Category Archives: News

EVENT: Climate forces across scales

Climate forces across scales: Exploring how new experimentation for large-scale fluid dynamics can address climate, energy, and infrastructure challenges.

Hosted by the Andlinger Center for Energy and the Environment affiliated faculty Dr. Forrest Meggers (ARC), Dr. Marcus Hultmark (MAE), and Dr. Elie Bou-zeid (CEE) for a culmination of research leading to the upcoming installation of a new one-of-a-kind pressurized wind tunnel to enable new experimental research on large scale systems.

The project was supported in part by the Andlinger Center and began in 2018. The goal of the workshop is to review the current state of knowledge about experimental and theoretical approaches for understanding large-scale fluids problems and discuss associated research challenges and opportunities in the areas of energy, climate, and infrastructure. 

The workshop will be held virtually on Thursday, January 28 between noon and 2:30 p.m. Please register in advance here.

We look forward to your participation. Please share with other collaborators or researchers you think would contribute to and benefit from the workshop.


12:00 p.m. – 12:30 p.m. Welcome and Overview of Fluids Scales and the background on the new pressurized wind tunnel develoment
Forrest Meggers, ACEE/ARC
Marcus Hultmark, MAE
Elie Bou-Zeid, CEE

12:30 p.m. – 1:00 p.m. General Questions Raised in Fluid Dynamics and Implications for Applying CFD to Specific Topics in Infrastructure, Urban
Design, Energy, and Climate


1:00 p.m. – 1:30 p.m. Infrastructure – e.g. the fluid interactions for resiliency installation like flood walls, tall buildings, and the urban environment, also floating cities.
1:30 p.m. – 2:00 p.m. Energy – e.g. wind turbines, urban heat island phenomena, and scaling of of buoyancy driven flows and natural ventilation systems in buildings
2:00 p.m. – 2:30 p.m. Climate – e.g. large scale storms and associated damage and debris from large scale fluid dynamic interactions.
2:30 p.m. Adjourn

Exploring membrane-assisted radiant cooling for designing comfortable naturally ventilated spaces in the tropics! Read about it here in our new publication on Building Research and Information!

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

Kian Wee Chen, Eric Teitelbaum, Forrest Meggers, Jovan Pantelic, Adam Rysanek

First 50 copies free:

Full access to the paper here:


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.

Architectural implications of the retrofits (a) membrane-assisted panel system (b) decentralized membrane-assisted panel system with chiller and water tank, and centralized membrane-assisted panel system (c) decentralized air-based system (split unit) (d) centralized air-based system.

Membrane-assisted radiant cooling for expanding thermal comfort zones globally without air conditioning! Read about it here in our new publication on pnas!

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:


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

3d visualizations for facilitating multi-disciplinary research! Read about it here!

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.)

Full access to the paper at


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.

Limitations of black globe thermometer in an environment with high air to radiant temperature separation! Read about it in our new article on Scientific Reports

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


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.

More ways to achieve thermal comfort! Read about it in our new article on Energy and Buildings

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:


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

What is Mean Radiant Temperature? Read about it in our New article on renewable and sustainable energy review

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:


  • 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

Forrest wins Friend of Facilities Award

Forrest was the first Princeton faculty to be awarded the Friend of Facilities award for his efforts helping make the campus more efficient and sustainable.


Forrest giving WeLL seminar at Berkeley CBE – Rethinking Radiant

Rethinking Radiant with CHAOS: Reflecting thoughts for Transparent research Emitting new ideas

Talk Abstract (12:15-1:30 2/6):  As the director of CHAOS (Cooling and Heating for Architecturally Optimized Systems) Lab at Princeton who is starting a short sabbatical until April at CBE I will try to give an overview of research and then drill into topics of common interest and debate.  I will present a brief overview of the work we have been doing the past 5 year (including some discoveries of Harrison Fraker’s past) and then zoom in on our current work on radiant systems. CHAOS originated as fun acronym, but also refers a consideration of system entropy to generate novel thermal systems and architectures. Through that thrust we are researching three primary areas: 1. Deeper geothermal 2. Liquid desiccants, and 3. Radiant systems and sensors. I will attempt to magically weave the relationships of those topics together and then focus on radiant systems.

Workshop (2pm-4pm 2/6): Between 3 and 5 CHAOS researchers will be in town next week returning from Singapore and visiting from Princeton with SMART sensor in tow. After the talk we plan to have an informal workshop. We will plan to start around 2pm for those that might be busy for the talk but interested in the workshop. Meet in the large conference room. The workshop will include a detailed overview of MRT calculations and measurement systems, and also the thermal comfort history and models we have reviewed. We will also discuss IoT hardware we have used for sensor backbone and prototyping infrastructure we have leveraged. Data management practices the database and REST-API systems we have setup on various platforms will be reviewed

CHAOS Participants include:
Eric Teitelbaum: Princeton PhD candidate (defending winter 2019), leader and constructor of Cold Tube in Singapore, SMART co-inventor and CSO of Hearth Labs spinoff
Nicholas Houchois: Researcher, co-inventor and leader of SMART development, CEO of Hearth Labs spinoff
Dr. Kianwee Chen: ETH Phd previously with MIT SMART, now Andlinger Center postdoctoral fellow with CHAOS lab.
Hongshan Guo (remote): Princeton PhD candidate (defending spring 2019), human body exergy modeling and research, coaxial geothermal borehole modeling, and urban radiant heat exchange and sensing.
Mauricio Lloyola Vergara (remote): Princeton PhD candidate (defending spring 2020), Post occupancy evaluation of IEQ and architectural spatial quality compared to proposed use and informed by IoT sensing techniques
Dorit Aviv (Remote): Asst Prof. U-Penn, Princeton PhD candidate (defending spring 2020): Surface geometry and form relating to radiant and evaporative surface heat and mass transport for experimental pavilions and architectures.

Summary with links to papers and references
The CHAOS lab has been working on a series of project exploring radiant heat transfer leveraging unconventional methods of reflection, transparency and emissivity of materials. These include architectural pavilions like the Thermoheliodome (EnB paper) and review of measurement methods like the black globe (EnB paper). This also includes the development of a 3D radiant heat exchange “SMART” Sensor (Princeton news). In parallel to the SMART sensor development we have built up significant expertise in IoT sensor design and construction. We have used those expertise to build deployable air quality sensors motivated by our bias toward radiant systems that air should be for breathing, not heating and cooling. Last year we published a paper on the potential of these inexpensive distributed sensors to spatially define the sources of pollutants throughout all aspects of a building’s ventilation systems and spaces.

Most recently on January 18th we launched the ColdTube in Singapore, an outdoor radiant cooling pavilion in Singapore as reported by Today. It is a collaboration between Berkeley (Jovan Pantelic), ETH (Arno Schlueter), UBC (Adam Rysanek), and Princeton (CHAOS lab). I will present the most recent findings including new questions they present regarding the ability to mitigate condensation with transparent membranes and also decouple convection from radiant exchanges. Our ASR paper just came out last week in the journal where the original concept was published in 1963. In this context there are also new questions about the validity of black globe measurements, which initial results show are incapable of measuring MRT more than 2.5K below the ambient temperature. This relates to many assumptions that have been made about radiant heat transfer and thermal comfort, and to what I believe is a commonly held false assumption that MRT cannot be significantly shifted from air temperature. In addition, as shown in our Singapore prototype, we can create environments with nearly zero convective heat exchange with the body while maintaining >100W/m2 of heat dissipation. We are interested in expanding building environmental analysis beyond empirical comfort boxes on psychrometric charts to realtime management of Watts of heat exchange with occupants by all means of conditioning. As the SMART sensor has the capability of also sensing occupancy and skin temperature of occupants, one of the future goals is to try to understand if and how indirect feedback on metabolic rate and thermal state might be generated and used to directly manage the Watts exchanged with occupants for a truly human-centric control. Ideally these last provocations will provide for plenty of discussion and lead into the workshop in the afternoon for those who are interested with the SMART sensor and my researchers who are visiting.


New article on non-condensing radiant panel experiments in Architectural Science Review

Revisiting radiant cooling: condensation-free heat rejection using infrared-transparent enclosures of chilled panels

Eric Teitelbaum, Adam Rysanek, Jovan Pantelic, Dorit Aviv, Simon Obelz, Alexander Buff, Yongqiang Luo, Denon Sheppard & Forrest Meggers
Accepted 09 Dec 2018,  Published online: 31 Jan 2019

Download citation

In this study, we enhance the understanding and design of a radiant cooling technology for outdoor comfort in tropical climates, originally proposed by R.N. Morse in 1963, in this journal. We investigate a type of radiant cooling methodology whereby the cold temperature source is physically separated from the outdoor environment by an insulated enclosure using a membrane transparent to infrared radiation. The enclosure isolates the radiant cooling surface from ambient conditions, allowing the radiant surface to be cooled significantly below ambient dew point temperatures without incurring condensation. For this new study, a Fourier Transform Infrared (FTIR) Spectroscopy analysis on three candidate membrane materials is undertaken and a prototype experimental test panel is fabricated. Our study shows that for a 5°C chilled panel temperature, the exterior membrane surface temperature reaches 26°C in a 32°C / 70% RH environment resulting in an effective mean radiant temperature of 15.8°C. These results provide new evidence in support of Morse’s original proposal, that such panels could provide significant radiant cooling without condensation in humid environments. Radiant cooling products based on the studied technology may offer an ability to provide thermally comfortable conditions in hot environments without the energy required for dehumidification.