articles by Christoph Reinhart
Building designers rely on predictive rendering techniques to design naturally and artificially l... more Building designers rely on predictive rendering techniques to design naturally and artificially lit environments. However, despite decades of work on the correctness of global illumination rendering techniques, our ability to accurately predict light levels in buildings—and to do so in a short time frame as part of an iterative design process—remains limited. In this paper, we present a novel approach to parallelizing construction of an irradiance cache over multiple-bounce paths. Relevant points for irradiance calculation based on one or multiple cameras are located by tracing rays through multiple-bounce paths. Irradiance values are then saved to a cache in reverse bounce order so that the irradiance calculation at each bounce samples from previously calculated values. We show by comparison to high-dynamic range photography of a moderately complex space that our method can predict luminance distribution as accurately as RADIANCE, the most widely validated tool used today for architectural predictive rendering of daylit spaces, and that it is faster by an order of magnitude.
Papers by Christoph Reinhart
Building and Environment, Jul 1, 2018
Thermal comfort preferences of occupants and their interactions with building systems are top inf... more Thermal comfort preferences of occupants and their interactions with building systems are top influential factors of residential space heating demand. Consequently, housing stock models are sensitive to assumptions made on heating temperatures. This study proposes a heat balance approach, inspired by the classical degree-day method, applied to an extensive urban dataset. The goal of this analysis is to determine heterogeneous characteristics, such as temperature setpoints of heating systems and thermal envelope characteristics from an overall population of residential buildings. Measured energy data are utilized for the purpose of the study from the city of Aarhus, Denmark, where the energy usage for heating of circa 14,000 households was monitored over time via smart meters. These data are combined with actual weather data as well as data extracted by a national building database. Using linear regression and heat balance models, temperature setpoints for the whole dataset are determined with a median and average of 19 o C and 19.1 o C, respectively. Furthermore, building related characteristics such as thermal and ventilation losses per building and overall heat transfer coefficients are extracted at urban scale. The reliability of the method over its complexity is discussed with regards to the big sample that has been applied to. In general, the overall performance of the approach is satisfactory achieving a coefficient of determination with an average of 0.8, and is found to be in line with previous findings, considering 2 also the high uncertainty associated with building-related input parameters. The extracted setpoint distribution should be transferrable across Scandinavia.
This paper evaluates the accuracy of 18 design-phase building energy models, used for documentati... more This paper evaluates the accuracy of 18 design-phase building energy models, used for documentation for LEED Canada certification, and analyzes the effectiveness of simple model calibration steps applied to these models. The calibration steps included inputting actual weather data, adding unregulated loads, revising process loads (often with submetered data), and updating a minimal number of other inputs. In net, the design-phase energy models under-predicted the total measured energy consumption by 36%. Following the above outlined calibration steps, this error was reduced to a net 7% under-prediction. For the monthly Energy Use Intensity (EUI) the coefficient of variation of the root mean square error improved from 45% to 24%. Revising the process loads was particularly important in these cases. This step alone increased the EUI by 32% on average (15% median) in the models. This impact far exceeded that of calibrating the weather data, even in a sensitivity test using extreme weather years. These results suggest that although compliancetype energy models can be poor predictors of actual energy use, practitioners may be able to make initial strides toward calibration with relatively little effort.
Five glare indices are compared under 144 daylit conditions in three spaces in order to understan... more Five glare indices are compared under 144 daylit conditions in three spaces in order to understand the capability of glare analysis to support the design of visually comfortable spaces. It is found that Daylight Glare Probability (DGP) yields the most plausible results in the investigated spaces and lighting conditions as it is based on contrast and total vertical eye illuminance whereas other metrics rely wholly upon contrast. An adaptive visual comfort model, the 'adaptive zone,' is proposed by allowing users to change their view direction to avoid discomfort in front of a flexible workspace. It is found that applying the adaptive zone concept to a sidelit office with manually operated venetian blinds can significantly improve predicted occupant comfort and increase the annual daylight availability within the office by 28%.
Nature Communications
We work with policymakers in eight cities worldwide to identify technology pathways toward their ... more We work with policymakers in eight cities worldwide to identify technology pathways toward their near- and long-term carbon emissions reduction targets for existing buildings. Based on policymakers’ interests, we define city-specific shallow and deep retrofitting packages along with onsite photovoltaic generation potential. Without further grid decarbonization measures, stock-wide implementation of these retrofits in the investigated neighborhoods reduces energy use and carbon emissions by up to 66% and 84%, respectively, helping Braga, Dublin, Florianopolis, Middlebury, and Singapore to meet their 2030 goals. With projected grid decarbonization, Florianopolis and Singapore will reach their 2050 goals. The remaining emissions stem from municipalities not planning to electrify heating and/or domestic hot water use. Different climates and construction practices lead to varying retrofit packages, suggesting that comparable technology pathway analyses should be conducted for municipalit...
Five glare indices are compared under 144 daylit conditions in three spaces in order to understan... more Five glare indices are compared under 144 daylit conditions in three spaces in order to understand the capability of glare analysis to support the design of visually comfortable spaces. It is found that Daylight Glare Probability (DGP) yields the most plausible results in the investigated spaces and lighting conditions as it is based on contrast and total vertical eye illuminance whereas other metrics rely wholly upon contrast. An adaptive visual comfort model, the 鄂adaptive zone, 鈂 is proposed by allowing users to change their view direction to avoid discomfort in front of a flexible workspace. It is found that applying the adaptive zone concept to a sidelit office with manually operated venetian blinds can significantly improve predicted occupant comfort and increase the annual daylight availability within the office by 28%.
Building and Environment, 2021
Building Simulation, 2017
Between 2000 and 2015, annual electric peak demand in Kuwait has doubled to 15000 MW and the Mini... more Between 2000 and 2015, annual electric peak demand in Kuwait has doubled to 15000 MW and the Ministry of Energy and Water expects this number to double once more by 2030 attributing 70% of this growth to new housing projects. Within this context, this manuscript evaluates the effect of incorporating PCM-wallboards in low-rise airconditioned residential heavyweight buildings in Kuwait. Using an EnergyPlus single-zone model, a parametric study is performed considering several window-to-wall ratios (WWRs), different solar orientations and some PCMwallboards configurations. The main study goals are to: (i) explore the validity of a single PCM-wallboard solution that can be universally applied throughout residential buildings in Kuwait; (ii) evaluate the impact of PCMwallboard on the reduction of both cooling demand and peak-loads; (iii) provide some guidelines for incorporating PCM-wallboards in Kuwait. Following an extensive parametric study, a 4 cm thick PCM-wallboard with a meltingpeak temperature of 24 ºC yielded the lowest annual cooling demand across a variety of room orientations and WWRs assuming cooling-set point of 24 ºC. Its implementation lead to annual cooling energy savings of 4-5% across all the case-studies. Regarding the impact throughout the year, cooling demand and peak-loads can be reduced by 5-7% during summer months. The average daily cooling loads can be reduced by 5-8%.
Leukos, Jul 2, 2014
In recent years climate-based metrics, in particular daylight autonomy, have found their way into... more In recent years climate-based metrics, in particular daylight autonomy, have found their way into North American standards and green building rating systems. The authors showed in an earlier pilot study that subjective space evaluations by architecture students correlated well with daylight-autonomy-based daylit area simulations in a single north-facing studio space in Boston. For this manuscript the authors collaborated with educators at 11 schools of architecture and applied the method consistently to 13 spaces within the participating schools. The schools are located in Brazil (2), Canada (1), Egypt (1) and the United States (7). The authors also introduce the concept of a "partially daylight area" metric based on a minimum illuminance threshold for daylight autonomy of 150lux. The two metrics correctly determined in 18 out of 24 cases which parts of the study space are fully or partially daylit. The authors accordingly propose a two-tier evaluation system to rate the daylight availability in spaces.
Social Science Research Network, 2021
Building Simulation Conference Proceedings
Building Simulation Conference proceedings
Building Simulation Conference proceedings
This manuscript presents an early-design methodology that identifies actionable design goals that... more This manuscript presents an early-design methodology that identifies actionable design goals that maximize the effectiveness of natural ventilation in hybrid buildings. These design goals are presented using a compactness factor, recommended thermal mass area and target air change rates per hour (ACH) to maintain thermal comfort preferences of occupants. This approach will enable the consultant to explore viable design options that satisfy the identified design goals, such as optimum opening size based on the target ACH when wind and buoyancy ventilation forces are available, or incorporating fanassisted ventilation when natural ventilation is not sufficient. The method implements a single-node transient, analytical model using non-geometric mathematical representations of building parameters defined in a python routine.
Sustainable Cities and Society, 2021
Energy and Buildings, 2017
Significant research effort has gone into developing bottom-up, physics based, urban building ene... more Significant research effort has gone into developing bottom-up, physics based, urban building energy modeling (UBEM) tools, which allow evaluating district-wide energy demand and supply strategies. In order to reduce the simulation inputs required in UBEM, groups of buildings are typically classified into representative "archetypes". This approach necessarily simplifies the real diversity of occupant behaviors and construction variations, reducing in turn the variety of predicted building energy demands. To further understand the limitations of archetype-based modeling, this paper evaluates four characterization methods of increasing complexity, by comparing simulation results to measured Energy Use Intensity (EUI) distributions of 336 residential buildings in a district in Kuwait City. The first two methods follow a typical deterministic approach, organizing buildings into one and four archetypes respectively, while the third method introduces probabilistic uncertainty modeling for occupant related parameters. The fourth method introduces a new "Bayesian" calibration technique for archetype parameters, and applies it to occupant parameters in method three. In a first step, frequency calibrated distributions for occupancy, lighting power density, plug load density and cooling set points are generated through parametric modeling from a test set consisting of about half of the 336 buildings. The resulting joint distribution of parameters is then sampled using Latin Hyper Cube (LHC) for the probabilistic simulation of the remaining urban model. The comparison of simulated EUI distributions with measured data suggests that the proposed probabilistic Bayesian calibration leads to significantly closer predictions, with a maximum error in the 10th and 90th percentiles of 15% against 55%, 60% and 29% for the other three methods.
Physical Review Letters, 1997
We present experimental verification of type II band alignment in a coherently strained Si 0.7 Ge... more We present experimental verification of type II band alignment in a coherently strained Si 0.7 Ge 0.3 ͞Si͑001͒ quantum well by studying photoluminescence energy shifts under external strains. A recent determination of type I band alignment from a similar experiment is shown to result from band-bending effects due to high excitation. In high quality samples, the type II luminescence can be observed in the absence of external stress by using extremely low excitation. The type II luminescence differs from the well known type I spectrum in a dramatic but as yet unexplained change in the relative intensities of the phonon replicas. [S0031-9007(97)03558-8]
Building Simulation Conference Proceedings
Daylight in buildings is both aesthetically pleasing and a sustainable means of offsetting costs ... more Daylight in buildings is both aesthetically pleasing and a sustainable means of offsetting costs for space conditioning and electric lighting. However, poor use of daylight can cause glare that impedes worker productivity. Traditional means of predicting lighting levels for indoor spaces through simulation are timeconsuming, which inhibits exploration of daylighting potential in new buildings. This paper compares results from two lighting simulation engines, Radiance and Accelerad, with measurements taken in physical spaces. Radiance is an established backward ray tracer that runs on the CPU, whereas Accelerad is a recent porting of Radiance's algorithms for the GPU. Vertical eye illuminance, daylight glare probability, and monitor contrast ratio serve as metrics for comparison. Radiance and Accelerad produce similar errors in visual comfort metrics of around 10%, and Accelerad generates solutions between 3 and 24 times faster than Radiance in the tested scenes. These speedups are expected to scale up on new generations of graphics hardware.
Building Simulation Conference Proceedings
The authors test 168 luminance-calibrated high dynamic range photographs with associated subjecti... more The authors test 168 luminance-calibrated high dynamic range photographs with associated subjective user data against a set of plausible visual comfort metrics and identify metric thresholds at which discomfort can be consistently identified with minimal false-positives. Correlations were identified with vertical eye illuminance, DGI, DGP 5 * L task , max. window luminance and max. workplane luminance. These five metrics in combination, tested against a separate evaluation dataset consisting of 584 measurements, identify 65.2% of discomfort during periods where direct sunlight may enter the test room. The discussion identifies necessary aspects of future work in varied space types and consideration of the view of occupants.
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articles by Christoph Reinhart
Papers by Christoph Reinhart