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The use of energy in buildings has increased in recent years due to the growing demand in energy used for lighting, heating and cooling in buildings. Without energy buildings could not be operated or inhabited. Improvements have been made in insulation, lighting and controls and these are significant features that help towards achieving an energy efficient building. At this stage it is important to know what is meant by "Energy Efficiency".
3.1.1 Energy Efficiency
Energy efficiency means utilizing the minimum amount of energy that is required to maintain comfort conditions in a building.  An important factor impacting on energy efficiency is the building envelope. This includes all of the building elements between the interior and the exterior of the building such as; walls, windows, doors, roof and foundations. These components must work together in order to keep the building cool in the summer season and warm in the winter.
The amount of energy consumed varies depending on the design of the fabric of the building and its systems and how they are operated. The heating and cooling systems consume a considerable amount of energy in commercial buildings; however controls such as programmable thermostats and building energy management systems can significantly reduce the energy use of these systems. Some buildings also use zone heating and cooling systems, which can reduce heating and cooling in the unused areas of a building. In commercial buildings, integrated space and water heating systems can provide the best approach to energy-efficient heating.
Buildings also produce Carbon Dioxide (CO2) emissions, but this sector receives less attention compared to other pollution contributors such as the transportation and industry sectors. In addition to energy conservation and energy efficiency measures introducing renewable energy would be an advantage to the building sector as it will reduce the carbon dioxide emissions, and the energy generated from the renewable energy could be used for heating, cooling, ventilating or lighting.
Energy efficiency is a fundamental element in progress towards a sustainable energy future. As global energy demand continues to grow to meet the needs of people across the globe, actions to increase energy efficiency will be essential. This section of the chapter sets out the importance of energy efficiency. As suppliers and consumers of energy all over the world, strongly support and pursue economic approaches to energy efficiency. Energy efficiency makes sense to business in a wide range of sectors for compelling reasons  . Efficient energy strategies have the following benefits:
Reduces emissions of Co2 and other environmental impacts.
Extends the availability of non-renewable resources.
Energy prices become affordable to consumers, reducing the energy needs by following the energy efficient strategies. This is particularly important in developing countries where affordability to modern energy services is critical for development.
Improves competitiveness and improves overall productivity. 
Major progress has been made across the globe to improve energy efficiency. For example, the European Union has launched a major policy initiative on energy efficiency, which identifies the potential to reduce energy use by 20% through cost-effective measures. The G8* has identified energy efficiency as a key area for action that can deliver reduced greenhouse gas emissions while improving competitiveness, health and employment. 
3.1.2 Characteristics of Energy Efficient Buildings
Energy efficient buildings utilize the minimum energy for heating, cooling, equipments and lighting required to maintain the comfort condition of the building by using solar passive techniques & strategies.
Such building has less operative cost, thus can save energy from 30%-70%.
These buildings are mostly depending on the Passive solar techniques hence requiring minimum energy to operate their active systems including Interior lighting & HVAC.
In such buildings the architectural design/planning and systems are designed keeping in view the guidelines provided by the energy conservation standards & codes.
Such buildings are nature friendly & have less adverse impact on our ecosystems, by using renewable energy resources.
3.2 Factors affecting Energy use in Commercial Buildings
There are various building elements and system responsible to operate a building. The behavior of those elements and systems is very complex and interrelated to each other and playing a key role in consuming the energy in the form of heat and electricity. The energy consumption in buildings is related to the nature of their occupancy. The areas of energy consumption fall principally under the following categories of end use in commercial buildings.
Primary Usage for services systems like HVAC, Lighting etc.
A secondary use system includes Lifts, escalators and other building services equipment.
Individual use systems including mainly the office equipment such as office equipment.
These categories will be reviewed with regard to opinions from different authors, energy consumption trends and finally a set of decisions will be presented to identify the systems and elements responsible for the energy consumption in commercial buildings.
3.2.1 According to Literature Review
Yik, Burnett, Jones and Lee, In reference to the electricity consumption of commercial buildings for office use, have identified HVAC systems, lighting, plumbing and lift systems to contribute most significantly  . As in commercial buildings the electricity consumption is far heavier as compared to heat energy consumption. Therefore, due to the dominant use of electricity in the commercial building sector, this aspect cannot be ignored.
According to US Department of Energy 2006, air conditioning (HVAC) and space heating required the largest amount of energy consumption in commercial and domestic buildings. These sectors are consuming 32% and 35% of end-use energy respectively. 
Torcellini, The National Renewable Energy Laboratory Report identifies that Lighting is the largest single end use in commercial buildings, at 24% of the total primary energy used  . From a national perspective, the potential for day-lighting savings is significant. Based on the 1999 Commercial Buildings Energy Consumption Survey, nearly 80% of the total floor area in commercial buildings has an exterior ceiling or is within 15 ft of an exterior wall and therefore has good potential to be at least partially daylight.
According to Meier, Olofsson and Lamberts, an energy efficient building should have energy efficient technologies and spaces should be operated as originally designed. The buildings should be operated in a manner to conserve energy. But the conservation of energy should not be achieved by reducing the comfort level of the occupants. The internal comfort conditions should be achieved by implementing energy conservation codes. Therefore, based on the existing building energy codes, it is assumed that compliance to these standards is fully satisfied. 
3.2.2 According to Energy Consumption Trends
Based on the global energy consumption trends in commercial buildings presented by "Energy information Administration/Annual Energy Review 2008, it is obvious that the most significant areas of energy consumption in such should be analyzed. Eneegy Consumption .jpg
Figure 3.1 Energy Consumption Trends in Commercial Buildings
As it can be observed from the Figure [3.1]  , that Interior lighting "Lighting" and space cooling "HVAC" are the most critical areas responsible for the maximum energy consumption in commercial buildings. So it is important that these two areas should be analyzed completely to increase the efficiency of the components and systems of such buildings.
3.2.3 According to the aspects listed in Annex 2002/91/EC (Directive on the Energy Performance of Buildings)
The consideration of various aspects related to the building energy performance is listed in the Annex of Directive 200/91/EC, cannot be ignored, as shown in the Figure [3.2]  .ANNEX.jpg
Figure 3.2 The general Framework for the calculation of energy performance in Buildings
Official Journal of the European Communities, Annex of Directive 2002/91/EC
Part I and II of the framework are more significant. According to the current research part I of the framework is more related, this is because Part II of the framework is concerned with the new buildings before the commencement of construction process.
3.2.4 Qualitative Aspects
Within the same type of buildings different variation can be found in terms of energy consumption and their energy performance. It is also observed that the quality of building systems and elements can play a vital role in improving the energy efficiency of commercial buildings. Therefore, a description of qualitative features of the building systems and elements should be included along with the quantification process for assessing energy performance. Energy efficiency is often not effective in such buildings because of incorrect use and lack of maintenance of various systems equipment.
Considering the qualitative aspects in all cases, the common factors effecting the energy consumption in the commercial buildings are listed below;
The Building Envelope
Lifts and Escalators
The factors listed above can be categories by considering their energy consumptions. It can be observed that, HVAC systems including Ventilation fans and Lighting system are supposed to be the primary systems for maximum consumption of electricity. Lifts and escalators are categorized as secondary systems, consuming less energy as compared to primary systems. The office equipments, communication technologies and information services are categorized in the final user system.
The building envelope cannot be ignored because it concern with the issues related to heat losses, thermal barriers and other thermal fabric issues of the building's outer shell. The improvement in the thermal properties of the envelope fabric can affect significantly on the cooling and heating loads on HVAC system of the building, by reducing annual energy requirements of the building to operate. HVAC systems are one of the main consumers of electricity. However, the quality of the fabric materials can play an important role in optimizing the performance of the building systems like HVAC.
It is also important to analyze the aspect ratio and other architectural features of the building to optimize the performance of the envelope and other systems. Such features may affect the building energy performance positively or negatively.
Envelope design is a major factor in determining the amount of energy a building will use in its operation, and decisions about its components play a crucial role in energy costs needed for cooling, in addition to realizing the required passive cooling. There is always an interplay relationship between building form, materials, and climate, and each of them affects the thermal comfort of human being. Members of the design team should coordinate their efforts to integrate optimal design features for every building type to reach the lowest energy for realizing thermal comfort for its occupants, and Careful study is required to arrive at a building footprint, shape, form, and orientation that work with the building envelope components to maximize energy benefit, and to achieve energy savings.
3.3 Assessment of Energy Performance in Buildings
Today, a great deal of effort is placed all over the world in achieving sustainable development in the construction industry with the aim of reducing energy consumption in the design construction and management of buildings, thus limiting its consequences on the local and global environment. Such effort can be seen at international levels with the launching of voluntary building environmental schemes to measure the energy performance of buildings. The most representative and widely used schemes are (LEED)" Leadership in Energy and Environmental Design", (BREEAM) "Building Research Establishment Environmental Assessment Method" and "Green Star".
LEED was developed by the U.S. Green Building Council (USGBC) and is nationally accepted as a benchmark for green building practices. BREEAM was launched by the U.K. Building Research Establishment (BRE) and is adopted by the U.K. government as a measure of best practice in environmental design and management. Green Star was launched by the Green Building Council of Australia (GBCA) and is established as a national guide to evaluate the environmental design and achievements of buildings.
All three schemes are based on a rating system of collecting credits that applies to a wide range of building types, both new & existing buildings. All cover a range of environmental issues such as materials, energy, water, pollution, indoor air quality and building site. One of important credits in all the three schemes, which is also the essential factor in the overall effort to achieve sustainable development, is the consumption of energy or resulting carbon emissions in buildings.
3.3.1 Energy Performance Assessment Process
The assessment of the energy performance of a building consists of several stages. The organization of the assessment process is not standard but depends on the specific circumstances and the type of the building. There are nevertheless very common stages that are relevant in the majority of assessment processes. Each of the stages has its specific characteristics as shown in the Figure [3.4].
The assessment process typically starts with an intake interview with the client in order to discuss and define starting points and conditions to take into account during the assessment and create the overall perception of the building and its peculiarities. This stage is a starting point for the acquisition of the necessary data in order to perform energy analyses. Based on these results, the energy performance can be established together with the cost-effective energy saving measures to be advised. Having reached this stage, the assessment is completed. Of course in addition the results have to be expressed into an Energy Performance Certificate and presented to the client. The impact of the certificate in terms of taking measures depends on the combination of the quality of the assessment and the acceptance of the advice by the actors in the market. A good quality assessment with a poor acceptance is ineffective. Four major stages can be distinguished. As already mentioned, each project has its own most adequate approach; stages may be combined or subdivided. 
buildingt Efficient assessment EP-6.jpg
Figure 3.4. Stages Efficient Assessment of the Energy Performance of the Buildings
The main objective of the intake stage is to gain information about availability of the data and establish the process of data acquisition. The clients approach towards energy saving and the financial constrains may also be relevant in relation to relevant energy saving measures. It is also important to be aware of maintenance activities foreseen by the client. Combining maintenance with energy saving measures is in general much more cost-effective.
3.3.1.b Acquisition of data
The acquisition of data starts with a clear understanding of the building in terms of its energy behavior. Especially in case of more complex buildings it is necessary to derive a clear understanding on how to interpret the building. For instance: one has to define the boundaries of the main zone (thermal envelope) and how to deal with adjacent spaces. Also the HVAC system can sometimes be modeled in different ways. These considerations are not just matters related to the building itself, but also relate to the possibilities and constrains of the calculation model.
When the interpretation of the building is clear it is possible to define the necessary data for the calculation. By means of desk research (building description and drawings), interviews about user aspects and malfunctioning of building components, and inspection, the necessary data is collected and verified. Also the assumptions made as a basis for the interpretation of the building will be verified.
3.3.1.c Calculation and analyses of the energy performance
The data will be transformed into input for the calculation model. After execution of the calculation the results (e.g. energy consumption, primary energy, CO2-emmission) are analyzed. Apart from the physical quality of the calculation model, the quality of input and default values affect the accuracy and validity of the results.
3.3.1.d Reporting results - determination of the outcome
Based on the knowledge gained during the assessment, the energy saving measures can be defined and quantified together with the overall energy performance of the building. In order to achieve a good match with the situation and considerations of the client it is advisable to take the possibilities and constrains mentioned by the client into account. 
3.4 Building Energy Codes and Standards
Energy-efficient buildings offer energy, economic, and environmental benefits. They reduce energy expenditures and environmental pollutants. They also create economic opportunities for business and industry by promoting new energy efficient technologies. Unfortunately, the marketplace does not guarantee energy-efficient design and construction. Owners of commercial buildings generally pass on energy costs to consumers or tenants, eliminating any incentive for energy-efficient design and construction. Homebuyers often are motivated more by up-front costs than operating costs. 
"Energy codes and standards" play an important role in the establishment of minimum requirements for energy-efficient building design and construction. These codes and standards are developed for new buildings as well as for the renovation projects.
3.4.1 Energy Codes, Energy Standards, and the Model Energy Code
126.96.36.199 Energy codes
Energy codes are guidelines which are written in mandatory and forceful language that explains how buildings must be designed and constructed to reduce the energy consumption. The energy codes are supposed to implement by the state and local government.
188.8.131.52 Energy standards
Energy standards explain and illustrate how buildings should be designed and constructed to reduce the energy consumption in buildings. National organizations like the "American Society of Heating, Refrigerating, and Air-Conditioning Engineers" (ASHRAE), are responsible to formulate and publish these energy standards. These standards are not written in mandatory or forceful language, but act as national recommendations based on the regional climatic change. Local government and state departments frequently follow these standards as a technical document for the development of energy codes.  Untitled-1.jpg
Table 4.1.An overview of energy standards and the model energy code
184.108.40.206 Model energy code
"The International Energy Conservation Code (IECC)", known as a model energy code, is formulated and published by "The International Code Council (ICC)". The model energy code explains the minimum requirements of a building design and construction for different climatic zones in a region. A model energy code is always written in mandatory and forceful language implemented by the state and local government authorities. Table [4.1]  provides an overview of energy standards and the model energy code.
3.4.2 Development of Energy Codes, Energy Standards, and the Model Energy Code
220.127.116.11 Development of Energy Codes
The most recent model energy codes are the 1998 IECC and the 2000 IECC. These are developed and published by the International Code Council through an open public-hearing process. Prior to 1998, the IECC was known as the "Council of American Building Officials Model Energy Code (MEC)".
The IECC Code Development Committee typically comprises of seven to eleven individuals appointed by the ICC. Most of the committee members are code officials. Committee also includes officials other than the members of ICC.
18.104.22.168 Revision of Energy Codes
The officials from ICC or anyone who has no concern with the International code council may suggest a revision to the IECC, in the form of a proposed revised code. Anyone can suggest a code's change or revision to IECC by requesting through a proposed recommended change. The committee first publishes the proposed recommended change in the code for review. The process requires about six week's time for public response on the revised code. The committee receives written comments of the proposed change after a public hearing in the form of approval or deny. Finally committee publishes the results according to the written comments received after a public hearing. The members, who are wishing to accept the proposed change, can submit a challenge to the board of directors of ICC.
3.4.3 Development of Energy Standards
Standards 90.1 and 90.2 are revised and developed by consensus, through a public hearing process that are critical to widespread support for their adoption. ASHRAE has a collaborations with other standards organizations including; IESNA, ANSI," American Society of Testing and Materials (ASTM)", "Institute of Air Conditioning and Refrigeration (ARI)", and "Underwriters Laboratories (UL)". The consensus process includes the following professionals;
Architects / Designers.
Mechanical and electrical engineers.
Officials for the buildings codes organizations and state regulatory authorities.
Also includes buildings owners and operators.
Industry and manufacturers.
Representatives from the Department of Energy.
Pacific Northwest National Lab, energy advocacy groups, and the academic community.
22.214.171.124 Revision of Energy Standards
Standards are continuously maintained by an independent standing committee. Total strength of the committee varies from 10 to 60 members. Committee membership includes representatives from Architectural community, designers, mechanical engineers, lighting professionals, buildings owners, Industrialists and manufacturers, officials for the buildings codes organizations and state regulatory authorities.
Any proposed change or revision is the standard is proposed by the committee to be reviewed through public hearing. When the majority of the members agree on a certain revision or change, the revised standards is forwarded to the board of Directors of ASHRAE. The members not agree with the overall consensus can submit an appeal to the Board. If the Board refuses or denies the submitted appeal, then publication of the revised standard would then proceed. The entire process requires minimum two years and maximum ten years to complete.
126.96.36.199 Development of Model Energy Codes
The most recent model energy codes are the 2000 IECC and the 2009 IECC. These are developed and published by the International Code Council through an open public-hearing process. Prior to 1998, the IECC was known as the Council of American Building Officials Model Energy Code (MEC). The IECC Code Development Committee typically comprises of seven to 11 individuals appointed by the ICC. It is not compulsory that all committee members should be code officials. They may not be the members of International Code Council ICC. 
188.8.131.52 Revision of Model Energy Codes
Anyone can suggest a model energy code's change or revision to IECC by requesting through a proposed recommended change. The committee first publishes the proposed recommended change in the model code for review. The process requires about six week's time for public response on the revised model code. The committee receives written comments of the proposed change after a public hearing in the form of approval or deny. Finally committee publishes the results according to the written comments received after a public hearing. The members, who are wishing to accept the proposed change, can submit a challenge to the board of directors of ICC.
3.5 Computer Simulation Tools for Energy Performance Assessment in Buildings
The transfer of energy from one surface to another in buildings is a complex phenomenon. Very large & complex calculations are involved to get the results. Fifty years back the professionals & engineers start working on the development of such energy modeling simulation tools. That effort was very helpful to calculate the energy situation within a building in different climate zones. With the passage of time the software become more mature with friendlier interface. Selection of a simulation tool for the energy simulation is a hard task, because each software has its own limitation with different working environment.
This part of the chapter will explore the capability of some well known energy simulation tools with respect to their scope in energy simulation. A comparison will be developed based on the information provided by the program developers, so one can select the software according to requirements. Following software will be explained with respect to their features;
3.5.1 Energy Plus
Energy-Plus was officially released on 12 April 2001. Energy-Plus is a building energy simulation program for modeling building heating, cooling, lighting, ventilating, and other energy flows. Energy-Plus based on the most popular capabilities and features of two predecessor programs: the Building Loads and System Thermodynamics (BLAST) program (developed by the ERDC/CERL), and the DOE-2 program (developed by the U.S. Department of Energy [DOE]). Energy-Plus includes many innovative simulation capabilities such as energy simulation for less than one hour, multi-zone air flow, thermal comfort, and photovoltaic systems. 
Energy-Plus can perform life-cycle costing during the initial design process and can make certain decisions for low energy operative cost. Changes made early in the facility design process can yield a more cost-effective, energy-conservative building. Due to the complexity of building interactions, a computerized means for predicting energy consumption and system performance is necessary. Energy-Plus simulation can assist designers, engineers and building owners to reduce energy use in buildings dramatically. The software can calculate the impacts of internal and external heating loads on HVAC equipment, and internal comfort conditions of the building. Energy-Plus can suggest various types of lighting and windows to optimize energy efficiency of the building and occupant comfort conditions. The software can simulate the effect of window-blinds, fenestration, and advantage of day-lighting.
Energy-Plus is a standalone simulation engine without graphic interface. Energy-Plus writes text files for input and output data. Several private sector companies are developing more user-friendly, graphical, and domain specific interfaces for Energy-Plus.
DOE-2 is a validated computer program that calculates energy use within a building on hourly basis including the energy cost of the given monthly/annual schedule by following the weather information of the local climate, thermal properties of the building elements, the HVAC equipment & utility rates. DOE-2 enables the designers to choose the building parameters that can improve the building energy performance without compromising on the required comfort conditions and cost effectiveness.
The objective of DOE-2 is to facilitate the analysis of energy issues in buildings. The vision and experience of the architects /engineers still remain the most important considerations of the building design.
The new updated version DOE-2.2 was developed in a collaborative effort between Lawrence Berkeley National Laboratory and James J. Hirsch & Associates, with major support from the U.S. Department of Energy and the Electric Power Research Institute. DOE-2.2 is based on DOE-2.1E, which was released in 1994. The main goals of the DOE-2.2 are;
To make some basic improvements to the simulation portions of the program
To make the Building Description Language (BDL) processor more capable of being used in an interactive environment.
The new capabilities of DOE-2.2 will provide more accurate and flexible simulation of window, lighting, and HVAC systems, and will allow integration with interactive user interfaces. 
ESP-r is a transient energy simulation program, which allows modeling of energy and fluid flows within a combined building and plant system. The program is composed of a series of modules which each contribute to certain areas in the modeling and simulation process. The central desktop manager the Project Manager activates the relevant modules when required. ESP-r works in a UNIX and Linux environment where Figure [3.5] is displaying ESP-r started in a Red-Hat Linux environment. The displayed ESP-r platform is controlled by the Project Manager.
Figure 3.6 Project Manager with 3D Model
Figure 3.5 Red-Hat Linux Environment for Esp-r
The modules in ESP-r have a similar interface like the one displayed for the Program Manager in Figures [3.5] and [3.6]. The geometry is among other things composed in the Project Manager and is displayed as a 3D-model in the upper left hand, Figure [3.6]. Addition the menu containing menu items used to access the different possibilities within the program is displayed in the upper right hand, Figures [3.5] and [3.6].
3D Models can be coupled with Radiance for a pre-calculation of daylight coefficients, direct simulation runtime coupling and for visualization studies where glare can be evaluated. Radiance is a strong tool for calculating and analyzing the visual environment in a design project and the generated images can be used for presentation purposes. The calculation of glare in the coupling between ESP-r and Radiance and the calculation of the illuminance distribution as a separate task in Radiance for the ESP-r generated building models can help decide the type and control scheme for shading.
3.5.4 eQuest Ver 3.6
eQUEST allows to perform detailed analysis of building design technologies using sophisticated building energy simulation techniques without requiring extensive experience in building performance modeling. This is accomplished by combining a building creation wizard, an energy efficiency measure (EEM) wizard, and a graphical results display module with a simulation "engine" derived from an advanced version of the DOE-2 building energy use simulation program. 
After two decades of continuous development and enhancement, DOE-2 is the most widely recognized and trusted building energy simulation program available today. eQUEST is a self guided software through the creation of a detailed DOE-2 building model, automatically performs parametric simulations of building design alternatives, and provide graphical results that highlight the performance of building design alternatives.
Sophisticated energy simulation programs have been in existence for more than two decades. These programs have always required detailed knowledge of building energy use analysis and the energy analysis program itself. The result has been that only specialists could reliably use the sophisticated simulation programs. eQUEST helps to overcome past barriers to simulation by incorporating following building creation wizards;
The Schematic Design Wizard, "Schematic Wizard".
The Design Development Wizard, "DD Wizard".
An Energy Efficiency Measure wizard, "EEM Wizard".
Either Wizard guides through a series of steps designed to fully describe the principal energy related features of the building design. The wizards then create a detailed description of the proposed design as required. At each step of describing your building design, the wizards provide easy-to-understand choices of component and system options.Â 
3.5.5 Autodesk Ecotect 2010
Sustainable design is more important than ever. Building information modeling (BIM) solutions make sustainable design practices easier by enabling architects and engineers to more accurately visualize, simulate, and analyze building performance earlier in the design process. The intelligent objects in the building information model enable the advanced functionality of the desktop tools that are included with Autodesk Ecotect 2010 software. Using Autodesk Ecotect 2010, architects and designers can gain better insight into building performance earlier in the process, helping to achieve more sustainable designs. Autodesk Ecotect 2010 is a detail sustainable design analysis tools that can measure the impact of climatic changes on a building's energy performance.
The intelligent objects made possible through building information modeling enable the advanced analysis and simulation functionality in Autodesk Ecotect Analysis. With a 2D AutoCAD file the information required to conduct the analysis would need to be manually calculated from 2D drawings, using building plans, elevations, and details to collate spaces (type, area, volume), surfaces (including adjacency and thermal properties), and shading. With BIM, all this information is latent in a model, and in a form that is much easier to interpret than 2D drawings. The net result is a time-intensive task that might only be done once, very late in the design process. Building information modeling (BIM) is core to Autodesk's sustainable design approach for building performance analysis and simulation. Developing and evaluating multiple alternatives at the same time enables easy comparison and helps inform better sustainable design decisions. 
3.5.6 Computer Simulation Tool Selection
Currently, computer simulation techniques are used to assess the energy consumption in existing and proposed buildings. The building energy codes also require the computer simulation results of energy performance of a building to be submitted for the approval from local authorities. It is a totally new field and not yet practiced in Pakistan.
After the comprehensive study of the available energy simulation tools for the assessment of energy performance in selected case studies, a criteria for the selection of suitable simulation tool has been developed.
The computer simulation tool should fulfill the following requirements;
The software results should be validated.
The software should have a graphic interface for building modeling & data input.
The software should perform whole building performance assessment.
The software should have the capability to calculate cooling & heating loads of the buildings.
The software should be from the open source.
Literature to understand the software should be easily available.
A comparison is developed after detail investigation of already discussed energy simulation tools including;
Autodesk Ecotect 2010
Fig. 2.20 The Comparison of different energy simulation tools
After comparison of various energy simulation tools as shown in the Figure [2.20], it has been concluded that software including Energy Plus, Esp-r and DOE 2, are difficult to learn due to non-graphic modeling interface and non-existent training facilities. The Ecotect 2010 and ESPr are though good programmes, however, there results are not yet validated. Therefore, e-Quest is selected to calculate the energy performance of the selected case studies.
3.4 Building Performance Assessment Tools
Accreditation systems for measuring the environmental performance of buildings have been around for at least 20 years. They have been instrumental at driving innovation regarding sustainability issues within the construction industry. BREEAM and LEED are the two most widely recognized environmental assessment methodologies used globally in the construction industry today. 
BREEAM (Building Research Establishment Environmental Assessment Method) was conceived by BRE and was first used in 1990. The Leadership in Energy and Environmental Design (LEED) Green Building Rating System, developed by the U.S. Green Building Council (USGBC), provides a suite of standards for environmentally sustainable construction. 
3.4.1 BREEAM (The Building Research Environmental Assessment Method)
BREEAM is the Building Research Establishment Environmental Assessment Method for buildings provides an overview of an existing and established a checklist methodology currently used for the environmental evaluation of the building. This method includes the simultaneous evaluation of heat and electricity consumption that would assess the energy performance / efficiency of the buildings. 
BREEAM is supposed to be the world's most widely used method of reviewing and improving the environmental / energy performance of buildings, where "BREEAM for Offices" is widely used for "reviewing and improving the environmental performance of office buildings". BREEAM is developed in the United Kingdom by the Building Research Establishment (BRE) in the 1990; it includes both a checklist assessment and a detailed methodology for both new and existing office buildings, regardless of occupancy durations and densities. In the existing buildings the assessment method can be carried out on existing occupied office buildings, by applying the "Management and Operation BREEAM" section.
Within the "Management and operation BREEAM" section of the assessment method, energy performance issues regarding heat and electricity efficiency are covered accordingly, and it is the review of these aspects that are of significance to the assessment of building energy performance.
Generally the assessment method, is largely based on checklist assessment criteria, credits the setting of minimum requirements with regards to the energy and Co2 emissions (GHG) of a building, as well as an annually based reviews and reporting procedures for both internal and external purposes. The other particular areas of interest in this assessment method are related to the "Health and well-being" and "Energy" sections. In the "Health and well-being" section, factors pertaining towards indoor air quality are assessed and ranked. The criteria in the section includes considerations for HVAC and natural air ventilation systems, the use of daylight management, load control for temperature adjustments, and the operational compliance of other mechanical services in the building including;
Heating /cooling systems
District hot water systems
The "Energy" section of BREEAM analyses both the heat and electricity consumption of an existing commercial office building. The assessment recommends audit procedures, performed after every three years, suggest improvements based on the audits and monitoring using previous data. The assessment tool similarly favors maintenance records covering the calibration and operation for all heating and cooling system controls.
It is of interest to note that this assessment tool is not offered in its entirety except through licensed BREEAM assessor organizations and the checklist assessment reviewed is based on a pre-assessment checklist. The purported aim of this methodology lies in rating the assessed building, in order to compare similar commercial office buildings against a BREEAM performance rating score.
3.4.2 LEED (Leadership in Energy and Environmental Design).
The Leadership in Energy and Environmental Design (LEED) for Existing Buildings is another method for the assessment of energy performance for existing buildings. It is currently used throughout the United States and is based on the original "LEED Green Building Rating System for Improving Building Performance through Upgrades and Operations".
In-contrast with the "BREEAM pre-assessment checklist", LEED for Existing Buildings is a "set of performance standards for the sustainable operation of existing buildings" which earns the "LEED 2.0" certification upon satisfactory compliance. In general, the system addresses building operations and performance improvements. The focus area of this system is within the sections of energy efficiency performance and system upgrades towards;
The improvement of building energy
Indoor air quality
Lighting performance in relation to "green" performance standards
The LEED EB "Existing Building" system works in a similar manner to the BREEAM assessment, given that credits are awarded for compliance to certain performance standards, and the final score is tallied accordingly in a final scorecard. However, the public-version of this assessment standard is significantly more detailed than that of the BREEAM pre-assessment checklist.
In the "Energy and atmosphere" section, 3 prerequisites are to be satisfied before accreditation of the existing system can take place. These involve the verification and assurance that the "fundamental buildings systems and elements are designed, installed and calibrated, to operate as required" and for the establishment of a minimum energy performance for the base building systems.86 Compliance to these prerequisites are listed within LEED EB with methodological procedures, and are benchmarked on existing requirements based on the United States Environmental Protection Agency (US EPA) Energy Starâ„¢ label and the American Society of Heating, Refrigeration and Air-conditioning Engineers (ASHRAE) 90.1-1999 system.
Issues pertaining to the optimization of energy performance focuses on the intent of "rising levels of energy performance above the required standard to reduce the use of fossil fuels and to reduce the adverse impacts on the environment associated with excessive use of energy", with regulated energy components including the HVAC systems, building envelope and lighting systems, as per defined by ASHRAE. What is of interest is the unit of measure for performance - typically the energy metric, kWh of energy consumption per square meter of net building area - expressed in terms of the annual energy cost in US dollars in LEED EB. Requirements for compliance involve the provision of calculations showing that the actual energy efficiency and performance of the building exceeds those described by ASHRAE.
The "Indoor environmental quality" section focuses largely on the establishment of indoor environment conditions for the comfort of the occupant. It includes sections on the establishment of minimum indoor air quality performance and the provision of an adequate level of lighting, ventilation, temperature control, hazardous chemical control and carbon dioxide monitoring for occupant health and comfort. While this may not affect the energy performance of a building directly, the gain of energy efficiency and low energy use in a building must not be achieved through a compromise of these standards, therefore, the review of the indoor environment is important in the assessment of energy performance in a building.