Marie-Claude Dubois

Shading devices and daylight quality. An evaluation based on simple performance indicators

The impact of seven shading devices on daylight quality in a south-oriented office was investigated by simulations with Radiance at three specific times on three sunny days. Daylight quality was assessed for a large number of desk positions by considering simple performance indicators: the absolute and relative work plane illuminance and the absolute and relative luminance of surfaces. The results indicated that the white awning, overhang and horizontal venetian blind provided adequate work plane illuminances for traditional office tasks but yielded high window luminances. The 45° venetian blind, white screen and blue awning provided suitable work plane illuminance for computer work and acceptable luminance ratios between the VDT, work plane and surroundings. The grey screen yielded unacceptably low illuminances and luminances, poor uniformity and unacceptable luminance ratios.

Daylight utilisation in perimeter office rooms at high latitudes: Investigation by computer simulation

A simulation study of daylight autonomy in perimeter office rooms at high latitudes is presented where the following variables are studied: Glazing-to-wall ratios (GWR), climate, orientation, inner surface reflectance, glazing visual transmittance, Venetian blind management and electric lighting dimming and switching systems. Based on daylight utilisation alone, the results indicate an optimal GWR ranging between 20% and 40%, with a North orientation requiring a larger GWR (40%), a South orientation a smaller GWR (20%) and an East/West orientation an intermediate GWR (30%). The reflectance of inner surfaces has a significant effect on daylight autonomy and the use of low transmittance glazing demands a larger GWR (60%) to achieve the same daylight autonomy as 20% GWR with high transmittance glazing. Also, the results indicate that the choice of electric lighting dimming and switching systems has a more significant impact on electricity use than the GWR, orientation and the other variables examined.

Low-energy office buildings using existing technology: simulations with low internal heat gains

Although low-energy and nearly zero-energy residential houses have been built in Sweden in the past decade, there are very few examples of low-energy office buildings. This paper investigates the design features affecting energy use in office buildings and suggests the optimal low-energy design from a Swedish perspective. Dynamic simulations have been carried out with IDA ICE 4 on a typical narrow office building with perimeter cell rooms. The results from the parametric study reveal that the most important design features for energy saving are demand-controlled ventilation as well as limited glazing on the façade. Further energy-saving features are efficient lighting and office equipment which strongly reduce user-related electricity and cooling energy. Together, the simulation results suggest that about 48% energy can be saved compared to a new office building built according to the Swedish building code. Thus, it is possible, using a combination of simple and well-known building technologies and configurations, to have very low energy use in new office buildings. If renewable energy sources, such as solar energy and wind power, are added, there is a potential for the annual energy production to exceed the annual energy consumption and a net zero-energy building can be reached. One aspect of the results concerns user-related electricity, which becomes a major energy post in very low-energy offices and which is rarely regulated in building codes today. This results not only in high electricity use, but also in large internal heat gains and unnecessary high cooling loads given the high latitude and cold climate.

Architects' design process in solar-integrated architecture in Sweden

Architects can play a key role in future solar-integrated architecture as they are involved in the building process from the beginning. Solar-integrated architecture takes both passive and active use of solar energy into account. The aim of this research was to gain insight into the actual design processes of solar-integrated buildings. Therefore, semi-structured interviews were conducted with Swedish architects who designed such buildings. Results showed that teamwork was experienced as crucial and building performance simulation tools were hardly used by the architects themselves. Results from these interviews serve as input for the development of new architectural guidelines for designing solar-integrated architecture as part of IEA-SHC Task 41: Solar Energy & Architecture.

Daylight harvesting control systems design recommendations based on a literature review

In indoor spaces, lighting control systems are highly effective to reduce electric lighting use. Daylight harvesting systems (DHS) promise to deliver the greatest energy savings. This article presents a review about DHS based on recent scientific and technical literature. The review shows that the energy saving potential of DHS lies between 20-60% in comparison with non-dimmed installations. However, many studies outline serious limitations of these systems such as e.g. limited user acceptance. The review suggests that, during the design and commissioning of a DHS, the following aspects deserve attention: technical robustness, architectural integration and human acceptance. The review concludes that, while further research in the technical area is still needed, the architectural and human aspects have been so far insufficiently studied. The review emphasizes that competent designers and installers, as well as post-commissioning are mandatory to ensure the success of DHS installations.

Lighting control systems in individual offices at high latitude: measurements of lighting conditions and electricity savings

This paper presents measurement results of electricity use and lighting conditions in individual office rooms located in Lund, Sweden. The aim is to demonstrate the energy saving potential by using different lighting systems and the satisfaction of users. The measurements are carried out in one empty reference room and four fully occupied test rooms equipped with different electric light control systems. The tested systems include: a presence detector (automatic switch on/off), a manual switch at the door combined with absence detector (automatic switch off), a photoelectric dimming combined with presence detector, and a switchable task light with no ambient lighting except daylight. The four rooms are fully occupied by test persons performing their normal computer-based tasks, and who make a subjective evaluation of lighting conditions in the room and control system once a week. The results for the first monitoring period show that the automatic switch on/off (presence) system is the one yielding the highest electricity use, which repeats earlier simulation results. The photoelectric dimming system which combines a presence detector yields very modest energy savings compared to the presence detector system, a result which contradicts earlier findings but which may be explained by malfunctions and poor sensor position. The room with the task lamp achieves the lowest energy use, which is mostly attributed to the low levels of illumination in the room, which is further confirmed by the test persons. The system with manual switch at the door combined with absence detector achieves the best results in terms of combined low energy use and user satisfaction, and the magnitude of the savings are generally greater than anticipated in earlier simulation studies achieved in the same context.