Improvement of a measurement system for solar heat gain through fenestrations

This paper presents a study on the improvement of a system for measuring solar heat gain through fenestrations. The system allows the quantification of the thermal fraction that penetrates into a room through a fenestration due to solar radiation, and also the determination of the Solar Factor. To test and improve the functioning of the system, some field measurements and calibration of sensors (heat flux meters) were carried out. Initial measurements demonstrated that there was an error in the Solar Factor obtained and also that there was an increase in the temperature of the heat flux meter support plate. Currently the equipment uses a heat dissipation system with fans that insufflate air directly onto the rear side of the heat flux meter support plate. The increase in the temperature difference between the plate and the external air reduces the heat flow through the sensors, causing errors in the measurements. New tests were carried out using a cooling system with water circulation in a thermostatic bath. The decrease in the temperature difference between the heat flux meter support plate and the air provided good results, demonstrating the necessity for modifications to the currently used cooling system.     

Effect of solar gain through walls and windows on annual building heat needs

A window with an open south facing aspect can admit large solar gains in cold but sunny conditions and will then reduce the need for back up heating. In cold overcast conditions the same window will cause a bigger demand for heat to be placed upon the heating plant. The net energy need depends upon the local climate, the comfort temperature chosen, ventilation losses and the design of the window or glazed wall. A study is reported in which 50 years of jointly occurring daily values of temperature and irradiance at 53.4°N on a U.K. site are used. A rank order is suggested for the effectiveness of various constructions as energy saving components.     

A laboratory experiment on natural ventilation through a roof cavity for reduction of solar heat gain

The study targets the reduction of roof solar heat gain through the use of natural ventilation in a roof cavity. This study is mainly concerned with factory buildings. Experimental outcomes were obtained from an inclined cavity model which was heated on the upper surface to mimic solar radiation on a roof. The dimensions of the cavity were 4882 mm× 400 mm × 78 mm. The two opposing smallest sides were allotted as the inlet and outlet, and narrowed to simulate resistance of the air flow in practical applications. Temperature and velocity measuring facilities were prepared in the experimental model. A number of measurements were carried out by varying the combinations of different heat production, inclination angles, and opening ratios. It was found that resistance to heat and air flow in the cavity was strongly influenced by the opening size. When the Reynolds number was examined, it showed that the flow belonged to the laminar region. The average velocity reached to 0.25 m/s at the highest in the examined cases. In other words, the cavity air was turned over 184 times in an hour. Natural ventilation in the roof cavity seemed to be effectively applicable to solar incidence discharges in factory buildings.     

Solar heat gain through vertical cylindrical glass

Spaces with nonplanar glazed envelopes are frequently encountered in contemporary buildings. Such spaces represent a problem when calculating the solar heat gain in the course of estimating the cooling or heating load; and hence, sizing of cooling or heating systems. The calculation, using the information currently available in the literature, is tedious and⧹or approximate. In the present work, the computational procedure for evaluating the solar heat gain to a space having a vertical cylindrical glass envelope is established, and, a computer program is coded to carry out the necessary computations and yield the results in a detailed usable form. The program is versatile and allows for the arbitrary variation of all pertinent parameters.     

建筑围护结构传热得热量计算方法的比较

比较了围护结构传热得热量的两种计算方法:周期性反应系数法和传递函数法。与传递函数法相比,周期性反应系数法简化了计算,而且周期性反应系数能反映围护结构对周期性扰量的热响应,可作为评价围护结构热稳定性的指标。推导了传递函数系数与周期性反应系数间的关系式,可根据ASHRAE的数据库RP 626建立典型围护结构周期性反应系数的数据库,从而减少周期性反应系数法的计算量。     

Prediction of solar heat gain of double skin facade windows

A linear model involving the solar heat gain coefficient and U value is often used to calculate the solar heat gain of traditional windows; however, it is not known if such linear model is applicable to double skin facades, which is typically featured by ventilated cavity and often with blinds inside. This paper reports on an experimental investigation into the relation between the two coefficients and the energy gain by a double skin facade without blinds. A small-scale solar calorimeter was constructed to measure the energy gain of a double skin facade window about 1.1 m high. Four tests with solar radiation intensity ranging from 205 to 793 W/m² showed that the energy gain can be represented by such linear model. The solar heat gain coefficient can be determined from the data fitting process with more accuracy than the U value, which, being a minor determinant of the heat flow in the presence of the solar radiation, may require more data for reasonable accuracy. The advantage of this linear model lies in its simplicity, which makes it easy to incorporate into present building energy simulation tools.     

Development of solar heat gain factors database using meteorological data

In tropical and subtropical regions, solar heat gain via fenestration, particularly on vertical surfaces, plays an important role in determining the thermal performance of a building. For sizing air-conditioning equipment, maximum solar heat gain factors (SHGFs) are used for estimating the design peak load. Recently, the SHGF data representing the prevailing weather conditions have become essential and more practical for part load performance designs and daylighting schemes evaluation. In the absence of measured solar radiation data for the determination of SHGFs, meteorological radiation models may be used. This paper presents the validation of SHGFs prediction models based on sunshine hours and horizontal solar data. Statistical assessments for the models have shown that using sunshine hours to predict the hourly SHGFs may not be appropriate for dynamic building simulation studies. For the average SHGFs computation, all models present acceptable results. In determining the SHGFs for horizontal and vertical surfaces at the peak and other significant levels, all prediction models perform better than the ASHRAE clear sky approach, particularly at high significant levels. This finding also provides information for the estimation of total air-conditioning plant capacity at both the peak load operation and the multiple equipment sizing under part load condition.     

Useful solar gains through a glazed south-facing wall in the U.K. climate

A glass skin attached to a southfacing wall may serve to direct a sizeable fraction of the solar gain absorbed at the outer surface of the wall to the wall interior. The heat flow may help to make good ventilation heat losses, and conduction losses to other parts of the building. A wall of high thermal resistance tends to restrict this flow, but it also restricts the outward flow of heat. For given conditions there may be an optimum thickness. Tables are presented giving the heat needs for an unglazed wall, and for a wall with one or two glass skins attached to it. The variation in heat need with choice of month, ventilation loss and comfort temperature is shown as a function of the wall resistance. The results are based on weather data for the north Wirral, U.K. 53.4° N.     

Quantification of model form uncertainty in the calculation of solar diffuse irradiation on inclined surfaces for building energy simulation

Traditional uncertainty quantification (UQ) in the prediction of building energy consumption has been limited to the propagation of uncertainties in model input parameters. Models by definition ignore, at least to some degree, and, in almost all cases, simplify the physical processes that govern the reality of interest, thereby introducing additional uncertainty in model predictions that cannot be captured as input parameter uncertainty. Quantification of this type of uncertainty (which we will refer to as model form uncertainty) is a necessary step towards the complete UQ of model predictions. This paper introduces a general framework for model form UQ and shows its application to the widely used sky irradiation model developed by Perez et al. [1990. “Modeling Daylight Availability and Irradiance Components from Direct and Global Irradiance.” Solar Energy 44 (5): 271–289], which computes solar diffuse irradiation on inclined surfaces. We collected a data set of one-year measurements of solar irradiation at one location in the USA. The measurements were done at surfaces with different tilt angles and orientations, for a wide spectrum of sky conditions. A statistical analysis using both this data set and published studies worldwide suggests that the Perez model performs non-uniformly across different locations and produces a certain bias in its predictions. Based on the same data, we then use a two-phase regression model to express model form uncertainty in the use of the Perez model at this particular location. Using a holdout validation test, we demonstrate that the two-phase regression model considerably reduces the model bias errors and root mean square errors for every tilted surface. Lastly, we discuss the significance of including model form uncertainty in the energy consumption predictions obtained with whole building simulation.     

特殊造型太阳能工程集热循环管路的水力计算——上海可口可乐饮料有限公司太阳能热水工程

现太阳能热水工程不仅要强调使用功能的完善化,更加强调了外型的美观化及设计与施工的科学化、合理化。本文主要介绍了上海可口可乐有限公司特殊造型(集热器呈可乐瓶造型布置)的太阳能热水工程,楼顶热水管路的水力计算。     

Experimental research on performance of the solar heat gain (SHG) insulation panel

Recently, research on energy efficiency for buildings has been performed due to a shortage of energy and increased concern about the environment. Building envelopes have vital roles in energy efficiency. Insulation depth, opening designs, double skins and other methods have been discussed to improve the performance of building envelopes. Among these methods, the use of opaque insulation has a role for blocking the inner heat loss, but also for inefficiently blocking the natural solar heat coming to the inside of a building. This paper looks at a way of bringing solar heat to the inside of a building, which is impossible with normal insulation. The research measures the amount of heat gain and provides the possibility of energy savings through solar heat in a test building.     

A study of solar heat gain to multistorey buildings in hot and arid regions

The paper presents an empirical study of solar heat gain to multistorey buildings at the peak degree hour on the hottest day of summer in hot and arid regions of India. The effects of surface to floor area ratio of a building form, orientation, fenestration percentage and shading devices on the cooling loads have been quantified. Case studies simulating realistic situations have been subjected to empirical calculations by computer.Conclusions drawn from the results afford a guideline to practising architects and air-conditioning engineers to make suitable adjustments at the initial building design stage in order to reduce the cooling loads caused by solar radiation.Finally, a field study demonstrates the possibility of reducing solar heat gain by striking a compromise between scientifically recommended shading devices and architecturally acceptable forms of external louvres.     

A new value of average beam solar heat gain coefficient for innovative daylighting systems

The majority of the fenestration systems are available in the market today are of the type whose solar gain properties can be determined through the use of a computational procedure. However there is a class of fenestration systems (or attachments) that cannot be handled with the conventional procedures like solar path diagrams and shading masks. This class includes the daylight systems. These systems are an innovative technology for sunlight redirection or sunlight exclusion. A new formula for the solar heat gain coefficient (SHGC) is introduced, which can help in the discussion process concerning the optimization of solar gains through the above mentioned systems. This formula is solar positioned and radiation weighted value and can provide an accurate way to estimate the energy flux through the window and can be used as a performance rating methodology for the above mentioned systems.     

Effect of roof solar reflectance on the building heat gain in a hot climate

The effect of the roof solar reflectance on the thermal performance of a building is often ignored. However, there are significant differences in heat gain from light and dark-coloured roof surfaces. In this paper an equation for the average daily downward heat flow of a sunlit roof is derived. Using building simulation, it is first shown that the thermal mass of the roof does not significantly affect the overall daily heat gain (although it causes a time lag and reduction in peak heat flow). As a consequence the daily heat gain from the roof may be estimated by integrating the equation for the steady-state downward heat transfer over the day. For north Australia the derived equation suggests that a light-coloured roof has about 30% lower total (air temperature difference and solar-driven) heat gain than a dark-coloured one. The effect of aging (change in solar reflectance with time) is considered in the calculations and a relationship between the solar absorptance of new and aged material is suggested. A classification of roof colours with respect to their solar absorptance (dark, medium, light and reflective) is proposed to enable a quick and simple assessment of the effect of roof colour on the heat gain and R-value.     

CFD analysis of heat collection in a glazed gallery

A glazed gallery in most old buildings is a space located on the first floor (and/or higher floors), facing south and almost fully glazed. As a result of the large glazed area and the orientation of the gallery, its temperature is warmer than the exterior and, in cold weather, it is used both as a space to insulate the adjacent rooms and as a leisure area, among other applications. In the framework of the ARFRISOL project (Bioclimatic Architecture and Solar Cooling), a demonstration container has been constructed in northern Spain (Asturias) which includes, among other bioclimatic elements, a glazed gallery. This gallery is considered as an element of Bioclimatic Architecture that enables solar radiation to be collected and the energy obtained to be used to support the building's air conditioning system. It consists of a south-facing glazed exterior wall, an intermediate space or passage and a partially glazed interior wall. Dampers located in the floor and ceiling of the intermediate space and connected to the air ducts enable the air circulating inside the gallery to be heated or cooled, depending on the season of the year, before it is further conditioned and conveyed to the rooms. This paper focuses on the three-dimensional numerical simulation of the airflow inside the gallery. The aim is to obtain a model to evaluate the thermal energy obtained in this architectural feature, integrating the effect of certain variables, such as the incident solar irradiation, the outdoor temperature and the air flow rate circulating in the gallery.     

混凝土结构日照效应计算中换热参数的修正

日照辐射作用下换热参数的合理计算会直接影响混凝土结构温度效应分析结果的优劣。综合分析建筑和桥梁混凝土结构服役过程的实际情况,考虑风速、温差、结构朝向、所处位置等环境因素的变化,对通过试验室取得的混凝土表面对流换热、总热换热参数进行合理修正。由于风速和结构朝向是影响换热参数的主要因素,计算公式中主要针对这两个因素进行修正,提出符合实际情况的混凝土表面对流换热、总热换热参数计算公式,为混凝土结构日照效应分析中换热参数的计算提供较精确的方法。     

A universal calculation method for simple predetermination of natural radiation on building surfaces and solar collectors

This article is concerned with the need for an instructive and simple but universal and general set of relations (formulae) defining the direct solar, diffuse sky and ground reflected components of total (global) natural radiation. By their help, the irradiance (in W/m²) on exterior building surfaces or solar collectors of arbitrary slope in various localities on the Earth can be predetermined. This mathematical model is immediately applicable in design offices equipped with the simplest pocket or table programmable calculators. Based on a review of present problems of calculation when computing solar positions, an international standardization draft is recommended in an Appendix.     

Effect of courtyard proportions on solar heat gain and energy requirement in the temperate climate of Rome

The present study focuses mainly on the effect of solar heat gain on the energy demand of courtyard building form with different proportions. Several methods can be employed to improve the building's utilization of solar heat gain. This includes using light colours for the external surfaces to reduce the solar radiation absorption in summer, using shading devices and improving the thermal properties of the external walls and roof. However, it is of great importance before using any of these methods to have the courtyard building's architectural design adapted to have full advantage of the available solar heat gain. Therefore, the main objective of the present examination was to find out to what extent the building's solar heat gain and consequently the energy requirements are influenced by the building's configurations. A computer Tool (IES) was used to carry out the investigation taking Rome as an empirical background to temperate climate. The results showed that the proportions of the courtyard building considerably influence the need for heating and cooling.     

反射隔热涂料对屋顶表面温度、室内温度及屋顶得热的影响

通过简化建筑传热模型,分析反射隔热涂料对建筑屋顶表面温度、室内温度与屋顶得热的影响。以杭州的气候参数为依据,模拟结果表明:随着屋顶传热系数的增大,屋顶表面温度缓慢下降,而室内温度与屋顶至室内的传热量则显著提高;屋顶传热系数为1W/(m~2·K)时,屋顶喷涂反射隔热涂料后室内温度仅39.3℃,相对于混凝土沥青砂浆屋顶降低54℃,相对于普通涂料降低2.8℃;空调致冷温度为26℃时,则喷涂反射隔热涂料后屋顶得热量相对混凝土沥青砂浆屋顶可降低41.4%,相对普通涂料可降低22.7%。