Incoming Direct Solar Radiation Research Articles

Tailored WBGT as a heat stress index to assess the direct solar radiation effect on indoor thermal comfort

Uncontrolled solar radiation and the related effects on occupant productivity can lead to considerable indoor thermal discomfort in office environments. In this paper, the Radiance Daylight Coefficient (DC) method is used to assess incoming solar radiation and consequent indoor thermal discomfort through delta mean radiant temperature (ΔMRT). The ΔMRT allows expressing an adjusted predicted mean vote (Adjusted PMV). Under the conditions of direct solar radiation, the Adjusted PMV value surpasses the applicability range of the standard PMV in terms of MRT value. To overcome this limitation, the assessment of the effect of incoming shortwave solar radiation is expressed in the heat stress index of wet bulb globe temperature (WBGT). This procedure was tested under a variety of climatic conditions (e.g., Sol-air temperature) to estimate dissatisfaction in indoor office environments located in Milan (Italy) for an occupant positioned at different distances from the fenestration (0.75 m, 1.25 m, and 1.75 m) and exposed to direct solar radiation (e.g., without shading devices). The condition with no shading device was then compared with the condition with shaded glazing to test the impact of the solar radiation on the indoor thermal stress conditions. The results reported through ΔWBGT allow the estimation of the heat stress conditions on an annual basis when ΔWBGT > 0. Finally, it is proposed that the metric of Annual Radiation Heat Stress (ARHS) should include ΔWBGT and assess the heat stress spatially due to the incoming direct solar radiation.

Graphic method of calculation of the direct solar radiation received on the facade with available opposing building

Introduction. An approach to the development of a method for taking into account the influence of a single opposing building on direct solar radiation inflows to the building under study, taking into account all the irradiation periods of the facade under study, is presented. When calculating the consumption of thermal energy for heating and ventilation of a building in accordance with the method presented in regulatory documents, it is necessary to perform calculations of heat gain to the building from solar radiation. These calculations are carried out without taking into account the influence of the opposing building, what reduces the accuracy of the results. In foreign and domestic literature sources not found suitable for construction calculations and taking into account all periods of exposure methods. The objectives of this study are: the mathematical substantiation of the method, the possibility of its practical application, the formation of the calculation algorithm. Materials and methods. Calculations of the angular height and azimuth of the Sun by astronomical formulas, trigonometric calculations, construction of graphs of the tangents of changes in solar coordinates from the true solar time are applied. Results. The graphical method is proposed for determining irradiation periods by direct solar radiation of a facade of any orientation. The method is based on consideration of the formulas of the solar coordinates and the location of the opposing building. In this case, the graphic field is used to plot the changes in the tangents of the angular height of the Sun and the tangents of the difference between the azimuths of the Sun and the normal to the surface of the facade from the true solar time. The parameters of the building are applied to the graphic field and, in accordance with the proposed recommendations, the periods of irradiation of the facade are determined. Then the summation of direct solar radiation for the periods of irradiation of the facade is made. The algorithm of calculations on the example of a building in the presence of an opposing building is presented. The decrease of incoming direct solar radiation is shown. Conclusions. The developed graphic method is mathematically justified, has a practical orientation, which makes it relevant to the purpose and easy to use. The calculations for the presented method showed a significant decrease in the received direct solar radiation compared with the calculation without taking into account the influence of the opposing building, which shows the need to apply the method. The implementation of the method will contribute to an increase in the accuracy of calculations of direct solar radiation received on the facade and, therefore, the accuracy of calculations of energy consumption for heating and ventilation of the building.

DIRECT SOLAR RADIATION AND ATMOSPHERIC TURBIDITY IN MIKOŁAJKI IN THE YEARS 1971–1980 AND 1991–2000

The present study deals with the changing amount of incoming direct solar radiation and the optical state of the atmosphere in Mikolajki in the years 1971–1980 and 1991–2000. The highest level of solar irradiance in these two decades occurred on 23rd June 1977 and amounted to 1043.9 W·m-2. Compared to the first decade analysed, the percentage of the solar constant reaching the Earth in the second decade was higher. The spectral structure of the radiation also changed – the share of the shortest waves (λ<525 nm) increased, whereas the amount of waves with a wavelength of 710 nm or more decreased. In both study periods the annual course of solar extinction (expressed in terms of Linke’s turbidity factor) turned out to have been typical, with the highest values in summer and the lowest in winter. In the years 1991–2000, in all seasons, a lower atmospheric turbidity was observed in comparison with the years 1971–1980. The atmospheric turbidity was also analysed with relation to the air masses. In both decades in question the lowest turbidity occurred in arctic air masses and the highest in tropical air masses. An improved optical state of the atmosphere was observed in all considered air masses, though the biggest decrease in turbidity was found in polar air masses, particularly in the polar maritime old air ( T LAM2 dropped by 0.75) and polar continental air (by 0.70).

The role of shading devices to improve thermal and visual comfort in existing glazed buildings

Buildings with large glazed surfaces may show severe thermal and visual discomfort issues, as an effect of the large incoming direct solar radiation. In order to avoid excessive solar gains and glare issues to the occupants, it is necessary to adopt suitable solutions that limit the incoming solar radiation, such as highly reflective coatings or movable shading devices. However, such devices must be accurately selected, according to the building location and to the exposure of the glazed façades, while also taking into account possible regulatory measures. This paper evaluates the effectiveness of a series of shading devices applied to an existing office building in Southern Italy. The building shows large glazed surfaces and has no overhangs, thus significant thermal discomfort is perceived in summer by the occupants. The aim is to identify those solutions that allow to improve thermal comfort while also keeping a sufficient illuminance level indoors, without disregarding the compliance with Italian regulations about the installation of shading devices and, of course, the need to keep costs on a reasonable level. The analyses are repeated for different building orientations, in order to provide general information.

Non-parametric and least squares Langley plot methods

Abstract. Langley plots are used to calibrate sun radiometers primarily for the measurement of the aerosol component of the atmosphere that attenuates (scatters and absorbs) incoming direct solar radiation. In principle, the calibration of a sun radiometer is a straightforward application of the Bouguer–Lambert–Beer law V = V0e−τ ⋅ m, where a plot of ln(V) voltage vs. m air mass yields a straight line with intercept ln(V0). This ln(V0) subsequently can be used to solve for τ for any measurement of V and calculation of m. This calibration works well on some high mountain sites, but the application of the Langley plot calibration technique is more complicated at other, more interesting, locales. This paper is concerned with ferreting out calibrations at difficult sites and examining and comparing a number of conventional and non-conventional methods for obtaining successful Langley plots. The 11 techniques discussed indicate that both least squares and various non-parametric techniques produce satisfactory calibrations with no significant differences among them when the time series of ln(V0)'s are smoothed and interpolated with median and mean moving window filters.

Numerical modelling of mean radiant temperature in high-density sub-tropical urban environment

Outdoor thermal comfort has been a widely concerned issue in tropical and subtropical cities. In order to assess the conditions of outdoor thermal comfort, quantitative information on different spatial and temporal scales is required. This paper employs a numerical model (SOLWEIG – SOlar and LongWave Environmental Irradiance Geometry) to examine the spatial and temporal variations of mean radiant temperature (Tmrt), as an indicator of radiant heat load and outdoor heat stress in high-density sub-tropical urban environment in summer. The SOLWEIG model is found to simulate the six-directional shortwave and longwave radiation fluxes as well as Tmrt very well. Simulation results show that urban geometry plays an important role in intra-urban differences in summer daytime Tmrt. Open areas are generally warmer than surrounding narrow street canyons. Street canyons are sheltered from incoming direct solar radiation by shading of buildings while open areas are exposed to intense solar radiation, especially along the sunlit walls where high Tmrt is observed due to reflected short-wave radiation and long-wave radiation emitted from the sunlit building walls. The present study confirms that there are great potential in using urban geometry to mitigate high radiant heat load and daytime heat stress in the compacted urban environment. In high-density subtropical cities where high daytime Tmrt causes severe thermal discomfort in summer, dense urban structures are able to mitigate the extremely high Tmrt and improve outdoor thermal comfort. However, the shading strategy has to be cautious about air ventilation in such a dense urban environment.

Impact of Terrain and Cloud Cover on the Distribution of Incoming Direct Solar Radiation over Pakistan

This study investigates the spatial distribution of direct solar irradiation on rugged terrain over Pakistan. Digital elevation model (DEM), observational data of solar radiation from 6 meteorological observatories located in Pakistan and 5 meteorological observatories located in China were used in the present study. This conjunction is based on the same climatic conditions. MODIS Level-2 (L2) cloud fraction products and observational data of cloud cover from 21 meteorological observatories in Pakistan were incorporated to quantify the cloud cover influences on solar radiation amount and spatial distribution. The emerging field of remote sensing and GIS makes it possible to calculate solar radiation with finer spatial resolution and better understanding of terrain and cloud effects. ArcGIS with RS platform were used to simulate the model for direct solar radiation for the first time over Pakistan region. The results show clear quantitative influences of local topography and cloud cover on the DSR. Similarly, the area (east of Indus river) affected by monsoon receives less solar radiation during summer compared to the west of the Indus River.

Comparison of long‐term monitoring of temperature and precipitation between wetland and other ecosystems

AbstractAir temperature and precipitation changes in the decades 1961–2006 at Wet Meadows wetland ecosystem near Třeboň, South Bohemia were compared with the changes in these characteristics at other stations in the Czech Republic. Mean daily maximum air temperature measured during the vegetation growing season at wetland station Wet Meadows rose from 19·7 °C during the period 1961–1970 to 21·5 °C in the period 2001–2006 (i.e. 1·8 °C during 40 years). At Churáňov, a mountain forest station, this increase was from 14·7 to 15·8 °C (1·1 °C) and at Praha Ruzyně, a city station, the increase was from 20·0 to 20·7 °C (0·7 °C) during the same time. Mean number of precipitation days changed at Wet Meadows from 94·5 to 80·7 days per vegetation season, at Churáňov from 101·2 to 105·0 days per vegetation season and at Praha Ruzyně from 83·9 to 83·0 days per vegetation season during this time. We attribute the rise in temperature at Wet Meadows to a combined effect of climate change and a local change of the hydrological cycle. The disturbances in the short water cycle are attributed to the decrease in vegetation cover and the lack of water in the landscape. The consequent increase in the incoming direct solar radiation along with the rise in the heat coming into the area via precipitation as well as a decrease in and redistribution of precipitation events are considered major drivers of the meteorological changes that have resulted in the observed warming at Wet Meadows. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Direct Solar Radiation and Atmospheric Turbidity in Mikołajki in the Years 1971–1980 and 1991–2000

Abstract The present study deals with the changing amount of incoming direct solar radiation and the optical state of the atmosphere in Mikołajki in the years 1971-1980 and 1991-2000. The highest level of solar irradiance in these two decades occurred on 23rd June 1977 and amounted to 1043.9 W·m-2. Compared to the first decade analysed, the percentage of the solar constant reaching the Earth in the second decade was higher. The spectral structure of the radiation also changed - the share of the shortest waves (λ&lt;525 nm) increased, whereas the amount of waves with a wavelength of 710 nm or more decreased. In both study periods the annual course of solar extinction (expressed in terms of Linke’s turbidity factor) turned out to have been typical, with the highest values in summer and the lowest in winter. In the years 1991-2000, in all seasons, a lower atmospheric turbidity was observed in comparison with the years 1971-1980. The atmospheric turbidity was also analysed with relation to the air masses. In both decades in question the lowest turbidity occurred in arctic air masses and the highest in tropical air masses. An improved optical state of the atmosphere was observed in all considered air masses, though the biggest decrease in turbidity was found in polar air masses, particularly in the polar maritime old air (TLAM2 dropped by 0.75) and polar continental air (by 0.70).

The Non-Gravitational Perturbations impact on the BepiColombo Radio Science Experiment and the key rôle of the ISA accelerometer: direct solar radiation and albedo effects

The paper is focused on the estimate of the impact of the non-gravitational perturbations on the orbit of the Mercury Planetary Orbiter (MPO), one of the two spacecrafts that will be placed in orbit around the innermost planet of the solar system by the BepiColombo space mission. The key role of the Italian Spring Accelerometer (ISA), that has been selected by the European Space Agency (ESA) to fly on-board the MPO, is outlined. In the first part of the paper, through a numerical simulation and analysis we have estimated, over a time span of several years, the long-period behaviours of the disturbing accelerations produced by the incoming direct solar radiation pressure, and the indirect effects produced by Mercury’s albedo. The variations in the orbital parameters of the spacecraft, together with their spectral contents, have been estimated over the analysed period. The direct solar radiation pressure represents the strongest non-gravitational perturbation on the MPO in the very complex radiation environment of Mercury. The order-of-magnitude of this acceleration is quite high, about 10−6 m/s2, because of the proximity to the Sun and the large area-to-mass ratio of the spacecraft. In the second part of the paper, we concentrated upon the short-period effects of direct solar radiation pressure and Mercury’s albedo. In particular, the disturbing accelerations have been compared with the ISA measurement error and the advantages of an on-board accelerometer are highlighted with respect to the best modelling of the non-gravitational perturbations in the strong radiation environment of Mercury. The readings from ISA, with an intrinsic noise level of about \(10^{-9}\,m/s^{2}/\sqrt{Hz}\) in the frequency band of 3·10−5–10−1 Hz, guarantees a very significant reduction of the non-gravitational accelerations impact on the space mission accuracy, especially of the dominant direct solar radiation pressure.

Distributed estimation of incoming direct solar radiation over a drainage basin

Because of topographic variability, the global flux of incoming direct solar radiation over a drainage basin of high relief should be evaluated by grid modelling. Alternatively, line integration throughout the catchment boundary can be substituted for areal integration over the detailed three-dimensional representation of basin topography. This method is based on the Stokes' theorem and it yields a general and efficient solution, which can also account for shadowing effects. Application to three small mountainous catchments is reported for varying solar geometry and the performance of a lumped model is also examined. The approach can be applied to estimate the contribution of shortwave radiative fluxes to the processes of snowmelt and evapotranspiration at the basin scale.