Primary energy implications of ventilation heat recovery in residential buildings

In this study, we analyze the impact of ventilation heat recovery (VHR) on the operation primary energy use in residential buildings. We calculate the operation primary energy use of a case-study apartment building built to conventional and passive house standard, both with and without VHR, and using different end-use heating systems including electric resistance heating, bedrock heat pump and district heating based on combined heat and power (CHP) production. VHR increases the electrical energy used for ventilation and reduces the heat energy used for space heating. Significantly greater primary energy savings is achieved when VHR is used in resistance heated buildings than in district heated buildings. For district heated buildings the primary energy savings are small. VHR systems can give substantial final energy reduction, but the primary energy benefit depends strongly on the type of heat supply system, and also on the amount of electricity used for VHR and the airtightness of buildings. This study shows the importance of considering the interactions between heat supply systems and VHR systems to reduce primary energy use in buildings.     

核废料处置库近场岩石热应力半解析方法研究

针对地下核废物处置库近场环境为饱和裂隙岩体时的情况,提出了一种由分布热源、饱和稀疏裂隙和岩石构成的简化概念模型,根据Goodier提出的热弹性位移势,采用拉普拉斯变换、格林函数法和数值积分等方法,计算求解概念模型中处置库近场岩石的温变热应力。并以实际算例分析分布热源作用下稀疏裂隙岩体受三维水流-传热过程影响的热应力特征以及裂隙水流速和分布热源间距对裂隙岩体热应力分布的影响。结果表明,裂隙水的流动传热作用将处置库近场岩石的热量向下游传递,从而降低了近场岩石的温度,减小了近场岩石中的热应力,裂隙水流速越快,对近场岩石中热应力的影响越明显;热源间距越小时,处置库近场岩石的热应力越大;当热源间距小于一定值时,不同热源间传热作用的叠加将使处置库近场岩石的热应力峰值急剧增大。     

冷凝式锅炉辅助太阳能供热系统性能分析

根据我国北方太阳能供热的特点，提出了冷凝式锅炉辅助太阳能热水器供热系统，分析了该系统的特点；并与其他两种热源辅助太阳能热水器供热系统(电加热器和家用燃气锅炉辅助太阳能热水器供热系统)进行了经济性和环保性比较。     

Electrical savings by use of wood pellet stoves and solar heating systems in electrically heated single-family houses

This study investigates how electrically heated single-family houses can be converted to wood pellets- and solar heating using pellet stoves and solar heating systems. Four different system concepts are presented and system simulations in TRNSYS evaluate the thermal performance and the electrical savings possible for two different electrically heated single-family houses. Simulations show that the electricity savings using a wood pellet stove are greatly affected by the level of comfort, the house plan, the system choice and if the internal doors are open or closed. Installing a stove with a water-jacket connected to a radiator system and a hot water store has the advantage that heat can be transferred to domestic hot water and be distributed to other rooms. Such systems leads to that more electricity can be replaced, especially in houses having a traditional plan. Though it is unnecessary to have too many radiators connected to a stove with a low fraction of energy heating the water jacket. Today's most common control strategy for stoves (the on/off-control) results in unnecessarily high emissions. A more advanced control varying the heating rate from maximum to minimum to keep a constant room temperature reduces the number of starts and stops and thereby the emissions.     

Reducing temperature stratification using heated air recirculation for thermal energy saving

Using discrete heat sources such as a radiator or a gas heater, a large amount of heated air is accumulated under the ceiling surface where it is usually far enough from the occupancy zone. The idea of transferring this heated air into the occupancy zone has been the subject of the present study. A full length-scale model of a compartment was constructed and equipped with a radiator and an air circulating mechanism. Temperature distribution on the symmetry plane was specified for the two cases of usual heating and heating with air circulation. Heat loss from the surfaces of the enclosure was also determined using thermal maps of both the internal and the external surfaces of the enclosure. In order to examine the effect of circulating air on the thermal energy saving quantitatively, a numerical model was developed and validated using experimental results. The input heat rate of the enclosure was compared for the two cases of usual heating and heating with air circulation considering different heights for a typical heating space. Based on the results, having the same mean air temperature within the occupancy zone, the input heat rate of a compartment could be moderated using circulating air criterion.     

Conversion of electric heating in buildings: An unconventional alternative

To decrease the electric energy used for heating buildings it has become desirable to convert direct electrical heating to other heat sources. This paper reports on a study of the possibility of using an unconventional method for conversion to avoid installing an expensive hydronic system. The conversion method combines the ventilation and heating systems and uses air instead of water for distribution of heat within the building, taking advantage of thermal forces and the special properties of gravity currents. Full-scale tests have been carried out in a test apartment inside a laboratory hall where the conditions could be controlled. Temperatures and efficiency of ventilation have been measured to ensure that the demands with respect to thermal climate and air exchange were fulfilled. The results show that it is possible to use the method for heating and ventilation when converting the heating system, but further work has to be done to develop a detailed solution that works in practice.     

The effect of floor heat source area on the induced airflow in a room

We examine the role of heat source geometry in determining rates of airflow and thermal stratification in natural displacement ventilation flows. We modify existing models to account for heat sources of finite (non-zero) area, such as formed by a sun patch warming the floor of a room. Our model allows for predictions of the steady stratification and ventilation flow rates that develop in a room due to a circular heat source at floor level. We compare our theoretical predictions with predictions for the limiting cases of a point source of heat (yielding a stratified interior), and a uniformly heated floor (yielding a mixed interior). Our theory shows a smooth transition between these two limits, which themselves result in extremes of ventilation, as the ratio of the heat source radius to the room height increases. Our model for the transition from displacement to mixing ventilation is compared to previous work and demonstrates that the transition can occur for smaller sources than previously thought, particularly for rooms with large floor area compared to ceiling height.     

Foundation heat loss from heated concrete slab-on-grade floors

In recent years, there has been a renewed interest in heated concrete slab floors to provide for space heating in both residential and commercial buildings. The existing design procedures for these heating systems are based on simplified thermal models with several assumptions. In particular, the simplified models assume that both the upper and the lower concrete slab surface are isothermal and that the heat transfer through the bottom of the slab surfaces is uniformly distributed over the entire surface. In this paper, a more realistic and flexible model for heated or cooled concrete slab floors is considered to determine the heat transfer between the concrete slab and the ground. In particular, steady-state and steady-periodic semi-analytical solutions are developed to determine the temperature field within the ground medium and within the concrete slab-on-grade floor where hot or chilled water pipes are embedded. The solution presented in this paper is applied to determine the ground heat loss/gain for a heated or cooled floor under various design conditions including the level of floor insulation, and the temperature of the water pipes. These solutions are obtained using the interzone temperature profile estimation (ITPE) procedure. Detailed analysis is presented to determine the effect of the slab insulation configuration on soil and slab temperature field and on the monthly variation of the total slab heat loss.     

基于人工神经网络的地板辐射空调系统预测控制方式

由于地板层的热容量较大,地板辐射空调系统的调节控制必须考虑房间热惰性的影响。建立了以热泵机组为冷热源的地板辐射空调系统的预测控制模型,该模型利用RBF人工神经网络技术,根据预测出的下一时刻的房间温度值来控制热泵机组的运行时间并调节房间的温度。将此预测模型用于实验系统冬季供暖工况房间温度的调节控制,实验结果表明,房间温度的预测值与实测值比较吻合。     

Performance evaluation of two types of heated cables for distributed temperature sensing-based measurement of soil moisture content

Distributed temperature sensing(DTS)using heated cables has been recently developed for distributed monitoring of in-situ soil moisture content.In this method,the thermal and electrical properties of heated cables have a significant influence on the measurement accuracy of soil moisture content.In this paper,the performances of two heated cables,i.e.the carbon-fiber heated cable(CFHC)and the metalnet heated cable(MNHC),are studied in the laboratory.Their structures,uniformity in the axial direction,measurement accuracy and suitability are evaluated.The test results indicate that the MNHC has a better uniformity in the axial direction than CFHC.Both CFHC and MNHC have high measurement accuracy.The CFHC is more suitable for short-distance measurement(500 m),while the MNHC can be used for longdistance measurement(500 m).     

Evaluation of hydronic loop energy and modeling of heated water loop containing multiple variable air volume units with hydronic reheat coils

Experimental data recorded for a heating, ventilating, and air conditioning system showed that the daily heated water loop energy calculated by summing the hourly-averaged loop heat transfer for the heated water loop is almost 35% higher than the sum of the daily energy consumed by variable air volume hydronic reheat coils in each zone. The main reason for this difference was attributed to the time delay of the loop return water temperature caused by the water traveling along the loop. This study examines methods to evaluate the heated water loop energy when there are time varying conditions. Data for a heated water loop are used to demonstrate the effects of the time delay on the evaluation of the loop energy. A pipe heat transfer model characterizing the transient response of a fluid flowing through a single pipe is developed to examine the effects of time varying conditions on the pipe thermal response. Based on the pipe heat transfer model, a loop model is constructed to simulate the actual loop with multiple hydronic reheat coils. The comparisons of the simulation results with the data indicate that the loop model is capable of predicting the loop return water temperatures and loop heat transfer based on data.     

基于电路理论的多尺度城市热环境网络 构建及格局优化：以成都市中心城区为例

高密度、高强度的城市建设和扩张导致城市热岛效应不断增强，研究城市热环境网络格局以优化规划布局是改善城市热环境的有效方法。将形态学空间格局分析与电路理论相结合，立足多尺度，以成都市中心城区及其核心区为研究对象，选取连通性强的冷岛、热岛源地，根据景观格局特征与地表覆盖构建阻力面，运用Linkage Mapper识别廊道、冷岛障碍点和热岛夹点，并进行分级和评价，构建研究区热环境网络，提出多尺度下的格局优化建议。结果表明：1)中心城区尺度识别出23处冷岛源地、34条关键廊道、48处障碍点，廊道呈“串珠状”环绕研究区边缘分布，连通性和稳定性较弱；2)中心城区核心区尺度识别出34处热岛源地、81条关键廊道、98处夹点，廊道呈网状分布且普遍连通性较高，夹点是未来阻断热岛廊道连通的关键区域；3)研究区形成“两环多分支五组团多点”结构的城市热环境网络格局。研究结果可为成都市及其他城市的热环境改善提供科学参考，丰富电路理论在热环境领域中的应用。     

A comparative performance study of some thermal storage materials used for solar space heating

One of the most common methods used in passive heating is the utilization of a massive wall for heat storage. Many factors affect the performance of the wall, such as the thickness and the media used for heat storage. A numerical study has been conducted on a zone heated by a thermal storage wall. Three different storage materials are examined, namely concrete, the hydrated salt CaCl₂·6H₂O and paraffin wax (N-eicosane). A numerical model is presented in this paper which judges the suitability of these materials as thermal storage mediums under the actual weather conditions of Iraq. For that purpose, the room temperature fluctuation in the zone is evaluated for each material using different thickness for each wall. The study concluded that an 8-cm-thick storage wall made from the hydrated salt is capable of maintaining the comfort temperature in the zone with the least room temperature fluctuation.     

The function of solar absorbing window as water-heating device

While window glazing will be more and more extensively used in modern architecture, the increase in space thermal load as a result will deteriorate the global environment, incurring problems of air pollution and climate change. By connecting the cavity of a double pane window to a water-flow circuit, absorbed solar heat at the window glasses can be readily removed by the water stream. The water passage in this way can effectively lower the glass pane temperature, reduce room heat gain and therefore, the air-conditioning electricity consumption. Thermal comfort can be enhanced. Furthermore, the water-flow window can function as a hot-water preheating device. This article reports the integrative thermal performance of a water-flow absorbing window as compared to the conventional single and double pane absorptive glazing. The results based on the operation in health club environment are very encouraging. This demonstrates its good application potential in domestic–commercial buildings with stable hot-water demands.     

基于火炕的热水供暖火墙系统供暖效果研究

将火墙式火炕与热水供暖系统相结合,在火墙燃烧室的正上方加设集热器,在房间布置散热器,利用热水循环将火墙燃烧室的部分热量转移,供给其他无炕、无火墙房间.对加设热水系统后的火炕和热水系统的热工性能及室内热环境进行了实验研究.结果表明,该供暖系统在保证火炕房间供暖条件下,能够满足无炕、无火墙房间的短期供暖要求,并且提高了火炕的热舒适性;可以燃用各种生物质燃料,从而减少农村商品能的消耗.     

Primary energy implications of end-use energy efficiency measures in district heated buildings

In this study we explore the effects of end-use energy efficiency measures on different district heat production systems with combined heat and power (CHP) plants for base load production and heat-only boilers for peak and medium load productions. We model four minimum cost district heat production systems based on four environmental taxation scenarios, plus a reference district heat system used in Östersund, Sweden. We analyze the primary energy use and the cost of district heat production for each system. We then analyze the primary energy implications of end-use energy efficiency measures applied to a case-study apartment building, taking into account the reduced district heat demand, reduced cogenerated electricity and increased electricity use due to ventilation heat recovery. We find that district heat production cost in optimally-designed production systems is not sensitive to environmental taxation. The primary energy savings of end-use energy efficiency measures depend on the characteristics of the district heat production system and the type of end-use energy efficiency measures. Energy efficiency measures that reduce more of peak load than base load production give higher primary energy savings, because the primary energy efficiency is higher for CHP plants than for boilers. This study shows the importance of analyzing both the demand and supply sides as well as their interaction in order to minimize the primary energy use of district heated buildings.     

Validation of Heat Transfer,Thermal Decomposition,and Container Pressurization of Polyurethane Foam Using Mean Value and Latin Hypercube Sampling Approaches

Polymer foam encapsulants provide mechanical, electrical, and thermal isolation in engineered systems. It can be advantageous to surround objects of interest, such as electronics, with foams in a hermetically sealed container in order to protect them from hostile environments or from accidents such as fire. In fire environments, gas pressure from thermal decomposition of foams can cause mechanical failure of sealed systems. In this work, a detailed uncertainty quantification study of polymeric methylene diisocyanate (PMDI)-polyether-polyol based polyurethane foam is presented and compared to experimental results to assess the validity of a 3-D finite element model of the heat transfer and degradation processes. In this series of experiments, 320 kg/m³ PMDI foam in a 0.2 L sealed steel container is heated to 1,073 K at a rate of 150 K/min. The experiment ends when the can breaches due to the buildup of pressure. The temperature at key location is monitored as well as the internal pressure of the can. Both experimental uncertainty and computational uncertainty are examined and compared. The mean value method (MV) and Latin hypercube sampling (LHS) approach are used to propagate the uncertainty through the model. The results of the both the MV method and the LHS approach show that while the model generally can predict the temperature at given locations in the system, it is less successful at predicting the pressure response. Also, these two approaches for propagating uncertainty agree with each other, the importance of each input parameter on the simulation results is also investigated, showing that for the temperature response the conductivity of the steel container and the effective conductivity of the foam, are the most important parameters. For the pressure response, the activation energy, effective conductivity, and specific heat are most important. The comparison to experiments and the identification of the drivers of uncertainty allow for targeted development of the computational model and for definition of the experiments necessary to improve accuracy.     

采暖方式对农村住宅室内热环境影响

以农村住宅采暖房间为研究对象,分析火炕和散热器采暖方式对其室内热环境的影响。室内空气自然对流采用Boussinesq假设,辐射传输方程采用净热流法,湍流采用k-ε模型描述,建立采暖房间室内热环境数学模型,利用Fluent对火炕及散热器采暖的室内热环境进行数值模拟。     

A review on assessment of fatigue strength in welded studs

Welding is one of the most important and highly developed joining methods; nevertheless unwanted side effects occur like thermal strains and altering of certain material properties induced by heating and melting. These effects lead to distortions and high residual stresses which should be kept to a minimum. To minimize distortion, various strategies are being developed. Stud welding is widely used in steel structures, power plants, and ship buildings due to the significantly technology including highest quality of production processes by continuous electrical control and the efficiency of such a process. Therefore, varying the heat input typically will affect the material properties including yield strength, tensile strength, hardness, and notch toughness in the stud arc welding. Well-defined heat sources offer a reproduced heat input into a highly localized area. The fatigue strength of stud welding has been investigated by performing welding process and microstructural observations. This paper is going to discuss the influence of heat input on the structural changes in stud arc welding.     

含跨季节储热的多能互补分布式能源系统容量配置优化

为了满足我国对环保及能源的需求,多能互补分布式能源系统成为了分布式能源系统的发展的趋势.文章针对北京地区某办公建筑构建了含跨季节储热的多能互补分布式能源系统,以年总成本最低为目标函数,在满足全年负荷的情况下利用P SO算法(粒子群算法)对该系统中的跨季节储热系统关键设备(储热水箱和基岩储热设备)的容量进行优化,得出了其...