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Article Excerpt
Abstract: Energy standards impact upon building performance. This paper presents a framework to develop energy standards for buildings based upon established benchmarks. The framework first optimised building design, and then used the outcome to develop energy standards for office buildings. Energy-10 was used to model and achieve energy performance targets by optimising the energy design of a single storey-building model. The outcome of optimising the model provided the basis for developing two types of energy standards--prescriptive standards and performance standards. As the developed model may not fit with other sensitivities and elements of building design, a performance scale was provided in order to present optimum and close-to-optimum designs. It was intended that this study would show how the building design optimisation, structured towards established benchmarks, could support the development of energy standards. The applicability of the performance scale is demonstrated through a case study from Bahrain.
Keywords: Design optimisation, Energy standards, Office buildings
Introduction
There is no question that the majority of buildings in the Gulf States, particularly offices, are designed and built without due attention being paid to energy consumption and the local environment. Today, under the umbrella of a worldwide international style of buildings, and in an attempt to embark on a new trend of modern architecture, huge glass facades facing the sun have appeared in cities such as Dubai, Riyadh, Doha, and Manama. In energy terms, this glazing strategy is generally applied to maximise solar gain in order to heat up buildings and to utilise daylight--consequently, this strategy it is often used for cold climates. For hot climates, however, such as those of the Gulf States, using this strategy may lead to a different scenario with respect to cooling load. To apply this strategy in hot climates, the energy design should utilise the availability of useful daylight by striking a balance between light and heat gain. This is, however, not the case in Gulf States. Huge projects have been constructed with enormous glazed facades facing the southeast and southwest without protection against overheating and sun glare in the summer. It is, therefore, not surprising that 45%, 70%, 83% and almost 70% of the yearly electric energy consumption is consumed by building systems in Kuwait, Saudi Arabia, Bahrain and the United Arab Emirates respectively (Electricity and Water Authority, 2003; Iqbal & Al-Homoud, 2007; Maheshwari & Al-Murad, 2001). These statistics imply the necessity of developing new energy standards and setting benchmarks for the maximum allowable electricity consumption in buildings.
Development of Building Energy Standards
Over the last few decades, many nations have been responding to the increase in energy demand by introducing suitable building standards. These standards have been used and developed to provide a degree of control over building design and to encourage awareness of energy efficiency. Title-24 in California (California Energy Commission, 2008), the Approved Document part L2 in the UK (Triker & Algar, 2007) and the Overall Thermal Transfer Value (OTTV) in the Asian countries are examples of such standards (Yik & Wan, 2005). There are two approaches for energy standards: prescription and performance. Prescription sets minimum design requirements for key energy use aspects in buildings, whereas performance concerns itself with the energy performance of the building as a whole by setting a target or a benchmark for the level of energy performance without prescribing the procedures and methods to achieve that benchmark. The prescriptive approach is simpler to comply with where each building component is passed separately from the others. The prescriptive approach often contains specified maximum or minimum values to ensure the proposed design meets specific energy efficiency criteria. However, if the design fails to meet even one requirement then the component does not comply with the standards. Importantly, this approach also limits the freedom of the building designer and gives less flexibility for architectural innovation. Conversely, the performance approach provides greater flexibility to the building designer for choosing alternative energy efficiency measures since it considers in its evaluation the energy consumption, C[O.sub.2] emissions or the energy cost for the building as a whole.
In developing energy standards different techniques are used, namely experimental and analytical methods, good practice and building simulation (CIBSE, 2004). For instance, the DOE-2 simulation program was a key tool in developing the energy standards in over 30 countries, including the USA, Singapore, Australia, Mexico and Egypt (Deringer, Lyer & Huang, 2004). Developing the Mexican and Egyptian standards followed almost the same methodology. Firstly, models were developed for buildings based on the physical characteristics of the existing buildings; secondly, analytical methods were used to determine the factors influencing the energy consumption; thirdly, standards were developed and, finally, building simulations were performed to evaluate the impact of these standards on the energy performance of the case models. This methodology helped in developing standards for commercial and residential buildings for Egypt similar to those of ASHRAE-90.1 (Huang, Deringer, Krarti, & Masud, 2003). Many benefits can be obtained when such a methodology is used--it takes into account a great number of variables that impact upon the energy consumption, it generates performance targets and it compares a wide rang of design alternatives. However, the judgment is based on the human experience (as the user of the simulation program determines the combination of design variables), which may imply that some better alternatives have been omitted. To avoid this situation a new methodology was presented by Shaviv, Yezioro and Capeluto (2008) in which a conceptual framework was first proposed and then an optimisation model was incorporated into a simulation program (Yezioro & Capeluto, 2007) to provide optimum prescriptions for office and residential buildings. The outcome of this optimisation represented the base for the prescriptive standards. This optimisation used the climatic design as a basis to develop energy standards. A prime advantage of this methodology is the use of sensitivity analysis techniques to find different design solutions.
The optimisation technique has been used in many projects with different agendas. The Building America...
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