Experimental study and evaluation of latent heat storage in phase change materials wallboards

Phase change materials (PCM) can be applied in building envelops to conserve heat energy. Wallboards incorporated with PCM can automatically absorb indoor redundant heat, which can greatly reduce the load of HVAC systems and save electric energy. In experiments, a PCM wallboard room was constructed by attaching PCM wallboards, developed by incorporating about 26% PCM by weight into gypsum wallboards, to the surface of an ordinary wall. The transition temperature and latent heat of these PCM wallboards were tested by differential scanning calorimetry (DSC). The room testing was conducted to determine the latent heat storage of PCM wallboards. Through experiments, it could be proved that DSC can effectively predict the performance of a full-scale installation of PCM wallboards. Compared with an ordinary room, it was found that the PCM wallboard room could greatly reduce the energy cost of HVAC systems and transfer electric power peak load to valley.     

Effects of wallboard design parameters on the thermal storage in buildings

The phase change material (PCM) could be added to the wallboard to increase the thermal mass to decrease in indoor temperature fluctuation and improve thermal comfort. In this study, experimentally validated simulation was performed to investigate the effects of various parameters of PCM including the nominal average phase change temperature, its range, the convective heat transfer coefficients and the wallboard thickness on the thermal storage performance of the wallboard such as the thermal energy storage and the time shift.It was found that the average phase change temperature should be close to the average room temperature to maximize the thermal heat storage in the wallboards. The phase change temperature should be narrow to maximize the thermal heat storage in the PCM wallboards. The thermal heat storage increased with the convective heat transfer coefficient, and the optimal average phase change temperature to maximize the storage shifted a bit to a higher temperature with it. The time shift was found to decrease with the convective heat transfer coefficient and the phase change temperature range.     

Eutectic mixtures of capric acid and lauric acid applied in building wallboards for heat energy storage

Capric acid (CA) and lauric acid (LA), as phase change materials (PCM), can be applied for energy storage in low temperature. The phase transition temperature and values of latent heat of eutectic mixtures of CA and LA are suitable for being incorporated with building materials to form phase change wallboards used for building energy storage. 120, 240 and 360 accelerated thermal cycle tests were conducted to study the changes in latent heat of fusion and melting temperature of phase change wallboards combined with the eutectic mixtures of CA and LA. Differential scanning calorimetry (DSC) tested the transition temperature and latent heat. The results showed that the melting temperature and latent heat of these phase change wallboards with eutectic mixtures have not obvious variations after repeated 360 thermal cycles, which proved that these phase change wallboards have good thermal stability for melting temperature and variations in latent heat of fusion for long time application. Therefore, they can be used for latent heat storage in the field of building energy conservation.     

Thermal testing and numerical simulation of a prototype cell using light wallboards coupling vacuum isolation panels and phase change material

Light envelopes are more and more frequently used in modern buildings but they do not present sufficient thermal inertia. A solution to increase this inertia is to incorporate a phase change material (PCM) in this envelope. This paper presents the performance of a test-cell with a new structure of light wallboards containing PCMs submitted to climatic variation and a comparison is made with a test-cell without PCMs. To improve the wallboard efficiency a vacuum insulation panel (VIP) was associated to the PCM panel. This new structure allows the apparent heat capacity of the building to be increased, the solar energy transmitted by windows to be stored without raising the indoor cell temperature, and the thickness of the wallboard to be decreased compared with that of traditional wallboards. An experimental study was carried out by measuring temperature and heat fluxes on and through the wallboards. The indoor temperature, which has a special importance for occupants, was also measured.A numerical simulation with the TRNSYS software was carried out in adding a new module representing the new wallboard. It showed a good agreement with experimental results. This new tool will allow users to simulate the thermal behaviour of buildings having walls with PCMs.     

Novel concept of composite phase change material wall system for year-round thermal energy savings

A new type of composite wall system incorporating phase change materials (PCMs) was proposed and its potential for air conditioning/heating energy savings in continental temperate climate was evaluated. The novelty of the wall system consists of the fact that two PCM wallboards, impregnated with different PCMs are used. The structure of the new wall system is that of a three-layer sandwich-type insulating panel with outer layers consisting of PCM wallboards and middle layer conventional thermal insulation. The PCM wallboard layers have different functions: the external layer has a higher value of the PCM melting point and it is active during hot season and the internal layer with a PCM melting point near set point temperature for heating is active during cold season. A year-round simulation of a room built using the new wall system was carried out and the effect of PCM presence into the structure of the wall system was assessed. It was found that the new wall system contributes to annual energy savings and reduces the peak value of the cooling/heating loads. The melting point values for the two PCMs resulting in the highest value of the energy savings were identified.     

相变换热系统对室内温度影响的探究

相变换热系统利用相变材料的蓄热特性,在夜间谷电时段使用廉价电能蓄热,并在白天释放热量,控制室内温度。试验表明相变换热系统在夜间蓄热之后,实现连续30小时出风温度在20℃以上,将空间体积为50 m3的试验房维持在10℃以上的效果,实现电力的移峰填谷,提高室内的舒适性。     

相变墙体冬季传热性能评价及相变参数优化

本文从相变墙体冬季的传热过程出发,提出“保温因子”和“放热因子”评价其传热性能。然后,利用热阻法建立相变墙体在冬季的传热模型,并利用单因素分析的方法研究相变墙体内外层热阻和相变温度对“保温因子”和“放热因子”的影响,结果显示当相变墙体的作用是保温的情况下,相变层应布置在墙体的外侧,相变温度应该接近室内空气温度。当相变墙体的作用是放热的情况下,相变层应布置在墙体的内侧,相变温度应该尽量高一些。本研究可以为相变墙体的应用提供理论支持。     

相变墙房间传热模型数学简化与求解探索

相变材料是一种高效的贮能物质,相变技术也是当前研究的热点。总结了相变材料的传热机理,以及相变材料的制备和热物理性能,并对相变墙房间模型的建立和求解的一般研究方法进行了汇总,最后针对目前的研究现状提出了急需解决和进行研究的问题。     

覆土建筑冬季室内热舒适性研究

通过对西安地区某覆土建筑冬季室内热环境的测试,分析了测试房与对比房的温度测试数据。结果表明测试房内各测点逐时温度均高于对比房,室内温度变化幅度也明显小于对比房,且覆土建筑的室内温度略高于当地室内设计采暖温度。在测试的基础上采用主观温度法对室内热舒适性进行参考性评价,结果显示测试房室内热环境较好地满足了使用者对热舒适的需求。因此,覆土建筑在冬季能够有效维持室内温度,提高热舒适性,同时能够降低建筑采暖能耗。     

地板辐射供暖房间温度调节方法

研究分别以室内温度、地板表面温度及两者作为控制参数,控制循环水泵启停,调节房间温度的方法,发现了地板结构层热延迟性可延迟室内温度的下降,得出了地板辐射供暖系统运行调节规律。分析了以地板表面温度作为控制参数时,室外温度、围护结构热延迟性及地板表面温度对墙体内表面平均温度的影响,地板表面温度对墙体内表面平均温度的影响较大．且两者变化趋势一致,而室外温度对供暖房间墙体内表面平均温度的影响很小。     

相变材料应用于外墙表面隔热的研究

根据表面隔热机理,通过对普通外墙的理论计算分析,设计了新型的相变墙体。相变材料应用于外墙体外表面,夏季能有效的改善建筑物的外表面热环境,降低传入室内的热量,缓解室内空调冷负荷。同时,提出隔热相变材料的相变温度、掺量在不同气候环境下的选择方法。     

Experimental investigation and computer simulation of thermal behaviour of wallboards containing a phase change material

In the objective to define passive components for the light envelope of buildings, different types of wallboards containing a phase change material (PCM) were studied. The high storage capacity should enable the overall thickness of wallboards to be less than 5 cm. To lower the investment costs, the wallboards were made from commercial panels after a first attempt of using gypsum walls. Three types of wallboards were studied: (i) a polycarbonate panel filled with paraffin granulates; (ii) a polycarbonate panel filled with polyethylene glycol PEG 600; (iii) a PVC panel filled with PEG 600 and coupled to a VIP. An experimental set-up was built to determine the thermal response of these wallboards to thermal solicitations. Experimental results were compared to those obtained by a numerical simulation in which an apparent heat capacity method was used. The final results show that the last studied wallboard could be used in the test cells under construction and then validate the concept.     

相变材料与建筑围护结构蓄能一体化设计及应用

相变材料是传统材料与相变物质复合形成的一种新型储能材料,伴随着温度的变化改变自身物质状态而提供潜热的物质。依据相变材料不同的化学组成、相变温度和相变形式可以分为不同的种类。封装的相变材料可以广泛应用于建筑墙体、地板和吊顶中,使建筑围护结构具有自调节的功能,提高建筑室内环境的热舒适性和稳定性,从而达到节约能源的目的。     

太阳能通风结合相变墙在苏北沿海的应用研究

结合苏北沿海地区的气候特点,通过对苏北沿海代表性城市盐城地区的室外温度、太阳光线强度等外部环境展开分析,选择相变温度以及潜热较为合理的相变材料展开实验,从而了解太阳能烟囱以及相变蓄热墙在改变室内热环境和针对负荷所表现出的削峰移峰2个方面影响作用。实验结果显示,在盐城同样的室外温度环境下,采用相变墙的房间具有明显的隔热保温作用,有效提升了室内环境的舒适度。充分说明,相变房温度条件得到了改善,房间给人更高的舒适感,降低了空调负荷,达到了节约能源的目的。     

垂直绿化改善建筑室内、外热环境效果分析

垂直绿化已成为一种节省空间的节能措施。为研究夏热冬暖地区垂直绿化改善室内热环境和周围热环境的效果,对用爬山虎绿化的建筑的内外壁温及建筑周围室外温度进行实测分析;并用CFD模拟了有、无绿化房间的辐射温度,室内空气温度,PMV、PPD热舒适性指标进行对比分析。测试结果表明,垂直绿化建筑周围热岛效应仅为0.9℃;不同朝向的有绿化墙壁比没绿化的壁面温度有不同程度的降低。效果最好的外壁温平均降低了6.8℃,内壁温平均降低了1.72℃。CFD模拟结果显示,绿化后房间空气温度和辐射温度的平均值分别降低了0.4℃和1℃;PMV-PPD也有改善,而且舒适指标的最大值也减小了。分析可得垂直绿化是一种绿色有效、主动的隔热节能方式。     

Thermal response of brick wall filled with phase change materials (PCM) under fluctuating outdoor temperatures

Based on the enthalpy-porosity technique, a model of thermal conduction accompanied with solidification and melting processes is developed and numerically analyzed to investigate the thermal response of the brick wall filled with phase change materials (PCM). The thermal response, which is represented by indoor wall surface temperature response, of brick wall filled with PCM is evaluated and compared with that of solid brick wall. The effects of PCM filling and its filling amount on thermal response of brick wall are investigated and discussed. It is indicated that, compared to the common solid brick wall, the thermal storage of brick wall filled with PCM is elevated by the alternate process of melting and solidification under fluctuating outdoor temperatures. The use of PCM in the brick walls is beneficial for the thermal insulation, temperature hysteresis and thermal comfort for occupancy. In addition, with the increasing filling amount of PCM, the fluctuation of indoor wall surface temperature is significantly smoothed. Correspondingly, the hysteresis in response to the outdoor temperature fluctuation is enhanced. Moreover, the present model is verified by experimental data available in the literature.     

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.     

Performance of phase change material boards under natural convection

The high thermal storage capacity of phase change material (PCM) can reduce energy consumption in buildings through energy storage and release when combined with renewable energy sources, night cooling, etc. PCM boards can be used to absorb heat gains during daytime and release heat at night. In this paper, the thermal performance of an environmental chamber fitted with phase change material boards has been investigated. During a full-cycle experiment, i.e. charging–releasing cycle, the PCM boards on a wall can reduce the interior wall surface temperature during the charging process, whereas the PCM wall surface temperature is higher than that of the other walls during the heat releasing process. It is found that the heat flux density of the PCM wall in the melting zone is almost twice as large as that of ordinary wall. Also, the heat-insulation performance of a PCM wall is better than that of an ordinary wall during the charging process, while during the heat discharging process, the PCM wall releases more heat energy. The convective heat transfer coefficient of PCM wall surface calculated using equations for a normal wall material produces an underestimation of this coefficient. The high convective heat transfer coefficient for a PCM wall is due to the increased energy exchange between the wall and indoor air.     

基于Ansys的相变墙体传热特性计算分析

基于Ansys软件建立数学模型,计算分析了不同厚度相变储能材料、不同相变墙体结构的传热特性.计算结果表明,相变储能材料越厚,相变墙体内层与室内环境界面温度随外界温度变化幅度越小,能够有效降低室内空调设备的能耗;相变储能材料厚度一定时,不同结构的相变墙体从节能降耗角度差别不大:相变储能材料位于墙体中心位置时节能效果较好.     

外窗遮阳对室内温度的影响

建筑遮阳系数对建筑能耗和室内热环境均有影响,而室内空气温度作为影响热舒适的主要因素与窗户遮阳存在必然联系.采用DOE-2软件计算方法分析遮阳系数变化时室内温度降低的分布情况,说明夏季设置外遮阳对室内热环境改善的效果.