Thermal Performance of Radiantly Cooled Rammed Earth
Dishanka Kannan, Ningxu Luo, Yujia Cui, Max Hakkarainen, Xiang Zhang, William Braham & Dorit Aviv
+ Abstract
This study assesses the effectiveness of radiant cooling to mitigate higher temperatures resulting from direct heat exposure. The core hypothesis proposes that integrating an externally cooled closed-loop hydronic system (CLHS) within the building structure can significantly improve indoor comfort with relatively low energy expenditure compared to conventional designs. A sectional prototype module of a radiant cooling wall embedded with water pipes is physically tested. In addition, the thermal performances of cement versus rammed earth as structural materials are compared. The comparison aims to address the existing research gap in the integration of an active radiant cooling technology like CLHS with rammed earth as thermal mass. The comparison between the proposed system and the conventional cement-based radiant CLHS system provides insights into the potential performance of a rammed earth-based CLHS and serves as a benchmarking method. Additionally, an assessment of the climate change potential of these modules is used to gain an overall perspective of the advantages and disadvantages of using these systems in practical applications.
Dynamic Insulated Shutter System for a Double-Layer Building Façade: a Case Study with Physical Prototype
Li Pan, Zhirui Bian, Xiang Zhang, Max Hakkarainen, William Braham and Dorit Aviv
+ Abstract
Adaptive building envelopes (ABEs) enable the dynamic response of building enclosures to environmental conditions. Movable window insulation is a powerful adaptive technique, but its potential has not been sufficiently explored. Based on a case study, an insulated shutter system with a double-layer façade capable of adapting to varying environmental conditions, especially the hot days and cold nights of the desert, was investigated. Specifically, the control operation schedules of different facades and layers were based on temperature and solar position to maximize energy efficiency, daylighting, and thermal comfort. Dynamic shading simulations were used to optimize the façade performance. Subsequently, temperature thresholds are established based on the optimization of vital parameters like Useful Daylight Illuminance (UDI), Energy Use Intensity (EUI), and Predicted Mean Value (PMV). Moreover, two complementary physical models were tested to evaluate natural ventilation and the physical mechanism of operation respectively.
Multi-objective design exploration for integrated structural-environmental performance of buildings: A review
Zherui Wang, Masoud Akbarzadeh and Dorit Aviv
+ Abstract
Building performance optimization has been developed and frequently deployed in building design over recent years. However, the division of disciplines in architecture results in optimization processes performed for a singular function either structurally or environmentally, rather than a holistic optimization process for both. With the increasing urgency to mitigate climate change in a world of finite resources through reducing both embodied and operational energy expenditures, researchers have recently begun to embed multi-functional objectives into the design and engineering process. To assist designers in assessing the full spectrum of design options, multi-objective design explorations (MODE), such as multi-objective optimization (MOO), multidisciplinary optimization (MDO), and computational design exploration (CDE), have demonstrated the potential to explore building performance-driven design space while maintaining design freedom, particularly in the early design stage. This paper presents a review of research on the potential for an integrated structural-environmental MODE workflow. The review examines the design and optimization topic domain, variable selection and software used during design space formation in existing literature, and subsequently seeks to identify knowledge gaps and opportunities in uniting the two disciplines. A survey of scientific journal articles reveals an ongoing relationship between structural design and operational energy, solar control and daylighting, and acoustic design, while structural design and thermal mass is an emerging research direction. Part two of the paper reviews precursor demonstrator and built case-study projects with an integrated structural-environmental approach in order to deduce potential design variables for future multi-objective design exploration workflows. Areas of future research on an integrated structural-environmental design are outlined and associated design variables are reviewed.
An Early Design Stage Parametric Exploration of Integrated Concrete Funicular Floor Element and Thermal Mass Performance for Carbon Footprint Reduction
Zherui Wang, Hua Chai, Xiaoxiao Peng, Ryan Welch, Masoud Akbarzadeh and Dorit Aviv
+ Abstract
In response to the imperative of reducing material use and carbon footprint, building structural elements can be designed with structural and environmental design considerations for duo-functions. We present an early-stage, parametric design workflow that integrates thermal mass performance with structurally optimized, prefabricated, funicular, concrete floor elements. Thermally massive building structures, like concrete floors, can act as a thermal battery that reduces reliance on and carbon emission associated with mechanical cooling. The proposed co-design workflow forges an integrated structural and building energy simulation framework that assesses the operational carbon saving associated with cooling induced by different building structural thermal mass design options, while constraining the embodied carbon associated with material volume. Polyhedral Graphic Statics (PGS) is utilized as the geometric form-finding method to intuitively design and optimize the discrete floor geometry via Polyframe, a parametric plugin developed in Grasshopper. The floor geometries are then placed in the whole building energy simulation environment to evaluate its thermal mass performance impact on lifecycle carbon emission reduction related to space cooling with Future Typical Meteorological Year (fTMY) weather data. Projected hourly average grid emission factors from 2020 to 2079 are referenced for emission calculations. Using the US Department of Energy Secondary School Reference Building as a case study, the 60 year life cycle cooling carbon emission savings associated with structurally optimized thermal mass floors are investigated in two representative cities in two climate zones and grid emission scenarios (marine climate in San Diego, California, and cold climate in Denver, Colorado). Our results reveal that using co-designed concrete funicular floors as building thermal mass can achieve 25% and 15% annual cooling carbon emission reduction compared to the flat slab of the same material volume in San Diego and Denver respectively from 2020 to 2039. With further grid electrification, a 9% and 10% reduction can be obtained from 2040 to 2059, and 0 and 6% from 2060 to 2079 in the respective locations.
SimbioBrick: Carbon Sequestering Living Bricks by Fungi-Plant Symbiosis
Ji Yoon Bae, Dorit Aviv, Laia Mogas-Soldevila
+ Abstract
Harnessing the symbiotic association of plant and fungi, we devised SimbioBrick; a living system that encases mycorrhizal fungi and alfalfa in a portable pot-like brick cassette that promotes plant growth and carbon sequestration. SimbioBrick contains fungal spores, seeds, water, and nutrient-storing hydrogels emulating wet soils. Their outer geometries are designed to provide structural support in modular assemblies and to expose plants to sunlight for photosynthesis. Their inner structures mediate depth for fungal colonization and porosity for adequate drainage. The SimbioBrick system is multifunctional in providing (1) biological behavior driven modular brick design, (2) indoor and outdoor oxygen production, (3) continuous carbon sequestration, (4) retaining water to self-irrigate, as well as (5) soil-bioremediation in our future work. Applications of the SimbioBrick system are living building components supporting bio-receptive architecture, such as substitution of heavy, multi-material, energy intensive, and non-recyclable green facades, or production of new outdoor flooring able to pave walkways while offsetting carbon emission from buildings and bio-remediating polluted soils beneath.
Augmenting Thermal Mass Performance without Added Carbon Footprint: Surface Area Modulation of Structural Slabs in Naturally Ventilated Buildings
Zherui Wang, Xiang Zhang, Xiaoxiao Peng, Saeran Vasanthakumar, Dorit Aviv
+ Abstract
Internal thermal mass (ITM) is a well-known passive technique that provides lag and damping for extreme diurnal temperature fluctuations when combined with natural ventilation and night flushing. Thermally massive concrete slab elements, vital for ITM, often feature a compact solid design, limiting their thermal storage potential due to restricted contact with indoor airflow. With the advent of architectural geometry and digital fabrication, floor elements can be designed and fabricated with greater exposed surface area under the constraint of the same material volume, thus maintaining the same embodied carbon footprint but increasing thermal performance potential. This study examines the impact of increasing the exposed surface area of ITM through geometric modulation while keeping the material volume constant to reduce the building’s embodied carbon. The objective is to investigate how varying ITM surface area, within a fixed material volume constraint, influences indoor thermal comfort in a free-running building. We examine a case study of a midsize office building in two climatic zones (Tucson, AZ, and San Diego, CA) with an increased ITM ceiling surface area of the structural slab. We then apply natural ventilation optimization and night flushing to further enhance ITM performance. The results show that in the hot-dry and marine climates, expanding ITM surface area by 1.7 times yields an improvement of 6% and 7% annual thermal comfort hours when coupled with natural ventilation. These findings suggest a substantial energy-saving potential for enlarging the surface area of ITM in buildings within the studied climates.
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A design stage, multi-objective assessment: material selection with environmental life-cycle analysis, labor, and material health considerations for building structure
Zherui Wang, Xiaowen Yu, Kayleigh Houde, Dorit Aviv
+ Abstract
During the schematic design stage of a building, assessing trade-offs of lifecycle impact of building elements and materials is crucial for the decision-making process when aiming to reduce negative impacts holistically. A multi-objective assessment is proposed, for environmental, labour exploitation risk (LER), and material health lifecycle impact of the structure and foundation elements in the schematic design stage. Using a real, mid-size, mass timber, educational building in Philadelphia, United States as a case study, we deployed multi-objective optimization (MOO) to consider the range of global warming potential (GWP), LER rating, and material health impact of nine product types over 1602 structure and foundation elements. The parametric workflow paired with Building Information Modelling (BIM) objects aims to provide designers a holistic overview on the cumulative, per material, and per building element impact upstream in the supply chain. The Pareto front solutions reveal that concrete floor with metal deck, hollow structural section framing, and concrete foundation slab, footing, and column pose the greatest risk overall for the case study building, and warrant design consideration to substitute with less impactful alternatives.
Blockchain + IoT sensor network to measure, evaluate and incentivize personal environmental accounting and efficient energy use in indoor spaces
Nan Ma, Alex Waegel, Max Hakkarainen, William W. Braham, Lior Glass, Dorit Aviv
+ Abstract
Electric demand flexibility in buildings is highly dependent on occupant behavior. Evaluating and incentivizing these behaviors can provide grid-responsive support and encourage demand response (DR) participation. To achieve these goals, we developed an infrastructure for connecting Internet of Things (IoT) sensors to a distributed ledger (blockchain network) for long-term monitoring of energy and environmental performance. This study presents a novel Blockchain + IoT paradigm for the building science research community, applied in a real-world application. This Blockchain + IoT Network (BIN) uses Raspberry Pi minicomputers as platforms for connecting sensors to a blockchain network, to provide and analyze real-time indoor environmental quality (IEQ), energy, and carbon intensity data. As part of the study, we propose various metrics to evaluate the environmental footprints of building users. Novel algorithms for normalizing energy usage and carbon intensity, with consideration of a variety of related environmental factors, are executed as smart contracts on the blockchain network. All measurements and the smart contract transactions are reported and visualized on live dashboards. The use of smart contract allocates tokens based on the reward algorithms to incentivize individuals’ energy conservation, and similarly to DR pricing, can help influence occupant consumption patterns towards carbon reduction goals. We further test the smart contract’s algorithm in relation to real sensor data we have collected in two case studies: single-unit households and carbon intensity in the energy market. The combination of proposed metrics translates measured sensor data into token awards, demonstrates upper and lower limits dictated by the grid generation mix profile, and indicates that there is the potential for load shifting to minimize carbon emissions without considering the scale of consumption.
Open Architecture
Dorit Aviv
In: The Pandemic Effect: Ninety Experts on Immunizing the Built Environment. Edited by Blaine Brownell. Princeton Architectural Press, 2023
Abstract
We can overcome the fraught relationship between health and energy savings by restoring natural ventilation systems.
Resolving Indoor Shortwave and Longwave Human Body Irradiance Variations for Mean Radiant Temperature and Local Thermal Comfort
Miaomiao Hou, Dorit Aviv, Arnab Chatterjee, Eric Teitelbaum, Mohamad Rida, Forrest Meggers, Dolaana Khovalyg
+ Abstract
A spatially and directionally resolved longwave and shortwave radiant heat transfer model is presented via a series of experiments in a thermal lab to input surface temperatures and geometries, as well as skin temperature readings from a human subject, in order to test mean radiant temperature (MRT) and thermal comfort results for the person. Combining novel scanning and thermography methods together with ray-tracing simulation, high-resolution thermal models are derived fully characterizing the longwave and shortwave radiant heat fluxes in space and resolving the impact of these variations on MRT. The study demonstrates the significant amount of spatial variation of both shortwave and longwave radiant heat transfer on MRT through the room and also across body segments: the experimental results show variations of up to 14.5°C across the room, leading to PMV comfort variations from -0.27 to 2.45, clearly demonstrating the importance of mapping the entire radiant field rather than assuming one MRT value for a thermal zone. Furthermore, local radiant temperature, newly defined body segment plane radiant temperature (BSPRT), variations across the body of more than 30°C are found. Finally, a detailed human thermo-physiology model was used to evaluate the variation in thermal sensation between the different body segments due to the large differences in local MRT.
Large-Scaled and Solar-Reflective Kirigami-Based Building Envelopes for Shading and Occupants’ Thermal Comfort
Heesuk Jung, Miaomiao Hou, Byungsoo Kang, Zherui Wang, Hyojeong Choi, Hyeong Won Lee, Yongju Lee, Doh-Kwon Lee, Phillip Lee, Dorit Aviv, Hyeok Kim, Shu Yang
+ Abstract
Conventional air conditioning in buildings consumes substantial energy contributing to an increase in greenhouse gas emissions, which aggravates global warming. Kirigami envelopes with reflective surfaces offer a promising option to reduce indoor heat gain. So far none has performed outdoor testing of kirigami envelopes nor numerical simulation to understand how they interact with the environment. To understand the impact of the geometric design of the kirigami shading system on both daylighting and temperature variation in the indoor environment, a series of prototypes and simulations is devised to investigate the real-time shading behavior in an outdoor environment. Large-scaled and silver-coated kirigami-based envelopes of different cut patterns and stretching ratios are fabricated and placed in front of custom-designed chambers equipped with six thermo-sensors. Simulation is performed to investigate the effect of light modulation and hence temperature inside the chamber, which corroborates with the experiments. The indoor daylighting pattern and temperature are significantly influenced by the geometry of the stretched kirigami envelope, and overall, both the indoor temperature and the spatial distribution of illuminance are more uniform compared with that without the kirigami envelope. These results indicate that the installation of kirigami envelopes can improve building energy saving and occupants’ comfort.
Estimating time-dependent solar gains through opaque building envelope parts: an explorative study on a test box
Xiang Zhang, Dorit Aviv, Dirk Saelens, Staf Roels
+ Abstract
Accurate estimation of the energy gain from solar radiation in buildings is necessary for building energy performance characterization, model predictive control (MPC), fault detection and diagnostics, etc. Solar radiation affects the buildings’ internal air temperature dynamics, either (directly) by penetrating the glazing or (indirectly) through the opaque building envelope. Nevertheless, no research has investigated the on-site data-driven modelling of the indirect effects of solar radiation i.e., additional solar gain through the opaque building envelope, marked as indirect solar gain. Therefore, this work aims to develop grey-box model-based techniques to characterize the dynamics of indirect solar gain. A test box, with overall dimensions of 120 x 120 x 120 cm3, that represents a simplified scale model of a building is examined, to provide an initial understanding of this matter. This test box is south-north orientated and has only one window of 60 x 60 cm2, positioned on its southern wall. On-site data associated with this text box was recorded during the summer (June-July) in Almeria, Spain. This simplified reduced-size text box satisfies the research goal very well to serve as a pilot case study, since the indirect solar gain was the dominant effect of solar radiation. Based on the in-situ data from this case, a three-dimensionally decomposed solar irradiance integrated grey-box modelling technique is proposed for characterizing the dynamics of indirect solar gain. Preliminary results from this study show that this technique can effectively reveal the key dynamics of indirect solar gain and outperform the classic grey-box model, based on limited low-frequency on-site measured data.
Impacts of building envelope design on indoor ozone exposures and health risks in urban environments
Nan Ma, Max Hakkarainen, Miaomiao Hou, Dorit Aviv, William W. Braham
+ Abstract
Much of human exposure to ozone takes place indoors. However, few studies have focused on human ozone exposures in normally occupied residential houses in the U.S. urban environments. Only rare studies have explored the implication of building envelope design variables on outdoor ozone penetration. Our study reveals the extent to which outdoor ozone penetrates and persists in the occupied houses in one of the most ozone-polluted cities, as influenced by building characteristics, building geometry, envelope design variables, window conditions and urban meteorology conditions. Through a set of analysis and variable regressions, we found that (1) the ratios of indoor to outdoor ozone concentration (I/O) were higher with windows open (0.700 ± 0.13) than with the windows closed (0.53 ± 0.22); (2) the indoor ozone concentration is typically elevated when the outdoor ozone concentration is high; and (3) design variables such as exterior envelope finishes, wall surface area and window-to-wall ratio are reasonably effective predictors. Our results of health risk evaluation suggest that the observed levels of indoor ozone exposure could pose a considerable risk to human health. Further work is needed to discover how building envelopes can be designed, constructed and maintained to support occupant health.
Simulating invisible light: a model for exploring radiant cooling’s impact on the human body using ray tracing
Dorit Aviv, Miaomiao Hou, Eric Teitelbaum, Forrest Meggers
+ Abstract
Radiant systems are an energy-efficient method for providing cooling to building occupants through active surfaces. To assess the impact of the radiant environment on occupants in space, we develop a ray-tracing simulation, which accounts for longwave radiation. Thermal 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 is still not well characterized or understood within the design community. In order to make the embodied effect of radiant surfaces’ geometry and configuration legible, we have developed a Mean Radiant Temperature (MRT) simulation method, which is based on a ray-tracing technique. It accounts for the detailed geometry of the human body and its surrounding environment. We use a case study of a pavilion built with an envelope consisting of active cooling panels in Singapore. Using measured data for the surrounding surface temperatures in the pavilion, we explore the impact of both the active panels and the surrounding passive elements and thermal environment on a person’s radiant heat exchange in different postures. The reflectivity and emissivity values of different surfaces are taken into account, and the ray-tracing process allows for multiple-bounce simulation. The model accounts for both longwave and shortwave radiation, and the simulation results are compared with field measurements for validation. The results are expressed both numerically and as spatial radiant-heat-maps. These show a variation of up to 11°C in MRT across the space studied. Furthermore, a digital manikin is used to assess the impact of the radiant cooling panels across the human body. The results show a 10°C variation in radiant temperature perceived by different regions of the body in one position. The findings reveal a significant heterogeneity of radiant heat transfer that current analysis methods typically overlook for both architectural space and the geometry of the human body.
Resolving Radiant: Combining Spatially Resolved Longwave and Shortwave Measurements to Improve the Understanding of Radiant Heat Flux Reflections and Heterogeneity
Coleman Merchant, Forrest Meggers, Miaomiao Hou, Dorit Aviv, Florian Arwed Schneider, Ariane Middel
+ Abstract
We introduce and demonstrate new measurement and modeling techniques to fully resolve the spatial variation in shortwave and longwave radiant heat transfer in the outdoor environment. We demonstrate for the first time a way to directly resolve the shortwave radiant heat transfer from terrestrial reflected and diffuse sky components along with the standard direct solar radiation using an adapted thermopile array and ray-tracing modeling techniques validated by 6-direction net radiometer. Radiant heat transfer is a major component of heat experienced in cities. It has significant spatial variability that is most easily noticed as one moves between shade and direct solar exposure. But even on a cloudy and warm day the invisible longwave infrared thermal radiation from warm surfaces makes up a larger fraction of heat experienced than that caused by convection with surrounding air. Under warm or hot climate conditions in cities, radiant heat transfer generally accounts for the majority of heat transfer to people. Both the shortwave (visible/solar) and the longwave (infrared/thermal) have significant spatial variation. We demonstrate sensor methods and data analysis techniques to resolve how these radiant fluxes can change the heat experienced by >1 kW/m2 across small distances. The intense solar shortwave radiation is easily recognized outdoors, but longwave is often considered negligible. Longwave radiation from heat stored in urban surfaces is more insidious as it can cause changes invisible to the eye. We show how it changes heat experienced by >200 W/m2. These variations are very common and also occur at the scale of a few meters.
Ray-tracing MRT and human thermophysiology model combination for local discomfort prediction
Mohamad Rida, Miaomiao Hou, Arnab Chatterjee, Eric Teitelbaum, Forrest Meggers, Dorit Aviv, Dolaana Khovalyg
+ Abstract
Thermal comfort and discomfort based on the local sensation of different body parts have been an important development in thermal comfort studies from the past decade. The human thermophysiology model can be a handy tool to predict local skin and core temperatures, which can then be projected into diverse human’s local and overall thermal sensation and comfort. When local environmental parameters are incorporated in the thermophysiology model, the degree of modeling information improves. One of the important input parameters is the mean radiant temperature. Variations in radiant heat fluxes when shortwave radiation is present in the room can be significant. Combining novel scanning and thermography methods together with ray-tracing simulation, we derived a high-resolution thermal model to fully characterize the variations of radiant heat fluxes experienced by different body parts of a human, both longwave (LW) and shortwave (SW). The shortwave heat flux varied in the range of 0-216 W/m2 throughout the day in the experiments conducted in an office room prototype on 23/02/2021 in Fribourg, Switzerland. The radiant temperature experienced by different body parts varied widely, from 24 °C to 58 °C, due to uneven exposure to solar radiation through a window, while the air temperature remained relatively uniform, as it was controlled by a mechanical system. To demonstrate the importance of combining detailed MRT modeling together with the thermophysiology model, we input detailed MRT distribution into the human thermophysiology model, along with the environmental parameters from the experimental measurements. The calculated skin temperatures were compared with the measured ones using iButtons and thermal sensation and comfort values with the survey results collected from the human subject. A combination of these detailed methods can be used as a design tool to assess local (dis)comfort and thermal perception of an occupant exposed to shortwave radiation and for dynamic shading and personalized comfort systems control strategies.
Validation of radiant and convective heat transfer models of photonic membrane using non-invasive imaging of condensation pattern
Eric Teitelbaum, Dorit Aviv, Miaomiao Hou, J Li, Adam Rysanek, Forrest Meggers
+ Abstract
Cooling a sample of a material until condensation is observed is a standard technique for accurately measuring the dewpoint and associated relative humidity in a volume. When conducting an experiment with a membrane-assisted radiant cooling panel, we found that membrane surface temperatures were difficult to measure directly. Instead, the onset of condensation was used to infer the membrane's surface temperature. However, the radiant cooling panels displayed variations of membrane surface temperature at steady state, and thus a resulting condensation contour was observed, forming a curve on which the membrane surface temperature was accurately known and constant - the dewpoint. The curve was in equilibrium between the internal panel temperature driven by internal free convection in the air gap and the view factor to surrounding surfaces, which can be evaluated at each point along the curve. In this paper, we assess the convective and radiative heat transfer balances using simulations. Our methods expand the "sensing" of condensation to provide information about view factor and thermal stratification, both of which are quantities that are difficult to measure adequately in the field.
Integration of raytracing and CFD simulation to assess the impact of UVGI technology on the control of aerosol transmission in an occupied room
Miaomiao Hou, Jihun Kim, Jovan Pantelic, Dorit Aviv
+ Abstract
A simulation technique is proposed as a tool to assess the efficacy of Ultraviolet Germicidal Irradiation (UVGI) devices as measures for controlling virus spread in occupied rooms’ retrofits. UVGI devices disinfect the air and surfaces in their range through intense UV-C radiation that causes DNA or RNA damage to microorganisms. This disinfection method is proved to be highly effective in reducing aerosol transmissions. For UVGI to be effective, maintaining a high level of UV-C fluence rate in the upper zone of the room is required for a sufficient time to achieve the necessary radiation dose for deactivating the microorganism. At the same time, it is necessary to ensure the safety of the lower zone with a low level of irradiation to avoid any potential damage to human eyes and skin in the room. To determine the proper spatial distribution of the UV irradiation, we created an integrated workflow with raytracing and CFD simulation so that the airflow patterns and virus concentration can be accounted for along with the radiation intensity. This paper presents how design variables can optimize the distribution for effective disinfection and what safety precautions must be taken to avoid overexposure of people to UV radiation when deploying these devices within existing buildings.
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
+ Abstract
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
+ Abstract
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
+ Abstract
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
+ Abstract
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
+ Abstract
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
+ Abstract
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
+ Abstract
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
+ Abstract
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
+ Abstract
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
+ Abstract
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
+ Abstract
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
+ Abstract
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
+ Abstract
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
+ Abstract
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.