## 4 Discussion and Conclusions  
Identifying energetic and environmental optimization potentials requires the systematic evaluation of processes and products using appropriate methods. Assessment methods vary in terms of their suitability for a specific application area--such as cooling towers. Therefore, the methods need to be classified, systematically compared, and, if necessary, extended or combined. The long-term goal is to standardize such a comparison method, something to which this study contributes, on the basis of previous approaches. This paper provides comparison criteria for a systematic selection of methods for analyzing and assessing cooling towers. By knowing the strengths and weaknesses of each of the methodologies before starting the evaluation, extensions and combinations of methods can be considered early on. The criteria were chosen to cover an exhaustive range of aspects in environmental evaluation. Consequently, some criteria within the objectives'scientific soundness' and 'usability' could only be qualitatively estimated. None of the methods met all of the secondary criteria that we defined for cooling towers. Nevertheless, all of the methods can be applied to cooling towers since all of them fulfill the exclusion criterion. The multi-criteria comparison led to the conclusion that MFA comprising energy flows is more suitable for most cooling tower analysis than pure energy analysis, ENA, or LCI. LCI is included in LCA when the entire life cycle is analyzed. Furthermore, the comparison shows that only LCA comprises the multidimensional environmental impacts. To ensure comparability between plants under different outside conditions, a uniform functional unit must consider the outside temperature, humidity, and operational requirements. In this regard, however, further research and standardization are needed. In general, the criteria's weighting depends on each study's goal and scope. The method must fulfill different criteria for other goals and scopes to be successfully applied. Similar to other studies in the field of criteria-based method comparison, we found that the methods have different strengths and weaknesses. However, our results differ in terms of the application area. For example, [PERSON] et al. [12] showed that for the energy efficiency assessment of agricultural systems, _emergy_ analysis is the most suitable; LCA and MFA are moderately suitable; and ENA and exergy analysis are the least suitable. In general, we agree with the conclusions of previous studies that the methods should be combined or extended depending on the application objectives. Future methodological developments should address the general challenges of assessing cooling systems: the dependence on dynamic outside conditions, the difficulties in defining one utility as an efficiency reference or the functional unit, and the multidimensional environmental impacts. To examine heat flows, a second-law perspective can be included, and exergy should also be considered to help define the physical benefits of a cooling system. Although this paper focuses on cooling systems, applying the evaluation method to other application areas is possible. Future studies should strengthen the standardization of the comparison method proposed in this paper and in previous studies for the long-term goals of systematic selection, combination, and the development of evaluation methods for all use cases. Experts should further review, adjust, and sharpen the criteria-based classification of the methods. This paper enables the systematic selection of assessment methods for cooling towers by comparing and analyzing different evaluation methods and their limitations based on different criteria. Quantifying the benefits of cooling for the efficiency assessment and, generally, developing an evaluation approach that ideally meets all necessary criteria is the main challenge in evaluating cooling towers. P.M.W. : conceptualization, formal analysis, investigation, methodology, and writing--original draft preparation. P.R.