Thermal Management Of Buildings Research Articles

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.

Radiative cooling-assisted thermoelectric refrigeration and power systems: Coupling properties and parametric optimization

A CP2–127–06 Melcor module is incorporated into a radiative cooling (RC) system to work as a thermoelectric refrigerator (TER) at daytime and a thermoelectric generator (TEG) in nighttime. Through analysis of the single RC system, only a small temperature span between environment and building can be achieved. However, the temperature span can be significantly improved by combining RC and TER. The TER's input electrical current is optimized to obtain the maximum coefficient of performance (COP) 4.85 and the maximum cooling power density (CPD) 9.64 × 103 W m−2. Making trade-off between COP and CPD, the optimal regions of the COP, CPD, temperatures of cold side and hot side, and electrical current are determined. Further, the RC-TEG system's maximum power density 5.10 W m−2 and maximum efficiency 0.369% and the corresponding optimal conditions are obtained. With increasing the area ratio of emitter to TER or TEG, the performances of the systems are firstly improved and then remain almost unchanged. This work may provide guidance for building's thermal management at daytime and power generation in nighttime.

Experimental study on a hybrid solar photothermic and radiative cooling collector equipped with a rotatable absorber/emitter plate

Taking the frigid outer space as the heat sink, a terrestrial body can cool itself to a sub-ambient temperature via radiative sky cooling (RC) scheme. However, poor seasonal and regional adaptabilities and low cooling power density of the RC technology confine its effective applications only in hot seasons and regions with RC-friendly ambient conditions. Similarly, a solar thermal collector cannot work at night and is of little value when heat is needless. To tackle these challenges, a hybrid solar photothermic and radiative cooling (PT-RC) collector equipped with a rotatable absorber/emitter panel is proposed and experimentally investigated. This dual-mode collector can flexibly switch between PT and RC to match specific energy demands in different scenarios. The daily solar thermal efficiency of the PT-RC system at zero-reduced temperature reached 50.4%, a typical level of flat-plate solar water heating systems. The PT-RC system could not provide cooling energy during most daytime hours. However, the system could easily achieve nighttime cooling, with the cooling power of the collector decreasing from about 60 to 50 W/m2 as the circulated water being continuously cooled down from around 20 to 12 °C. The average nocturnal cooling power of the PT-RC collector ranged from 30.5 to 57.5 W/m2 in a multi-night RC test. This rotatable PT-RC collector offers a new strategy to flexibly deliver heat and coldness in a renewable and environmental-friendly manner and shows the potential of smart thermal management in buildings, vehicles, agriculture, etc.

Preparation of chiral polymer/cholesteric liquid crystals composite films with broadband reflective capability for smart windows and thermal management of buildings

In this study, a new method to prepare the chiral polymer/cholesteric liquid crystals composite films with broadband reflective capability was reported. A negative dielectric anisotropy liquid crystal material was utilized as the mesogenic solvents and a chiral mesogenic monomer was employed as the chiral dopant. The chiral mesogenic monomer not only induced the liquid crystal molecules to align to form the helical structure, but also as the polymerizable monomer to be crosslinked under UV light to stabilize the pitch gradient in the materials. The UV absorbing dye was used to generate the intensity gradient of UV light and promoted the diffusion of the chiral mesogenic monomer from the backlight side to the light side. The effect of the content of the chiral mesogenic monomer and the intensity of the UV light applied during the preparation process of the composite film on the broadband reflective capability was studied systematically. The chiral polymer/cholesteric liquid crystals composite film that can reflect the light covering the wavelength from 820 nm to 2100 nm was achieved successfully and was used as the functional film in the windows for shielding part of near-infrared light to achieve the thermal management effect of buildings. This work is expected to provide a new method for the preparation of smart windows and thermal management of buildings. • A composite film with broadband reflective capability was presented. • The composite film contributed to shielding part of near-infrared light. • The film can reflect the light covering the wavelength from 820 nm to 2100 nm. • The composite film can be applied in the thermal management effect of buildings. • The film was capable of reducing the thermal effect of sunlight in the house.

Recent progress on hygroscopic materials for indoor moisture buffering

Once in contact with the indoor air, hygroscopic materials can moderate the indoor humidity fluctuation by adsorbing or releasing water vapour, and then improve the moisture regulation and thermal management of buildings. It is desirable to explore the characterized properties of these materials about moisture buffering behaviour. In this regard, we review various hygroscopic materials used for the built environment control. The hygrothermal properties of hygroscopic materials often can be characterized by some parameters, such as water vapour adsorption/desorption capacity, water vapour adsorption/desorption rate, water vapour diffusion coefficient, and so on. To provide an insight on the existing research on humidity control materials, different research studies and the recent progress on humidity control materials have been summarized. The materials include traditional and conventional building materials, some natural materials, and novel humidity control materials. Besides, the relevant parameters are considered as well as the improvement suggestions to enhance the application of humidity control materials in building environments. Finally, new multifunctional materials and intelligent moisture control materials together with the corresponding systems are collated to summarize the latest research trends. The overview of the application of hygroscopic materials can provide current and future researchers guidelines for the science-oriented design of moisture control systems for new energy-efficient buildings.

Potential building energy savings by passive strategies combining daytime radiative coolers and thermochromic smart windows

Reducing the energy consumed by space cooling and providing outstanding thermally insulated windows are essential requirements for a smart green building. In this study, a new building design concept for envelope/façade is proposed and demonstrated, providing a solution for thermal management in buildings. This new design for the envelope/façade of buildings comprises two major passive and energy-free technologies, a daytime radiative cooler and a thermochromic smart window. The PDMS-silica-silver daytime passive radiative cooler can provide a cooling effect to the indoor environment without energy input, meanwhile the thermochromic smart window using PNIPAm hydrogel can passively modulate the solar irradiance entering buildings through windows. Hence, the energy needed for indoor heating, cooling and lighting can be reduced significantly. To evaluate the energy-saving performance, model houses are built, one of which is assembled using the proposed building design. The orientation effect on the indoor air temperature of the model houses is investigated. Under intensive solar irradiance, a maximum reduction of 4.8 °C of the indoor air temperature is achieved in the model house constructed using the proposed building design. An energy saving of about 17% of air-conditioning systems in buildings constructed with this new design is expected during daytime operation.

Thermally conductive and form-stable phase change composite for building thermal management

Phase change materials (PCMs) have aroused tremendous interest in building thermal management (BTM) owing to their operational simplicity and comparable energy storage density. However, the application of PCM-based BTM is generally hindered by the bottlenecks of low thermal conductivity and liquid leakage. To solve this problem, a novel thermally conductive and form-stable phase change composite (PCC) is prepared by employing n-Octadecane (ODE) as PCM, olefin block copolymer (OBC) as supporting material, and expanded graphite (EG) as thermally conductive additives. The characterization results show that the as-synthesized PCCs exhibit good physicochemical compatibility. The introduction of EG enables PCC an enhanced and antistrophic thermal conductivity. The radial thermal conductivities of PCCs reach up to 3.8–20.6 W/m∙K with EG loading of 5–25 wt%. The thermogravimetric analyzer (TGA) and leakage-proof analysis indicate that the resultant PCCs have a good thermal stability and the combination of OBC and EG greatly alleviated the leakage problem. In addition, BTM test shows that the indoor temperature of the PCM room is more stable and the maximum temperature differences between PCM room and reference room are 2.5 °C and 3.6 °C during the heating and cooling processes. These results indicate that the as-synthesized ODE-OBC/EG composites have significant potential for BTM application.

Experimental and Numerical Analyses of Thermal Storage Tile-Bricks for Efficient Thermal Management of Buildings

Due to the tremendous increase in the population and emerging energy crisis, the surging demand for the thermal management of buildings has become essential. Thermal management of buildings is of high importance for maintaining optimum thermal comfort and controlling the drastic environmental impacts. To avoid high energy consumption strategies and continuous operation such as active air heaters and air conditioners, passive strategies driven by phase change material-based thermal storage are expected to leverage the energy challenges. This work attempts to present the form-stabilized thermal storage tile-bricks (TSTBs) that are fabricated by a combination of octadecane, phosphogypsum, kaolin clay and cement. The optimal percent contents of each entity were found with respect to the design criterion of form-stability and effective temperature control capacity. Two TSTBs with a thickness of 10 mm and 15 mm were constructed, which are then applied on ordinary clay bricks to build a prototype wall. The optimal TSTBs are experimentally and numerically evaluated by subjecting them to transient thermal performance analysis, providing longer temperature retardation (~3000 s) compared with ordinary clay bricks (~400 s). It is thus implied that TSTBs can provide a viable solution against energy mismanagement by inhibiting the heating in summer and reserving the cold in winter.

Numerical analysis of nanomaterial-based sustainable latent heat thermal energy storage system by improving thermal characteristics of phase change material.

Thermal energy conversion and storage plays a vital role in numerous sectors like industrial processing, residential and mass cooking processes, thermal management in buildings, chemical heating, and drying applications. It will also useful in waste heat recovery operations in industrial/thermal power stations. The effect of Al2O3 nanoparticle volume fraction (0%, 2%, and 5%) in a paraffin phase change material (PCM) and heater location (Bottom and Sidewall) in a 2D square thermal energy storage system have been numerically analyzed in this study. Transient thermal analysis has been carried out in ANSYS Fluent R18.1 for 500, 1000, and 3000 s. Laminar flow conditions with an enthalpy porosity model are used to study the solidification and melting behavior of nano-PCM. A Grid independence test has been conducted and selected an optimum number of elements as 115538. The results revealed that the addition of nanoparticles in PCM improves its thermal characteristics. The variation of liquid fraction and temperature profile with time has been recorded, and this is due to Rayleigh-Benard convection. At a given time, the melting rate increases with an increase in nanoparticle concentration up to 2% insertion after that the melting fraction reduces for both bottom wall and sidewall heating. This is mainly due to viscous domination with the increase in physical characteristics like density and viscosity of the fluid. Also, the melting rate in the case of sidewall heating augmented more than the bottom wall heating due to negligible buoyancy effects in former than later. The outcome of this analysis helps to find out the optimum volume concentration of nanoparticles to maximize the thermal energy storage applications.

A Heat Pump-Based Multi-source Renewable Energy System for the Building Air Conditioning: The IDEAS Project Experience

The current paper presents the state-of-the-art of the ongoing IDEAS research project, funded under the Horizon 2020 EU framework programme. The project involves fourteen partners from six European countries and proposes a multi-source cost-effective renewable energy system for the decarbonisation of the building envelope. The system features a radiant floor fed by a heat pump for the building thermal management. The heat pump can exploit sun, air, and/or ground as thermal sources through the use of photovoltaic/thermal solar panels, air heat exchangers, and shallow ground flat-panel heat exchangers. Thermal energy storage is achieved by means of phase change materials spread along several system components, such as: radiant floor to increase its thermal inertia, solar panels for cooling purposes, ground to enhance soil thermal capacity. Within the project framework, a small-scale building, featuring a plethora of sensors for test purposes, and two large-scale buildings are meant to be equipped with the renewable energy system proposed. The small-scale building is currently in operation, and the first results are discussed in the present work. Preliminary data suggest that while multi-source systems coupled with heat pumps are particularly effective, it is complex to obtain suitable thermal energy storages on urban scale.

Numerical simulation and parametric study of various operational factors affecting a PV-battery-air conditioner system under prevailing European weather conditions

The building sector currently accounts for approximately 40 % of final energy consumption. In the near future, renewable energy driven heat pump systems will play an important role in the thermal management of buildings. The work described here deals with the effect of weather conditions as well as operational characteristics on the energy and economic performances of a solar PV powered air conditioning unit (ACU) with a battery system (PBAS) based on numerical and experimental investigations. The experiments were carried out to test the developed TRNSYS model. In the assessment, various performance indicators were used while a novel performance indicator, the so-called annual grid independence ratio, was also proposed. The simulated studies revealed that annual energy performance indicators (self-consumption, self-sufficiency, grid independence and energy conversion ratios) are greatly affected by climatic conditions and operational characteristics. Besides, the economic analysis has shown that the net present value and the energy consumption profiles or diverging values for state of charges are directly proportional for the hottest (Seville) climate. However, they are inversely proportional for the coldest (Stockholm) climate for the considered PBAS configuration (PV-2.5 kWp, ACU-2.52 kW cooling and 2.84 kW heating, batteries-9.6 kW h) under the selected economic status of the sites.

Thermal performance analysis of a thermal enhanced form-stable composite phase change material with aluminum nitride

Phase change material is a competent candidate for thermal energy storage technology application of building envelope thermal regulation. But the low thermal conductivity of organic phase change material hinders its building thermal management utilization from fully functioning. In this study, a kind of thermal enhanced form-stable composite phase change material is prepared, aiming at enhancing the pure phase change material thermal conductivity by employing aluminum nitride as the matrix material. A series of tests are carried out attempting to figure out the thermal characteristics of the newly made compound. And an experiment is conducted, trying to find out its thermal performance in practice. The results turn out that the proposed composite possesses a thermal conductivity of 3.154 W∙(m·K)−1, 2903% improved than that of pure phase change material. Besides, the obtained experimental middle layer temperature of the newly made composite board sample is 27.93 °C. Compared with the phase change point of the pure material, the use ratio of phase change material in the board can be calculated as 100%, meaning that the newly made composite functioned well with little waste. Thus, these performances indicate a bright future for the aluminum nitride based thermal enhanced form-stable composite phase change material.

Experimental Analysis of PCM Based Helical Heat-Exchanger for Thermal Management of Buildings

Experimental Analysis of PCM Based Helical Heat-Exchanger for Thermal Management of Buildings

Humidity-Dependent Thermal Boundary Conductance Controls Heat Transport of Super-Insulating Nanofibrillar Foams

Summary Cellulose nanomaterial (CNM)-based foams and aerogels with thermal conductivities substantially below the value for air attract significant interest as super-insulating materials in energy-efficient green buildings. However, the moisture dependence of the thermal conductivity of hygroscopic CNM-based materials is poorly understood, and the importance of phonon scattering in nanofibrillar foams remains unexplored. Here, we show that the thermal conductivity perpendicular to the aligned nanofibrils in super-insulating ice-templated nanocellulose foams is lower for thinner fibrils and depends strongly on relative humidity (RH), with the lowest thermal conductivity (14 mW m−1 K−1) attained at 35% RH. Molecular simulations show that the thermal boundary conductance is reduced by the moisture-uptake-controlled increase of the fibril-fibril separation distance and increased by the replacement of air with water in the foam walls. Controlling the heat transport of hygroscopic super-insulating nanofibrillar foams by moisture uptake and release is of potential interest in packaging and building applications.

An Adaptive Vent System for Localized and Customized Thermal Management in Buildings

Abstract This paper introduces an innovative ventilation system that is capable of providing localized and customized thermal conditions in buildings. The system has diffusers with individually operable flaps that facilitate asymmetric air inlet to control air flow inside a room in an effective way. Moreover, the system involves distributed temperature sensors, a user interface, and a control unit that allows creation and management of “thermal subzones” within a room in accordance with the different preferences of occupants. As a specific case, the thermal management of a typical office in an academic building is considered. Both experimental and numerical studies were conducted to show that it is possible to achieve several degrees of temperature differences at different room locations in a transient and controllable fashion. The dynamic management of the temperature distribution in a room can prevent the waste of conditioning energy. It is shown that the system provides a practical and impactful solution by adapting to different user preferences (UPs) and by minimizing the resource use. In order to deal with the complexity of design, development, and operation of the system, it is considered as a cyber-physical-social system (CPSS). The core of the CPSS approach used here is an enhanced hybrid system modeling methodology that couples human dimension with formal hybrid dynamical modeling. Based on a coherent conceptual framing, the approach can combine the three core aspects, like cyber infrastructure, physical dynamics, and social/human interactions of modern building energy systems to accommodate the environmental challenges. Besides physics-based achievements (managing temperature distribution inside a room), the new AVS can also leverage user engagement and behavior change for energy efficiency in buildings by facilitating a new practice for occupants' interaction with heating, ventilation, and air conditioning (HVAC) system.