*3.2. Perspectives on the Use of Advanced Simulation Methods*

Provided that the ideal physical model for built environment and energy performance assessment is available, it could be integrated to a decision-making procedure in the context of a retrofitting strategy. Building design optimization is indeed a complex task, since the optimal solution should satisfy many criteria, e.g., energy saving, emissions' avoidance, and cost-efficiency indicators (NPV, payback period, etc.). Scientific research has already presented advanced optimization methods and tools to respond to the aforementioned challenge. For example, Nguyen et al. [157] reviewed simulation-based optimization methods in the building sector. They provided an overview on the subject focusing on discontinuous multi-modal building optimization problems, the performance of optimization algorithms, multi-criteria optimization, surrogate models, stochastic optimization, and the propagation of optimization techniques into real-world design challenges. The paper is recommended as a good source of studies and approaches for building energy optimization. Handling of large databases that emerge by extensive parametric simulation analysis towards the identification of optimal solutions is a cutting-edge issue, especially in the context of recent energy regulations. For example, the EU directive 244/2012/EU suggests the exercise of extensive parametric analysis in the scope of identifying the cost-optimal minimum energy performance requirements of buildings and, furthermore, the identification of the nearly zero energy building (NZEB) levels. Responding to the NZEB challenge, Cao et al. [158] reviewed the feasibility of categorized state-of-the-art technologies, namely, passive energysaving technologies, energy-efficient building service systems, and Renewable Energy Sources. Based on data derived from international energy reports for the US, China, and the EU, they introduced a ZEB concept.

Although new developments regarding advanced physical modelling have flourished during the last 20 years, it is true that they lack acceptance by the wider engineering and architects' community. An extensive survey presented by Fernandez-Antolin et al. [159] showed that one of the main reasons for limited preference on using advanced simulation tools by recent graduate architects is that they consider them inconvenient and challenging to learn. The study suggests that a key driving force to boost the use of such simulation tools in practice is to integrate related education courses, even at the undergraduate level, e.g., in design courses and in building system courses. In the same study, recommendations to software vendors to improve user-friendliness of the problem setup (geometrical model and input conditions) are also reported. Emphasis on bridging the gap between the use of building energy simulation tools and architectural design is given by researchers of the same team [160]. The study raises the dilemma of suggesting the use of energy simulations in the early design stages and concluded that modern architects should be capable to understand simulated results in the context of suggesting design solutions. To that direction, it is acknowledged that teachers in higher education institutes should bring and exercise advances of simulation tools to the attention of students (future architects and engineers). From the software vendors' side, it is expected that no further increase in cost is presumed in case of providing additional information and guidelines when requested. In addition, the administration of educational institutions should also encourage their use

in a constructive way, envisaging subsidies and incentives to boost their adoption, and being responsible for reviewing the projects before granting a license.

The usefulness of utilizing reliable simulation tools in the architectural design stage has been highlighted and demonstrated in many studies (refer, for example, to ref. [161]). In this context, Xie and Gou [162] exploited two case studies (a Sports' Centre and a Hotel) that compare building performance simulation as an early intervention and a late verification tool in the architectural design process, contextualizing the building simulation research in real building practices. In the first case study, a simulation tool was integrated in the early-design stage, while, in the other one, the simulation tool was used at the post-design stage, mainly to verify the results obtained by the suggested architectural design. Through collating technical results with those of designers' perceptions regarding the usefulness of simulation tools via questionnaire surveys, it was concluded that a design team must not only provide quantitative results to obtain accredited building design but also provide documentation of at least two design strategies towards the confirmation of the schematic design. This suggests that the focus of green building rating systems is shifting from simply obtaining accurate quantitative goals for the decision-making process. The present focus is to encourage the selection of multiple design plans and optimize the design solutions.
