双层玻璃幕墙的传热特征研究

展示了一个通过计算流体动力学(CFD)计算机模拟获得双层玻璃幕墙传热特征的方法。通过CFD模拟计算的结果,拟合得到了双层玻璃幕墙系统和单层玻璃幕墙系统的室内得热与太阳辐射和室内外温差两个变量之间的线性近似公式。该关系表征了幕墙系统的传热特征:太阳得热系数和有效传热系数(或U值)。用该公式估算夏冬季透过幕墙的室外冷(热)负荷十分方便,工程实用性很高。     

Coupled heat transfer modes for calculation of cooling load through hollow concrete building walls

A CFD model was developed to study thermal performance of hollow cement wall constructions of buildings under hot summer conditions. The approach employed couples conjugate, laminar natural convective flow of a viscous fluid in hollow building blocks with long-wave radiation between the cavity sides. Realistic boundary conditions were employed at the outdoor and indoor surfaces of the wall. A state-of-art building energy simulation program, ESP-r, was used to determine the outdoor thermal environment that included solar radiation, equivalent temperature of the surroundings and convective heat transfer coefficient. The CFD problem is put into dimensionless formulation and solved numerically by means of the control-volume approach. The study yielded comprehensive, detailed quantitative estimates of temperature, stream function and heat flux throughout the wall domain. A detailed parametric study showed that using a wider cavity within a building block does not necessarily reduce heat flux through the block. Radiation heat transfer between cavity sides may account for a significant fraction of heat flux through the block and neglecting its effect can lead to errors that could be as large as 46%. The geometry of the hollow blocks was demonstrated to affect the heat flux by as much as 30%.     

Conjugate conduction convection and radiation heat transfer through hollow autoclaved aerated concrete blocks

A computational fluid dynamics (CFD) model is developed to study thermal performance of hollow autoclaved aerated concrete (AAC) blocks in wall constructions of buildings under hot summer conditions. The goal is to determine size and distribution of cavities (within building blocks) that reduce heat flow through the walls and thereby lead to energy savings in air conditioning. The model couples conjugate, laminar natural convective flow of a viscous fluid (air) in the cavities with long-wave radiation between the cavity sides. Realistic boundary conditions were employed at the outdoor and indoor surfaces of the block. A state-of-the-art building energy simulation programme was used to determine the outdoor thermal environment that included solar radiation, equivalent temperature of the surroundings, and convective heat transfer coefficient. The CFD problem is put into dimensionless formulation and solved numerically by means of the control-volume approach. The study yielded comprehensive, detailed quantitative estimates of temperature, stream function and heat flux throughout the AAC block domain. The results show a complex dependence of heat flux through the blocks on cavity and block sizes. In general, introducing large cavities in AAC blocks, being a construction material of low thermal conductivity, leads to greater heat transfer than the corresponding solid blocks. Several small cavities in a block may lead to small reductions in heat flux, but the best configuration found is a large cavity with a fine divider mesh in which case heat flux reductions of 50% are achievable.     

Numerical investigation on thermal performance and correlations of double skin façade with buoyancy-driven airflow

This paper briefly reviews the primary parameters for a double skin façade (DSF) design. The research presents an integrated and iterative modeling process for analyzing the thermal performance of DSF cavities with buoyancy-driven airflow by using a building energy simulation program (BESP) along with a computational fluid dynamics (CFD) package. A typical DSF cavity model has been established and simulated. The model and the modeling process have been calibrated and validated against the experimental data. The validated model was used to develop correlations that can be implemented in a BESP, allowing users to take advantage of the accuracy gained from CFD simulations without the required computation time. Correlations were developed for airflow rate through cavity, average and peak cavity air temperature, cavity air pressure, and interior convection coefficient. The correlations are valuable for “back of the envelope” calculation and for examining accuracy of zonal-model-based energy and airflow simulation programs.     

Vertical greening systems and the effect on air flow and temperature on the building envelope

The use of horizontal and vertical greening has an important impact on the thermal performance of buildings and on the effect of the urban environment as well, both in summer and winter. Plants are functioning as a solar filter and prevent the adsorption of heat radiation of building materials extensively. Applying green façades is not a new concept; however it has not been approved as an energy saving method for the built environment. Vertical greening can provide a cooling potential on the building surface, which is very important during summer periods in warmer climates. In colder climates evergreen species create an external insulation layer and contribute to energy savings and loss of heat. In this study an analysis of the effect on air flow and (air and surface) temperature of vertical greening systems on the building level is presented. An experimental approach was set up to measure the temperature (air and surface) and the air flow near and on different types of green façades and a living wall system to evaluate the influence of wind velocity and its effect on the thermal resistance. A comparison between measurements on a bare façade and a plant covered façade has taken, in the beginning of autumn, to understand the contribution of vegetation to the thermal behaviour of the building envelope.     

Dynamic thermal building analysis with CFD – modelling radiation

In an attempt to reduce the high computational effort required for dynamic thermal simulation of buildings using computational fluid dynamics (CFD) the authors have recently developed an adaptive freeze-flow method (i.e. freezing of flow equations over variable time periods). This article documents the work that has been carried out to predict the surface heat transfer in dynamic thermal building processes using CFD with particular focus on radiation. The Monte Carlo (MC) and discrete transfer (DT) radiation models were investigated and results compared with analytical solutions. The DT model has shown good performance whereas an unrealistic radiation distribution on the surfaces was observed when using the MC model. A further investigation of the DT model for the cooling of a solid wall has shown that the adaptive freeze-flow method is an efficient and accurate means of conducting dynamic thermal CFD simulations which involve radiation. Finally, application of the technique to a more realistic space comprising an uneven distribution of solar gain showed very good results when compared with a zonal dynamic thermal simulation program.     

基于CFD模拟的双层玻璃幕墙通风性能研究

双层玻璃幕墙作为新型的建筑外围护结构,对于建筑内部的采光、通风、隔热起着非常重要的作用。衡量双层玻璃幕墙通风性能最重要的两个指标是内部空气流动速度及热传导,利用CFD软件模拟得出与实际数据最吻合的电脑模型,利用这个标准电脑模型的参数,模拟得出不同几何尺寸的双层玻璃幕墙的这两项指标的图像及数据。进一步定量研究影响双层玻璃通风性能的关键几何因素,通过比较得出双层玻璃幕墙通风口及空腔大小对其通风性能的影响的一般规律,并以此来指导商业生产。     

Energy efficient surfaces on building sandwich panels—A dynamic simulation model

The choice of building envelope is critical for the energy performance of buildings. The major part of the energy used by a building during its lifetime is used for maintaining a suitable interior thermal climate under varying exterior conditions. Although exterior heat radiation properties (i.e. total solar reflectivity and long wave thermal emissivity) have been well accepted to have a large impact on the need for active cooling in warmer climate, the effect of a reduced thermal emissivity on interior surfaces on the building thermal energy flux is rarely studied. This paper addresses the sensitivity of the thermal energy flux through a sandwich panel, by systematically varying the surface thermal emissivity (both interior and exterior) and total solar reflectance of exterior surface, for three geographical locations: southern, middle and northern Europe. A model is introduced for calculating the effect of both interior and exterior optical properties of a horizontal roof panel in terms of net energy flux per unit area. The results indicate potential energy saving by the smart choice of optical properties of interior and exterior surfaces.     

干热干冷地区围护结构热工设计对内表面温度及室内热舒适的影响

为了分析干热干冷地区围护结构热工性能对室内热环境的影响,采用物理环境实测结合动态模拟方法对比分析了2组墙体的保温、蓄热性能对内表面温度的影响,并结合太阳辐射季节变化探究了太阳辐射吸收比对室内热舒适的影响.研究表明:实测结果与模拟结果吻合较好,对于干热干冷地区,提高围护结构蓄热性能能够降低夏季内表面温度,对冬季内表面温度...     

A CFD approach to evaluate the influence of construction and operation parameters on the performance of Active Transparent Façades in Mediterranean climates

Implementation of Active Transparent Façades (ATF) in buildings has been an object of broad application in recent years, both in new or existing buildings. However, there is little experience in the predicting the operating behavior of an ATF. Sometimes the results obtained are not satisfactory and an extra energetic cost is necessary to obtain suitable comfort conditions in the inner space of the building, especially in Mediterranean climates, where large solar gains are a constant condition along throughout the year, and such large semi-transparent areas can produce significant over-heating in buildings. Computational Fluid Dynamics (CFD) has proven to be a useful tool for modeling flow and heat transfer in ATF including conduction, convection and radiation heat transfer phenomena. The aim of this work was to evaluate, by means of CFD, the influence of several construction and operation parameters of the ATF (such as optical properties of the materials, geometrical relations of the façade or flow stream conditions) in terms of energy savings, measured as a reduction of the solar load entering the building. Conclusions on the thermal behavior under several configurations of ATF were obtained. It was found that the parameters that affect the most the reduction on solar load gain are related with the optical properties of the glass. It was also seen that an increase of the length-to-depth ratio causes a decrease on the ATF efficiency in terms of solar load gains. For the tested cases, an increase on the turbulence intensity does not lead to improvements in the reduction of solar load gains. Although an increase on flow velocity necessarily means an increase on the turbulence mixing levels within the flow stream, the added mass effects due to the increase on flow velocity are more significant than the turbulence mixing effects over heat fluxes through the ATF.     

Predicting thermal and energy performance of mixed-mode ventilation using an integrated simulation approach

Mixed-mode ventilation can effectively reduce energy consumption in buildings, as well as improve thermal comfort and productivity of occupants. This study predicts thermal and energy performance of mixed-mode ventilation by integrating computational fluid dynamics (CFD) with energy simulation. In the simulation of change-over mixed-mode ventilation, it is critical to determine whether outdoor conditions are suitable for natural ventilation at each time step. This study uses CFD simulations to search for the outdoor temperature thresholds when natural ventilation alone is adequate for thermal comfort. The temperature thresholds for wind-driven natural ventilation are identified by a heat balance model, in which air change rate (ACH) is explicitly computed by CFD considering the influence of the surrounding buildings. In buoyancy-driven natural ventilation, the outdoor temperature thresholds are obtained directly from CFD-based parametric analysis. The integrated approach takes advantage of both the CFD algorithm and energy simulation while maintaining low levels of complexity, enabling building designers to utilize this method for early-stage decisionmaking. This paper first describes the workflow of the proposed integrated approach, followed by two case studies, which are presented using a three-floor office building in an urban context. The results are compared with those using an energy simulation program with built-in multizone modules for natural ventilation. Additionally, adaptive thermal comfort models are applied in these case studies, which shows the possibility of further reducing the electricity used for cooling.     

西藏地区太阳能采暖建筑热工性能优化研究

西藏地区太阳能资源非常丰富且冬季温度低,该地区非常适合大面积推广太阳能采暖系统,以达到节能减排的目的。但是由于实际大部分太阳能采暖工程,忽略了建筑围护对太阳能主动式采暖系统初投资与运行费用的影响,造成了太阳能主动式采暖系统初投资过高、太阳能保证率低。为了分析建筑热工性能对太阳能主动式采暖系统的影响,笔者利用数值模拟方法,将建筑热工性能与主动式太阳能采暖系统作为一个整体进行计算分析,利用初投资费用最低与全寿命周期总费用最低两个目标函数,对主动式太阳能采暖建筑热工性能的保温性能进行优化。结果表明,提高建筑围护结构热工性能,不仅可以降低太阳能采暖建筑的采暖运行费用,而且可降低整个系统的初投资。     

Measurement of albedo and analysis of its influence the surface temperature of building roof materials

The growth of the cities is characterized by a great increase in built and paved areas, energy use and heat generation. The phenomenon of urban warming is called heat island. Heat islands cause not only thermal discomfort. High temperatures are responsible for the increase of energy demand for air conditioning in buildings and photochemistry effects that increase atmospheric pollution, as well as increasing environmental impacts due to the demand of energy generation. Materials with high albedo and emittance attain lower temperatures when exposed to solar radiation, reducing the transference of heat to the environmental air. This paper focuses on presenting the results of the measurement of albedo of materials used for building roofs in Brazil, using a spectrophotometer with an integrating sphere accessory, and evaluating the heat gain on roofs, by calculating the surface temperature that each material can reach when exposed to solar radiation. Albedo is defined as the specular and diffuse reflectance integrated over the 290 and 2500 nm wavelength range, which corresponds to approximately 96% of the solar radiation that reaches the earth’s surface.     

Wall heat loss from intermittently conditioned spaces—The dynamic influence of structural and operational parameters

The intermittent daily operation of the HVAC equipment is currently a method usually adopted for reasons of proper building energy management in geographical regions with temperate climatic conditions. Under these conditions, the influence of the building envelope and the specific operational schedule of the mechanical equipment under the effect of time-varying ambient temperature and incident solar radiation is responsible for the development of complex transient heat transfer phenomena, which leads to continuous heat exchange with the environment. The heat exchange through the building envelope, which determines its energy efficiency, is strongly influenced by several parameters along with the thermal characteristics of the building elements like the wall thermal resistance and heat capacity as well as the thermal time constant and operational conditions of mechanical equipment. In the present investigation, an analysis is developed for the evaluation of the daily quasi steady-state energy losses from composite walls under the effect of time-varying meteorological driving forces, when heating at the room side is intermittent.The effect of various significant design and system operational parameters like wall heat capacity, thermal time constant and the insulation layer configuration, daily heating cycle duration and phase, as well as room heat capacity and net heating power input are investigated on the quasi steady-state energy loss and daily room temperature swing under typical winter conditions.     

Appropriate energy efficient building envelope technologies for social housing in the Irish climate

Extensive dynamic thermal simulation parametric analyses have been undertaken of energy efficient fabric alterations to social housing in Northern Ireland culminating in priorities for deployment. Five ȁ8basecaseȁ9 simulation models were used to represent the predominant characteristics of the existing social housing stock. The majority of technologies studied provided annual space-heating energy savings of more than 10%. The variation of energy savings and economic performance across the basecases highlights the value of a dwelling specific approach to selecting energy efficient building envelope technology solutions for energy rehabilitation programmes. The paper further outlines a framework for prioritising appropriate energy efficient building envelope technological solutions for a large regional building stock, i.e. existing social housing stock in Northern Ireland, highlighting influential parameters. An energy efficient building envelope inter-technology ranking approach provides a method of comparison across the various different dwellings in the regional housing stock. Airtightness ranked consistently highest across the dwellings studied with some solar technologies performing better than more technologically mature solutions such as insulation.     

不同气候区建筑获得太阳辐射的动态分布特征

提高太阳能资源在建筑中的利用水平是减缓建筑对传统能源依赖程度的重要途径,也是推广可再生能源建筑应用的基本举措。基于全国五类气候分区代表性城市全年典型气象数据,结合计算模型研究分析了建筑屋面、东面、南面、西面、北面获得太阳辐射量的动态分布特征,确定了建筑各个方位利用太阳能资源的潜力。研究结果表明除了传统地发挥屋面利用太阳能的方法外,建筑立面接收太阳能辐射的能力也能达到良好的效果,即建筑立面利用太阳能具有较好的应用价值。     

Evaluation of a prototype active building envelope window-system

Active building envelope systems represent a new enclosure technology that uses solar energy to compensate for passive heat losses or gains through building envelopes. In ABE systems, energy obtained from solar radiation is converted into electrical energy by using photovoltaic cells. This electrical energy is subsequently used to power a series of solid-state thermoelectric modules, which can control the flow of heat through the enclosure. In order to assess the practical feasibility of ABE systems, we have developed a prototype ABE window-system and an outdoor testing room. A testing system was developed to measure the ABE system's temperatures, solar radiation, current and voltage. Theoretical and experimental results are presented and compared. Finally, the performance of the ABE window-system was evaluated.     

Effects of double glazed facade on energy consumption,thermal comfort and condensation for a typical office building in Singapore

Fully glazed facade that has been increasingly used in Singapore causes higher energy consumption and thermal discomfort due to higher solar gain. The use of double glazed facade system with ventilation system is one way to solve these problems. The objective of this paper is to investigate the effects of double glazed facade with ventilation system on the energy consumption, thermal comfort and condensation and compare to single glazed facade system. TAS and CFD software were utilized to calculate energy consumption, thermal comfort and condensation for single glazed facade building as well as double glazed facade building. The simulation results showed double glazed facade with natural ventilation were able to minimize energy consumption as well as to enhance the thermal comfort. Turning the mechanical fans on could also solve the condensation problem due to high humidity.     

节能建筑启停供热后房间温度变化分析

介绍长春市某节能住宅建筑围护结构及其热工特性,启停供热系统时对该建筑物房间温度变化进行跟踪实测。分析了室外气温,太阳辐射,窗墙面积比对房间温度下降与上升的影响。提出行为节能有效措施。     

黑球温度对房间热舒适性的影响分析

本文通过分析黑球温度计的工作原理,依据青藏铁路某被动太阳房试验数据研究,分析了太阳房室内黑球温度、空气温度和围护结构内表面温度之间的关系,提出用室内黑球温度和室内空气温度以及围护结构内表面温度的温差来评价房间热舒适性的方法和依据。