Membrane-assisted radiant cooling for expanding thermal comfort zones globally without air conditioning
Edited by Alexis T. Bell, University of California, Berkeley, CA, and approved July 20, 2020 (received for review January 28, 2020)
Significance
In this paper, we present results from a radiant cooling pavilion, demonstrating a method of cooling people without cooling the air. Instead, surfaces are chilled, and thermal radiation is used to keep people cool. A thermally transparent membrane is used to prevent unwanted air cooling and condensation, a required precursor to deploying radiant cooling panels without humidity control in tropical environments. The results from this thermal-comfort study demonstrate the ability to keep people comfortable with radiation in warm air, a paradigm-shifting approach to thermal comfort that may help curb global cooling-demand projections.
Abstract
We present results of a radiant cooling system that made the hot and humid tropical climate of Singapore feel cool and comfortable. Thermal radiation exchange between occupants and surfaces in the built environment can augment thermal comfort. The lack of widespread commercial adoption of radiant-cooling technologies is due to two widely held views: 1) The low temperature required for radiant cooling in humid environments will form condensation; and 2) cold surfaces will still cool adjacent air via convection, limiting overall radiant-cooling effectiveness. This work directly challenges these views and provides proof-of-concept solutions examined for a transient thermal-comfort scenario. We constructed a demonstrative outdoor radiant-cooling pavilion in Singapore that used an infrared-transparent, low-density polyethylene membrane to provide radiant cooling at temperatures below the dew point. Test subjects who experienced the pavilion (n = 37) reported a “satisfactory” thermal sensation 79% of the time, despite experiencing 29.6 0.9 °C air at 66.5 5% relative humidity and with low air movement of 0.26 0.18 ms−1. Comfort was achieved with a coincident mean radiant temperature of 23.9 0.8 °C, requiring a chilled water-supply temperature of 17.0 1.8 °C. The pavilion operated successfully without any observed condensation on exposed surfaces, despite an observed dew-point temperature of 23.7 0.7 °C. The coldest conditions observed without condensation used a chilled water-supply temperature 12.7 °C below the dew point, which resulted in a mean radiant temperature 3.6 °C below the dew point.
Data Availability
All study data are publicly available along with an accompanying Jupyter Notebook that was used to create the figures from the dataset. Data is permanently available on GitHub at https://github.com/eteitelb/coldTubeData.
Acknowledgments
This project was supported by National Research Foundation IntraCREATE Grant NRF2016-ITC001-005 (to J.P. and A.R.). The authors acknowledge the use of Princeton’s Imaging and Analysis Center, which is partially supported by the Princeton Center for Complex Materials, a National Science Foundation Materials Research Science and Engineering Centers program (DMR-1420541). This study was funded in part by the US National Science Foundation’s Sustainability Research Network Cooperative Agreement #1444758. We also personally thank Simon Thomas and the UWCSEA Facilities staff for all of their help facilitating the construction of the Cold Tube demonstrator. This paper is the full and complete thermal-comfort study and performance characterization of the Cold Tube, greatly extending some initial system performance results we originally presented in a conference paper.
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Copyright
Copyright © 2020 the Author(s). Published by PNAS. This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).
Data Availability
All study data are publicly available along with an accompanying Jupyter Notebook that was used to create the figures from the dataset. Data is permanently available on GitHub at https://github.com/eteitelb/coldTubeData.
Submission history
Published online: August 18, 2020
Published in issue: September 1, 2020
Keywords
Acknowledgments
This project was supported by National Research Foundation IntraCREATE Grant NRF2016-ITC001-005 (to J.P. and A.R.). The authors acknowledge the use of Princeton’s Imaging and Analysis Center, which is partially supported by the Princeton Center for Complex Materials, a National Science Foundation Materials Research Science and Engineering Centers program (DMR-1420541). This study was funded in part by the US National Science Foundation’s Sustainability Research Network Cooperative Agreement #1444758. We also personally thank Simon Thomas and the UWCSEA Facilities staff for all of their help facilitating the construction of the Cold Tube demonstrator. This paper is the full and complete thermal-comfort study and performance characterization of the Cold Tube, greatly extending some initial system performance results we originally presented in a conference paper.
Notes
This article is a PNAS Direct Submission.
Authors
Competing Interests
Competing interest statement: A.T.B., M.T., and J.P. are affiliated with University of California, Berkeley.
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Cite this article
Membrane-assisted radiant cooling for expanding thermal comfort zones globally without air conditioning, Proc. Natl. Acad. Sci. U.S.A.
117 (35) 21162-21169,
https://doi.org/10.1073/pnas.2001678117
(2020).
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