Comparison between ray-tracing simulations and bi-directional transmission measurements on prismatic glazing

Evaluation of solar heat gain and daylight distribution through complex window and shading systems requires the determination of the bi-directional transmission distribution function (BTDF). Measurement of BTDF can be time-consuming, and inaccuracies are likely because of physical constraints and experimental adjustments. A general calculation methodology, based on more easily measurable component properties, would be preferable and would allow much more flexibility. In this paper, measurements and calculations are compared for the specific case of prismatic daylight-redirecting panels. Measurements were performed in a photogoniometer equipped with a digital-imaging detection system. A virtual copy of the photogoniometer was then constructed with commercial ray-tracing software. For the first time, an attempt is made to validate detailed bi-directional properties for a complex system by comparing an extensive set of experimental BTDF data with ray-tracing calculations. The results generally agree under a range of input and output angles to a degree adequate for evaluation of glazing systems. An analysis is presented to show that the simultaneously measured diffuse and direct components of light transmitted by the panel are properly represented. Calculations were also performed using a more realistic model of the source and ideal model of the detector. Deviations from the photogoniometer model were small and the results were similar in form. Despite the lack of an absolute measurement standard, the good agreement in results promotes confidence in both the photogoniometer and in the calculation method

Bi-directional light transmission properties assessment for venetian blinds : Computer simulations compared to photogoniometer measurements

An accurate evaluation of daylight distribution through advanced fenestration systems (complex glazing, solar shading systems) requires the knowledge of their Bi-directional light Transmission Distribution Function (BTDF). An innovative equipment for the experimental assessment of these bi-directional functions has been developed, based on a digital imaging detection system. An extensive set of BTDF measurements was performed with this photogoniometer on venetian blinds presenting curved slats with a mirror coating on the upper side. In this paper, the measured data are compared with ray-tracing results achieved with a virtual copy of the device, that was constructed with a commercial ray-tracing software. The model of the blind was created by implementing the measured reflection properties of the slats coatings in the ray-tracing calculations. These comparisons represent an original and objective validation methodology for detailed bi-directional properties for a complex system; the good agreement between the two methods, yet presenting very different parameters and assessment methodologies, places reliance both on the digital-imaging detection system and calibration, and on the potentiality of a flexible calculation method combining ray-tracing simulations with simple components measurements

Bi-directional Photogoniometer for the Assessment of the Luminous Properties of Fenestration Systems

Most energy saving applications of advanced fenestration systems (solar blinds, novel types of glazing and daylight redirecting devices) require a precise knowledge of their directional light transmission features. These photometric properties can be described by a Bi-directional Transmission Distribution Function (BTDF) whose experimental assessment requires appropriate equipment. A novel bi-directional transmission photogoniometer, based on digital imaging techniques, was designed and set up for that purpose. The apparatus takes advantage of a modern video image capturing device (CCD digital camera) as well as of powerful image analysis software (pattern recognition) to considerably reduce the scanning time of a BTDF measurement, in comparison to existing devices that use a conventional approach (mobile photometer). A detailed calibration and validation procedure was used to obtain optimal experimental accuracy for the device during the assessment of BTDF data. It included a spectral, a photometric and a geometrical calibration of the digital video system, as well as several additional corrections, leading to an overall relative accuracy better than 11% for BTDF data. A special effort was made to improve the user-friendliness of BTDF measurement by facilitating the data acquisition and treatment (definition of a data acquisition and electronic data format) and by offering different possibilities of BTDF visualisation (hemispherical representation, axonometric view of photometric solids, C-planes). Overall, the photometric equipment was used to assess the BTDFs of more than 20 novel fenestration products of the industrial partner of the project (Baumann-Hüppe Storen AG). The experimental data produced was successfully used by the company to optimise the visual and energy saving performance of their products, which confirms the adequacy of the novel bi-directional photogoniometer for practical building applications

Shallow geothermal energy potential for heating and cooling of buildings with regeneration under climate change scenarios

Shallow ground-source heat pumps (GSHPs) are a promising technology for contributing to the decarbonisation of the energy sector. In heating-dominated climates, the combined use of GSHPs for both heating and cooling increases their technical potential, defined as the maximum energy that can be exchanged with the ground, as the re-injection of excess heat from space cooling leads to a seasonal regeneration of the ground. This paper proposes a new approach to quantify the technical potential of GSHPs, accounting for effects of seasonal regeneration, and to estimate the useful energy to supply building energy demands at regional scale. The useful energy is obtained for direct heat exchange and for district heating and cooling (DHC) under several scenarios for climate change and market penetration levels of cooling systems. The case study in western Switzerland suggests that seasonal regeneration allows for annual maximum heat extraction densities above 300 kWh/m2 at heat injection densities above 330 kWh/m2. Results also show that GSHPs may cover up to 55% of heating demand while covering 57% of service-sector cooling demand for individual GSHPs in 2050, which increases to around 85% with DHC. The regional-scale results may serve to inform decision making on strategic areas for installing GSHPs

Compression of multi-year meteorological data

Dynamic simulation programes require hourly values of solar radiation and ambient temperature forming large files, which are usually difficult to handle with available personal computers (PC). This report describes stochastic models of these variables which have been constructed to overcome this difficulty. They are based on Markov chains and autoregressive processes, determined using multi-year hourly data of both variables. A validation of the model has been carried out for five different Swiss locations. It has shown that the main statistical characteristics of these variables are reproduced by the models. A very good agreement was also obtained between results of dynamic simulations carried out using measured and synthetic data. The generalization of the method to 30 Swiss locations has been made to facilitate the transfer of these developments into practice

Outdoor comfort simulation of complex architectural designs: a review of simulation tools from the designer perspective.

The expanding design interest in outdoor comfort design is today supported by a few software tools. Given their different user-friendliness, modelling environments and simulation engines, a rational inquiry is how they are integrated into the digital design flow of architects and urban planners, which may include complex forms developments. Preliminary work is conducted to select architect-friendly tools that support the analysis of urban microclimate. A minimum set of criteria (amongst them the use of 3D models, the capability of calculating Mean Radiant Temperature and visual graphical outputs) led to the pre-selection of CitySim Pro, ENVI-met, Autodesk Thermal CFD, Grasshopper plug-ins Honeybee / Ladybug. The complex modelling experiment is conducted by simulating the outdoor thermal comfort of the space underneath the Rolex Learning Centre in Lausannewith each of the tools above. The paper describes and compares the principles, the procedures and the resources needed to prepare sound models that reduce the time of computation without compromising the quality of results. The potential applicability of tools in design is finally discussed from a user’s point of view. The tools’ capability of creating a 3D complex geometric model, or of importing one from a typical architectural tool, such as Rhino, is studied. Furthermore, it is debated how models can be used in the broader digital environment

Bi-directional transmission properties of Venetian blinds: experimental assessment compared to ray-tracing calculations

An accurate evaluation of daylight distribution through advanced fenestration systems (complex glazing, solar shading systems) requires the knowledge of their Bidirectional light Transmission (Reflection) Distribution Function BT(R)DF. An innovative equipment for the experimental assessment of these bi-directional functions has been developed, based on a digital imaging detection system. An extensive set of BTDF measurements was performed with this goniophotometer on Venetian blinds presenting curved slats with a mirror coating on the upper side

Thermochromic films of VO 2 :W for smart solar energy applications

Overheating is a problem with the use of active/passive solar energy in thermal solar energy systems. A solution to these problems might be provided by a thermochromic material such as vanadium dioxide. In order to simulate the optical behaviour of multilayered coatings, knowledge on its optical properties is necessary. We determined point-by-point the dielectric function for VO2:W by ellipsometry. For validation, the solar spectra were measured by spectrophotometry. Such data have been compared with the computer simulations based on the determined optical properties. Finally, we collect optical data by infrared-imaging to detect the switch in emissivity of VO2:W at around 45°C

Vernacular housing practices in Burkina Faso: Representative models of construction in Ouagadougou and walls hygrothermal efficiency

peer reviewedIn Burkina Faso, particularly in Ouagadougou, the walls of the houses are made of several local materials. The choice of a material implies a suitable constructive technique and an appropriate architecture. The walls are either earth-based, i.e. Compressed Earth Blocks (CEBs) or Adobe, or based on cement-based materials such as hollow concrete blocks. This paper proposes a description of the vernacular construction practices according to the material used for the walls and tries to explore the hygrothermal behaviour of various wall compositions. A hygrothermal simulation of a hollow concrete blocks wall and a CEBs wall using the WUFI®Pro software is carried out in order to compare the humidity flux passing through interior surface of each wall and to analyze the influence of integrated moisture in the calculation of heat flow. It is shown that, for CEBs wall, both thermal and hygrothermal simulation of heat flow give similar results. © 2017 The Authors. Published by Elsevier Ltd