User operations and preferences in a test room equipped with advanced natural and artificial light sources

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1 User operations and preferences in a test room equipped with advanced natural and artificial light sources Michele Zinzi, Gaetano Fasano ENEA-UDA Italian Agency for Energy, Environment and New Technologies, Rome, Italy. ABSTRACT: The lighting of indoor spaces is crucial for the energy balance of buildings and for the occupants comfort. The issue became more important because of the effect of the large glazed surfaces in the modern building envelope. The possibility of modulating the light sources, both natural and artificial, according to the users and energy management requirements is an important added value for the building. The paper present the results of an experimental campaign, which took place at the experimental building Casa Intelligente (Smart House) of ENEA. Thirty subjects spent part of a day in test room equipped with electrochromic (EC) glazings, internal blind and four dimmable luminaries, and manually operated such systems to achieve the visual comfort conditions. It was asked the users to do their usual office work, as video terminal activities, writing and reading. A dedicated questionnaire was compiled and submitted to the users in order to collect their impressions about the potentialities and the constraints of the tested systems. The analysis of this first campaign results permits to get information about users preferences concerning illuminance levels, daylighting requirements and user operations of advanced systems as EC windows and the dimmable system. Conference Topic: 3 Comfort and well-being in urban spaces Keywords: daylighting, visual comfort, smart glazing 1. INTRODUCTION The dynamic building envelope is one of the most attractive issue of the modern architecture. The use of large glazed area make makes the building envelope permeable to the solar radiation, which means useful solar gains in winter but very strong cooling loads in summer. The possibility of modulating the solar energy transmitted through the envelope is an added value to optimise the energy performance of buildings. Electrochromic (EC) glazing materials change their colour, with associated change of optical and solar properties, through a small voltage applied to the external layer of the system [1]. This technology permits regulating the energy flux entering into that building and the control of the colouration state can be applied as a function of thermal or visual comfort for users, or to minimise the building energy use, taking into account that the variation of the solar gains causes a variation of both, heating and cooling loads. The experimental building Casa Intelligente is one of the first full size case studies of building integration of electrochromic windows. It was funded by the Ministry of Industry to provide knowledge in the field of demotic and home automation. Smart glazing, which can run manually or by remote control strategies, were a suitable technology to install. Another applied technology is the dimmable artificial lighting system that can be manually run or by automated control. The experiment main objective was to study the reaction of people working in an environment where they can set the luminous conditions to reach the visual comfort. The dynamic shading of the glazing, the extra shading of a semitransparent blind and the modulating artificial lighting, give the users a wide variety of facilities to set the ideal conditions. Of course not in all case it is possible to reach the optimal comfort condition, but it is interesting the evaluation of the improvement that advanced technologies and materials can offer for the comfort conditions of the built environment occupants. An experiment based on manual control and related to user preferences on switchable windows, shading and artificial lighting preferences was performed and the main results are here presented. A dedicate questionnaire was also prepared to analyse the user response upon such visual comfort issues, together with a set of illuminance measurements. 2. EXPERIMENTAL FACILITIES The test was run at the experimental building Casa Intelligente (Smart House) at ENEA, which was funded by the Italian Ministry of Industry, in order to carry on experimental researches to improve the energy performance, the safety, security and comfort for users, in residential dwellings. The main area to investigate is, in particular, the added value that smart domotic technologies can offer respect to the traditional solutions for heating, cooling, ventilation,

2 lighting systems, as well as for the loads management. Even if the building is a residential house, the test room was equipped as an office room, whit furniture and appliances typical of that kind of building. Grey carpet on the floor, white walls and ceiling, luminaries equipped with neon lamps for the artificial lighting. The working desk was equipped with a personal computer grid connected, in order to make the users doing their usual work. The experiment was carried out in a test room, which has a pentagonal area of about 13.3 m2 and its layout is shown in figure 1. The room has white walls and suspended ceiling and grey carpet. The room has two electrochromic windows, one facing west and one facing north. The daylighting of the test room is ensured by the two openable windows north and west oriented. Such windows, as the rest of the experimental house, are equipped with commercial electrochromic devices, supplied by the company Flabeg, their luminous transmittance can switch from 50% in the bleached state to 15% in the fully coloured state [2]. Both windows are 120 by 160 centimetres and they consist of two glazing devices 45 centimetres large and 130 centimetres high. The glazing colouration depth can be regulated by a dedicated controller, which can be automatically operated or, as in the present experiment, manually operated by the users. The controller, mounted on the desk, has an user friendly interface with two buttons and five led, which help the user to choose the level of colouring starting from the clear state, one led lighted, to the fully coloured state, all the five led lighted on. The switching time depends on the depth of the colouration and on the thermal conditions of the glazing. Generally about 15 minutes are needed for a full colouration from the clear state. Shorter time is needed for intermediate position switching. The cross section of the test room is presented in figure 2. To be noted that, being the window mounted about 25 centimetres inside respect to the façade, the further shading effect of the window-wall assembly, also occurs. Figure 2 Schematic cross section of the test room Together with the EC devices and the self-shading of the window/wall assembly, a third shading solution is given to the occupants during the test. The west window is equipped with a movable internal semitransparent blind, luminous transmittance 50%, manually operated by the occupants if and when needed. For artificial lighting system the room is equipped with four luminaries, each of them consisting of 4 cold temperature lamps of 18 Watts. The lighting system is of the dimmable type, it can be remotely managed and controlled, or manually switched by the user. At the maximum power an illuminance of 1000 lux is measured on the working plane. More measurements were carried out to measure the illuminance levels when the lighting system is operating at intermediate power (10, %). For this experiment the personnel was recruited at the ENEA-Casaccia research centre. At eh end 30 users was selected, they equally divided between men and women. The users include all different kinf of ENEA workers, as managers, researchers, technicians, graduation students. The age of the participants was between 23 and 58 years for men, and 26 and 63 for women, the average is 43.2 and 40.2 respectively. Going into more details, 10 subjects were younger than 35 years (3 M and 7 W), 12 subjects were aged between 35 and 50 years (8 M and 4 W) and 8 person were older than 50 (4 M and W). 3. EXPERIMENTAL PROCEDURE Figure 1 Schematic layout of the test room According to the literature, the luminous transmittance of the glazing in the fully coloured state (15%) was not enough to prevent from glare in case of direct sun. On the basis of this assumption and considering the room orientation, it was decided to perform the test when the luminance of the sky was high to require shading but, at the same time, avoiding the direct sun on the working plane, unsustainable for users. The test went on between the beginning of August and the beginning of October 2001, which was the most suitable according to the sun path in the sky and to the working schedule of ENEA employees. The starting time of the test was fixed in the afternoon. In fact, at the beginning the daylgihting is ensured by the light diffused by the sky, but later the luminance of

3 that portion of the sky seen by the west window dramatically increase. In those hours the need of shading to prevent glare was monitored, by visual inspection and illuminance measurements. This event was caused by the high luminance of the sky for the windows facing west, even without direct sun on the working plane. The preparation of the test room, with the cabling of the electrochromic controllers and the positioning of the personal computer, are shown in figure 3. electrochromic glazings, and switch on/off and regulate the dimmable artificial lighting. Before starting the experiment the questionnaire is explained. The questionnaire is intended to collect information about user response and preferences related to the luminous environment of the space they are working in. Issues are about general visual comfort conditions, systems operation, perception and alteration of indoor and outdoor environments [3, 4]. The questionnaire was compiled taking into account important experiences found in literature [5, 6, 7]. The set of questions was preventively checked by third persons, in order to check if some parts were not clear or easy to understand. The questions is of the multiple choice type, with the following options respect to the assertion: 1. complete agreement, 2. partial agreement, 3. neutral position, 4. partial disagreement, 5. complete disagreement. At the beginning of the test, the user is seating at the desk and luminous environment is determined by the initial conditions. It is asked the occupant to get familiar with the room, to get conscious of the indoor environment and to start working. When or if the luminous conditions are not satisfactory, the occupant starts changing the lighting systems, both natural and artificial, trying to achieve the maximum comfort. This include colouring the glazing systems, pulling on and off the blind, switching on and off, and dimming the artificial lighting. The questionnaire must be compiled by the subjects in different phases during and at the end of the test. 4. RESULTS Figure 2 Preparation of the test room It was impossible to start and finish all the tests at the same time, but it was possible to have one hour (between and 16.05) when all the users were in the test room. It was also noted that the darkening the two windows would have created a too dim luminous environment, because of the limited dimension of the transparent surfaces. On the basis of this consideration, it was decided to keep the north windows (providing only diffusing daylighting) always in the bleached state, and allow the users to manage the west windows (source of possible glare phenomena). A luxmeter was installed working plane to measure the horizontal illuminance, the data were scanned every 60 seconds and stored every 5 minutes. The intelligent system of the house recorded the power of the artificial lighting system in real time. The glazing and blind states were monitored by visual inspection. The initial conditions in the test room are: glazing systems in the clear state, internal blind off, electric lighting off. The user goes trough a short explanation of the experiment, he will be involved in, standing in a twin room with one window in the bleached state and another is fully coloured. There he can see the difference of coloration level learn to switch the The 30 tests were carried out during sunny days but 4, even if only in one case there was the overcast sky for all the test long. This means that almost always there was strong irradiation on the room façade with consequent needs of shading. Concerning the frequency distribution of the averaged illuminance levels, the 93% of the users chose a luminous environment with giving more than 300 lux on the working plane, in the 56.7% of the cases this values was higher than 500 lux, reference value for design of the lighting system. In particular, it is found out that 2 people (6.7%) had less than 300 lux, same percentage for those who had between 300 and 400. The majority preferred higher illuminance levels: 9 users (30%) between 400 and 500, 6 users (20%) between 500 and 600 and 7 users (23.3%) between 600 and 800. Few people preferred very high levels: 2 subjects chose between 800 and 1 Klux, and 2 users wanted more than 1 Klux on the working plane. Concerning the daylighting availability, in this case too the 93% of the users chose a luminous environment with more than 300 lux on the working plane, but the number of users requiring more than 500 lux decreased to 33%. 2 users preferred less than 300, 6 users between 300 and 400 and 16 subjects (53.3%) between 400 and 500 lux. Only one

4 user required an amount of natural light on the working plane between 500 and 600 and 5 occupants (16.7%) had between 600 and 800 lux. All the occupants used the smart window to improve the luminous environment. The majority of the users, he 70% of the total, set the window in the fully coloured position, 7 subjects chose intermediate colouration levels. The blind was used by 15 users (50%), significant amount considerin that there was no direct sun on the working plane. It is finally important summarising the results about the artificial lighting. During the test, 13 users (43.6%) switched the artificial lighting on, the dimmable system allow them to modulate the intensity and to choose the best luminous output. Among them, 6 users chose an emitted luminous flux lower than the 20% of the total. Concerning the others, 5 users chose a value comprises between the 20 and 40%, and 2 users between 70 and 80%. To be noted that in the latter cases the users decide to use the artificial light as the main lighting system. In table I are presented the questionnaire results related to user preferences for their visual comfort. The results are expressed as percentage and to each subject corresponds the 3.3% of the total. It is interesting the comparison the occupants response regarding the glare phenomena from outside before and after the colouring of the window, where the usefulness of switching glazings in preventing glare under some conditions is stressed, questions 1 and 2. The percentage of those who answered (no or little glare) increased from 43.4% to 56.7%, with a consequent reduction of unsatisfied subjects. The percentage of those who answered 1 (glare) decreased from 40% to 16.7%, and the sum decreased from 56.7% to 23.4%. The questions 3 to 6 aimed at investigating eventual disturbing events, due to the change of the natural and artificial light sources. If it is kept in mind that only 13 people used the artificial lighting system, the number of 5 users at least partially disturbed by the mix of artificial lighting and coloured windows is not negligible. On the other side the alteration of the internal and external environment, caused by the darkening of the windows, is not cause of disturb for the large majority of the users. Heavily disturbing is the blind that 15 subjects had to use. Referring to the question 6, the 40% of the users were at least partially bothered by the obstruction to the external vision through the window, and 7 of them expressed a strong disappointment with this situation. Table I Results of the questionnaire. Questions NA 1. There are there glare phenomena from windows (EC clear) There are there glare phenomena from windows (EC dark) The luminous environment coming from the mix of natural and artificial lights bother you 4. The alteration of internal luminous environment caused by the colouring of windows bother you 5. The alteration of external luminous environment caused by the colouring of windows bother you 6. The visual obstruction of the external environment due to the blinds bother you The manual operation of electrochromic window bother you The manual operation of the semitransparent blinds bother you The manual operation of the artificial lighting system bother you You would prefer an automatic control of EC-windows You would prefer an automatic control of semitransparent blinds You would prefer an automatic control of artificial lighting The switching time of the electrochromic glazing is enough rapid The results of question from 7 to 9 show that the occupants were not disturbed by having a manual operation of artificial lighting and EC windows. Concerning the blind operation only, if it is taken in mind that only half of the people used the blind and those answering 1 and 2 are among them, it comes out that the almost the half of them was bothered by pulling on and off the shading device. To go more in detail about this issue it was asked if an eventual automated control would have been preferred. The results are in table 1, question from10 to 12.In this case, the results are grouped on the two extreme options, with few users selecting the intermediate options (2, 3, 4). The majority, according to the previous answers, still prefer a manual operation. But it is worthwhile mentioning that, the percentage of those who prefer the automated control

5 is not negligible, between 30 and 43%, the latter for the artificial lighting. Last question refers to a real problem of switching glazing: the colour change rapidity. Since the sky luminance change can be very rapid, and it is expected to have similar reaction by the EC glazing, which instead require several minutes. The 50% of users is complaining with the slowness of the system, significant number since in several cases the windows was not fully coloured. Slower luminance changes due to normal movement of sun in the sky can, can be sufficiently adjusted by the EC windows, especially if a deep colouration is not required. 5. CONCLUSIONS The experiment main objective was to study the reaction of people working in an environment where they can set the luminous conditions to reach the visual comfort. During the test it was found the importance of supplying a dynamic natural and artificial light systemì that the users is able to modfy according to his personal requirements. Both, the EC windows (with additional blind) and dimmable lighting system, are strongly supported by almost the whole subjects, who were involved in the campaign. Electrochromic glazing windows can be very useful to prevent user from glare and guarantee their visual comfort, even if some limitations still remain, as: depth of colouration (crucial in case of direct sun), switching rapidity, integration with the management system of the building. Further shading of the blind is still useful, but causes complains because of the outdoor vision obstruction. Very useful is also the possibility, given to the users, to modulate the intensity of the artificial lighting, appreciated by most of the subjects. This wide range of options gives more chance to achieve the luminous comfort conditions for users, and, at the same time, the manual operation of such systems is preferred to an automated control for the majority of the users. This aspect is in conflict with the energy saving issue, which aims at an automated control based on optimised algorithms to reduce the primary energy consumption of the buildings. This aspect needs further investigations to be completely clarified, especially for what concerns the user acceptance and response in a built environment where the lighting sources are controlled by a completely automated system. of the Illuminating Engineering Society, 27(1), , 1998 [4] J. Veicht, G. Newsham Psychological process influencing lighting quality Journal of the Illuminating Engineering Society, 30(1), , 2001 [5] Vine et al. Officer worker response to an automated venetian blind and electric lightingsystem: a pilot study Energy and Buildings 28, (1998). [6] Bulow-Hube Officer worker preferences of exterior shading devices: a pilot study Proceedings of Eurosun 2000, Copenaghen, Denamrk (2000). [7] Hygge S. and Lofberg H. A. Post Occupancy Evaluation of Daylight in Buildings IEA SHC Task 21 / ECBCS Annex 29 Report (1999) REFERENCES [1] S. K. Deb, Applied Optics Suppl. 3, [2] H. Wittkopf, J. Cardinal, V. Gumprich, Pilkington E-control, the new electrochromic glazing for optimization of lighting, heating and air conditioning Proceedings of Glass Processing Days, Tampere, Finland, June [3] J. Veicht, G. Newsham Determinants of lighting quality: state of the science Journal