Multi-criteria optimization of closed-loop hydronic pavement systems in urban heat island mitigation: Balancing performance and cost

Abstract

Large parking lots intensify urban heat island (UHI) effect by storing solar radiation and increasing pavement temperatures and pedestrian heat exposure. Hydronic pavement systems mitigate this heating by circulating fluid through embedded pipes to extract surface heat. However, most prior studies have examined open-loop systems, single design parameters, or winter applications, with limited attention to cooling-focused optimization or thermal-comfort outcomes in closed-loop systems. This study evaluates closed-loop hydronic parking lots using a Taguchi DOE framework to identify performance-driving factors and cost-effective designs. Three variables—pipe material, initial circulating-fluid temperature, and flow rate—were tested under simulated irradiance levels of 200, 600, and 1000 W/m², representing overcast to peak-summer solar conditions. Thermal performance was quantified using peak surface-temperature reduction and the area under the temperature–time curve (AUC), which was integrated with system cost in a multi-objective optimization. Closed-loop systems reduced surface temperatures by 4.4–36.5 °C and cumulative thermal loading by 12–37%. Initial fluid temperature was the dominant performance factor, while pipe material primarily influenced cost. Surface cooling lowered mean radiant temperature by up to 2.55 °C and improved the Universal Thermal Climate Index (UTCI) by up to 0.76 °C, demonstrating measurable improvements in pedestrian thermal comfort. Overall, closed-loop hydronic pavements effectively reduce pavement heating and pedestrian exposure, and the proposed framework provides a practical, cost-informed basis for hydronic-system design and evaluation in UHI mitigation.