多孔介质墙体热湿耦合传递模拟计算模型及其验证

考虑传湿对多孔介质墙体传热的影响,根据单元体质量守恒和能量守恒,建立了非稳态热湿耦合数学模型模拟多孔介质墙体的热湿传递过程,并在长沙对一墙体的热湿耦合传递开展了实验测试,应用COMSOL Multiphysics软件对所建模型进行数值计算,将计算结果与EN15026, HAMSTAD等验证实例和实验测试结果对比,验证了所建数学模型的正确性。结果表明,模型的计算结果与验证实例的结果高度吻合,与实验测试结果吻合良好,室内侧分界面处空气相对湿度的平均偏差为4.7%,最大偏差为8.6%,温度的平均偏差为0.4℃,最大偏差为0. 74℃,室外侧分界面处空气相对湿度的平均偏差为3.7%,最大偏差为7.2%,温度的平均偏差为0.93℃,最大偏差为1.97℃,证明了该模型有很好的准确性。     

蒸压加气混凝土砌块墙体热湿耦合传递特性

运用开尔文定律和克劳修斯-克拉贝龙方程,将多孔建筑材料内水蒸气传递量和液态水传递量转变为以水蒸气分压力为驱动势的统一函数,以温度和水蒸气分压力为驱动势建立了热湿耦合传递模型,并模拟分析了上海地区自然干燥状态下加气混凝土砌块墙体10a的热湿性能变化规律.结果表明:对于初始温度为298K,含湿量(质量分数,下同)分别为2.91%,3.45%,5.03%,8.60%的4种工况,经过1a的使用后,墙体内的温湿度分布不再受初始条件影响;在正常情况阶段,墙体内表面相对湿度均小于1.0,不会出现结露现象,但是在部分时段超过了0.8,易产生霉变;墙体内部含湿量呈周期性变化,空调季为3.34%~8.31%,平均值4.45%;采暖季为3.31%~3.69%,平均值3.47%.     

粉煤灰加气混凝土墙体表面传热传质系数实验研究

本文以粉煤灰加气混凝土墙体试样作为研究对象,在室内环境温度25℃、相对湿度50％和环境温度突变至6.6℃,而后再次稳定在温度25℃、相对湿度50％2个阶段分别测得试样表面平均温度、总重变化和内部含湿量分布,分析得出实际墙体内部热湿传递特性.结果表明:经过温度突变,第2阶段表面平均温度达到稳定的时间比第1阶段多12h,且稳定后的温度比第1阶段低0.7℃;内部水分的迁移呈现出由内自外的过程;计算得到试样表面的平均传热系数为3.46 W/(m2·K),平均传质系数为0.002 m/s.实验结果对建筑热湿负荷特性的进一步研究提供了基础性数据参考.     

高湿地区保温墙体防结露措施效果分析

为探究高湿地区复合保温墙体空气层、隔汽层两种防结露措施的效果,建立了以温度与相对湿度为计算驱动势的热湿耦合传递模型,并根据实验数据对模型进行了验证。进一步使用模型模拟了冬夏季高湿工况条件下,内外两种保温墙体内部的热湿变化情况。根据模拟结果得出,保温墙体在两种材料界面处具有较高的结露风险。在全年高湿地区,空气层可有效降低墙体内部的结露风险,隔汽层在此工况下防结露效果不佳。     

多层墙体热湿耦合传递模型及验证

从非平衡热力学角度论证了多层墙体热湿耦合过程采用水蒸气分压力和温度作为驱动势的合理性。由于水蒸气分压力是含湿量和温度的函数,利用全微分思想,建立了多层墙体热湿耦合传递模型,该方法可避免Budaiwi方法在热湿耦合模型建立过程中采用的空气含湿量与相对湿度间的近似表达式,而且简化了方程系数,便于方程的求解。通过对多层墙体求解结果的对比,验证了该模型的有效性。     

三相水分共存的多层墙体热湿耦合传递模型

考虑水分升华、凝华、气液和固液相变,以温度和水蒸气分压力为驱动势建立了气、液、固三相水分共存的多层墙体热湿耦合传递模型.构建了1面500mm(长)×450mm(高)×240mm(厚)试验墙体,利用恒温恒湿箱试验测试了箱体温度范围为常温~-33.94℃时墙体内部温度和平衡相对湿度的变化,分析了水分固液相变过程的特征,并对热湿耦合传递模型数值模拟计算结果的正确性进行了验证.结果表明:试验墙体内部温度和水蒸气分压力数值模拟计算结果和实测结果变化趋势相同,具有良好的一致性,各点温度数值模拟计算结果的最大相对误差为1.68%,平均相对误差为0.44%;水蒸气分压力数值模拟计算结果的最大相对误差为27.92%,平均相对误差为13.50%.该模型数值模拟计算结果能够满足一般工程领域的精度要求,可应用于三相水分共存的多层墙体热湿耦合传递过程数值模拟研究.     

湿迁移对墙体传热的影响分析

考虑温湿度对墙体材料热湿物性参数的影响,建立以相对湿度和温度为驱动势的墙体热湿耦合传递模型。在变温湿度边界条件下对墙体非稳态热湿耦合传递过程进行分析,计算得到墙体表面温湿度及热流密度,与不考虑传湿情况进行对比分析。结果表明：不考虑吸放湿时墙体内表面温度比考虑吸放湿时变化幅度大,且前者内表面平均温度与后者相差约0.9℃;因墙体内表面吸放湿作用引起的相变潜热约占总壁体传热量的27.5%,在负荷计算中不可忽略。     

太阳辐射对南方多层墙体热湿性能影响的研究

本文以空气含湿量和温度为驱动势建立模型对南方地区典型多层墙体进行了动态模拟。在主模型中,将太阳辐射总热量分解,得到了建筑不同朝向外墙的太阳辐射得热量,进而分析了在太阳辐射影响下墙体的热湿性能;在子模型中,不考虑太阳辐射得热对墙体热湿性能的影响。将模拟结果同实验测试数据进行对比后可知,太阳辐射得热对多层墙体外层的温度影响较明显,而墙体温度的升高会造成墙体内空气含湿量的增大。     

热湿气候地区湿传递对吸放湿墙体热湿性能的影响

以墙体中的空气含湿率和温度为驱动势建立了多层墙体的一维瞬态热湿耦合传递方程,将用此方程计算出的值跟用忽略湿传递的导热方程计算出的值进行对比得出湿传递对墙体热湿性能的影响。结果表明,对于吸放湿墙体而言,湿传递对墙体的热湿性能有着非常重要的影响。在进行墙体传热计算时,如果忽略墙体中的湿传递会产生较大误差,不能精确的预测墙体内的温度分布情况,并且导致计算出的空调负荷偏小,进而影响到空调的实际效果。     

地下洞室多孔墙体热湿传递的数值模拟

提出了一种以温度与相对湿度为驱动势的多孔墙体热湿耦合传递的数学模型,该模型同时考虑了水蒸气与毛细孔内液态水的传递。采用控制容积法将理论方程组离散并编制了计算程序,对深埋地下洞室的墙体进行了热湿传递的数值模拟,得到了墙体温度、相对湿度、热流率、湿流率的变化规律。结果表明,墙体传热过程趋于稳定的时间远小于传湿过程。     

Evaluating the role of ivy (Hedera helix) in moderating wall surface microclimates and contributing to the bioprotection of historic buildings

The role of ivy (Hedera helix L.) on building walls is much debated, with arguments being put forward for it playing a biodeteriorative role (for example through ivy rootlets exploiting cracks and holes) as well as suggestions that it might provide some bioprotection (for example by the ivy canopy protecting the walls from other agents of deterioration such as frost). We have carried out a year-long study of the influence that ivy canopies play on wall surface microclimates at five sites across a range of climatic settings within England, using iButtons to monitor temperature and relative humidity fluctuations at the wall surface on ivy-covered and exposed walls. Hourly data illustrates a general mediating effect of ivy canopies on both temperature and relative humidity regimes. The ivy reduces extremes of temperature and relative humidity, with the most clearcut differences for temperature. Across all five sites the average daily maximum temperature was 36% higher and the average daily minimum temperature 15% lower on exposed vs ivy-covered surfaces. Differences in the exposure level of studied walls (i.e. whether they are shaded or not by trees or other walls) influenced the degree of microclimatic alteration provided by the ivy canopy. Other important factors influencing the strength of the ivy impact on microclimate were found to be thickness of the canopy and aspect of the wall. A detailed analysis of one site, Byland in North Yorkshire, illustrates the seasonal differences in impact of ivy on microclimates, with insulation against freezing being the dominant effect in January, and the removal of high temperature ‘spikes’ the dominant effect in July. The observed moderating role of ivy canopies on wall surface microclimates will reduce the likelihood of frost and salt deterioration to the building materials, thus contributing to their conservation. Further research needs to be done on other potentially deteriorative roles of ivy before an overall bioprotective role can be assumed, but the significant impact of ivy on wall surface microclimates across England is clear.     

Newspaper sandwiched aerated lightweight concrete wall panels—Thermal inertia, transient thermal behavior and surface temperature prediction

Experimental investigation on aerated lightweight concrete (ALC) wall panels in terms of thermal inertia, transient thermal behavior and surface temperature prediction using finite difference method (FDM) are the main focus of this study. ALC wall panels of different density and different aerial intensity of newspaper sandwiched were produced and installed on a prototype house. The ALC wall panels were facing east direction and subjected to Malaysia natural environment condition. The inner and outer surface temperatures of the wall panels were recorded at 3 min interval, 24 h a day for a period of one year. Time lag and decrement factor were computed from the surface temperatures recorded. The results showed that thermal diffusivity has a positive relationship to the thermal inertia of ALC wall panels. FDM was used to predict the surfaces temperature and the predicted temperature was close to the observed temperature. The average differences between the observed and the predicted outer wall surface temperature lied between 1.4 and 2.4% whereas for the inner wall surface, the range was 1.3-2.2%. Greater deviations were detected on the predicted outer surface temperature could be due to some unaccounted factors such as wind direction and relative humidity in the present FDM.     

Impacts of energy-efficiency investments on internal conditions in low-income households

Living in cold conditions poses a risk to health, in particular to low-income, fuel-poor households. Improving the energy efficiency of the housing stock may bring multiple positive health gains through improved indoor temperatures and reduced fuel consumption. This study used a multilevel interrupted time-series approach to evaluate a policy-led energy-performance investment programme. Long-term monitoring data were collected for intervention and control households at baseline (n?=?99) and follow-up (n?=?88), creating a dataset with 15,771 data points for a series of daily-averaged hydrothermal outcome variables. The study found that the intervention raised indoor air temperature by on average 0.84?K as compared with control households, thereby bringing the majority of indoor temperature measurements within the ‘healthy’ comfort zone of 18–24°C, while average daily gas usage dropped by 37%. External wall insulation was the most effective measure to increase indoor air temperature. The greatest increases were found in the evening and at night, in the bedroom, and in British steel-framed buildings. No evidence was found that the intervention substantially increased indoor relative humidity levels when accompanied by mechanical ventilation. The study concludes that the multilevel interrupted time-series approach offers a useful model for evaluating housing improvement programmes.     

基于粗骨料多孔界面的再生混凝土内部相对湿度响应机理试验研究

再生混凝土内部湿度场的变化会对结构的耐久性造成影响。文章基于再生粗骨料界面的多孔特性,对比研究100%取代率下再生混凝土和普通混凝土在不同温度、距离表层不同深度及有、无荷载作用下的内部相对湿度的响应规律及响应机理。结果表明：再生混凝土内部的相对湿度响应速率快于普通混凝土,距离再生混凝土表层越近,相对湿度响应速率越快,且随着温度的增加而增加;弯曲荷载作用对再生混凝土和普通混凝土的相对湿度响应速率均具有促进作用,且对再生混凝土的影响更为显著;对于再生混凝土内部相对湿度滞后上升现象,提出“再生粗骨料分区 界面热湿传递模型”,分析相对湿度滞后上升的机理;采用多元非线性曲线分段拟合的方法,建立再生混凝土内外环境相对湿度响应计算模型。     

Performance of straw bale wall: A case of study

This research aimed to evaluate a straw bale house located in Bavaria, Germany. An extensive test program was carried out. The experimental work includes compression tests, moisture content, thermal stability of bales and pH. The in situ work includes temperature and relative humidity inside the straw bale wall. The stress-strain behavior of straw bales was investigated including nonlinearity and anisotropy. Thermal stability of bales under constant temperature and relative humidity was studied considering time dependence. The moisture content of straw bale was about 11%, while pH value inside the bale was about 7.29. Moreover, the temperature and the relative humidity between the interior (inside straw bale wall) and the exterior were investigated.     

Theoretical predictions of transient natural displacement ventilation

The transient natural displacement ventilation driven by a localized heat source at the floor of a room is examined to understand the airflow behavior and the relevant thermal stratification characteristic. Two modified theoretical models are developed on the basis of classical plume theory and Kaye and Hunt’s model. The buoyant layer is modeled as composed of a near-ceiling layer and a warm layer rather than being well-mixed. Some assumptions on the buoyancies of the near-ceiling layer and the outflow through the upper opening are made in the two modified models for simplicity. Comparisons are made between the predictions of Kaye and Hunt’s model and the two modified models and experimental data reported in the literature. Two modified models are shown to perform better than Kaye and Hunt’s model. Meanwhile, the predictions of the modified model I seem to agree slightly better with the experimental data than those of the modified model II. Typically, the average relative deviation between the three models’ predictions of the lowest interface height and the experimental data are about 4.2% (modified model I), 4.6% (modified model II), and 4.9% (Kaye and Hunt’s model).     

湿热环境下粘钢加固混凝土界面的粘结性能

钢板-混凝土界面粘结性能是粘贴钢板加固混凝土结构的关键。通过对湿热环境下27个钢板-混凝土试件进行试验研究,分别进行5、10、15d的加速湿热老化,然后进行双剪试验,获得了钢板-混凝土界面发生剪切剥离破坏过程中的极限荷载、钢板应变分布及荷载-位移关系。分析了环境温度、湿度耦合作用对钢板-混凝土界面粘结耐久性能的影响,并综合考虑钢板-混凝土的粘结破坏模式、受力过程、粘结界面相对位移发展规律,提出了粘结界面剪应力、滑移与温度和湿度相关的表达式。建立了考虑温度、湿度影响的粘结-滑移本构关系模型,数值模拟结果与试验结果吻合较好。     

湿传递对建筑墙体传热性能的影响

建筑物的耗能与建筑围护结构的传热传湿密切相关,了解建筑墙体内部的热湿传递对建筑节能有重要影响。以相对湿度和温度梯度为驱动势建立墙体一维非稳态热、湿和空气耦合传递模型(HAM模型),并利用有限元法进行了数值求解,重点关注了湿传递对传热的影响。数值结果表明:考虑传湿时墙体内部温度波动小,墙体进行热湿传递会产生湿积累,降低墙体使用年限;考虑传湿时通过墙体总传热量比不考虑传湿时多7.5%;考虑传湿时内壁面最大平均数比不考虑传湿时大0.78。     

Impact of Temperature and Humidity on Chemical and Sensory Emissions from Building Materials

Abstract The chemical and sensory emissions from five building materials (carpet, polyvinyl chloride (PVC) flooring, sealant, floor varnish and wall paint) were tested under different combinations of temperature and relative humidity in the ranges 18–28°C and 30–70% relative humidity (RH). The experiment was performed in a climate chamber where a specially designed test system was built to study emissions from the five materials. The test system could provide different temperatures and humidities of air around the materials, while the air, after being polluted by the emissions from the materials, could be reconditioned to 23°C and 50% RH for sensory assessments. The experiment was designed to separate the direct impact of temperature and humidity on perception from the impact on sensory emission. The study found little influence of temperature on the emissions from the five materials whether expressed in chemical or sensory terms. The effect of humidity was found to be significant only for the waterborne materials – floor varnish and wall paint. Compared with the direct impact of temperature and humidity on the perception of air quality, the impact of temperature and humidity on sensory emissions from the building materials has a secondary influence on perceived air quality.