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.     

Simplified architectural method for the solar control optimization of awnings and external walls in houses in hot and dry climates

In extremely hot and dry climates, like northwestern Mexico, solar gain reduction in houses using solar passive techniques is important for improving comfort inside the construction and to save costs in electrical cooling during the whole year, because the winter season is also hot in those regions. A new one-dimension method is proposed to analyze the interaction between two common shading devices: awnings and external walls to reduce insulation on the facade and inside the house due to fenestration. The method is demonstrated by optimizing a typical dwelling with an azimuth of 90° (east), which, achieves 45% reduction in direct solar insulation during the summer solstice on the profile of the facade. Results showed that this method is simple and reliable in increasing the shadow on the facade and to block completely the solar beam radiation on the windowpane with optimal relations between these shading devices.     

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.     

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.     

Prospects for solar cooling – An economic and environmental assessment

Producing refrigeration and/or air conditioning from solar energy remains an inviting prospect, given that a typical building’s cooling load peaks within 2 or 3 h of the time of maximum solar irradiation. The attractiveness of “free” cooling obtained from the sun has spawned a wealth of research over the last several decades, as summarized in a number of review articles. Obstacles—especially high initial costs—remain to the widespread commercialization of solar cooling technologies. It is not clear at the present time if thermally driven systems will prove to be more competitive than electrically driven systems. We therefore describe a technical and economic comparison of existing solar cooling approaches, including both thermally and electrically driven. We compare the initial costs of each technology, including projections about future costs of solar electric and solar thermal systems. Additionally we include estimates of the environmental impacts of the key components in each solar cooling system presented. One measure of particular importance for social acceptance of solar cooling technologies is the required “footprint,” or collector area, necessary for a given cooling capacity. We conclude with recommendations for future research and development to stimulate broader acceptance of solar cooling. The projections made show that solar electric cooling will require the lowest capital investment in 2030 due to the high COPs of vapor compression refrigeration and strong cost reduction targets for PV technology.     

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.     

上海某图书馆建筑内外遮阳负荷研究

针对上海某图书馆建筑内外遮阳,采用计算法进行负荷计算,通过结果分析得到此图书馆在计算时刻下的日最大负荷值。从中可以看出除北向外,外遮阳都有不同程度的节能效果,而北向由于窗口不受太阳直射,没有遮阳效果;内遮阳的节能效果都随着材料的遮阳系数增加而增加。最后进行内外遮阳效果的对比,得到东、西向随遮阳板挑出长度增加,外遮阳节能效果更为显著;南向和北向以遮阳材料系数为0．5的内遮阳为佳。     

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.     

Analytic model for passively-heated solar houses—1. Theory

A simple analytic method for the prediction of the long-term thermal performance of passively-heated solar houses is presented. The treatment includes a new coarse method for “energy bookkeeping” and the use of a distribution function which represents the frequency of occurrence of different values of the solar load ratio. Due to its generality, this formalism is applicable to any passive heating element. As specific examples, the cases of direct gain and water wall houses are treated in detail. Relative to the parameterization of computer simulation results, this method offers the user a design tool that can be used to predict, in closed form, the thermal effect on the house of different building and climatic parameters and is not restricted to a “reference” building. Agreement with published numerical simulation results in satisfactory. The presentation is divided into two separate papers: a users guide for the reader who may not be interested in the details of derivation and validation, and the present paper, in which the theory is presented in detail.     

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.     

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.     

External window shading treatment effects on internal environmental temperature of buildings

External shading treatment affects the solar energy incident on a window, and the energy deposited in the room through the window. Since the temperature in a room is dependent on how much solar energy goes into or is lost from the room through the fenestration areas, the walls, roofs and other enclosing surfaces, it would be expected that the modifying effect of an external shading treatment does also affect the inside temperature. This paper presents the procedure for determining such an effect. Two numerical examples are presented. Using the procedure, the inside environmental temperatures for windows with different external shading treatments are studied. The results indicate that the temperature drops with increasing shading depths. The results also show that reveals are by far the most effective shading treatment in the tropics followed by over-hangs. Vertical side-fins are seen to be least effective.     

建筑外窗热工性能对空调能耗与节能的影响分析

利用建筑环境模拟软件DeST-c,对广州某办公建筑外窗热工性能对空调能耗的影响进行了计算,计算结果表明减小外窗遮阳系数能显著降低空调能耗,当遮阳系数从0.9减小至0.2时空调耗冷量可降低26%;而外窗传热系数对空调能耗影响较小.并通过对全年逐时空调节能率进行分析,研究了遮阳系数影响空调能耗的机理,发现遮阳系数减小引起较...     

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 XXI building: Proof of concept or a concept to be proved?

Solar XXI building is a low energy office building where passive and active solar strategies have been applied to reduce the use of energy for heating, cooling and lighting, combining also an extensive photovoltaic façade for electricity production. Solar XXI opened in 2006 and is considered a high efficient building, close to a net zero energy building (NZEB), where the difference between the energy consumed and that produced is 1/10^th of the energy consumed by a Portuguese standard new office building. Its design includes many energy efficiency concepts, such as a high insulated envelope, south sun exposure, windows external shading, photovoltaic panels heat recovery, ground-cooling system, daylighting, stack effect and cross ventilation. The solar gains of the windows and the effectiveness of shading devices were evaluated in order to correlate solar radiation, external and indoor air temperatures. It was also verified that amplitude-dampening of ground-cooled air ranged between 5 and 8 °C, following the trend of the analytical solution for heat diffusion of a cylindrical air/soil heat-exchanger.     

Solar hybrid cooling system for high-tech offices in subtropical climate – Radiant cooling by absorption refrigeration and desiccant dehumidification

A solar hybrid cooling design is proposed for high cooling load demand in hot and humid climate. For the typical building cooling load, the system can handle the zone cooling load (mainly sensible) by radiant cooling with the chilled water from absorption refrigeration, while the ventilation load (largely latent) by desiccant dehumidification. This hybrid system utilizes solar energy for driving the absorption chiller and regenerating the desiccant wheel. Since a high chilled water temperature generated from the absorption chiller is not effective to handle the required latent load, desiccant dehumidification is therefore involved. It is an integration of radiant cooling, absorption refrigeration and desiccant dehumidification, which are powered up by solar energy. In this study, the application potential of the solar hybrid cooling system was evaluated for the high-tech offices in the subtropical climate through dynamic simulation. The high-tech offices are featured with relatively high internal sensible heat gains due to the intensive office electric equipment. The key performance indicators included the solar fraction and the primary energy consumption. Comparative study was also carried out for the solar hybrid cooling system using two common types of chilled ceilings, the passive chilled beams and active chilled beams. It was found that the solar hybrid cooling system was technically feasible for the applications of relatively higher cooling load demand. The annual primary energy consumption of the solar hybrid cooling system was lower than that of the conventional vapour compression refrigeration system up to 36.5%. Between the two options of chilled ceilings, the passive chilled beams were more energy-efficient to work with the solar hybrid cooling system in the hot and humid climate. Harnessing solar energy for driving air-conditioning would help in reducing the carbon emission, hence alleviating the climate change.     

Computer simulation of solar cooled buildings in Khartoum

The transient state heat transfer formulation has been used to determine the air conditioning cooling load for two selected one room buildings in Khartoum: one made from brickwork and the other from wood. This formulation has been achieved by applying an explicit finite difference numerical techniques and adopting thermal network of electrical analogy to solve the transient conduction heat transfer equations. A computer program was developed to analyse the thermal network and to determine the cooling load for the wall, roof, window, ventilation and the total cooling load for each building for a typical hot summer day in Khartoum.A solar cooling system comprising mainly of a flat plate solar collector, a Lithium Bromide-Water absorption air conditioner, a storage and auxiliary tanks was integrated in the building and the energy equation for each component was obtained. A general simulation program for the solar cooled buildings has been developed and it was found that about 65% of the total cooling load demanded by the brick building could be supplied by energy from the solar collector, the other 35% portion had to be met by the auxiliary tank compared with 70% of the total cooling load demanded by the wood building which could be supplied by energy from the solar collector.     

General model to build awnings and external walls with optimum shading interaction

A general model is proposed to optimize the shading interaction between an awning and an external wall that project shadows on the facade of a construction. The original method was presented by the authors in Renewable Energy 28 (2003): 111, for a particular shading proposal. They emphasize the advantage of a one-dimensional approach to solve the problem of this interaction, analyzing the shadows projected by these elements from a side view. The generalized method, presented in this paper, is useful for architects to design shelter projects with more alternatives in the use of such shading devices. The general model also permits study and evaluation of any strategy chosen by the builder to shadow a facade, with an emphasis on windowpane shading, through graphical outputs of the solar performance.     

Systematic comprehensive techno-economic assessment of solar cooling technologies using location-specific climate data

A methodology for assessing solar cooling technologies is proposed. The method takes into account location specific boundary conditions such as the cooling demand time series, solar resource availability, climatic conditions, component cost and component performance characteristics. This methodology evaluates the techno-economic performance of the solar collector/chiller system. We demonstrate the method by systematic evaluation of 25 feasible combinations of solar energy collection and cooling technologies. The comparison includes solar thermal and solar electric cooling options and is extended to solar cooling through concentrated solar power plants. Solar cooling technologies are compared on an economic and overall system efficiency perspective. This analysis has implication for the importance of solar load fraction and storage size in the design of solar cooling systems. We also stress the importance of studying the relation between cooling demand and solar resource availability, it was found that overlooking this relation might lead to overestimations of the potential of a solar cooling system in the range of 22% to over 100% of the actual potential.     

An empirical validation of modeling solar gain through a glazing unit with external and internal shading screens

Empirical validations are integral components in assessing the overall accuracies of building energy simulation programs. Two test cell experiments were performed at the Swiss Federal Laboratories for Material Testing and Research’s (EMPA) campus in Duebendorf, Switzerland to evaluate the solar gain models with external and internal shading screens in four building energy simulation programs including: (1) EnergyPlus, (2) DOE-2.1E, (3) TRNSYS-TUD, and (4) ESP-r. Detailed information about the shading screen properties, modeling procedures, and thorough statistical and sensitivity analyses of simulation results are provided. For the external shading screen experiment, the mean percentage of the absolute difference between measured and simulated cooling power to maintain a near-constant cell air temperature for EnergyPlus, DOE-2.1E, TRNSYS-TUD and ESP-r were 3.7%, 5.5%, 10.6%, and 7.5%, respectively. EnergyPlus and DOE-2.1E were considered validated within 95% credible limits. For the internal shading screen experiment, the mean percentage of the absolute mean differences for EnergyPlus, DOE-2.1E, TRNSYS-TUD, and ESP-r were 6.7%. 13.8%, 5.7%, and 4.3%, respectively; only ESP-r was considered validated within 95% credible limits.