Laura Bellia

Setting up a CCD photometer for lighting research and design

Abstract Recent availability of video-cameras with CCD-type sensors (charge coupled device) has proved to be particularly stimulating for all those applications requiring photometric measurements, above all for the measurement of luminance values related to the physical and technical qualities of a built environment. This method allows the instantaneous capture of an image, thus enabling collection of luminance values relating to the points of measurement; this in turn leads to the evaluation of luminance distribution and lighting levels of the surfaces that make up the environment. Setting up this system requires the following basic configuration: a photopic filter V ( λ ), an optic interface, a computer equipped with an appropriate card for the capture and digitalisation of the acquired image (the “frame grabber”) and, finally, suitable software for the processing of collected data. In this article a detailed description of this acquisition system is reported, and subsequently a report on the procedure adopted for its calibration so as to enable the capture of relevant photometric values. Final analysis and validation of results are carried out by means of field test. A case study of CCD photometer application has been then performed using a basic software tool autonomously developed to evaluate indoor lighting level; the luminance map of a diffuse light source has been used as “input” data for the developed software, and the “output” data, i.e. illumination levels, have been then compared with measured values.

A simple evaluator of building envelope moisture condensation according to an European Standard

Abstract The object of this work is the thermal and moisture performance analysis of building exterior walls, by means of a software code developed by the authors, according to the European Standard ISO 13788:2001. In particular, the European Standard focuses on two of the main reasons that cause moisture degradation in building envelopes: critical surface humidity and interstitial condensation. The approach is based on the steady-state diffusion theory and calculations are carried out on monthly basis, taking into account internal moisture production rates and outdoor climatic conditions. A user-friendly software tool (TMCE, i.e. thermal and moisture control for envelopes), developed in order to quickly and easily assess moisture and thermal behaviour of building components, is presented. The software, with graphical user interface, allows: (i) to determine the minimum thermal resistance of a building component in order to avoid critical surface humidity, and (ii) to check if interstitial condensation occurs in a multi-layer wall. In case of condensation occurrence during the winter months, the rate of condensed vapour is calculated, and the possibility that the moisture is completely removed during the warmer periods is evaluated. TMCE has been then used to analyse moisture and thermal characteristics of building components on varying input parameters such as outdoor climatic conditions and indoor moisture production; some relevant results and a case study are also presented.

Weather data for building energy cost-benefit analysis

This paper deals with European TRY weather data processing for climatic indexes generation, useful for HVAC energy and cost simplified evaluation. For nine Italian locations are presented: 99 and 2.5% dry bulb temperatures, 2.5% wet bulb temperatures, heating and cooling degree days, latent enthalpy days, unitary sensible and latent loads. TRY psychrometric data were processed according to a bin method that preserves the correlation between dry bulb temperature and moisture content, and then reduced by an averaging technique. An example is worked out in order to present an engineering shorthand for energy and cost evaluation of HVAC system.

Indoor artificial lighting: Prediction of the circadian effects of different spectral power distributions

The study presented in this paper aims to evaluate if and how the environment affects the circadian impact of a light source by predicting circadian stimulus (CS) resulting from the exposure to different light scenes, using equations reported in studies by Rea et al. The main findings are: (1) Above 600 lx at eye level the increase of CS is little; (2) Between 50 lx and 200 lx at the eye level an increase of only 50 lx determines a significant increase of CS; (3) Light sources with correlated colour temperatures between 2900 K and 4200 K have similar impacts on the circadian system according to the calculation method used; (4) Even an almost neutral environment affects the circadian impact of a light source.

A proposal for a simplified model to evaluate the circadian effects of light sources

In order to evaluate the circadian effects of light, an approach based only on a circadian sensitivity function makes it possible to easily obtain efficiency functions and action factors. However, it does not take into account the circadian human response to light stimuli, which is not linear. Non-linear models are more sophisticated and accurate but they are not easy to apply. In this paper a proposal for an easy way to evaluate the potential ‘circadian effects’ of light sources is presented. Although the model is quite simple, results are in good agreement with those obtained by means of one of the most accurate non-linear models.

HDR luminance mapping analysis system for visual comfort evaluation

The use of daylight in interior design is becoming more and more common and also its use for energy saving reasons that it is now possible to get through an appropriate daylighting and an optimal integration of day/ electric light. At the same time, in a working environment, the use of daylight for the indoor lighting has an influence on satisfaction, as well as on performance and therefore on labor productivity. In this paper, the definition of a system set up to analyze the field of vision based on the High Dynamic Range (HDR) analysis is presented. More specifically, the system allows to evaluate easily not only the photometric parameters but also the geometric ones that are needed for any type of quality evaluation of the lit environment. In particular, a field application related to the Daylight Glare Index (DGI) calculation has been presented. The proposed system allows a rapid evaluation and an index comparison for real situations, also giving the opportunity to take into account different evaluation criteria in the future.

De-Light: a software tool for the evaluation of direct daylighting illuminances both indoors and outdoors—comparison with Superlite 2.0 and Lumen Micro 7.1.

Abstract Regarding techniques used to evaluate daylighting illuminances, recent years have seen a steady increase in the use of computer programs, owing to increased computer speed and memory capacity. Despite a rise in the amount of available daylighting data, even the latest programs on the market only use standard CIE and IES sky models; besides, input climatic data and calculation procedures used by these programs do not always lend themselves to easy comparison: consequently, in the presence of different results from the programs, it is not always clear which parameters are responsible for these differences. From what has been said above and in order to examine closely various daylighting problems, we can better understand the need to develop a software tool to analyse the influence exerted by the choice of different parameters and calculation models on final results. As regards the various daylighting components (direct-from-sky, direct-from-sun, internally-reflected and externally-reflected), this paper is concerned with the direct-from-sky component, since it is essential for the internally-reflected component calculation. In particular, the procedure which has been developed calculates the direct-from-sky illuminance component on the work plane and on the other interior surfaces that make up the room. Exterior illuminances on unobstructed horizontal and vertical surfaces are also calculated, because they are necessary for the calculation of the externally-reflected component and useful for the reliability evaluation of simplified methods for the calculation of interior illuminances (daylight factor method and lumen input method). The computer program, named De-Light, has been developed in Visual Basic, an object-oriented program language, in order to obtain the greatest flexibility in input and output procedures. In this paper, following a description of the program, we compare the results obtained by De-Light with those obtained by two of the most common and reliable daylighting computer programs, Superlite 2.0 and Lumen Micro 7.1.

Velocity fields in proximity of local exhaust hood openings: An intercomparison between current recommended formulas and experimental studies

Abstract This article is the second part of a previous paper [F. Cascetta, Building and Environment 31, 437–449 (1996)] which illustrated the test facility in use, the measurement procedure, and fully described the velocity fields in front of hood openings. A comparison between the main current formulas available in the literature, and the experimental results collected by the authors, is introduced and discussed. The predicted centerline velocities inferred from the recommended formulas are compared with the ones experimentally measured by the authors, for both plain and flanged free-standing circular and rectangular exhaust openings. The velocity field outside the axis of the exhaust hood is also presented. It was experimentally determined and is expressed in terms of velocity contours.

Photometric characterisation of small sources with high dynamic range illuminance mapping

In this paper a system for obtaining the luminous intensity distribution of a small light source, based on high dynamic range imaging, is described. The system uses a dark room, a lambertian screen and a video-luminance-meter mounted on a workbench. The luminous intensity distribution of the light source is derived from the illuminance map on the screen by applying the photometric inverse law. The geometry of the system is presented and the measurements’ uncertainties are estimated. Finally, an application to a LED source is presented.

Daylighting contribution in interior lighting: Experimental verification of software simulation results

A study was carried out in an office building to investigate daylight impact comparing SUPERLITE 1.01 and LUMENMICRO 5 simulation results with measured data.Referring to the CIE standard Clear (with direct sun) and Overcast sky luminance distributions, calculated illuminance and daylight factor data for the work plane are compared with on-site data collected under real sky conditions. The main aim of the paper is not a comparative evaluation of simulation programs, but to define the meaning and/or uncertainty attached to the quoted results from the programs.