We highlight the importance of building energy simulation and describe its various applications aimed at achieving energy efficiency solutions. The advent of desktop computing has made it possible to perform detailed calculations and building energy performance simulation at low costs. With appropriate computerised engineering tools, professionals would be able to evaluate various energy saving options before deciding on implementation. In this presentation, we also describe and teach the use of a specially developed computer code for energy standards compliance and energy efficiency calculations.

Large commercial buildings that require air conditioning all year round are energy-intensive. Air conditioning typically contributes more than half of the energy consumption of a commercial building. As the building sector accounts for more than one-third of the total electrical consumption in Singapore, it is imperative that today’s buildings be designed for energy efficient operation throughout its lifetime. To achieve this, the response of a building to weather conditions and load changes need to be well understood. Conventional design methodologies are now being surpassed by computerised engineering tools that allow the performance of the building to be simulated long before its construction.

Meanwhile, building authorities worldwide have begun or completed the drafting of building performance standards taking advantage of the proliferation of personal computers and the rapid increase in computational power available to run sophisticated building simulation programs. Ensuring energy efficiency is important because it helps to reduce a nation’s energy needs and leads to better utilization of existing energy resources. Concentrated efforts to reduce energy consumption will help to mitigate adverse impacts on our environment. Achieving energy efficiency also helps to reduce our dependence on fuel imports and improve our economic competitiveness.

It is to this end that the Building and Construction Authority (BCA) formulated the Building Energy Efficiency Master Plan (BEEMP) as part of Singapore's efforts to improve building energy efficiency. This plan contains programmes and measures dealing with energy efficiency that span the whole life cycle of a building. Today, the need to achieve higher energy efficiency and better building designs has spurred BCA to focus on an energy performance standard for buildings in Singapore. This is a substantial upgrade from standard criteria as specified in the Handbook on Energy Conservation in Buildings and Building Services [1].

Correspondingly, Building Energy Standards (BEST), a Windows based software has been developed by the National University of Singapore (NUS) in collaboration with BCA. It is designed to be used as an engineering tool for compliance with the building envelope, air-conditioning and mechanical ventilation systems and artificial lighting requirements as depicted in the BCA Approved Document as well as the overall energy performance criterion.

The thermal interactions between a building and its environment are complex. To account for the complexities of the energy transfer processes occurring between the external environment and the building and among its various components and systems, building energy simulation (BES) is adopted as a standard technique. BES is a necessary routine employed to analyse the energy performance of a building as an integrated system. With BES, the possibility of a prediction of future reality at the design stage can now be realised [2] and can lead to a more energy efficient building stock. While the more detailed BES tools remain mostly within the research community, the wide-spread availability of desk-top computing and global connectivity offered by the internet have contributed significantly to the application of BES in professional practice as design tools. Hong and others [3] provide valuable information on BES and the various engineering tools available to professionals.

BES involves the use of computer analysis techniques to determine the energy performance of a building and its systems. Besides offering an effective design decision support, building energy simulation can be applied in practice by designers with limited knowledge of technology [4]. Nowadays, BES is used in areas such as building design, operation, management and air-conditioning system design. Some applications of BES [3] are highlighted in the following sections:

1. Study of load profiles and energy usage patterns of building
2. Selection of building systems for better energy performance of building
3. Economic analysis
4. Calculation of energy budget of a building
5. Evaluation of energy saving options
6. Complying with building regulations, codes, and standards

BES can be employed to design the building to the requirements of local building regulations, codes, and standards. Subsequently, BES can supplement energy auditing to check the energy performance of the as built building.

There are currently many computerised BES codes available to professionals. As different BES codes vary in complexity, calculation algorithms, ease of use and cost, the codes have their advantages and disadvantages. The user’s experience and computer literacy skills also play an important role in performing building energy simulation. It is foreseen that BES will be more frequently and widely applied in building design and analysis as it can be under-taken with greater ease and lower costs using personal computers.

The Department of Mechanical Engineering of the National University of Singapore has developed a window-based, BES code, BEST, specifically aimed at performing standard compliance calculations. BEST (synonym for Building Energy STandards) is a design tool that can be used by engineers, architects and building services professionals to meet the requirements of prescriptive and energy performance standards relating to air-conditioned commercial buildings. With this software, users are able to perform building energy calculations while designing an energy efficient building.

The energy performance standard calculations adopted in BEST require the user to specify two buildings, namely the design building and the prototype building. The design building is the proposed building under study having the actual design specifications and operating conditions. This building may deviate from the prescriptive standards when its energy estimate is being determined. On the other hand, the prototype building has the same design, shape, size and usage of the proposed building, but meets all the requirements of the prescriptive standards. This building is used to establish an annual energy consumption budget for the building being designed. Figure 1 illustrates the compliance process for the prescriptive and energy performance standards incorporated in BEST.

The above methodology is in line with the Building Energy Cost Budget Method proposed by ASHRAE Standard 90.1 [5]. Using a simple yet accurate energy analysis procedure, the methodology, as illustrated in Figure 1, is to determine the annual energy demand and consumption of both the prototype building and the design building. Then, for the proposed design to comply with the energy performance standard, its annual energy consumption must be shown to be lower than that of the prototype building. This approach effectively allows professionals to innovate and achieve the standard with suitable trade-offs.

Among other possible trade-offs, of interest is the energy saving options made available by the energy performance standard. When considering retrofitting of the existing building or embarking on the design of a energy conscious building, these saving options could be used to reduce the annual energy estimate of the designed building.

BEST is capable of the following:

1. Calculation of the envelope thermal transfer value (ETTV) and the roof thermal transfer value (RTTV) for prescriptive standard compliance.
2. Estimation of the annual energy consumption of buildings.
3. Estimation of the peak design loads for air-conditioning equipment sizing and zone thermal comfort design.
4. Calculation of the building’s lighting power allowance and receptacle power density using user-defined design values.
5. Prediction of effects of multi-parametric changes on the energy use of buildings.
6. Selection of energy saving options to reduce annual energy consumption of buildings.

Figure 1: The compliance process for the energy performance standard.

BEST uses the standard Windows Graphics User Interface (GUI) that contains forms, which allow the user to enter the necessary data and read the desired results. The forms are represented through a main interface, which provide easy access to sub menus. These sub menus which facilitates the viewing of the various inputs and outputs are as follows:

1. Inputs and Standards Sub Menu

The Inputs and Standards sub menus contain forms that allow the end user to input the basic information. Through these forms, which have input objects, the end user is allowed to input the abovementioned information into BEST. The basic input requirements and the corresponding sub menus and forms in which these inputs can be made are summarized in Table 1. The energy performance standard and one of the prescriptive standard forms are illustrated in the Appendix.

 

2. Results Sub Menu

The results obtained from the building energy calculations performed in BEST are represented through the results sub menu. This sub menu contains a result summary form and a final summary form that presents the annual energy estimates without saving options and with savings option respectively. In addition, a total savings summary form is also included in this sub menu to show the amount of energy saved using the various saving options available in BEST. The result summary form is shown in the Appendix.

 

3. Savings Sub Menu

The various saving options incorporated into BEST are available to the user through forms in the Savings sub menu. These options include daylighting, solar water heating, and the use of heat pump, heat wheel as well as external shading devices.

1. The heat pump energy recovery system is a cost-effective option for meeting hot water requirements in buildings. Operating with an efficient thermodynamic cycle, it could reduce energy costs and conserve valuable energy resources.
2. Another energy saving option is to use a heat wheel energy recovery system. The heat wheel is basically a rotary regenerator where heat transfer is achieved with a disk rotating between a cold air duct and a warm air duct.
3. Another energy saving option is to use solar energy to provide for water heating in buildings. Solar collectors with relatively good conversion efficiency could be used for moderate temperature applications in buildings.
4. The use of external shading devices to reduce heat due to solar radiation into buildings is another possible saving option. BEST is capable of calculating the effective shading coefficient of the external shading devices at each building facade. The method of computing horizontal, vertical and egg-crate types of shading devices is contained in a handbook [1].
5. Daylighting involves the strategy to bring natural light from outside a building into the building. There is potential for savings in commercial buildings as lighting energy consumption of a building may be reduced during its peak operating period. Also, daylight is cooler than electric light while having higher luminous efficacy.

The forms and required inputs for the respective various saving options are summarized in Table 2. A sample form of one of the saving options in the Savings sub menu is illustrated in the Appendix.

In addition, the Savings sub menu form also contains the Life Cycle Cost and the Tariff Rates forms. The Life Cycle Cost (LCC) methodology employed in BEST would allow the user to be able to calculate and present the cost of a building’s energy consumption as well as investments made in implementing saving options. In order to calculate the cost of electricity to a building, tariff rates levied onto electricity bills must be know. The user can input these rates in the Tariff Rates forms. The method used to calculate the electricity cost in BEST mimics the actual billing structure levied upon the consumer by Singapore Power. With these forms, the user has the capability of making cost effective choices for a given building, facility or system in deciding to accept or reject a given investment aimed at lowering building cost.

Table 1: Basic Input Requirements for BEST

Table 2: Input Requirements for BEST Saving Options

Besides functioning as a design tool, BEST also incorporates a number of additional features that are accessible to the end user via the Utilities sub menu. These features are:

1. Parametric analysis. This feature has built-in functions that allow the end user to vary a number of parameters to see its effects on ETTV, annual cooling energy and annual total energy consumption of the design building.
2. Quick energy estimates. This feature allows the end user to enter certain parameters of the design building to make a quick estimate of the building's annual cooling energy without having to fill in the various input forms in the sub menus.
3. PEAKLOAD. This is an external windows based software that allows the end user to calculate the design day cooling loads of a building based on the ASHRAE transfer function method [6].
4. Thermal Transmittance Kalculator (TASK). This is another external window based software that was developed to complement the use of BEST. It was developed with close reference to the various methods of computation recommended in the ASHRAE Handbook of Fundamentals – 1980 [7]. TASK allows the end user to compute the thermal transmittance or U values of walls and fenestrations quickly and easily.
5. ETTV calculator. This feature allows the end user to determine the maximum allowable ETTV for a building given the prescriptive limit for the OTTV. In essence, the ETTV calculator serves as an easy-to-use tool for converting OTTV to ETTV.

A sample form in the Utilities sub menu is shown in Appendix A.

In addition to the sub menus in BEST, a Win Help file BEST.HLP is available to help the end user operate BEST efficiently and cost-effectively when calculations are performed in complying with the building energy standards. This help file can be accessed via the on-line help menu or by pressing the F1 key anytime when BEST is being run. The file also contains 5 worked examples for different building types with and without applying saving options to demonstrate the use BEST to new users.

There are many issues pertaining to the use of BES for specific purposes, the choice of building simulation package to be used, and the development of such engineering and design tools [8]. Factors affecting the choice of BES packages include costs, ease of use, program interface, performance of program and background knowledge of user. In Singapore, large commercial buildings are becoming more energy intensive because of the demand for more sophisticated services and thermal comfort. With the availability and lower costs of computer technology nowadays, appropriate computerised engineering tools can be used for the design and operation of energy-efficient large buildings to meet thermal comfort and indoor air criteria. Building energy simulation can also be performed at lower costs.

In addition, the internet can serve as an effective medium for introducing and disseminating information on building energy simulation to interested parties [9], including building professionals and academics.

New technologies in planning, design and operation for energy efficiency often require the use of computers, and with the advent of desktop computing, building energy simulation is expected to grow in importance. A new energy performance standard is being proposed for use in Singapore so as to achieve higher efficiency levels and greater energy savings. We demonstrated an engineering compliance software, BEST, tailored for use by professionals to perform calculations aimed at achieving energy efficiency in buildings and compliance of energy performance standards. Ultimately, it is worth emphasizing again that energy efficiency will have to be translated to "in the pocket" savings for the public for it to be readily accepted and practised.

1. Public Works Department. Handbook on Energy Conservation in Buildings and Building Services, Development and Building Control Division Publication, Ministry of National Development, Singapore, 1983.
2. Clarke, J. A. and D. Irving. Building Energy Simulation: An Introduction, Energy and Buildings, 10(3), pp. 157-159, 1988.
3. Hong, T., S. K. Chou, and T. Y. Bong. Building Simulation: An Overview of Developments and Information sources, Building and Environment, 35(4), pp. 347-361, 2000.
4. Clarke, J. A. Assessing Building Performance by Simulation, Building and Environment, 28(4), pp. 419-427, 1993.

5. ASHRAE. ASHRAE Standard 90.1-89, American Society of Heating, Refrigeration and Air-Conditioning Engineers, Inc., Georgia, U.S.A, 1989.
6. ASHRAE (1997). ASHRAE Handbook of Fundamentals 1997, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta, USA.
7. ASHRAE (1980). ASHRAE Handbook of Fundamentals 1980, American Society of Heating, Refrigerating and Air-Conditioning Engineers, New York, USA.
8. Hensen, J. L. M., J. A. Clarke, J. W. Hand, and P. Strachan. Joining Forces in Building Energy Simulation, In Proc. 3^rd IBPSA World Congress on Building Simulation ’93, International Building Performance Simulation Association, Adelaide, August 1993, pp. 17-24, 1993.
9. Hensen, J. L. M., M. Janak, N. G. Kaloyanov, and P. G. S. Rutten. Introducing Building Energy Simulation Classes on The Web, ASHRAE Transactions, 104(1A), pp.488-494, 1998.