Surrogate models for outdor thermal comfort evaluation and improvement. A systematic review of an emerging field

Enhancing the thermal resilience of our cities has become increasingly important. To enable designers, urban planners, and policymakers to improve outdoor thermal comfort, there is a need for new, fast, and user-friendly tools to simulate the city environment. This systematic review, based on the PRISMA guidelines, focuses on identifying emerging methods for quickly predicting thermal comfort indices, such as UTCI (Universal Thermal Climate Index) and PET (Physiologically Equivalent Temperature), using Surrogate Models—mathematical models that can replace time consuming simulations. This approach aims to facilitate data-driven performance assessments and urban design improvements. The findings indicate that current research primarily focuses on two different applications of these models: OTC evaluation and OTC improvement. In the first approach, Surrogate Models are used to evaluate the thermal comfort conditions of existing environments and to study the relationships between various factors that influence thermal perception in the built environment. In the second approach, these models can assess the effectiveness of different design strategies based on comfort performance, along with single and multi-objective optimization algorithms to identify the best-performing options. In conclusion, this review discusses the main advantages and disadvantages of adopting this methodology, highlighting the opportunities it presents for accelerating time-intensive simulations and exploring design options. Despite the promising nature of this approach, only a limited number of studies have embraced it comprehensively. Therefore, this review aims to consolidate previous scientific achievements and encourage the future adoption of this methodology.