Subtask A - Fundamentals

Subtask leaders: Bjarne Olesen (Technical University of Denmark) and Vincenzo Corrado (Politecnico di Torino)

Subtask A establishes essential criteria for boundary conditions between buildings and outdoor space as well as key performance indicators (KPIs) on urban cooling, to provide solid foundation for the Annex activities.

In this subtask, we will collect and develop relevant key performance indicators (KPIs) to assess the performance, sustainability, and resilience of cooling solutions. Our focus will be on how well these solutions integrate with resilient building technology and urban heat mitigation strategies. We will take a holistic approach, considering indoor and outdoor air quality, comfort, physical and mental health, productivity, safety, energy efficiency, environmental impact (such as greenhouse gas emission reduction), as well as cultural, social, and economic facotry, including affordability, usability, and availability. Our primary focus will be on people working outdoors as well as those engaging in leisure activities or taking outdoor breaks during working hours. The targeted activities of Subtask A are structured as described below. Gathering and synthesizing current knowledge are crucial aspects of this endeavor. The collaborating institutions and countries should work closely together and acitvely exchange information.

Activity A.1: Develop a knowledge base for urban cooling. This activity will involve a comprehensive review and synthesis of current knowledge on urban cooling technologies and solutions, as well as human exposure to outdoor and semi-outdoor environments. It will include a thorough examination of literature and case studies from various countries, focusing on best practices in urban cooling and the impact of exposure to outdoor conditions during work, breaks, leisure, and transportation. The results will be compiled into a detailed database, which will serve as a foundation for defining Key Performance Indicators (KPIs) in Activity A.2 and establishing boundary conditions in Activity A.3.

Activity A.2: Define fundamental boundary conditions. This activity focuses on the definition of fundamental boundary conditions that influence the performance of cooling strategies in cities by Page 5 of 30 considering the physical properties of building envelopes and outdoor features, urban layout and design, microclimate and local climate data, energy systems, and socio-economic and cultural factors. The boundary conditions derived from this research activity will be integrated into the activity of subtask B.

Activity A.3: Establish comprehensive KPIs. This activity focuses on establishing a comprehensive set of KPIs to evaluate the comfort, health, productivity, safety, resilience, and sustainability of cooling solutions in urban environments. By reviewing existing literature, consulting with experts, and conducting stakeholder workshops, the activity aims to create a validated list of KPIs that can be applied to measure the effectiveness of various cooling solutions in different urban settings. The KPIs derived from this research activity will be integrated into the activity of subtask C. 

Activity A.4. Classify and create a taxonomy of urban cooling. The preliminary activity carried out in Subtasks B (Activity B.1 - Review simulation tools and their validation level), and C (Activity C.1 - Review and compare existing solutions) will be used to classify methods and cooling solutions, and to create a taxonomy.

Subtask B - Methods

Subtask leaders: Auline Rodler (CEREMA) and Claudia Fabiani (Università degli Studi di Perugia) / Anna Laura Pisello (Università degli Studi di Perugia)

Subtask B aims to develop simulation and experimental methods to provide a strong foundation for the Annex activities related to urban spaces and cooling technologies. The goal is to address the need for adapted methods and heat vulnerability indexes in various urban contexts. 

This subtask is divided into five main contributions:

Activity B.1: Review simulation tools and their validation level. Urban microclimate tools are effective for testing the impacts of climate adaptation strategies and comparing different strategies, while BEM tools display the influence of local climate on indoor comfort and on building energy demand. For the Annex, the most important aspect is linking both tools to study the dependencies between urban heat mitigation and the scope for sustainable cooling of buildings.

This involves assessing variables such as air temperature, humidity, wind speed, and surface temperatures, among others. This method enables high-resolution spatial and temporal analysis of urban climate and indoor overheating. Using input files representing future climate scenarios, these tools can evaluate the impact of cooling strategies tailored to future climates. The review of each urban microclimate and BEM simulation tool involves three steps:
First, we will compare their features and capabilities to select a supporting tool. These tools will be described based on aspects including but not limited to:

• Use (research tool/ practice-oriented for stakeholders in the design and planning)
• Mathematical approach (analytical, physical based, artificial intelligence)
• Complexity and assumptions of the considered physical exchanges (e.g., accuracy of radiation to consider a retroreflective material)
• Coupling of indoor (BEM)/outdoor models
• Use of future climate data

Second, the level of validation of each tool will be introduced and presented to consolidate the different protocols. This will help to establish a comprehensive global validation protocol and possible assessment of the different tools.

Third, we will develop a validation protocol definition, such as Building Energy Simulation Tools Test Procedures (BESTEST), to facilitate a step-by-step assessment and pinpoint any inconsistencies. This will include reference data and benchmarks for method comparison. We need high-quality experimental data sets for both simple and complex real configurations to connect with the experimental aspect.

Activity B.2: Review and evaluate existing experimental methods. In this activity, methods for evaluating the performance of urban cooling solutions, including both fullscale outdoor experimental approaches and sub-scale tests, will be systematically analyzed and compared. The goal is to gain a comprehensive understanding of each methodology, offering a detailed overview of their strengths, weaknesses, and opportunities. This will support the strategic selection of appropriate methods based on the specific cooling solution, the scale of investigation, and the unique characteristics of the urban environment. Key methods to be considered include:

• Transect Monitoring: This method involves the systematic collection of environmental data by moving across different urban zones, typically along predefined routes or transects. By measuring variables such as air temperature, humidity, wind speed, and surface temperatures, transect monitoring helps identify local microclimates and hotspots where cooling solutions are most needed. This method also allows for high-resolution spatial analysis of urban heat patterns, highlighting areas that are vulnerable to heat stress and could benefit from targeted cooling interventions.
• Satellite Measurements: Remote sensing via satellite imagery offers a broad and comprehensive view of urban areas. Satellite data can capture land surface temperatures, vegetation cover, and impervious surfaces, all of which are critical indicators of urban heat islands. These measurements provide a valuable macro-level perspective on how different parts of a city respond to heat and can help identify large-scale areas that require cooling. This method is especially useful for large urban areas where ground-based measurements may not be feasible.
• Weather Station Networks: A network of weather stations distributed across an urban environment can provide continuous, real-time data on key environmental variables such as temperature, humidity, wind, and solar radiation. This method allows for the monitoring of temporal variations in urban heat and helps capture local variations in climatic conditions. The data collected from these stations can also be used to validate and calibrate models or to track the performance of cooling interventions over time.
• Multimodal Information: Combining data from different sensory sources—including environmental sensors, satellite data, and human physiological and societal sensing—enables a more holistic understanding of urban heat dynamics and the human comfort. This multimodal approach allows for the assessment of both physical and experiential factors, bridging the gap between objective measurements and subjective human perceptions. Multimodal data can include wearable devices to track human physiological responses to heat (e.g., heart rate, skin temperature), along with environmental data to better understand how individuals interact with and perceive their urban surroundings. Each of these methods provides unique insights into the urban environment and the challenges associated with heat stress. Comparing these approaches will help identify the most appropriate methods for specific cooling solutions, considering the scale of the intervention (e.g., building, neighborhood, or city-wide) and the intended outcomes.
• Sub-scale tests, such as water tunnel, wind tunnel, and helium wind tunnel tests, allow for evaluating cooling solutions under controlled conditions. These tests help improve the performance of the solutions and gather accurate and calibrated experimental data for model validation.

By combining these different methods, we can create specific guidelines (Activity B.5) for effectively applying each technique in different urban settings. These results will help evaluate and implement innovative cooling solutions, especially those suggested in Subtask C. A unified framework for choosing and using these methods will guarantee that cooling strategies are tailored to the particular requirements of urban areas, maximizing their effectiveness in reducing heat stress and enhancing overall urban comfort.

Activity B.3: Define urban archetypes and adapted metrics.The first part of this activity will focus on defining typical urban archetypes to help evaluate urban cooling solutions through modelling and simulation and to understand building-environment interactions. These archetypes will provide a standard reference for assessing the performance of different cooling solutions and ensuring comparability across studies.

The second part will involve identifying and proposing integrated time and/or spatial indicators as well as heat vulnerability indexes. This process will include adapting and developing new neighborhood performance indicators, with a particular focus on mitigating overheating while considering the building archetypes, city urban configurations, and infrastructures. The first task will be to propose physics-based indicators for specific urban configurations that have been simulated. This task will be carried out in close cooperation with Subtask A.

Activity B.4: Develop a framework for integrating user perceptions and experiences into the evaluation of cooling solutions. User perceptions and experiences are crucial for a comprehensive evaluation of urban cooling solutions, the priovide important insights beyond quantitative data from models or field monitoring. By using a multidomain analysis and integrating environmental monitoring with a multisensory approach, we can better assess vulnerabilities and individual responses to urban cooling interventions. This will involve designing a comprehensive multi-modal survey tool that captures
qualitative aspects of user feedback and integrates data from multi-sensory monitoring, including physiological responses, sensory experiences, and environmental stressors. This multisensory approach allows for a deeper understanding of how users perceive comfort and vulnerability across different conditions. In addition to gathering user feedback, methods for analyzing and interpreting this multimodal data will be explored and compared. By combining subjective perceptions with objective environmental metrics, the assessment framework becomes more holistic and human centered. The result will be a more robust evaluation of urban cooling solutions, one that reflects the complexity of human-environment interactions and addresses varying degrees of vulnerability across populations.

Activity B.5: Develop guidelines for experiments & simulations. 

This activity will focus on developing comprehensive guidelines to support both experimental testing (outdoor environmental monitoring) and simulation approaches for evaluating urban cooling solutions. The aim is to standardize methodologies for both real-world data collection and simulation-based analyses, ensuring consistency and accuracy in performance assessments. Building upon the analyses from Activity B.1 and B.2, this activity will address the following key components:

• Outdoor Environmental Monitoring Guidelines: For outdoor environmental monitoring, the guidelines will define the minimum requirements necessary to conduct effective measurements, considering factors such as temporal and spatial resolution, spatial coverage, and the appropriate scale of analysis. The goal is to develop standardized protocols for various monitoring techniques, including mobile monitoring, fixed weather stations, remote sensing methods, and sub-scale tests. Drawing on the analyses from previous activities, this phase will seek to optimize monitoring strategies by potentially combining different methods to achieve the required level of detail for evaluating the performance of cooling solutions across various urban environments.
• Simulation Guidelines: For outdoor and indoor simulations, the focus will be on providing detailed guidelines for selecting the appropriate simulation tools based on the type of cooling solution, the scale of the project, and the specific urban context. The guidelines will consider factors such as the limitations and assumptions of different simulation models, their validation levels, and their availability and ease of use. This phase will also build on previous analyses to ensure that the recommended simulation approaches are aligned with the real-world testing protocols, creating a holistic framework for evaluating cooling solutions through both monitoring and modelling.

The integrated guidelines will help users choose appropriate monitoring techniques and simulation tools, ensuring that both real-world testing and modelling are aligned to achieve reliable assessments of urban cooling solutions.

The outcome will be a set of integrated guidelines that support users in both empirical data collection and simulation-based assessments, ensuring that the methodologies for testing and modelling urban cooling solutions are complementary and reliable.

Subtask C - Solutions

Subtask leaders: Chen Zhang (Aalborg University), Dahai Qi (Université de Sherbrooke), Priya Rajagopalan (RMIT University), Ronnen Levinson (Lawrence Berkeley National Lab)

Subtask C (Solutions) will review, assess, and compare existing approaches to cooling in cities, such as urban morphology modifications, air flow, shading, evaporation, evapotranspiration, cool materials, district cooling, and human behavior, and advance innovative solutions. It will explore their effects on individuals, buildings, and communities under current and future hot weather and heat events. Its scope will include desk studies, case studies, simulations, monitoring, experiments, and proof-of-concept demonstrations. The outcomes should be useful to practitioners. In this task we will: 

Investigate and describe interdependencies of buildings and outdoor space:

• Investigate and quantify the interactions between local outdoor climatic conditions and thermal resilience of buildings.
• Evaluate and quantify the physical effects of outdoor heat mitigation measures – such as blue and green infrastructure, cool surfaces, and radiative cooling, in the context of changing climate and urban heat islands in cities
• Identify and optimize heat mitigation and solar shielding strategies for outdoor spaces in urban structures
• Examine different building shapes in relation to their ability to reduce heat 

Develop further sustainable and energy efficient cooling strategies and technologies.

• Advance sustainable and energy efficient cooling strategies in hot, humid or dry climates on the small, medium and large scale, avoiding mechanical cooling where possible
• Asses the need for active cooling systems and heat dissipation strategies and optimzie their implementation at the city level
• Advance renewable energy integration and cross-sector solution sets for district-level systems, such as heat sinks from industrial processes
• Develop affordable, low-tech, and robust technologies for heat mitigation and cooling in buildings, particularly for refurbishing existing buildings.
• Identify and optimize supportive active cooling and heat dissipation strategies for outdoor spaces
• Quantify the performance of the following solutions under current and projected future climates including hot seasons, extreme heat events in cities.
  • Water features in the city (blue infrastructure)
  • Trees and vegetation on buildings and in outdoor spaces (green infrastructure)
  • Reflective cool surface materials including sky radiative cooling
  • Public shade structures
  • Temporary as well as permanent misting technologies
  • Heat harvesting from public urban spaces and terrestrial heat sinks
  • Cool breeze towers, breezeways, and natural ventilation in buildings
  • District cooling that uses the excess heat, e.g. for industrial processes
• Develop guidelines for the operation of sustainable cooling solutions beyond physical and thermal implications.

Activity C.1: Review and compare existing solutions (desk studies). This activity will examine, evaluate, and compare current urban cooling technologies and solutions. Each technology or solution will be assessed based on its physical principle, benefits, limitations, and performance, particularly focusing on the solution's in cooling cities, sustainability and energy efficiency characteristics, applicability in various climate zones and urban morphologies, and availability within the energy system. This review will contribute to the development of a classification of cooling solutions in Subtask A.

The review will cover all types of solutions within the project's scope, including nature-based solutions (such as blue and green infrastructures, airflow), mechanical solutions (such as advanced air conditioning, radiative cooling, and district cooling), grey solutions (referring to design and interventions in the built environment), and soft solutions (referring to operational and behavioral measures).

Activity C.2: Develop and test innovative solutions, proving concepts (simulations, experiments, and demonstrations, including case studies). We will conduct specific R&D projects aimed at developing innovative solutions by integrating various technologies and expanding application possibilities. We will evaluate the performance of these solutions through numerical simulations, experiments, and practical demonstrations to identify any performance gaps and research needs. 

Activity C.3: Co-design with heat-vulnerable communities to assess and advance solutions in collaboration with local governments, community-based organizations, citizen scientists. This activity will involve understanding the vulnerability to heat and the resilience of buildings and communities. It will also focus on understanding how people perceive comfort, the health impacts of hot weather, and the different ways that vulnerable communities respond to it.  Additionally, there will be potential collaborations with communities and decision-makers to develop vulnerability indices and tools.

Activity C.4: Coordinate solution analysis, innovation, and demonstrations across participating institutions and nations to help countries learn and benefit from the activities of other members. This activity will focus on developing a Community of Practice to share local knowledge about heat exposure, its health impacts, and practical and affordable cooling, mitigation, and adaptation strategies that meet the needs of the policy and practice communities.

Activity C.5: Generate urban cooling ‘Technology Profiles’. Summarize and promote the operational characteristics and benefits of each technology/solution. This activity will develop recommendations for exemplary implementation, commissioning, and operation. It will also identify both barriers to application and further research opportunities.

Activity C.6: Develop guidelines for selecting climate-appropriate cooling solutions.  In this activity we will develop a guideline for selecting appropriate technologies/solutions suitable for different climatic conditions and urban typologies. The guideline is intended to assist planners and local governments during the initial planning stages by helping them explore potential technologies suitable for their specific needs that address outdoor thermal comfort, health risks, energy and water use as well as considering climatic conditions and urban contexts (low-, medium-, high-density areas). 

Subtask D – Policy

Subtask leaders: Abhishek Gaur (National Research Council Canada) and Theofanis Psomas (Habitat Survey)

The goal of Subtask D (Policy) is to thoroughly analyze current policies, strategies, and standards concerning urban cooling, with a focus on mitigating heat buildup. This involves evaluating their real-world impact, identifying current gaps and best practices, and offering practical guidance for decision-makers, policymakers, stakeholders, and others. Additionally, the subtask aims to enhance existing networks and form partnerships with city networks to promote the global acceptance of sustainable cooling practices.

The specific objectives are:

• Assess existing policies and strategies to evaluate their promotion of sustainable cooling in cities
• Identify and systematically describe best practices for policy implementation
• Formulate concrete policy recommendations
• Develop procedures to disseminate research outcomes and promote the practical implementation of sustainable cooling strategies and solutions
• Connect to existing programs to leverage the impact of the developed strategies

Activity D.1: Review existing policies and standards. This activity will involve a comprehensive literature review of existing policies, regulations and standards on cooling cities. It aims to identify key performance indicators (KPIs) that measure the effectiveness of cooling policies, considering their socio-economic, environmental, and technical impacts. Additionally, best practices and successful policy implementation across different cities and climates will be documented to inform future policy development. This activity will also identify and analyze gaps, challenges, and opportunities in current policies to improve their effectiveness in promoting sustainable cooling practices.

Activity D.2: Strengthen networks and support implementation of policies. This activity aims to identify and understand the scope of existing networks and programs related to cooling in cities, as well as facilitating collaborations and potential partnerships between cities, research institutions, and industry stakeholders. Key organizations include C40 Cities, Rethink Cities, ENEP Cool Coalition, Clean Cooling Collaborative, Sustainable Energy for All (SEforALL), and other international city networks. Additionally, it seeks to identify platforms for regular communication, knowledge sharing, and joint initiatives on sustainable cooling. Ongoing support will be provided to cities in tracking the performance of their cooling policies and making necessary adjustments.

Activity D.3: Develop and disseminate policy guidance

This activity will focus on developing a policy guidance document based on findings from the policy review and case study analysis. To ensure effective dissemination, we will organize workshops and webinars for stakeholders, including policymakers, city planners, and industry professionals. We will also create accessible communication materials, such as briefs and infographics, to facilitate the understanding and adoption of the recommended policies by cities.