The availability of daylight from tropical skies—a case study of Malaysia

In Malaysia, no long-term daylight data are measured. It was only recently that the need to measure the availability of daylight became urgent when the importance of daylighting in buildings was rediscovered. The hourly daylight availability has been simulated for the Malaysian sky using daylight modelling techniques based on empirical and measured solar irradiation and cloud cover data. This paper presents the techniques involved in producing exterior illuminance data. These data were then compared with measured illuminance at Shah Alam and Bangi, Malaysia. The global illuminance levels are generally high, with values exceeding 80,000 lux at noon during the months when solar irradiation is highest. Even during the months when the ground receives less solar irradiation, the peak illuminance can reach 60,000 lux. Applications and uses of such data are in daylighting design, both for visual and thermal comfort, task illuminance and energy-conscious design of buildings. Recommendations are made at the end of the paper on the various climatic data that are required to be measured for overall daylighting design applications.     

A study on luminous efficacy of global radiation under clear sky conditions in Athens, Greece

The current interest in energy efficient design has led to a demand for methods of predicting daylight availability in buildings. However, basic daylight data, which are the basis of these prediction methods, are not available for most regions of Greece, as well as for many areas worldwide. For that purpose luminous efficacy can be used in order to generate daylight illuminance from solar radiation data, which are much more widely recorded.This paper concentrates on the analysis of global luminous efficacy in Greece under clear sky conditions. The study involves the evaluation of existing models with respect to daylight data recorded in Athens, Greece, as well as the development of new luminous efficacy models for global radiation.The study was based on climatic data provided by the National Observatory of Athens during the years 1996–2000 and tested according to CIE. recommendations. The proposed luminous efficacy models were derived by the analysis, correlation and linear regression of the accepted values of measured data. Statistical analysis techniques were used for the assessment of their performance, as well as for the evaluation of the accuracy in predicting global illumination provided by the proposed and the existing models.The new proposed models can offer engineers and researchers a more reliable and accurate approach for estimating the global illumination levels under clear skies. Nowadays, the knowledge of daylight levels is considered highly important in local architecture, the energy conservation and environmental policies in general, particularly in the case of Mediterranean regions, where clear sky conditions dominate.     

Solid-state photovoltaic power and battery unit

The feasibility of an integrated battery/solar module system is demonstrated using a rechargeable lithium battery and a commercially available polycrystalline silicon solar module. The solar module was parallel connected to a prismatic 500 mAh battery and a constant resistance load. This arrangement was subsequently tested under conditions which simulated daylight and night conditions. The combined system was cycled 20 times without severe degradation of the battery or solar module performance.     

Daylight availability and models for global and diffuse horizontal illuminance and irradiance for Bangkok

We present results of a study on measurement of illuminance of daylight and solar irradiance from a station in the Asian Institute of Technology (AIT) campus, which is situated in a tropical region. Availability of daylight illuminance and solar irradiance on the horizontal and on vertical planes in cardinal directions is first presented. Mathematical models of global and horizontal daylight illuminance and solar irradiance are then presented. Our results reinforce earlier expectation of good potential for daylighting in tropical climate.     

On the air flow and radiation transfer through partly covered external building openings

Solar control devices placed in front of large building openings disturb air flow and the radiation transfer. Although solar radiation transfer through obstructed openings is a relatively well researched area, very little information is available regarding the air flow perturbations and daylighting alterations created by external solar control devices. The present paper reports a series of experiments aiming at investigating natural ventilation and daylight phenomena associated with the use of specific shading devices. Experiments have been carried out in outdoor test cells, and 28 different configurations have been tested for several window characteristics under various climatic and radiation characteristics. Based on the experimental results, specific modeling activities have been undertaken and theoretical methods of calculating air flow and daylight through openings equipped with specific solar control devices have been developed and are now presented. Theoretical predictions are compared with the corresponding experimental data and a very satisfactory agreement has been found for both air flow and daylight processes.     

Occurrence of standard skies during typical daytime half-days

The current trials to introduce new daylight assessment criteria for future building designs as well as for renewable energy simulations with the trend to implement annual daylight profiles for a specific locale or region need more detail information on the exterior daylight conditions. Bratislava is the only locality in Central Europe where a CIE-IDMP general station is recording 1-min regular daylight measurements since 1994 and 10-year data gathered can be used now to derive models valid for wider regions. In this paper, the analysis of measurements and sky-type occurrence is representing daylight conditions only for this single site. As the meteorological net of observatories register sunshine duration for longer periods worldwide, also this information may serve as the basis for modelling exterior daylight illuminance courses as well as typical sky conditions when no other measurements are available. Furthermore, the new General Sky Standard adopted by CIE in 2003 and by ISO in 2004 gives the possibility to study actual skies occurring under four characteristic daylight situations associated with sunshine duration during typical half-days.     

An analysis of luminous efficacies under the CIE standard skies

Designing a building to integrate daylight requires an accurate estimation of the amount of available outdoor illuminance. The common method for predicting daylight has been the derivation of illuminance from the more widely measured solar irradiance using the luminous efficacy approach. Recently, the International Commission on Illumination (CIE) has adopted a range of 15 standard skies which cover the whole probable spectrum of skies in the world. This paper presents the work to model the luminous efficacy of diffuse component under the 15 CIE standard skies. Sky luminance distributions measured between 1999 and 2005 were used for the standard sky classifications. An approach to develop luminous efficacy for inclined surfaces was proposed. The predicted vertical outdoor illuminance data for the four cardinal planes (i.e., N, E, S and W) using the proposed luminous efficacy were evaluated against data measured in 2004. Statistical analysis indicated that the estimated daylight illuminance data give acceptable agreements with measured data for all vertical planes.     

Quantifying the potential of automated dynamic solar shading in office buildings through integrated simulations of energy and daylight

The façade design is and should be considered a central issue in the design of energy-efficient buildings. That is why dynamic façade components are increasingly used to adapt to both internal and external impacts, and to cope with a reduction in energy consumption and an increase in occupant comfort. To gain a complete picture of any façade’s performance and subsequently carry out a reasonable benchmarking of various façade alternatives, the total energy consumption and indoor environment need to be considered simultaneously. We quantified the potential of dynamic solar shading façade components by using integrated simulations that took energy demand, the indoor air quality, the amount of daylight available, and visual comfort into consideration. Three types of façades were investigated (without solar shading, with fixed solar shading, and with dynamic solar shading), and we simulated them with various window heights and orientations. Their performance was evaluated on the basis of the building’s total energy demand, its energy demand for heating, cooling and lighting, and also its daylight factors. Simulation results comparing the three façade alternatives show potential for significant energy reduction, but greater differences and conflicting tendencies were revealed when the energy needed for heating, cooling and artificial lighting were considered separately. Moreover, the use of dynamic solar shading dramatically improved the amount of daylight available compared to fixed solar shading, which emphasises the need for dynamic and integrated simulations early in the design process to facilitate informed design decisions about the façade.     

Prediction of daily global solar irradiance on horizontal surfaces based on neural-network techniques

In this study, a prediction model of global solar irradiance distribution on horizontal surfaces has been developed. The methodology is based on neural-network techniques and has been applied to the meteorological database of NTUA, Zografou Campus, Athens (37°58′26″N, 23°47′16″E). The investigation of the correlation between weather conditions, duration of daylight and the representative peak value of a Gaussian-type function plays an essential role in the development of the model. The weather conditions are categorized into six different states, whereas the daylight duration is obtained by familiar equations. Thereafter, a correction methodology for the Gaussian-type function—which stands for all six different states—is applied. Finally, the reliability of the developed model is investigated through a suitable validation procedure.     

Models for obtaining solar radiation from other meteorological data

The application of solar energy requires a knowledge of long-term solar radiation and daylight data. Because of the limited availability of measured data, various formulae have been derived to compute the solar irradiance using other, more commonly available, weather data. In this article two such models are presented, MRM (meteorological radiation model) and CRM (cloud-cover radiation model). MRM requires hourly data for sunshine duration, dry- and wet-bulb temperature; while CRM requires only cloud amount. Both models can generate hour-by-hour data for horizontal global, diffuse, and beam irradiance. A brief comparison of the two models is presented. Results showed that MRM has the advantage over CRM, on account of its consistency with the measured data. Both models are now available via the Internet in the form of electronic spreadsheets.     

First conference on measurement and modeling of solar radiation and daylight “Challenges for the 21st Century” Napier University,Edinburgh, 15–16 September 2003

This was the opening paper to the Conference. The paper combines the historic experience of the author on solar radiation climatology built up over the last 50 years with a more detailed account of his contribution to a number of recent European funded projects dealing with solar radiation in the context of applications. These projects have been especially concerned with the improved delivery of accurately estimated and reliable solar radiation data to users. The recent European projects have made extensive use of satellite data in conjunction with reliable ground truth sites. The paper explains the special emphasis now being placed on the effective use of IT to provide user selected data delivery on the world wide web. The paper finishes with a suggested road map for the future for solar radiation and daylight measurement and applications research. The importance of achieving an improved understanding of diffuse radiation through improved measurement approaches is especially stressed. The need for an improved understanding of spectral radiation is also underlined.     

Instrumentation for the measurement of the variation, quantity and quality of Sun and sky radiation

Many biological responses, such as reproduction, differentiation and morphological development are regulated by radiant energy in particular wavelengths of the solar spectrum. Biologists are concerned with the influence of the spectral quality of natural daylight on these biological responses. Data, concerning spectral quality of daylight over a sufficient time period, required by biologists are usually not available. The described system will provide the information with sufficient accuracy and precision to discern small but significant changes. To produce such a monitoring system, a standardization program was evolved using the original Smithsonian solar standards and instruments. These were compared to each other and finally to commercial units which were used in the monitoring system. The system was designed so that data would be accurate at 0.01 ly min⁻¹ and could be automated to give high precision readings every 3 min with errors less than 2 per cent.     

Daylight illuminance control with fuzzy logic

The purpose is to take full advantage of daylight for inside illumination. The inside illuminance and luminous efficacy of the available solar radiation were analyzed. The paper deals with the controlled dynamic illuminance response of built environment in real-time conditions. The aim is controlled functioning of the roller blind as a regulation device to assure the desired inside illuminance with smooth roller blind moving. Automatic illuminance control based on fuzzy logic is realized on a test chamber with an opening on the south side. The development and design of the fuzzy controller for the corresponding positioning of the roller blind with the available solar radiation as external disturbance is the subject of this paper.     

Influence of architectural design on indoor environment in apartment buildings in Havana

The paper presents the results of research focused on evaluating the influence of the architectural design of apartment buildings located in different locations in Havana city. The object under study has been the volume of buildings in relation to their surroundings, which determines the relationship between indoor and outdoor spaces and how indoor spaces are exposed to daylight and solar radiation.Three urban areas were selected taking into account the opinion of some architectural experts. The apartment buildings were classified according to their architectural volume, considering the transitional spaces: streets and corridors, yards and indentations. Sixty six indoor spaces linked to different transitional spaces with varied dimensions, proportions and orientation were chosen to take temperature measurements and make daylight simulations.The comparative assessment of the results considered the difference between the indoor temperature and that measured in an external reference point, mainly at night, when the family is at home. The temperatures taken in the reference points confirmed the effect of the urban heat island. The best transitional space from the thermal point of view is the corridor type. On the contrary, yards offer the worse conditions, except in compact urban areas as Centro Habana.Regarding daylight, no studied space meets the minimum daylight requirement established by Cuban daylight standards, and only one achieves minimum uniformity. The best transitional space is also the corridor type, which guarantees a higher percentage of daylight with respect to an unobstructed outdoor space on a roof.Based on these results, urban form generated from detached buildings separated by corridors is more appropriate for the warm and humid climate of Havana than the compact colonial urban model, although it was considered a good option in studies carried out twenty years before. These results reinforce some conclusions reached at during the last ten years regarding the advisability of reducing land occupancy in current compact urban areas and to avoiding the use of small yards to provide daylight and natural ventilation in apartment buildings.     

A program for calculation of solar energy collection by fixed and tracking collectors

, a realistic and versatile program, has been developed to estimate net solar energy collected by a solar collector per unit collection area. This program was developed to study the properties of various solar collectors. It is made useful to a wide spectrum of users by allowing them to choose any or all of 15 possible solar collector types for calculation and comparison. Additional collectors can be included without undue labor. Either or both of two selective absorbers can be selected for energy collection calculations. allows input for a third selective absorber. is programmed to use solar radiation and surface meteorological data taken from The National Solar Radiation Data Base (NSRDB) for 239 stations over the USA. It can be adjusted to read other data sets. It takes 20 s on a Compaq Presario 2700 1.13 GHz computer to calculate net solar energy collection per unit area for one solar collector design using each of two selective absorbers at five fixed absorber temperatures for all the daylight hours of 1 year at one location. The program output includes sums of solar energy collection for each day, month and year along with averages and distributions. Averages and distributions for the solar radiation and surface meteorological data are also obtained so solar energy collection can be related to these data. can be downloaded from the website: www.sci.sdsu.edu/SOCOL/.     

Modern insulation requirements change the rules of architectural design in low-energy homes

In the design of very well-insulated homes, there is a need for a more nuanced design that takes into account winter and summer conditions. In this paper, we compare a traditional design for a typical Danish single-family house with large glazing areas oriented towards the south and smaller glazing areas towards the north, and a design with an even window distribution where the glazing-to-floor ratio is the same for each room. We found that the use of solar gains through south-oriented windows is not as important as is traditionally believed because, in well-insulated homes, space heating demand is not reduced much by having larger south-facing windows. Furthermore, we found that there is a g-value above which the additional solar gains through south-oriented windows do not help reduce space heating demand, and it becomes important to use solar shading or glazing with solar-control coating as a cheaper alternative to reduce overheating. Maximum window sizes from an overheating perspective were identified that are larger than the optimal window sizes for space heating demand. However, we show that the difference in space heating demand with optimal window size and with larger window sizes is small, so it is up to the building owner to decide whether or not he wants larger glazing areas to allow for more daylight. And windows can be positioned in the façade with considerable architectural freedom. However, we do recommend an even distribution of the glazing-to-floor ratio, because this generally provides an improved thermal indoor environment in south-oriented rooms and will ensure a better daylight level especially in north-oriented rooms. We also show that the optimal window size is influenced by thermal zone configuration and that there is a need for models in which a difference is made between zones with direct and with non-direct solar gains.     

Daylight optimization of multifunctional solar facades

Multifunctional solar facades consisting of a transparent window and an opaque photovoltaic section are analyzed and optimized. Employing numerical daylight estimation techniques, the optimal shape, position, and area of the window section is determined. Maximum yearly average daylight availability is achieved with a similarly shaped window as the facade which is placed near the centre of the facade. For non-residential buildings, the yearly average useful interior daylight illuminance does not increase significantly for windows larger than 30% of the total facade area. Considering both the artificial lighting requirement replaced by daylight through the window and the electricity produced by the PV section of the facade, the maximum electricity benefit for a south-facing facade is achieved with a window area of about 10% of the total facade area in Southern Europe (38° N) and 15% in Northern Europe (60° N).     

Daylight, sunlight and solar gain in the urban environment

In cities, site layout has a substantial impact on the daylight, sunlight and solar radiation received by windows. This paper discusses ways to ensure solar access in obstructed situations, both within new developments and in existing buildings nearby.     

A study of atmospheric turbidity for Hong Kong

Clear skies are important in predicting the peak solar irradiance and daylight illuminance levels for active solar energy utilisation and passive energy-efficient building designs. The clearness of a sky is affected by the clarity of the atmosphere which is usually expressed in terms of a turbidity index. This study considers two common turbidity parameters including the Linke turbidity factor (T_L) and Angstrom turbidity coefficient (β). The annual and monthly average values, frequency of occurrence and cumulative frequency distribution of individual turbidity indices based on different approaches have been established to describe the clear sky atmospheric conditions in Hong Kong. The general features and characteristics of the findings are discussed.