Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

Efficient outdoor thermal comfort via radiant cooling and infrared-reflective walls

Nature Sustainability volume 8, pages 642–650 (2025)Cite this article

Subjects

Abstract

As climate change accelerates, extreme heat events will intensify, threatening vulnerable populations experiencing dangerous heat outdoors. Active radiant cooling has recently emerged as a promising strategy for outdoor thermal comfort, at it offers cooling at a distance without the inefficiency of conditioning unconfined air. However, for radiant cooling structures to be effective, the overwhelming majority of their internal surfaces must be actively cooled, typically with visibly opaque panels, raising practicality and safety concerns. Here, we demonstrate that thermal comfort can be achieved in an outdoor cooling structure that lightly uses radiant cooling and amplifies this cooling effect using visibly transparent, infrared-reflective surfaces. This approach enables visibly open cooling structures that will be accepted by a wide range of communities. We first derive an analytical model that relates the mean radiant temperature to the proportion of cold and reflective surfaces in a structure. We then experimentally demonstrate such a structure, with human subject testing revealing a substantial enhancement in thermal comfort as experienced by occupants. Our results highlight how next-generation radiant cooling structures can use fewer actively cooled surfaces without compromising on cooling effectiveness. This is a practical approach to enabling thermal comfort outdoors in extreme heat conditions.

Access through your institution
Buy or subscribe

This is a preview of subscription content, access via your institution

Access options

Access through your institution

Buy this article

  • Purchase on SpringerLink
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Ray-tracing model of the MRT in a radiant cooling structure with reflective surfaces.
Fig. 2: Experimental investigation of the reduction in MRT due to reflective surfaces.
Fig. 3: Field testing a radiant cooling structure with reflective surfaces.
Fig. 4: Thermal comfort survey results.

Similar content being viewed by others

Data availability

The datasets generated during the current study are available from the corresponding author on reasonable request.

Code availability

Any code used to process data generated during the current study can be found under Radiant Cooling Ray Tracing Model at: https://github.com/Raman-Lab-UCLA/.

References

  1. Tuholske, C. et al. Global urban population exposure to extreme heat. Proc. Natl Acad. Sci. USA 118, e2024792118 (2021).

    Article  CAS  Google Scholar 

  2. Ebi, K. L. et al. Hot weather and heat extremes: health risks. Lancet 398, 698–708 (2021).

    Article  Google Scholar 

  3. Oke, T. R. The energetic basis of the urban heat island. Q. J. R. Meteorol. Soc. 108, 1–24 (1982).

    Google Scholar 

  4. Zhou, Y. & Shepherd, J. M. Atlanta’s urban heat island under extreme heat conditions and potential mitigation strategies. Nat. Hazards 52, 639–668 (2010).

    Article  Google Scholar 

  5. Kelly Turner, V. et al. More than surface temperature: mitigating thermal exposure in hyper-local land system. J. Land Use Sci. 17, 79–99 (2022).

    Article  Google Scholar 

  6. Keith, L. & Meerow, S. Planning for Urban Heat Resilience (American Planning Association, 2020).

  7. Bowler, D. E., Buyung-Ali, L., Knight, T. M. & Pullin, A. S. Urban greening to cool towns and cities: a systematic review of the empirical evidence. Landsc. Urban Plan. 97, 147–155 (2010).

    Article  Google Scholar 

  8. Wang, C., Wang, Z.-H., Kaloush, K. E. & Shacat, J. Cool pavements for urban heat island mitigation: a synthetic review. Renew. Sustain. Energy Rev. 146, 111171 (2021).

    Article  Google Scholar 

  9. Wang, Z.-H., Zhao, X., Yang, J. & Song, J. Cooling and energy saving potentials of shade trees and urban lawns in a desert city. Appl. Energy 161, 437–444 (2016).

    Article  Google Scholar 

  10. Peng, Y. et al. Coloured low-emissivity films for building envelopes for year-round energy savings. Nat. Sustain. 5, 339–347 (2021).

    Article  Google Scholar 

  11. Yang, J., Wang, Z.-H. & Kaloush, K. E. Environmental impacts of reflective materials: is high albedo a ‘silver bullet’ for mitigating urban heat island? Renew. Sustain. Energy Rev. 47, 830–843 (2015).

    Article  CAS  Google Scholar 

  12. Santamouris, M. Cooling the cities – a review of reflective and green roof mitigation technologies to fight heat island and improve comfort in urban environments. Sol. Energy 103, 682–703 (2014).

    Article  Google Scholar 

  13. Qin, Y. A review on the development of cool pavements to mitigate urban heat island effect. Renew. Sustain. Energy Rev. 52, 445–459 (2015).

    Article  Google Scholar 

  14. Santamouris, M. Using cool pavements as a mitigation strategy to fight urban heat island—a review of the actual developments. Renew. Sustain. Energy Rev. 26, 224–240 (2013).

    Article  Google Scholar 

  15. Rode, P., Keim, C., Robazza, G., Viejo, P. & Schofield, J. Cities and energy: urban morphology and residential heat-energy demand. Environ. Plan. B: Urban Anal. City Sci. 41, 138–162 (2014).

    Article  Google Scholar 

  16. Shao, Z. et al. Tri-band electrochromic smart window for energy savings in buildings. Nat. Sustain. 7, 796–803 (2024).

    Article  Google Scholar 

  17. Sui, C. et al. Dynamic electrochromism for all-season radiative thermoregulation. Nat. Sustain. 6, 428–437 (2023).

    Article  Google Scholar 

  18. Martilli, A., Krayenhoff, E. S. & Nazarian, N. Is the urban heat island intensity relevant for heat mitigation studies? Urban Clim. 31, 100541 (2020).

    Article  Google Scholar 

  19. Turner, V. K. et al. How are cities planning for heat? Analysis of United States municipal plans. Environ. Res. Lett. 17, 064054 (2022).

    Article  Google Scholar 

  20. Turner, V. K., Middel, A. & Vanos, J. K. Shade is an essential solution for hotter cities. Nature 619, 694–697 (2023).

    Article  CAS  Google Scholar 

  21. Turner, V. K., Middel, A., Rogers, M., Engel, R. & Schneider, F. A. Site Design and Human Heat Burden in Pacoima, California (UCLA Luskin Center for Innovation, 2023).

  22. Chakraborty, T., Hsu, A., Manya, D. & Sheriff, G. Disproportionately higher exposure to urban heat in lower-income neighborhoods: a multi-city perspective. Environ. Res. Lett. 14, 105003 (2019).

    Article  Google Scholar 

  23. Doulos, L., Santamouris, M. & Livada, I. Passive cooling of outdoor urban spaces. The role of materials. Sol. Energy 77, 231–249 (2004).

    Article  CAS  Google Scholar 

  24. Santamouris, M., Synnefa, A. & Karlessi, T. Using advanced cool materials in the urban built environment to mitigate heat islands and improve thermal comfort conditions. Sol. Energy 85, 3085–3102 (2011).

    Article  Google Scholar 

  25. Nakayama, T. & Fujita, T. Cooling effect of water-holding pavements made of new materials on water and heat budgets in urban areas. Landsc. Urban Plan. 96, 57–67 (2010).

    Article  Google Scholar 

  26. Gilbert, H. E. et al. Energy and environmental consequences of a cool pavement campaign. Energy Build. 157, 53–77 (2017).

    Article  Google Scholar 

  27. Raman, A. P., Anoma, M. A., Zhu, L., Rephaeli, E. & Fan, S. Passive radiative cooling below ambient air temperature under direct sunlight. Nature 515, 540–544 (2014).

    Article  CAS  Google Scholar 

  28. Saaroni, H., Amorim, J., Hiemstra, J. & Pearlmutter, D. Urban green infrastructure as a tool for urban heat mitigation: survey of research methodologies and findings across different climatic regions. Urban Clim. 24, 94–110 (2018).

    Article  Google Scholar 

  29. Wang, C., Wang, Z. & Yang, J. Cooling effect of urban trees on the built environment of contiguous United States. Earth’s Future 6, 1066–1081 (2018).

    Article  Google Scholar 

  30. Santamouris, M. et al. Passive and active cooling for the outdoor built environment – analysis and assessment of the cooling potential of mitigation technologies using performance data from 220 large scale projects. Sol. Energy 154, 14–33 (2017).

    Article  Google Scholar 

  31. Ulpiani, G. Water mist spray for outdoor cooling: a systematic review of technologies, methods and impacts. Appl. Energy 254, 113647 (2019).

    Article  Google Scholar 

  32. Ulpiani, G., Giuseppe, E. D., Perna, C. D., D’Orazio, M. & Zinzi, M. Design optimization of mist cooling for urban heat island mitigation: experimental study on the role of injection density. IOP Conf. Ser.: Earth Environ. Sci. 296, 012025 (2019).

    Article  Google Scholar 

  33. Ulpiani, G., Di Perna, C. & Zinzi, M. Mist cooling in urban spaces: understanding the key factors behind the mitigation potential. Appl. Therm. Eng. 178, 115644 (2020).

    Article  Google Scholar 

  34. Zheng, K., Ichinose, M. & Wong, N. H. Parametric study on the cooling effects from dry mists in a controlled environment. Build. Environ. 141, 61–70 (2018).

    Article  Google Scholar 

  35. Zheng, K., Yuan, C., Wong, N. H. & Cen, C. Dry mist systems and its impact on thermal comfort for the tropics. Sustain. Cities Soc. 51, 101727 (2019).

    Article  Google Scholar 

  36. Vanos, J. K. et al. Evaporative misters for urban cooling and comfort: effectiveness and motivations for use. Int. J. Biometeorol. 66, 357–369 (2022).

    Article  Google Scholar 

  37. Feustel, H. E. & Stetiu, C. Hydronic radiant cooling - preliminary assessment. Energy Build. 22, 193–205 (1995).

  38. Khan, Y., Khare, V. R., Mathur, J. & Bhandari, M. Performance evaluation of radiant cooling system integrated with air system under different operational strategies. Energy Build. 97, 118–128 (2015).

    Article  Google Scholar 

  39. Hu, R. & Niu, J. A review of the application of radiant cooling & heating systems in Mainland China. Energy Build. 52, 11–19 (2012).

    Article  Google Scholar 

  40. Memon, R. A., Chirarattananon, S. & Vangtook, P. Thermal comfort assessment and application of radiant cooling: a case study. Build. Environ. 43, 1185–1196 (2008).

    Article  Google Scholar 

  41. Teitelbaum, E. et al. Membrane-assisted radiant cooling for expanding thermal comfort zones globally without air conditioning. Proc. Natl Acad. Sci. USA 117, 21162–21169 (2020).

    Article  CAS  Google Scholar 

  42. Park, Y. & Garcia, M. Pedestrian safety perception and urban street settings. Int. J. Sustain. Transp. 14, 860–871 (2020).

    Article  Google Scholar 

  43. Abenoza, R. F., Ceccato, V., Susilo, Y. O. & Cats, O. Individual, travel, and bus stop characteristics influencing travelers’ safety perceptions. Transp. Res. Rec. 2672, 19–28 (2018).

    Article  Google Scholar 

  44. Vogel, M. & Pettinari, J. L. Personal Safety and Transit: Paths, Environments, Stops, and Stations (Univ. Minnesota, 2002).

  45. Morse, R. N. Radiant cooling. Archit. Sci. Rev. 6, 50–53 (1963).

    Article  Google Scholar 

  46. Lindberg, F. & Grimmond, C. S. B. The influence of vegetation and building morphology on shadow patterns and mean radiant temperatures in urban areas: model development and evaluation. Theor. Appl. Climatol. 105, 311–323 (2011).

    Article  Google Scholar 

  47. Nazarian, N., Fan, J., Sin, T., Norford, L. & Kleissl, J. Predicting outdoor thermal comfort in urban environments: a 3D numerical model for standard effective temperature. Urban Clim. 20, 251–267 (2017).

    Article  Google Scholar 

  48. He, R. et al. Radiant air-conditioning with infrared transparent polyethylene aerogel. Mater. Today Energy 21, 100800 (2021).

    Article  CAS  Google Scholar 

  49. Du, K., Wu, H., Huang, G., Xu, X. & Liu, Y. Condensation-free radiant cooling with double-skin infrared-transparent membranes. Build. Environ. 193, 107660 (2021).

    Article  Google Scholar 

  50. Dharmasastha, K., Zhong, Z., Niu, J. & Liang, H. A comprehensive review of cover-shield-assisted radiant cooling system. Energy Build. 291, 113121 (2023).

    Article  Google Scholar 

  51. ASHRAE-55-1992R Proposed Revision to an American National Standard: Thermal Environmental Conditions for Human Occupancy. Tech. Rep. BSR/ASHRAE Standard 55-1992R (ASHRASE, 2001).

  52. Guo, H. et al. On the understanding of the mean radiant temperature within both the indoor and outdoor environment, a critical review. Renew. Sustain. Energy Rev. 117, 109207 (2020).

    Article  Google Scholar 

  53. Johansson, E., Thorsson, S., Emmanuel, R. & Kru¨ger, E. Instruments and methods in outdoor thermal comfort studies – the need for standardization. Urban Clim. 10, 346–366 (2014).

    Article  Google Scholar 

  54. Guo, H., Teitelbaum, E., Houchois, N., Bozlar, M. & Meggers, F. Revisiting the use of globe thermometers to estimate radiant temperature in studies of heating and ventilation. Energy Build. 180, 83–94 (2018).

    Article  Google Scholar 

  55. Teitelbaum, E. et al. Globe thermometer free convection error potentials. Sci. Rep. 10, 2652 (2020).

    Article  CAS  Google Scholar 

  56. Vanos, J. K. et al. Improved methods for estimating mean radiant temperature in hot and sunny outdoor settings. Int. J. Biometeorol. 65, 967–983 (2021).

    Article  Google Scholar 

  57. Ergonomics of the thermal environment — Instruments for measuring physical quantities. Technical Report ISO 7726 (ISO, 1998).

Download references

Acknowledgements

This research was supported as part of the Heat Resilient LA project funded by the UCLA Sustainable LA Grand Challenge. This material is also based upon work supported by the National Science Foundation (CAREER Grant No. 2146577 to A.P.R.) and by the National Science Foundation Graduate Research Fellowship (Grant No. 2034835 to D.E.A.). Additional support for K.S. was provided by the National Science Foundation.

Author information

Authors and Affiliations

  1. Department of Materials Science and Engineering, University of California, Los Angeles, CA, USA

    David E. Abraham, Robert Yang, Jyotirmoy Mandal, Xin Huang & Aaswath P. Raman

  2. VA Los Angeles and UCLA National Clinician Scholars Program, VA Greater Los Angeles Healthcare System HSR&D Center of Innovation, Los Angeles, CA, USA

    Mackensie Yore

  3. Department of Emergency Medicine, West Los Angeles VA Medical Center, VA Greater Los Angeles Healthcare System, Los Angeles, CA, USA

    Mackensie Yore

  4. Department of Emergency Medicine, UCLA David Geffen School of Medicine, Los Angeles, CA, USA

    Mackensie Yore

  5. Urban Planning Department, Luskin School of Public Affairs, Los Angeles, CA, USA

    V. Kelly Turner, Walker Wells & Kirsten Schwarz

  6. Department of Environmental Health Sciences, Fielding School of Public Health, Los Angeles, CA, USA

    Kirsten Schwarz

  7. David Geffen School of Medicine at UCLA, Department of Medicine, Los Angeles, CA, USA

    David P. Eisenman

Authors
  1. David E. Abraham
    View author publications

    Search author on:PubMed Google Scholar

  2. Robert Yang
    View author publications

    Search author on:PubMed Google Scholar

  3. Jyotirmoy Mandal
    View author publications

    Search author on:PubMed Google Scholar

  4. Mackensie Yore
    View author publications

    Search author on:PubMed Google Scholar

  5. Xin Huang
    View author publications

    Search author on:PubMed Google Scholar

  6. V. Kelly Turner
    View author publications

    Search author on:PubMed Google Scholar

  7. Walker Wells
    View author publications

    Search author on:PubMed Google Scholar

  8. Kirsten Schwarz
    View author publications

    Search author on:PubMed Google Scholar

  9. David P. Eisenman
    View author publications

    Search author on:PubMed Google Scholar

  10. Aaswath P. Raman
    View author publications

    Search author on:PubMed Google Scholar

Contributions

The core innovation was conceived by A.P.R. and D.E.A. The ray-tracing model was developed by D.E.A. Material properties were measured by D.E.A. The panels were designed by D.E.A., R.Y., J.M., X.H. and A.P.R. and constructed by D.E.A. and R.Y. The cooling structure was constructed and operated by D.E.A., R.Y. and A.P.R. The structure design and setting in an urban environment were informed by V.K.T. and W.W. The survey was designed, administered and processed by M.Y., D.P.E., K.S., W.W., D.E.A. and A.P.R. All figures were made by D.E.A. and A.P.R. The paper was written by D.E.A. and A.P.R., and edited by M.Y., D.P.E., W.W., D.E.A. and A.P.R.

Corresponding author

Correspondence to Aaswath P. Raman.

Ethics declarations

Competing interests

The authors declare no competing interests.

Peer review

Peer review information

Nature Sustainability thanks Xun Cao, Forrest Meggers, Kyu-Nam Rhee, Eric Teitelbaum and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Figs. 1–9, discussion and Tables 1–3.

Reporting Summary

Rights and permissions

Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Abraham, D.E., Yang, R., Mandal, J. et al. Efficient outdoor thermal comfort via radiant cooling and infrared-reflective walls. Nat Sustain 8, 642–650 (2025). https://doi.org/10.1038/s41893-025-01558-0

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue date:

  • DOI: https://doi.org/10.1038/s41893-025-01558-0

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing