Perez Model Research Articles

Luminous efficacy model validation and computation of solar illuminance for different climates of India

Three luminous efficacy models namely Perez model, Muneer–Kinghorn model, and Littlefair model have been evaluated against measured solar illuminance and solar irradiance at New Delhi. Both these quantities are measured simultaneously, every half an hour, on a horizontal surface, in clear sky as well as intermittent sky. Among three models, Perez model has been found to perform best, with minimum mean bias error and minimum root mean square error. Experimental results also reveal that diffuse luminous efficacy has higher values as compared to global luminous efficacy and beam luminous efficacy. Further, Perez model has been used to assess daylight availability in summer, winter, and monsoon seasons at six Indian stations: New Delhi, Jodhpur, Pune, Kolkata, Shillong, and Leh, covering all climatic conditions in India. This model is used to obtain hourly values of solar illuminance for both global and diffuse components, in a typical meteorological year for each of the six stations. Analysis also shows that Indian climates have clear or intermittent skies for 60%–80% of day-time in a typical year, revealing immense potential for daylight exploitation for energy conservation. Solar global illuminance level assumes the highest value in summer months of April and May, whereas it becomes lowest in winter month of December. In monsoon season, solar illuminance is around 60–65 klx. It is also found that cumulative frequencies for global illuminance increases linearly with solar illuminance, in the range of 0–100 klx. Cumulative frequency for diffuse illuminance increases exponentially with solar illuminance, in the range of 0–60 klx.

Covering photo-realistic properties of outdoor components with the effects of sky color in mixed reality

Outdoor rendering is an attractive topic in computer graphics. In this paper our main concern is to reveal the interaction between sky color and virtual objects in Mixed Reality environments. Although registration and tracking are two of the main issues in building effective Augmented Reality (AR) systems the creation of more realistic virtual objects indistinguishable from their real-world counterparts is our target which is currently the ultimate goal in AR. Two classes of sky color generation are employed to reveal the outdoor-element interaction. Virtual Sky Modelling (VSM) based on the Perez Model is capable of generating the sky color in a specific location, date and time. The second technique is to generate a virtual model based on the real image of the sky which is called in this paper Real Sky Modelling (RSM). Subsequently, preprocessing of the sky color bleeding is based on the radiosity technique to give the sky color effect to the virtual objects as well as the real ones. Through designing a test AR set-up and applying software and hardware the goal of a robust generation of realistic virtual objects with effect of sky color is achieved.

Modelling of the UV Index on vertical and 40° tilted planes for different orientations

In this study, estimated data of the UV Index on vertical planes are presented for the latitude of Valencia, Spain. For that purpose, the UVER values have been generated on vertical planes by means of four different geometrical models a) isotropic, b) Perez, c) Gueymard, d) Muneer, based on values of the global horizontal UVER and the diffuse horizontal UVER, measured experimentally. The UVER values, obtained by any model, overestimate the experimental values for all orientations, with the exception of the Perez model for the East plane. The results show statistical values of the MAD parameter (Mean Absolute Deviation) between 10% and 25%, the Perez model being the one that obtained a lower MAD for all levels. As for the statistic RMSD parameter (Root Mean Square Deviation), the results show values between 17% and 32%, and again the Perez model provides the best results in all vertical planes. The difference between the estimated UV Index and the experimental UV Index, for vertical and 40° tilted planes, was also calculated. 40° is an angle close to the latitude of Burjassot, Valencia, (39.5°), which, according to various studies, is the optimum angle to capture maximum radiation on tilted planes. We conclude that the models provide a good estimate of the UV Index, as they coincide or differ in one unit compared to the experimental values in 99% of cases, and this is valid for all orientations. Finally, we examined the relation between the UV Index on vertical and 40° tilted planes, both the experimental and estimated by the Perez model, and the experimental UV Index on a horizontal plane at 12 GMT. Based on the results, we can conclude that it is possible to estimate with a good approximation the UV Index on vertical and 40° tilted planes in different directions on the basis of the experimental horizontal UVI value, thus justifying the interest of this study.

The effect of functionalization on the viscoelastic behavior of multi-wall carbon nanotube/epoxy composites

Functionalized multi-walled carbon nanotubes with hydroxyl groups (MWNT-OH) and non-functionalized MWNT were used to fabricate MWNT/epoxy composite samples by sonication technique. The viscoelastic properties of the composite samples were evaluated by performing dynamic mechanical thermal analysis (DMTA) test. The results showed that addition of nanotubes to epoxy had significant effect on the viscoelastic properties. Samples containing functionalized nanotubes showed a stronger influence on Tg in comparison to composite samples containing similar amount of non-functionalized nanotubes. The viscoelastic behavior was modeled by plotting the COLE–COLE diagram using the results of DMTA test. There was a good agreement between the Perez model and the viscoelastic behavior of the composite specimen.

Perez Model을 적용한 태양광 시스템 별 최적 설치 조건 및 최대 발전량 분석

Photovoltaic(PV) system is one of power generation systems. Solar light in PV system is like the fuel of the car. The quantity of electricity generation, therefore, is fully dependent on the available quantity of solar light on the system of each site. If a utility can predict the solar power generation on a planned site, it may be possible to set up an appropriate PV system there. It may be also possible to objectively evaluate the performances of existing solar systems. Based on the theories of astronomy and meteorology, in this paper, Perez model is simulated to estimate the available quantity of solar lights on the prevailed photovoltaic systems. Consequently the conditions for optimal power generation of each PV system can be analyzed. And the maximum quantity of power generation of each system can be also estimated by applying assumed efficiency of PV system. Perez model is simulated in this paper, and the result is compared with the data of the same model of Meteonorm. Simulated site is Daejeon, Korea with typical meteorological year(TMY) data of 1991~2010.

Thermo-Mechanical Properties of Multi-Walled Carbon Nanotube (MWCNT)/Epoxy Composites

The thermo-mechanical and tensile properties of multiwalled carbon nanotube (MWCNT)/epoxy composite samples were evaluated by performing dynamic-mechanical thermal analysis (DMTA) and tensile tests. The composite samples were fabricated by sonication and a cast molding process. The results indicated that the addition of multiwalled nanotubes (0.1, 0.5, and 1.5 wt.%) to the epoxy matrix had significant effect on the thermo-mechanical properties. The use of 0.5 wt.% MWCNT was the most effective in increasing the storage modulus value, while the sample containing 1.5 wt.% MWCNT demonstrated the best tensile properties. The experimentally obtained DMTA results were modeled by plotting a Cole-Cole diagram. The results showed quite good agreement between the Perez model and the experimental thermo-mechanical data.

Viscoelastic Properties of Multi Walled Carbon Nanotube/Epoxy Composites at the Different Nanotube Content

The viscoelastic properties of composites multi walled carbon nanotube / epoxy at different weight fractions (0.1, 0.5 and 1wt %) were evaluated by performing dynamic mechanical thermal analysis (DMTA) test. The MWCNT/ epoxy composite were fabricated by sonication and a cast molding process. The results showed that addition of nanotubes to epoxy had a significant effect on the viscoelastic properties. However, the use of 0.5wt% increased the viscoelastic properties more significantly. Concerning viscoelastic modeling, the COLE-COLE diagram has been plotted by the result of DMTA tests. These results show a good agreement between the Perez model and the viscoelastic behavior of the composite.

Viscoelastic and mechanical properties of multi walled carbon nanotube/epoxy composites with different nanotube content

The viscoelastic and mechanical properties of composites multi walled carbon nanotube (MWNT)/epoxy at different weight fractions (0.1, 0.5, 1 and 2wt.%) were evaluated by performing tensile and dynamic-mechanical thermal analysis (DMTA) tests. The MWNT/epoxy composite were fabricated by sonication and a cast molding process. The results showed that addition of nanotubes to epoxy had significant effect on the viscoelastic and mechanical properties. However, the use of 0.5wt.% increased the viscoelastic properties more significantly. Concerning viscoelastic modeling, the COLE–COLE diagram has been plotted by the results of DMTA test. These results show a good agreement between the Perez model and the viscoelastic behavior of the composite.

Viscoelastic properties of multi-walled carbon nanotube/epoxy composites using two different curing cycles

Along with carbon nanotubes (CNT) morphology, impurity, and functionalization, polymer curing cycle is another important factor in determining the mechanical properties of the CNT/polymer composite samples. This work investigates the effect of two different curing cycles on mechanical and thermo-mechanical properties of the nanotube in the composite in order to optimize the curing condition in term of time and temperature. Nanocomposite samples were prepared by mixing multi-wall carbon nanotubes with epoxy resin using sonication method. The mechanical and viscoelastic properties of the resulting composite samples were evaluated by performing tensile and dynamic mechanical thermal analyses (DMTA) test. The results indicate that the mechanical and viscoelastic properties of pure epoxy and composite samples have been affected by the condition curing process. Concerning viscoelastic modeling, the COLE–COLE diagram has been plotted by the result of DMTA tests. These results show a good agreement between the Perez model and the viscoelastic behavior of the composite.

Determining seasonal optimum tilt angles, solar radiations on variously oriented, single and double axis tracking surfaces at Dhaka

The performance of a solar radiation conversion system is affected by its orientation and tilt angle with the horizontal plane. This is because both of these parameters change the amount of solar energy received by the surface of solar system. Three mathematical models- the Isotropic, the Klucher and the Perez model for the point source with parameters optimized for a variety of climatic conditions have been employed to determine hourly and seasonal optimum tilt angles. Theoretical optimum tilt angles (10° for Mar–Sep and 40° for Oct–Feb) were compared with measured data for Nov 2007 to Oct 2008 at Dhaka. The anisotropic Perez model showed least rmse of 0.09 for monthly tilt factor estimation. This model was also used for theoretical study of solar radiation on variously oriented, single axis and double axis tracking surfaces.

Illuminance estimation and daylighting energy savings for Indian regions

In this manuscript, potential of daylighting in reducing electrical lighting load, has been explored. The analysis has been carried out for four different types of windows and for three different climatic conditions of India. Two Perez models have been used to estimate illuminance on horizontal and for vertical surfaces as this data is not available in India. Effect of different glazed areas, that of orientation and that of climatic conditions on the reduction in lighting load, has been analysed. The daylighting software, ADELINE 3.0, has been used for computation of lighting energy savings. It has been found that for a given climate and orientation, if the window visible transmittance is low (0.07 for reflective window and 0.20 for solar control window) the energy saved due to daylighting increases with the glazed area but if window transmittance is high (0.78 for double glazed clear window and 0.73 for double glazed low-e window) it almost remains constant with glazed area. Energy saved is highly dependent on the window type, being highest for double glazed clear glass window and lowest for reflective window. By using Perez model and by associating this with average daylight factor, daylighting energy savings have also been computed and compared with the ADELINE simulated results.

Statistical analysis of solar radiation models onto inclined planes for climatic conditions of Lower Silesia in Poland

The paper presents the statistical analysis’ results of major models of the solar radiation intensity onto an inclined plane. Models with various degrees of complexity: from the simplest classical isotropic model to the most complex anisotropic model (the Perez model) were analyzed. The data yielded by the theoretical models were compared with a four-year measurement database from the actinometric station in the SolarLAB Photovoltaic Laboratory in Wroclaw. Also the potential benefits of using albedo data characteristic of the measurement location versus the classical 0.2 albedo assumption were examined.

Solar Illumination and Estimating Daylight Availability of Global Solar Irradiance

In this article, it is aimed to determine the daylight availability and luminous efficacy of global irradiance for Izmir, which has Mediterranean climatic conditions. Daylight availability and luminous efficacy were put forward by using existing valid models, including Aydinli Model, Perez Model, and IESNA Model. Yearly exterior illuminance levels have been estimated by the use of hourly data of the Meteorological Station of Solar Energy Institute. The models were compared in consideration with their luminous efficacies. Monthly average hourly exterior daylight illuminance levels estimated by Aydinli Model, Perez Model, and IESNA Model were put forward for Izmir. Frequency distributions of luminous efficacies (lm/W) for hourly values calculated by these theoretical methods were evaluated. The frequency distributions were examined in consideration with the reference value referred to in the literature. Yearly correlations between hourly average daylight illuminance by Aydinli Model, global illuminance by Perez Model, daylight illuminance by IESNA Model, and measured hourly global solar irradiance were established and determined to be able to estimate daylight availability data for Izmir. According to these correlation equations, it is shown that the linear correlation coefficients (R2) are 0.9536 for Aydinli Model, 0.9994 for Perez Model, and 0.9747 for IESNA Model. Finally, the potential of daylighting and the feasibility of natural lighting systems for Izmir were evaluated according to these results.

Predicting diffuse illuminance on vertical surfaces at Arcavacata di Rende (Italy) for various types of sky

The diffuse natural illuminance of variously oriented vertical surfaces was calculated by nine models under various sky conditions, subdividing the experimental data into eight types of sky, on the basis of the value of the Perez sky clearness index parameter. The calculated data were compared with the experimental data measured over a complete year at Arcavacata di Rende (Italy) (latitude 39°21′N, longitude 16°13′E). The comparison between calculated and experimental data showed that the best models appear to be an author's model, which assumes a constant value of the luminous efficacy of the radiation for each surface in each sky clearness index bin and a version of a Perez model whose coefficients were recalculated for each surface orientation. If all the data are considered together, without distinguishing between the different types of sky, almost all the models, for the various surfaces, present low errors and behave in a quite similar manner.

Evaluation of vertical illuminance and irradiance models against data from north Bangkok

This paper presents results of a study on measurement of illuminance of daylight and solar irradiance on four cardinal orientations (N, E, S, W). Performances of mathematical models for computing value of vertical illuminance and irradiance proposed by various authors were investigated. The functional form of Perez's model was selected for developing localized models of vertical irradiance and illuminance. Sets of local coefficients of Perez's model were derived from measured data taken from a station at the Asian Institute of Technology (AIT), located north of Bangkok. Several models were examined and it was found that Perez's model gave more accurate results when its coefficients were derived from our experimental data. Accuracy of the results could be further improved when two separate models are used for a vertical surface, one model for the case when the sun is in front of the surface and another model for the case when the sun is at the back of the surface.

Empirical validation of models to compute solar irradiance on inclined surfaces for building energy simulation

Accurately computing solar irradiance on external facades is a prerequisite for reliably predicting thermal behavior and cooling loads of buildings. Validation of radiation models and algorithms implemented in building energy simulation codes is an essential endeavor for evaluating solar gain models. Seven solar radiation models implemented in four building energy simulation codes were investigated: (1) isotropic sky, (2) Klucher, (3) Hay–Davies, (4) Reindl, (5) Muneer, (6) 1987 Perez, and (7) 1990 Perez models. The building energy simulation codes included: EnergyPlus, DOE-2.1E, TRNSYS-TUD, and ESP-r. Solar radiation data from two 25 days periods in October and March/April, which included diverse atmospheric conditions and solar altitudes, measured on the EMPA campus in a suburban area in Duebendorf, Switzerland, were used for validation purposes. Two of the three measured components of solar irradiances – global horizontal, diffuse horizontal and direct-normal – were used as inputs for calculating global irradiance on a south-west façade. Numerous statistical parameters were employed to analyze hourly measured and predicted global vertical irradiances. Mean absolute differences for both periods were found to be: (1) 13.7% and 14.9% for the isotropic sky model, (2) 9.1% for the Hay–Davies model, (3) 9.4% for the Reindl model, (4) 7.6% for the Muneer model, (5) 13.2% for the Klucher model, (6) 9.0%, 7.7%, 6.6%, and 7.1% for the 1990 Perez models, and (7) 7.9% for the 1987 Perez model. Detailed sensitivity analyses using Monte Carlo and fitted effects for N-way factorial analyses were applied to assess how uncertainties in input parameters propagated through one of the building energy simulation codes and impacted the output parameter. The implications of deviations in computed solar irradiances on predicted thermal behavior and cooling load of buildings are discussed.

Measurement and comparison of diffuse solar irradiance models on inclined surfaces in Valladolid (Spain)

This paper presents the performance of 10 arithmetic models used to estimate diffuse solar irradiance on inclined surfaces in a comparative study with actual data readings made available on an hourly and a daily basis. The data readings have been taken from a south facing surface inclined at 42° in an area at some distance from the provincial capital in the Spanish province of Valladolid. In order to confirm the results, three statistical parameters have been used in the study; root mean square error (RMSE), mean bias error (MBE) and Stone’s t-statistic. The results obtained favour the Muneer model, followed by the Reindl model, for hourly as well as for daily values. The Temps–Coulson model gives rise to great discrepancies with respect to the values measured. The results for the Perez model are not good due to the use of parameters that are not specifically calculated for the area in this study, which underlines the need to take an area’s features into account so that predictions for diffuse irradiance measured on inclined surfaces may be as accurate as possible.

Estimation of global illuminance on inclined surfaces for clear skies

In the present work, we have studied the luminous efficacy of global solar radiation incident on vertical surfaces for clear skies (cloudless and rather clean skies) and mean hourly values of global solar radiation (i.e. averaged over each hour). Luminous efficacy models similar to those previously obtained for a horizontal surface have been developed using solar elevation as the independent variable. Thus, the hypothesis that the slope of the surface does not influence the general formulation of the model has been assumed. However, the final formulation of the models clearly depends on the insolation conditions of the inclined surface and, more specifically, on whether direct radiation is or is not incident on it. As a consequence, two different types of models have been proposed to take both insolation conditions into account. On the other hand, global luminous efficacy models have also been obtained as the best fits of the experimental data. Global illuminance has been estimated for the vertical surfaces considered, facing north, east, south and west, with the models obtained as the best fits of the experimental data and the other two types of models mentioned in the preceding paragraph. Comparison of the performance of models for global illuminance estimation has validated the initial hypothesis that the slope of the surface does not influence the general formulation of the model. The performances of the known Perez model and the proposed models are also compared.

An analysis of all-sky zenith luminance data for Hong Kong

Sky luminance distribution data are of great importance to estimate internal daylight illuminance for building energy modelling. Sky luminance of a particular sky patch is always expressed as a ratio of the corresponding zenith luminance. For places where measured zenith luminance is not available, generating the required data from conversion models would be an appropriate alternative. This paper describes the sky luminance measurements made in 1999 at the City University of Hong Kong and reports the findings. A simple model relating zenith luminance and horizontal diffuse illuminance has been proposed. An evaluation of the proposed model and the Perez zenith luminance model has been carried out. It has been found that the proposed model gives reasonably good agreement with the measured data and outperforms the Perez model. The simplicity nature of the proposed model provides a convenient and reliable approach for building designers in estimating the zenith luminance as well as the whole sky luminance distribution.

A new approach for predicting vertical global solar irradiance

Solar irradiance, particularly on vertical surfaces, plays a major role in determining the thermal and energy performance of a building. It is important to the design and analysis of both active solar systems and passive solar buildings. Many mathematical models are mainly developed to predict the sky-diffuse irradiance on inclined surfaces from the measured horizontal diffuse component. This paper presents an approach to estimate the vertical global irradiance based on direct beam and ground-reflected components which can be accurately determined. Hourly data recorded from January 1996 to December 1998 in Hong Kong were used for the model development. The performance of the proposed model and two well-known anisotropic inclined surface models (Muneer and Perez) was evaluated against data measured in 1999. Statistical analysis indicated that the proposed model gives reasonably good agreement with measured data for all vertical planes. Although the new model has been found less effective than the Perez model, its simplicity nature provides buildings designers a convenient and reliable alternative in the estimation of vertical solar irradiance.