Total Solar Energy Transmittance Research Articles

Component-based SHGC determination of BIPV glazing for product comparison

Building-integrated photovoltaic (BIPV) systems are intrinsically designed to generate electricity and to provide at least one building-related function. When BIPV modules act as glazing products in windows, skylights or curtain walls, their ability to control the transmission of solar energy into the building must be characterised by a Solar Heat Gain Coefficient (SHGC) or g value (also known as Total Solar Energy Transmittance – TSET – or “solar factor”). For the comparison of BIPV glazing products consisting of one PV laminate and possibly further, conventional glazing layers separated by gas-filled cavities, the procedures documented in international standards for architectural glazing (e.g. ISO 9050 and EN 410) form a suitable starting point. Easily implemented modifications to these procedures are proposed to take both optical inhomogeneity (if relevant) and extraction of electricity from BIPV glazing units into account. Geometrically complex glazing and shading devices, and light-scattering glazing layers, are outside the scope of the proposed methodology; SHGC determination for obliquely incident solar radiation is also excluded. For these cases, the experimental calorimetric approach documented in [ISO 19467:2017; ISO 19467-2:2021] is recommended.The paper also presents results and conclusions from an implementation exercise and sensitivity study carried out by participants of the IEA-PVPS Task 15 on BIPV. The cell coverage ratio in the PV laminate, the thermal resistance offered by the glazing configuration, the choice of boundary conditions and the effect of extracting electricity were all identified as parameters which significantly affect the SHGC value determined for a given type of BIPV glazing. A practicable approach to accommodate the great variety of dimensions typical for BIPV glazing is also proposed. These findings should pave the way for modifying the existing component-based standards for architectural glazing to take the specific features of BIPV glazing into account.

Optimizing the Building Refurbishment Process Using Improved Evolutionary Algorithms

An optimization model that may be applied to analyze building retrofit strategies is presented in this research. The aim of this research paper is to identify the optimal thermal envelope configuration that will assure the minimum energy requirement for heating in the case of a residential building, while also considering price restrictions obtained through a specific market survey. To achieve this, several values for the following parameters are considered: thermal insulation materials’ conductivities and thicknesses, windows’ overall heat transfer coefficients and total solar energy transmittance and doors’ thermal proprieties. Additionally, this paper presents a method used to find the best option from among the available heat pumps that could cover most of the energy requirements for heating and domestic hot water systems, also considering the products’ prices. The proposed method is based on a Non-dominated Sorting Genetic Algorithm II (NSGA-II) model developed in the Pymoo (Multi-Objective Optimization in Python) library. The result shows that the energy requirement for heating can be reduced by up to approximately 75% compared to that obtained in the case of a non-insulated building by using suitable insulation materials and doors and windows with superior thermal proprieties chosen by the NSGA-II.

Passive Building Energy Saving: Building Envelope Retrofitting Measures to Reduce Cooling Requirements for a Residential Building in an Arid Climate

In arid climates, a significant portion of the urban peak energy demand is dedicated to cooling and air-conditioning during the summer. The rapid urbanization rates in developing countries, particularly in the Gulf Cooperation Council (GCC), have intensified the pressure on energy resources to meet the indoor comfort needs of residents. As a result, there has been a substantial increase in energy demand, with a 2.3% rise recorded in 2018. Electricity consumption in residential buildings accounted for over 48.6% of the total electricity consumption. The choice of building fabrics used in a residential building can significantly impact the building’s passive performance and carbon footprint. This study aimed to enhance our understanding of how specific fabric details influence cooling energy usage in arid climates. To achieve this, a validation simulation model was initially created as a base case for a residential housing typology in Al Ain, UAE. This was followed by a parametric energy evaluation of various building envelope features. The evaluation was based on the reduction of yearly cooling load energy. The simulation results indicate that incorporating 50 mm of expanded polystyrene insulation into the outside walls significantly reduced energy consumption for cooling requirements in the arid UAE climate. Furthermore, no substantial difference was observed in the various roofing choices, including cool and green roofs, gravels, and sand roofs. Additionally, we concluded that the total solar energy transmittance (g-value) of windows played a more significant role than thermal transmittance (U-value) in reducing solar heat gain within the spaces. These findings should guide strategic decisions on building envelope upgrading for sustainable societies.

Improvements of simplified hourly models for the energy assessment of buildings: The application of EN ISO 52016 in Italy

The Italian National Annex (NA) to EN ISO 52016-1 is aimed at improving the simplified hourly calculation method of the building thermal performance assessment by introducing different modelling options. The present work deepens the influence of the Italian NA improved method on the thermal energy needs for heating and cooling of a residential building-type in two different climate zones. In particular, the Italian NA improved options are applied one-at-the-time, and their effect is evaluated in comparison with the EN ISO 52016-1 standard method. The use of solar angle and time dependent correction factors for the total solar energy transmittance of glazing proved to be the most sensitive modelling option, among those analysed. Negligible variations were instead reported for the other tested options.

Methods of Preliminary Estimation of Total Solar Energy Transmittance (TSET) on a Sun Protected Window with Climatic Chamber and Hot Box Apparatus

Abstract The total solar energy transmittance (TSET, g - value) is a parameter of transparent system, which can significantly affect the heat demand for cooling of buildings in the summer. A wide range of progressive transparent and shading systems have been developed and applied to a large number of buildings. Their energy performance and efficiency can be determined using simulation tools or measurements. The methodology for accurate g - value determination is described in ISO 19467: 2017. The aim of the study was to derive and verify an alternative methodology for estimating the total solar energy transmittance of selected specimens of transparent systems in case when the standardized equipment is not available or the aim is not to know the exact TSET value. Window specimens were tested under laboratory conditions, which were retrofitted with elements that improve their original properties in terms of heat transfer coefficient and protection against overheating. In total, three methodologies were designed and described, based on A) monitoring of heat fluxes through glazing, B) monitoring of temperature rise in the hotbox and simulation, and C) determination of the difference in heat fluxes of an irradiated specimen and in the absence of radiation. A solar simulator and a heated hotbox were used for the measurements according to the needs of the chosen methodology. The results from the different approaches for determining g - values differ only slightly but are informative. The conclusion from all measurements is the fact that the tested specimens representing type of windows applicable in building retrofitting showed high potential in terms of reducing heat gains from the sun.

Optimization of Architectural Thermal Envelope Parameters in Modern Single-Family House Typologies in Southeastern Spain to Improve Energy Efficiency in a Dry Mediterranean Climate

The increasing regulatory requirements for energy efficiency in Europe imply a significant increase in insulation and solar control of buildings, especially in hot and semi-arid climates with high annual insolation such as the Spanish Mediterranean southeast. The consequences in architectural design to optimize compliance with the new technical and regulatory requirements of nearly zero-energy buildings are high. This paper analyzes the energy performance of a modern single-family house on the Spanish Mediterranean coast. The objective is to determine which design parameters most influence the energy improvement of this case study in order to establish design strategies that can be generalized to other new construction or energy retrofit projects, taking into account the specific characteristics of the warm and semi-arid Mediterranean climate. The scientific novelty of the work is to demonstrate that the design criteria of most modern single-family houses built or rehabilitated in the Spanish Mediterranean in the last decade comply with the energy efficiency requirements of Directive 2010/31/EU but are not specifically adapted and optimized for the special characteristics of the dry Mediterranean climate. This is the case of the house studied in this paper. The methodology used consisted of a systematized study of the main construction and geometric parameters that most influence the thermal calculation of this project: the thermal insulation thickness, thermal transmittance of the glazing, solar control of the glazing, total solar energy transmittance of the glazing with the movable shading device activated, size of glazing and the size of façade overhangs. The results obtained show that the use of mobile solar protection devices in summer, such as awnings or blinds, reduces the cooling need in summer up to 44% and the overall annual energy need (Cooling + Heating) up to 20%. This implementation is more efficient than increasing the thermal insulation of facades and glazing, reducing the size of windows or increasing overhangs. The most optimal solution is the simultaneous modification of several parameters. This reduces both heating need in winter and cooling need in summer, achieving an overall reduction in an annual need of 48%. This multiple solution improves the annual energy performance of the house much more than any solution consisting of modifying a single individual parameter. The results determine trends, explanations and deductions that can be extrapolated to other projects.

The Influence of Glazing on the Functioning of a Trombe Wall Containing a Phase Change Material

Among the technological solutions for external walls, the Trombe wall is an interesting proposition for obtaining solar radiation energy. The aim of the presented research is to determine the influence of glazing parameters on the thermal performance of the Trombe wall containing a phase change material (PCM). In the experimental tests, three glazing (G1, G2, and G3) with different heat transfer coefficient (Ug) and total solar energy transmittance factor (g) were used. The tests were carried out under laboratory conditions in a small-scale simulation chamber. The thermal energy of absorbed solar radiation was simulated with a heating panel. All of the walls are characterized by high dynamics of operation in the first two days. From the moment of heating, the walls achieve the minimum value of the heat flux after 16–18 h. In practice, this means the highest thermal efficiency of the wall during the night of the next day. A noticeable influence of the type of glazing on the operation of the barrier was found. The obtained results suggest that the most effective barrier for “sunny days” is the B1 barrier. The B2 barrier is suitable for alternating days in the cycle: “sunny day”, “cloudy day”. However, the B3 barrier is the most advantageous in periods with a predominance of “cloudy days”. In addition to the experimental studies, a numerical model of the B1 barrier was developed and simulation was carried out using the finite element method. The simulation results were consistent with the experimental tests. The second numerical simulation confirmed the rightness of using the heating panel in experimental tests.

Experimental and Numerical Study on the Heat Transfer Characteristics of a Newly-Developed Solar Active Thermal Insulation System

A newly-developed solar active thermal insulation system (SATIS) is introduced with the main objective to accomplish a highly-dependent total solar transmittance on the irradiation angle. SATIS is also designed to obtain the maximum transmittance at a prescribed design irradiation angle and to reduce it remarkably at higher irradiation angles. A purely mineral thermal insulation plaster with micro hollow glass spheres is applied to manufacture the investigated SATIS prototype. Light-conducting elements (LCEs) have been introduced into SATIS and suitable closing elements have been applied. The SATIS prototype has been investigated both experimentally and numerically. It turned out that the contributions of conduction, radiation and convection to the effective thermal conductivity of SATIS, without the closing elements (49 mWmK), amount to 86.2%, 13.2% and 0.6%, respectively. The angle-dependent short-wave radiation exchange within the LCE has been investigated via ray tracing. At the incidence angle of 19% (design angle), 27% of the radiation within the LCE is absorbed by the absorber plate, resulting in measured and computed total solar energy transmittances of 11.2%/11.7%, respectively. For a typical summer irradiation angle of 60%, 98% of the incident radiation is absorbed by the surfaces at the entrance of the LCE. The corresponding total solar energy transmittance amounts to 2.9%.

Solar Aperture of a Building Enclosure: The Case Study of a Well-Insulated Family House in Semi-Continental Climate

As thermal insulation of building enclosure has substantially improved over the last decades, solar heat gains comprise more important part in thermal balance of a building in semi-continental climate, often leading to overheating. The quality of the whole building enclosure should be assessed by its ability to transmit solar heat gains. Such thermal characteristic need to aggregate properties like glazing area in each facade, total solar energy transmittance of glazing, the efficiency of fixed shading devices and the operation of movable shading devices. In this paper, the surrogate horizontal effective collector area is used for the characterization of solar heat gains through a building enclosure. The parameter is called the solar aperture of a building enclosure. First, the formula for solar aperture is derived. Then, building energy simulation of a model family house is performed. The correlation of the solar aperture with overheating and space heating demand is analysed. Based on the analysis, the recommended trade-off values of the specific solar aperture are proposed for family houses in semi-continental climate. The trade-off values of the solar aperture will lead to reasonable promotion of solar heat gains during cold season and significant reduction of solar heat gains during warm season.

Influence of Window Parameters on the Thermal Performance of Office Rooms in Different Climate Zones of Turkey

Window and facade characteristics significantly influence the energy consumption of office buildings. This paper investigates the influence of window configuration on its energy performance regarding shading levels, orientation, geometrical characteristics and thermo-physical properties. A series of simulations of two common type of office room models were conducted with changing parameters such as window to wall ratio of the facade, total solar energy transmittance value of the glazing, as well as shading levels regarding orientations. The energy simulations were performed using TRNSYS software for the climatic conditions of Istanbul, Ankara, Izmir and Hakkari. It was found that appropriate selection of windows and shading devices regarding climatic conditions would lead to a significant reduction of the annual energy consumption and greenhouse gas emissions. The recommendations presented can be applied to any location around the world that has similar climatic conditions with the cities studied in this work.

Calorimetric determination of the solar heat gain coefficient g with steady-state laboratory measurements

The paper describes procedures for the direct calorimetric measurement of the solar heat gain coefficient g in detail. g is also called SHGC, solar factor, g-value or total solar energy transmittance TSET. All these terms are used synonymously in this document although there are some differences in the details of the definitions of these properties (e.g. different reference wind conditions or reference solar spectra). The document aims to summarize more than 25 years of experience in g-value testing at Fraunhofer ISE, Freiburg, Germany, which includes many different transparent and translucent building materials ranging from transparent insulation materials to daylighting and solar control systems and active solar energy harvesting facade components like building-integrated PV systems (BIPV) or building-integrated solar thermal collectors (BIST). The document focuses on methods for the calorimetric measurement of g under steady-state laboratory conditions. Transient outdoor measurements are beyond the scope of this paper. It also describes the corresponding error analysis and methods to correct experimentally determined values gexp to reference conditions, if it is not possible to reproduce the reference boundary conditions exactly in the laboratory.

Total Solar Energy Transmittance vs. Dynamic Thermal Characteristics of Non-Transparent Building Components

Occasionally, there are suggestions from professional public to use the total solar energy transmittance coefficient, g (solar factor), to describe not only transparent, but also opaque structures, particularly with regard to overheating of the under-roof spaces. The standard EN 410:1998 (Glass in building - Determination of luminous and solar characteristics of glazing) introduces the g-value as the sum of primary solar heat gain, g1, due to the transparency of the glazing and the secondary solar heat gain, g2, due to the absorption of solar radiation and its conversion into heat conduction and radiation over the total incident solar heat flux, φe. Nevertheless the value of g1 may have zero or nearly zero value, e.g. in case of non-transparent glass. In addition to it, the standard ISO 15099:2003 (Thermal performance of windows, doors and shading devices - Detailed calculations) introduces equation for calculation of the frame g-value (actually the frame total solar energy transmittance), where window frames are clearly opaque components. What is then the difference between glass and "standard" opaque wall or roof? Why is in the latter case always introduced zero and in the first one some value different from zero? Won't it be practical, especially in time of large existing opportunities of computer use, to implement the use of g-values also in case of ordinary opaque structures and express their resistance to the absorption and conversion of solar radiation and thus overheating the adjacent interior spaces? This paper attempts, using EN ISO 13786 (Thermal performance of building components - Dynamic thermal characteristics - Calculation methods) and computer-aided models of transient heat transfer, to explain why the suggestion of using of the g-value in case of opaque components is not entirely correct and, why priority should be given to the dynamic thermal characteristics specified in this standard.

The effect of neutron and mixed gamma and neutron irradiation on the solar properties of borosilicate glass

Neutron and mixed gamma and neutron irradiation, at different absorbed doses, of borosilicate glass with four different chemical compositions was conducted to investigate the effects on the solar properties of the glass. Irradiation was performed in the tangential beam tube and central thimble of a nuclear reactor. The effect of thermal and epithermal neutrons on such solar properties as secondary heat-transfer factor, solar factor (the total solar energy transmittance), and shading coefficient of the borosilicate glass were investigated to determine the effect on the solar properties of borosilicate glass, because of its neutron absorbance property.

Variable g value of transparent façade collectors

Transparent solar thermal collectors (TSTC) represent a new development. An adequate model is needed to predict their performance. This paper presents a collector model with an advanced calculation of the transmission of diffuse radiation and a connection to the building which allows analysis of the collector gains and of the g value, also called “solar factor”, “solar heat gain coefficient (SHGC)” or “total solar energy transmittance”. The model is implemented as a TRNSYS Type and a coupled simulation between a collector and a room is presented for different façade constructions. Façade areas with glazing and venetian blinds are simulated with a second new TRNSYS Type which introduces high modelling accuracy for façades with solar control systems. An HVAC system is presented together with a first estimate of possible reductions of primary energy. It indicates primary energy savings of about 30% by replacing opaque walls with transparent collectors. The g values prove to depend not only on the irradiation, but also on the operation of the solar collectors and vary e.g. between 0.04 and 0.21. Detailed modelling of active façades like TSTC is therefore essential for accurate predictions of the collector gain, the heating and cooling loads and the thermal comfort.

Energy performance of glazings in European climates

Windows can cause significant thermal energy gains or losses in buildings. Focusing on wintertime, a simple method for analyzing and discussing energy flows through glazings is presented. The impact of the glazing quality, the façade orientation, and the severity of the climate on the ratio of solar gains to thermal losses through glazings are shown. As regards the passive solar heating of buildings, the glazing quality is represented by the ratio of the total solar energy transmittance to the thermal transmittance ( g/U). The severity of the climate is determined by the ratio of the interior-exterior temperature difference to the solar irradiance (Δ θ/I). In this study, the method is based on monthly mean values of interior-exterior temperature difference and solar irradiance. Not at least because the approach is straightforward, it might also be valuable for educational purposes. For eight case study locations in Europe namely Bucharest, London, Madrid, Moscow, Rome, Stockholm, Warsaw and Zurich, charts are presented, which display condensed information on the energy performance of glazings. At a given location, the gain-to-loss ratio varies by a factor of roughly 30 depending on the glazing quality and the façade orientation. At all locations and façade orientations, modern triple glazings perform best and enable net gains at south façades in December even in Moscow and Stockholm.

NUMERICAL ANALYSES ON THE PERFORMANCE OF THE TRANSLUCENT THERMAL INSULATION WALL OF DETACHED HOUSES FOR HEATING, COOLING AND LIGHTING ENERGY REDUCTION

Translucent thermal insulation walls for detached houses are to take solar radiation gain and daylight indoor for heating and daytime lighting energy reduction and for comfortable lighting environment. In this paper, study on the wall performance by means of computer simulation is described. The computer simulation shows that, a higher light transmittance brings a large reduction of daytime lighting energy. In order to reduce heating energy, the total solar energy transmittance is most important factor. The higher the total solar energy transmittance, the more the heating energy is reduced. The optical and thermal performance of a wall which brings the largest total energy reduction (heating, cooling, daytime lighting) depends on climate. The wall with 0.4[W/K•m2] of U value (overall heat transfer coefficient), 0.32 of the solar transmittance, and 0.38 of the luminous transmittance can reduce a total energy brings a large energy reduction in total, in Tokyo or most region in Japan.

Evaluation of optical and thermal properties of coatings for energy efficient windows

Over the past couple of decades a number of coated glazing products have appeared on the market, converting the window from an energy drain to a possible resource in the building's energy supply system. In this paper the light transmittance, total solar energy transmittance, and thermal transmittance of coated glazing currently available on the market and future dynamic electrochromic coatings are reviewed and their function in heating or cooling dominated climates discussed. Electrochromic coatings can switch between a transparent state and an absorbing or reflecting state when a small electrical potential is applied, and hence adapt their optical properties to the present condition. Energy balance calculations for the window component stress the importance of selecting the window depending on climate. In a heating dominated climate a low-e coating with a high g-value can result in a net energy gain on a south facing façade and thus be better than an ideal wall.

Experimental and numerical determination of the total solar energy transmittance of glazing with venetian blind shading

In response to the increased occurrence of overheating problems in glazed buildings in recent years, EMPA has focussed on the determination and modelling of the total solar energy transmittance (TSET) of multiple glazing combined with different shading systems. Measurements were performed in a calorimetric outdoor test facility near Zurich, Switzerland. In the first phase, average TSET-values related to the incident global solar radiation were identified for various Venetian blind configurations with a measurement period of a few days each. As expected the results strongly depend on the slat tilt angle as well as on the solar reflectance of the slat surface. The influence of the directional distribution of the incident radiation is demonstrated by comparison of results from different measuring periods with the identical shading–glazing configuration. An extended identification model accounting for the angle-selective transmittance is presented. The experimental results are also compared with weighted g-values from numerical modelling, which are based on a view factor method extended for curved slats in a louver type shading device. In general, the agreement between the measured and calculated results is satisfactory. Some deviation is explained by a significant non-diffuse albedo component in the hemispherical radiation field.

Silica aerogel granulate material for thermal insulation and daylighting

Silica aerogel granulate is a nanostructured material with high solar transmittance and low thermal conductivity. These properties offer exciting applications in building envelopes. One objective of the joint R&D project ISOTEG at ZAE Bayern was to develop and characterize a new glazing element based on granular silica aerogel. Heat transfer coefficients of less than 0.4 W/(m 2 K) and a total solar energy transmittance of 35% for the whole glazing unit were achieved. The glazing has a thickness of less than 50 mm. Another application for granular silica aerogel is, for example, in solar collectors. The thermal properties of the glazing as well as the optical and thermal properties of the granular aerogels are presented here. The solar transmittance of a 10 mm packed bed of silica aerogel was 53% for semi-translucent spheres and 88% for highly translucent granulate. In our heat transfer experiments the gas pressure, external pressure load, temperature and gas filling were varied. The various thermal conductivity values measured for the glazing and collector applications were compared to the values calculated using two different packed bed models. For the gas-dependent measurements the intergranular voids in the granulate were 1.0 ± 0.1 mm before loading the packed bed, 0.3 ± 0.1 mm at an external load of 3.2 bar (3.2 × 10 5 Pa) and 0.6 ± 0.1 mm after release. A direct radiative conduction of λ direct = 4.5 ± 0.5 × 10 −3 W m −1 K −1 was obtained.

04/02539 Total solar energy transmittance of glass doublefaçades with free convection: Manz, H. Energy and Buildings, 2004, 36, (2), 127–136

04/02539 Total solar energy transmittance of glass doublefaçades with free convection: Manz, H. Energy and Buildings, 2004, 36, (2), 127–136