This research proposes the use of membrane-assisted radiant panels to improve the thermal comfort of naturally ventilated spaces in hot and humid climates. These radiant panels are capable of conditioning naturally ventilated spaces, which is impractical with conventional mechanical cooling systems. For conventional systems, a permeable envelope will result in energy wastage from conditioned air escaping or condensation occurring on the radiant surfaces. In our system, there is no air-conditioning and we avoid condensation by separating the radiant surfaces from humid air using a membrane transparent to thermal radiation. The membrane-assisted radiant panels are an unutilized technology for architects to design comfortable naturally ventilated spaces. We propose a cooling system based on the technology and discuss the architectural implications, particularly the permeability of the building envelope and requirements for mechanical spaces, of employing this system in a case study that is a naturally ventilated classroom. Our system is compared to conventional cooling systems. Although our system requires a ceiling space reconfiguration, it does not require duct works and envelope retrofits. The comparative case study shows a potential 52% reduction in cooling energy demand from initial estimation. Considering the trade-offs, our system can be a good alternative for retrofit projects.
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.
Modelling the Built Environment in 3D to Visualize Data from Different Disciplines: The Princeton University Campus
Kian Wee Chen & Forrest Meggers
The Journal of Digital Landscape Architecture award 2020 on SCIENTIFIC MERIT. (The paper is given the highest score possible by one of the blind reviewers and the second highest score possible by the other blind reviewer.)
In this research, we have developed a 3D city model of Princeton University campus for the Campus as Lab (CAL) program using openly available 3D data. The sources include the official open data portal from the United States Geological Survey, OpenStreetMap and Google Maps. The 3D city model is used as a tool for visualizing and analyzing multidisciplinary data to enhance the communication of research between different disciplines. We demonstrate the 3D model’s capabilities through a use case where we investigate the viability of powering a golf cart for short commutes across the campus with a Photovoltaic panel. We visualized environmental and transportation data. The two sets of data are solar irradiation and the travel behavior of the golf cart. Through the use case, we show that the 3D model is useful for conducting research that requires data from different disciplines. Our long-term goal is to establish the use of the 3D city model as a tool for the documentation, visualization and communication of research results in the context of the CAL program.
For thermal comfort research, globe thermometers have become the de facto tool for mean radiant temperature, tr, measurement. They provide a quick means to survey the radiant environment in a space with nearly a century of trials to reassure researchers. However, as more complexity is introduced to built environments, we must reassess the accuracy of globe measurements. In particular, corrections for globe readings taking wind into account rely on a forced convection heat transfer coefficient. In this study, we investigate potential errors introduced by buoyancy driven flow, or free convection, induced by radiant forcing of a black globe’s surface to a temperature different from the air. We discovered this error in an experimental radiant cooling system with high separation of air to radiant temperature. Empirical simulations and the data collected in a radiant cooling setup together demonstrate the influence of free convection on the instrument’s readings. Initial simulation and data show that tr measurements neglecting free convection when calculating tr from air temperatures of 2 K above tr could introduce a mechanism for globe readings to incorrectly track air temperatures. The experimental data constructed to test this hypothesis showed the standard correction readings are 1.94 ± 0.90 °C higher than the ground truth readings for all measurements taken in the experiment. The proposed mixed convection correction is 0.51 ± 1.07 °C higher than the ground truth, and is most accurate at low air speeds, within 0.25 ± 0.60 °C. This implies a potential systematic error in millions of measurements over the past 30 years of thermal comfort research. Future work will be carried out to experimentally validate this framework in a controlled climate chamber environment, examining the tradeoffs between accuracy and precision with globe thermometer measurements.
We present an expansion of the psychrometric chart for thermal comfort analysis using a new contour shading method that demonstrates a wider range of potential comfort conditions through the incorporation of additional comfort parameters. These extra dimensions include mean radiant temperature, air movement, metabolic rate, skin wettedness and the transitional behavior of occupants. The representations allow us to think outside the thermal comfort box with the use of innovative thermal design and comfort feedback for occupants. Building on the Olgyay bioclimatic chart, allowing architects to “Design with Climate”, the new chart vizualizes a wide range of conditions that illustrate a physical basis for expanding comfort zones. It uses basic spatially invariant metrics employed in adaptive and other comfort models to allow “design with comfort” across all thermal comfort variables. The development of these methods has resulted in an open-source repository and web app available for designers and researchers to reproduce the charts and color-shading for their own projects