Thermal Management Of Buildings Research Articles

Synchronous Radiative Cooling and Thermal Insulation in SiO2/Poly(vinyl alcohol) Composite Aerogel for Energy Savings in Building Thermal Management

Synchronous Radiative Cooling and Thermal Insulation in SiO₂/Poly(vinyl alcohol) Composite Aerogel for Energy Savings in Building Thermal Management

Low-voltage electrochromic behaviour of polymer-stabilised liquid crystal with considerable broadband reflection

ABSTRACT In this work, a novel method was proposed to achieve electric-induced colouration of polymer-stabilised liquid crystal (PSLC) with considerable broadband reflection. The formation of broadband reflection was due to the introduction of the UV absorber that induced a light intensity gradient within the liquid crystal system and promoted the non-uniform distribution of the pitch. Experiments were performed to optimise the components and polymerisation conditions, allowing the bandwidth to be broadened from 252 nm to 906 nm. The texture of PSLC was characterised using POM, revealing that the planar texture was not disrupted. Thereafter, the addition of ionic liquid as supporting electrolyte enabled the PSLC to be switched from colourless to coloured at DC voltage as low as 1.7 V and the colouration behaviour can be independently modulated by changing the voltage level and the duration. Meaningfully, after the DC electric field was removed, the colour of the PSLC can also disappear gradually. In addition, the as-prepared electrochromic PSLC presented enhanced UV shielding, IR thermal control efficacy and good colouration performance on flexible substrates, which can be applied to low-energy smart glass and thermal management of buildings. This study provided a promising approach for the development of smart optical devices.

An Explainable Evaluation Model for Building Thermal Comfort in China

The concentration of atmospheric greenhouse gases is being amplified by human activity. Building energy consumption, particularly for heating and cooling purposes, constitutes a significant proportion of overall energy demand. This research aims to establish a smart evaluation model to understand the thermal requirements of building occupants based on an open-access dataset. This model is beneficial for making reasonable adjustments to building thermal management, based on factors such as different regions and building user characteristics. Employing Bayesian-optimized LightGBM and SHAP (SHapley Additive exPlanations) methods, an explainable machine learning model was developed to evaluate the thermal comfort design of buildings in different areas and with different purpose. Our developed LightGBM model exhibited superior evaluation performance on the test set, outperforming other machine learning models, such as XGBoost and SVR (Support Vector Regression). The SHAP method further helps us to understand the interior evaluation mechanism of the model and the interactive effect among input features. An accurate thermal comfort design for buildings based on the evaluation model can benefit the carbon-neutral strategy.

Smart Building Thermal Management: A Data-Driven Approach Based on Dynamic and Consensus Clustering

A customized and cost-effective building thermal control system is critical for accommodating thermal performance differences within the building, as well as satisfying the individual thermal comfort needs of occupants. Moreover, incorporating a building indoor thermal simulation procedure into the thermal control system can reduce the necessity of installing various expensive sensors (e.g., wearable sensors for personal thermal comfort management) in individual offices, as well as the requirement of extensive computing facilities without rendering the control performance, resulting into more sustainable building operations. An important step in achieving the above-mentioned goal is understanding how different offices/rooms behave differently given the same outdoor weather conditions. This study proposes a smart building indoor thermal profiling system to identify underlying physical factors that affect thermal performance in different seasons and to track dynamic cluster trajectories of considered offices to suggest indoor thermal optimization strategies. A consensus-based clustering approach is adopted to robustly cluster offices into different groups based on their hourly indoor temperature profiles for different seasons. Experimental results showed that our proposed approach could effectively discover more indoor thermal patterns in the buildings and is able to identify distinct dynamic cluster trajectories across four seasons (i.e., eight distinct dynamic trajectories in our case study). The data-driven analysis conducted in this study also indicated promising applications of the proposed smart building indoor thermal profiling system in effectively guiding the design of customized thermal control strategies for buildings. It also suggested that the proposed approach could be applied to a wide range of other applications, such as customized building energy management, energy pricing, as well as the economic benefit analysis of building retrofits and design.

Low-cost and highly thermally conductive silver modified mica-paraffin multifunctional composite phase change materials for photo-thermal conversion and electrical insulation

To improve the utilization efficiency of renewable energy and adaptability of composite materials, a new mineral-based composite phase change material (Ag-Mica/CNF/PW) was designed and prepared by chemically modifying natural mica, attaching silver nanoparticles to the mica surface as functionalized support material, and using paraffin wax as the phase change functional medium. As expected, the thermal conductivity of the composite phase change material (CPCMs) increased significantly to 0.9 W/m k, which was 330.1% higher relative to pure paraffin. With the addition of silver-modified mica, the volume resistivity of CPCMs reached 11.9 × 1012 Ω cm. The relative enthalpy efficiency achieved 104.8%, and the photothermal conversion efficiency reached 91.3%, proving that the silver-modified mica-based CPCM was successful and feasible. The heat resistance index of CPCMs was 137.2 °C, and the enthalpy loss rate after 50 cycles was only 0.7 %, indicating that CPCMs have excellent thermal stability. The designed CPCMs are a promising candidate for developing thermal storage and building thermal management, electrical insulation and solar energy conversion.

Extended Kalman filter based extremum seeking algorithm for model-free control of building thermal environment under uncertainty

Online optimization of building thermal environment is no trivial task due to the complex and uncertain indoor thermodynamics. In this study, an extended Kalman filter-based extremum seeking control (EKF-ESC) strategy for model-free control of thermal environment under uncertainty is proposed. The EKF-ESC uses extended Kalman filter for estimating gradient of the objective function of the extremum seeking controller, which enables real-time optimization of thermal environment with fast convergence time. In addition, a co-simulation platform is developed by combining EnergyPlus and Simulink/Matlab for validating effectiveness of the EKF-ESC strategy for controlling thermal environment. Our study demonstrates that the EKF-ESC strategy has good adaptivity to uncertainties resulting from changes in weather, electrical equipment and occupancy. Moreover, it is shown that the EKF-ESC is robust to measurement noise. In addition, comparison of convergence performance among EKF-ESC, adaptive ESC, and classical ESC is conducted. It is shown that the EKF-ESC based control strategy has the fastest convergence time towards indoor temperature setpoints. Compared with the classical ESC and adaptive ESC schemes, about 77% and 55% reduction of the convergence time are realized through EKF-ESC. According to the research results, it could be inferred that EKF-ESC strategy has the potential for effective building thermal management under uncertainty with fast convergence time.

Shape-Stable Hybrid Emulsion Gel with Sodium Acetate Trihydrate and Paraffin Wax for Efficient Solar Energy Storage and Building Thermal Management.

Organic-inorganic composite phase change materials (PCMs) are promising in the fields of solar energy storage and building thermal management. However, combining inorganic with organic PCMs meets a great challenge. In the current work, a shape-stable hybrid emulsion gel (EGel/GO) is developed via Pickering emulsion polymerization, which seamlessly combines sodium acetate trihydrate (SAT) in the water phase with paraffin wax (PW) in the oil phase. The polymer dual-phase cross-linking in EGel/GO forms a supporting framework that effectively enhances the material's shape stability, slows the loss of crystalline water in hydrates, and reduces supercooling. The addition of graphene oxide (GO) enhances EGel/GO-0.5's optical absorption properties, resulting in photothermal conversion efficiency as high as 89.1%. Furthermore, EGel/GO not only has high latent heat of 225.08 J/g but also has almost no leakage and no phase separation. The Pickering emulsion polymerization method paves a broad avenue for combining organic with inorganic PCMs, which is an ideal choice for the effective utilization of solar energy and building energy storage.

Optimal Neural Network PID Approach for Building Thermal Management

The process of thermal control and regulation in buildings is considered complex. Its complexity lies in the various internal and external physical phenomena impacting its control, and also in the increasingly important requirements of occupant comfort, energy optimization and efficiency, and optimization of measuring and monitoring equipment. Recently, the establishment of technical rules for optimal building thermal control has gained interest in academia and industry. These rules have focused mainly on three aspects: the use of renewable energy, optimal management, and the use of equipment and materials allowing the optimization of energy. However, optimal control has not been addressed enough. In this article, we present a PID controller based on a Neural Network approach for thermal building management and control. The proposed approach is based on two processes: an optimal identification process dedicated to the thermal building behavior prediction impacted by variable and invariable elements, measured and unmeasured factors, and a control process to ensure the desired performance with optimal energy control. The results obtained show the advantages of the adopted system in terms of energy optimization, with an important energy gain of 8% to 11%, along with better regulation and control performance, and in terms of occupant comfort with minimal temperature variations.

Thermal management mechanism employing transparent nanostructures for winter and summer seasons for indoor environments

Metamaterials aim to recognize and emphasize their impact on multiple applications, and the objective of this study is to achieve higher performance of metamaterial solar absorbers for thermal management during winter and summer seasons. This paper outlines the metamaterial design strategy using low-cost materials, with its essence being the exploitation of the unique properties of the metamaterial to extend the composite performance of transparent planar solar absorbers. We designed a transparent multilayer planar absorber coating by using Iron Sesquioxide (Fe2O3) as the dielectric spacer and Titanium (Ti) metal for ground and resonator metal layers with both the cladding made of Silicon dioxide (SiO2) within thin resin film. The proposed MIM design affirms the presence of the negative refraction property of light, a unique property for metamaterials, Additionally, it can be used to retain sufficient energy during absorption which will enhance winter thermal management in buildings for angles of incident θ < 50° and the same setup accessed at θ > 50° will highly reflect the energy and will maintain the low temperatures in a given room during the summer season.

Biomimetic optimized vertically aligned annular fins for fast latent heat thermal energy storage

Latent heat thermal energy storage (LHTES) technology has been widely used in balancing energy demand and intermittent energy supply, as well as thermal management in buildings, but suffers from slow heat storage rates. Here, biomimetic topology-optimized vertically aligned annular fins are proposed to accelerate heat storage performance. Taking the maximum average temperature as the optimization objective function, optimized biomimetic fins can shorten the melting time by 45.9% compared with traditional fins as verified by experimental measurements. Such a fast heat storage rate is also superior to that of pitch-varying fins and diameter-varying fins by 18.4% and 23.5%, respectively. Meanwhile, the temperature uniformity is greatly improved by biomimetic fins with a reduction of average temperature difference in phase change materials (PCMs) by 75.3%. The underlying mechanism can be attributed to accelerated melting of PCMs close to the outer bottom boundary due to unique bifurcation structures of topology optimized fins. The fractal dimension of optimized fins is similar to that of leaf vein structures, demonstrating that proposed topology structures are close to Natural’s optimal solutions. This study provides novel biomimetic structures for accelerating thermal energy storage rate and promotes the application of biomimetics in LHTES techniques.

Nano Engineered Paraffin-Based Phase Change Material for Building Thermal Management

Thermal energy storage (TES) and harvesting is an effective technique for optimum building thermal management. Phase-change materials (PCMs) are commonly used for TES applications but are troubled by their degraded thermal conductivity. Recent research progress in latent heat energy storage using PCMs and nano additives provides a viable solution for solar TES. A series of hybrid nano-enhanced phase change materials (HNePCMs) were prepared via two-step synthesis. Hybrid graphene–silver nanofillers were dispersed in commercial paraffin (melting point 25 °C) under different dispersion rates (0.1%, 0.3%, 0.5%). Different characterization techniques, e.g., FESEM, FT-IR, UV-VIS, TGA, XRD, DSC, and Tempos, were used in material characterization. A maximum enhancement of 6.7% in latent heat and 5% in heat storage efficiency was noted for nanocomposites with 0.3 wt% of additives. The nanocomposite with 0.3 Wt% showed great potential in shielding UV rays and showed a reduction of 6.5% in bandgap energy. Furthermore, the thermal conductivity of samples was boosted by a maximum of 90% (from 0.2 W/mK-0.39 W/mK) with 0.3 wt% dispersion of graphene–silver nanofillers. The thermophysical characterization results establish that the synthesized paraffin/graphene–silver hybrid nanocomposites are well suited for building thermal management.

A constrained model predictive control for the building thermal management with optimal setting design

&lt;span lang="EN-US"&gt;Today, the building sector is the most important consumer of energy. The main challenge in building management is to obtain the desired performance taking into account many aspects such as comfort requirements, variation of building physical characteristics, system constraints, and energy management. For this purpose, a predictive control approach applied to the building thermal has been designed to achieve desired performances combined with an energy optimization approach based on intrinsic system parameters. The developed approach is applied with an online identification system for effective predictive control to take into account the reel building characteristics and to choose the optimal tuning parameters. The simulation results show good performances in terms of accuracy and robustness face to internal and external disturbances with respect to system constraints.&lt;/span&gt;

Impact of exothermic chemical reaction on MHD unsteady mixed convective flow in a rectangular porous cavity filled with nanofluid

The rectangular enclosure filled with nanofluid has several technical applications including building thermal management systems and photovoltaic thermal management systems. This investigation theoretically investigates the transport features of the time-dependent, mixed convective, electrically conducting nanofluid flow inside a cavity saturated with permeable medium. The impact of a uniform magnetic field applied in the transverse direction to the fluid flow and Arrhenius kinetics theory based exothermic chemical reaction are considered. The Buongiorno's model is adopted in the present analysis to characterize the nanofluid. The constitutive partial differential equations are solved by using the Marker and Cell (MAC) technique. The impact of the nondimensional numbers on transport phenomena of the present study is elucidated graphically. The outcomes disclose that the pertinent parameters such as the Reynolds number (Re), Hartmann number (Ha), Darcy number (Da), Lewis number (Le), Richardson number (Ri), thermophoresis parameter , Brownian motion parameter , and Frank-Kamenetskii number (Fk) play a main role on regulating the transport characteristics of the present study. Results demonstrate that the isotherms increase with escalating Frank–Kamenetskii number values. Higher Richardson number values improve the heat transfer inside the enclosure.

Solar-driven dual-mode cascading cycle based on ammonia complexation reaction for flexible seasonal thermal management

Flexible seasonal thermal management, including the summer refrigeration and winter heat pump with seasonal energy storage, is one of the promising routes to achieve the goal of buildings carbon neutrality. However, the previous sensible and latent heat storage technologies were unable to realize seasonal heating supply and refrigeration, and the single-stage sorption cycle was proven inefficient under the severe conditions of high condensation and sorption temperatures. To face the challenge, we propose a solar-driven flexible seasonal thermal management (FSTM) strategy enabled by the MnCl2-CaCl2-NH3 cascading cycle based on ammonia complexation reaction, which can efficiently utilize the solar heat with severe temperature fluctuations to satisfy indoor summer refrigeration and winter heating supply with seasonal energy storage. Subsequently, we design a proof-of-concept FSTM device with two sorption reactors and an ammonia working tank. Experimental results exhibit that when the outdoor ambient temperature is as high as 35°C, the specific cooling capacity and coefficient of performance of FSTM are still up to 157 kJ∙kg−1 and 0.11 respectively in summer, while the thermal energy storage density can exceed 100 kJ∙kg−1 in winter with the highest sorption temperature of 90°C, which illustrates that the cascading cycle is suitable for harsh working conditions to achieve long-term thermal energy storage. Our work provides a promising low-carbon route for seasonal solar energy storage and thermal management of buildings.

Graphene Infrared Radiation Management Targeting Photothermal Conversion for Electric-Energy-Free Crude Oil Collection.

Graphene has been widely used as a solar absorber for its broad-band absorption. However, targeting a higher photothermal efficiency, the intrinsic infrared radiation loss of graphene requires to be further reduced. Herein, band structure engineering is performed to modulate graphene infrared radiation. Nitrogen-doped vertical graphene is grown on quartz foam (NVGQF) by the plasma-enhanced chemical vapor deposition method. Under the premise of keeping high solar absorption (250-2500 nm), graphitic nitrogen doping effectively modulates the infrared emissivity (2.5-25 μm) of NVGQF from 0.96 to 0.68, reducing the radiation loss by ∼31%. Based on the excellent photothermal properties of NVGQF, a temperature-gradient-driven crude oil collecting raft is designed, where the crude oil flows along the collecting path driven by the viscosity gradient without any external electric energy input. Compared with a nondoped vertical graphene quartz foam raft, the NVGQF raft with a superior photothermal efficiency shows a significantly enhanced crude oil collecting efficiency by three times. The advances in this work suggest broad radiation-managed application platforms for graphene materials, such as seawater desalination and personal or building thermal management.

Solar-absorbing energy storage materials demonstrating superior solar-thermal conversion and solar-persistent luminescence conversion towards building thermal management and passive illumination

Nowadays, building energy consumption accounts for more than 50% of the total energy consumption. Exploiting advanced solar energy strategy is of great significance to achieve the building energy saving by spontaneously providing energy for a building. Herein, novel solar-absorbing energy storage materials constructed by solar-thermal conversion material, phase change material gel and persistent luminescence material are proposed to efficiently utilize the full spectrum of renewable solar energy towards the building thermal management and passive illumination. A flow chemical synthesis strategy is designed to continuously prepare the solar-thermal conversion material N, S-co-doped conjugated polybenzobisthiazole towards the robust solar energy harvesting (solar absorbance of 94.1%) and considerable thermal energy production (solar-thermal conversion efficiency of 88.3%). The liquid phase blending and sol–gel transition are proposed to fabricate the phase change material gels demonstrating high latent heat of 192.12 Jg−1 and self-supporting capacity, which can store the heat generated by N, S-co-doped conjugated polybenzobisthiazole and release the heat in the night. The persistent luminescence materials can absorb the ultraviolet–visible light in the solar spectrum in the daytime and emit the multicolour luminescence in the night. Taking advantages of the synergistic effect of the functional components, the proposed solar-absorbing energy storage materials demonstrate full spectrum utilization of solar energy (total solar absorbance of 91.93%) towards the building thermal management and passive illumination with a solar-light conversion efficiency of 1.65% and a solar-thermal conversion efficiency of 10.52%. The solar-absorbing energy storage materials create a state-of-the-art alternative for the next-generation energy saving buildings.

Hierarchical-Morphology Metal/Polymer Heterostructure for Scalable Multimodal Thermal Management.

The cooling and heating energy consumption of buildings poses a serious threat to the energy supply and increases greenhouse gas emissions, thus adversely impacting global warming and the long-term climate change trends. Here, inspired by the structure of the louver, this work demonstrates a multimodal device that integrates radiative cooling, natural lighting, and solar heating to deal with the grand challenge of building energy consumption. The blades integrate a selective radiative cooling material with a solar heating material. The selective radiative cooling material (solar reflectance ∼97%, selective emittance ∼0.82 in the 8-13 μm waveband) combines a solar reflective melt-blown polypropylene film and a solar transparent mid-infrared emitter polyethylene/silicon dioxide film. In addition, the heating material (solar absorptance ∼91%, thermal emittance ∼0.04) is zinc (Zn) film deposited with copper (Cu) nanoparticles, based on the Cu-Zn galvanic-displacement reaction. Hence, by rotating the blades, the conversion of radiative cooling, solar heating, and natural lighting functions can be realized. In the daytime, the multimodal device displays a subambient temperature of 4 °C, a superambient temperature of 2 °C, and a superambient temperature of 5 °C for the cooling mode, transmitting mode, and solar heating mode, respectively. On the basis of the energy-savings simulation, integrating these modes and dynamic converting these modes in the corresponding climate could save ∼746 GJ in the contiguous United States for one year (38% of the baseline energy consumption), which is equivalent to ∼147 tons of carbon dioxide emission reduction. Because of its excellent multimodal thermal management performance, this multimodal device will push forward the transformative change of building thermal management toward decarbonization and sustainability and being more green.

Thermal management and natural convection flow of nano encapsulated phase change material (NEPCM)-water suspension in a reverse T-shaped porous cavity enshrining two hot corrugated baffles: A boost to renewable energy storage

Renewable energy systems may be turning to be more effectual and inexpensive and contributing lion's share of whole energy utilization in today's power hungry planet. The efficacious usage of solar energy needs a storage appliance which could simplify the storage of surplus energy, and finally provide such energy when it desires. One of the efficacious approach of storing thermic energy of higher density from renewable source is executed in a varying range of temperature positions by phase change materials (PCMs) or nano encapsulated phase change material (NEPCM) as their significant role in air-conditioning systems, thermal energy storage, computer chipsets, and thermal management of buildings. In view of this, the present investigations aims at natural convection flow, heat transfer, and entropy of NEPCM-water suspension in a reverse T-shaped porous cavity enshrining two hot corrugated baffles. The thermal control within the cavity is maintained by hot corrugated baffles, cooling of bottom and upper walls and managing the side walls as adiabatic. The governing equations are well established and converted into dimensionless structure and then solved subsequently by Finite Element method (FEM). Simulated outcomes might well be validated accurately and the influence of Rayleigh number (104≤Ra≤106), porosity (0.4≤ε≤0.8), Darcy number (10−4≤Da≤10−2), NEPCM particle volume fraction (0≤φ≤5%), length of the corrugated walls (0.10L≤b≤0.20L), and fusion temperature (0.2≤θf≤0.8) on the heat transfer features, isotherms, heat capacity ratio and streamlines is explored efficaciously. The outcomes of this study are that amplifying Raleigh number leads to the intensification of streamlines, velocity fields and structural change of phase change zone while decaying of Darcy number exhibits the opposite effect. Strengthening porosity of porous medium intensifies the streamlines, horizontal and vertical velocity. Growth of the length of baffles yields emaciation of streamlines, flow fields, and enormous rate of heat transfer. Heat capacity ratio attains a constant value 0.97 outside melting-solidification zones within the cavity. Rise in the fusion temperature results in the expansion and shifting of melting-solidification zone. When φ rises from 1% to 2%, Nuave uplifts and yields its minimum enhancement while with rise of φ from 1% to 5%, Nuave upgrades and yields its maximum enhancement at fixed Darcy and Raleigh numbers.

An Updated Review on Low-Temperature Nanocomposites with a Special Focus on Thermal Management in Buildings

Buildings contribute to 33% of total global energy consumption, which corresponds to 38% of greenhouse gas emissions. Enhancing building’s energy efficiency remains predominant in mitigating global warming. Advancements in thermal energy storage (TES) techniques using phase change material (PCM) have gained much attention among researchers, primarily to minimize energy consumption and to promote the use of renewable energy sources. PCM technology stays as the most promising technology for developing high-performance and energy-efficient buildings. The major drawback of PCM is its poor thermal conductivity which limits its potential use which could be resolved by dispersing conductive nanofillers. The acquired database on synthesis routes, properties, and performance of nano-dispersed phase change materials (NDPCMs) with various techniques presented in the paper should deliver useful information in the production of NDPCMs with desirable characteristics mainly for building construction applications. An outline of contemporary developments and use of NDPCMs as TES medium is delivered. Finally, a brief discussion on challenges and the outlook was also made. In-depth research is needed to explore the fundamental mechanisms behind the enhanced thermal conductivity of NDPCM with nanofillers dispersion and also a thorough investigation on how these mechanisms drive improvement in building performance.

Thermal management analysis of PCM integration in building using a novel performance parameter - PCM effectiveness index

Integration of phase change material (PCM) in walls and roof of a building is done to augment human comfort at places where variation of local diurnal temperature of ambient air is extensive. An exhaustive tool to study on year-round thermal effect due to solar radiation falling on a building is generally required to identify the correct PCM and the portion of a year that warrants better thermal management. The transient behavior associated with PCM heat transfer through building roof and walls vary in accordance with location and orientation of the building and the prevailing seasons. Hence, it becomes necessary to carry out a detailed analysis with the integration of PCM layers and to collect information with suitable theoretical approach as experimental study on energy performance of a building is time-consuming and expensive. In this paper, a 3-D building model has been developed and analyzed using ANSYS FLUENT for performing CFD analysis for comparing two identical buildings with and without PCM located at Chennai. The PCM was integrated in roof and walls of the building and analysis was carried out for different days of the year. A novel concept of PCM effectiveness index is introduced to measure the thermal performance due to PCM integration in building. This novel concept is useful for building engineers to measure the effectiveness of PCM integration and to select the correct PCM for thermal management in buildings at any location and time of the year.