现代木结构住宅墙体热物理性能研究
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摘要
现代木结构房屋凭借其独特的优势得到了人们越来越多的关注。与古代木建筑相比,在建筑风格、材料的选择与制造、节能保温性、健康与舒适性、建造水平等都存在很大差异,设计、制造和验收规范还不完善,所以系统研究木结构住宅的建造技术非常必要。
     墙体是建筑物的重要组成部分,对整个建筑的保温、隔热、隔声等性能起到至关重要的作用。在建筑外围护结构中墙体所占的比例最大,墙体传热造成的热损失所占的比例也最大,研究表明,建筑物通过维护结构传热,其耗热量占整个建筑使用能耗的73%到77%,其中外墙耗热量占了30%左右。而墙体的传热是一个极为复杂的过程,它关系到整个建筑环境的热舒适度和节能问题。因此,如何降低围护结构特别是外墙传热系数一—K值,成为研究人员们关注的焦点。研究现代木结构墙体的热物理性能不仅有助于科学地设计墙体参数,空调负倚计算,同时对合理评价整个房间的节能效果也具有重要意义,为合理地设计木结构墙体和开发理想的墙体材料提供依据。
     本论文以现代木结构住宅建筑的墙体为研究对象,采用防护和标定热箱法对其稳态热物理性能进行了研究,分析了不同的墙骨柱种类、墙骨柱间距、保温材料种类对墙体热物理性能的影响,并计算了墙体的传热量;采用有限差分数值计算方法结合Matlab软件和PDE工具箱,以及有限元法对现代木结构住宅墙体的非稳态热物理性能进行了评价,分析了使用过程中现代木结构住宅墙体的温度场;采用Dest建筑能耗模拟软件结合现场实际检测初步评价了现代木结构建筑的节能性能,获得的主要结论如下:
     1.通过标准试件标定后,防护和标定热箱法不仅适用于一般钢混结构建筑墙体的稳态热物理性能检测和评价,该方法也同样适用于现代木结构建筑墙体的稳态热物理性能的检测与评价。
     2.现代木结构墙体具有良好的保温隔热特性。无论是2X4还是2X6墙体,其稳态热物理性能都明显要好于一般的钢混结构建筑墙体,包括外墙外保温墙体和外墙内保温墙体。
     3.现代木结构墙体的稳态热物理性能受到墙骨柱种类、墙骨柱间距、保温材料的影响。
     ①在墙骨柱间距、保温材料种类相同的情况下,2X6墙体的热物理性能优于相应的2X4墙体。②保温材料的不同对木结构墙体的热物理性能有着重要影响,研究结果表明,在相同墙骨柱种类和墙骨柱间距下,挤塑保温板构成的墙体热物理性能最好,岩棉保温板构成的墙体次之,聚苯保温板构成的墙体最差。③墙骨柱间距对木结构墙体的热物理性能也有着重要影响。在保温材料和墙骨柱种类相同的条件下,随着墙骨柱间距的增加,墙体的热物理性能也相应提高。因此,在强度允许和结构安全的情况下,可以适当增大墙骨柱间距。
     4.在相同的外界条件和室内热环境条件下,木结构墙体的日传热量明显低于钢混结构的外墙外保温墙体和外墙内保温墙体,木结构建筑墙体比钢混结构建筑墙体的节能效果更明显。
     5.采用有限差分数值计算方法结合Matlab软件和PDE工具箱,可以有效地对现代木结构住宅墙体的非稳态热物理性能进行评价。计算时采用傅立叶变换将一个周期内离散的温度数据转化为连续的边界条件,同时选用PDE工具箱中的抛物线型偏微分方程,墙体两侧边界条件按Neumann边界条件计算。
     6.在相同的边界条件下,现代木结构住宅墙体温度场分布情况与一般钢混结构建筑类似。但是现代木结构住宅墙体的非稳态热物理性能明显好于一般的钢混结构建筑墙体包括外墙外保温和外墙内保温墙体。主要表现为:①与钢混结构建筑相比,现代木结构住宅墙体内表面温度明显高于钢混结构建筑墙体。②现代木结构住宅墙体较一般钢混结构建筑墙体具有更高的抵抗温度波动的能力。③现代木结构住宅墙体不仅能有效地改善室内热环境的舒适性,还能降低整个建筑的使用能耗。
     7.通过有限单元法,可以准确方便地求解现代木结构住宅墙体温度场分布情况,并获得墙体内部温度分布情况。在木结构建筑墙体中,保温材料、空气隔层主要起到保温作用,抵抗外界温度波动,在保温材料和空气隔层内外两侧温差较大。木墙骨在木结构住宅建筑中不仅起到结构承重作用,同时也起到一定的保温作用。
     8.Dest建筑能耗模拟软件可以有效地对现代木结构住宅在使用过程中的能耗情况进行分析。在相同的使用条件下:①现代木结构住宅房间的自然室温(无采暖和空调)在16~29℃范围内的天数大于钢混结构建筑,现代木结构住宅的舒适度优于钢混结构建筑。②现代木结构住宅建筑的采暖热负荷钢混结构建筑低25.5%;空调冷负荷比钢混结构低8.4%。③木结构建筑一年内采暖和空调耗电量比钢混结构建筑节能21.5%。
     9.通过现场检测,可以看出:①木结构住宅墙体能够有效地抵抗外界环境温度的波动。室内外温度均以24小时为周期变化,但是室内温度波形分布在较窄的范围内。室内温度峰值比室外温度峰值的出现时间有2到3小时的滞后。②室外环境相对湿度以24小时为周期变化,室内环境相对湿度基本保持在一定数值,平均约为40%左右,变化幅度基本受外界环境影响较小。③北美轻型现代木结构住宅墙体内表面不会产生冷凝。而墙体内部有可能会产生冷凝,产生冷凝的部位在聚苯乙烯保温板和空气各层之间。通过测试计算,木结构墙体可能的冷凝量为1.1221g/(m~2h),满足国标中GB50176-93的要求。经过检测,木结构墙体内部未见冷凝水,墙体内材料处于干燥环境中,未发生腐朽,保温性能不会因为潮湿而性能降低。
The modern wood framed construction has drawn people's attention for its advantages such asgood heat insulation property, easy to build, good to health and comfortable to live in. Itdistinguishes the traditional wood flamed construction in China from architectural style,architectural methods, architectural materials and so on. The information about wood flamedconstruction design, material standardization as well as related technologies is scarce. So it isnecessary to systematically study the building technology for wood framed construction.As one of the most important parts of a construction, the outdoor wall plays a significant rolein heat insulation, heat preservation, sound insulation and energy saving. The wall takes up themaximum ratio in the exterior building envelope. Researches show that the heat loss from theoutdoor wall amounts to 30% of the whole heat loss in a construction. Heat transfer of theoutdoor wall is a sophisticated process, which has something to do with the thermal comfortand the energy saving of the whole construction. Researchers focus their research on how tolower the heat transfer coefficient of exterior wall, ie K value. Studying the thermalcharacteristics of the outdoor wall of the wood framed construction is significant not only forreasonably designing wall parameters and air-conditioner load but also for accuratelyevaluating the energy saving effects of the whole building. It will promote the development ofwood flamed construction in China and will provide fundamental reference for wall design andmaterial development of the wood flamed construction.
     This paper studies the thermal properties of modern wood framed construction wall.Guarding and calibration heat box method is applied to examine the steady thermalcharacteristics of wood framed construction wall. Different wood studs, wood studs distance,heat insulation materials and their influence on the thermal characteristics of wood framedconstruction wall are analyzed and discussed. The heat conductance value of different walls iscalculated. The finite difference method combined with Matlab, PDE tool and finite elementanalysis methods are utilized to study the unsteady thermal characteristics of wood framedconstruction wall. The temperature fields of wood flamed construction wall during applicationare analyzed. The architecture energy simulation software named Dest and onsite measurementare applied to evaluate the energy saving properties of wood framed construction. The mainresults are as follows.
     1. After being calibrated by standard sample, the Guarding and calibration heat box method isnot only suitable for the measurement and evaluation on the steady thermal characteristicsof concrete structured construction wall; it also fits for the measurement and evaluation on the steady thermal characteristics of wood framed construction wall.
     2. The modern wood framed construction wall has excellent heat insulation properties. Both2X4 and 2X6 structure wall has better thermal characteristics than common concretestructured construction including the exterior insulator wall and interior insulator wall.
     3. The steady thermal characteristics of wood framed construction wall are influenced bydifferent wood studs, wood studs distance and heat insulation materials. The detailedresults are:①When the wood studs distance and heat insulation materials are same, 2X6wall has better thermal characteristics than 2X4 wall.②The properties of heat insulationmaterials have significant impact on thermal characteristics of the wood framedconstruction wall. In this experiment, when the wall constitutes with the same type of woodstuds and wood studs distance, wall fixed with the extruded insulation board has the bestthermal characteristic, then is the wall with rockwool insulation board, the wall with thepolystyrene insulation board is marked third among the three above.③Wood studs alsohave significant impact on thermal characteristics of the wood framed construction wall.When the heat insulation material and type of wood studs are same, the thermalcharacteristics of wood framed construction wall increase with the wood studs distanceincreasing. So under the precondition of meeting the safety requirement, large wood studsdistance is preferred.
     4. Under the same exterior and interior environmental condition, the heat conductance valueof wood framed construction wall is obviously lower than concrete structured constructionwall including exterior insulator wall and interior insulator wall. The energy saving effectof wood framed construction wall is more obvious than concrete structured constructionwall.
     5. The finite difference method combined with Matlab and PDE tool can effectively assess theunsteady thennal characteristics of wood framed construction wall. Flourier transformationcan change the discrete data into continuous boundary condition, the parabolic partialdifferential equations is applied. The boundary condition of wall is the Neumann boundary.
     6. Under the same boundary conditions, the temperature field of wood framed constructionwall is similar with the one of concrete structured construction wall. The unsteady thermalcharacteristics of wood framed construction wall are better than concrete structuredconstruction wall. The detailed results are:①Compared with the concrete structuredconstruction wall, the wood framed construction wall has higher inner surface temperature.②Wood framed construction wall has better competence of counterbalancing the temperature surge.③Wood framed construction wall can not only better the heatcomfortability of the interior environment but also lower the energy consumption of thewhole construction.
     7. The finite element analysis method can accurately predict the temperature field of woodframed construction wall and can acquire the temperature in the wall. In the wood framedconstruction wall, the heat insulation materials and air cavity are the main parts to insulateheat transfer and counterbalance temperature surge. The temperature difference betweentwo sides of the heat insulator materials and air cavity is large. Wood studs serve as bothstructural load bearing and heat insulation.
     8. The architecture energy simulation software, Dest, can effectively analyze the energyconsumption of wood framed construction during utilization. Under the same condition:①wood framed construction has more days with natural temperature (16~29℃,withoutheating and cooling) than concrete structured construction. Wood framed construction hasbetter comfortability than concrete structured construction.②The heat load of woodframed construction is 25.5% lower than concrete structured construction and the coolingair-condition load of wood framed construction is 8.4% lower than concrete structuredconstruction.③The energy consumption of wood framed construction is 21.5% lowerthan concrete structured construction.
     9. From the onsite measurement, conclusions can be reached as follows:①Wood framedconstruction wall can effectively counterbalance the exterior environmental temperaturesurge. Both exterior and interior temperature changes periodically in 24 hours. The interiortemperature changes in a narrow range. The interior temperature peak lags behind theexterior temperature peak for about 2 to 3 hours.②The exterior relative humiditychanges periodically in 24 hours, while the interior relative humidity changes in a narrowrange and is hardly affected by the exterior ambient, the average relative humidity is about40%.③No condensation will occur on the inner surface of wood framed constructionwall. Condensation may occur in the wall at the layer of polystyrene and air cavity. Thepossible condensation value is 1.1221 g/(m~2h), which meet the requirement of GB50176-93.No condensation water is detected in the wood framed construction wall. All the wallmaterials are in dry state. No decay occurs. The heat insulation properties will not belowered caused by moisture.
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