Lighting preferences in individual offices

Abstract Workplaces with good daylighting offer visual comfort to users, give them a series of physiological and psychological benefits and allow good performance of visual activities, besides saving energy. However, this solution is not always adopted: lighting type preferences involve many variables besides the availability of daylight. This paper explores a case study through the analysis of questionnaire answers and computer simulations of a series of metrics related to quality of lighting with the aim of finding explanations for the lighting preferences of individual office users. The results show that, although the offices present good daylighting conditions and no glare potential, and users are satisfied with daylighting, these parameters are not sufficient to explain the predominant lighting preferences. The findings have also shown that there is no consensus about which parameters potentially cause visual comfort, while the parameters that cause discomfort are clearly identified. In addition, in this study, 49% of the preference for mixed lighting (daylight plus electrical light) can be explained by the fact that mixed lighting produces better modeling than daylighting alone

Proposta de um procedimento alternativo para avaliar o ofuscamento: uma abordagem temporal da direção da visão

Resumo O ofuscamento pode ser considerado como um dos aspectos mais complexos do processo de avaliação da iluminação natural devido a sua natureza subjetiva e às limitações nas formas de avaliação. Embora o brilho seja uma resposta subjetiva, muitos índices foram desenvolvidos para quantificar este fenômeno. Os modelos de avaliação de brilho existentes assumem usuários com direções da visão fixas, ignorando o caráter temporal/dinâmico da visão. Neste estudo, um professor foi adotado como sujeito dinâmico para a caracterização das diversas direções da visão. Sendo um trabalho experimental, os procedimentos adotados envolveram o uso de vídeo, um programa para edição de vídeo, imagens HDR e o uso do programa Photolux para o processamento das imagens. Com o valor do DGI obtido para cada direção da visão, a partir de cada posição, em todos os cenários e o tempo que o professor manteve a sua visão para cada direção, foram realizadas duas ponderações pelo tempo de permanência: DGItd (em cada direção) e DGItp (em cada posição), permitindo calcular o índice total para a sala de aula. Os resultados indicaram reduções de até 30% no DGI total da sala, com relação ao DGI estático. Este estudo reforça a relevância de se incorporar a condição temporal na avaliação do ofuscamento

On the influence of building design, occupants and heat waves on comfort and greenhouse gas emissions in naturally ventilated offices. A study based on the EN 15251 adaptive thermal comfort model in Athens, Greece

According to the Intergovernmental Panel on Climate Change the buildings sector has the largest mitigation potential for CO2 emissions. Especially in office buildings, where internal heat loads and a relatively high occupant density occur at the same time with solar heat gains, overheating has become a common problem. In Europe the adaptive thermal comfort model according to EN 15251 provides a method to evaluate thermal comfort in naturally ventilated buildings. However, especially in the context of the climate change and the occurrence of heat waves within the last decade, the question arises, how thermal comfort can be maintained without additional cooling, especially in warm climates. In this paper a parametric study for a typical cellular naturally ventilated office room has been conducted, using the building simulation software EnergyPlus. It is based on the Mediterranean climate of Athens, Greece. Adaptive thermal comfort is evaluated according to EN 15251. Variations refer to different building design priorities, and they consider the variability of occupant behaviour and internal heat loads by using an ideal and worst case scenario. The influence of heat waves is considered by comparing measured temperatures for an average and an exceptionally hot year within the last decade. Since the use of building controls for shading affects thermal as well as visual comfort, daylighting and view are evaluated as well. Conclusions are drawn regarding the influence and interaction of building design, occupants and heat waves on comfort and greenhouse gas emissions in naturally ventilated offices, and related optimisation potential.<br /