Membrane-assisted radiant cooling for expanding thermal comfort zones globally without air conditioning

Eric Teitelbaum, Kian Wee Chen, Dorit Aviv, Kipp Bradford, Lea Ruefenacht, Denon Sheppard, Megan Teitelbaum, Forrest Meggers, Jovan Pantelic, Adam Rysanek

Full access to the paper here: https://doi.org/10.1073/pnas.2001678117

Abstract

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.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 m⋅s−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.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.