An arctic low-energy house as experimental setup for studies of heat dynamics of buildings

This paper addresses the difficulties in pinpointing reasons for unexpectedly high energy consumption in construction, and in low-energy houses especially. Statistical methods are applied to improve the insight into the energy performance and heat dynamics of a building based on consumption records and weather data. Dynamical methods separate influences from outdoor temperature, solar radiation, and wind on the energy consumption in the building. The studied building is a low-energy house in Sisimiut, Greenland. Weather conditions like large temperature differences between indoors and outdoors throughout long winters, strong winds, and very different circumstances regarding solar radiation compared to areas where low-energy houses are usually built, make the location very interesting for modeling and testing purposes. In 2011 new measurement equipment was installed in the house, which will be used to develop more detailed models of the heat dynamics and energy performance in relation to different meteorological variables, heating systems, and user behavior. This type of models is known as a graybox model and is been introduced in this paper.     

Heat transfer modelling on windows and glazing under the exposure of solar radiation

Due to the effect of solar radiation on windows and glazing system the evaluation of heat flow is of primary importance in modeling the thermal performance within building interiors to account thermal comfort and overall energy consumption of a building. In this context the optical properties of window glazing are measured to determine the percentage absorption of incident solar radiation. An experimental study was performed in a room to measure the glazing surface temperature due to the global radiation on it. The corresponding window plane global radiation and horizontal global radiation were measured outside for simulation. Mathematical models have been developed to simulate the window plane solar radiation and corresponding glazing surface temperature aiming at validating the measured values. The thermal model is concerned with laminar heat transfer for natural and forced convection process according to the ambient conditions. The estimated errors between experimental and simulated values of window plane radiation and glazing temperature are shown to be within ±5%. Using the developed thermal model the heat flow inside the room through windows is determined. Thus overall heat transfer coefficient of glazing (U-factor) and the Solar Heat Gain (SHG) of building interior have been predicted from the simulation.     

套室内人体热舒适的研究

借助于通用流场计算软件PHOENICS，在考虑了外界气温、太阳的热辐射条件，家具以及人员等室内微气候影响的情况下，预测了两室一厅套室内气流三维流场和温度场。得到了套室内气流的速度、温度和人体热舒适指数等参数的分布，并经过评定，该套室内的热环境达到了人体的舒适性要求。模拟计算结果对套室的设计及其空调系统的配置具有重要的参考价值，并为套室内人体热舒适的进一步研究和室内空气品质问题的研究奠定了基础。     

磁浮轨道钢箱梁日照温度场及变形研究

磁浮轨道梁日照作用下的温度变形是轨道梁设计需考虑的重要因素,文章根据传热学与有限元理论,结合上海夏季气象参数与日照辐射半经验公式,利用ANSYS建立上海磁浮线轨道钢箱梁日照温度场三维瞬态模型,经实测构件验证,计算值与实测值吻合良好。分析磁浮轨道梁的最大竖向与横向温差发生时刻的温度梯度分布,并以指数函数为基础拟合得到对应温度梯度曲线,竖向温差拟合值略低于德国磁浮规范值,横向温差拟合值高于德国磁浮规范值。基于日照温度场分析结果,计算不同支承形式钢轨道梁的温度变形,得到磁浮轨道钢箱梁在双跨连续形式下能够较好抵抗温度变形的结论。提出磁浮轨道钢箱梁外露部分涂料的选取建议,以减小日照辐射吸收能量,从而降低截面温差及温度梯度变形。     

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。     

Frequency- and time-domain thermal response of dwellings

A system of algorithms is developed for calculation of the frequency- and time-domain responses of the heat transfer equations for a dwelling. Conduction through the walls, considered as multi-layered slabs, as well as convection to the inside air, infiltration, solar radiation deposition in the space, and radiative interaction between the walls is included in the calculation. The first part of this system of algorithms provides a means whereby a set of frequency responses of the dwelling as a whole may be calculated, one frequency response for each input-output pair, considering internal temperature or heat flow as the output, and the sol-air temperatures on each surface, infiltration, and the solar heat gain to the interior as inputs. The second part of the system of algorithms is then used to obtain from these frequency responses sets of digital transfer function coefficients of the type presented in the ASHRAE Handbook of Fundamentals, but relating the total dwelling heat gain, rather than that for a single wall, with specified internal temperatures, or internal temperature with specified heat gains, to the sol-air temperatures on each surface, infiltration, and solar heat deposited in the interior. The method is shown to produce rapidly calculatable, accurate results in the time-domain. Further the plots of the frequency responses themselves are expected to prove useful in seeking optimal thermal designs.     

Performance study of underground thermal storage in a solar-ground coupled heat pump system for residential buildings

This paper is performed to analyze the performance of underground thermal storage in a solar-ground coupled heat pump system (SGCHPS) for residential building. Based on the experimental results, the system performance during a longer period is simulated by the unit modeling, and its parametric effects are discussed. The results show that the performance of underground thermal storage of SGCHPS depends strongly on the intensity of solar radiation and the matching between the water tank volume and the area of solar collectors. Compared with the solar radiation, the variations of the water tank temperature and the ground temperature rise lag behind and keep several peaks during the day time. For the case of Tianjin, the efficiency of underground thermal storage based on the total solar radiation and absorbed solar energy by the collectors can reach over 40% and 70%, respectively. It is suggested that the reasonable ratio between the tank volume and the area of solar collectors should be in the range of 20–40 L/m².     

夏热地区热通道玻璃幕墙的热工数学模型

本文介绍了热通道玻璃幕墙的简单数学模型。模型的物理概念和Trombe墙相似。该幕墙由外侧单层和内层中空玻璃组成热通道。列出稳态状态下热通道的热平衡方程,通过线性矩阵求解了两个玻璃和通道内空气的半均温度,并使用热阻网络表达在太阳辐射条件下,热通道的传热过程。计算机模拟表明,夏热地区热通道幕墙内层中空玻璃的外表面温度较传统幕墙的表面温度有明显降低,由太阳透射引起的房间得热也有较大减少。     

槽式太阳能集热器传热模型及性能分析

槽式太阳能集热器一维和二维传热数学模型是一组非线性代数方程,为改进求解的稳定性和计算精度,将槽式太阳能集热器一维和二维传热模型的求解看作有约束优化问题,建立了集热器传热过程求解的有约束优化数学模型,应用MATLAB软件优化函数fmincon进行求解。分析了传热流体入口温度及太阳能辐射热流密度变化对集热器性能的影响。采用fmincon函数求解集热器传热过程,计算速度快,计算过程稳定。分析表明,传热流体温度变化对集热器效率的影响大于太阳能辐射热流密度对集热器效率的影响。     

A study of non-flashover and flashover fires in a full-scale multi-room building

Realistic fire environments in a prototype multi-room apartment in a multi-storey building are studied. The fires are designed as non-flashover and flashover types, using standard polyurethane mattresses as fuel. A comprehensive set of experimental data is presented. The measured results include flame spread velocity, mass release rate, gas temperature, radiation heat flux and gas analysis. A computational fluid dynamics (CFD) model, called a CESARE-CFD fire model, has been used to simulate these polyurethane slab fires. The CFD model is described by three-dimensional transport equations for mass, momentum and enthalpy. The turbulence flow was modelled using the k−ϵ model. A soot formation model and a flame spread model were incorporated into the CFD model. The flame spread velocity and the mass release rate of the polyurethane slab fires were predicted in this study. It was found that the CFD model provided reasonable predictions of the magnitude and trends for the experiments both in the non-flashover and flashover fire cases.     

“SOLVENT”: development of a reversible solar-screen glazing system

Preliminary experiments with a novel glazing system developed at the Desert Architecture and Urban Planning Unit of Ben-Gurion University of the Negev in Israel indicated that it may provide improved visual and thermal performance in buildings with large glazed areas located in sunny regions, regardless of orientation. In winter, it reduces glare, local over-heating and damage to furnishings caused by exposure to direct solar radiation, with only a small reduction in solar space heating. In summer, it reduces the penetration of unwanted radiation without obstructing the view through the window, to an extent that may render external shading devices unnecessary. The SOLVENT project was contracted to complete the development of the glazing system, which is based on the concept of converting short-wave solar radiation to convective heat and long wave radiation. The glazing system was modeled and evaluated experimentally; a suitable frame was developed for it; and a design tool required for its application was developed. The current paper reports on physical modeling and experimental evaluation of the glazing system.     

空气源热泵在学生公寓的热水改造工程中的应用

以重庆某学校采用燃气锅炉房作为热源的洗浴热水加热系统作为研究对象。对热水系统日用热量进行了分析。对原加热系统提出两种改造方案:空气源热泵加热系统、太阳能辅助空气源加热系统,探讨了这两种加热系统的系统流程,与原加热系统的年运行费用进行了比较,太阳能加热系统的年运行费用最低。     

Internal convective heat transfer modeling: Critical review and discussion of experimentally derived correlations

Heat is transferred through building envelopes by conduction, radiation, and convection. Of these, convective heat transfer is often the weakest ‘link’ in the overall heat transfer model. While conduction and radiation heat transfer are supported by well-established analytical and numerical models, the treatment of convection is much less rigorous. Convection modeling involves solution of fluid dynamics problems in which the complexity of an enclosed space's geometry and the diversity of indoor airflow patterns require many fit-for-purpose convection correlations. These must take into account specifics of the space and of the heating ventilation and air-conditioning (HVAC) system. This paper provides an overview of the current knowledge on the modeling of convective heat transfer in load calculation and building energy simulation programs. The paper also discusses various issues related to the robustness of convection coefficient correlations, and reports on new experiments conducted to test the sensitivity of existing convection correlations. The discussed issues relate to: (1) the non-uniformity of the indoor temperature field; (2) the selection of a proper characteristic dimension; (3) the effect of adiabatic and non-adiabatic obstructions in the zone; and (4) the impact of airflow disturbance.     

混水供暖系统的动态仿真

建立了某区域供暖系统的动态模型,分析了系统的动态特性及散热损失、补水率、混水比、太阳辐射及室内得热量对室内温度的影响。模拟了四种不同控制策略下的室温动态变化过程。结果显示,回水温度控制策略不但能满足室温的要求,而且可获得9.7%的锅炉燃料节能效益。     

Numerical analysis on heat transfer characteristics of ionic liquids in a tubular heat exchanger

ABSTRACT

The efficiency of the solar thermal system depends on the performance of the solar collectors. There is a need to operate solar collector at higher possible temperature to attain maximum efficiency limits. However, the performance of the collector system is limited by the heat transfer characteristics of the working fluid called as the heat transfer fluid (HTF). Water is widely used as the HTF in the solar collector, but the major problem of using water as the HTF is its limited operating temperature. The objective of the work is to investigate the heat transfer characteristics of ionic liquids in tubular heat exchanger (HE) suitable for the solar thermal application. The HE was designed for a heat duty of 1?kW based on the thermal transport property of available ionic liquids and the computational fluid dynamics (CFD) analysis was performed. The results indicate that there is only minimal deviation between the assumed and CFD data.     

太阳能热泵系统制热季节性能系数的分析

介绍了太阳能热泵（空气源＋水源热泵）供热系统的流程。选取单纯空气源热泵运行模式（运行模式1）、太阳能热泵运行模式（运行模式2）,在室外温度-10～7℃范围内,对两种运行模式制热量、设备功耗的计算式进行了拟合。计算比较了两种运行模式下的制热季节性能系数,运行模式1、2的制热季节性能系数约为2．56、3．48。     

Modeling and simulation on the thermal performance of shape-stabilized phase change material floor used in passive solar buildings

Shape-stabilized phase change material (PCM) is a kind of novel PCM. It has the following salient features: large apparent specific heat for phase change temperature region, suitable thermal conductivity, no container. In the present paper, a kind of shape-stabilized PCM floor is put forward which can absorb the solar radiation energy in the daytime and release the heat at night in winter. Therefore, in winter the indoor climate can be improved and the energy consumption for space heating may be greatly reduced. A model of analyzing the thermal performance of this shape-stabilized PCM floor is developed. By using the modeling, the influence of various factors (thickness of PCM layer, melting temperature, heat of fusion, thermal conductivity of PCM, etc.) on the room thermal performance was analyzed. The model was verified by the experimental results. The model and the analysis are helpful for the application of shape-stabilized PCM floor in solar buildings.     

A simple procedure for selection and sizing of indirect passive solar heating systems

Equivalent sol-air temperatures have been defined for four indirect gain passive solar heating concepts, namely, mass wall, water wall, Trombe wall and solarium. Steady state thermal efficiencies have also been defined as a measure of the ability of each system to deliver heat into the living space.

Design curves have been developed which relate the average instantaneous solar radiation incident on the passive element to thermal efficiency for different values of ambient temperature. These curves are useful in selection of an appropriate passive heating concept for a particular location.

It is inferred that a solarium is most effective at very low levels of incident radiation and low ambient temperature. Water walls and Trombe walls are most efficient at higher levels of incident radiation.

A simple procedure has been developed for a first approximation of sizing the selected system using these design curves and a minimum of meteorological information, namely, monthly average of daily global solar radiation, monthly average maximum and minimum ambient temperatures.     

Energy performance of a dual airflow window under different climates

Ventilated windows have shown great potential in conserving energy in buildings and provide fresh air to improve indoor air quality. This paper reports our effort to use EnergyPlus to simulate the energy performance of a dual airflow window under different climates. Our investigation first developed a network model to account for the two-dimensional heat transfer in the window system and implemented it in EnergyPlus. The two-dimensional assumption and the modified EnergyPlus program were validated by the measured temperatures of the window and the energy demand of a test cell with the window under actual weather conditions. Then EnergyPlus was applied to analyze energy performance of a small apartment installed with the dual airflow windows in five different climate zones in China. The energy used by the apartment with blinds windows and low-e windows was also calculated for comparison. The dual airflow window can reduce heating energy of the apartment, especially in cold climate. The cooling energy reduction by the window was less important than that by shading solar radiation. The dual airflow window is recommended for colder climate. If improving air quality is a major consideration for a building, the window can be used in any climate.     

高校学生公寓太阳能与建筑一体化设计与节能分析

通过太阳能空气源热泵辅助热水系统在高校学生公寓热水系统设计中的运用,提出了太阳能与建筑一体化的设计,并对热水系统的节能量和减排量进行了分析。