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

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 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.

Radiant Conditioning Retrofitting for Residential Buildings

“…However, the early hydronic chilled ceiling system developed in the 1930s was unsuccessful due to the high condensation risk. Condensation remains one of the most significant problems of radiant cooling systems and prevented radiant cooling from being widely utilised for several decades [76]. Condensation can also reduce the air quality of a conditioned space and reduce the thermal efficiency of the radiant cooling systems [63].…”

Exploring membrane-assisted radiant cooling for designing comfortable naturally ventilated spaces in the tropics

“…The thermal radiation transparent membrane separates the chilled surface from the ambient air while still allowing for radiative exchange between the occupants and the panels. The supply temperature can be 13°C lower than the dew point temperature (Teitelbaum, Chen, et al, 2020) or lowered to 7°C, 14.4°C and 19.3°C when the relative humidity is 65%, 80% and 90%, respectively (Xing et al, 2020) without condensation. Thus, overcoming the condensation and cooling capacity limitation when running in a naturally ventilated space.…”

“…The Cold Tube pavilion was used as an apparatus to evaluate the effectiveness of the membrane-assisted cooling panels through physiological measurements and thermal comfort studies (Teitelbaum, Chen, et al, 2020). Physiological measurements have shown that the radiant panels can provide a significant amount of cooling through radiant exchanges only, and it is possible to independently control radiant exchange in a naturally ventilated space without much effect on the air temperature.…”

“…It is assumed to be 3 K above the chilled water supply temperature (Conroy & Mumma, 2001). The lowest supply temperature permitted before condensation occurs on the membrane of the panels is calculated using Equation (4) (Teitelbaum, Chen, et al, 2020). The AUST is calculated assuming the surface temperatures are the same as the interior air temperature and factoring in the occupants' skin temperatures.…”

Controlling radiative heat flows in interior spaces to improve heating and cooling efficiency

“…In an indoor environment, where most people stay in a sedentary state, more than 50% of the heat generated by the human body is released through thermal radiation in the long-wave infrared part of the spectrum ( Arslanoglu and Yigit, 2016 ). A recent experimental study used a membrane-assisted radiant cooling system to show that radiation and convection can be separated for comfort conditioning and, relying on radiation alone, thermal comfort can be maintained based on existing metrics even in unusually high ambient air conditions ( Teitelbaum et al., 2020 ). Radiative heat transfer between human occupants and their environment largely depends on the radiative properties of clothing, the walls, and other surroundings.…”