Solar Gain Factor Research Articles

Time-dependent solar aperture estimation of a building: Comparing grey-box and white-box approaches

This paper proposes a B-splines integrated method combining in-situ data with grey-box modeling to estimate buildings' dynamic solar gain more efficiently than the conventional white-box model and much more precisely than the classic grey-box model. Solar gain, referring to the overall indoor energy gain supplied by solar radiation, plays a vital role in the indoor energy balance. Estimating dynamic solar gain precisely is essential to building energy optimization, e.g., in model predictive control. However, in almost all existing grey-box modeling works, a constant solar gain factor (solar aperture; gA) is assumed to estimate dynamic solar gain, which almost certainly will result in solar gain prediction errors, especially in buildings with unevenly distributed windows. To fill this gap, this study presents an advanced B-splines integrated grey-box model, using customized B-splines to advance the constant gA assumption toward its nature of time-dependence and precisely characterize the dynamic solar gain conclusively. On-site measured datasets of a portable site office (PSO) representing a ‘simplified’ building, under two scenarios with windows fully or partially uncovered, serve as test cases. To verify the physical interpretation of outcomes estimated by the proposed method, based on the said test cases, the proposed B-splines integrated grey-box model is compared with a classic white-box simulation. It is concluded that the proposed method can reveal the main trends and key dynamic features of solar gain very well, but still has some limitations of quantifying ‘local’ details with acceptable variations. Nevertheless, given that the proposed method merely asks for a very limited amount of low-frequency data, the proposed method is considered as a much more effective alternative to the classic white-box simulation approach, which requires massive and often hard-to-collect input data.

A Proposed Methodology for retrofit the Efficiency of Facades of High Educational Buildings in Egypt

A Proposed Methodology for retrofit the Efficiency of Facades of High Educational Buildings in Egypt

Statistical analysis of 200 digital twins for thermal load of Swiss buildings created from smart grid monitoring data

Exploiting thermal inertia of buildings as flexibility for the electric grid requires information about thermal dynamics in the system. The presented paper proposes a new method to create digital twins based on smart meter monitoring data and has been applied to 200 Swiss residential buildings. The statistical analysis of these heat pump based heating systems shows expected distributions of key parameters such as heat losses, solar gain factors and thermal capacities. Regional comparisons for crucial building parameters have been carried out and the remote identification of potential renovation candidates has shown promising results.

Semi-parametric modelling of sun position dependent solar gain using B-splines in grey-box models

Modelling the effects of solar irradiation plays an important role in various applications. This paper describes a semi-parametric (combined grey-box and spline-based), data-driven technique that can be used to model systems in which the solar gain depends on the sun position. The solar gain factor is introduced, i.e. the absorbed fraction of measured solar irradiation, and estimated as a continuous non-parametric function of the sun position. The implementation of the spline-based solar gain factor in a grey-box model framework is described. The method is tested in two case studies—in a model of the internal temperature of a dwelling in Aalborg, Denmark, and a model of the return temperature of a solar collector field in Solrød, Denmark. It is shown that the solar gain factor as a function of sun position is able to account for structural variations in solar gain that may occur due to factors such as shading obstacles and window or absorber orientation. In both test cases, the spline-based solar gain function improved the model accuracy significantly, and largely reduced structural errors in prediction residuals. In addition, the shape of the estimated function provided insight into the dynamics of the system and the local solar input characteristics. Accurate representation of such site characteristics was not possible with any data-driven method found in the literature. Besides the grey-box models used in this study, the solar gain factor can be used in a variety of data-driven models, for example in linear regression models.

Implementation of a multi-criteria and performance-based procurement procedure for energy retrofitting of facades during early design

Decisions taken during the early design of facade retrofits have a major influence on the final performance of buildings. However, current procurement procedures do not promote the evaluation of how facade systems design affects the overall building performance, which includes energy efficiency, comfort, cost and their complex interactions. Tenders are commonly based on single values which describe single properties of façade components like thermal transmittances and solar gain factors and do not consider interrelation between these components, the dynamic behavior of buildings and specific local climate. This paper presents a concept to drive public procurement processes based on overall building performance criteria. The methodology is operationalized by a user-friendly tool (FIT) predicting the overall performance according to façade design variations. These performance criteria are integrated into tenders by calculating a total score for every design proposal. This approach sensitizes designers and contracting authorities to consider the overall performance of a façade from the very early design and helps in making informed design decisions. An application in a simulated case study of a public school building shows its potential to guide public procurement processes and that further research and validation in actual procurement procedures is needed.

Design, Fabrication and Performance Evaluation of Awning/Canopy for Thermal Comfortability

This paper presents the design, fabrication and performance evaluation of retractable awning/canopy system for thermal comfortability. It consists of frame (mild steel bars), linear actuator, fabric (acrylic), adapter, roller pathways and photo sensor (for easiness of control). After fabrication and coupling of the whole components of the retractable awning system, it was connected to the adapter and power source for performance test evaluation. It was observed that, the actuator arm which was coupled to the fabric began projecting outward and once the photo sensor was shaded from sunlight using a dark material, the fabric retracted into the roller. Also a reduced solar heat gain factor of 28.16 W was achieved by shading the window compared to the solar gain factor of 498.54 W before shading with a cooling load of 415.37 W. This can be incorporated into building plans especially those at the sunheating direction and tropical region to reduce inner-house temperature air-conditioner loading for longer life and efficient operation.

Experimental Determination of Optical and Thermal Properties of Semi-transparent Photovoltaic Modules Based on Dye-sensitized Solar Cells

The demand for energy efficiency of buildings and on-site electricity production is rising. Building integrated photovoltaic can provide a part of the electricity demand. Many studies are related to the module efficiency. However, architectural integration, optical and thermal properties also require attention. Semi-transparent modules are especially interesting for architectural integration in the glazed part of the façade. Dye sensitized solar cells, offering color and semi-transparency, are in the process of market introduction. However, dye-sensitized solar cells are fragile and there are not many examples of architectural integration due to the technical challenge of introducing these cells in a glazing. A glazing containing colored photovoltaic modules could be used to design an active façade.In order to determine the thermal behaviour of the building, the precise optical and thermal properties of the used materials need to be known. Performances of semi-transparent photovoltaic modules based on dye-sensitized solar cells were investigated. These modules come from the same manufacturer, using the same technology. However, they differ in terms of shades and nuances. Common practice is to indicate optical properties at normal angle of incidence. Yet, for most latitudes, the properties for a large range of angles of incidence are more relevant. Therefore, the spectral transmittance and the reflectance were measured at 12 angles of incidence ranging from 0° to 75°. From these data, the solar direct transmittance τe, the solar direct reflectance ρe and the visible transmittance τv and selectivity were calculated.The solar gain factor was determined on a prototype double glazing under illumination with a solar simulator by measuring the temperatures of the external and inner surface of the product. Combined with the values of absorptance obtained from the transmittance and reflectance values, this measurement allows us to determine the internal heat transfer coefficient qi and thus the solar gain factor of the double glazing (also called total energetic transmittance or g-value).Final performance of a façade containing these modules will depend on the composition of the double glazing in which they will be laminated. The performance of the module itself will help to determine the best composition for each climate. For instance, a solar protection coating may be needed. The modules can be laminated to a glass pane and then be assembled in a double glazing. Therefore the architectural integration is facilitated and compatible with existing façade systems. In highly glazed building, a part of the façade could then be a photovoltaic façade and deliver a fraction of the energy demand while providing colourful options to enhance the aesthetic of the building.

Energy Retrofit of Historical Buildings Based on Windowed Elements

The study of the building energy performance is based on simplified procedures that estimates the energy demand using monthly values of environmental parameters. It is well known that it is possible to use advanced dynamic softwares able to analyze the real building’s behavior along time. For this reason in this study a historical building energy retrofit has been performed through a dynamic software considering the influence of different kind of windowed elements on the annual energy demand. Four simulations, taking into account transparent elements characterized by progressively improved properties of thermal transmittance and solar gain factor, have been performed. The results obtained have been analyzed and compared.

Building energy performance analysis: A case study

International standards, in particular the Italian one, evaluate buildings energy performance assuming steady-state working conditions: currently, the study of the energy performance of buildings is based on a simplified calculation that estimates the energy demand using monthly or seasonal average outdoor temperatures. For this reason we have conducted a comparative analysis of the energy performances of an old building using a semi-stationary software and a dynamic one. The studied building is placed in the peripheral part of an historical city located in the center of Italy. We have performed three simulations considering transparent elements characterized by progressively improved properties of thermal transmittance and solar gain factor. A comparison between the outputs of the two codes, in order to highlight the different ways of evaluating the energy contributions to annual energy demand, has been performed. Finally, the models were validated by means of an in-situ measurement campaign using a heat flow meter – in order to measure the thermal transmittance of the opaque walls – and a thermographic camera. This modus operandi allowed us to appreciate how the use of a dynamic software is essential to deal with the inertial properties of the structure and to calculate in an accurate way the annual energy demand.

Buildings Energy Efficiency: Interventions Analysis under a Smart Cities Approach

Most of the world’s population lives in urban areas and in inefficient buildings under the energy point of view. Starting from these assumptions, there is the need to identify methodologies and innovations able to improve social development and the quality of life of people living in cities. Smart cities can be a viable solution. The methodology traditionally adopted to evaluate building energy efficiency starts from the structure’s energy demands analysis and the demands reduction evaluation. Consequently, the energy savings is assessed through a cascade of interventions. Regarding the building envelope, the first intervention is usually related to the reduction of the thermal transmittance value, but there is also the need to emphasize the building energy savings through other parameters, such as the solar gain factor and dye solar absorbance coefficients. In this contribution, a standard building has been modeled by means of the well-known dynamic software, TRNSYS. This study shows a parametrical analysis through which it is possible to evaluate the effect of each single intervention and, consequently, its influence on the building energy demand. Through this analysis, an intervention chart has been carried out, aiming to assess the intervention efficiency starting from the percentage variation of energy demands.

LRT Digest 2 Tubular daylight guidance systems

Executive summaryThis Digest concerns passive tubular daylight guidance systems (TDGS), the most commercially successful method of daylight guidance. TDGS were introduced some 20 years ago and thus...

An Integrated Approach for an Historical Buildings Energy Analysis in a Smart Cities Perspective

Currently, the study of the energy performance of buildings is based on a simplified calculation that estimates the thermal loads using monthly or seasonal average outdoor temperatures. In addition, the employed software require technical data such as the specific heat capacity of materials, but at the same time they are not able to properly consider the thermal inertia of buildings. The more precise evaluation allows to assess the correct interventions for energy requalification under a smart cities perspective. This study was performed considering a stationary software (Aermec MC11300) and a dynamic software (TRNSYS). Three simulations considering transparent elements characterized by progressively improved properties of thermal transmittance and solar gain factor have been performed. It has been performed a comparison between the outputs of the two software in order to highlight the different ways of evaluating the energy contributions on thermal loads. Finally, the models were validated by means of an in-situ measurement campaign using a heat flow meter - in order to measure the thermal transmittance of the opaque walls - and a thermographic camera. This modus operandi allowed to appreciate how the use of a dynamic software is more appropriate to deal with the inertial properties of the structure to calculate in a more detailed way the annual thermal loads and to obtain more information on individual heating zones.

Bus for Urban Public Transport: Energy Performance Optimization

Nowadays many people use public transports in urban centers. Consequently, every day a lot of buses move within cities, trying to ensure the best service to citizens. During the year buses become crowded places and using an air conditioning system in constant operation, it tries to ensure a certain condition of comfort for the passengers on board. The aim of this study is to analyze and optimize the energy performance of a bus shell, identifying practical solutions have not yet been adopted in order to reduce the impact of air conditioning on bus’ consumption and, therefore, on air pollution. For this reason it was decided to conduct a thermal analysis of a bus for public transport, in order to understand the behavior of the bus shell and to deduce possible optimization measures that have not yet been made until now. The analysis was carried out considering the hottest day of July and the coldest day of January, considering the operating conditions based on the most common graphics TGM (Average Daily Traffic) able to define the concentration of traffic city during the 24hours per day. The study was done using the dynamic simulation software TRNSYS. With this software it was possible to recreate faithfully the structure of the bus and the external environmental conditions, assessing the impact of different technical solutions for an improvement of internal conditions and a reduction of the cooling capacity required. As the presence of passengers on public transport are considered like a “benefit” during the winter, the analysis is started with the identification of a summer solution and the subsequent evaluation of this solution for the winter time. The aim of this study was to optimize the bus shell and select the most appropriate solutions. Regarding the transparent surfaces it has been given importance to factors such as the thermal transmittance and the solar gain factor (g-value). Aware of the influence given by the solar radiation on the energy loads, bus energy performance were simulated also considering different types of paintwork with high reflectance.

Application of U and g values for sizing passive heating concepts

The concept of solar gain factor and the overall heat loss coefficient, obtained for solar passive heating concepts, has been extended to size these as building elements for different climatic conditions. As an example, India's four climatic zones where winter heating is required have been selected and the required area of passive heating concepts calculated by a steady-state analysis applied to a single zone building. The size of various concepts expressed as percentages of the south wall area are independent of the building size as confirmed for the case of army shelters in cold and sunny conditions of Laddakh in northern India. For a building with capacity effects in walls and roof, the dynamic simulation confirms the values of room temperature at a comfortable level assumed to be 18.3°C in the steady-state analysis.

Solar heat gain factors and heat loss coefficients for passive heating concepts

The concept of solar heat gain factor has been introduced for calculating the net energy gain of passive heating elements and other components of a building as a result of incident solar radiation. For passive heating concepts (namely, the direct gain, mass wall, water wall, Trombe wall, and solarium), exact analytical expressions have been obtained for the solar heat gain factors and the corresponding overall heat loss coefficients. These will allow a building designer to calculate immediately the overall heat gain/loss in a building. Numerical calculations have been done for typical values of solar radiation and ambient temperature of typical climatic conditions in India. The method has been compared with the other methods reported in the literature so far. A good comparison is found between the earlier methods and the method of using solar gain factors and the corresponding heat transfer values.

The passive solar heated school in Wallasey. V. Energy requirements for A passive school building

The near-south-facing glazed wall of the Wallasey School admits large solar gains in sunny weather, sufficient to meet in full the heat need in cold weather. It permits large heat losses, however, and during dull weather, and during the long winter nights there is little or no compensating solar gain. The net effect of such glazing over a season might be either to save, or to waste energy as compared with a windowless building, according to the sunniness and coldness of the climate and the window characteristics. To examine the action of the glazing, use was made of 50 years of daily mean ambient temperature, and contemporary sunshine hours, in conjunction with the solar gain factor for the translucent and pinboarded areas of the solar wall, and for certain values of design temperature and ventilation rate. It is concluded that such glazing leads to modest savings, of around 5 to 10 W/m2 daily average. Most of the saving appears to be achievable by around 30 per cent glazing; further glazed area tends to supply unwanted solar gain in sunny periods while increasing the losses in sunless conditions. The annual electricity consumptions are noted for the 20 year life of the building. Their costs suggest that the building has been economical to heat.

Building energy needs and ambient temperature and solar radiation statistics

A procedure is developed to enable a building designer to estimate seasonal heating needs for an enclosure taking into account the passive solar gain through a window or glazed wall. The distributions of ambient temperature and solar radiation are required and in this procedure are each described by their first four moments. The window is characterized by its solar gain factor and transmittance, the loss of heat from the remainder of the enclosure by conduction and ventilation by an overall loss coefficient; a comfort temperature must be chosen. Excess solar gain is taken to be dumped. The results of the present statistical approach agree satisfactorily with the results of an earlier day by day approach, using the same 50 years of meteorological data.

Solar radiation through windows—theory and equations

This paper is concerned with the heating effect on buildings of solar radiation through windows. The theory and equations which lead to an hour-by-hour prediction of the solar gains and cooling loads are documented. These provide the algorithms for computer programs which derive solar cooling loads directly from basic data and for programs which produce solar gain factors used for manual calculations.