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Meeting Energy Demands of the Growing Population

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Literature review

Nowadays, an important factor for economic and social development is energy sufficiency. Energy is the fuel of growth. Scientist's predictions show that by the year 2050, energy demand will increase significantly due to the fact of the increasing population of the earth and that more buildings are going to be constructed. (Ref: Facts and trends, energy and climate, world business).

A lot of predictions are published about how fast the population, the economy and the energy consumption of the world will increase in the years and decades to come. In reference to the matter of growth, development and energy demand, most of the predictions were wrongly made. Most predictions are reciprocally dependant on each other, and each one relies on many other factors. However, the only prediction that can be securely made is for the population and that "the growth will be larger in the less development countries than the developed countries". (UNITED NATIONS) Developed countries are managing to improve the living conditions and decrease the death rates, but at the same time the birth rates have been decreasing at about the same rate over the last century. By this way the population growth is around 0.4% per year, in the industrialized world. On the other hand, less developed countries are managing their development and as a result have increased birth rates and decreased death rates. Consequently, their average population growth has increased from about 1% per year, from fifty years ago to about 2.1% per year today. At the moment, the world's population is increasing at an annual rate of 1,7%, whereas the population in developed countries is around 1,2 billion (25% of the total) and in less developed countries is around 4 billion (75% of total world population). (United Nations)

Population increases are directly connected with the energy demand and the building sector. It is therefore essential to develop new energy technologies on a massive scale for everyone to be able to survive on this planet. Ordinary buildings are unable to contribute to these essential needs, and cover the gush of the energy demand which is going to follow over the next decade.

Energy use and climate impacts

Power plants use fossil fuels for their energy productions and therefore this way cover the energy demands of the people. As a consequence though, from the burning of the fossil fuels, green house gases are produced and emitted into the atmosphere. As mentioned in the introduction, these anthropogenic activities have a significant contribution to the green house effect and the climate changes.

Generally, in reference to the climate changes issues, scientist's opinions are split into two. On the one hand, it is believed that the changes are part of the earth's life and it is something normal which has been accelerated by our human activities and there is a possibility to stabilize the climate changes. On the other hand, it is believed that these changes are not normal and are going to make the world uninhabitable. For this reason, fast and immediate actions should be taken by all countries, targeting to reduce the energy demands and green house gases. It is almost definite that any of these actions will have a deep impact on the economy of each country.

Many people believe that energy saving, means diminishing the current quality of living and reducing economy activity. In addition, economists believe that without economic growth, investments on technology will be reduced as it will difficult to confront climate changes. On the other hand, scientists argue that technological development is the key to the solution in reference to the climate changes problem. The truth is that, any solution in reference to climate changes will need an effort from everyone and investments on technological research and development, giving us this way a chance for a better future!

IPCC's fourth assessment report further concluded that the building sector is not only the largest potential for significantly reducing greenhouse gas emissions, but also that this potential is relatively independent of the cost per ton of CO2 eqv. achieved. With proven and commercially available technologies, the energy consumption in both new and old buildings can be cut by an estimated 30-50 percent without significantly increasing investment costs. Energy savings can be achieved through a range of measures including smart design, improved insulation, low-energy appliances, high efficiency ventilation and heating/cooling systems, and conservation behaviour from the buildings users. (Reference- IPCC's fourth assessment report)

Summarising the above it is obvious that the population growth, economic development, human habits, way of living and environmental restrictions influence the energy demand around the world. Scientists and in general, the governments who are trying to give solutions to the big problem of the growing energy demands and its consequences, have to take into account all of these factors.

Reshaping the energy future

It is necessary for all countries to reshape the future of energy, as all scientific researches show. The actual word reshape, includes new innovation technologies and sources which are going to contribute to the energy needs of the world. It is necessary to find new paths which are further environmental friendly and will permit a better future.

A lower carbon world is feasible in the next decade even during the next few years, if all countries can realize that significant changes that should be done. This especially applies to the developed countries as they have to reconsider and find a link between the quality of life and their energy consumption. It is necessary for everyone to understand that a high standard of living does not demand a high consumption of energy and to adapt to the new energy sources.

The good news is that small changes in the energy scenery are now visible as many have started to be influenced. For example, the raised use of gas, the use of renewable energy on buildings, everyday life and high efficiency cars are some of the small steps that have been offered to people due to technological development. As figure three shows, the IPCC scenarios (A1B-AIM and B2-AIM) were based on the new technological achievements in the energy sector. It is definite that this evolution is not enough for our earth's climate but the two scenarios predict a possible CO2 stabilization. Finally, efforts to create an energy efficient world are starting, in reference to low carbon technologies and effective measures. (Reference-world business ...facts and trends on climate change)

As stated in the report of the World Business Council for Sustainable Development (WBCSD) 'a lower carbon world would require a marked shift in the energy/development relationship, such as similar development levels to be achieved with an average of 30% less energy use. Both energy conservation through behavioural changes and energy efficiency via technology plays a role. Such a trend is a feature of the IPCC B1 storyline, which sees a future with a globally coherent approach to sustainable development. It describes a fast-changing and convergent world toward a service and information economy, with reductions in material intensity and the introduction of clean and resource efficient technologies. The scenario leads to relatively low GHG emissions, even without explicit interventions to manage climate change.'(Reference Energy and climate change, world business)

A Sustainable World Energy Perspective

An important key to the world's energy problem is sustainable development. Sustainability includes the economic and technological development, which respect and protect the environment. Searching literature for an exact definition of sustainable development, guided us to the 'The Brundtland Report' of the UN World Commission on Environment and Development. In this report a definition of sustainable development, is given: 'Humanity has the ability to make development sustainable – to ensure that it meets the needs of the present without compromising the ability of future generations to meet their own needs'

However it is difficult to find exact definitions which represent the sustainable development accurately, due to the fact that it is an idea which involves too many parameters. (Reference Engineering_for_Sustainable_Development)

It is amazing to see how the sustainable development concept, stays on important issues of discussion even with the passing of tweedy years from the Brundtland report. In this concept, development faces three important paths: the economic, the social and the environmental (figure 4). If governments want to meet these targets it is necessary to carry out innovative technologies and a socio-economic approach.

Nevertheless, sustainable development is not the only problem and therefore it is always important to consider the three major paths. Protection of the environment, economic success and improvement of social conditions, will be the achievements of a flourishing sustainable development. These three paths are linked together for a sustainable development and their integration must be equal without any compromises.

The goal of sustainable development is, to point out the importance of the environment to the public who are now alive and for the coming generations. It is important for everyone to understand that our existence depends on the global environment and every decision of this generation is going to affect the lives of our future generations. Thus for this goal to be achievable, it is necessary to take measures for low green house emissions, use renewable sources and improve the energy consumption of our current lives. Governments and engineers are searching for the best way to come within reach of this goal as it is very difficult for developed and developing countries to achieve it.

Presently, the building sectors involvement is essential because of its deep impact on energy consumption, its significant emissions and its use of huge natural sources. The buildings that currently exist will continue to exist, for more than 30 years and therefore this influences the lives of future generations. A sustainable approach of this sector is necessary due to its rapid growth. The new approach for the buildings sector will include buildings which will need less energy to operate, produce low carbon emissions, use environmental friendly materials and produce their own energy from renewable sources. It is almost definite that the sustainable green development of the building sector will help countries accomplish the targets of the Kyoto Protocol, whilst also guarantee at the same time, the future for coming generations.

Evolution of the buildings and the opportunity for change.

As believed by many, 'buildings are our third skin' and this plays an important role for humans to survive. From the beginning of human history, human's always aimed to try and protect themselves from all weather conditions and all changes, developing due to this, different kinds of shelters. Over the years, human's adapted and managed to survive all the different changes that have happened on earth. The question now, is what will happen whilst we are facing the rapid climate changes and what will be the future consequences?

Hundreds of thousands year ago, people moved from place to place and tried to create the best conditions to live in. Depending on the place, whether hot or cold, human's developed different kind of shelters to protect themselves from the heat of the sun in the deserts, or the cold of the northern climates. Studies of these people movements over the years, shows us a big variety of shelters and developments of different ways in order to face the climate conditions.

Other factors, which determine the human's survival techniques in extreme conditions from the past, like the lower attitude of the Arctic Circle, were the design of the buildings, the quality of clothes and the behavioural adaptations, like changing posture, activity level sand choosing the most comfortable space to occupy, by moving around rooms and buildings and landscapes; and then of course the use of energy from the burning of fossil fuels or the careful use of stored energy in heat or cold stores. (Adapting building & cities for climate change)

Another extraordinary point from past decades is the energy issue. People mainly used coal, wood and water to provide themselves with enough energy, whether in a passive or active manner and covered in this way, their need for heating or cooling. By taking advantage of the natural and available energy resources, humans managed to develop houses which were ready for all extreme weather conditions. All these extreme weather conditions made humans innovate new approaches for buildings, and provide them with a more comfortable life.

An interesting approach of surviving all the climate changes is to move to different areas at the respective time of the year, which is when they are comfortable, and to leave them again when they are not – to migrate. (Adapting building & cities for climate change) This approach is an impossible one to apply, in the modern way of life and the new cities. Nevertheless what could be extracted from the past is the expertise of the ancient people and the way they faced the climate changes. In our day and age, engineers and scientists use the knowledge from the past whilst at the same time search for new innovative approaches for the buildings.

The evolution of the buildings sector involves the innovation of new technologies whilst the same time, protecting the environment and its natural sources. It is not just a matter of how to build or what to build but it is also a matter to make the buildings adaptable to the new challenges of the climate changes and energy efficient. This evolution is directly connected with the world surviving because buildings are part of the global environment which at the moment is in danger.

As written in the book titled 'Adapting Buildings and Cities for Climate Change' 'the risk of not surviving in a particular building type and region will be largely dependent on the nature of that building and on how much the climate changes. Both are crucial in the challenge of designing buildings today in which people can be comfortable in 50 years' time'.

At the point where the evolution of the building sectors began, there are great opportunities to change the current negative predictions of the climate changes. Significant reductions on energy consumption, better design, adequate technology and appropriate behaviours are some of the keys points which could accomplish the transformation of the buildings sector (figure 7). This transformation needs the participation and contribution from the businesses, the markets, the politicians and engineers. All together, they must act right away because the use of renewable sources is slowly growing and the energy demand is rapidly increasing, setting this way, tight deadlines in order to transform the sector. As it is mentioned in the Energy Efficiency, Buildings report and the IPPC 4th Assessment report, Residential and commercial buildings, 'action is essential as part of the world's response to climate change because energy use in buildings is 30-40% of final energy consumption and carbon dioxide emissions in most countries'. (Reference- Energy Efficiency in the Buildings report and the IPPC 4th Assessment report, Residential and commercial buildings)

There are many opportunities to transform the buildings sector into the new era, as well as being feasible and applicable for old and new buildings. Significant energy reductions can be achieved by using new technologies, e.g. energy efficiency appliances, low consumption cooling systems etc, use of renewable sources, better design and operation and use of environmental friendly materials. Using these methods it will be possible to reduce the energy demand of up to two-thirds. 'Low-energy buildings must become the norm rather than the novelty project'. (Reference- Energy Efficiency in the Buildings report)

Beyond the opportunities given to change the buildings sector and stabilize the climate changes, this transformation will additionally contribute to the economy growth by giving new opportunities for jobs and businesses. (Reference- Energy Efficiency in the Buildings report)As already mentioned, the transformation will only succeed in the case where, building energy becomes a high priority to the governments and businesses leaderships, whilst cooperation between engineers, businesses and authorities is also established in reference to this issue.( Reference- Energy Efficiency in the Buildings report)

Buildings types: characteristics and profiles

Around the world, a vast variety of different types of buildings can be found, and each different type covers multiple and different needs. It is therefore essential at this point, to present the different types of buildings, as this report will focus on the buildings sector and the energy demands. Despite the fact that in the literature review, it is possible to find a plethora of terminology of the building types, nevertheless the general idea of this separation, of the buildings into categories is the same. Usually the separation of the buildings is a result of its use.

It is very important to additionally mention at this point, that in most countries, many of the buildings were built before any energy regulation and these buildings will be around for at least the next 40 years. As figure 8 shows, in Europe, 50% of the buildings were built before 1975.

Residential Buildings

Residential buildings are commonly found all over the world. However, big and small differences can be found in all of them depending on the climate varieties of each country. For example, in hot climates the important need is for cooling and keeping the temperatures comfortable all over the house. This is achieved by the use of control systems, high insulation materials, shading systems and double or triple glazing. Additionally, this way, the energy demands and cost stays under control. In addition, a high use of passive or active solar systems is found in these hot climate countries. On the other hand, buildings in the cold climates have different needs to achieve temperature comfort. In these climates, the need for heating is essential but this is directly related with other parameters, such as low emissivity windows, good insulation materials and good design. It is very important in these climates, whilst designing, to consider the thermal mass of the building, as this may contribute during the night to the heating. (Low-Energy Building Design Guidelines)

Where residential buildings are concerned, it is easy to use renewable sources and cover the energy needs of a house because the demand is not so big. For example, photovoltaic systems can be used as the main source of energy, minimizing the CO2 emissions and the operation costs of the building.

Non-Residential Buildings

Non-Residential Buildings are also commonly located all over the world. In contrast with the Residential buildings, these kinds are appropriate for extreme hot or cold climates, without any access to utilities. As it is described in the Low-Energy Building Design Guidelines report of the U.S. Department of Energy these building types 'have a natural connection with the outdoors; and the structures present an opportunity to interpret the resource-conservation mission of the agency to the visiting public. These structures typically combine a need for window area, massive construction, and a tolerance for temperature swings—all of which are highly compatible with low-energy building design. Day lighting is another key strategy for deployment in these building types'. (Low-Energy Building Design Guidelines)

However, the energy balance of a Non-Residential building is almost independent, from lighting and internal gain. A great opportunity on these kinds of buildings, is to apply the low energy methods and design, due to the fact that such buildings have low energy consumption. A visitor centre is a good example, of this kind of building, and usually they have big budgets allowing the choice of high tech materials and technologies. (Low-Energy Building Design Guidelines)

Urban Office Buildings

Urban office buildings are usually located in the city centres because these buildings offer public services, to the people. As known, urbanization in most countries carries negative consequences for the city centres, for example, expensive land prices.

Due to this fact, the design and use of these buildings must be compact and offer the maximum possible. The use of the building is generally defined by the services that are offered, and the space is then separated into offices and support facilities. (Low-Energy Building Design Guidelines)

Quite frequently, another characteristic of office buildings is their old style, as well as other restrictions, due to the fact that many countries conserve the old buildings in the city centres. Thus the changes for energy conservation or better energy performance on these buildings are limited and therefore it is difficult to apply low energy strategies. In addition, the development of the surrounding area and the high tower new buildings are an important factor, which influence the energy performance of an office building due to the shade provided. (Low-Energy Building Design Guidelines)

On the other hand, new urban office buildings have a great opportunity to save energy as new technologies and design can be afforded and are significant potentials. Another point which helps low energy designs to be applied on office buildings is the wide use of curtain walls, mainly in most of the downtown buildings. The problems which can occur from the use of this kind of buildings is lack of thermal comfort, lack of orientation and the overuse of glass enhance low energy buildings design. New approaches on the office buildings, has started to be applied and they are getting transformed into high technology buildings, which offer better services to the people who work there.

A key factor of successful low energy office buildings is the placement of the private office at the back side of the building. As a result of this design, the artificial lighting will be reduced as natural lights are directed further into the buildings. This will have a significant impact not only for energy demands but also to the HVAC systems. Nevertheless, Urban Office Building's demand a careful design which takes into account the climate, the orientation, the facade design, the HVAC, shading from the surrounding buildings and the complex interactions amongst lighting. (Low-Energy Building Design Guidelines)

All the above types of buildings constitute the common categories that serve the different human needs. However, there are many subcategories which are adapted specifically for each different climate and different needs.

Energy impacts of the buildings

The energy impacts of a building, is a very important factor to consider, in order to succeed with the design of low energy buildings. The different types of buildings and the differences between their energy demands, is the key for the development of zero energy buildings. As mentioned before, each type of building is designed for a specific use and to cover different needs.

Starting with the residential buildings, studies show us, greater energy consumption than the commercial buildings. The report includes six different regions which are Brazil, China, Europe, India, Japan and the United States. During this report the residential sector is divided into two categories, consisting of the single family and the multi-family buildings, this way being able to focus on the energy performance for each case. (Reference- energy efficiency in buildings –market)

Consumption Survey; Federcasa, Italian Housing Federation (2006), Housing Statistics of the European Union 2005/2006; Statistics Bureau, Ministry of Internal Affairs and Communications (2003), 2003 Housing and Land Survey (Japan); EEB core group research) (Reference- energy efficiency in buildings –market)

As the above figure shows (figure 9), single family buildings are more common in Brazil, India and the United States, in contrast with China, Europe and Japan where the single family buildings are at the same level as multifamily buildings. It is possible that in a few years, this global scenery will change and more multifamily buildings will be required, due to an increasing population of the earth and the growing urbanization in big countries. On the other hand, the development of the countries and economies will allow more people to get richer and own a single family house. (Reference- energy efficiency in buildings –market)

Generally, the residential buildings tend to increase the energy demands all over the world. Unfortunately, the modern way of life "includes" extra comforts which are offered by the high technological appliances and the bigger buildings. As the quality of life increases, the energy consumption grows and more natural sources are needed to cover these human needs. Nevertheless, the energy demand is changing from country to country, as the climate and economy growth, are affecting peoples habits. (Figure 10)

The above graph shows us that in six different regions, the economic growth and the climates have different impacts on the energy consumption of each country. For example, space heating is essential in Europe and China, in contrast with Japan and India where the use is low. Additionally in Japan, water heating is very important, whilst in other countries not so much. Another important point to notice on this graph, is cooking in India, as many areas do not have access to electricity therefore their main energy use, is cooking. (Reference- energy efficiency in buildings –market)

Amongst the residential buildings, one big subcategory is the single family buildings. (Figure 11) All around the world, single family buildings have the greatest impact on energy consumption and CO2 emissions. In the developed countries, people tend to consume more energy at their homes, as they demand more comfort and have bigger spaces, better heating and cooling systems, artificial lighting and use more appliances. For example, whereas in Japan people tend to heat only one of the rooms instead of the whole house, but in Europe they tend to install central heating systems and heat the whole building. All these factors reflect the changes of people's behaviour, as they become wealthier from the economic growth. It is a fact, that as more people will become wealthier the demand for single family homes will also increase, and the demand will then be greater than today, therefore increasing the energy consumptions. (Reference- energy efficiency in buildings –market)

The issue of reducing consumption in single family buildings is not so simple. In general, all countries encounter serious barriers when it comes to taking effective measures for lower energy consumption. In Europe, many of the buildings that already exist, have an enormous challenge to retrofit these old buildings and apply low energy building principles. Definitely, these changes will cost money and everyone is interested in getting financial backing from the governments. Another issue at hand is to raise awareness, about all the changes that everyone needs to know about, especially with regards to the green technology and the proposed energy solutions which will cover their needs, and be easy to install. Unfortunately until now, the lack of information and financial measures has not helped the development of green technologies and designs for single family houses.

The World Business Council for Sustainable Development mention that 'there are two key barriers to transforming what is currently a refurbishment market into an energy-efficient market: the first one is that people do not know where to find the relevant information on options, prices and suppliers; there are no "one-stop shops" for retrofitting and the second one is that homeowners base decisions largely on the first cost rather than overall financial returns'. (Reference- energy efficiency in buildings –market)

In developing countries, the biggest problem is the lack of regulations and mechanisms which would then force the people and the market to change. For example, in China the building codes are not effectively applied and in Brazil, 75% of the single homes are "illegally" built. In addition, developing countries as mentioned before have different needs to the developed countries, so the need to provide houses is more essential that the need to reduce energy consumption. (Reference- energy efficiency in buildings –market)

In Japan and the US, the growing population is followed by high rates of constructions. This rapid development of the market causes huge problems to also then apply the green principles on a big scale. Another major problem in these countries is the big differences between the submarket which block, in some ways, the measures of low energy design. The key to the solution in these countries is strengthening their regulations, by giving more information to the public and changing their behaviour. (Reference- energy efficiency in buildings –market)

In the cases of the multifamily buildings, which belong in Residential buildings sector, another approach is necessary for energy efficiency. These types of buildings are commonly located in cities where the urbanization problems are huge. In Europe, the US and Japan these buildings vary from very small to luxury apartments, so the energy demand is also varied. As referred to before, many of the buildings in the centre of the towns were built many years ago, so to achieve energy efficiency and apply the low energy principle is a great issue. In developing countries, incomes influence the preference for bigger houses and more energy consumption, therefore making a multifamily building a key factor for lower energy demand. (Reference- energy efficiency in buildings –market)

Still, comparing single family homes with apartments, obviously the energy needs in an apartment are less due to their small size and space and lower exterior wall area. Looking at the example of the US (figure 12), apartments use almost half the heating energy and lighting energy than a single family house. In general, the energy profile of a single family house is much higher than that of the multifamily building. It is almost definite, that due to the increasing population the living standards in developing countries are growing fast which influences the energy demand. (Reference- energy efficiency in buildings –market)

The office sector in most countries has a significant impact on the energy consumption. These kinds of buildings belong to the commercial buildings sector and they are one of the biggest categories, as they use large amounts of space and energy! The actual buildings, depending on their use, can be found having a great variety, which are from small single buildings to skyscrapers. Usually though, due to the rapid world development which demands more public services, the office buildings are newer rather than older buildings. In China, where technological developments and services increase rapidly, the office sectors are growing rapidly. Additionally, the technological developments influence and change one's working life as with new high technology, it is easier for some people to work from their homes. The results of these new trends, is the reduction of the floor space needed per person, having fewer large offices and more flexible space. All these factors influence the energy consumption of an office building.

Some other factors that affect the energy demand in office buildings are the same ones as the ones for residential buildings, such as the climate, the type and the size of the building and its use. Usually the biggest percentages of energy consumption come from heating, cooling and lighting needs. The biggest challenge for this sector is the growing demand of energy, due to the use of more technological and office equipment. As mentioned in the World Business Council for Sustainable Development report the "total greenhouse gas emissions from IT equipment (including data centers) are growing at about 6% a year" (reference- The Climate Group (2008), "Smart 2020: Enabling the Low Carbon Economy in the Information Age", a report on behalf of the Global e-Sustainability Initiative, with analysis by McKinsey & Company.) In addition, the use of extra office equipment affects the temperature comforts in that space, as more heat is enfranchised, demanding then the use of cooling and ventilation systems.

In general the energy consumption of the office sector in six regions of EEB report varies, but generally heating has the largest percentage. For example, in the US, heating requires 25% of all the office energy and in Japan its 29 % (figure 13). It is important therefore that the efforts made for a significant energy reduction, to continue, from all manufactures who try and develop energy efficient products for office use.

The office sector is the most difficult one to apply the low energy principles on, but it has great potentials. Those who use an office don't care about saving energy or using energy efficient systems plus developers and investors prevent the development of green design technologies and methods. Everyone just cares about their direct profit and the costs related to the green investments rather than the life cycle costs and the future benefits from green technologies. Due to this outlook, transforming the office sectors and changing the behaviours is extremely difficult.

Another vital barrier for energy efficiency in the office sector is the complexity of the sector as it involves many different types of players, such as the developers, the construction companies, the material and equipment suppliers, the agents and the different owners. (Figure 14) Also the lack of experts and engineers who can afford, support and monitor the low energy design and principles is another serious barrier for energy efficiency in the office buildings. Finally, you can find the actual physical restrictions applicable for a low energy office due to its design and the construction of the building. For example, the installation of photovoltaic panels is difficult because of the small roof space compared with the building size and the energy demand. (Reference- energy efficiency in buildings –market)

The concept of Zero Energy Building (ZEB)

The concept of Zero Energy Buildings might not be something new. Over the past years, different engineers and scientists have attempted to give new approaches for the contraction and designs of the buildings, proposing new ideas and technologies. Unfortunately up to today, these new concepts have just been thoughts which have been supported from only a few.

However phrases like 'a zero energy house', 'a neutral energy autonomous house' or 'an energy-independent house' have appeared in articles as from the late seventies, due to the fact that the oil crisis consequences started to become visible. It was then, where the bug issue started in reference to the natural sources and fossil fuels which caused researches to look for alternative energy sources and started energy use discussions. Despite the fact that the energy problems were serious, the first approaches of the buildings sector were only to talk about, energy efficient technologies and passive solutions. Additionally, the word 'zero' included only the energy for heating, cooling and domestic water. (Zero Energy Building (ZEB) definitions – A literature review)

Throughout the years, ZEB's definitions varied due to the different approaches from all the engineers and scientists. Many articles and papers were published around this issue of ZEB, but lack of a common understanding and definition caused wide discussions. During of all these attempts, many definitions were given including each time different factors and approaches such as 'how the zero energy goal is achieved', 'what is the building grid interaction', 'unequal energy qualities in the energy balance', 'what are the project boundaries for the balance?' (Zero Energy Building (ZEB) definitions – A literature review)

In general, all the approaches from all over the world target to create new generation buildings which are going to be energy efficient with a low operation energy profile and energy that needs to be supplied from renewable sources. The issue of Zero Energy Buildings is still under research, as scientists are trying to combine into words what energy efficiency, renewable sources technology, low CO2 emissions and the environmental impacts are. As it is said in the 'Zero Energy Buildings: A critical look at the definition' report ' the heart of the ZEB concept is the idea that buildings can meet all their energy requirements from low-cost, locally available, non-polluting, renewable sources.' (Zero Energy Buildings: A critical look at the definition' report)

The common definition of Zero Energy Buildings is essential and very important for all the governments so that it will be possible to develop common strategies for the buildings sector and for all to follow the same principles. The transformation of the building sector, energy savings and the stabilization of the climate will be possible only when a global action and cooperation is achieved.

Zero Energy Buildings Definitions

The Zero Energy Building definition presents a wide diversity through the publications and reports that came out over the last few years. Each time a different definition is given relating to the project goals and values of the design team. For example, the owners care about the energy costs, the organizations are interested in the primary and sources energy, the architectures care about a sites energy use for energy code requirements and the environmentalists care about the CO2 emissions and the environmental impacts of the buildings.

However, an important issue is to focus on the actual word 'zero' and how this is defined within the ZEB definition. This word may include CO2 emissions, primary energy, available energy (exergy) or energy cost. The Torcellini report which was published in 2006 make use of the U.S. Department of Energy (DOE) definition which says that "A net zero energy building (ZEB) is a residential or commercial building with greatly reduced energy needs through efficiency gains such that the balance of energy needs can be supplied with renewable technologies." In the same report the authors refer to "zero" by saying "Despite the excitement over the phrase "zero energy," we lack a common definition, or even a common understanding, of what it means". (Reference-Torcellini, P., Pless, S. & Deru, M. (2006). Zero Energy Buildings: A Critical Look at the Definition. National Renewable Energy Laboratory (NREL), USA Web address: http://www.nrel.gov/docs/fy06osti/39833.pdf) In addition the Torcellini report attempted to cover all the different approaches by giving the most frequently used definitions:

  • Nett Zero Site Energy: A site where ZEB produces at least as much energy as it uses in a year, when accounted for at the site.
  • Nett Zero Source Energy: A source where ZEB produces at least as much energy as it uses in a year, when accounted for at the source. Source energy refers to the primary energy used to generate and deliver the energy to the site. To calculate a building's total source energy, the imported and exported energy is multiplied by the appropriate site-to-source conversion multipliers.
  • Nett Zero Energy Costs: The cost of ZEB, is the amount of money the utility pays the building owner for the energy that the building exports to the grid which is at least equal to the amount the owner pays the utility for the energy services and energy used over the year.
  • Nett Zero Energy Emissions: A net-zero emissions building produces at least as much emissions-free renewable energy as it uses from emissions-producing energy sources.

It was expected that the Torcellini report would create new discussions around the issue of the ZEB's definition. Another author, Kilkis, in 2007 referred to the Torcellini report but with a new approach at that time. The new definition for ZEB given by Kilkis said that "Nett-Zero Exergy Building is a building, which has a total annual sum of zero energy transfer across the building-district boundary in a district energy system, during all electric and any other transfer that is taking place in a certain period of time". (Reference- Kilkis, S. (2007). A new metric for net- zero carbon buildings. Proceedings of ES2007. Energy Sustainability 2007, Long Beach, California, pp. 219-224).In another report, also in 2007, the authors in their definition paid attention to the balance of energy use and energy production of the building. As they said the "energy use should be equal to the energy production" (Refernce- Laustsen, J. (2008). Energy Efficiency Requirements in Building Codes, Energy Efficiency Policies for New Buildings. International Energy Agency (IEA).Web address: http://www.iea.org/g8/2008/Building_Codes.pdf Mertz, G.A., Raffio, G.S. & Kissock, K. (2007). Cost optimization of net-zero energy house. Proceedings of ES2007. Energy Sustainability 2007, Long Beach, California, pp. 477-488 )

Nevertheless, another interesting approach is facing the problem on the site of the buildings, which is energy demand and balance. Over the past few years, the biggest energy consumption in the buildings has been from the space heating and hot water. Due to this fact, many publications were affected and tried to set the problems around the heating demands. Esbensen's definition, in 1977, is one example of this approach which reported that "With energy conservation arrangements, such as high insulated constructions, heat-recovery equipments and a solar heating system, the Zero Energy House is dimensioned to be self-sufficient for space heating and hot-water supply during normal climatic conditions in Denmark. Energy supply for the electric installations in the house is taken from the municipal mains." (Reference- Esbensen, T.V. & Korsgaard, V. (1977). Dimensioning of the solar heating system in the zero energy house in Denmark. Solar Energy Vol. 19, Issue 2, 1977, pp. 195-199)

In many cases, the ZEB definition is focused on the electricity consumption of the building and its relation with the total energy. The definitions which were given by Gilijamse and Iqbal, respectively, represent this approach and refer to it as "A zero energy house is defined here as a house in which no fossil fuels are consumed, and the annual electricity consumption equals annual electricity production. Unlike the autarkic situation, the electricity grid acts as a virtual buffer with annually balanced delivers and returns" and "Zero energy home is the term used for a home that optimally combines commercially available renewable energy technology with the state of the art energy efficiency construction techniques. In a zero energy home no fossil fuels are consumed and its annual electricity consumption equals annual electricity production. A zero energy home may or may not be grid connected" (reference-Gilijamse, W. (1995). Zero-energy houses in the Netherlands. Proceedings of Building Simulation '95. Madison, Wisconsin, USA, August 14–16; 1995, pp. 276–283. Web address: http://www.ibpsa.org/proceedings/BS1995/BS95_276_283.pdf Iqbal, M.T. (2003). A feasibility study of a zero energy home in Newfoundland. Renewable Energy Vol. 29, Issue 2 February 2004, pp. 277-289)

Another definition, given by Lausten, attempts to include the total energy demand, heating and electricity demand. The result was the new definition of ZEB's which said that "Zero Nett Energy Buildings are buildings that over a year are neutral, meaning that they deliver as much energy to the supply grids as they use from the grids. Seen in these terms they do not need any fossil fuel for heating, cooling, lighting or other energy uses although they sometimes draw energy from the grid." (reference-Laustsen, J. (2008). Energy Efficiency Requirements in Building Codes, Energy Efficiency Policies for New Buildings. International Energy Agency (IEA). Web address: http://www.iea.org/g8/2008/Building_Codes.pdf)

However, it is important in literature that the definitions consider the embodied energy of the construction and the materials. This approach has been developed lately, and there is a great living example close to London city, called the Bed ZED project. As mentioned from Morbitzer " the BedZED is built from natural, recycled or reclaimed materials. All the wood used has been approved to be sourced from sustainable resources, and construction materials were selected for their low embodied energy and were sourced within 35-mile radius of the site if possible." (reference- Morbitzer, C. (2008). Low energy and sustainable housing in the UK and Germany. Open House International. Vol. 33, Issue 3, 2008, pp. 17-25)

Amongst wide discussions in reference to the definition of ZEB another issue raised was regarding electricity grids. This issue has to do with the off grid and on grid ZEB. The on grid Zero energy building is the one that is connected with the grid but also produces its own energy. These kinds of buildings can purchase energy or feed some back to the grid if they produce more energy than demanded. On the other hand, off grid Zero energy buildings are not connected with the grid and produce their own. These kinds of buildings, most of the time, cover their energy needs from renewable energy sources. An example of the off grid ZEB is given in the Laustsen's definition: "Zero Stand Alone Buildings are buildings that do not require connection to the grid or as they have the capacity to store energy for night-time or wintertime use." At the same time, Lautsen gave another definition for the on grid ZEB: "Zero Nett Energy Buildings are buildings that over a year are neutral, meaning that they deliver as much energy to the supply grids as they use from the grids. Seen in these terms they do not need any fossil fuel for heating, cooling, lighting or other energy uses although they sometimes draw energy from the grid" (reference- Laustsen, J. (2008). Energy Efficiency Requirements in Building Codes, Energy Efficiency Policies for New Buildings. International Energy Agency (IEA). Web address: http://www.iea.org/g8/2008/Building_Codes.pdf)

Last but not least, is the fact that some ZEB definitions focus on the renewable energy that is used to cover the needs of the buildings. It is important to remember that the main concept of ZEB is the replacement of the fossil fuels with renewable sources which include solar energy, wind energy, wave energy, biomass energy and geothermal energy. Until now, the most known technologies are the solar thermal and photovoltaic technologies. An example of this kind of definition is given by Charron: "Homes that utilise solar thermal and solar photovoltaic (PV) technologies to generate as much energy as their yearly load are referred to as nett-Zero Energy Solar Homes (ZESH)." (Reference Charron, R. (2008). A review of design processes for low energy solar homes. Open House International Vol. 33, Issue 3, 2008, pp. 7-16)

To conclude, from the above definitions it is obvious that the Zero Energy Buildings and in general the Building sector involves many different aspects and factors that influence the energy performance of the buildings. For that reason it is very difficult to adopt a general definition for Zero energy buildings, which will be able to include all the different aspects. The best approach for a Zero Energy Building is to consider during the designing phase all the parameters which are going to affect the energy performance of the building.

The definition impacts in ZEB design

The definition of a Zero Energy Building is essential during the design procedure. Each definition includes different aspects, as mentioned before, and the results can vary significantly. Later on you can find a description of all the differences, the advantages and the disadvantages of a Nett Zero Site Building, Net Zero Source Energy Building and Nett Zero Energy Emissions Building.

Nett Zero Site Building

The Nett Zero Site Building is the building that produces energy on a site and the production is equal to the consumption. Usually the energy production comes from the renewable energy sources like photovoltaic systems (roof or parking mounted PV), solar water collectors, wind power, low impact hydro and geothermal energy. (Zero Energy Buildings: A critical look at the definition' report)

A site ZEB produces as much energy as it uses, when accounted for at the site. Generation examples include roof-mounted PV or solar hot water collectors (Table 1, Option 1). Other site-specific on-site generation options such as small-scale wind power, parking lot-mounted PV systems, and low-impact hydro (Table 1, Option 2), may be available. As discussed earlier, having the on-site generation within the building footprint is preferable.

A limitation of a site ZEB definition is that the values of various fuels at the source are not considered. For example, one energy unit of electricity used at the site is equivalent to one energy unit of natural gas at the site, but electricity is more than three times as valuable at the source. For all-electric buildings, a site ZEB is equivalent to a source ZEB. For buildings with significant gas use, a site ZEB will need to generate much more on-site electricity than a source ZEB. As an example, the TTF would require a 62-kWDC PV system to be a site ZEB, but only a 45-kWDC PV system for a source ZEB (Table 2); this is because gas heating is a major end use. The net site definition encourages aggressive energy efficiency designs because on-site generated electricity has to offset gas use on a 1 to 1 basis.

A site ZEB can be easily verified through on-site measurements, whereas source energy or emissions ZEBs cannot be measured directly because site-to-source factors need to be determined. An easily measurable definition is important to accurately determine the progress toward meeting a ZEB goal.

A site ZEB has the fewest external fluctuations that influence the ZEB goal, and therefore provides the most repeatable and consistent definition. This is not the case for the cost ZEB definition because fluctuations in energy costs and rate structures over the life of a building affect the success in reaching net zero energy costs. For example, at BigHorn, natural gas prices varied 40% during the three-year monitoring period and electricity prices varied widely, mainly because of a partial shift from coal to natural gas for utility electricity production. Similarly, source energy conversion rates may change over the life of a building, depending on the type of power plant or power source mix the utility uses to provide electricity. However, for all the ZEB definitions, the impact of energy performance can affect the success in meeting a ZEB goal.

A building could be a site ZEB but not realize comparable energy cost savings. If peak demands and utility bills are not managed, the energy costs may or may not be similarly reduced. This was the case at Oberlin, which realized a 79% energy saving, but did not reduce peak demand charges. Uncontrolled demand charges resulted in a disproportionate energy cost saving of only 35%.

An additional design implication of a site ZEB is that this definition favors electric equipment that is more efficient at the site than its gas counterpart. For example, in a net site ZEB, electric heat pumps would be favored over natural gas furnaces for heating because they have a coefficient of performance from 2 to 4; natural gas furnaces are about 90% efficient. This was the case at Oberlin, which had a net site ZEB goal that influenced the design decision for an all-electric ground source heat pump system.

Nett Zero Source Energy Building

A source ZEB produces as much energy as it uses as measured at the source. To calculate a building's total source energy, both imported and exported energy are multiplied by the appropriate site-to-source energy factors. To make this calculation, power generation and transmission factors are needed. Source Energy and Emission Factors for Energy Use in Buildings (Deru and Torcellini 2006) used a life cycle assessment approach and determined national electricity and natural gas site-to-source energy factors of 3.37 and 1.12. Site gas energy use will have to be offset with on-site electricity generation on a 3.37 to 1 ratio (one unit of exported electricity for 3.37 units of site gas use) for a source ZEB. This definition could encourage the use of gas in as many end uses as possible (boilers, domestic hot water, dryers, desiccant dehumidifiers) to take advantage of this fuel switching and source accounting to reach this ZEB goal. For example, the higher the percent of total energy used at a site that is gas, the smaller the PV system required to be a source ZEB. At BigHorn, for a source ZEB, 18,500 ft2 of PV are required; however, 31,750 ft2 of PV are required for a site ZEB (Table 2).

This definition also depends on the method used to calculate site-to-source electricity energy factors. National averages do not account for regional electricity generation differences. For example, in the Northwest, where hydropower is used to generate significant electricity, the site-to-source multiplier is lower than the national number. In addition, national site-to-source energy factors do not account for hourly variations in the heat rate of power plants or how utilities dispatch generation facilities for peak loading. Electricity use at night could have fewer source impacts than electricity used during the peak utility time of day. Further work is needed to determine how utilities dispatch various forms of generation and the corresponding daily variations of heat rates and source rates. Using regional time-dependent valuations (TDVs) for determining time-of-use source energy is one way to account for variations in how and when energy is used. TDVs have been developed by the California Energy Commission to determine the hourly value of delivered energy for 16 zones in California (CEC 2005). Similar national TDVs would be valuable to accurately calculate source energy use to determine a building's success in reaching a source ZEB goal. A first step in understanding regional site-to-source multiplier differences is available (Deru and Torcellini 2006); multipliers are provided for the three primary grid interconnects and for each state.

There may be issues with the source ZEB definition when electricity is generated on site with gas from fossil fuels. The ZEB definitions state that the building must use renewable energy sources to achieve the ZEB goal; therefore, electricity generated on site from fossil fuels cannot be exported and count toward a ZEB goal. However, this is unlikely, because buildings are unlikely to need more heat than electricity and the inefficiencies of on-site electricity generation and exportation make this economically very unattractive. The best cost or energy pathways will determine the optimal combination of energy efficiency, on-site cogeneration, and on-site renewable energy generation.

The issue of unmanaged energy costs in a site ZEB is similar for a source ZEB. A building could be a source ZEB and not realize comparable energy cost savings. If peak demands and utility bills are not managed, the energy costs may or may not be similarly reduced.

Nett Zero Energy Emissions Building

An emissions-based ZEB produces at least as much emissions-free renewable energy as it uses from emissions-producing energy sources. An on-site emission ZEB offsets its emissions by using supply-side options 1 and 2 in Table 1. If an all-electric building obtains all its electricity from an off-site zero emissions source (such as hydro, nuclear, or large scale wind farms), it is already zero emissions and does not have to generate any on-site renewable energy to offset emissions. However, if the same building uses natural gas for heating, then it will need to generate and export enough emissions-free renewable energy to offset the emissions from the natural gas use. Purchasing emissions offsets from other sources would be considered an off-site zero emissions building.

Success in achieving an emissions ZEB depends on the generation source of the electricity used. Emissions vary greatly depending on the source of electricity, ranging from nuclear, coal, hydro, and other utility generation sources. One could argue that any building that is constructed in an area with a large hydro or nuclear contribution to the regional electricity generation mix would have fewer emissions than a similar building in a region with a predominantly coal-fired generation mix. Therefore, an emissions ZEB would need a smaller PV system in areas with a large hydro or nuclear contribution compared to a similar building supplied by a utility with a large coal-fired generation contribution.

The net zero emissions ZEB definition has similar calculation difficulties previously discussed with the source ZEB definition. Many of these difficulties are related to the uncertainty in determining the generation source of electricity. Like the source definition, one would need to understand the utility dispatch strategy and generation source ratio to determine emissions from each of these sources.

Factors influencing ZEB design

The complexities of Zero Energy Buildings demand during the design phase, careful studying and understanding of the different factors. It is very important for an engineer to understand and predict the impact of each factor to the energy performance of the building.

As the following picture shows (figure 15) there are too many factors that affect the energy consumption of a ZEB, such as the building envelope, the orientation, the insulation, the shading, the lights, the air-conditioning systems, the heating systems, peoples behaviour, the technical installation and the daylight control.

However some factors are more important than others and influence the operation and consumption energy much more.

The location and the climate play an important role in the energy consumption, especially when the external environment is too severe for comfort. The more extreme, the external climate is, the more energy is used, to create a comfortable internal environment. The building placement can be used in combination with landscaping to produce mild microclimate. For instance, in cold climates the heating demands are more therefore this must be combined, with passive solar heating strategies, as they are essential. On other hand, hot climates means cooling demands are more important, and the high degree of sin control is significant for the building. Also in these climates, a good design can offer better lighting via the building spaces. Another point that is affected from the location and the climate is the natural ventilation of the building which is directly related with the current climate conditions of the place. (Reference- low energy building design guidelines AND Richard Nicholls (2002), Low Energy Design)

The building size of a Zero Energy Building is related with the operation energy consumption. Usually, apart from the outdoor climate, the indoor climate has a significant contribution on all the aspects of the building design too. In some cases, the outdoor climate supplements the indoor climate, for instance, the very cold climate will have a building which has a lot of internal heat gains sited. Otherwise, when the two climates are antagonistic, hot climate will also have a building which also has a lot of internal heat gains. The building size for these cases determine is some ways, the indoor climate, and the implications of the current outdoor climate. The size of the surface area and volume are prescribed by the form of the building. These two parameters are directly proportional to the fabric and ventilation heat loss rates, respectively. For example in hot climates "buildings with large footprints and a large amount of floor space far from the exterior of the building will require heat removal in the interior zones (generally by mechanical cooling) all or much of year." In addition, form plays an important role to the capability of the building to collect and use natural energy such as solar heat, light and natural ventilation. (Reference- low energy building design guidelines AND Richard Nicholls (2002), Low Energy Design)

The buildings fabric relates to the fabric heat loss rates which are affected by the buildings envelope. To slow down the heat losses, low density materials and insulators can be used. In contrast dense, thermally massive materials can be applied in the interior to assist cooling the building in the summer time. (Reference- low energy building design guidelines AND Richard Nicholls (2002), Low Energy Design)

The buildings ventilation is a result of the mechanical ventilation, that consumes energy and in case of an uncontrolled infiltration, it is possible to have cold air admissions or warm air losses from the building. It is thus very important to minimize the infiltration, whilst at the same time, mechanical systems should operate efficiently and only in the case of necessity.

The heating and cooling systems demand a thorough analysis so as to operate correctly. Mechanical heating systems consume a huge amount of energy to produce heat and also fossil fuels, so it is important to operate them, only when required. Good insulation of the buildings makes it possible to minimize the uses of the systems. Mechanical cooling systems also demand a huge amount of electricity but with passive methods, such as shading and exposing mass, in combination with night time ventilation, the replacement of the system could be achieved. . (Reference- low energy building design guidelines AND Richard Nicholls (2002), Low Energy Design)

Another important factor of the Zero Energy design is the internal heat gains. Most of the electric appliances such as lights, TV, computers, refrigerator etc., in addition with the building occupants, irradiate heat affecting the indoor climate. At the early stages of a design, it is very important to calculate the possible heat gains and take the necessary measures for this problem. Sometimes, heat gains in combination with hot climates can affect the HVAC system design and the energy consumption. For example, cafeterias, restaurants and laundry buildings are strongly influenced by the heat gain factor as the use of big appliances irradiate significant amounts of heat. The identification of these kinds of factors should be at an early stage of the design, giving therefore, the opportunity of appropriate design strategies. (Reference- low energy building design guidelines AND Richard Nicholls (2002), Low Energy Design)

The lighting requirements play an important to the energy performance of the building. Today's designers, tend to use artificial lightning as a decoration in modern buildings, which is in contrast with the Low or Zero Energy principles. Lighting must only be used where it is necessary and cover serious needs. Also these needs vary from building to building, depending on what is the buildings use. At the stage when one is designing the quantitatively and qualitatively lighting needs must be identified and designed with the ZEB principles. The design team is responsible to choose the suitable electrical lighting systems with integrated occupancy sensors. In addition, the concept of ZEB is to use a good combination of daylight via a good design of the glazed openings which is essential. Natural daylight entering the building means that energy consumption is reduced, minimizing this way the energy demands. (Reference- l


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