Effect of fixed horizontal louver shading devices on thermal perfomance of building by TRNSYS simulation

Buildings in most countries around the world require large amounts of energy both for cooling and heating. In fact cooling loads due to solar gains represent about half of global cooling loads for residential as well as non-residential buildings. While solar gains through windows contribute largely to these loads, any method of decreasing these gains through shading should be applied with caution, since a balance is required; decreasing cooling loads by shading may increase heating loads drastically and vice versa. So the overall energy requirements both for heating and cooling should be considered. With this in mind a study was done on the thermal performance of a building by TRNSYS simulation, and a shading model for windows was incorporated in it. The shading devices adopted were external fixed horizontal louvers with different slat lengths and tilts. The study was conducted for four different cities in Italy. The optimization of the shading devices was done with respect to primary energy loads for the whole year, and the optimum design was found to depend on location and weather conditions. It was also found that shading factor varies with time of day and is different for summer and winter. For example, for Milan it was found that 70% of gain is cut off in summer, while only 40% is cut off in winter by using optimum shading, which is desirable.     

建筑表面太阳投影面积的数值计算研究

根据太阳运动模型和光学几何原理建立建筑外部遮阳设施动态遮阳效果分析的数学模型.利用该模型,建筑表面上的太阳投影面积可以由建筑地点、建筑几何形状确定.算例的计算结果表明,基于该数学模型的计算值与理论值相比差别很小.该模型对建筑表面太阳投影面积和太阳辐射得热的计算具有实际应用价值,并为动态遮阳效果的研究以及新型遮阳设备的研制提供理论依据.     

Overhang shading factor values for windows of general azimuthal angle evaluated under extraterrestrial and terrestrial conditions

An Erratum has been published for this article in International Journal of Energy Research 1999; 23(9):831. This article deals with assessing the differences between the values of the shading factors for windows with overhangs calculated under extraterrestrial and terrestrial conditions. It has been shown that the shading factor can be estimated under terrestrial conditions employing the available algorithms for the monthly average daily tilt factor for beam radiation. The present results have been validated by comparing with the values obtained by hour‐by‐hour calculations employing solar radiation data. The shading factor values evaluated under terrestrial conditions can differ by 25% compared to the extraterrestrial value for non‐south facing windows shaded by overhangs. Copyright © 1999 John Wiley & Sons, Ltd.     

Using a shading matrix to estimate the shading factor and the irradiation in a three-dimensional model of a receiving surface in an urban environment

In an urban environment, grid-connected building integrated photovoltaic (PV) systems can be subject to complex shading patterns. The study of the shadows projected by nearby buildings and other elements around a PV surface permits cutting down energy losses due to the module’s partial shading and improving the system’s performance ratio, so that the energy production costs can be lower. This paper presents a methodology that estimates the shading factor and irradiation on a three-dimensional model of a receiving surface in an urban environment. The main innovations introduced by this methodology are the building of a shading matrix composed by direct shading factor values around the whole sky dome and the analysis of the shading impacts on direct beam, isotropic diffuse, circumsolar diffuse and horizon brightening diffuse solar radiation components. The shading matrix improves the time spent on long simulation periods and permits an easy numerical integration over the sky to obtain the diffuse shading factors. Using this feature, a plug-in to the Google SketchUp three-dimensional modeling software was built to test this methodology. A series of similar results were obtained between actual measurements and estimates conducted by the plug-in.     

ShadingPlus—a fast simulation tool for building shading analysis

Shading system plays a significant role in reducing building energy demand. To analyse the performance of a shading system, traditional method is either conducting experimental tests for solar heat gain coefficient (SHGC) or through detailed energy simulation for energy saving during specific period. But no simulation tool is able to accomplish the two objectives at the same time, and the latter is always too detailed and cumbersome with traditional simulation tools. To help architects analyse the shading system in a more comprehensive and simple way, a fast simulation programme—ShadingPlus—is proposed and developed in this work. With EnergyPlus as its core simulation engine, ShadingPlus applies an optimal methodology to calculate SHGC. Moreover, annual energy saving calculation is also available with ShadingPlus which reflects shading system in a more realistic way. It is expected that the analysis for shading system can be greatly simplified using this tool. Case studies are also given to illustrate the way ShadingPlus works.     

Evaluation of overheating protection with sun-shading systems

Sun-shading systems have to provide thermal and visual comfort both reliably and economically. At the same time, they should prevent unwanted solar gains in summer and permit high solar gains in winter. This paper describes a method to assess the overheating protection offered by different types of sun-shading systems together with the associated control strategy.The objective of the new method is to provide a simple but reliable and realistic approach to evaluate the effectiveness of internal and external shading devices in combination with glazing, which is independent of the building type. The new method consists of the angle-dependent determination of the total solar energy transmittance, g, based on ray-tracing methods, which has been validated using calorimetric measurements. Combination with annual irradiance distributions allows for the evaluation of different control strategies. This paper shows that it is essential for the reliability of calculated cooling and heating loads, that the calculation is based on a control strategy, which reflects the priorities of the users of the building.     

SOMBRERO: A PC-tool to calculate shadows on arbitrarily oriented surfaces

Shaded areas of windows, solar thermal collectors or photovoltaic modules are of major importance for the calculation of solar heating- and cooling-loads of buildings as well as for the determination of thermal or electrical output of corresponding solar equipment. SOMBRERO, a PC-program written in Turbo-Pascal, calculates the GSC (geometrical shading coefficient), the proportion of shaded area of an arbitrarily oriented surface surrounded by shading elements as a function of time and location. Shading elements are treated as polygons (not necessarily rectangles) located in a plane and can be combined to bodies such as buildings or trees. They may also represent overhangs and side-wings of the building under consideration. Elements which are far away from the receiver area are treated as horizontal shading profiles. The reduction of (isotropic) diffuse radiation caused by different kinds of obstacles is calculated by means of view-factors. Calculated results of the GSC are stored in ASCII-format and can be used as an input for dynamic solar system simulation programs. This is demonstrated in two illustrative examples showing the coupling of SOMBRERO with SUNCODE and TRNSYS in order to calculate the effects of shading on passive solar heating and passive cooling, respectively.     

Simulation for an optimal application of BIPV through parameter variation

The degree of efficiency of Building Integrated Photovoltaic (BIPV) as a shading device and the variation of the electrical power generation over 1 year in a real building has already been experimentally investigated in my earlier research. In this paper, the influence of the angle of the solar cell panel, albedo of earth, building azimuth, and of solar cell panels under shading on the power generation are theoretically studied to further optimize BIPV implementation. For the validation of the theoretical work, experimental results of the Samsung Institute of Engineering and Construction Company building are used with a wind velocity of the weather data (TRY, test reference year) of Suwon area, Korea. The efficiency of the BIPV system as a shading device was compared at different months. In this work, the simulation program SOLCEL, for the calculation of a shading/sunlit area on solar cell module and facade, surface temperature of solar cell module, effective solar irradiance on solar cell module and the power generation of a BIPV as a shading device, was developed and validated. The SOLCEL can be applied to develop a multi functional Building Integrated Photovoltaic which could improve power generation, thermal comfort, natural lighting, cooling and heating, etc.     

Assessment of fixed shading devices with integrated PV for efficient energy use

The use of external fixed shading devices to adjust solar influx radiation and to save energy is well known. However, fixed shading devices can reduce daylight availability, increase artificial light needs and block the beneficial winter solar radiation.This paper is part of a research on the characteristics of the optimum shading device. The aim is to investigate the balance between the energy needs for heating and cooling the space that the shading device is used for and the energy that is used for lighting the same space and the energy that the shading device can produce.In order to investigate the balance between the above mentioned parameters, thirteen types of fixed shading devices have been studied and categorized according to their energy performance, for a single occupant office room. The same office room is tested for two different Mediterranean latitudes in Athens and in Chania, Crete in Greece and for two different south facing windows’ sizes.The thermal behavior of the devices is assessed through computer simulation application and the daylight analysis is assessed with both computer simulation and physical modeling. Stable parameters were the internal loads in the office room, the south orientation of the façade and the type of glazing. Variable parameter was the type of the fixed shading device.The study shows that all shading devices with integrated south facing PV can efficiently produce electricity which may be used for lighting. The study highlights the fact that shading devices such as Surrounding shading, Brise–Soleil full façade and Canopy inclined double work efficiently against thermal and cooling loads and may be used to produce sufficient electricity and control daylight. The study defines the geometrical parameters that will be incorporated to the overall characteristics of the optimum fixed shading device and proposes new fields of development for the BIPV technologies.     

The impact of shading design and control on building cooling and lighting demand

Shading should be considered as an integral part of fenestration system design for commercial and office buildings, in order to balance daylighting requirements versus the need to reduce solar gains. In this paper, the simultaneous impact of glazing area, shading device properties and shading control on building cooling and lighting demand was calculated using a coupled lighting and thermal simulation module. The interactions between cooling and lighting energy use in perimeter spaces were evaluated as a function of window-to-wall ratio and shading parameters. An exterior roller shade was used as an example. The impact of shading device type, properties and control on building cooling and lighting energy demand was quantified and analyzed. The simulation results indicate that, if an integrated approach for automatic control of motorized shading is used in conjunction with controllable electric lighting systems, substantial reduction of energy demand for cooling and lighting could be achieved in perimeter spaces, depending on climatic conditions and orientation.     

Hot-cool box calorimetric determination of the solar heat gain coefficient and the <Emphasis Type="Italic">U</Emphasis>-value of internal shading devices

In several developing countries, energy performance rating programs are currently in progress. Complex fenestration systems (CFS) are building components that play a key role in reducing energy consumption. The development and testing of equipment is central for beginning the energy efficiency rating process of complex glazing systems in these countries. This paper validates the use of a low-cost hot-cold box calorimeter for measurement of the solar heat gain coefficient (SGHC) and overall heat transfer coefficient (U-value) of interior shading systems. This work aims to determine the energy performance of three types of often employed shading systems: solar control films, interior horizontal venetian blinds, and indoor drapery curtains. Results show that the energy performance of solar shading devices studied depends on both their morphological and optical properties. The shading systems analyzed present similar U-values, where technological features are represented by the thickness and the thermal conductivity of the material. SHGC is mainly defined by the transmittance and, to a lesser extent, the absorptance of the systems, which differ significantly according to the analyzed shading device. The three types of curtains analyzed demonstrate an SHGC dependent on the fabrics openness factor: jacquard curtains (openness factor 0.05) present a SHGC of 0.7, whereas organza curtains (openness factor 0.45) have a SHGC of 0.82. The SHGC of the venetian blinds analyzed varies on average 36% according to the slat tilt (0°–45°). The solar control films examined modify their solar gain according to their spectral selectivity.     

Seasonal shading of vertical south-facades with prismatic panes

Using prismatic panes, a seasonal shading responsive to the Sun's position can be realized. Thus the solar gains from direct radiation can be closely matched to the annual pattern of the heating energy requirements of buildings. The panes are suitable for window or facade elements, preferably in applications which do not need a clear view, and especially in front of transparently insulated solar walls. The direct radiation received on a vertical south-facade is reduced to 10% on clear summer days, while 90% is transmitted on clear winter days.     

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.     

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.     

Simulation of façade and envelope design options for a new institutional building

This paper presents a simulation case study of façade and envelope preliminary design options for the new Engineering building of Concordia University in Montreal. A major principle of the analysis was to create a high quality building envelope in order to optimally control solar gains, reduce heating and cooling energy demand and reduce electricity consumption for lighting, while at the same time maintain a comfortable and pleasant indoor environment. The stated approach of the design team was to aim for an energy-efficient building, employing innovative technologies and integrating concepts such as daylighting and natural ventilation. Detailed energy simulations were therefore performed from the early design stage, in order to present recommendations on the choice of façade, glazings, shading devices, lighting control options, and natural ventilation. Integrated thermal studies, a daylighting analysis and the impact of the above on HVAC system sizing were considered. Simulation results showed that, using an optimum combination of glazings, shading devices and controllable electric lighting systems, the energy savings in perimeter spaces can be substantial. Perimeter heating could be eliminated if a high performance envelope is used. The building is currently being commissioned.     

基于并联光伏组件外特性的最大功率点跟踪方法

当阴影条件变化时,并联光伏组件的全局最大功率点(MPP)会随之改变.为了实现太阳能发电最大化,要求最大功率点跟踪(MPPT)方法始终能实时而准确地锁定住并联光伏组件的全局MPP.不同阴影条件下并联光伏组件会呈现不同的外特性特征,如多阶梯的电流电压特性以及多峰值的功率电压特性.基于此现象,该文提出一种基于并联光伏组件外特...     

Solar radiation calculation methodology for building exterior surfaces

The present article shows a new methodology of calculation of the direct, diffuse and reflected incident solar radiation, in all type of surfaces, either in open urban environments or inside buildings. This methodology is applicable in problems related to solar access (space heating in buildings, shadowing of open spaces), solar gains (space cooling in buildings), and daylighting. Solar radiation is the most important contribution to the surface and volumetric energy balance during the daytime. Particularly, solar radiation is the main contributor to heat gains in buildings, especially in residential buildings, where internal gains are very low. Utilization of daylight in buildings may result in significant savings in electricity consumption for lighting while creating a higher quality indoor environment. Additional energy savings may also be realized during cooling season, when reduction of internal heat gains due to electric lighting results in a corresponding reduction of cooling energy consumption.The analysis of the existing calculation methods and proposed in the scientific bibliography for the calculation of the solar radiation in problems of solar access in winter, solar gains in summer, and daylighting, takes us to the necessity of outlining a new and complete methodology. This new methodology is applicable to all these problems with a great accuracy and calculation speed.     

Comprehensive review and performance evaluation of maximum power point tracking algorithms for photovoltaic system

A photovoltaic array is environmentally friendly and a source of unlimited energy generation. However, it is presently a costlier energy generation system than other non-renewable energy sources. The main reasons are seasonal variations and continuously changing weather conditions, which affect the amount of solar energy received by the solar panels. In addition, the non-linear characteristics of the voltage and current outputs along with the operating environment temperature and variation in the solar radiation decrease the energy conversion capability of the photovoltaic arrays. To address this problem, the global maxima of the PV arrays can be tracked using a maximum power point tracking algorithm (MPPT) and the operating point of the photovoltaic system can be forced to its optimum value. This technique increases the efficiency of the photovoltaic array and minimizes the cost of the system by reducing the number of solar modules required to obtain the desired power. However, the tracking algorithms are not equally effective in all areas of application. Therefore, selecting the correct MPPT is very critical. This paper presents a detailed review and comparison of the MPPT techniques for photovoltaic systems, with consideration of the following key parameters: photovoltaic array dependence, type of system (analog or digital), need for periodic tuning, convergence speed, complexity of the system, global maxima, implemented capacity, and sensed parameter(s). In addition, based on real meteorological data (irradiance and temperature at a site located in Addis Ababa, Ethiopia), a simulation is performed to evaluate the performance of tracking algorithms suitable for the application being studied. Finally, the study clearly validates the considerable energy saving achieved by using these algorithms.     

Daylighting and energy analysis of private offices with automated interior roller shades

This paper presents a comprehensive analysis to study the balance between daylighting benefits and energy requirements (control of solar gains) in perimeter private office spaces with interior roller shades taking into account glazing properties, shading properties and control together with window size, climate and orientation in an integrated daylighting and thermal manner. Daylight autonomy and useful daylight illuminances were computed as a function of façade design parameters. A thermal simulation module using the explicit finite difference thermal network approach runs at the same time step and calculates heating, cooling and lighting source energy consumption as well as surface temperatures and operative temperature. Based on the daylighting results, lighting internal gains (continuous dimming control) are simultaneously input to the thermal module. The model also considers the air in the gap between shade and interior glass as a separate thermal node.Detailed results for Chicago and Los Angeles showed that windows with visible transmittance higher than 50% have the ability to allow enough daylight into the space for all locations and orientations for window-to-wall ratios higher than 50%. Useful daylight illuminances between 500 and 1000 lux were considered in detail – it was found that this index can be maximized for specific window-to-wall ratios and that depends on the glazing properties and fabric properties for each orientation. Moreover, the complex interactions of the studied parameters and their impact on the heating, cooling and lighting energy performance revealed an interesting result: windows occupying 30–50% of the façade can actually result in lower total energy consumption for most cases with automated shading. This illustration of daylighting benefits can be realized only if the integration of daylighting and thermal climate-based analysis is modeled efficiently and depends on glazing and shading properties and control. Finally, best designs for each orientation and location were pointed out based on both daylighting and thermal results.     

Building cluster and shading in urban canyon for hot dry climate: Part 2: Shading simulations

Under low latitude conditions, minimisation of solar irradiance within the urban environment may often be an important criterion in urban design. This can be achieved when the obstruction angle is large (high H/W ratio, H=height, W=width). Solar access to streets can always be decreased by increasing H/W to larger values.It is shown in this paper that the street canyon orientation (and not only the H/W ratio) has a considerable effect on solar shading and urban microclimate. The paper demonstrates through a series of shading simulation and temperature measurements that a number of useful relationships can be developed between the geometry and the microclimate of urban street canyons. These relationships are potentially helpful to assist in the formulation of urban design guidelines governing street dimensions and orientations for use by urban designers.