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To carry out design optimization based on LCA in the design process, the following require- ments are both mandatory:

- Self-contained workflow - Maximum time for application

In addition to these mandatory requirements, which can be clearly defined, an optional requirement to evaluate the time-efficiency of the method is provided. Despite the high importance of this criterion, it is designated as optional, because measurement is difficult. 2.4.1. Self-contained workflow

Description: As described in Section 1.3.4, optimization in the architectural design process is based on a comparison of variants. Therefore, the generation and comparison of design variants is absolutely necessary. There are two approaches for design optimization: manual improvement by the architect or application of computational optimizers (see Section 1.3.4). Both approaches have their advantages and disadvantages. The optimizer can generate and evaluate a lot of variants in a short space of time and, according to a test by Szalay et al. (2014, p.22), probably find a better solution than the architect’s own experiments with manually generated variants. Therefore, the opportunity to employ computational optimiz- ers should be provided.

However, if the architect is not familiar with the algorithms that drive the optimization process, it may appear to be a ‘black box’. Furthermore, the architect needs basic knowledge about how to adjust the parameters to be varied by the optimizer to the specific boundary conditions for the design, such as required setbacks or specifications of the master plan. Besides, the automatically derived solution may not appeal to the architect for other reasons, such as aesthetic appearance or functional requirements. The optimization of a window layout on a building facade, for example, can be easily assigned to an optimizer. Exclusive use of the LCA results as an optimization criterion will probably lead to a solution that does not fulfil functional requirements, such as daylight availability or views to the outside, and might also not be satisfying in aesthetic appearance. Manually changing the design allows the architect to consider additional aspects and boundary conditions. These boundary conditions can also be integrated into the constraints of the computational optimizer, however, this implies a detailed knowledge of the optimizer. Therefore, the opportunity for manual design improvement should be provided as well. Manual generation of variants by the architect requires the opportunity to quickly adjust the geometry, building

materials, and building services. The measurement of the time needed for adjustment is discussed in the requirement for time-efficiency.

Manual input and data import hinders the application of computational optimizers and results in unnecessary effort for manual adjustment. Therefore, it should be avoided. For both optimization approaches – the application of computational optimizers and manual adjustment – a self-contained workflow of the method employed is a crucial prerequisite. Yes-no question: Is the method’s workflow self-contained?

Documentation: Description of the calculation algorithms and the workflow of the method.

2.4.2. Maximum time for application

Description: As described in Section 1.4.3, the time needed for LCA depends on the method itself and the boundary conditions, including the size of the building, amongst others. This makes it difficult to define an exact maximum acceptable amount of time for the calculation of an LCA for a building. In the literature, no exact maximum time can be found. Most studies evaluate tools qualitatively and describe the time-efficiency with attributes like “quick data input” (Weytjens et al. 2011, p.2449) or “calculation time is short” (Meex et al. 2016, p.1313), for example. Other studies on building performance analysis state that the results have to be calculated and visualized in real time in order to serve as a design support tool (see Schlueter & Thesseling 2009, p.159; de Souza 2009, p.295), but do not provide a maximum acceptable amount of time for the input. Therefore, a maximum acceptable time for the application of the method can only be assumed here.

The Federal German Chamber of Architects recommends that its members do not spend more than 140 hours up to design stage 3 for a regular single-family house in order to work cost-effectively62_{. Considering all of the tasks that architects have to carry out, it is assumed}

that the maximum amount of time they can spend on an LCA for a building, including all data input and optimization, is one work day, respectively 8 hours, for a small to mid-size

residential building. For very large or complex buildings, including mixed-use, two work days (16 hours) can be assumed as a realistic maximum time.

62 _{The recommendations can be downloaded at http://www.byak.de/start/informationen-fur-}

Yes-no question: Is the time required for application of the method less than 8 hours for typical residential buildings and less than 16 hours for complex, mixed- use buildings?

Documentation: Declaration of the time required to apply the method. 2.4.3. Time-efficiency

Description: Although very important, this requirement is described last, because it is based on many of the requirements described previously. As described in Section 1.4.3, the time- efficiency of an environmental design optimization method can be defined as the ratio between the reduction in environmental impact and the time needed for the application of the method. In order to measure time-efficiency, both the reduction in impact due to application of the method and the time needed for its application have to be measured. To measure the reduction in impact, the optimized solution can be compared to a bench- mark or a baseline solution. Benchmarks can be found in the literature, for example Braune (2014, p.173) or König et al. (2010, pp.52-57), or in guidelines for building certification systems. An overview is provided by Wittstock et al. (2012, pp.348–351). In the case of a building refurbishment, the design variant can be compared to the original state of the building. As the reduction in impact is highly dependent on the choice of the baseline scenario employed, this requirement is recommended as an optional criterion for evaluating an environmental building design optimization method, but no minimum reduction is prescribed. Furthermore, for reasons of transparency, the reference values should be communicated clearly.

The time required for input, calculation, and output of the first variant varies significantly from the calculation of the following variants for the commercial LCA tools for buildings analysed in Section 1.4.2.1. Therefore, when measuring the time needed for application of the environmental building design optimization method, a distinction is made between the time necessary for the first variant and the time required for the further variants developed to optimize the design. Furthermore, based on the recommendations of Schlueter & Thesseling (2009, p.159) and de Souza (2009, p.295), the optional recommendation is that the calculation itself should occur in real-time in order to allow the architect to receive direct feedback during the design process.

Optional questions: a) How much can the environmental impact be reduced? b) How much time is needed for the first design variant? c) How much time is needed for the optimization process?

Documentation: a) Description of the baseline scenario and declaration of the improve- ment.

b) Declaration of the time required for the first variant and the bounda- ry conditions, including the experience level of the user, the type of building, and the performance of the computer employed.

c) Declaration of the time required for optimization and the number of variants analysed.

2.4.4. Summary of Section 2.4

Which requirements are necessary for optimization?

To carry out design optimization based on LCA in the design process, the two following requirements are mandatory:

- Self-contained workflow (M): To allow for optimization using computational optimiz- ers and to facilitate manual improvement, the method’s workflow needs to be a closed loop. This can be demonstrated by describing the calculation algorithms and the workflow of the method.

- Maximum time for application (M): It is assumed that, in order to be applicable to the design process in architectural practice, the time needed for application of the method needs to be less than 8 hours for typical residential buildings, and less than approximately 24 hours for complex mixed-use buildings. The time required should be documented, including a description of the boundary conditions for applying the method, such as the performance of the computer or the experience level of the us- er.

- Time-efficiency (O): In addition to the mandatory requirement to set a time limit for application, time-efficiency can be assessed by measuring the reduction in environ- mental impact compared to the time needed for the optimization process. As the reduction in impact is highly dependent on the choice of benchmark, considering time-efficiency is recommended as an optional criterion only, despite its importance.