This Chapter provides an overview of the backgrounds for energy
consumption, façade design, natural ventilation and thermal comfort issues in high-rise commercial buildings in the tropics, and set out the research
questions, scope and methodology of the research and the structure of the Thesis.
1.1 Introduction
The amount of energy used and spent in the modern world has been escalating in an alarming way. Air-conditioning accounts for the major portion of the total energy consumption used for the operation of most of the present high-rise buildings. The situation is even more alarming in the case of high-rise buildings in a hot and humid climate where greater energy consumption is desired to provide comfort in the man-made environment. However, the call for energy efficient building design is growing and the situation is particularly critical for the design of office buildings, because the energy consumed by this building type constitutes the most energy usage intensive built environment within the building industry sectors.
This thesis seeks to find a design solution for reducing the energy usage in office buildings, in particular those in the tropics. There are numerous methods and techniques that can be employed to achieve the purpose of designing an energy efficient building and the latest development in façade technology of double-skin façade system claims to be able to reduce energy usage
substantially by allowing natural ventilation especially for commercial buildings. With that in mind, the thesis explores the viability of double-skin façades in providing natural ventilation as an energy efficient solution for office buildings in a hot and humid environment.
Double-skin façades (DSF) are multiple layer skin constructions, with an external skin, an intermediate space and an inner skin. The external and
internal skins can be either single glaze or double glazed glass panes of float glass or safety glass. An adjustable sun-shading device is usually installed in the intermediate space for thermal controls. This research has involved the study of various types of DSF used in office buildings, and the behaviour of airflow and thermal transfer through the DSF, and the internal thermal comfort levels are analyzed through the use of computational fluid dynamic (CFD) simulations.
1.2 Sustainable development
Environmental damage and current climate change concerns are directly linked to human activity. The economic blueprint for industrialised societies was first publicly questioned in 1968 by the newly founded international think-tank, the Club of Rome. In 1972 members of this group published the now-famous report, “The Limits to Growth”, putting forward the idea that economic development must be combined with environmental protection. In 1984, the United Nations Assembly gave the then Prime Minister of Norway, Gro Harlem Brundtland, the mandate to form and preside over the World
Commission on Environment and Development, also known as the Brundtland Commission. The work of the Commission led to the release in 1987 of the report entitled Our Common Future, also called the Brundtland Report, which popularized the term ‘sustainable development’ and its definition as ‘ meets the needs of the present without compromising the ability of future generations to meet their own needs’. Today the Commission’s work has been recognized for having promoted the values and principles of sustainable development.
At the 1992 Rio Earth Summit, heads of states committed their nations to exploring ways of achieving “development which fulfils current needs without
and social factors. This concept of sustainable development is based on three principles:
- Consideration of the “whole life cycle” of materials
- Development of the use of natural raw materials and renewable energy sources
- Reduction in the materials and energy used in raw material extraction, product use and the destruction or recycling of waste
The Kyoto Summit in 1996 was designed to achieve more concrete measures after the Rio Summit’s emphasis on social and cultural factors. Under the Kyoto Protocol, participating nations pledged to bring average greenhouse gas emissions over the period 2008 to 2012 back to 1990 levels. To keep to this agreement, the industrialised countries need to make progress in three areas:
- Reductions in energy consumption
- Replacement of energy from fossil reserves by energy from renewable sources
- Carbon storing
The principles of the Rio Declaration are connected with the formulation of a development plan for the 21st century, known as Agenda 21. The
recommendations in Agenda 21 are:
- protection of the earth’s atmosphere
- integrated land-use planning and management - combating deforestation
- preservation of fragile ecosystems
- promotion of sustainable development in a rural and agricultural context
- maintenance of biodiversity
- an environmentally rational approach to biotechnology - protection of the oceans and coastlines
- protection of water supplies and quality
- environmentally acceptable treatment of waste, including toxic chemicals, radioactive and other dangerous waste, solid waste and waste water
In 2002, the World Summit on Sustainable Development, or commonly called Earth Summit 2002, was help in Johannesburg, South Africa. The participating nations had renewed their commitment to the principles defined in the Rio Declaration and the Agenda 21 objectives. They pledged to develop national sustainable development strategies to be implemented before 2005.
Implementation of the measures agreed at Kyoto has wide-ranging implications in terms of land use, urban planning and architecture. The attempt to reduce the consumption of energy and natural resources, bring down greenhouse gas emissions and produce less waste will have a particularly significant impact on the building and civil engineering sectors.
The application of sustainable development principles to building is one of the most efficient responses we have to the need to reduce greenhouse effect and the destruction of our environment. Such a response is based on three
complementary, closely linked tenets:
- Social equity
- Environmental caution - Economic efficiency
1.3 Energy consumption in commercial buildings
Global consumption of primary energy to provide heating, cooling, lighting and other building related energy services grew from 86 exajoules in 1971 to 165 exajoules in 2002. This is an everage annual growth rate of 2.2% per year (Price et al., 2006). Energy demand for commercial buildings grew about 50%
faster than for residential buildings during the same period.
conditions, and behavioural factors. The rapid urbanization that is occurring in many developing countries has important implications for energy consumption in the building sector.
The two most important sources of energy demand in the U.S. commercial buildings are space heating, ventilation, and air conditioning (HVAC) systems, which accounted for 31% of total building primary energy use; and lighting, which accounts for 24% of total building primary energy use (USDOE, 2005).
The results for large commercial buildings in many other countries are thought to be similar to those for the United States, although no such statistical
breakdown is available for other IEA member nations or for the developing world.
The above statistic has called for a great attention to reduce energy usage for commercial buildings to in turn reducing the emission of Green House Gases.
This is also the thought behind the aims of this Thesis to focus unto proposing an effective way to reduce energy consumption of office buildings in the tropics to give a ‘little’ contribution to the building sector.
1.4 Air conditioning in office buildings and human comfort
The Larkin Building built in 1960 at Buffalo, USA by Frank Lloyd Wright is thought to have been the first air-conditioned building in the world where cooled air was pumped into the building via specially designed air-ducts. The popularity of the International Style that followed saw the upsurge of buildings with strong geometric forms, with an emphasis on large windows and a curtain wall system.
This preferred style at that time, and the advances in technology caused the dissociation of the buildings’ indoor environment from their surrounding climate. An office building which is not constrained by daylight, ceiling height
and plan depth could have a deeper plan, lower ceiling height and greater floor-to-envelope ratio, which has a great impact on the occupants and the effect on human comfort is tremendous.
1.5 Façade design for office buildings
The late 19th century saw a time of accelerated economic growth that led to a global building boom. Real estate values skyrocketed, especially in the city center areas and together with the advancement of building technology like steel skeleton construction and the invention of elevators, this led to the creation of the first high-rise building. Skidmore, Owings and Merrill (SOM) in New York achieved the ‘true’ curtain wall system for office buildings during the middle of the 20th century. Since then, glass curtain wall buildings have appeared everywhere, under the influence of the so call International Style, until in the late 20th century office buildings with glass façades had become a normal feature in all the cities around the world and the building facades for our offices had degenerated into monotonous surfaces.
Since the awareness of the need for energy efficiency increased dramatically in the wake of the oil crisis of the 1970s, the design of smooth glass containers for most of our office buildings, which rely heavily on artificial means to provide an acceptable internal environment, has come under intense scrutiny. The building façade has become even more increasingly important in recent years in the areas of research and development as a result of growing awareness of the importance of sustainable living. High-rise buildings are within the critical category, as more than 80% of the façade for these types of building are constructed using some sort of glazing for their envelopes. The urgency to improve the energy usage of our ‘glass-box’ office buildings with original
required external energy to enter the indoor environment but at the same time to expel any unwanted built-up heat within it. The present technologies have allowed very complex façade systems to be developed and to function
according to the clients’ requirements so as to dramatically reduce the energy usage of large buildings.
The availability of technologies, the desire for an all-glass facade and the commitment to improve the energy usage of large buildings had lead to the development of double-skin façade, which originally is a European Union architectural phenomenon believe to be able to improve indoor air quality through natural ventilation without the acoustic and security constrains of naturally-ventilated single-skin facades.
1.6 Energy consumption for office buildings in Singapore
The 2000 World Competitiveness Yearbook, complied by the World Economic Forum (WEF), ranked Singapore 25th out of 45 countries in terms of energy intensity or the amount of commercial energy consumed per dollar of GDP.
This could be due to the fact that Singapore depends heavily on
air-conditioning to cool its buildings all year round. The hike in recent oil prices and the global decline in the supply of fossil resources, together with the growing international concern about carbon dioxide emissions and greenhouse effects, have all resulted in a call for an effective use of energy resources.
The 1998 Kyoto Protocol of the United Nations Framework Convention on Climate Change, to which Singapore is a signatory, established a legally binding obligation on the developed countries to reduce their emissions of carbon dioxide and other greenhouse gases by an average of 5.2% below 1990 levels by the years 2008-2012. Singapore’s energy consumption growth over the period 1980-1995 was 11.9%. The average annual growth in GDP over the same period was around 7.6%. All this means that Singapore will come under
increasing international pressure to reduce its CO2 emissions and to directly lower its energy consumption.
Energy consumption in Singapore can be attributed to the three main sectors of industry, residential and commercial buildings, and transport (Figure 1.1). In the hot and humid climate of Singapore, most of the electricity consumed in buildings goes towards air-conditioning and refrigeration, especially in work places like commercial and institutional buildings, which are mostly designed to be fully air-conditioned. Figure 1.2 shows the distribution of electricity consumption in the building sector, with commercial and industrial buildings constituting close to two-thirds of the total electrical energy consumed.
Energy Consumption in Singapore by Sectors
29%
34% 37%
Transport
Industries
Buildings (Residential/
Commercial)
Figure 1.1 Energy consumption by sectors (Source: Power Supply Pty Ltd)
Electricity Consumption in the Building Sector
18%
25%
57%
Public Residential Buildings
Private Residential Buildings
Commercial/Industrial Buildings
Figure 1.2 Electricity consumption by sectors (Source: Power Supply Pty Ltd)
1.7 Natural ventilation and indoor environment
Most vernacular buildings in the world were naturally ventilated designed, even though some of the buildings have been compromised by the additions of internal walls and mechanical systems. Natural ventilation has become an increasingly attractive method for reducing energy use and costs, and for providing acceptable indoor air quality in order to maintain a healthy,
comfortable and productive indoor climate. In favorable climates and building types, natural ventilation can be used as an alternative to air conditioning plants with savings of 10%-30% of total energy consumption.
However, using natural ventilation to prevent overheating within a building presents a great challenge to maintaining acceptable indoor air quality (IAQ) standards. Controlling indoor air quality appears to be more of a concern during winter periods when interior spaces need to be heated to provide
acceptable thermal comfort and most of the windows in a building may be closed. The control of airflow rates then becomes the ultimate consideration.
For summertime cooling, important considerations are internal heat loads, external solar gains, building characteristics such as thermal mass and insulation levels, the overall building floor area, and site layout. Controlling airflow rates is not as much of a concern here, as long as the occupants are comfortable. The higher the airflow rate the greater the cooling effect.
1.8 Thermal comfort standards
There are a number of international thermal comfort standards that have make substantial contribution to the knowledge of thermal comfort. The main
thermal comfort standard is ISO 7730, which is based upon the predicted mean vote (PMV) and predicted percentage of dissatisfied (PPD) thermal comfort indices (Fanger, 1970). The standard also provides methods for assessing the local discomfort caused by draughts, asymmetric radiation and temperature gradients. Other thermal comfort standards include ISO 8996, which describes six methods for estimating the metabolic heat production and it is an important requirement in the use of ISO 7730 and the assessment of thermal comfort. ISO 9920 provides a database of the thermal properties of clothing and garments that based upon measurements on heated manikins, and ISO 7726 supports thermal comfort assessment with measuring instruments.
Thermal comfort research carried out in Europe and the USA during the mid-20th century was mainly concentrated on using climate chamber studies. The thermal comfort standards of ASHRAE Standard 55, Thermal Environmental Conditions for Human Occupancy, were first established in 1966. Since then,
body. Six key variables were identified as affecting the perception of thermal comfort, namely air temperature, radiation, relative humidity, air movement, clothing and metabolic rate. The standard attempted to provide an objective criterion for thermal comfort by specifying personal and environmental factors that will produce acceptable interior thermal environment for at least 80% of a building’s occupants. The standard defined thermal comfort as ‘the condition of mind which expresses satisfaction with the thermal environment and is assessed by subjective evaluation’ (p. 2). It also defines thermal sensation as a conscious feeling, commonly graded into categories of cold to neutral to hot.
The ASHRAE Standard 55 was originally developed to provide guidelines for centrally controlled HVAC (Heating, Ventilation and Air-Conditioning) systems. The general application of the standard has limited the efforts to develop more person-centered strategies for thermal control in naturally ventilated or mixed-mode buildings. Such strategies may provide important social and environmental benefits through energy consumption reduction and increase occupant satisfaction and work efficiency, especially in office buildings.
1.9 Adaptive thermal comfort model and natural ventilation in buildings
The primary limitation of the original ASHRAE Standard 55 is its “one-size-fits-all” approach where clothing and activity are the only modifications one can make to reflect seasonal differences in occupant requirements. The standard has allowed important cultural, social and contextual factors to be ignored which lead to an exaggeration of the “need” for air conditioning in indoor environment. In view of the standard limitation, many researchers argued that the level of occupant satisfaction with indoor environment and the energy consumption of buildings could be reduced if we allowing people greater control of their indoor environments. This has lead to the development
of adaptive thermal comfort model with consideration for naturally ventilated buildings.
The latest ASHRAE Standard 55 -2004 has incorporated the adaptive thermal comfort model with an analytical method based on the PMV-PPD indices and the introduction of the concept of adaptation with a separate method for naturally conditioned buildings. The standard is intended for use in design, commissioning and testing of new or existing buildings and other occupied spaces (residential or commercial) and their HVAC systems.
One important criterion in applying an adaptive model for thermal comfort like ASHRAE Standard 55-2004 is the possibility of individual control. Occupants of naturally ventilated buildings have possibilities for changing the air velocity in the indoor environment by operating the windows and can often create an acceptable environment even with a relatively high indoor temperature.
Psychological adaptation also plays an important part in naturally ventilated buildings because the occupants have a more direct contact with the external weather, and higher temperatures are expected for the indoor environment.
1.10 Thermal comfort analysis and double-skin façades
A number of interesting investigations and findings are reported in the literature pertaining to passive ventilation in buildings and the thermal performance of double-skin facades. Even though most of the research has been done in temperate conditions, it has revealed a close link between natural ventilation design and the function of a double-skin façade.
Grabe et al. (2001) developed a simulation algorithm to investigate the
similar natural convection ventilation studies. Most of these have used the concept of stack effect or the solar chimney and found that passive ventilation in summer is possible even for multi-storey buildings. In particular Priyadarsini et al. (2003) have established the energy efficiency of a stack system used in residential buildings in a hot and humid climate region. Li and Delsante (2001) went a step further to investigate the effects of natural ventilation caused by wind and thermal forces in a single zone building with two openings.
Ventilation graphs are plotted using the air change parameters (thermal air change, wind air change and the heat loss air change) for design purposes.
Gratia and Herde (Gratia and Herde 2004) also attempted to look at the impact of double-skin façade facing a southern direction in a temperate climatic condition. Thermal analysis using simulation software for the different seasons of a year was done for a low-rise office building with and without double-skin façade. It was found that significant energy saving is possible if natural
ventilation could be exploited through the use of a double-skin façade.
1.11 Research questions
Natural ventilation strategies and double-skin construction are not new
Natural ventilation strategies and double-skin construction are not new