Globe thermometer free convection error potentials
Eric Teitelbaum, Kian Wee Chen, Forrest Meggers, Hongshan Guo, Nicholas Houchois, Jovan Pantelic & Adam Rysanek
Full access to the paper at https://doi.org/10.1038/s41598-020-59441-1
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.
Design with Comfort: Expanding the psychrometric chart with radiation and convection dimensions
Eric Teitelbaum, Prageeth Jayathissa, Clayton Miller, Forrest Meggers.
Full access to the full paper before February 12, 2020 at: https://authors.elsevier.com/a/1aHm21M7zG%7EOya
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
On the understanding of the mean radiant temperature within both the indoor and outdoor environment, a critical review.
Hongshan Guo, Dorit Aviv, Mauricio Loyola, Eric Teitelbaum, Nicholas Houchois, Forrest Meggers.
Full access to the full paper before January 02, 2020 at: https://authors.elsevier.com/a/1a33f4s9Hvxk%7E7
- We have expanded the conclusion section with both numerical conclusions and expanded discussions on the limitations of existing MRT usages.
- Included new citations that covers the latest development of MRT research and standardization effort (ASHRAE Standard 55-2017, for example).
- Adding new illustration of the MRT as a concept in relation to the human body geometry.
- Expanded review on how indoor MRT variations due to shortwave radiation are characterized
CHAOS Lab symposium on the Energy Water Nexus and the role of carbon and natural systems for the challenges in our urban environment and infrastructures
9:00 am: Welcome message and Introduction to Energy+Water+Urban by Dr. Forrest Meggers
9:30 am: Noah Stern, Water + Carbon + Environment. Followed by Q/A
The Water and Carbon cycles are arguably the most important cycles for humankind to understand. The water cycle is the largest cycle on the planet, and the carbon cycle is at the heart of the threat of climate change. Current models of sediment carbon dynamics focus on preservation of organic carbon through formation of carbon-mineral aggregates. However, the preservation of carbon in these soil aggregates depends on their stability. My research focuses on the importance of particulate organic carbon in the development of microbial hot-spots where highly elevated release rates of CO2 and CH4 occur. Connecting the contribution of particulate organic carbon to the freshwater carbon cycle has large implications for natural and engineered environments.
10:00 am: Hongshan Guo & Erica Edwards, NSF-SRN UWIN – Urban water, humidity, surfaces and radiant comfort
11:00 am: Eric Teitelbaum & Michael Bozlar,
I.) Applications of Liquid Desiccant in Building Dehumidification.
II.) Evaporative Cooling using Hydrophilic Substrates
12:00 pm: James Coleman & Nicholas Houchois, Distributed and Intelligent Sensors
12:30 pm: Concluding remarks by Forrest Meggers
12.45 pm Adjourn – Lunch
Forrest was invited to Berkeley for the annual meeting of the CBE including meetings with former collaborator in Singapore and at Princeton, Jovan Pantelic, in his new role as professional researcher at the Berkeley Center for the Built Environment. Research in advanced sensors, comfort, and radiant heating and cooing were all discussed, and current CHAOS research projects were well-received and many potential collaborations were initiated. Forrest also met with Prof. Ed Arens, who shares a mutual appreciation for the Olgyay research in Princeton in the 50’s and 60’s. Arens will be a Highlight Seminar speaker at the Andlinger Center Feb 8th.
The Thermoheliodome was featured on the cover of the Andlinger Center for Energy and Environment Annual Report
View Report here: http://acee.princeton.edu/wp-content/uploads/2014-Anglinger-Annual-Report-FINAL.pdf