Thermal Inertia Index Research Articles

Evaluation of thermal insulation capacity and mechanical performance of a novel low-carbon thermal insulating foam concrete

The use of building insulation materials is an effective measure to reduce building energy consumption. To improve the sustainability of insulation materials, desert sand (DS) was used to replace part of the binder, and rice husk ash (RHA) was incorporated to further improve the performance of foamed concrete. The fresh properties, strengths, thermal properties and thermal insulation function of DS-based foamed concrete (DSFC) were systematically investigated. The use of DS and RHA to replace part of Portland cement (PC) and fly ash reduces the flowability of the mixture when the water/binder (PC, fly ash, DS and RHA) ratio is constant. Although the incorporation of DS into foamed concrete increases its density and thermal conductivity, it improves the volume stability of the sample. The strength of specimen with DS decreases due to the low reactivity of DS, which also reduces the content of hydration products. Further incorporation of RHA not only improves the matrix strength by increasing the C-S-H content but also improves the pore structure of the DSFC by increasing the yield stress of the paste. The joint application of DS and RHA effectively reduces the heat storage coefficient and thermal inertia index of DSFC, which is beneficial to improve the thermal insulation capacity of buildings and reduce energy consumption. Incorporating DS and RHA can effectively improve the environmental and economic benefits of the foamed mixture, and the unit strength cost and carbon emission per cubic meter of the 5%–10% RHA-modified samples are reduced by 20.3%–39.1% and 20.2%–38.9%, respectively, compared with the DS35. This research provides a new approach and theoretical basis for building energy saving and external wall insulation.

Analysis of the indoor thermal environment of traditional residents in the South Sichuan China region in summer and plum rainy seasons—taking Baiyang village in Yibin city as an example

ABSTRACT In hot summer and cold winter areas, the humid and sultry summer and rainy season problems have long affected the health of residents. Through a questionnaire survey and site measurements, the indoor thermal environment of typical southern Sichuan village houses was investigated. The average indoor humidity of the old traditional dwelling (85–95%) in the rainy season was much greater than that of the new rural house (70–80%), both of which are outside the standard thermal comfort range of the human body. In summer, the situation is slightly better but still uncomfortable. The APMV evaluation results reveal that in the rainy season, the new residential house is more comfortable than the traditional residential house, while in summer, the opposite situation occurs. The measurements show that the thermal inertia index of the old stone masonry house is large, which indicates that the house has a strong ability to resist temperature fluctuations. Therefore, we discussed different performance improvement strategies for these two types of rural residences. This study is conducive to improving the thermal environment of local residential buildings and provides a reference for the future design of rural ecological residential buildings.

Studying Thermal and Mechanical Properties of Recycled Concrete by Using Ceramic Aggregate

Ceramic aggregate has the characteristics of light weight, heat insulation, and low cost, and recycled aggregate is a type of green material that realizes the re-crushing of construction waste. This paper studied the impact of replacing natural coarse aggregate with ceramic aggregate and natural sand with recycled fine aggregate, on the physical, mechanical, and thermal properties of concrete. Recycled fine aggregate was used to completely replace natural sand. A total of five concrete mixes (including a reference mix) were prepared with different levels of ceramic aggregate (0%, 30%, 50%, 70%, 100%). Density, compressive strength, thermal conductivity, and thermal inertia index were measured to evaluate the performance of each mixture, and ceramic concrete board and hollow blocks were designed for testing the thermal properties. Results of testing show that density, strength, and thermal performance are interrelated. The smaller the density, the lower the strength, and it indicates that ceramic aggregate has a negative influence on strength in concrete. Meanwhile, the smaller the density, the higher the thermal resistance, and the addition of ceramic aggregate can improve the thermal insulation of concrete. The mechanical and thermal properties are both affected by the ceramic replacement ratio. Ceramic aggregate improves the thermal properties of recycled concrete, and the negative influence of ceramic aggregate on compressive strength can be controlled by the replacement ratio of aggregate in concrete. Based on the overall comparison and analysis, a mix with 50% ceramic aggregate shows relatively better strength and thermal insulation compared to other mixes. The use of ceramic aggregate in combination with recycled fine aggregate can effectively reduce the environmental pollution and make an economical substitute for their natural counterparts.

Optimization of Wall Thickness Based on a Comprehensive Evaluation Index of Thermal Mass and Insulation

The thermal performance of buildings in the south of China focuses on thermal mass design, while in the north it favors thermal insulation design, which makes it impossible to achieve a balance between the thermal mass and insulation. Here, a comprehensive evaluation index is developed to measure the thermal performance of a building’s external envelope, which aims to find out the optimal range of the wall thickness under the influence of the thermal mass and insulation, and to seek the correct balance between a building’s energy consumption and the thermal performance of walls. In this paper, four dimensions, namely the heat transfer coefficient, thermal inertia index, attenuation degree, and delay time, are discussed, and the weight coefficients of each subfactor are calculated and isotropically treated to create comprehensive evaluation indicators. Then the distribution laws of the composite index values of common building materials in different climatic zones are examined. The result shows that the correlation coefficient (R2) between M and building energy consumption is about 0.7736–0.8215, which is higher than 0.3494–0.384, the heat transfer coefficient, and is more accurate in predicting building energy demands. Furthermore, through the analysis of the thermal improvement rate and the building energy-saving rate, the suitable wall thickness of commonly used building materials in different climate zones is determined, and the application prospects of the research results are described. With the above research findings, the thickness ranges of walls can be determined at the initial period of building design by combining regional environmental factors and material characteristics to provide a reference for building energy-saving design.

Thermal storage performance of building envelopes for nearly-zero energy buildings during cooling season in Western China: An experimental study

Adapting to the local climate is the key to developing nearly-zero energy buildings (NZEBs). During cooling season in Western China, the climate conditions are characterized by a large daily temperature range and high solar radiation, and improving the thermal storage performance of buildings is an effective passive cooling design strategy for NZEBs. This study aims to investigate the thermal storage performance of building envelopes under free-running conditions. A phase change material (PCM) is integrated in an experimental wallboard to enhance its thermal storage performance. To simulate the thermal environment in free-running buildings, a double-sided periodic thermal effect is applied as the indoor and outdoor conditions during the experiment. Different orders of the material layers and thicknesses of the PCM layer are compared to investigate the key factors that affected the thermal storage performance. The thermal inertia index and coefficient of heat accumulation are employed as key parameters to quantify the two factors. The results indicated that enhancing the coefficient of heat accumulation for the wallboard by optimizing the material layer order can reduce the fluctuations in the indoor air temperature by 31%. However, only increasing the thickness of the heat storage material does not significantly improve the attenuation and time delay effect of the wallboards. The coefficient of heat accumulation is proposed as a key parameter for NZEBs design. The design prototype and key parameters of the thermal storage wall considered in this study may provide a reference for the development of NZEBs in Western China.

Preparation and experimental study on the thermal characteristics of lightweight prefabricated nano-silica aerogel foam concrete wallboards

The optimal mix ratio of nano-silica aerogel foam concrete was determined through preliminary design and orthogonal experiment optimization. Based on the design of the size, reinforcement, and interface form of the prefabricated wallboard, a prefabricated foam concrete wallboard which met the requirements for use in the cold region (B region) of China was developed. The dry bulk density, thermal conductivity, compressive strength, and porosity were tested respectively. Besides, the microscopic characteristics of the foam concrete were tested through scanning electron microscopy(SEM). The thermal characteristics of the wallboard were tested under steady-state and unsteady-state conditions. The heat transfer coefficient is 0.5518 W/(m2·K) under steady-state conditions. The test results are that the temperature amplitudes of the inside and outside wall surfaces are 5.2℃ and 0.054℃ respectively, the temperature attenuation multiple and attenuation coefficient are 96.3, 0.0104, The delay time of the wall surface is up to 11.8 h, the heat storage coefficient of the surface is 2.48 W/(m2·K), thermal inertia index is 4.15, tested by using self-designed test device, and the periodic variation of sol–air temperature of Xuzhou area in summer is taken as boundary conditions. It shows that the developed wallboards have good thermal characteristics.

Insulation effect evaluation model of green building materials under ecological environment

<p>Green building materials are an important material basis for promoting the development of green buildings, and also the foundation of building energy conservation. In view of this, an insulation effect evaluation model of green building materials is constructed. The outer wall temperature index, the equivalent thermal resistance index, the inner surface maximum temperature and the thermal inertia index are used to characterize the insulation effect of the green building materials. According to the insulation effect evaluation principle of green building materials, the outer surface and inner surface temperature deviation curves and its’ fitting curves are made. The integral area between the fitting curve and the standard line is the temperature factor. The temperature factor can be used as an evaluation parameter for the insulation effect of green building materials in a fixed temperature range. It can characterize the average insulation effect of green building materials under a certain temperature range and comprehensive evaluation of different characterization indicators. The greater the temperature factor value is, the better the insulation effect is. The experimental results show that the model can accurately reflect the overall insulation effect of green building materials under the influence of various indicators in a certain temperature range, and the evaluation accuracy is high.</p>

Thermal Performance of Phase Change Material Wallboard with Typical Structure: Artificial Controlled Condition Experimental Investigation

Phase change material (PCM) integrated with building envelopes could enhance thermal storage performance of building envelopes significantly. Due to the variable physical property of PCM, the thermal performance of PCM envelopes is different from traditional envelopes such as clay brick and concrete wall. In the present paper, the thermal performance of PCM envelopes are experimentally investigated in an artificial climate chamber. The experimental PCM wallboard is made by PCM layer, concrete layer and insulation layer, which could reflect the real envelopes structure in typical office buildings in Western China. The thermal performance of the wallboard with different material layer locations is compared, and the thickness of PCM layer is optimized. During the experiments, the PCM wallboard is under double-sides heat effect, including periodic outdoor air temperature fluctuation and indoor heat source. Two indicators named thermal inertia index and coefficient of heat accumulation of interior surface are introduced as the key parameters to evaluate the thermal storage performance of the PCM envelopes. The results show that, under double-sides periodic thermal effect, the indoor air temperature is mainly affected by the coefficient of heat accumulation of interior surface of the PCM wallboard. However, the increment of the thermal inertia index of the whole wallboard has little influence on the indoor thermal environment under double-sides periodic thermal effect.

On Parameterizing Soil Evaporation in a Direct Remote Sensing Model of ET: PT‐JPL

AbstractRemote sensing models that measure evapotranspiration directly from the Penman‐Monteith or Priestley‐Taylor equations typically estimate the soil evaporation component over large areas using coarse spatial resolution relative humidity (RH) from geospatial climate datasets. As a result, the models tend to underperform in dry areas at local scales where moisture status is not well represented by surrounding areas. Earth observation sensors that monitor large‐scale global dynamics (e.g., MODIS) afford comparable spatial coverage and temporal frequency, but at a higher spatial resolution than geospatial climate datasets. In this study, we compared soil evaporation parameterized with optical and thermal indices derived from MODIS to RH‐based soil evaporation as implemented in the Priestley Taylor‐Jet Propulsion Laboratory (PT‐JPL) model. We evaluated the parameterizations by subtracting PT‐JPL transpiration from observation‐based flux tower evapotranspiration in agricultural fields across the contiguous United States. We compared the apparent thermal inertia (ATI) index, land surface water index (LSWI), normalized difference water index (NDWI), and a new index derived from red and shortwave infrared bands (soil moisture divergence index [SMDI]). Relationships were significant at the 95% confidence band. LSWI and SMDI explained 18–33% of variance in 8‐day soil evaporation. This led to a 3–11% increase in explained ET variance. LSWI and SMDI tended to perform better at the irrigated sites than RH. LSWI and SMDI led to markedly better performance over other indices at a seasonal time step. L‐band microwave backscatter can penetrate clouds and can distinguish soil from canopy moisture content. We are presently fusing red‐SWIR‐RADAR to improve soil evaporation estimation.

Predictive control of floor radiant heating system via fuzzy logic and particle swarm optimization for reducing room temperature fluctuations

ABSTRACT Most of the activities in human life are in buildings, and suitable room temperature control is helpful for energy consumption, cost savings, and thermal comfort. A TRNSYS simulation model of floor radiant heating system for a typical 100 m2 building in the cold region of the northern China was developed, and fuzzy logic control table was determined to develop predictive control on buildings. According to the differences between room temperature and setting temperature, room temperature change, valve operation time was predicted in the control cycle. The control table was optimized by particle swarm optimization and the best control table was obtained to reduce room temperature fluctuations. Control period was studied that comparing control period of 1 h, 0.5 h control period can reduce cumulative-unsatisfied time by 83.1%. Furthermore, the control performance impacts of room temperature, water temperature, insulation thicknesses of exterior wall, thermal inertia index of exterior wall and thicknesses of floor filling layer on room temperature fluctuations under this method were studied. Among them, the floor filling layer heat storage capacity of the building envelope plays a great important role which floor filling layer thickness from 60 mm to 100 mm is increased cumulative-unsatisfied time by 129.6%. The study results show that the room temperature can be maintained in the range of room setting temperature ±0.5°C by combining fuzzy logic with particle swarm optimization under the above influencing factors. The particle swarm optimization is combined with fuzzy logic to develop a predictive control strategy, which is stable and reliable, and has high control precision.

Composite foamed alkali-activated concrete with slag and steel slag

Thermally expandable foaming microspheres (FMS) are used as a foaming agent in many different fields due to their excellent dimensional stability and elastic properties. In this study, lightweight thermal insulation materials were prepared by adding FMS to foamed concrete containing alkali-activated steel slag and blast-furnace slag. The dry bulk density, cube strength, thermal conductivity and drying shrinkage of samples with different compositions were investigated and their microstructure was analysed using scanning electron microscopy and X-ray diffraction. With the addition of FMS, foamed materials with a dry bulk density of 625 kg/m3 and 40 mm cube strength of 3·6 MPa could be obtained. The 28 d drying shrinkage was 0·8 mm/m and the thermal conductivity was 0·102 W/m.K (thermal inertia index of 4·66). The results showed that FMS can be used as an organic foaming agent to prepare lightweight thermal insulation materials with improved insulation performance and mechanical properties.

Thermal Performance Analysis of Concrete Small Hollow Block

In this paper, the thermal insulation coefficient and thermal inertia index of small hollow concrete blocks with different hole types are calculated by theoretical method and numerical method, and the block structure with the best thermal insulation property and heat-shielding performance is respectively determined. The relationships between thermal insulation property and heat-shielding performance and block structure parameters are analyzed. The conclusion obtained provides a good reference value for the manufacturer of the block.

Study on the Thermal Performance of a Wall System Integrated Solar Thermal Collector

With the promotion of renewable energy, how to coordinate the efficient use of solar energy and indoor thermal comfort environment has become the key point for applying building integrated solar thermal system broadly. Thus, this paper presents a wall system integrated solar thermal collector. The influences of material and thickness of main layer on thermal performance of the wall system were calculated and analyzed. The results show that thermal performance parameters of the wall differ greatly in heating condition and non-heating condition. Compared with heating condition, heat transfer coefficient of the wall is smaller, and thermal inertia index and attenuation factor are larger in non-heating condition. The delay time of the wall in non-heating condition is 3.5h more than the time in heating condition.

Study on heat transfer characteristics of straw block wall in solar greenhouse

A new type of solar greenhouse with straw block north wall was developed. The heat transfer characteristics, temperature, heat absorption, release and loss of its north wall were investigated by theoretical and experimental analyses and the economic and environmental evaluations of north walls were carried out. The thermal storage coefficient of heat storage layer, the total thermal inertia index and the total thermal resistance of the new type straw block north wall (ST) were 38.5%, 13.9% and 25.4% higher than that of porous clay block north wall (CL), respectively and the average air temperature of Chinese solar greenhouse with ST was 0.7°C higher than that of Chinese solar greenhouse with CL on cloudy day. The temperature of heat storage layer as well as the heat absorption and release of ST were higher than that of CL. The heat loss of ST was less than that of CL. Compared to CL, the cost, energy consumption and CO2 emissions of ST were reduced 26.3%, 81.7% and 29.4%, respectively. ST had better thermal properties and could improve thermal environment of greenhouse. Besides, it was low-cost and environmentally friendly.

Indicators evaluating thermal inertia performance of envelops with phase change material

Phase change material (PCM) has been widely integrated in building envelops to increase their thermal inertia performance. To evaluate the thermal inertia performance of materials and envelops, Chinese Thermal Design Code has provided three indicators, namely, thermal storage coefficient, thermal resistance and thermal inertia index. The existing simplified method calculating the thermal storage coefficient is only applicable for materials with constant thermal properties. For those with varying thermal properties, such as PCM, however, further developments are still required. To solve this issue, both dimensional analysis and numerical simulation were carried out to develop relationships between the thermal storage coefficient of PCM and its other thermal properties (e.g. thermal conductivity, density and the effective equivalent specific heat). Based on the developed relationships, a simplified method calculating the thermal storage coefficient of PCM was proposed in this study. This simplified method was then combined into the thermal inertia index for evaluating the thermal inertia performance of building envelops with PCM.

The Influence Law of Thermal Properties on Building Thermal Stability in Hot-Humid and Cold-Humid Area

By means of the establishment of thermal stability evaluation model and simulating in Hua-feng factory residential building ,the influence law of thermal properties on building thermal stability are obtained,especially the influence law of heat storage on building thermal stability and the best thermal inertia index value of envelope enclosure in Hot-humid and Cold-humid Area.

Analytical optimization of the transient thermal performance of building wall by using thermal impedance based on thermal-electric analogy

Abstract An effective analytical method for analyzing the transient thermal performance of building envelopes is very important to optimize their thermal performance design. However, the influence of thermal mass and insulation material distribution cannot be analyzed well by using the current steady state thermal resistance (i.e. R value) and thermal inertia index (i.e. D value). Moreover, the substitution effect between the thermal resistance R and the thermal capacitance C has not been theoretically studied before. A novel analytical approach based upon thermal impedance of evaluating the transient thermal performance of building envelopes is developed in this paper. By using that, the optimal material distribution (corresponding to the minimal space heating or cooling load due to building envelope heat loss or gain) can be analytically determined. In addition, the substitution relationship between R and C can be theoretically derived. The results show that putting concrete material in the middle and evenly distributing the insulating materials on the inside and outside surface can maximize the module of thermal impedance for given conditions. The proposed approach provides an effective way to theoretically optimize the transient thermal performance of building external wall.

The Optimization Ratio Study of Steady State Heat Transfer and Dynamic Heat Transfer in Hot-Humid and Cold-Humid Area

By means of the establishment of thermal stability evaluation model and simulating in Huafeng factory residential building ,the relationship between the D value and building thermal stability and the optimal distribution ratio are obtained.The results show that:at the shape coefficient≤0.40, the most optimal matching relation is :heat transfer coefficient is 1.0, thermal inertia index is 2.0;at the shape coefficient >0.40, the most optimal matching relation is :heat transfer coefficient is 0.8, thermal inertia index is 2.0.

Simulation and optimization of solar greenhouses in Northern Jiangsu Province of China

Abstract A simulating model was used to simulate and improve the thermal performance of solar greenhouses. Simulations with the weather conditions of Xuzhou, Jiangsu Province show that the greenhouse with clay brick wall (0.6 m thick) insulated with polystyrene boards (0.1 m) and the greenhouse with soil wall (3 m thick) perform better than the one with hollow concrete block wall (0.6 m thick). The lowest air temperature increases with thermal resistance and thermal inertia index of north wall. The thermal performance of the solar greenhouse with hollow concrete block wall can be improved by increasing the density and reducing the thermal conductivity of north wall. The soil wall can be conceptually divided into three layers from inside to outside: energy-storing layer, thermal stable layer, and thermal insulating layer. Thermal stable layer shrinks with the reduction of the size of north wall and it would disappear when the wall is reduced to a certain size. A trapezoidal soil wall with a top of 0.5 m and a base of 1.7 m appears to be a proper design if the air temperature is to be maintained above 10 °C under the weather conditions of Xuzhou, Jiangsu Province of China.

The Influence of Thermal Inertia Index on the Residential External Walls in Hot-Summer and Cold-Winter Areas

The evaluation method of residential building envelope thermal performance in hot-summer and cold-winter area is different from the method of the cold northern regions, that is, the merit of the thermal performance of walls and roofs should not be determined only by the heat transfer coefficient K or thermal resistance R, the impact of the thermal inertia index on the thermal performance of building envelope should also be considered. The analysis results show that, with the different values of thermal inertia index D, the difference of residential summer air-conditioning power consumption is not big, but the difference of residential winter heating power consumption is bigger, therefore, the high thermal inert wall is more conductive to reduce the winter heating power consumption than the low thermal inert wall.