.
In a thermal comfort survey conducted by Tanabe et al (1987) involving 172 Japanese college-age students in a hot and humid climatic chamber, it was determined that the neutral temperature for Japanese subjects was 26.3°C This temperature is slightly higher than the neutral temperatures reported for American and Danish subjects, indicating regional variations in thermal comfort preferences.
Research indicates that the preferred or neutral temperature for individuals dressed in standard clothing during sedentary activities, under moderate humidity, is approximately 25.5°C to 26°C This temperature range appears to be consistent globally, irrespective of variations in climate, ethnicity, or cultural background.
2.2.4 Thermal comfort prediction in actual built environments
A thermal comfort model for Vietnamese
Study background and the proposed approach
Thermal standards in the built environment are crucial for architects and engineers to enhance occupant comfort, health, and productivity Accurate environmental assessments not only provide a comfortable thermal sensation but also influence the energy consumption of heating and cooling systems In light of climate change and global warming, integrating advanced thermal comfort concepts into these standards supports the adoption of energy-efficient strategies, aligning with sustainable development goals and addressing contemporary challenges.
Fanger's (1970) 'steady-state' thermal comfort theory serves as the foundation for various international and national thermal comfort standards, including ASHRAE and ISO The PMV-PPD comfort model, derived from Fanger's research, is widely utilized to assess occupant comfort in climate-controlled environments, which closely resemble the conditions of climatic chambers used in the model's development Extensive studies confirm the model's effectiveness, particularly with Asian subjects, as noted by Fanger and Tứftum (2002), and the ASHRAE RP-884 project further validates its application in air-conditioned buildings (de Dear & Brager, 1998).
Numerous field studies indicate that the existing model is inadequate for predicting the thermal sensations of occupants in "free-running" or naturally ventilated buildings, affecting both hot and temperate climates This inadequacy arises from the model's inability to account for specific environmental and behavioral factors influencing thermal comfort in these settings.
The PMV-PPD model fails to account for the complex ways humans interact with their environment, particularly how they adapt their behaviors, expectations, and preferences over time As a result, the adaptive comfort approach has emerged as a valuable alternative for assessing thermal comfort in these scenarios Research by McCartney and Nicol (2002) highlights that implementing adaptive comfort standards in actual office buildings can significantly enhance energy efficiency, potentially reducing cooling loads by approximately 30% compared to traditional fixed thermostat methods.
Over the past two decades, the adaptive comfort theory has been increasingly validated, leading to the development of an applied comfort model for naturally ventilated (NV) buildings in Vietnam's hot and humid climate, based on the principles of adaptive comfort.
Developing an adaptive comfort model for a specific region requires extensive and repeated transverse field surveys over several years to account for a wide range of outdoor conditions, from cold to hot weather Additionally, a substantial number of observations or respondents is essential to ensure that the findings are statistically significant and reliable This process is both time-consuming and labor-intensive, making the creation of an adaptive comfort model for Vietnam based on direct field surveys unfeasible within the scope of this thesis.
South-East Asia, particularly Vietnam, experiences hot and humid climates year-round, with a population sharing a similar cultural background Residents favor NV buildings, as these structures effectively meet their socio-economic and socio-cultural needs This leads us to hypothesize that individuals in this region have comparable thermal preferences Consequently, the author suggests a two-phase approach to create an adaptive thermal comfort model tailored for the Vietnamese context.
- First, an adaptive comfort model for people living in hot humid climate South- East Asia is established by reusing the data from earlier field surveys conducted within this region
The developed adaptive comfort model will be validated through a comprehensive comfort survey conducted in Vietnam, utilizing extensive observations and comparing the findings with those from Southeast Asia.
The subsequent sections will describe in detail the two steps mentioned above.
Adaptive thermal comfort model for hot humid South-East Asia
Recent thermal comfort studies utilizing adaptive comfort theory have raised questions about its global applicability due to varying human adaptation across different climates and cultures A meta-analysis by Nicol (2004) of 25 comfort surveys in hot humid climates revealed significant differences in adaptive comfort temperatures compared to temperate or hot dry climates Consequently, there is a need for an adaptive comfort model tailored for hot humid South-East Asia This section details the research methodology, presents the findings, and discusses the development of the adaptive comfort model for this region, while also addressing related comfort issues and comparing various adaptive comfort models.
The adaptive approach to thermal comfort involves analyzing data from field surveys using statistical methods to ensure reliability despite potential errors from various sources To achieve this, a large sample size is necessary for accurate statistics This study employs meta-analysis, as introduced by Glass in 1976, to synthesize results from multiple surveys and develop a robust adaptive comfort model based on a comprehensive database from methodologically sound research It is crucial to refine the data by eliminating inconsistencies and standardizing it While this method has its advantages and drawbacks, as noted by Rosenthal (1979) and Hunter & Schmidt (1990), it remains a popular choice in thermal comfort research involving field survey data, as demonstrated by studies from Humphreys (1978), de Dear et al (1997), Nicol & McCartney (2001), and Nicol (2004).
The comfort surveys selected were based on the following criteria:
(1) Survey locations are scattered around hot humid regions of South-East Asia (climatic boundary instead of political one);
(2) Quality of the survey and subsequently the data was ensured by final research publications;
(3) Raw data file (not only the research reports or publications) created by the original researchers is available
Table 3-1 presents key information from 11 comfort surveys included in this research database All survey observations were compiled into a meta-file in a spreadsheet format for statistical analysis, resulting in a total of 5,176 sets of environmental data.
11 By the classification developed for the Macquarie University undergraduate teaching program in climatology
12 By t he classification system used in the final report of the ASHRAE RP-884 project
Table 3-1: Summary of the field survey database for the present adaptive model
40 subjective observations were included in the database (3430 records in NV buildings) Only
The data standardization process will eliminate 402 observations from the database In comparison to other studies, such as the European SCATs project (Nicol & McCartney, 2001), which includes a total of 4,655 records (1,449 from free-running buildings), this remaining dataset is deemed sufficiently large for a reliable meta-analysis.
In conducting statistical analysis of longitudinal surveys, such as those in Guangzhou and Manila, we treated the responses of all subjects as independent, similar to cross-sectional surveys This approach is based on the assumption that human thermal perception and preference remain stable over time, despite the earliest survey being conducted 25 years ago.
In the ASHRAE RP-884 project conducted by de Dear et al (1997), individual responses were consolidated into a statistical unit for each building, reducing 21,000 responses to 160 buildings Buildings where regression analysis did not achieve statistical significance (P = 0.05) were excluded from the study However, this approach has a limitation: when the temperature range or number of respondents in a building is low, the resulting linear regression may produce an inaccurate model, leading to a mean thermal sensation vote that does not accurately represent the building's thermal environment.
This study consolidated a vast number of building observations into half-degree Celsius increments based on sample size A weighted regression analysis was conducted to establish the relationship between variables, with each scatter point in the graph representing its own weight, indicated by its relative area This approach aims to reduce the influence of outlier bins with fewer observations The advantage of using small temperature ranges (0.5ºC) ensures that the mean thermal sensation vote accurately reflects the thermal environment For instance, the scatter plot of operative temperature (T i,o) against thermal sensation vote (TSV) was streamlined from 3,430 observations to approximately 36 weighted bins Each bin represents the average comfort votes corresponding to a specific half-degree indoor temperature range, meticulously organized using Excel® A strict criterion was applied, accepting only significant weighted regressions with P < 0.01 and a correlation of R² > 0.50.
The comfort studies in the database utilized distinct methodologies, yet predominantly adhered to a similar approach regarding adaptive comfort To facilitate a meta-analysis, data normalization is crucial Information on research methodologies was primarily gathered from official publications and direct communication with the original authors This section outlines the data assimilation process in detail.
3.2.2.1 Consistency in clothing insulation and chair insulation effects
Clothing insulation poses significant challenges in comfort field surveys due to the diverse range of clothing worn by subjects Accurate estimation typically requires a thermal manikin, yet variations in insulation values can occur even in controlled experiments (de Dear et al., 1997) The ASHRAE database utilizes the ASHRAE 55-1992 clo estimation method to standardize clothing insulation values from field surveys In contrast, our recent data collection in Southeast Asia employed ISO 9920-1995, ASHRAE 55-2004, and ASHRAE 55-1992 for clo estimation To ensure reliability, the consistency among these four methods was assessed, revealing that they yield nearly identical results, as they are derived from the foundational research of McCullough and Olesen.
The clo estimation method used across the database was deemed consistent, as indicated by Dukes-DuBos (1988) Additionally, the original authors consistently incorporated an insulation effect for chairs, ranging from 0.1 to 0.15, into the database.
The key calculated parameters include mean radiant temperature (Tmrt), operative temperature (Ti,o), new effective temperature (ET*), standard effective temperature (SET*), predicted mean vote (PMV), and predicted percentage dissatisfied (PPD) These parameters were meticulously verified for consistency, with recalculations performed as needed A PMV-PPD calculator was developed in a Spreadsheet format, utilizing the code recommended by ISO 7730 (ISO, 2005) to facilitate the calculation of PMV-PPD indices in series.
The SET* values were derived using the calculator from Dear (2010), yielding results that were slightly different but acceptable compared to those obtained with Wincomf © in the RP-884 project The operative temperature was recalculated using straightforward equations from ASHRAE 55-2004, which incorporate mean radiant temperature, air temperature, and air speed However, due to insufficient data on measurement instruments and calculation methods for mean radiant temperature (Tmrt), the values provided by the original authors were accepted.
3.2.2.3 Gathering means of outdoor temperature
To establish a correlation between observed neutral temperature and outdoor weather conditions, it is essential to obtain relevant environmental data for each observation The exponentially weighted running mean outdoor temperature (To,rm), utilized in the European SCATs project, is identified as the most suitable index for this analysis However, To,rm necessitates continuous and detailed outdoor condition data, which can only be gathered through specifically designed surveys like the SCATs project.
The monthly mean outdoor temperature, calculated by averaging daily maximum and minimum temperatures, serves as a reliable outdoor reference index This metric is particularly effective in hot, humid regions where weather conditions remain stable and day-night temperature variations are minimal throughout the year In instances where this value is unavailable, historical mean monthly temperatures from official climatological sources, such as the U.S Department of Energy, can be utilized for accurate climate assessments.
2012), was assigned to each observation
3.2.2.4 Refining the data and bias control in meta-analysis
A Chi-squared test was conducted for each regression analysis to determine the statistical significance of the linear relationship between the two variables examined Given the large sample size of this study, a stringent significance threshold of P-value 0.01 was established, as conventional levels (P = 0.05) would lead to the rejection of equilibrium Consequently, any surveys and data analyses that did not achieve this level of statistical significance were eliminated from the study.
Model validation under conditions of Vietnam
The adaptive thermal comfort model, derived from field surveys in South-East Asia, holds significant promise for application in Vietnam due to its central location and comparable climate and cultural context However, it is essential to validate this comfort model scientifically before implementation in the Vietnamese setting.
In another way, this study will examine whether Vietnamese and people living in South- East Asia have similar thermal preference and comfort temperature
3.3.1 The thermal comfort survey in Vietnam
In April, May, and June 2012, a transverse comfort survey was conducted in Danang, Vietnam, over six independent days, with two surveys each month The primary goal was to validate the adaptive thermal comfort model, requiring a substantial number of subjective comfort responses The survey took place in NV classrooms and libraries, allowing participation from numerous university students in Danang Ultimately, over 1,200 students participated, yielding 1,198 qualified responses, all independent, as the students came from different institutions, ensuring uniform classroom conditions to minimize bias in responses.
Class III protocols for followed while measuring the indoor environment Indoor variables measured were air temperature, surface temperature, relative humidity, and air velocity temperature was calculated surfaces and their angle factor was recommended by ASHRAE calculated from air and mean radiant temperature by the of hand held digital instruments was as listed in Table 3-5 and in Figure
The Infrared thermometer HI 9950 and Anemometer LCA6000, while not calibrated due to limited local facilities, were still functioning properly and met standard specifications The HOBO data logger was preprogrammed, and data was compared across three loggers These loggers were positioned on students' working tables for at least 45 minutes before recording data every five minutes, with the recorded values representing the mean of the data collected Additional measurements were taken three times, and average values were calculated accordingly.
Figure 3-11: Measuring equipments used downward arrow indicates the position of the d
In a study involving 57 classrooms, each classroom is expected to yield a distinct mean thermal sensation vote that reflects specific indoor conditions This approach aims to address and eliminate issues typically encountered in field surveys.
Class III protocols for a thermal comfort field study (de Dear, et al., 1997) followed while measuring the indoor environment Indoor variables measured were air temperature, surface temperature, relative humidity, and air velocity temperature was calculated from the measured temperature of surrounding walls surfaces and their angle factors with respect to the occupant’s seat in the class This method
ASHRAE (2009) and Fanger (1982) Operative temperature ed from air and mean radiant temperature by the method of ASHRAE nd held digital instruments was employed to measure indoor environmental variables
The Infrared thermometer HI 9950 and Anemometer LCA6000, though not local facilities, were well-preserved and fully operational HOBO Data loggers were calibrated by comparing data from three units, ensuring accuracy Positioned at a height of 0.85m on students' working tables, the loggers recorded data every five minutes for at least 45 minutes prior to questionnaire distribution The recorded values represented the mean of the measurements, while additional measurements were taken three times to calculate average values This setup aimed to accurately assess the thermal conditions in the classroom and eliminate variability in the mean thermal sensation vote.
The study by de Dear et al (1997) established a methodology for assessing indoor environmental conditions, focusing on key variables such as air temperature, surface temperature, relative humidity, and air velocity Mean radiant temperature was calculated based on the temperatures of surrounding walls and the classroom environment, in accordance with ASHRAE standards (2004) This comprehensive approach allows for an accurate measurement of indoor environmental variables.
The Infrared thermometer HI 9950 and Anemometer LCA6000 were not preserved in the laboratory, but the data loggers were calibrated through preprogrammed settings and by comparing recorded data among three devices Measurements were taken at a height of 0.85m above the floor, with data recorded every five minutes The average values of these recordings, along with additional measurements taken three times, were calculated in the survey conducted in the middle of the classroom.
Name of instrument Measurement range
Resolution Accuracy Country of origin
-10 to 300ºC 1ºC ±2% of reading or ±2ºC
Wind velocity Air flow anemometer LCA
0.1 to 20 m/s 0.01m/s ± 1% of reading or ± 1 digit
A tailored questionnaire was developed to validate a survey requiring extensive participation After completing their courses, students received the questionnaire, where they were instructed to indicate their thermal sensation using the ASHRAE seven-point scale ranging from 'hot' to 'cold' (translated to Vietnamese as ‘nóng’ to ‘lạnh’) Additionally, participants provided personal details including age, gender, weight, and room location A sample of the questionnaire in Vietnamese is illustrated in Figure 3-12 The concise format allowed for completion in approximately two minutes, and students generally expressed satisfaction in participating with minimal need for clarification.
Table 3-5: Technical specifications of measuring instruments
Figure 3-12: Screen shot of the questionnaire (in Vietnamese) used in the survey
3.3.2 Survey data and validation results
Table 3-6: Statistical results of the survey
During 3 months of the campaign, hourly outdoor temperature and humidity were obtained by recorded data from a National Meteorological Station and from a self- manufactured station in Danang city From these data, the monthly mean outdoor temperature can be calculated easily
The survey results and related statistics are detailed in Table 3-6, although some information, such as room number and participant demographics (gender, age, and weight), has been omitted due to space constraints The mean monthly temperature presented is derived from the average daily maximum and minimum air temperatures reported by the National Meteorological Station The survey was structured to examine eight classes each month, conducted around the 10th and 20th, to determine both the overall mean neutral temperature for the entire period and the adaptive comfort temperature for each month.
3.3.2.1 Comparison of Neutral operative temperature
This comparison highlights the similarities and differences in thermal preferences between Vietnamese individuals and those from Southeast Asia Utilizing weighted linear regression, as outlined in section 3.2.1 and considering the sample size, the relationship between operative temperature and thermal sensation votes was analyzed, with results illustrated in Figure 3-13.
Figure 3-13 illustrates the weighted regression analysis between operative temperature and thermal sensation votes in NV buildings across Vietnam Each data point reflects the average thermal sensation vote for different classes, with sample sizes ranging from a minimum of 10 to a maximum of 95 participants.
The correlation observed in the study is significant (P = 0) and robust (R² = 0.7), although slightly lower than that of South East Asia This discrepancy may stem from the survey methodology in Vietnam, which focused on groups rather than individuals, leading to less precise responses Nonetheless, this approach effectively facilitates the collection of a large number of observations and average thermal sensation votes The neutral operative temperature derived from the regression equation is 27.83°C, closely aligning with the South-East Asia figure of 27.91°C, indicating that thermal preferences between Vietnamese individuals and those in South-East Asia are nearly identical.
3.3.2.2 Comparison of predicted and observed adaptive comfort temperature
Long-term evaluation of the general thermal comfort condition
Fanger’s PMV-PPD comfort model effectively predicts occupants' thermal sensations based on immediate thermal conditions The model utilizes the PMV (Predicted Mean Vote) and PPD (Predicted Percentage of Dissatisfied) indices, which have demonstrated reliability in assessing thermal comfort in air-conditioned environments.
The adaptive comfort model for South-East Asia is designed to establish an operative temperature range that ensures thermal acceptability for the majority of individuals, rather than predicting thermal sensation This defined temperature range serves as the foundation for assessing thermal comfort in naturally ventilated (NV) buildings.
To evaluate the thermal conditions of a space over a specific timeframe, such as a month or year, it is essential to utilize the summation of comfort indices This summation can be obtained from either long-term measured values or the results generated by a thermal simulation tool According to the standard ISO 7730, five methods are recommended for this assessment For the purposes of this research, methods A and D from ISO 7730 were selected.
Table 3-7: Comparison between predicted and observed comfort temperature
To assess the comfort levels within a building during occupancy, Method A involves calculating the total hours or percentage of time that the operative temperature falls outside the designated range of the adaptive comfort model This evaluation is crucial for understanding and improving occupant comfort in indoor environments.
- Method D: calculate the mean of hourly PPDs over the occupied period The lower the mean PPD, the better the thermal condition
The choice between method A or D for the thermal comfort model in the building will depend on the specific requirements of the project To ensure precise calculations for these methods, the simulation will be configured to operate at 20 time steps per hour.
Implementation of the adaptive model into a building simulation program
In a recent study, a thermal comfort model's mathematical algorithm was integrated into a building thermal simulation program to evaluate thermal conditions effectively This integration enables building scientists to conduct energy analyses while assessing occupant comfort levels The thesis focuses on evaluating the thermal environments of naturally ventilated (NV) and air-conditioned (AC) buildings, necessitating the selection and implementation of suitable comfort models within a simulation tool For this purpose, EnergyPlus version 6.0 was chosen as the primary building energy simulation tool, noted for its advanced features detailed in section 5.3.1.
EnergyPlus 6.0 offers three 'steady-state' thermal comfort models, including Fanger's model, which integrates the PMV and PPD indices into its outputs This integration enhances the assessment of thermal comfort in air-conditioned buildings.
The latest version 7.0 of EnergyPlus includes the adaptive comfort models from ASHRAE 55–2004 and EN15251, but their absence in earlier versions posed challenges for assessing NV buildings in Vietnam To address this issue, the thesis employed a creative solution by integrating the adaptive comfort model specific to South-East Asia into the EnergyPlus framework.
An HVAC system was installed in a NV thermal zone, designed to operate at an extremely low capacity This configuration ensures that the system's heating and cooling effects do not impact the thermal environment or the energy consumption of the zone.
- The thermostat of the HVAC system was established at upper and lower bounds of the comfort range given by the adaptive comfort model
The EnergyPlus output dictionary provides critical data on thermal comfort, specifically through the metrics 'Time heating setpoint not met' and 'Time cooling setpoint not met.' These metrics are only applicable when a thermal zone is equipped with an HVAC system They indicate the total hours during which the zone's temperature deviates from the thermostat setpoints, highlighting the duration of thermal discomfort experienced in that space.
With these techniques, EnergyPlus can solve all the questions that this research has to deal with Tested simulation runs indicated that the results were quite satisfied.
Chapter conclusion
This chapter explores thermal comfort models specifically tailored for the Vietnamese context, focusing on their application in air-conditioned (AC) and naturally ventilated (NV) buildings It examines both the steady-state comfort model and the adaptive comfort model, recommending their use in assessing thermal environments Notably, Section 3.1 highlights the Fanger comfort model from 1970, which is selected for implementation in AC buildings due to its robust scientific backing.
Section 3.2 presents a full description of an adaptive comfort study for South-East Asia Meta-analysis was performed on field observations collected from field surveys conducted around South-East Asia While some studies assumed a minor role of “Griffiths constant” in the establishment of the adaptive comfort equation, this thesis gives proofs of its crucial role Consequently, it must be chosen with much care The adaptive equation obtained from the present study is rather similar to some other standards although the methods used were not identical The resulted comfort equation is:
The study indicates that in high temperature and humidity conditions, adaptive actions are less effective, resulting in a narrower comfort range compared to more favorable climates A statistically significant correlation was found between temperature, wind velocity, and clothing insulation, providing strong evidence of occupants' adaptation In hot and humid environments, the neutral ambient temperature is notably affected.
NV buildings is nearly 2ºC higher than that in AC buildings However, the same neutral SET* in these buildings gave some proofs that this deviation mainly came from various
65 behavioral adaptations of occupants Under favorable conditions, the difference between neutral operative temperature in NV and AC buildings might become minor, as the case of Guangzhou in mild seasons
Under standard conditions—specifically, at sea level with 50% relative humidity, still air at speeds of 0.1 to 0.15 m/s, and typical clothing for specific activities—the neutral standard effective temperature (SET*) in naturally ventilated (NV) and air-conditioned (AC) buildings ranges from 25.5°C to 25.7°C This consistency suggests that individuals in South-East Asia and globally share similar thermal preferences Variations in neutral operative temperatures may arise from different adaptive behaviors of occupants in NV buildings.
This thesis rigorously analyzed the correlation between predicted PMV and actual TSV in NV buildings, ultimately advising against the use of the PMV-PPD model for similar comfort studies, even with potential adjustments.
In section 3.3, the adaptive comfort model was validated through a field survey conducted in Vietnam during April to June 2012, comparing the mean neutral operative temperature and adaptive comfort temperature of Vietnamese individuals with those from South-East Asia The validation results demonstrate that the model is effective for application in Vietnam Additionally, a unique technique was successfully implemented to integrate this adaptive comfort model into the EnergyPlus 6.0 program, enabling long-term thermal comfort evaluations in NV buildings.
Our observations in NV buildings indicate that the mean outdoor temperature typically ranges from 24ºC to 30ºC To enhance the validity of these findings, further studies should be conducted in environments with temperatures below 24ºC or above 30ºC These additional surveys would provide more reliable evidence regarding thermal sensitivity and its correlation with varying temperature ranges and outdoor conditions.