Location Based Study of the Annual Thermal Loads with Microstructured Windows in European Climates

Glazed envelopes can cause significant thermal energy gains or losses. The installation of a novel design of Complex Fenestration Systems (CFS), such as embedded mirrors, could significantly contribute to reduce the energy consumption. In order to determine the influence of this glazing technology on thermal loads, a parametric study considering twenty-two European locations has been carried out. Simulations were performed for each location, to evaluate the range of latitudes for which the installation of the microstructures is advantageous. Optical microstructures found to be a valid solution to increase energy savings up to 20% when compared to a sun protective glazing.

Towards a Minergie Standard for tropical climates

Fouad Aabid, Claude-Alain Roulet, Jean-Louis Scartezzini, Franco Vigliotti

The Swiss Minergie®-standard is, by the number of labelled buildings (> 20'000) one of the most successful building energy labels in the world. It is obviously a strong incentive for designing comfortable, low energy buildings. This standard is now valid for temperate - cold climates only. There is therefore a need for a similar standard for buildings dominated by cooling loads, as it is common in the tropical and sub-tropical climates of the world. Since the new EPFL campus planned in Ras al Kaimah (United Arab Emirates) should be exemplary, a project was launched by the Dean of EPFL Middle East, together with Minergie®-Association and the Solar Energy and Building Physics Laboratory of EPFL, aiming to set-up such a standard. In order to initiate this project, two buildings (a single family dwelling and an office building) were chosen. The single-family dwelling was simulated at an hourly time step using a detailed dynamic thermal model based on the computer simulation programme Energy plus issued from LBNL. The monthly energy consumption of the dwelling shows a good correlation with the monitored data. In addition to that, both energy consumptions, calculated with the dynamic and the simplified models are close to each other, giving confidence to the predictions of the latter. Therefore, both buildings were assessed using a simplified monthly energy balance method. Starting from the current buildings configurations, several variants implementing various improvements towards energy efficiency were considered. These simulations show that considerable energy saving (up to a factor 5) can be achieved by implementing together several improvements to these buildings. In addition, the building reaches a higher level of users comfort.

EPFL2011

Microstructured glazing for daylighting, glare protection, seasonal thermal control and clear view

André Gabriel Kostro

The appropriate choice of glazing in a facade depends on many factors. They include amongst other criteria: location, orientation, climatic condition, energetic efficiency, usage of the building, required user comfort, and the architectural concept. On the south facade of high-rise buildings in particular, it is a challenge to have simultaneously large glazed area, no glare, no excessive cooling loads, a clear view and sufficient natural light flux. In Switzerland, electric lighting, heating and air conditioning account for about 74% of the total energy demand in private housing and 32% of the overall Swiss electricity usage. This energy consumption can be strongly influenced by using the most appropriate fenestration system. A software was developed during this thesis to engineer new complex fenestration system (CFS) that have a two dimensional profile. The originality of the implemented Monte Carlo ray tracing algorithm is the separation of intersection and interaction. The model also calculates an accurate bidirectional transmission distribution function that is used in combination with Radiance to obtain a rendering of the daylighting distribution in an office space or dynamic daylight metrics such as the daylight factor and daylight autonomy. Finally, to estimate the thermal performances, a simple nodal thermal model was added to simulate the temperature evolution and the thermal loads in a given office. This tool was validated. A glazing combining several functions and that can contribute to significantly reduce energy consumption in buildings was developed using this novel ray tracing approach. It was designed to obtain a strongly angular dependent transmission and a specific angular distribution of transmitted light. The engineered geometry provides elevated daylight illuminance by redirecting the incoming light towards the depth of the room. This redirection simultaneously reduces the glare risk. For an optimised usage of available solar radiation, the transmission of direct sunlight is maximised in winter and minimised in summer. Taking advantage of the changing elevation of the sun between seasons, such a seasonal variation can be created by a strongly angular dependent transmittance. A fabrication process was identified and samples of embedded micromirrors were produced to demonstrate the feasibility. The fabrication of such structures required several steps. The fabrication of a metallic mould with a high aspect ratio and mirror polished surfaces is followed by the production of an intermediate polydimethylsiloxane mould that was subsequently used to replicate the structure with a ultraviolet (UV) curable polymer. Selected facets of these samples were then coated with a thin film of reflective material. Finally, the structures were filled with the same polymer to integrated the mirrors. The blocking effect can be obtained by a combination with well placed reflective stripes, those were fabricated by lift-off lithography. The samples were characterised during the various fabrication steps using various microscopy techniques, energy-dispersive X-ray spectroscopy, profilometry and optical measurements. A setup was built for the measures of angular dependent transmittance. The final samples redirect up to 70% of the light flux and are very transparent when looking through at normal incidence.

EPFL2015

Microstructured glazing for daylighting, glare protection, seasonal thermal control and clear view

André Gabriel Kostro

EPFL2015