Internal Thermal Loads Research Articles

Climate change mitigation and adaptation in Spanish office stock through cool roofs

In a context of climate change, the cooling period of buildings is increasing every year in Mediterranean countries. This will become a relevant issue when existing buildings are retrofitted. Cool roofs have a passive cooling effect on a building and can contribute to decreasing the annual cooling demand. In office buildings, thermal comfort has a considerable influence on workers’ performance. In these buildings cooling energy demands tend to be high due to the high internal thermal loads. This paper describes annual energy simulations of Spanish office stock to evaluate the potential energy savings of cool roofs within the context of building retrofitting. The energy demand and thermal comfort of representative office buildings is compared before and after the application of a cool roof coating, in the present time and in the year 2050, for all climate areas of Spain, under the most optimistic and most pessimistic future weather scenarios. Results showed that the cooling energy demand of Spanish office stock can be potentially reduced by 25 % when a cool roof is applied, and the annual energy demand for heating and cooling can be cut by 6 %, 11 % and 12 % in the present, the optimistic future scenario and the pessimistic future scenario, respectively.

Analysis of the thermal control system for the 3U CubeSat nanosatellite – “IXAYA”

Abstract In recent years, space exploration has become increasingly accessible to a diverse array of countries, facilitated in part by CubeSat nanosatellites. These versatile nanosatellites find applications in a wide spectrum of fields, from forest fire detection and meteorological observation to communication systems, particle analysis, and hot spot identification. This article delves into the outcomes of a comprehensive thermal analysis conducted on the IXAYA nanosatellite. The primary mission of this nanosatellite is to identify hot spots in the vicinity of Mexico City. The thermal analysis process entails a meticulous review of each subsystem along with the associated boundary conditions. This study commences with the definition of an optical payload and a thorough assessment of subsystem requirements. Subsequently, we calculate both external and internal thermal loads. With these foundational data points, we progress to ascertain the temperature distribution across the entirety of the satellite, ensuring that all constituent elements remain within their designated operational temperature ranges. In the closing section, we present our findings and conclusions.

Thrust Restraint of Buried Pipelines Subjected to Internal Pressure, Thermal, and Earthquake Loads

Thrust Restraint of Buried Pipelines Subjected to Internal Pressure, Thermal, and Earthquake Loads

Semi-analytical solution for dynamic thermo-mechanical responses of multi-layered thermo-poroelastic media

Dynamic thermo-mechanical responses of multi-layered thermo-poroelastic media induced by internal thermal and mechanical loads are investigated utilizing a semi-analytical approach. To investigate the transient behavior of the thermo-poroelastic media, the governing equations that consider both the fluid inertia and the soil skeleton inertia are established. The Laplace–Hankel transform is then applied to derive solutions for a single thermo-poroelastic layer and a half-space in the transformed domain. The multi-layered thermo-poroelastic model is assembled using the layer and half-space elements with the continuity assumptions. Solutions for the multi-layered thermo-poroelastic model are obtained in the transformed domain using boundary conditions, while the final solutions are calculated using a numerical procedure. Comparisons with published results validate the accuracy of the multi-layered model. Finally, effects of the coupled internal dynamic thermo-mechanical load, as well as the influences of material stratification and permeability, on the dynamic responses, including vertical displacement, temperature, vertical stress, and pore water pressure, are graphically presented.

Extending the IFC-Based bim2sim Framework to Improve the Accessibility of Thermal Comfort Analysis Considering Future Climate Scenarios

Future weather scenarios significantly affect indoor thermal comfort, influencing people’s well-being and productivity at work. Thus, future weather scenarios should be considered in the design phase to improve a building’s climate change resilience for new constructions as well as renovations in building stock. As thermal comfort is highly influenced by internal and external thermal loads resulting from weather conditions and building usage, only a dynamic building performance simulation (BPS) can predict the boundary conditions for a thermal comfort analysis during the design stage. As the model setup for a BPS requires detailed information about building geometry, materials, and usage, recent research activities have tried to derive the required simulation models from the open BIM (Building Information Modeling) Standard IFC (Industry Foundation Classes). However, even if IFC data are available, they are often faulty or incomplete. We propose a template-based enrichment of the BPS models that assists with imputing missing data based on archetypal usage of thermal zones. These templates are available for standardized enrichment of BPS models but do not include the required parameters for thermal comfort analysis. This study presents an approach for IFC-based thermal comfort analysis and a set of zone-usage-based templates to enrich thermal comfort input parameters.

Numerical simulation of fatigue crack growth in an engine heat shield

In order to prevent the body from overheating, a corresponding thermal protection device is usually designed on the inner wall of the combustion chamber. The working environment of this thermal protection device is very harsh, and it needs to withstand internal and external pressure loads and thermal radiation loads of the combustion chamber, especially at the connection between the cylinder and the support parts, the force is harsher. In order to avoid engine damage, causing unnecessary losses. In this article, the thermal–mechanical coupling analysis of the heat shield is carried out by finite element method to analyze the thermal stress and mechanical stress. According to the finite element simulation results, the initial cracks are inserted, respectively, at the stress concentration. Using linear elastic fracture mechanics and Forman–Newman–de Koning models, the crack growth lifetimes of cracks at different locations were calculated. The results of the study show that comparing the initial cracks at different locations, the cracks on the side near the edge of the heat shield have the largest reduction in crack growth life of 64.4% and the critical crack length of 52.0%. The linear superposition of thermal and mechanical stresses under different working conditions has different degrees of nonlinear effects on the crack growth life and critical crack length. The research work in this article can provide a basis for the evaluation of fatigue crack growth life of heat shield and can also provide a reference for engine maintenance.

Small-scale experiments on the operational performance of a lightweight thermally active building system

Thermally active building systems (TABS), which are integrated with the structure of a building, provide a robust approach for utilising renewable energy. However, reinforced concrete, where TABS are typically placed, is responsible for a significant proportion of initial embodied energy and related greenhouse gas emissions. Therefore, combining lightweight structural elements and thermal systems reduces initial embodied energy usage while retaining the active material’s thermal storage and heat transport benefits. The present experimental work explores the operational performance of a prototype of a lightweight TABS at ceiling level. A small-scale climate chamber was constructed and equipped to evaluate the prototype in the key operating modes. The study investigated the relationship between the supply temperature of the lightweight TABS and the climate chamber’s internal air temperature for active heating, active cooling and natural ventilation modes. The experiments compared the reaction time in active heating mode for a range of supply temperatures. In addition, we examined the dynamic characteristics of the thermal mass of the lightweight TABS in passive natural ventilation mode and passive cooling mode in the presence of an internal thermal load. The results provide insights into the dynamic performance in operation. In heating mode, we identified the time lag between the radiant surface achieving a steady state and the conditioned air reaching its target temperature. This feature emphasises the significance of refining control strategies when designing comfortable environments with low-temperature heating systems at ceiling level. Further, we highlighted the importance of balancing decisions on minimising embodied energy with the suitability of the selected material to leverage renewable energy sources. The experimental data can be used for validating high-resolution numerical models, which support the development of multifunctional elements with renewable energy sources for building heating and cooling.

Building energy consumption under occupants’ behavior uncertainty in pre and post-renovation scenarios: a case study in Italy

In Europe, the energy renovation of the existing building stock is a great opportunity to significantly reduce energy consumption and greenhouse gas (GHG) emissions and reach the European sustainability targets. In this framework, building energy simulations (BES) tools are very useful in verifying energy retrofit measures' effectiveness and compliance with national standards. However, an inaccurate numerical prediction, the so-called “performance gap” between measured and numerical performance, is often obtained, mainly due to the inherent uncertainty of model input. Due to its stochastic nature, the occupants’ behavior (OB) is considered among the key contributors to this gap. However, the most recent Building Energy Model (BEM) approaches adopt deterministic hourly-defined profiles for characterizing OB, thus neglecting the related uncertainty. In this work, the impact of OB uncertainties on energy consumption (EC) prediction is evaluated by adopting a Karhunen-Loève Expansion sampling technique, used to randomly perturb OB profiles such as heating setpoint (HS), internal thermal loads (IL), and windows opening (NV). Two BEMs of a typical Italian residential building in pre- and post-renovation scenarios are considered and calibrated on real EC data. The results demonstrated that HS uncertainty has the highest impact on EC in all scenarios. Moreover, the higher the energy performance of the building, the higher the impact of OB, especially for IL and NV patterns.

Development of Architectural Green Mortar Incorporating Waste Glass and its Impact on Energy Saving in Buildings

Waste materials are deemed an environmental burden; although, they can be recycled in the production of sustainable building materials. The aim of this study is to develop an aesthetic architectural rendering green mortar with utilizing recycled waste colored glass as supplementary fine aggregate. Limestone Calcined Clay Cement (LC3) has been prepared as a green and sustainable binder by replacing 60 wt% of white Portland cement () with a blend of limestone (LS) powder and metakaolin (MK) with a LS: MK of 1:2 (wt%). LC3-based mortars were prepared in which the binder was combined with expanded polystyrene beads (EPS) as fine aggregate with aggregate volume content of 75%. EPS was partially replaced with recycled waste glass (RWG) at various percentages of 10, 20, and 30 vol.%. Bulk density, thermal conductivity, solar reflectivity and flexural strength of the hardened mortars were determined after 7days of curing. The contribution of the newly developed mortars into reducing internal thermal loads and energy use has been evaluated for administrative/ office building in EGYPT. The mortars incorporating 10 and 20vol.% of RWG possessed thermal conductivity values in the range of thermal insulation rendering mortars. The incorporation of RWG led to enhanced solar reflectivity, an increase by about 77% has been achieved relative to the traditional one coat - rendering mortar; in addition, the newly developed rendering mortar provided a reduction in electric cooling energy annual consumption by about 30%

Numerical investigation on ballooning and rupture of a Zircaloy tube subjected to high internal pressure and film boiling conditions

Film boiling may lead to burnout of the heating element. Even though burnout does not occur, the heating element is subject to deformation because it is not sufficiently strong to withstand external loads. In particular, the ballooning and rupture of a tube under film boiling are important phenomena in the field of nuclear reactor safety. If the tube-type cladding of nuclear fuel ruptures owing to high internal pressure and thermal load, radioactive materials inside the cladding are released to the coolant. Therefore, predicting the ballooning and rupture is important. This study presents numerical simulations to predict the ballooning behavior and rupture time of a horizontal tube at high internal pressure under saturated film boiling. To do so, a multi-step coupled simulation of conjugated film boiling heat transfer and ballooning using creep model is adopted. The numerical methods and models are validated against experimental values. Two different nonuniform heat flux distributions and four different internal pressures are considered. The three-step simulation is enough to obtain a convergent result. However, the single-step simulation also successfully predicts the rupture time. This is because the film boiling heat transfer characteristics are slightly affected by the tube geometry related to creep ballooning.

МАТЕМАТИЧНІ МОДЕЛІ ВИЗНАЧЕННЯ ТЕМПЕРАТУРНИХ ПОЛІВ У НЕОДНОРІДНИХ ЕЛЕМЕНТАХ ЦИФРОВИХ ПРИСТРОЇВ ІЗ УРАХУВАННЯМ ТЕРМОЧУТЛИВОСТІ Primary tabs View(active tab) Edit Translate

Linear and nonlinear mathematical models for determining the temperature field and subsequently analyzing temperature regimes in isotropic spatial media with semi-through foreign inclusions subjected to internal and external thermal loads are developed. For this purpose, the heat transfer coefficient for such structures is described as a single unit using asymmetric unit functions, which makes it possible to consider boundary value problems of heat transfer with one linear and nonlinear differential equations of heat transfer with discontinuous and singular coefficients and linear and nonlinear boundary conditions on the boundary surfaces of the media. In the case of a nonlinear boundary value problem, the introduced linearizing function is used to linearize the original nonlinear heat conduction equation and nonlinear boundary conditions, and as a result, a partially linearized second-order differential equation with partial derivatives and discontinuous and singular coefficients is obtained relative to the linearizing function with partially linearized boundary conditions. For the final linearization of the partially linearized differential equation and boundary conditions, the temperature is approximated by one of the spatial coordinates on the boundary surfaces of the inclusion by piecewise linear functions, as a result of which both the differential equation and boundary conditions become fully linearized. To solve the resulting linear boundary value problem, the Hankel integral transformation method is used, which results in an analytical solution that determines the introduced linearizing function. As an example, the linear dependence of the thermal conductivity coefficient of structural materials of a structure on temperature, which is often used in many practical problems, is chosen. As a result, analytical relations in the form of quadratic equations were obtained to determine the temperature distribution in a thermally sensitive layer with a foreign semi-through inclusion under external heating in the form of a heat flux. A numerical analysis of the temperature behavior as a function of spatial coordinates for given values of geometric and thermophysical parameters is performed. The influence of a foreign inclusion on the temperature distribution is investigated if the VK94-I ceramic is chosen as the material of the medium and the inclusion is silver. To determine the numerical values of temperature in the above structures, as well as to analyze heat transfer processes inside these structures caused by internal and external thermal loads, software tools have been developed that have been used to perform a geometric image of the temperature distribution depending on spatial coordinates. The obtained numerical temperature values indicate that the developed mathematical models for analyzing heat transfer processes in spatially heterogeneous environments with internal and external heating correspond to a real physical process. The software also makes it possible to analyze such environments subjected to internal and external thermal loads in terms of their thermal resistance. As a result, it becomes possible to increase it and protect it from overheating, which can cause the destruction of not only individual elements but also the entire structure.

Design Methods for Variable-Stiffness Super-Ellipsoidal Pressure Vessels Under Thermomechanical Loading

Pressure vessels are widely used in a broad range of applications in many industries, including possible use for hydrogen storage. Additionally, pressure vessels comprise non-circular-cross-section fuselages such as in blended-wing–body aircraft. Failure performance, weight, and packing efficiency are important factors that should be considered when designing pressure vessels. Often, lightweight pressure vessels maximize their volume for a given available space volume and withstand substantial internal pressure. Bend-free super ellipsoids of revolution, enabled by stiffness tailoring via variable-angle tow placement of composite plies, present an appealing solution that makes them possible candidates for future composite pressure vessels. To date, the bend-free design methodology for super ellipsoids of revolution has only been developed under uniform internal pressure loading. However, in reality, pressure vessels can also be subjected to thermal loads during service. Therefore, this study develops an initial bend-free design methodology for super ellipsoids of revolution that are subjected to both uniform internal pressure and thermal loads.

Electricity peak load reduction of a refrigerator using phase change material

Phase change material (PCM) has become a topic of study in thermal management, as it has a high-energy storage density. Most refrigerators have a fixed-speed compressor, which operates randomly (on/off) during their cycle. This leads to a high-power peak of electricity when the refrigerators start at the same time. Therefore, this study aims to investigate the reduction potential of the power peak and energy consumption of a refrigerator using PCM as a heat absorber. Nine testing conditions were performed by using water as the internal thermal load, at 1, 2, and 3 kg. Besides, each internal thermal load condition was varied with a PCM mass of 500, 1,500, and 2,500 g. The necessary data, such as the internal temperature and power of a refrigerator and the outside ambient temperature, were collected. The results show that the mass of PCM significantly affected the peak power of the refrigerator and energy consumption. Moreover, the results clearly show that the PCM can be used to reduce the peak power and energy consumption of the refrigerator. The correlation of the power, related to the mass of the internal heat load, and the mass of PCM was also reported. The conclusion of this study is that the PCM is suitable for reducing the peak power and energy consumption of a household refrigerator.

Thermal and energy performance of a user-responsive microalgae bioreactive façade for climate adaptability

As a recent trend in the energy-efficient architecture, microalgae bio-reactive façades can control buildings’ thermal loads by the responsiveness to solar radiations and adaptive variations in culture density. Although these smart systems can provide adaptable shading during the year, they cannot meet the varying thermal comfort needs of building users in a short time because the microalgae medium’s culture remains almost unchanged during the day. This paper reports on an innovative method that helps microalgae bioreactive façade respond to solar radiation and users’ thermal needs in a short time. To achieve it, a smart window panel will be introduced, which contains two remotely-controlled adjustable bioreactors which can regulate the algae medium in height based on the users’ thermal needs. This novel panel can serve as a bio-adaptable sunshade integrated with the building facade. Thus, the internal building thermal loads can be adjusted via the height of the bioreactor façade. Experimental and simulation research was conducted to compare the thermal performance of bioreactor facades at different microalgae medium height levels in the BSk climate zone. The results indicate that indoor and outdoor temperature differences for full, ¾, ½, and ¼ medium height level every 15-minute time interval are 12.55, 11.50, 10.87, and 6.53, respectively, indicating that the full-height level has the most influence to control the thermal load of the system. According to the results, the bioreactor façade with adjustable medium height greatly impacts building thermal control in a short time.

МАТЕМАТИЧНІ ПРОСТОРОВІ МОДЕЛІ ВИЗНАЧЕННЯ ТЕМПЕРАТУРНОГО ПОЛЯ ІЗ ЛОКАЛЬНО ЗОСЕРЕДЖЕНИМ ТЕПЛОВИМ НАГРІВАННЯМ

Linear and nonlinear mathematical models for determining the temperature field, and later the analysis of temperature regimes in isotropic spatial inhomogeneous media exposed to internal and external thermal loads have been developed. To do this, the thermal conductivity for such structures is described as a whole using symmetric unit functions, which allows us to consider boundary thermal conductivity problems with one linear and nonlinear differential equation of thermal conductivity with discontinuous coefficients and linear and nonlinear boundary conditions on boundary surfaces. In the case of a nonlinear boundary value problem, the Kirchhoff transform is applied, which linearizes the initial nonlinear equation of thermal conductivity and nonlinear boundary conditions and results in a second-order linear differential equation with partial derivatives and singular coefficients with respect to the Kirchhoff function with linear conditions. To solve the obtained linear boundary value problem, the method of integral Fourier transform was used, as a result of which an analytical solution was obtained, which determines the Kirchhoff linearizing function. As an example, the linear and cubic dependences of the thermal conductivity of structural materials on the structure, which are often used in many practical problems, are chosen. As a result, analytical relations in the form of quadratic and biquadratic equations are obtained to determine the temperature distribution in the thermosensitive layer with foreign inclusion at external local heating. Numerical analysis of temperature behavior as a function of spatial coordinates for given values of geometric and thermophysical parameters is performed. The influence of foreign inclusion on the temperature distribution was studied if the material of the medium was selected ceramics VK94-I, and the inclusion – silver, aluminum and silicon. To determine the numerical values of temperature in these structures, as well as the analysis of heat transfer processes in the middle of these structures due to internal and external heat loads, developed software that uses a geometric representation of temperature distribution depending on spatial coordinates. The obtained numerical values of temperature testify to the correspondence of the developed mathematical models of the analysis of heat exchange processes in spatial inhomogeneous media with internal and external heating to the real physical process. Software also allows you to analyze this type of environment, which are exposed to internal and external heat loads, in terms of their heat resistance. As a result, it becomes possible to increase it and protect it from overheating, which can lead to the destruction of not only individual elements but also the entire structure.

Sensitivity analysis of coating mortars according to their specific heat, specific gravity, thermal conductivity, and thickness in contribution to the global thermal performance of buildings

Although coating (plastering) mortars are an important element of masonry systems, their impact on the building's overall thermal performance is still unclear. In this sense, the present work performed a sensitivity analysis on the influence of the thermophysical properties of coating mortars on the internal temperature and thermal load of two buildings. The authors aimed to fill the gap between the mortars' properties, their manufacturing specifications, and the actual effect of their application on the building's total energy performance. The methodology included energy simulations on EnergyPlus considering all Brazilian bioclimatic zones. We varied the mortars' specific heat, specific gravity, thermal conductivity, and thickness from 25% to 200% from baseline values. We also analysed the results through Decision Tree technique (XGBoost). The thermal conductivity (proportional to the specific gravity) was the less significant property, whereas the thickness and the specific heat were the most influential ones. The differences between the best and worst mortars reached 356 °C and 224 kWh/year for the house, and 736 °C and 45 kWh/year for the commercial building. The results showed that the optimal combination of the tested properties is a function of the bioclimatic characteristics of the region, the building layout, and the existence and schedule of the HVAC system. The simulations also evidenced that the strategy of solely decreasing the thermal conductivity without considerations for the thermal capacity, which is often used in the manufacturing of conventional insulating mortars, is ineffective. Therefore, assertively adjusting the mortars' thermophysical properties can be a promising complementary strategy for improving the thermal performance of buildings.

Thermo-mechanical assessment of heated bridge deck under internal cyclic thermal loading from various heating elements: pipe, cable, rebar

Heated bridge is an eco-friendly technology where embedded internal heating elements are utilized for deicing/snow melting of the bridge deck surface. A crucial factor preventing wide scale implementation of this technology is the lack of fundamental understanding of the thermo-mechanical behavior of the reinforced slab under cyclic internal thermal loads. This study presents a novel thermo-mechanical assessment of a heated bridge deck subjected to cyclic internal thermal loads implemented through three different heating elements: pipe, cable, rebar. A new finite difference based numerical model was developed and calibrated against small scale laboratory experiments; considering realistic thermal and mechanical boundary conditions, and incorporating thermal-induced degradation of the mechanical properties of concrete. Results revealed a considerably distinct thermo-mechanical response of the concrete slab under each heating system. The cable system resulted in the most substantial thermal-induced internal damage in the concrete slab. Findings indicate that the thermal conductivity and the linear thermal expansion coefficients of the heating elements are key factors governing the thermal efficiency and the extent of the internal damage in a heated concrete slab. A sensitivity analysis suggested that the thermo-mechanical performance of a heated slab can be notably enhanced through initiating heating at higher ambient temperatures, and reducing the depth of placement of the heating elements.

The impacts of COVID-19 pandemic on the hygrothermal environment of our homes

In 2020 the residential sector witnessed a complete transformation of the way people live and occupy the spaces. Indeed, different Countries introduced total lockdowns as a measure to contain and prevent the spread of COVID-19, forcing people to stay at home. These measures impact the indoor hygrothermal environment: higher internal thermal loads and moisture generation rate may create the perfect situation to support mould growth. This project aims to understand the impacts of increased work-from-home practices on the hygrothermal performance of residential buildings. The assessment uses a two-step methodology: firstly, whole building transient simulations (software trnsys) are used to generate the indoor temperature and humidity profiles, secondly hygrothermal transient simulations (software WUFI) are used to quantify the risk of mould growth. This research reveals the inadequacy of current design and construction practices to support flexible occupation patterns.

Stress distribution and performance of threaded bolts in gasketed flange joints

AbstractThe performance of the flange joint depends on the relaxation of load in bolts. This in turn affects the gasket stress and control of leakage. A finite element model of flange joint with threaded bolt‐nut fastener having zero helix angle is developed and analyzed for stress distribution in the threaded bolt. The stress concentration factor at the thread root region is observed to be non‐uniform along the circumference due to the bending behavior of the bolt in the flange joint. The maximum stress is observed in the first engaged thread. The variation in bolt load due to internal fluid, thermal and external loads are also investigated for both single and twin‐gaskets (two concentric half‐sized single gaskets). The gasket material and gasket configuration are observed to be potential factors causing variation in the distribution of load in the flange joint. In a flange joint subjected to external bending load, the maximum stress concentration in the bolt is observed to be in the first thread, instead of the first engaged thread. Under external bending load, the flange joint loses its structural integrity before the traces of leakage occur in the joint.

Analysis of filament-wound sandwich pipe under combined internal pressure and thermal load considering restrained and closed ends

Sandwich pipe consisting of inner and outer filament-wound (FW) skins bonded to a core material is a lightweight alternative to single-wall or pipe-in-pipe systems. In operation the pipe is subjected to thermomechanical loading. In this paper, a 3D finite element model is developed for analysing stresses in FW sandwich pipe under combined internal pressure and thermal load, incorporating temperature-dependent properties. Optimal reinforcement angles are determined for axially restrained ends (as per a long pipeline) and closed ends (pressure vessel condition). The effects of uniform and non-uniform heating on stress-based failure are evaluated. The pipe thermomechanical response is shown to depend on whether the pressure loading is hoop-dominated or biaxial. The core of the axially restrained pipe is highly temperature-sensitive under low pressure. With closed ends the coupled effect of mechanical and thermal loading on the skins is significant. The influences of core thickness and number of skin plies are investigated.