A data-driven ray tracing simulation for mean radiant temperature and spatial variations in the indoor radiant field with experimental validation
Dorit Aviv, Julie Gros, Hayder Alsaad, Eric Teitelbaum, Conrad Voelker, Jovan Pantelic, Forrest Meggers
+ Abstract
A data-driven simulation technique is proposed for the calculation of the 3-dimensional radiant temperature distribution across a room with the aid of a ray tracing method. The proposed simulation accounts for interreflections of radiant heat fluxes from surfaces reflective in the longwave range within the indoor environment. The simulation provides results which include high-resolution spatial radiant field maps for indoor spaces as well as human body mapping for radiant heat fluxes received by different body segments, depending on the bodily position of a person in space. The simulation technique is validated with a physical experiment in a controlled climate chamber, where a heat-flux sensor array is used to measure the mean radiant temperature (MRT) by measuring the average plane radiant temperature in 6 directions at multiple points in space. The results for the experiment show excellent agreement between the simulated and measured results. The simulation allows one to resolve and visualize spatial variations of the radiant field, identify impact of radiant asymmetry and surface materials on the room’s irradiation distribution as well as the variations on the human body in different positions and orientations.
Surface Generation of Radiatively-Cooled Building Skin for Desert Climate
Dorit Aviv, Zherui Wang, Forrest Meggers, Aletheia Ida
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A radiatively cooled translucent building skin is developed for desert climates, constructed out of pockets of high heat-capacity liquids. The liquids are contained by a wavelength-selective membrane enclosure, which is transmissive in the infrared range of electromagnetic radiation but reflective in the shortwave range, and therefore prevents overheating from solar radiation and at the same time allows for passive cooling through exposure of its thermal mass to the desert sky. To assess the relationship between the form and performance of this envelope design, we develop a feedback loop between computational simulations, analytical models, and physical tests. We conduct a series of simulations and bench-scale experiments to determine the thermal behavior of the proposed skin and its cooling potential. Several materials are considered for their thermal storage capacity. Hydrogel cast into membrane enclosures is tested in real climate conditions. Slurry phase change materials (PCM) are also considered for their additional heat storage capacity. Challenges of membrane welding patterns and nonuniform expansion of the membrane due to the weight of the enclosed liquid are examined in both digital simulations and physical experiments. A workflow is proposed between the radiation analysis based on climate data, the formfinding simulations of the elastic membrane under the liquid weight, and the thermal storage capacity of the overall skin.
Ope-Ed: A Better Way to Cool Ourselves
Forrest Meggers, Dorit Aviv, Adam Rysanek, Kian Wee Chen, Eric Teitelbaum
+ Abstract
A new technique doesn’t deprive us of fresh air. And because it uses less energy, it’s good for the climate as well (op-ed article in Scinetific American).
A fresh (air) look at ventilation for COVID-19: Estimating the global energy savings potential of coupling natural ventilation with novel radiant cooling strategies
Dorit Aviv, Kian Wee Chen, Eric Teitelbaum, Denon Sheppard, Jovan Pantelic, Adam Rysanek, Forrest Meggers
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Radiant cooling-assisted natural ventilation is an innovative technical approach that combines new radiant cooling technology with natural ventilation to increase fresh air delivery into buildings year-round with minimal energy cost and improvment of air quality. Currently, the standard paradigm for HVAC (heating, ventilation and air conditioning) is based on central air systems that tie the delivery of heating and cooling to the delivery of fresh air. To prevent heat loss, the delivery of fresh air must be tightly controlled and is often limited through recirculation of already heated or cooled air. Buildings are designed with airtight envelopes, which do not allow for natural ventilation, and depend on energy-intensive central-air systems. As closed environments, buildings have become sites of rapid COVID-19 transmission. In this research, we demonstrate the energy cost of increasing outdoor air supply with standard systems per COVID-19 recommendations and introduce an alternative HVAC paradigm that maximizes the decoupling of ventilation and thermal control. We first consider a novel analysis of the energy costs of increasing the amount of conditioned fresh air using standard HVAC systems to address COVID-19 concerns. We then present an alternative that includes a novel membrane-assisted radiant system we have studied for cooling in humid climates, in place of an air conditioning system. The proposed system can work in conjunction with natural ventilation and thus decreases the risk of indoor spread of infectious diseases and significantly lowers energy consumption in buildings. Our results for modeling HVAC energy in different climates show that increasing outdoor air in standard systems can double cooling costs, while increasing natural ventilation with radiant systems can halve costs. More specifically, it is possible to add up to 100 days’ worth of natural ventilation while saving energy when coupling natural ventilation and radiant systems. This combination decreases energy costs by 10–45% in 60 major cities globally, while increasing fresh air intake.
Spatial analysis of the impact of UVGI technology in occupied rooms using ray‐tracing simulation
Miamiao Hou, Jovan Pantelic, Dorit Aviv
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The use of Ultraviolet Germicidal Irradiation (UVGI) devices in the upper zones of occupied buildings has gained increased attention as one of the most effective mitigation technologies for the transmission of COVID‐19. To ensure safe and effective use of upper‐room UVGI, it is necessary to devise a simulation technique that enables engineers, designers, and users to explore the impact of different design and operational parameters. We have developed a simulation technique for calculating UV‐C fluence rate within the volume of the upper zone and planar irradiance in the lower occupied zone. Our method is based on established ray‐tracing light simulation methods adapted to the UV‐C wavelength range. We have included a case study of a typical hospital patient room. In it, we explored the impact of several design parameters: ceiling height, device location, room configuration, proportions, and surface materials. We present a spatially mapped parametric study of the UV‐C irradiance distribution in three dimensions. We found that the ceiling height and mounting height of the UVGI fixtures combined can cause the largest variation (up to 22%) in upper zone fluence rate. One of the most important findings of this study is that it is crucial to consider interreflections in the room. This is because surface reflectance is the design parameter with the largest impact on the occupant exposure in the lower zone: Applying materials with high reflectance ratio in the upper portion of the room has the highest negative impact (over 700% variation) on increasing hot spots that may receive over 6 mJ/cm2 UV dose in the lower occupied zone
Energy and Water Autonomy for Off-Grid Waterfront Floating Structures
Dorit Aviv
+ Abstract
Floating structures are designed to adapt to rising water, and have proved capable of withstanding sea level rise as well as the increased frequency and intensity of storms. However, because of their siting on water, they present a major operational challenge: they must operate off-grid as connections to central water and energy infrastructure become difficult or even unfeasible. Instead, such structures must be designed to be self-sufficient; their requirements raise specific questions on water and energy autonomy at the building scale. The Thermal Architecture Lab, is part of a collaboration with the RETI Center and the Water Center at Penn, to develop energy and water autonomous systems for off-grid floating structures.
Ventopenings: Conditioning in Pandemic Times. Part 3—A Conversation about Air Quality
Daniel A. Barber, Ahu Aydogan, Dorit Aviv, Marta Gutman
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In this piece, architects Ahu Aydogan and Dorit Aviv along with the architectural historians Daniel A. Barber and PLATFORM’s Marta Gutman discuss air quality during the pandemic. Daniel, a historian of architectural environmentalism, convened this discussion inviting Ahu and Dorit, designers and researchers specializing in the fields of energy and ecology, and Marta, an historian of children’s spaces, to the “table.”
The conversation includes a discussion about natural ventilation, air filtering technology, and radiant heating and cooling.
Evaluating radiant heat in an outdoor urban environment: Resolving spatial and temporal variations with two sensing platforms and data-driven simulation
Dorit Aviv, Hongshan Guo, Ariane Middel, Forrest Meggers
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Instruments measuring the outdoor radiant environment are limited spatially. They aggregate observations to singular points, eliminating variations from surrounding surface temperatures. Computational methods can characterize the heterogeneous outdoor radiant environment, but spatial validation with accurate tools remains difficult. We use two novel sensing platforms (MaRTy and SMaRT) and an innovative computational validation method to explore Mean Radiant Temperature (MRT) spatial variation outdoors. MaRTy is a mobile instrument that evaluates MRT with directional weighting for hemispherical radiation flux density observations. The SMaRT sensor uses a non-contacting infrared surface temperature sensor and LIDAR to map surrounding surface temperatures. We conducted a case study combining the methodology of both instruments to improve spatial mapping of MRT for five locations on Temple University's main campus in Philadelphia, PA in July. For comparison, we collected thermal images to build a data-driven simulation model for MRT. Results demonstrate the improved resolution of combining both sensors to resolve variations in outdoor longwave radiation fluxes. The instruments show variations in surface temperatures up to 10 °C for SMaRT from longwave radiation and MRT variations of 40 °C for MaRTy, which included shortwave influences. These demonstrations of significant spatial variations were measured across an area typically evaluated at one position.
Simulating Invisible Light: Adapting Lighting and Geometry Models for Radiant Heat Transfer
Dorit Aviv, Miaomiao Hou, Hongshan Guo, Eric Teitelbaum, Forrest Meggers
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Thermal radiation, being the infrared spectrum of electromagnetic radiation, shares many characteristics with visible light, and thus is highly dependent on surface geometry. Much research effort has been dedicated to characterizing the behavior of visible light in the built environment and its impact on the human experience of space. However, longwave infrared radiation’s effect on the human perception of heat within the indoor environment is still not well characterized or understood within the design community. In order to make legible the embodied effect of radiant surfaces’ geometry and configuration, we have developed a Mean Radiant Temperature simulation tool which is based on a raytracing technique and accounts for the detailed geometry of the human body and its surrounding environment. This paper is meant to provide an overview of the geometric characteristics of radiant heat transfer with a dual purpose: 1. the integration of these principles into a Mean Radiant Temperature simulation technique in order to better characterize radiant energy exchanges and 2. the development of architectural design strategies based on these principles, which are tested in a case-study prototype. The MRT simulation method and results for the experiment are discussed.
Hydrogel-Based Evaporative and Radiative Cooling Prototype for Hot-Arid Climates
Dorit Aviv, Maryam Moradnejad, Aletheia Ida, Zherui Wang, Eric Teitelbaum, Forrest Meggers
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A roof aperture lined with hydrogel membrane is proposed for combined evaporative and radiative cooling in the desert climate. In order to determine the design, materials and predicted performance of this device, several types of digital simulations and physical experiments were performed. The proposed full-scale prototype, planned to be built and tested in Tucson, Arizona, responds to the climate's extreme diurnal temperature gradient through the use of adaptive materials. During the day, the roof aperture acts as a downdraft chimney, trapping the hot dry air passing through it. The funnel-shaped top of the chimney is embedded with a wet hydrogel membrane, which humidifies the air, causing instantaneous cooling and a consequent downdraft airflow into the building's interior. During the night, pockets of enclosed hydrogel encapsulated in the roof's structural frame are exposed to radiative cooling from the night sky and act as thermal storage for additional cooling during daytime. The complexity of the system requires several simulation and physical testing methods to be employed simultaneously: digital simulation tools of CFD, solar radiation analysis, radiative heat loss analysis were employed to analyze the overall geometry's effect on airflow radiant heat exchange; physical bench tests were conducted to analyze the performance of hydrogel membrane and compare it to other materials. A full-scale prototype will be built to validate the results of the model.
Measuring the Right Factors: A review of variables and models for Thermal Comfort and Indoor Air Quality
Nan Ma, Dorit Aviv, Hongshan Guo, and William Braham
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The indoor environment directly affects health and comfort as humans spend most of the day indoors. However, improperly controlled ventilation systems can expend unnecessary energy and increase health risks, while improved thermal and air quality can often result in higher energy consumption. One way to approach this dilemma is by understanding the effectiveness of the variables influencing indoor air quality (IAQ) related health and comfort. The objective of this paper is to highlight evidence and variables from empirical and deterministic models, which are combined in analytical models that current machine learning techniques often overlook. This paper reviews the analytical models and identifies the corresponding input variables, discussing their application in models based on artificial neural networks (ANNs) and reinforcement learning (RL). ANN and RL models have accurately described non-linear systems with uncertain dynamics and provided predictive and adaptive control strategies. The first part of this study focuses on the most common thermal comfort models and their variables, mainly related to steady-state and adaptive models. The second part reviews typical models of determining indoor air pollutants and their relationship with ventilation requirements and health effects. Forty-five works closely related to the field are summarized in multiple tables. The last part identifies the factors needed to predict thermal comfort and IAQ.
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, and Adam Rysanek
+ 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.
Generation and Simulation of Indoor Thermal Gradients: MRT for Asymmetric Radiant Heat Fluxes
Dorit Aviv, Eric Teitelbaum, Tyler Kvochick, Kipp Bradford, Forrest Meggers
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The inherent geometric and material dependence of radiant heat transfer can be leveraged to improve system efficiency and thermal comfort. Unlike in air-based systems, non-uniform temperature distribution can be highly controlled and beneficial in radiant systems, where temperature perception can be manipulated locally. An experiment was devised with the aim of creating a significant temperature gradient in a single space by using radiant heat transfer to cool certain parts of a room while simultaneously heating other parts. This was achieved by inducing radiant fluxes from hot and cold emissive pipes and directing them at different areas of the room through the use of curved infrared reflective surfaces. A 3D simulation was created to analyze the consequences of such a configuration for the Mean Radiant Temperature (MRT). The simulation utilizes a ray-tracing technique to account for multiple reflection bounces. The results are compared to MRT measurements taken in the physical experiment using Black Globe Thermometers. A simulation study of the heat transfer characteristics of a single pipe in a parabolic trough is also discussed.
Thermal Reality Capture Merging Heat-Sensing with 3D Scanning and Modeling to Characterize the Thermal Environment
Dorit Aviv, Nicholas Houchois, Forrest Meggers
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Architectural surfaces constantly emit radiant heat fluxes to their surroundings, a phenomenon that is wholly dependent on their geometry and material properties. Therefore, the capacity of 3D scanning techniques to capture the geometry of building surfaces should be extended to sense and capture the surfaces' thermal behavior in real time. We present an innovative sensor , SMART (Spherical-Motion Average Radiant Temperature Sensor) that captures the thermal characteristics of the built environment by coupling laser geometry scanning with infrared surface temperature detection. Its novelty lies in the combination of the two sensor technologies into one analytical device for radiant temperature mapping. With a sensor-based dynamic thermal-surface model, it is possible to achieve representation and control over one of the major factors affecting human comfort. The results for a case-study of a 3D thermal scan conducted in the recently completed Lewis Center for the Arts at Princeton University are compared with simulation results based on a detailed BIM model of the same space.
No Longer an Object: Thermodynamics and New Dimensions of Architectural Design
Dorit Aviv
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A reconsideration of what constitutes the ‘design space’ today from the perspective of thermodynamics is necessary in order to expand the realm of architecture into new domains. Building form is dominated in every era by the technological means that produce it. Today, the ubiquitous representations of architecture on computer screens as a context-less object in an empty virtual Cartesian space inherently ignore the constant energetic exchange between a building, the human body and its environment. These exchanges extend not only to the immediate surrounding but all the way to the cosmic scale of the sky and the stars. A pedagogy that engages architecture students with climate and ecology must therefore develop new tools of representation that embody these multi-scalar relationships. In this article, projects produced by students in the design studio are examined as means to both characterize energy flows and intervene on them. As such, they are not just registers of environmental knowledge and sensory data but a first step in redefining the relationship between architecture and the environment.
Climate-Adaptive Volume: Solving the Motion Envelope of a Reconfigurable Cooling Aperture for Desert Climate
Dorit Aviv and Axel Kilian
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Through several prototypes of a roof aperture for passive cooling in a desert climate, the relationships between design, thermal performance, and measurement are explored. Optimization of both day and night cooling modes within the same device requires the kinetic transformation of the aperture from a narrow downdraft chimney into an open radiation apparatus. Different methods are examined, from premeasured geometric optimization with constrained motion to a generalized design that can acquire numerous configurations and deploy algorithmic controls with live sensing to measure optimized performance during operation. The results are evaluated based on the structural-mechanical operation of the prototypes as well as the cooling effect they produce. Future steps and the implications for open-ended feedback-based design approaches are discussed.
Thermally Informed Bending: Relating Curvature to Heat Generation Through Infrared Sensing
Dorit Aviv and Eric Teitelbaum
+ Abstract
The process of bending flat ductile surfaces such as metal sheets into curved surfaces that match a precise digitally predefined geometry so far has required either using a mold or a predetermined gauge and alloy-based predictive model to determine the necessary bending arc. Instead, our approach relies on the material itself to report its bending state during a simple actuation movement enabled by a robotic arm. We detect spontaneous heat generation triggered by the transition from elastic to plastic deformation using an infrared camera in real time. This information is used to determine the motion path of the robotic arm in order to reach the desired final geometry in one movement rather than incrementally. The bending process is generated through a RAPID code with a trap loop to guide the robot and a Processing script to control the thermal sensing and trap loop activation. Results for an IR sensor-guided geometric trap loop and the determination of a meaningful threshold for the onset of plastic deformation are discussed. This method’s efficiency and applicability to large scales of production and to a wide array of ductile materials with varying elastic modulus, suggest a potentially significant contribution to the fabrication of curved architectural skins.
Adaptive Roof Aperture for Multiple Cooling Conditions
Dorit Aviv
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We develop a kinetic cooling roof device for desert climate, which operates in multiple constellations triggered by sensor input. The device is designed for a dual response: as a wind catcher it captures external airflow and channels it into the building's interior volume by orienting the roof opening toward the current prevalent wind direction. At the same time, the aperture is responsive to radiation -either avoiding direct solar radiation during the day or maximizing radiant cooling during the night by exposing the building's interior to the night sky. To achieve these various states, the geometry of the design is simplified into a segmented cylinder with multiple blades that allow for myriad potential constellations to occur. A motorized joint with three degrees of freedom controls the position of each of the aperture's blades. The range of possible outcomes and functional relationships in the system is tested with both digital simulations and physical prototypes. A wind tunnel test was conducted to compare the performance of different configurations.
Cooling Oculus for Desert Climate – Dynamic Structure for Evaporative Downdraft and Night Sky Cooling
Dorit Aviv and Forrest Meggers
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We develop a model and prototype for a lightweight roof oculus structure, which integrates two complementing cooling strategies. During the day the roof oculus takes the shape of a downdraft evaporative cooling chimney. A water mist sprays inside the chimney crown, cooling and densifying hot dry air and causing it to fall down the chimney into the indoor space by free convection. During the night, the oculus structure is opened by geometric dilation designed with actuation kinetics to expose a maximum surface of the concrete slab below to the night sky above. The slab then acts as thermal mass, “storing” coolness for the following hot day. The results of the analytical model demonstrate the ability to cool a space in 40°C desert climate to comfort conditions. A scaled prototype was built and demonstrates the operation to evaporative cooling and the structural opening for expanded radiant view factor.