The use of a heavy internal wall with a ventilated air gap to store solar energy and improve summer comfort in timber frame houses

This paper considers supplementary heating and cooling within timber frame houses. The transmission of solar energy to an internal concrete cavity wall by air is analyzed. The objective of this work was initially to study the dynamic insulation in timber frame houses. The initial studies showed that it is more efficient to recover solar energy rather than heat losses, which is the principle of dynamic insulation. Clearly, the thermal regulations lead to lower heat losses through walls by conduction. Due to these factors we have decided to study a wall with an integrated solar air collector and a heavy ventilated internal wall. This internal wall, which is used to store solar energy will allow the reduction of heat demand in winter and will improve thermal comfort in summer because thermal mass increases and ventilation during the night will cool the internal wall. We have selected a closed loop air circulation system because, with an air to air heat exchanger, it can be proved to be more effective and the risk of unhealthy air pollution is reduced because the flow of fresh air will not pass through the ventilated air gap. We are constructing an integrated air collector prototype.     

双层通风玻璃幕墙的热过程及热工设计

通过对双层通风玻璃幕墙的节能原理及其传热过程的分析,并运用CFD流体模型对幕墙传热进行了模拟分析,验证了其节能原理,推导出幕墙的整体传热系数,为双层通风玻璃幕墙的热工设计提供计算依据,并提出相应的设计建议。     

建筑门窗玻璃幕墙传热系数现场测试研究

建筑门窗玻璃幕墙是建筑围护结构节能最薄弱部位,其传热系数目前只能在实验室通过热箱法测定,在现场准确、快捷地测试该值对于建筑的节能评估改造具有重要意义。在现场测试门窗幕墙内外空气温度和表面温度的基础上,推导出了基于"准稳态"测试原理和"热阻法"、"表面温度法"、"传热系数法"3种传热系数现场测试方法,现场测试值与实验室检测值的较高一致性表明了该现场测试方法的准确性,连续测试数据与平均值的较小偏差表明了该测试方法的稳定性。研究结果表明,建筑门窗玻璃幕墙传热系数可通过该方法在现场准确、快捷地测试得到。     

Analysis of thermal performance of building attached sunspace

The thermal performance of a sunspace attached to a living room located in Amman-Jordan has been investigated. Six configurations that differ by the ratio of glazed surface area to opaque surfaces area are studied. A novel configuration that utilizes an inclined front surface is thermally investigated. The effect of orientation of the sunspace, opaque wall and floor absorption coefficients and number of glass layers on the thermal performance is evaluated. Results show that the sunspace reduces the heating load during the winter, while it creates a serious overheating problem during summer. The contribution of reducing heating requirements increases with increasing the ratio of glazed surface to opaque surface area. Also, the optimal contribution was obtained when the sunspace was oriented to the south. Two passive cooling techniques are proposed and evaluated to overcome the summer overheating problem. Additionally, a passive heating technique is proposed to minimize the thermal losses during winter nights. Internal shading and night ventilation successfully minimize the overheating problem. Employing the three passive techniques with sunspace, results show that as high as 42% reductions in annual heating and cooling load can be achieved. Utilizing an inclined front surface with double layer of glass can further reduce heating and cooling load requirements.     

太阳能烟囱自然通风的一维稳态模型

太阳能烟囱是一种利用太阳能加热来强化自然通风的技术.在前人简化模型的基础上,考虑了玻璃盖板和集热墙的导热热阻的影响,建立了一个修正的太阳能烟囱自然通风的一维稳态数学模型.并利用此模型,对太阳能烟囱内的空气平均温度、集热墙温度、空气流量以及集热效率等进行了模拟计算和讨论.模型计算结果与相关实验数据及前人的简化模型进行了对...     

Model scale tunnel fire tests with automatic sprinkler

The study focuses on the performance of an automatic sprinkler system in a model scale tunnel with longitudinal ventilation. A total of 28 tests were carried out in a 1:15 model scale tunnel using an automatic sprinkler system with glass bulbs. The maximum heat release rate, energy content and failure of the automatic sprinkler system were analysed. The results show that high ventilation rates and low water flow rates result in a failure of the automatic sprinkler system in a longitudinal ventilated tunnel fire. The main reason for the failure under the tested water flow rates was the effect of the longitudinal flow on the fire development and the hot gas flow close to the sprinklers. The fire development and the activation heat release rate of the first activated bulb are intimately related to the ventilation velocity. The fire spread to the neighbouring wood crib was investigated and a presentation of tests conducted using a deluge system are given.     

带遮阳百叶热通道幕墙的热工数学模型

介绍了带遮阳百叶的热通道玻璃幕墙的简单数学模型。该幕墙由外侧单层玻璃幕墙和内侧中空玻璃幕墙组成热通道,通道中内置遮阳百叶以减少太阳能透射得热。在夏热地区,空气在通道中被太阳辐射加热,处于自然通风状态之下。列出了稳态条件下系统的热平衡方程,通过线性矩阵求解了太阳辐射和外界环境温度分别改变时,两个玻璃和通道内两个空气层及百叶的平均温度。计算模拟表明,内置遮阳百叶的热通道幕墙的内层中空玻璃的外表面温度较传统单层幕墙的表面温度有明显降低;与无遮阳百叶的热通道幕墙相比,室内透射得热量有很大减少,传热系数也比中空玻璃和无遮阳百叶的热通道幕墙有显著降低。     

Convective heat transfer coefficients in a full-scale room with and without furniture

The convective heat transfer coefficient at an outer ambient wall with a window exposed to natural climate was measured in a room with and without furniture. The method used was to estimate the heat flow from measured temperatures and solar radiation. The convective heat transfer was calculated as the difference between the heat flow through the building element and the calculated long-wave radiation. Even though the accuracy was at best ±15%, the effect of different heating and ventilation strategies could clearly be detected. Local coefficients may be more than 10 times the expected, due to ventilation or position of the radiator.     

Simulation of buoyancy-driven natural ventilation of buildings—Impact of computational domain

Two computational domains have been used for simulation of buoyancy-driven natural ventilation in vertical cavities for different total heat fluxes and wall heat distributions. Results were compared between cavities with horizontal and vertical inlets. The predicted ventilation rate and heat transfer coefficient have been found to depend on the domain size and inlet position as well as the cavity size and heat distribution ratio. The difference in the predicted ventilation rate or heat transfer coefficient using two domains is generally larger for wider cavities with asymmetrical heating and is also larger for ventilation cavities with a horizontal inlet than those with a vertical inlet. The difference in the heat transfer coefficient is generally less than that in the ventilation rate. In addition, a ventilation cavity with symmetrical heating has a higher ventilation rate but generally lower heat transfer coefficient than does an asymmetrically heated cavity. A computational domain larger than the physical size should be used for accurate prediction of the flow rate and heat transfer in ventilation cavities or naturally ventilated buildings with large openings, particularly with multiple inlets and outlets. This is demonstrated with two examples for natural ventilation of buildings.     

泡沫玻璃外墙外保温系统温度场的数值模拟

计算数据来源于泡沫玻璃外墙外保温系统墙体大型耐候性试验,结合COMSOL软件分别对泡沫玻璃外墙外保温系统耐候性试验的高温—淋水循环和加热—冷冻循环进行了数值模拟,以在耐候性试验机箱体内的环境实时温度作为试验墙体的温度条件,墙体内外表面考虑对流换热边界条件,忽略热辐射的影响,并且忽略层间热阻.对泡沫玻璃外保温系统的主要功能层沿厚度方向和同一层平面不同位置的温度场进行比较,模拟结果表明泡沫玻璃外保温系统具有良好的保温作用,窗户等周围部位是外保温墙体的薄弱位置,温度场和温度应力变化较大,易产生裂缝,在实际工程中应给予重视.     

Natural ventilation in an enclosure induced by a heat source distributed uniformly over a vertical wall

A simple multi-layer stratification model is suggested for displacement ventilation in a single-zone building driven by a heat source distributed uniformly over a vertical wall. Theoretical expressions are obtained for the stratification interface height and ventilation flow rate and compared with those obtained by an existing model available in the literature. Experiments were also carried out using a recently developed fine-bubble modelling technique. It was shown that the experimental results obtained using the fine-bubble technique are in good agreement with the theoretical predictions.     

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。     

Impact of computational domain on the prediction of buoyancy-driven ventilation cooling

Traditional solar heated cavity structures such as solar chimneys make use of the stored solar energy in the interior wall to enhance natural ventilation of buildings but integration of photovoltaic devices into the exterior wall of such a structure can result in different proportions of heat distribution on both interior and exterior walls. This paper presents results of CFD simulation of the buoyancy-driven airflow and heat transfer in vertical cavities of different heights and widths with different total heat fluxes and wall heat distributions for ventilation cooling. Two sizes of computational domain were used for simulation – a small domain same as the physical size of a cavity and a large extended domain that is much larger than the cavity. The predicted natural ventilation rate and heat transfer coefficient have been found to depend on not only the cavity size and the quantity and proportion of heat distribution on the cavity walls but also the domain size. The difference in the predicted ventilation rate or heat transfer coefficient using the small and large domains is generally larger for wider cavities where heat distribution on two vertical walls is highly asymmetrical; incoming air would be distorted from symmetrical distribution across the inlet opening; and/or significant reverse flow would occur at the outlet opening. The difference in the heat transfer coefficient is generally less than that in the ventilation rate. In addition, a cavity with symmetrical heating has a higher ventilation rate but lower heat transfer coefficient than does an asymmetrically heated cavity.     

外呼吸式双层玻璃幕墙模拟分析

对某办公建筑的外呼吸式双层玻璃幕墙应用AIRPAK软件进行了模拟分析,比较了自然通风和机械通风在不同风速情况下的流场与温度场。提出了较好的风口布置方式。     

外呼吸式双层玻璃幕墙模拟分析

对某办公建筑的外呼吸式双层玻璃幕墙应用AIRPAK软件进行了模拟分析,比较了自然通风和机械通风在不同风速情况下的流场与温度场.提出了较好的风口布置方式.     

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.     

拉萨某中学办公楼节能改造

根据国家公共建筑节能标准的指导思想,结合高原地区的气候条件,以改造后能源消耗降低50%作为评价建筑节能改造方案是否达标的下限。以拉萨中学办公楼实际改造工程为例,介绍了主要建筑部分的节能改造措施。改造后,新的外窗全部改为双层玻璃窗;外墙保温材料选用岩棉板材料,提高了外墙的保温性能和防火性能。屋顶保温材料选用硬泡聚氨酯,以提高防水性能。此外,根据外墙的实际情况,特别注意了热桥部分的保温改造。改造后进行能耗计算,结果显示改造后的建筑全部达到节能设计要求。     

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

The back-up heat needed to maintain a mean design temperature T_d in a room depends on the one hand upon the loss of heat by ventilation and through the opaque part of the fabric, and on the other hand upon the difference between conducted loss and solar gain through windows. This second term depends on a quantity T_sai (a form of sol-air temperature applicable to an enclosure interior), which includes the ambient temperature T_ao, and the solar gain and conducted losses for the glazing concerned. If T_sai is less than T_d, the glazing is disadvantageous as a contributor to the total heat needed.

Tables are presented of the month-by-month joint distribution of daily mean values of T_ao and the total irradiance on a near south-facing wall for a site on the north Wirral (53.4°N), based on 50 years' records. From these and assumed windows characteristics, cumulative functions of T_ao and T_sai are calculated. Estimates of the back-up heat needed to maintain T_d are presented in graphical and numerical form to show its dependence on month, fraction of glazed area, ventilation and fabric loss, glazing characteristics and design temperature.     

Natural convection in the cavity of a basement block wall

A full-scale experimental programme to study the ad freeze/heaving problem of an insulated basement is currently underway at the National Research Council of Canada. Apart from heaving results this experiment has also yielded interesting findings related to the natural convection in concrete-block wall cavities. Both the field data and a simplified finite element model calculation show that natural convection in a block basement wall can be a significant factor contributing to heat losses. Insulating only the inside upper portion of the wall, as is current practice, may not be effective in reducing heat losses with block walls, while full length insulation may lead to significant lowering of ground temperatures near footing levels.     

Glass–azimuth modification to reform direct solar heat gain

A means of reforming the solar heat gain, and hence, energy conservation in air-conditioning systems is suggested and studied. The main idea is to control the solar gain by horizontal rotation of glass windowpanes, i.e. modifying the glass–azimuth irrespective of the original orientation of the building wall. The influence of the rotation angle, magnitude and direction, on the instantaneous, daily and seasonal solar heat gain is investigated in detail. A computer program is coded to carry out the extensive computations. This program is prepared in a general and versatile form, in the sense that it can be used at any location and time, for any wall orientation and any type of glazing characterized by the extinction coefficient, index of refraction, and thickness. The study helps the designer to select an optimum glass rotation angle which increases or decreases the heat gain depending on the objective. There may be two optimum rotation angles, the first results in reducing the air-conditioning system size, while the second angle decreases the energy consumption.