Jean-Louis Scartezzini

A stochastic model of user behaviour regarding ventilation

Abstract Airflow rates are directly affected by the amount of open area connecting rooms to the outside and consequently by the inhabitant behaviour with respect to window opening. In this paper, a stochastic model using Markov chains is proposed to generate time series of window angle. It is based on data from four office rooms and a whole heating season (from October to May). The model is then validated by a comparison of the real and generated data. The use of this model within building air infiltration design programmers should significantly improve their realism.

ANIDOLIC DAYLIGHTING SYSTEMS

Non-imaging optics, well known for its application to solar concentrators, was used to set up novel daylighting systems that aim at an efficient collection and redistribution of the diffuse component of daylight. These devices, called anidolic systems (an: without, eidolon: image), were designed, installed and monitored on experimental test modules under clear and overcast sky conditions. Three different anidolic systems with different specific objectives were considered (anidolic ceiling, integrated anidolic system, anidolic solar blinds). Installed on 6.55-m deep rooms, the first two showed a significant improvement of daylight factors monitored in overcast conditions in comparison to a reference facade (conventional double glazing): a substantial improvement of the daylighting autonomy can be expected as a consequence. Higher work plan illuminances were observed for the third system under clear sky conditions, demonstrating sunlighting control capabilities that improve visual comfort and overall performance. The present article gives a description of these anidolic systems, as well as an overview of their luminous performance, assessed experimentally within the framework of IEA Task 21.

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.

Experimental assessment of bi-directional transmission distribution functions using digital imaging techniques

Many daylighting applications require a precise knowledge of the directional transmission features of advanced fenestration materials. These photometric properties are described by a bi-directional transmission distribution function (BTDF), whose experimental assessment requires an appropriate equipment. A novel bi-directional photogoniometer, based on digital imaging techniques, has been designed and developed for that purpose. The main advantages of this device are the significant reduction of the time required for data measurement and its capability to assess an almost continuous BTDF function. These features can be achieved only through detailed and accurate calibration procedures of the bi-directional photogoniometer, which are described in this paper, together with digital image and data processing. Several experimental results, obtained for different fenestration materials, are used to illustrate the capabilities of this novel equipment.

A simplified correlation method accounting for heating and cooling loads in energy-efficient buildings

Abstract Simplified correlation methods are powerful tools to compare both the energy performance of buildings and the efficiency of different HVAC control systems. For buildings in which both heating and cooling loads contribute to the energy consumption, widely used methods, like the energy signature models, are not appropriate, since they cannot simultaneously handle both heating and cooling aspects. This paper proposes a new correlation method to overcome this difficulty. The ‘Eta method’ deals with internal gains, as well as solar gains, and can be used to calculate a utilization factor for free gains in the heating and cooling periods. Two examples to illustrate the method are given. The first one is a passive solar office room, on which different blind controllers were tested by simulation. The second example is a non-residential building in which two HVAC controllers were carefully monitored

Effects of prior light exposure on early evening performance, subjective sleepiness, and hormonal secretion

In sighted humans, light intensity, timing, exposure duration, and spectral composition of light are important to entrain the endogenous circadian pacemaker to the 24-h day-night cycle. We tested the impact of two realistic office lighting conditions during the afternoon on subjective sleepiness, hormonal secretion, and cognitive performance in the early evening hours. Twenty-nine young subjects came twice and spent 8 h (12:00-20:00) in our laboratory, where they were exposed for 6 h to either artificial light (AL) or to mainly daylight (DL). In the early evening, we assessed their salivary cortisol and melatonin secretion, subjective sleepiness, and cognitive performance (n-back test) under dim light conditions. Subjects felt significantly more alert at the beginning of the evening after the DL condition, and they became sleepier at the end of the evening after the AL condition. For cognitive performance we found a significant interaction between light conditions, mental load (2- or 3-back task) and the order of light administration. On their first evening, subjects performed with similar accuracy after both light conditions, but on their second evening, subjects performed significantly more accurately after the DL in both n-back versions and committed fewer false alarms in the 2-back task compared to the AL group. Lower sleepiness in the evening was significantly correlated with better cognitive performance (p < .05). In summary, even short-term lighting conditions during the afternoon had an impact on cognitive task performance in the evening. This rapid effect was only distinguishable on the second day of training, when a difficult task had been sufficiently practiced.

Effects of realistic office daylighting and electric lighting conditions on visual comfort, alertness and mood

Lighting conditions in workplaces contribute to a variety of factors related to work satisfaction, productivity and well-being. We tested whether different photometric variables also influence visual perception and the comfort of the lighting, as well as subjective non-visual variables such as mood, alertness and well-being. Twenty-five young subjects spent two afternoons either under electric light or daylighting conditions (without view from the window). Subjects overall preferred the daylighting for visual acceptance and glare. Changes of photometric variables modulated changes in visual light perception, alertness and mood in the course of the afternoon. Finally, we found several associations of visual and non-visual functions, indicating a potential relationship of visual comfort with other circadian and wake-dependent functions in humans, which consequently could impact office lighting scenarios in the future.

Diurnal variations of hormonal secretion, alertness and cognition in extreme chronotypes under different lighting conditions

Circadian rhythms in physiology and behavior are modulated by external factors such as light or temperature. We studied whether self-selected office lighting during the habitual waking period had a different impact on alertness, cognitive performance and hormonal secretion in extreme morning and evening chronotypes (N = 32), whose preferred bed- and wake-up times differed by several hours. The self-selected lighting condition was compared with constant bright light and a control condition in dim light. Saliva samples for hormonal analyses, subjective ratings of alertness, wellbeing, visual comfort and cognitive performance were regularly collected. Between the self-selected and the bright, but not the dim lighting condition, the onset of melatonin secretion in the evening (as marker for circadian phase) was significantly different for both chronotypes. Morning chronotypes reported a faster increase in sleepiness during the day than evening chronotypes, which was associated with higher cortisol secretion. Wellbeing, mood and performance in more difficult cognitive tasks were better in bright and self-selected lighting than in dim light for both chronotypes, whereas visual comfort was best in the self-selected lighting. To conclude, self-selection of lighting at work might positively influence biological and cognitive functions, and allow for inter-individual differences.

Different colors of light lead to different adaptation and activation as determined by high-density EEG

Light adaptation is crucial for coping with the varying levels of ambient light. Using high-density electroencephalography (EEG), we investigated how adaptation to light of different colors affects brain responsiveness. In a within-subject design, sixteen young participants were adapted first to dim white light and then to blue, green, red, or white bright light (one color per session in a randomized order). Immediately after both dim and bright light adaptation, we presented brief light pulses and recorded event-related potentials (ERPs). We analyzed ERP response strengths and brain topographies and determined the underlying sources using electrical source imaging. Between 150 and 261 ms after stimulus onset, the global field power (GFP) was higher after dim than bright light adaptation. This effect was most pronounced with red light and localized in the frontal lobe, the fusiform gyrus, the occipital lobe and the cerebellum. After bright light adaptation, within the first 100 ms after light onset, stronger responses were found than after dim light adaptation for all colors except for red light. Differences between conditions were localized in the frontal lobe, the cingulate gyrus, and the cerebellum. These results indicate that very short-term EEG brain responses are influenced by prior light adaptation and the spectral quality of the light stimulus. We show that the early EEG responses are differently affected by adaptation to different colors of light which may contribute to known differences in performance and reaction times in cognitive tests.

Accounting free gains in a non-residential building by means of an optimal stochastic controller

Abstract A prototype predictive controller, based on the theory of optimal stochastic control, was developed and installed in a non-residential building in Delemont (Switzerland). This building is very well insulated (U = 0.65 W/m2K for windows) and, moreover, equipped with an active floor heating and cooling system. Solar and free gains supply more than 50% of its heating energy during winter. The controller determines, with the aid of the predicted free gains, the heat to supply for the next hour in order to optimise comfort and minimise energy consumption over a period of 24 h. The performance of this controller is compared with that of an advanced external temperature controller installed in the same building. A detailed energy balance of the building is presented for both controller types. The maximal energy savings observed in favour of the predictive controller amount to 24% during the cold season (October through April) and even reach 31% during the hot season (May through September). The thermal comfort was evaluated through questionnaires filled in by the occupants, but also thanks to an analysis based on temperature monitoring in the building. The analysis results show that comfort was maintained by the predictive controller.