انرژی کارآمد طراحی ساختمان با استفاده از تجزیه و تحلیل حساسیت؛ مطالعه موردی

A case-study of a public building is presented as an example of the adequacy of timely analyses of building performance, based on a preliminary architectural design. The final design of the case-study building benefited of the thorough analysis performed at this early stage, the main motivation being the willingness of a town government of an intelligent design, leading to a sustainable town-hall building, in a town in the centre region of Portugal. A virtuous combination of a receptive building owner and a multidisciplinary design team, allowed a systematic methodology to be used, providing the opportunity for the consideration of several options for each class of constructive element and the possibility of choosing among the options for each case, based on quantitative results on the expected performance of the building. The options were created and analysed with the help of the VisualDOE™ building simulation tool, aiming at a comfortable and energy efficient building. Several parameters were used for enabling the sensitivity analyses, namely relating to wall structure and materials, window frames, HVAC system, etc.

The building sector is constantly expanding, with consequences on energy expenditure, be it in the residential sector or in the service sector. The energy consumption share of buildings in the European Union (EU) is about 40% of total final energy consumed [1], which shows the importance of efficient design and quality-oriented construction in the sustainability of the EU development. In Portugal, this share is about 23% [1] but the fact that this country signed the Kyoto Protocol and the problematic evolution of annual emissions since then, imposes the need for a strict policy of energy efficiency fostering. Despite the fact that this may not yet be a top government priority, it is nevertheless a hot topic, namely due to the recent oil price crisis. The approach used in this work was informed by three key elements. First, a multidisciplinary team was gathered together for an adequate compromise solution between functionality, aesthetics, comfort and energy efficiency. Architects, engineers and researchers worked in a coordinated way for the project development [2]. Second, comfort and energy performance of the building have been evaluated at the preliminary design stage, in order to allow critical choices to be made before the final design work started. Third, the main tool used was sensitivity analysis of the influence of each element's characteristics on the overall building performance [3]. This approach was specially effective for a better justification of certain options regarding constructive elements or equipment. The main steps and outcomes of the project were: (a) simulate the building under study on an hourly basis along the period of a whole year, exploring different building design details, materials and equipment; (b) assess the thermal behaviour of a real case-study building, obtaining annual heating and cooling load curves; (c) assess the building energy consumption characteristics and their dependence on the different alternatives considered in (a); (d) the validation of the proposed methodology based on sensitivity analysis.

Building design has better results, in general but also from the standpoint of energy efficiency, when a multidisciplinary team is active right from the beginning. The use of a building energy simulator is a key factor for supporting decisions during the design stage, as it anticipates relevant information on the influence of certain options in the future building performance. A systematic approach, as shown in the paper, to the consideration of the main aspects influencing building performance has a high potential of providing adequate answers at a low labour cost. Although the majority of the aspects of building performance are not referred at this point, some particular aspects are worth being mentioned. Design temperatures should be chosen in a conservative way, higher in summer and lower in winter than is usually taken by most designers. Control systems should be programmed to allow for a span around thermostat setting (that should, on its turn, correspond to the design temperature in each season) that should not exceed 1 °C in winter but allowing for a wider range in summer, from 1 to 3 °C, depending on the difference between design temperature and external air temperature. As far as openings are considered, a satisfactory compromise between direct gains in winter and an acceptable intensity of heat exchanges with the environment may be achieved by using double glazing, window frames with thermal break and fixed shading. Air renewals are to be in accordance with the applicable rules and legislation, besides following good practice for internal air quality. Therefore, infiltration, natural ventilation and mechanical ventilation must be considered together in simulations in order to assess the most adequate compromise, especially in terms of energy consumption in mechanical ventilation. If used also for free cooling in summer, the alleviation of cooling load may prove to be economically beneficial, both in the short-term and in a life-cycle oriented appraisal [10]. The choice of the HVAC system is very relevant, because there may exist very important performance differences between options. The methodology behind the analysis of the case-study presented in the paper will be discussed in a future work by the authors.