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Highlights • UNI 13786 describe a mathematical method to dynamic heat transfer. • Sinusoidal steady-state analysis is the "dynamic" model used. • Direct method: from mathematical model to physical propriety. • Proposal for inverse method: from physical propriety to mathematical model. • Test by the wall in climatic chamber and results. Abstract This study investigates energy efficiency in buildings. The accurate evaluation of energy consumption in existing buildings is a difficult task, particularly due to the Mediterranean climate, which is in the temperate zone. Among the various analytical models, the most effective measurement of the energy consumption of buildings is the dynamic type. In evaluating the energy consumption of buildings, the greatest contribution is provided by opaque components and particularly by the external walls of that building. In the model, which is reported in the EN ISO 13786, the thermal properties (the specific heat (J/kgK) and thermal conductivity (W/mK) of the layers of the wall were tested, and the technical standard reported that the physical properties (from which they derive the phase shift and decrement factor) transferred through the wall when a sinusoidal wave temperature variation was applied in a periodic steady state. We propose an inverse approach to measure the sinusoidal periodic steady state (temperature and thermal flux) on the two faces of the wall. With this approach, it is possible to obtain the thermal properties of the wall through an inverse analytical model. The model was applied in a real experiment on a full-size wall in a climatic chamber to verify the dynamic thermal and physical properties of the layers. [ABSTRACT FROM AUTHOR]

Highlights • A new lab test is proposed to study dynamic energy systems and composites with PCM. • Transient plane source technique and controlled dynamic environment sensing are coupled. • Concrete with PCM for thermal energy storage in buildings are dynamically tested. • The test method allows to identify PCM dispersion and activation and TES contribution. Abstract In recent years the combination of latent and sensible thermal energy storage processes within passive and active building components has gathered increasing attention among researchers all over the world. All this considered, an ever-increasing hunger for bridging the gap between chemistry-based characterization methods and engineering-scale monitoring solutions is spreading worldwide, with the aim of developing new experimental procedures allowing to test these advanced systems under realistic operative environmental conditions. In this view, the present paper aims at proposing an innovative characterization procedure for real-scale engineered applications with reference to dynamically variable composites, such as PCM-doped cement-based mixes for building envelope applications. Therefore, in this work, thermally enhanced concretes were produced using micro-encapsulated paraffin and their activation was investigated by means of an innovative experimental technique coupling transient plane source method and controlled environmental dynamic forcing. The dynamic-TPS analysis allowed to produce temperature dependent profiles for three basic material thermal properties, i.e. thermal conductivity, thermal diffusivity and volumetric specific heat. Results show that the proposed methodology is capable of detecting PCM activation within the engineered composites during the imposed hygrothermal cycle, where, for example, the effective thermal conductivity of the composites varied between 40 and 90% amid the melting/freezing process. Furthermore, the transient plane source method also showed to be suitable to investigate PCM dispersion within the composites. [ABSTRACT FROM AUTHOR]

The low thermal conductivity of Vacuum Insulation Panels (VIPs) degrades with time due to gas permeation through VIPs barriers. There is additional ageing of their envelope and core material. Accelerated experiments are carried out in order to better understand this ageing process but they are not sufficient to predict the long term performance of panels. Models have to be used to connect the short term evaluation and the long term behaviours in order to improve the prediction of the thermal conductivity evolution over 50 years. This paper describes the development of a VIP model in the Dymola ® software. This model takes into account the envelope and core material hydro-thermal characteristics and behaviours, and integrates the actual solicitations of the panels during accelerated ageing tests. The thermo-activation of the envelope permeance is integrated. Many properties of the core material are modelized: type of core material, sorption isotherm, hygro-thermal ageing, pore size distribution, etc. Simulations in constant conditions in temperature and humidity have been carried out. The results show that the real behaviour of the VIPs conductivity can’t be simply evaluated through a linear extension of its short-term evolution. Given the important impact of the core material detailed characteristics, it is absolutely necessary to get an accurate determination of the core material sorption curve and of the ageing of this curve. [ABSTRACT FROM AUTHOR]

The seawater source heat pump (SWHP) is a renewable energy utilization system. The beach well infiltration intake system (BWIS) effectively improves the stability, reliability, and energy efficiency of SWHP systems in cold climate areas. BWIS research requires a multidisciplinary approach that involves both hydrogeology and heat transfer theory. There are many factors influencing the energy consumption and life-cycle costs of the systems, with each factor having many possible values. This paper aims to determine the degree of influence of ten representative factors of BWIS: specific heat capacity of rock-soil, rock-soil density, thermal conductivity of rock-soil, void fraction of rock-soil, rock-soil permeability, beach well radius, site length, site width, row number of beach wells, and column number of beach wells. In this paper, a BWIS seepage and heat transfer model is established. Based on the model, an orthogonal design optimization method is presented and analyses are conducted for heat pump unit energy consumption, seawater pump energy consumption, and economic cost for various conditions using MATLAB code. The results indicate that a greater number of beach wells is not always better and the number and placement of beach wells should be scientifically and objectively optimized by the orthogonal design method. The optimization method can scientifically guide engineering design for BWIS and offset the design deficiency that results from the current practice of only using a hydrogeological report of randomly selected test wells. [ABSTRACT FROM AUTHOR]

Analyzing heat fluxes of plants and soil is necessary to explore the thermal performance of green roofs. This paper presents mathematical expressions of heat fluxes of green roofs, and specially a heat and mass transfer model is built to get the distribution of temperature and moisture content in soil. The developed model is validated with experimental data from the intensive planted roof located in Chongqing. And the effectiveness of the model for predicting the temperature and water content variations are demonstrated by the comparison between the experimental results and simulation. Furthermore, the performance of green roof during summer in Chongqing is discussed based on the experiment. Through analyzing heat fluxes of green roofs, the study presents the contribution of each thermal behavior including reflection, convection, evapotranspiration and thermal storage to the thermal effects of the green roof quantitatively. The weight of various thermal behaviors of the green roof changes in different time, resulting in different thermal performance of green roofs. The study of the transient heat fluxes of green roofs will not only contribute to a high efficient usage but also a better application of engineering. [ABSTRACT FROM AUTHOR]

Energy efficiency retrofit of buildings represents a key effort in reducing EU energy demand by 20% by 2020. However, predictions tend to overestimate savings by large percentages. The shortfall in savings can be attributed to incorrect predictive techniques, comfort takeback along with other behavioural and workmanship variables. Common predictive techniques related to heat loss tend to be based on the U-value of the building envelope. This paper presents the design of a more straightforward and compact version of the traditional Hot-Box apparatus (measures U-value) which instead determines the thermal resistance of samples of building envelope. U-value includes the need to measure/predict the effective surface resistances. In situ surface resistances, which include radiation and convection, are difficult to predict and vary depending on climatic conditions, exposure levels, surface emissivities among many other influences. The design of the test facility eliminates the need to incorporate these surface behaviour variables. This paper details the replicable apparatus and test methodology. The results of testing a hollow block wall of typical construction using the rig is then presented. The determined R-value is found to be within 1% of calculated values and the thermal time constant also matches closely with the most accurate predictive estimates. [ABSTRACT FROM AUTHOR]

Nowadays to reduce the energy loss as well as to minimize the emission of the green house gases of buildings can be solved by thermal insulating. Silica aerogels have a promising potential in the building and construction sector as thermal insulation due to their excellent thermal conductivity. At the present time the applications of silica aerogel blankets are truly widespread. This study focuses on the moisture induced degradation of the thermal conductivity of the above mentioned insulation slabs. Experimental studies show that the thermal conductivity of the aerogel blankets can be increased significantly (approximately 20–40%) after wetting them. For this case different types of investigations were carried out to investigate the changes in the thermal conductivity derived by the moisture content. Firstly, in order to see the temperature sensitivity of the moisture up-taking, sorption isotherm curves were registered at 283, 293 and 303 K after 24 h after drying and wetting at 5 different relative humidities. Secondly, the decrease of the thermal conductivity was followed with a Holometrix type heat flow meter of individual aerogel slabs after wetting the dried samples for 0, 4, 8, 12, 16, 20 h at 293 K and 90% relative humidity in a Climacell type climatic chamber. Finally, the change in the thermal resistance of a brick based wall covered with 0.013 cm thick aerogel insulation was registered by calibrated chamber method in function of the quantity of sprayed water. From the measurement results calculations were executed to see the changes of the thermo-physical properties of the aerogel samples due to the water absorption. The novelties of the article can be found in the comparison of the measurements of the same values and properties carried out by different methods Moreover, the measurement results formed the basis of Building Energetic Simulations in order to show roughly the effect of the moisture. [ABSTRACT FROM AUTHOR]

• Seepage can promote the temperature field around GHEs to reach the steady faster. • Seepage effects on temperature field around GHEs increases with seepage velocity. • Seepage will reduce the accumulation of heat around the heat exchangers. • Ground stratification effects on temperature field around GHEs depends on the thermal property of adjacent stratum. Heat transfer between the ground heat exchanger and surrounding stratum under the action of groundwater seepage is a potential problem in karst areas, few systematic studies on it have been carried out yet. A model test apparatus was built to experimentally investigate the effects of karst groundwater seepage and ground stratification on the heat transfer characteristics of ground heat exchangers. The heat and seepage transfer coupling model for ground heat exchangers was established, and verified with the measured data from the model test. Base on the model, the influence of seepage velocity and direction on the heat transfer of ground heat exchangers was analyzed and discussed. Test results show that the seepage can promote the temperature field around the heat exchanger to reach the steady state faster, and the influence of seepage on the soil temperature field around the heat exchanger increases with increasing the seepage velocity. The seepage will carry the heat released by the heat exchanger from the upstream side to the downstream, which effectively reduce the accumulation of heat around the heat exchanger. Soil boundary exists the sudden change of temperature when there are great differences in thermal properties between adjacent soil layers, which can be attributed to the influence of ground stratification. The numerical model proposed in this study can well predict the distribution of soil temperature field around heat exchangers in the model test. Simulation results show that the temperature of soil around the heat exchanger will change along the seepage direction. [ABSTRACT FROM AUTHOR]

The in-situ estimation of the thermal resistance (Rc-value) of walls in buildings is of major significance to determine their energy performance. The exact construction of walls is generally unknown, especially in older buildings, making the estimation of the Rc-value inaccurate. In-situ measurement is generally not being performed because, for the current standard method (ISO 9869), generally a measurement period of more than ten days is required. In the present paper, a new transient in-situ measurement method (Excitation Pulse Method, EPM) based on the theory of response factors is derived, applied experimentally on three walls, showing that it is possible to measure the Rc-value within less than 2 h. The results are compared to the ones obtained by ISO 9869 method, showing a good agreement. Additionnally, EPM measurement technique can provide the average Volumetric Heat Capacity and thermal conductivity. It is also shown that the ISO 9869 method can be easily improved by using an additional heat flux meter. EPM is believed to make a significant contribution to the quick and accurate estimation of the thermal resistance in unknown constructions and therefore to the accuracy of the prediction of energy consumption in buildings. [ABSTRACT FROM AUTHOR]

A room facing north in a fully monitored office building located in Madrid (Spain) has been studied. Data corresponding to a period of more than two years, recorded while the building was regularly used, have been employed. A regression analysis method based on averages has been applied. Although the used equation is analogous to the steady state, dynamic features of the test have been considered. A dynamic energy balance equation is first stated. Then this equation is integrated for a time interval long enough to make the accumulation term much lower than the other terms. Finally averages are used to estimate integrals. The minimum integration period that allows this simplification has been identified, studying integration periods from 1 to 20 days. It is concluded that integration period and variables needed depend on test conditions and the building. Daily averages are insufficient for this analysis in these test conditions. Heat supplied by the HVAC system was modelled avoiding flow measurements. Suggested terms including occupancy and door status improve the model remarkably. A spread in the Overall Heat Transmission Coefficient (UA) estimated under 10%, was found for a 7-day integration period. This narrow interval allows to hand this parameter as intrinsic. [ABSTRACT FROM AUTHOR]

• New 2-D heat transfer model for coaxial BHE was built to estimate layered λ s. • Novel estimation of layered λ s was presented by using DTRT data and GA. • Effect of layer conditions on estimation was almost eliminated by the method. • 2 h DTRT data was efficient to estimate the layered λ s by the method. Estimation of ground thermal conductivity plays an important role in design of borehole heat exchanger (BHE) for ground source heat pump (GSHP) systems, and the ground is usually heterogeneous with layered thermal properties. Therefore, this study presented a novel estimation method for layered ground thermal conductivity by using distributed thermal response test (DTRT) and genetic algorithm. Firstly, a comprehensive new 2-D heat transfer model for coaxial BHE was built to simulate borehole fluid temperature profiles, it revealed that the distribution of ground thermal conductivity showed a significant influence on outlet temperature and temperature profiles. Then, based on the built model, the vertical distribution of ground thermal conductivity was estimated through DTRT data by using the genetic algorithm. It was found that the DTRT data at 2 h was effective to estimate the layered ground thermal conductivity by using the new 2-D heat transfer model. Furthermore, the estimated distribution of ground thermal conductivity was almost independent of numbers or thickness of sub-layer, and the largest difference in distributions of ground thermal conductivity among different layer thickness was less than 0.3 W/(m·K). Also, the estimation convergence showed independence with layer thickness, converged results could be obtained after 10 iterations for different layer conditions. [ABSTRACT FROM AUTHOR]

Highlights: [•] The limited heat consumption per unit volume was proposed. [•] Equivalent heat transfer coefficient of external windows and wall was proposed. [•] Mathematical model on thermal insulation thickness of external wall was built. [•] Economical evaluation model was built for energy-saving renovation. [•] The economical model was verified to be feasible by an existing public building. [Copyright &y& Elsevier]

Highlights: [•] Holed bricks with internal protuberances having improved performance as thermal insulators. [•] Smart holed bricks, acting as better thermal insulators when operating under higher temperature differences. [•] Modified holed bricks allowing considerable energy savings in buildings. [ABSTRACT FROM AUTHOR]

Highlights: [•] Grey-box models are set up and statistically validated. [•] A method for estimating important thermal parameters of a wall is presented. [•] Testing time is reduced significantly compared to average methods. [•] It is seen as wind velocity influences the heat transfer of this wall significantly. [•] The surface temperature can be described with the models. [ABSTRACT FROM AUTHOR]

Highlights: [•] A heat transfer model based upon the multipole theory inside the borehole is developed. [•] The experimental validation of the multipole model has been performed. [•] The effects of some factors on the thermal effectiveness coefficient are analyzed. [•] The model could analyze the temperature field in complex profile and boundary. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an experimental and numerical case study of the heat transfer around the helical ground heat exchanger. With varying helical pitch, indoor thermal response tests were conducted in a dry sand. The tests were analyzed based on axisymmetric finite element analyses and recently published heat source models for spiral coil heat exchanger including our modifications of them by adding finite-length line source solution to consider vertical return pipe at center of helical heat exchanger. In addition to reasonable agreements in soil temperature rises at exteriors the helical heat exchanger, existence of return pipe was found to be important for estimation of heat transfer inside helical exchanger. Besides, the heat source models were found to be applicable to approximate mean fluid temperature during TRTs. The numerical and analytical models were applied to field thermal response test for an energy pile reported in literature. Compared with numerically estimations, the analytical solutions considerably overestimated temperature rise at the exterior of the energy pile. The results reveal that reasonable considerations in estimation of effective thermal properties may be needed when applying the heat source models for energy pile, even though they would evaluate reliable heat transfer behavior of helical heat exchanger embedded in a homogeneous ground. [Copyright &y& Elsevier]

Abstract: This paper proposed a new method based on modified composite model in the thermal response test (TRT) in the variable heat rate case study. The new method considered the unsteady-state heat transfer in the borehole instead of the line-source model assumption. A Matlab program was compiled which can perform inversion calculation to obtain the ground thermal properties. The superposition principle was used to process the variable-rate problem. This new method was applied to two thermal response tests. The simulation value based on the method shows a good agreement with the measurement data of water temperature. The proposed method would save the time and reduce the cost of TRT when power fluctuation or failure occurs. [Copyright &y& Elsevier]

Abstract: A Z-transfer function method is proposed to calculate transient heat flow through the envelope of an underground cavern in this paper. The envelope of an underground cavern has great heat capacity and high thermal inertia. In order to obtain the correct Z-transfer coefficients, indoor air temperature is expressed as a superposition of mean annual temperature, annual temperature wave and daily temperature wave. Corresponding to the three types of temperatures, three heat flows are calculated separately, and then are superposed. The thermal zones formed by annual temperature wave and daily temperature wave are different; thus, the ratio of amplitude frequency characteristics of the transfer functions is proposed to define the boundaries of the two different thermal systems. After transforming an underground cavern into an equivalent cylinder, the Z-transfer function coefficients of two thermal systems are calculated. Case study shows that heat fluxes at interior surface calculated by Z-transfer coefficient method have good agreement with those by numerical finite difference method, and the deviation between the results from two methods is only 1% of that from numerical method. However, the computation time of Z-transfer coefficient method is less than 1% of that of numerical method. [Copyright &y& Elsevier]

Abstract: This study seeks to improve the geometrical distribution of bricks to optimise the equivalent thermal transmittance of a wall built of Termoarcilla® ECO 29 voided clay bricks, using calculations according to Spanish UNE , AENOR , European EN and international ISO standards. The objective is to study improvements in the wall''s thermal conductivity, always remembering the limitations imposed by the manufacturing process. Simulations are made using a finite elements application . It is concluded that, within the possibilities allowed by the manufacturing process, with non-rectangular voids the heat flux has to cross a higher number of voids, which improves its thermal properties. A rhomboid layout of voids with the longer diagonal at right angles to the heat flux is the best internal void layout. If the internal perforations are also extended to the end of the tongue and groove, the direct thermal bridge in this type of brick is broken. Finally, a 290mm wide brick with 25 rows is obtained with the geometrical properties described above which shows an improvement of almost 16% over the original ECO 29 brick, performing well in all climatic areas of Spain, with a full-bed mortar joint 30mm thick. [Copyright &y& Elsevier]

Abstract: Vegetated (green) roofs alter the roof surface energy balance and hence affect both building energy consumption and the transport of heat into the environment. Quantitative evaluation of the energetics of green roof systems requires accurate knowledge of the moisture-dependent thermal properties of the growing media. To support this need for data and to supplement previously published data we conducted a laboratory study to measure thermal conductivity, volumetric heat capacity, and thermal diffusivity of 12 green roof soil samples of varying composition. The results indicate that thermal properties vary significantly as a function of growing media design. Growing media incorporating expanded slate as their aggregate had thermal conductivities that were two to three times those of media that used a porous silica-based aggregate. Media incorporating expanded clay as the aggregate had thermal conductivities roughly in the middle of these extremes. In general the thermal conductivity nearly tripled as the growing media moisture levels were increased from relatively dry to saturated. Also, it was found that compaction typical of green roof systems that have been installed for multiple seasons can increase thermal conductivity of moist soils by 30–40% over their uncompressed values. [Copyright &y& Elsevier]

Abstract: Over the last years the use of phase change slurries (PCSs) based on microencapsulated phase change material (MEPCM) increased considerably due to their capacity of adaptation to various heat storage systems. PCSs are obtained by dispersing a microencapsulated PCM (particle diameter 5–20μm) into a heat carrier fluid (e.g. water). Heat storage systems are used in applications where the available energy supply is not synchronous with the demand, such as solar thermal and waste heat recovery systems. The theoretical study conducted here – based on heat transfer and energy conservation equations – is intended to developing a theoretical model of the heat storage properties of phase change slurries capable of predicting the transient thermal response of a thermal energy storage system (TES). Most of the research work was focused on investigating the enthalpy–temperature curves resulting from a heating–cooling cycle around the melting point of the PCM. The influence of other parameters such as mico-particles diameter was assessed. [Copyright &y& Elsevier]

Abstract: In numerous fields, especially that of geothermal energy, we need to know about the thermal behaviour of the soil now that the monitoring of renewable forms of energy is an ecological, economic and scientific issue. Thus heat from the soil is widely used for air-conditioning systems in buildings both in Canada and in the Scandinavian countries, and it is spreading. The effectiveness of this technique is based on the soils calorific potential and its thermophysical properties which will define the quality of the exchanges between the soil and a heat transfer fluid. This article puts forward a method to be used for the in situ thermophysical characterisation of a soil. It is based upon measuring the heat exchanges on the surface of the soil and on measuring a temperature a few centimetres below the surface. The system is light, inexpensive, well-suited to the taking of measurements in situ without the sensors used introducing any disturbance into the heat exchanges. Whereas the majority of methods require excitation, the one presented here is passive and exploits natural signals. Based upon a few hours of recording, the natural signals allow us to identify the soils thermophysical properties continuously. The identification is based upon frequency methods the quality of which can be seen when the thermophysical properties are injected into a model with finite elements by means of a comparison of the temperatures modelled and those actually measured on site. [Copyright &y& Elsevier]

Abstract: In this study, the effect of carbon nanotubes (CNTs) on nucleate boiling heat transfer is investigated. Two halocarbon refrigerants of R123 and R134a for building chillers were used as working fluids and 1.0vol.% of CNTs was added to them to examine the heat transfer enhancement with CNTs. The experimental apparatus was composed of a stainless steel vessel and a 152.0mm long plain horizontal tube of 19.0mm outside diameter heated by a cartridge heater. All data were obtained at the pool temperature of 7°C in the heat flux range of 10–80kWm−2. Test results showed that CNTs increase nucleate boiling heat transfer coefficients for these refrigerants. Especially, large enhancement up to 36.6% was observed at low heat fluxes of less than 30kWm−2. With increasing heat flux, however, the enhancement was suppressed due to vigorous bubble generation. Fouling on the heat transfer surface was not observed during the course of this study. Optimum dispersion of CNTs should be examined for their commercial application to enhance nucleate boiling heat transfer in building air-conditioning applications. [Copyright &y& Elsevier]

Abstract: The intent of this paper is to describe and compare the two different two-dimensional frame/spacer heat transfer calculation methodologies used in North America (FRAME [EEL. The FRAMEplus Toolkit for Heat Transfer Assessment of Building Components, Version 3.0, Enermodal Engineering, Kichener, Ontario, Canada, 1995], THERM [LBNL. THERM 2: PC Program for Analyzing Two-Dimensional Heat Transfer Through Building Products, LBL-37371, Windows and Delighting Group, Lawrence Berkeley National Laboratory, Berkeley, CA, 1998], ASHRAE SPC 142P [ASHRAE. Standard Method for Determining and Expressing the Heat Transfer and Total Optical Properties of Fenestration Products, Public Review Draft of Standard 142P, American Society of Heating, Refrigerating and Air Conditioning Engineers, Atlanta, 1998]) and in Europe [ISO 10077-2. Thermal Performance of Windows, Doors and Shutters–Calculation of Thermal Transmittance—Part 2: Numerical Method for Frames, International Standards Organization, Geneva, 2003]. The two approaches, called the ASHRAE and ISO methods, are different in the way they treat the effect of the glazing spacer on the heat transfer through the frame and the glazing unit near the frame. The ASHRAE method assumes that the spacer effects both the heat transfer through the frame and the heat transfer through the glazing in an “edge-of glass” region 63.5mm (2.5in.) from the glazing/frame sight line. The ISO method assumes that the additional heat transfer due to the existence of the spacer is proportional to the glazing/frame sightline distance that is also proportional to the total glazing spacer length. An example calculation of the overall heat transfer and thermal transmittance (U-value or U-factor) using the two methods for a thermally broken, aluminum framed slider window is presented. The fenestration thermal transmittance calculations analyses presented in this paper show that small differences exist between the calculated thermal transmittance values produced by the ISO and ASHRAE methods. The results also show that the overall thermal transmittance difference between the two methodologies decreases as the total window area (glazing plus frame) increases. Thus, the resulting difference in thermal transmittance values for the two methods is negligible for larger windows. This paper also shows algebraically that the differences between the ISO and ASHRAE methods turn out to be due to the way the corner regions of the window frame and glazing are treated in the assembly of the overall thermal transmittance for a three-dimensional window from the two-dimensional calculations. Three-dimensional heat transfer calculations can be made and correction factors can be applied to both the ASHRAE and ISO two-dimensional results to bring them into agreement with the three-dimensional results. [Copyright &y& Elsevier]

• A hybrid composite-medium line-source model for vertical GHEs is created. • The new model is an excellent approximation of the ICMLS model. • Compared to the ICMLS model, the new model can greatly shorten the time needed for parameter estimation by 99%. • Test duration of the in-situ TRT can be reduced with the proposed solution. An energy pile is a special form of vertical ground heat exchanger that couples the roles of structural support and heat transfer. Modeling the transient heat transfer process inside an energy pile has importance; however, available analytical models either have insufficient calculation accuracy or are computationally demanding. Based on three existing models, this paper proposes a novel short-term hybrid composite-medium line-source (HCMLS) model, which is not only efficient in computation but also more accurate than most traditional analytical models. The model is suitable for ground heat exchangers of various radii. Comparisons between the hybrid analytical model and a numerical model are made for energy pile cases with different parameters, including the thermal properties, borehole radii, relative positions of tubes, and number of tubes. In general, the hybrid composite-medium line-source model gives credible prediction after 100 min. The new model is further validated by the infinite composite-medium line-source (ICMLS) model, which is currently the most theoretically complete short-term model. Moreover, the new model is applied to thermal response tests (TRTs). The least dimensionless test duration for interpretations based on the modified hybrid composite-medium line-source (C-HCMLS) solution is Fo > 1.7. This study renders the application of in situ TRTs to energy piles with large diameters feasible. [ABSTRACT FROM AUTHOR]

• Investigating the impact of different materials adjacent to the air cavities of ventilated facades. • Experimental evaluation on three prototypes in summer and winter. • The thermal mass in the outer side of the gap enhanced the stack effect. • The thermal mass in the inner side of the gap increased the heat transfer towards the indoor. In this paper we have investigated how different materials and thermal masses impact on the performance of ventilated facades with narrow cavities, by measuring the variation in terms of heat flows and ventilation efficiency. While geometry has been widely explored, the role of wall composition has received much less attention. To bridge the gap, three real-scale prototypes of ventilated facades were built and tested all over the year on a mock-up in Central Italy: (i) L, with a lightweight external enclosure, as a baseline reference, (ii) IM, with a massive layer enclosed in the gap and (iii) EM, with an external massive cladding. The results demonstrated that the EM solution more effectively mitigated the average surface temperatures (both external and internal), with values of –2 °C and –1 °C in summer and of –3 °C and –0.5 °C in winter, when compared to the L solution. Moreover, in the EM case, the ventilated cavity reduced both the incoming and outgoing heat fluxes, since the outer mass operated as a thermal buffer between the outdoor and the ventilation chamber. Conversely, the presence of an internal mass determined an increase of the heat transfer towards the indoor environment. The position of the thermal mass in the outer layer also increased the air velocity in the gap thus enhancing the stack effect. [ABSTRACT FROM AUTHOR]

• Thermal diffusivity is needed to determine the dynamic thermal characteristics of a wall. • Masonry walls have a heterogeneous structure. • The local measurement of thermal properties of large building components may be inaccurate. • It is possible to measure thermal diffusivity by measuring the temperature profile in the wall. • The time of measurement of thermal diffusivity by the method is about 90 min. For a better understanding of the energy characteristics of a building, it is useful to find heat fluxes and a temperature field in a transient state. To obtain the temperature in a solid using the Fourier equation a thermal diffusivity is needed. For thermal characteristics of existing buildings, measurement can provide data on this property for a specific case. Laboratory methods of diffusivity measurement encountered in the literature take into account the layers of material close to the surface. A measurement method dedicated to large elements, for example parts of buildings, has been proposed. It is based on temperature survey in the element's volume and assumption that the obtained results meet the Fourier equation. The temperature is approximated by a polynomial and then this function is substituted to the heat transfer equation and diffusivity is determined. In order to validate the method, the temperature measurements for the actual wall were made, the discrete values were approximated by a polynomial of various degrees with respect to the spatial coordinate and time. On the basis of obtained function, the inverse task was solved and thermal diffusivity was determined. The dependence of the results on the length of time in which the values of temperature were approximated and polynomial degree was analysed. A preliminary analysis of errors was made. The obtained values were compared with the results of other authors' research. [ABSTRACT FROM AUTHOR]