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• Control-based dynamic modeling of a temperature-driven coupled metal hydride (MH) system for building applications. • Methodology for selection of a metal hydride (MH) pair for selected application using MATLAB Toolbox. • Zr 0.76 Ti 0.24 Ni 1.16 Mn 0.63 V 0.14 Fe 0.18 –Ti 0.85 Zr 0.15 Cr 1.2 Mn 0.8 MH pair showed the highest coefficient of performance (COP). • Parametric investigation is performed on this MH pair to understand the effect of operating temperatures. • PI feedback controller is investigated to regulate the heat and mass exchange processes between the coupled MH pairs. A temperature-driven coupled metal hydride (MH) based thermal energy storage (TES) system can allow to shave and shift the peak energy demand in buildings. The high energy density and long-term (seasonal) energy storage capability are its major advantages over other energy storage methods. The dynamic nature of the MH operation, however, requires controlled hydrogen transfer between the coupled MHs at a rate needed to meet the building's transient load. While temperature-driven MH systems are studied in the literature, their application in buildings and control are scarcely reported. This paper presents a control-based dynamic modeling of the temperature-driven coupled MH-TES system for building cooling applications. The dynamic model is developed in MATLAB® Simulink environment, considering the thermodynamic and kinetic behaviors of the MH systems. Based on a preliminary analysis of a property database of over 337 hydrides, we select around 1600 MH pairs suitable for building cooling applications. Each of these MH pairs is studied for their performance using the dynamic model, and among all, Zr 0.76 Ti 0.24 Ni 1.16 Mn 0.63 V 0.14 Fe 0.18 –Ti 0.85 Zr 0.15 Cr 1.2 Mn 0.8 MH pair showed fast dynamics along with high coefficient of performance (COP) of 0.71. A parametric investigation is performed on this MH pair to understand the effect of operating temperatures. Finally, three proportional-integral (PI) feedback controllers are investigated to regulate the temperature, pressure and mass exchange between the coupled MH pairs. The developed PI controller is sufficiently capable of rejecting the signal noise from the hydrogen flow and internal heat exchange processes with root mean square error of 5.78 W between reference and actual cooling load. [ABSTRACT FROM AUTHOR]

• Annual thermal response characteristics of ULEBs was quantitatively analyzed. • An experimental platform with TCM was built and its thermal properties were studied. • The applicability of coupled TCM in ULEBs was evaluated using EnergyPlus. Enhancing the thermal performance of ultra-low energy buildings (ULEBs) is a critical technical challenge in the pursuit of low-carbon construction. This study investigates the thermal response characteristics of a ULEB located in cold climate, with measurements conducted under extreme weather conditions. The results reveal that while ULEBs exhibit strong resilience against harsh outdoor climates, the heat storage and release capacity of their enclosure structures is relatively limited. To address this limitation, Temperature Control Material (TCM) were introduced to improve the thermal storage and release performance. The capacity of TCM for heat storage and release was quantified through the establishment of an experimental platform incorporating TCM walls. Additionally, the applicability of ULEBs with TCM-enhanced walls was evaluated across various climate zones using EnergyPlus simulation software. The findings of this study offer significantly theoretical contributions to the promotion and implementation of ultra-low energy buildings. [ABSTRACT FROM AUTHOR]

• Existing operational administrative building was modeled and validated. • Passive application of PCM ceiling tiles show energy and demand savings. • Activation methods increase savings in annual energy and peak demand. • Peak cooling electricity demand can be fully shifted for the optimum solution. The aging U.S. building stock requires various retrofit measures to enhance their energy efficiency. This study explores the integration of thermal energy storage and advanced building controls as viable retrofit solutions for load flexibility and peak demand response while maintaining the occupants' comfort. A detailed assessment is conducted on the energy use of an administrative building in Sumner County, Kansas, focusing on the implementation of phase change materials (PCMs) in the ceiling of occupied zones. First, a time-resolved, whole-building energy model is developed in EnergyPlus, incorporating complex thermal behaviors such as air exchange between the plenum space and occupied zones, envelope leakage, and operational schedules. The model is then validated using experimental field test data, and subsequently a parametric assessment of key PCM properties and application strategies is performed to evaluate cooling electricity demand benefits. The parametric study shows that the optimal retrofit strategy, comprising a PCM with 23 °C peak melting temperature, 0.125 in. (3.17 mm) thickness, and 150 kJ/kg latent heat, combined with active controls that include 8 h of precooling, forced convection under the ceiling, and a 2 °C thermostat setback during peak hours, can result in a maximum load shift during the peak period of 99.6 % and the total electricity savings during the peak period of 98.9 % for the optimum case and thus provide significant cost savings under time-of-use pricing scenarios. [ABSTRACT FROM AUTHOR]

• A wide review is conducted to investigate the incorporation of phase change materials in bricks in residential structures. • Using phase change materials (PCMs) can lessen the fluctuation of interior temperature in construction bricks. • PCMs can reduce the heat flux peak in all types of dwellings while using a range of 28 – 30 °C of melting temperature. • An enhanced performance of reduced internal temperature is noticed in PCMs-bricks compared to the reference brick. • The peak temperature in the chamber is reduced by 24.1% by using PCMs for bricks, which prevents extreme heat penetration. To provide a thorough evaluation of the recent knowledge regarding the utilisation of phase change materials (PCMs) in bricks industry, the present study specifies a comprehensive review of most recent advancements (2020–2024) in integrating PCMs into building bricks for energy preservation and thermal regulation. The outcomes highlight significant advantages, including a reduction in internal temperatures by up to 4.7 °C, an increase in time lag by 2 h, and a 23.84 % decrease in temperature fluctuations when PCM is encapsulated within brick walls. This review also evaluates different PCM configurations, melting temperatures, and encapsulation approaches, enlightening their influence on thermal performance across different climates. By reducing peak heat flux and improving thermal comfort, PCM-integrated bricks exhibit considerable potential for energy-efficient construction. Recommendations for future research are delivered, highlighting optimisation in PCM placement, material innovations, and practical applications for various building types and climates. Finally, this review introduces a number of recommendations to expand the storage and release of thermal energy of building bricks via the efficient utilisation of PCMs. [ABSTRACT FROM AUTHOR]

• The integration of thermal energy storage and battery energy storage enhances system benefits. • System flexibility is improved by high system size. • System size is optimized in various application scenarios. • EV interaction save 16.13% cost in grid-unconnected, and improve system flexibility by 3.13% in grid-connected. To enhance the flexibility of the building energy system, this study proposes a design management and optimization framework of photovoltaic heat pump system integrating thermal energy storage and battery energy storage based on a nearly zero-energy building in cold region. An autonomous energy management strategy including day-ahead regulation strategy, load control strategy, and electric control strategy is proposed with six evaluation indexes including annual system consumption, self-consumption ratio, load match ratio, grid net power, levelized cost of energy and carbon emission. Single-objective and multi-objective optimizations are conducted to investigate the optimal sizing of photovoltaic heat pump system in different application scenarios. The results show that the integrated of thermal energy storage and battery energy storage has a better system performance. The optimum balance of system performance can be achieved by configuring a 12 kW photovoltaic power, 40 kWh batteries, 18 kW air source heat pump capacity, and 1.2 m3 water tank volume. The high system size enhances techno-flexible-economic-environmental benefits of system. Compared with grid-unconnected mode, grid-connected mode has higher system flexibility, economic and environmental benefits. The electric vehicle interaction, as the second energy storage, can save 16.13 % levelized cost of energy in grid-unconnected mode, increases the load match ratio (+3.13 %), grid net power (–14.68 %), and carbon emissions (–20.90 %) in grid-connected mode. The integration of renewable energy and energy storage technology provides guidance to stakeholders and facilitates the development of carbon–neutral buildings. [ABSTRACT FROM AUTHOR]

The integration of phase change materials (PCMs) with thermal energy storage capabilities in radiant heating systems can significantly enhance energy utilization efficiency and improve indoor thermal comfort. In our recent study, we developed a modified composite phase change material (CPCM) based on disodium hydrogen phosphate dodecahydrate (DHPD, Na 2 HPO 4 ·12H 2 O). This material was integrated into a radiant heating system and its thermal performance was evaluated in an experimental room. To address issues such as supercooling, liquid leakage, and the unstable morphology of DHPD, we selected appropriate nucleating agents and additives, combining them with vermiculite (VM) for adsorption. This led to the creation of a Modified DHPD/MVM CPCM with a melting point of 32.7 °C, a latent heat of 169.4 J/g, and a supercooling degree of 1.95 °C. The phase-change thermal storage module, prepared using a vacuum macroscopic encapsulation method, demonstrated good thermal reliability. Thermal performance tests indicated that the installation of phase change radiant heat storage panel effectively reduced fluctuations in ceiling and indoor air temperatures, extending the total indoor thermal comfort duration by an additional 5.7 h at a water supply temperature of 50 °C. This research offers valuable insights for the further development of phase change radiant heat storage technology. [ABSTRACT FROM AUTHOR]

• CLT reduces heating energy by 83.1 %, cutting greenhouse gases by over 60 %. • Enhancing airtightness lowers heating energy consumption to one-sixth of the original. • Thermal storage via PCM improves temperature stability and reduces energy use. • CLT homes emit 60.27 % less CO2, equal to 873 trees planted or 2.91 cars removed. • Improved CLT insulation reduces thermal bridging, enhancing indoor comfort levels. Cross-laminated timber (CLT) offers a unique opportunity for carbon sequestration in building construction due to its carbon-storing capability through photosynthesis. This study evaluates the energy-saving potential of a detached house constructed using CLT, comparing it to traditional light frame construction (LFC) methods. Initially, we analyzed the construction process and examined indoor environmental conditions to identify potential energy-efficiency improvements. Using the EnergyPlus simulation tool, we tested scenarios that enhanced insulation and airtightness, incorporating additional thermal storage materials and phase change materials (PCM) to maximize energy reduction. Our findings show that implementing these improvements can reduce heating and cooling energy consumption by up to 71.1 %. This reduction in energy use translates to a greenhouse gas (GHG) reduction of over 60 %, equivalent to planting 873 trees or eliminating the annual emissions of approximately 2.91 vehicles. The use of CLT in housing not only sequesters carbon but also significantly lowers energy demands, paving the way toward sustainable, low-energy, low-carbon buildings. [ABSTRACT FROM AUTHOR]

• Developed a method to quantify the merit of the TABE + TES system for building demand-side management. • Developed Time-Of-Day informed rule-based control strategies considering Time-Of-Use rates. • Significant peak, annual heating and cooling energy reductions were achieved. • TABE + TES system saves 38 %, 78 %, 48 %, and 77 % of the peak energy for Birmingham, Los Angeles, Oak Ridge, and Denver. • A high Time-Of-Use rate (on-peak to off-peak ratio) can increase the benefit of adopting the TABE + TES system. The thermally anisotropic building envelope (TABE) is a novel active building envelope that enhances energy efficiency and thermal comfort in buildings by transferring heat and cold between building envelopes and hydronic loops. When coupled with thermal energy storage (TES) units, the TABE + TES enables the storage of both heat and cold energy captured by the TABE roof or exterior walls. This stored energy can be later released by the TABE floor for indoor heating and cooling, benefiting both the grid and the end user. This paper evaluates the merits of TABE + TES for building demand-side management across various US climate conditions, focusing on peak load shaving, annual energy savings, and cost savings under time-of-use (TOU) electric rate schedules. Simulations were conducted by integrating time-of-day–informed, rule-based control strategies in MATLAB, TABE components and TES units in COMSOL Multiphysics, and whole-building energy analysis in EnergyPlus. A case study using the US Department of Energy's prototype single-family detached house model in Birmingham, Alabama; Los Angeles, California; Oak Ridge, Tennessee; and Denver, Colorado, showed that the TABE + TES system achieved (1) 70 % peak load shaving in Los Angeles and Denver and 20 % in Birmingham and Oak Ridge; (2) significant peak electricity savings of 351–497 kWh, reducing peak energy consumption by 38 %–78 %; and (3) annual heating cost savings of 0.79 $/m2–1.17 $/m2 and cooling cost savings of 0.60 $/m2–1.17 $/m2 using a normal utility rate or low-TOU rate. The benefits of employing the TABE + TES system are even more significant under high TOU rates. [ABSTRACT FROM AUTHOR]

• A solar coupled air source heat pump system for dairy barn heating was developed. • The TRNSYS model is established for analyzing energy consumption. • Life-cycle costs and climate performance are used in the assessment. • System configuration parameters are optimized using ANN and NSGA-II. The dairy farming industry is confronted with significant challenges regarding energy consumption and carbon emissions. Employing renewable energy sources is an efficient method to tackle these difficulties. However, the high initial capital costs (ICC) and carbon emissions with solar-coupled air source heat pump systems (SCASHPs) posed significant economic and environmental challenges, which remained major barriers to their application. Therefore, this study investigated the energy consumption of SCASHPs during 15 years using TRNSYS. Artificial neural network (ANN) and nondominated sorting genetic algorithm II (NSGA-II) were used to evaluate the environ-economic performance (life-cycle cost (LCC) and life-cycle climate performance (LCCP)) of heating systems under different design parameters (including the area of the solar collector (SC), the rated heating power, the volume of the heat storage tank (HST), and the start-stop temperature (SST) difference of the air source heat pump (ASHP)). The results indicated that the optimized SCASHPs achieved reduction of 12.5 % in ICC, a 7.86 % reduction in LCC, and a 9.48 % reduction in LCCP. This research delivered reliable optimization results and realized the lowest carbon emissions of the heating system, which provided a valuable reference for research and practice in related fields. [ABSTRACT FROM AUTHOR]

• Cementitious materials provide versatile chemical, thermal, and electrical energy storage for sustainable solutions • Phase change materials improve cementitious composites' thermal energy storage and release capabilities. • Cementitious storage enhances renewable integration, boosting grid stability during intermittent energy generation. This review paper investigates the use of cementitious materials for energy storage, emphasizing their role in advancing sustainable development. It starts with a comprehensive overview of energy storage technologies and explores the key properties of cementitious materials that make them suitable for energy storage, alongside the challenges and opportunities they present. The review covers different energy storage mechanisms, including chemical, thermal, and electrical methods, highlighting the efficiency and capacity of each approach. Performance evaluation is addressed through specific criteria, experimental techniques, and case studies, with numerical outcomes provided to illustrate the effectiveness of these materials in energy storage. The paper also discusses potential applications in energy infrastructure and construction, identifying emerging technological advancements and trends. Environmental and economic considerations, such as sustainability benefits and cost analysis, are evaluated in detail. Finally, the review summarizes key insights, outlines the implications for sustainable energy systems, and offers specific recommendations for future research and development to optimize the use of cementitious materials in energy storage. [ABSTRACT FROM AUTHOR]

Phase change materials (PCM) and embedded tube radiant terminals demonstrate considerable advantages with respect to heat storage, energy savings, and the provision of comfort in buildings. This paper puts forth the concept of an energy storage interior wall (ESIW) with embedded pipe radiant technology, comprising PCM, and coupled with low-grade energy sources. Compared to traditional TABS, this system uses PCM energy storage to compensate for the instability of solar energy supply, which expands the application scenarios of clean energy. At the same time, it can greatly improve the thermal mass of the building and provide cooling and heating for multiple rooms. Experimental results demonstrate that the ESIW is capable of markedly enhancing the thermal comfort and indoor temperature, with an average increase of 9.9 °C relative to the outdoor. In the numerical study based on test data, sensitivity analysis was performed on 10 characteristic parameters of the ESIW structure: wall thickness, wall density, wall thermal conductivity, wall specific heat capacity, PCM phase change temperature, PCM pipe diameter, PCM enthalpy, PCM pipe length, pipe flow diameter, and number of rows of PCM pipes. The results show that the key parameters affecting the first objective (thermal storage capacity) are: pipe flow diameter, wall density, wall thickness, and PCM pipe diameter; and the key parameter affecting the second objective (investment cost) is the diameter of the PCM pipe. After multi-objective optimization for these two objectives, the thermal storage capacity of the ESIW was improved by 96.7 %, and the investment cost was reduced by 11.49 %. [ABSTRACT FROM AUTHOR]

[Display omitted] In response to global climate change, achieving sustainable development through energy conservation and emission reduction has become a common goal for humanity. In this work, we present a general model for computing the energy consumption and carbon emissions of building with low computational complexity and effort. Based on this model, we designed smart green building walls (SGBW), which consist of conventional walls and thermal storage/release films applied to their external/internal surfaces. These films, which incorporate thermochromic materials can adaptively adjust their radiation properties according to environmental temperature. At high temperatures, the thermal storage film(TSF) absorbs heat utilizing a solar absorptance of 0.604 and storing the heat within the wall. Conversely, at low temperatures, the thermal release film(TRF) unidirectionally releases heat into the interior with an infrared emissivity of 0.821. The simulation results indicate that SGBW has enhanced heat storage capacity by 18.7 % and increased heat release capacity by 30.4 % compared to conventional cement walls. In addition, calculations using the general model show that each square meter of SGBW can save 417 ∼ 805 kWh of electricity and reduces CO 2 emissions by 225 ∼ 477 kg over the building's lifecycle in various climatic zones, aligning closely with results obtained from the commercial software. Thus, this model not only simplifies intricate simulation processes but also serves as a guide for designing surface devices. The SGBW is anticipated to be particularly beneficial in buildings located in regions requiring nighttime heating, contributing significantly to indoor temperature regulation while simultaneously reducing energy consumption and carbon emissions. [ABSTRACT FROM AUTHOR]

• Building integrated sorption storage combined with solar thermal collectors. • High solar fractions above 80% can be achieved. • Dynamic building simulations for optimal component sizing and system performance. • Simulations are based on a measured laboratory prototype. Thermochemical energy storage is an attractive option for seasonal thermal energy storage, particularly in building applications. However, several research gaps in the field of sorption storage systems such as restricted focus on specific reactor concepts or sorption couples or lack of systematic performance studies hinder their practical implementation. This study addresses these gaps by evaluating the performance and cost-effectiveness of a solar thermal space heating system integrated with liquid sorption storage across various building types (single and multi-family homes with different envelope qualities) and climates (Zurich, Switzerland; Harbin, China; Helsinki, Finland). The study systematically investigates the impact of different sizes of individual system components (number of ground heat exchangers, solar collector area, sorption reactor capacity, size and distribution of thermal buffers) on the overall system performance using a previously presented greybox sorption reactor model based on a lab-scale prototype. The simulation results demonstrate that high solar fractions above 80 % can be achieved with long-term sorption storage. To reach this, substantial storage volumes of around 0.8––1 m3 per m2 of solar collector area are needed for the multi-family home cases in Zurich climate despite the increased volumetric energy density of sorption storage when compared to classical water storage. This emphasizes the significance of building envelope quality, available roof area, and careful system component sizing for enhancing solar fractions and cost-effective renewable heat generation. The findings provide valuable insights into optimizing sorption storage systems, fostering the practical implementation of renewable energy solutions for space heating in buildings. [ABSTRACT FROM AUTHOR]

[Display omitted] • Both two systems use buried tubes for heat exchange. • It is easy to confuse the BTES system with the GSHP system. • There are essential differences between the BTES system with the GSHP system. • Top ten differences between BTES systems and GSHP systems. • BTES solves the contradiction between energy supply and demand in time and space. Since both the cross-seasonal borehole thermal energy storage (BTES) system and the ground source heat pump (GSHP) system use buried tubes for heat exchange, GSHP is often mistaken for a BTES system. However, there are essential differences between the GSHP system and the BTES system, and the purpose of this study is to elucidate in detail the differences between these two systems. This study first summarizes the practical application cases of seasonal BTES globally, and then deeply compares and analyzes the differences between the seasonal BTES system and GSHP system from ten different perspectives, including system definition, technology timeline, purpose of buried tube heat exchanger, heat sources, soil temperature changes, buried tube heat exchanger volume, design of the buried tube heat exchanger, energy storage modes, biggest drawback, system performance evaluation. Finally, the future development prospects and research directions of the seasonal BTES system are further discussed. In summary, although the GSHP system may be confused with the seasonal BTES system in some aspects, they are indeed two different systems. Compared to the GSHP system, the seasonal BTES system can solve the contradiction between energy supply and demand in time and space, and effectively improve energy utilization efficiency. [ABSTRACT FROM AUTHOR]

• Utilization of Gobi gravel soil for heat storage and heating of Gobi solar greenhouses (GSGs). • Significant field application of the system and excellent system performance. • In-depth analysis of the system's influence pattern on the thermal environment of GSGs. • This system greatly enhances the environmental and economic benefits of GSGs. The present study proposes an innovative active solar heating soil heat storage system to enhance the thermal environment of Gobi solar greenhouses (GSGs) and address the issue of uneven heat distribution. This system utilizes Gobi gravel soil as a heat storage medium, combining solar flat plate collectors and horizontal buried pipes at a depth of 0.15 m. To validate the system's practical efficacy, an 80-day field experiment was conducted in Jiuquan City, located in the northwest Gobi region of China. The experiment focused on investigating the impact of soil heat storage on the temporal and spatial distribution of air and soil temperatures within the greenhouse, as well as assessing the system's environmental and economic benefits. The results demonstrated that the system exhibited outstanding performance, with an average heat collection efficiency exceeding 56.96 % and a daily average heat storage amount of 132.13 kWh. Compared to the contrast greenhouse, the experimental greenhouse showed an increase in nighttime average air temperatures of 4.9 °C, 3.9 °C, and 3.6 °C on typical sunny, cloudy, and snowy days, respectively. The average surface soil temperatures increased correspondingly by 6.5 °C, 4.8 °C, and 4.5 °C. And the effective accumulated temperature increased by 40 %. Furthermore, the system significantly improved the uniformity of indoor temperature distribution. During nighttime heat release, the maximum temperature difference in the air, both span and vertically, did not exceed 0.8 °C; the maximum soil temperature differences in the span and length directions were no greater than 0.3 °C and 1.8 °C, respectively. During the daytime heat storage process, the maximum soil temperature differences in the span and length directions were no more than 0.4 °C and 1.7 °C, respectively. This study of the active solar soil heat storage system demonstrates significant application effects in improving the thermal environment of GSGs, with substantial environmental and economic benefits. [ABSTRACT FROM AUTHOR]

Renewable Energy Communities (REC) can largely contribute to building decarbonization targets and provide flexibility through the adoption of advanced control strategies of the energy systems. This work investigates how the role of flexibility sources will be impacted by shifting towards advanced control strategies under a high penetration of variable Renewable Energy Sources, in the following years. A large residential area with diverse energy systems, building envelope configurations, and energy demand patterns is modeled with the simulation environment RECsim, a virtual testbed for the implementation of energy management strategies in REC. Photovoltaic (PV) panels, Battery Energy Storage and Thermal Energy Storage (TES) of different sizes for each household provide a realistic description of a REC which includes both consumers and prosumers. This study explores a scenario in which advanced controllers based on Deep Reinforcement Learning (DRL) replace existing Rule-Based Controllers in building energy systems across a significant number of buildings. These control policies are simulated under three different scenarios that consider consumers with different pricing schemes and TES penetration. Efficient control strategies, have demonstrated significant potential, regardless of the presence of thermal storage and ToU pricing schemes, in reducing energy demand by 12.6%, cutting energy costs by 20.8%, and enhancing self-sufficiency and self-consumption, with minimal impact on Shared Energy. Implementing a flat tariff scheme under DRL enables consumers to increase their energy demand during periods of PV generation, which is particularly advantageous in a REC. Also, this approach lowers overall energy demand by 12.6% and boosts self-sufficiency, and it also decreases electricity exports from the REC to the grid by 18.2% compared to a ToU tariff scheme. When using ToU tariffs, thermal storage can be used to achieve cost savings, but total Shared Energy decreases, as do self-sufficiency and self-consumption of the REC. The results indicate that in a REC with high variable renewable energy and decentralized control, consumers using TES and ToU tariffs with peak prices during high irradiance periods may not be beneficial for the grid compliance. In conclusion, the coupling between DRL and thermal storage should be supported by more innovative pricing schemes for RECs and/or coordinated energy management, although it requires advanced communication and monitoring infrastructure. • DRL control in REC is compared to RBC under various flexibility scenarios. • DRL is always more favorable than RBC given the reduced demand and energy cost. • TES and ToU tariffs for consumers can be critical in RECs for grid compliance. • Flat tariff was the most grid-compliant among the tested configurations. [ABSTRACT FROM AUTHOR]

Latent heat thermal energy storage (LHTES) systems are designed to store excess thermal energy, addressing supply-demand mismatches during periods of low supply. Integrating such systems in the field is challenging due to the slow charging caused by the low thermal conductivity of phase change materials (PCM). This shortfall can be mitigated using composite PCM (CPCM) as the thermal storage medium, consisting of form-stable porous graphite foam impregnated with PCM. Compressed expanded graphite (CEG) is one such easily accessible form-stable porous material. The graphite foam in the CPCM causes a significant improvement in the effective thermal conductivity of the storage medium; however, it causes reduced latent heat storage capacity. Existing literature on CPCM mainly emphasizes positive aspects like enhanced thermal conductivity and reduced melting time while overlooking the adverse impact on latent heat storage capacity. This trade-off must be addressed while designing such a system, particularly when the storage unit is of fixed size and shape. This study aims to find the optimal volumetric proportion of CEG in CPCM, striking the best balance between these two conflicting attributes. Objective parameters such as energy storage ratio (ESR) and capacity ratio (CR) are introduced, along with charging duration, and they are optimized based on control parameters like CEG foam porosity (ε), HTF inlet temperature (T i n), and flow Reynolds number (Re). The analysis, obtained from a volume-averaged numerical model, involves diffusion-dominated energy transfer in the CPCM domain and provides crucial design guidelines for fixed-geometry LHTES units with CPCM as the storage medium. [ABSTRACT FROM AUTHOR]

This study focuses on the reuse of some industrial wastes in the development of innovative building materials and the thermal performance, environmental impacts and cost estimates of the gypsum composite material developed in the case of a phase change material impregnation. Lauryl alcohol (LA) was impregnated into paper pulp sludge (PPS) up to 45 % by weight without leakage to obtain shape-stable composites. The LA impregnated PPS (PPS/LA) was replaced with PPS at 50 % and 100 % by weight in gypsum composite. Characteristics of shape-stable composites were studied. Also, the physical, mechanical, thermal properties and solar thermoregulation tests of the produced gypsum composites were examined in addition to the embodied energy, CO 2 emissions and cost analysis. The melting and solidification enthalpies of PPS/LA were found to be 100.4–100.1 J/g, with only a 0.5 % reduction in latent heat storage capacity after 500 cycles, and approximately 3 % after 1500 cycles. Although the presence of PPS/LA in the gypsum composite caused a slight decrease in compressive strength, it significantly improved solar thermoregulation performance, maintaining ambient temperatures 2.55 °C to 5 °C warmer at night and 5.3 °C to 13.8 °C cooler during the day. Gypsum composites containing the PPS/LA offer a suitable alternative for energy-efficient sustainable building application by reusing around 57 % of three different industrial wastes providing a waste-reducing environmental approach and a high level of indoor thermal comfort. [ABSTRACT FROM AUTHOR]

Phase change materials (PCM) are an attractive seasonal thermal energy storage solution for load shifting due to relatively high energy density. Nevertheless, the choice of the right design parameters, such as storage size and phase-change temperature, is nontrivial, as these are tightly linked to the expected seasonal operation of the storage. This paper presents a combined design and operation optimization framework for sizing PCM-based seasonal thermal storage, which can capture dynamic behaviour of the storage in sensible and latent phases, and its impact on the efficiency of connected heat pumps and chillers. The proposed method, formulated as a mixed integer quadratically-constrained programming problem, was applied to a case study of heating-dominated district. It was found that the optimal PCM melting temperature equals to the heating demand supply temperature, thus removing the need of a heat pump to discharge the storage. The optimal operation of storage requires a full charging and discharging cycle of both latent and liquid phase. Higher C O 2 emission price does not lead to a significant reduction of C O 2 emissions, but the storage size does, leading to a higher heating coverage ratio of the storage, and consequently C O 2 emissions and cost savings, which can be further enhanced with PV integration. The economic analysis indicates that, unless other benefits such as storage volume reduction are accounted for, PCM cost should drop by a factor 4 to make this solution economically viable for seasonal storage. • Optimal use of phase change material (PCM) as a seasonal thermal energy storage. • Developed a method to choose the material phase-change temperature and storage size. • PCM storage is not currently economically viable as a seasonal thermal storage technology. • If volume reduction is not accounted as benefit, PCM cost should drop by a factor 4. [ABSTRACT FROM AUTHOR]

Residential air-conditioning load on the power demand side has gradually increased. The air-conditioning loads have thermal storage characteristics, and adjusting their temperature settings will not cause significant negative impacts to users, making them well-suited for demand response. In existing studies, load aggregators usually serve as demand response implementors, and reducing the energy consumption levels of air conditioning loads directly. However, this method often lacks a clear definition of the flexibility of individual air-conditioning units and fails to account for their variations. The absence of well-defined commodity characteristics for the flexible regulation potential complicates pricing, making it difficult to safeguard the interests of the load aggregator and each air-conditioning user. Furthermore, the diversity among residential air-conditioning loads introduces high-dimensional variables into demand response optimization, making it challenging to balance data security with computational efficiency. To address these challenges, this paper proposes a market-based load reduction method for heterogeneous residential air-conditioning loads using cloud-edge collaboration. First, the flexible adjustment capability of air-conditioning loads is defined as a tradable commodity. Then, a cloud-edge collaborative trading scheme is proposed to guarantee the benefits of the load aggregator and each air-conditioning user in a data-neutrality manner. Finally, a hybrid method based on encrypted clustering is developed to compute the optimal trading strategy, ensuring data security and computational efficiency. Simulation results based on data from the Austin area show that Pareto improvement is achieved compared to other load reduction schemes, and the proposed encrypted clustering method reduces computational complexity and data security risks compared to traditional analytical and iterative approaches. [ABSTRACT FROM AUTHOR]

In subtropical regions, phase change walls tend to release heat into rooms during nighttime, reducing building energy efficiency. In this work, we proposed an interlayer ventilation phase change wall (IVPCW) to address this challenge. The thermal performance, thermal storage influencing factors, annual cooling and heating loads, and energy saving potentials of IVPCW were analyzed by experiment and numerical simulation. The results show that: (i) IVPCW has the best thermal performance under non-air-conditioning and air-conditioning among ordinary wall, phase change wall, and IVPCW. (ii) Increasing the density and latent heat of CPCM and decreasing the thermal conductivity of CPCM can reduce daily heat gain (DHG). Moreover, the density impacts DHG more than latent heat, while latent heat surpasses thermal conductivity in influencing DHG. (iii) The annual load of IVPCW is reduced by 62.8% compared with PCW. (iv)The annual load of IVPCW is reduced by 41.6% compared with insulation enhanced wall (IEW) in Ganzhou, and 39.2% lower than that of IEW in Guangzhou. The findings offer theoretical support to aid in the implementation and performance optimization of IVPCW systems. [ABSTRACT FROM AUTHOR]

The huge heat loss/gain through windows is the reason for a large amount of energy consumption in buildings. Although using the heat storage capacity of phase change material (PCM) to improve the thermal inertia of windows is an important way to reduce energy consumption, leakage and overheating at noon limit the development of windows containing solid–liquid PCM. Smart windows based on temperature-sensitive hydrogel have aroused great interest due to their excellent ability to dynamically control solar energy. However, current temperature-sensitive hydrogels with single transition temperature and uncontrollable transition speed affect indoor light comfort. Meanwhile, the low heat storage performance of hydrogels limited their energy-saving effect. Therefore, a novel smart window (P3H6) integrating temperature sensitivity and energy storage was constructed by the prepared hydrogel and form-stable PCM. The double-network hydrogel with adjustable temperature band and mechanical enhancement was constructed by acrylamide and N-isopropylacrylamide, which realized the dynamic adjustment of solar energy. The prepared form-stable PCM avoided the leakage problem and improved the heat storage capacity of the window. The comprehensive transmittance of P3H6 can be changed between 3.3 %-62.7 %-2.6 % in a day, which blocked the sunlight from transmitting heat at noon and protected privacy at night. The outdoor experiments showed that P3H6 delayed the inner surface temperature of the window to 32 °C by 1.05 h compared with traditional windows, which reduced the thermal radiation of windows to the room and improved the thermal comfort of indoor personnel. More importantly, the application of P3H6 can reduce the daytime cooling load of buildings by 28.84 %. To sum up, the proposed smart window shows great potential in energy-saving buildings. [ABSTRACT FROM AUTHOR]

This paper proposes a solution approach to manage the heating plans of tenants served by a district heating plant located in Sweden. To do that, the daily temperature request of each household in the associated pilot region is obtained, and the daily temperature profile of each household is optimized with the help of the proposed decision support system and smart valves. The hot water inflow rates of radiators are remotely controlled via smart valves at each flat to minimize the total energy consumption, carbon emission and cost associated with the energy consumption of the district heating plant. We aim to shave the peak demands while fully satisfying the temperature requests of households without violating their thermal comfort. Peak demand shaving is achieved by generating preheating schedules via mathematical optimization and using the thermal storage potential of the insulated flats. The resulting mathematical optimization model presents significant computational challenges that cannot be efficiently solved using optimization solvers within a reasonable time limit. To this end, we develop three genetic algorithm approaches that are computationally scalable for realistically-sized instances and verified to yield near-optimal solutions for the test instances. Extensive numerical analyses show the effectiveness of the proposed approach and the genetic algorithm since we yield significant carbon emission reduction and cost savings compared with the method that the experts of the utility company propose.   [ABSTRACT FROM AUTHOR]

• A new enclosure structure based on multi-melting phase change materials was designed. • Experiments indicate that phase change materials improve indoor temperature control. • The optimal thickness and position of phase change materials were explored. • A greater melting point difference enhances indoor temperature control. To improve indoor thermal comfort and achieve building energy saving, a new envelope structure based on phase change material (PCM) was proposed. Firstly, an experimental platform was built around the room model, and the effects of ambient temperatures and PCM layout on the room temperature at different times were explored. Subsequently, a room numerical model heat transfer was constructed and the experimental verification was completed. The effects of PCM thickness, position, arrangement, and melting point difference on the room temperature at each time were analyzed based on the latent heat utilization rate, temperature fluctuation amplitude, and delay time. The experimental results show that when the walls all around the room contain PCM, the maximum indoor temperature can drop to 29.5 °C, and the maximum temperature drop is 3.2 °C. In addition, the greater the heat flow, the less effective the PCM is at controlling the temperature in the room. The simulation results show that when the PCM with a thickness of 15 mm is placed on the interior side of the wall, the maximum indoor temperature can be reduced to 29 °C, the maximum temperature drop is 2.9 °C, and the peak indoor temperature is extended by 0.8 h. When the PCM is arranged in series and the melting point difference is 3 K, the temperature control effect is the best, the maximum indoor temperature can be reduced to 25.7 °C, the maximum temperature drop is 2.9 °C, and the temperature fluctuation is the minimum, 2.6 °C. [ABSTRACT FROM AUTHOR]

• Graphene enhances PCM for better thermal management in double-glazing. • Graphene-PCM mix boosts peak temperature by 10 °C, developing energy efficiency. • Microencapsulated PCM with graphene improves solar energy absorption. • Grapne nanoplatelets in PCM demonstrates accelerated heat release, enhancing thermal comfort. • Study reveals potential for graphene in energy-efficient building materials. Effective heat energy storage is crucial for thermal energy management. The utilization of latent heat storage methods is widely prevalent across various engineering applications for enhancing energy efficiency. In this study, the energy storage performances of Phase Change Materials (PCMs) achieved by incorporating graphene nanoplatelets into a microencapsulated PCM were experimentally analyzed for double-glazing applications. Changes in thermal energy storage and heat transfer performance by incorporating graphene nanoplatelets into the PCM at two different mass ratios (1 % and 0.1 %) were investigated. The results obtained from light intensity and temperature measurements, as well as thermal camera imaging, were evaluated together. The results support the contribution of graphene nanoplatelets addition to microencapsulated PCMs in enhancing thermal performance during both heating and cooling periods. Among the investigated cases, the highest mass ratio of 1 % graphene nanoplatelets addition led to a major 10 °C increase in peak temperature compared to the reference condition. In contrast, this increase in peak temperature was accompanied by a mere 14 % decrease in average light levels. This research underlines the potential of graphene-enhanced microencapsulated PCMs in optimizing thermal management systems for double-glazing applications, offering a promising pathway towards enhancing energy efficiency and thermal comfort in building environments. [ABSTRACT FROM AUTHOR]

• An optimal water temperature scheduling method to response time–of–use tariffs is proposed. • Room model predicts indoor air temperature and return water temperature for the subsequent day. • Both demand response and heating performance of ASHP are improved. • Feild experiments are conducted on an ASHP-FCUs heating system. • Operating costs decrease by 20.8% to 43.0% with comfortable indoor temperatures maintained. Air source heat pump (ASHP) is a key technology for the electrification of building heating, and its participation in demand response (DR) has important implications for reducing the grid peak load. However, current DR strategies mainly focus on changing the setpoint of indoor temperature, using the building's thermal mass as a passive thermal storage, while the impacts of water temperature on the performance of ASHP units are often overlooked. Therefore, this study proposes an optimal water temperature scheduling (OWTS) method to respond time–of–use tariffs. It is developed based on a room thermal dynamic prediction model and an ASHP power consumption prediction model, optimizing supply water temperature schedule with objectives of maintaining indoor thermal comfort and reducing heating operating costs. The effectiveness of the OWTS method was tested on a field ASHP system in Beijing, and compared with two benchmark methods. Results demonstrate that the application of the OWTS method can enhance the DR capability of the ASHP heating system, with the average value of Flexibility Factor increasing from 0.134 to 0.728, and can reduce the heating operating costs by 20.8%–43.0%. This study thereby offers a promising method for ASHP heating systems to effectively participate in DR. [ABSTRACT FROM AUTHOR]

As a roadmap for carbon mitigation, reducing energy consumption and improving thermal comfort are key factors for achieving efficient and sustainable buildings. The integration of Phase Change Materials (PCM) as passive thermal regulators in thermal energy storage systems is an effective measure to reduce demand of fossil fuels and enhance building thermal mass. Nevertheless, there is still a scarcity of experimental research that combines the focuses on the type and positioning of PCM in buildings components with a large-scale experimental setup, to accurately evaluate the real effects of these materials. In this framework, the present research focuses on thermal characterization and performance analysis of a Light Steel Framing (LSF) building enhanced with macroencapsulated salt hydrate based PCM. Therefore, an experimental campaign was performed in two real scale and comparable buildings. First, the thermal properties of the material and construction solutions were tested and characterized, followed by a thorough evaluation of the building performance. A comparative analysis of the inner surface temperatures in the two buildings − one representing a common LSF solution as a reference solution; and the other representing a thermally enhanced building incorporating PCM − was conducted, as well as the detailed characterization of the temperature profile in all layers of the construction solutions. Monitoring scheme was also defined to study the PCM behaviour in terms of charging and discharging process. Results revealed a significant passive thermal regulation capacity in the thermally enhanced building, reducing inner surface temperature peaks up to 5 °C to 8 °C during the winter and spring seasons. In the cooling season, PCM mobilization was hindered by the high outdoor temperatures. Considering that the PCM went through the phase transition only approximately 20 % to 28 % of the monitored period, optimizing its performance is a further issue that involves either repositioning the PCM layer within the construction assemblies or selecting a different operating temperature range. [ABSTRACT FROM AUTHOR]

• Utilizes TRNSYS software to model three mining area heating systems. • Selects the optimal system based on backfill temperature balance, system COP, and PLR. • Evaluates regional applicability in four Chinese cities for the seasonal thermal storage solar-backfill hybrid heat pump system. • Simulates system performance metrics including heat collection, energy consumption, and efficiency. As global energy demand and carbon emissions continues to rise year by year, the use of renewable energy for heating becomes increasingly urgent. This study employs solar and geothermal energy to supply heat to mining facilities. Initially, three distinct heating systems for mining areas were modeled in TRNSYS: the Backfill Source Heat Pump (BSHP), the Solar Assisted Backfill Source Heat Pump (SABSHP), and the Solar Assisted Backfill Source Heat Pump with Seasonal Heat Storage (SABSHP-SHS). Following a decade of simulation, the optimal system was identified through a comparative analysis that encompassed backfill temperature equilibrium, the inlet and outlet water temperatures for buried pipes, Coefficient of Performance (COP), Partial Load Ratio (PLR), and economic factors. Over the 10-year simulation period, the COP and PLR of the SABSHP-SHS system outperformed both the BSHP and SABSHP systems, showing higher energy efficiency and better heat pump performance. To further assess the regional adaptability of the SABSHP-SHS system, simulations were conducted across four regions with diverse climatic profiles: Shijiazhuang, Yan'an, Xining, and Hegang. The analysis focused on heat collection, efficiency, backfill temperature variation, system energy consumption, and the energy efficiency ratio. The findings indicate that Hegang exhibits the highest solar heat collection efficiency at 89.9% during the non-heating season, while Xining achieves a significantly higher heat collection efficiency of 54.1% during the heating season. These results suggest that the SABSHP-SHS system is particularly effective in regions with pronounced seasonal variations, characterized by extended cold winters and brief, intense summers. [ABSTRACT FROM AUTHOR]

• System coefficient of performance (COP sys) − based switching strategy is proposed. • Energy, economic and environmental (3E) analysis method is used. • The performance under COP sys -based strategy is better than under conventional one. • Average COP* under COP sys -based strategy is improved by 13.36%. The photovoltaic-thermal integrated dual-source heat pump system can offer performance improvement by addressing the limitations of a single heat pump system, which not only improves energy efficiency and system performance but also reduces pollutant emissions. However, the operational performance of the system is significantly affected by different switching strategies between two heat sources, which has not been given adequate attention from researchers. Therefore, this study introduced a system coefficient of performance − based switching strategy, which can alternate between air-source heat pump and solar water heat pump modes to make full use of air and solar energy, to optimize the operation of the photovoltaic-thermal integrated dual-source heat pump system and compare with the conventional water temperature of the heat storage tank − based switching strategy. A TRNSYS model of the system was developed and validated, and the simulated results demonstrated the better performance of system coefficient of performance − based switching strategy in energy, economic and environmental perspectives. The average photoelectric and photothermal conversion efficiency under system coefficient of performance − based switching strategy were higher than those under water temperature of the heat storage tank − based switching strategy by 1.1 % and 4.0 %, respectively, with average modified coefficient of performance of 7.43 and 6.55. Furthermore, the system not only achieved savings of 5.63 % in annual electrical cost and 5.33 % in yearly operational cost but also reduced standard coal by 19.25 kg and total pollutant emissions by 242.55 kg per year under system coefficient of performance − based switching strategy, compared to water temperature of the heat storage tank − based switching strategy. [ABSTRACT FROM AUTHOR]

• The MPCM foamed cement were fabricated and characterised for physical/thermal properties. • The MPCM foamed cement exhibits favorable thermal insulation performance, stability, and inertia. • Simulation was used to investigate the energy-saving performance in various climate zones in China. • The optimal melting temperature is related to the average temperature of the climate zone. • Energy savings are greatest in cities with higher heating demand. The addition of phase change materials (PCMs) to building envelopes can improve building thermal stability and reduce energy consumption. In this study, phase change paraffin microcapsules are combined with foamed cement to create composite thermal insulation materials with varying mass ratios of microcapsules. A heat transfer characterization experimental platform was established to investigate the heat transfer laws. The incorporation of phase change microcapsules (MPCMs) into foamed cement resulted in a reduction in thermal conductivity. The thermal conductivity of the test blocks exhibited a linear relationship with the mass ratio of MPCMs, with an average thermal conductivity of 0.053 W/(m-K) observed for 20 % MPCMs. The impact of foamed cement containing MPCMs on building energy consumption was analyzed in five different climate zones in China using EnergyPlus. The results show that energy savings are more significant in cities with higher heating demand. In non-cold regions, energy savings are highest when the phase change temperature is close to the local annual average temperature. The optimal energy saving program is evaluated by energy consumption simulation. The results show that it achieves the highest energy savings in Harbin, which saves a total of 1074,007 kWh. Additionally, it has the highest energy saving rate in Beijing, with a rate of 14.66 %. [ABSTRACT FROM AUTHOR]

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

The application of phase change materials (PCMs) combined with radiant cooling systems (RCS) in the building sector has attracted enormous interest in recent years owing to its thermal storage potential and feasibility for small-scale energy renovation of existing buildings. Different configurations of these systems and their performance have been experimentally tested and academically investigated. The present study experimentally tested a newly conceived PCM-equipped modular cooling wall and evaluated the impact on thermal performance under different feed water temperatures and PCM concentrations using numerical methods. From the parametric study, we found that the feed water temperature, in comparison to the PCM concentration, is the dominant factor influencing cooling power and the final radiant surface temperature of the wall module. During charging, these two factors impact the time constant τ 95 much more than τ 63. Comparing the time required for the wall surface to reach the set reference temperature of 23 C ∘ during discharging, it takes 2.37 times longer in the 30% PCM scenario than in the scenario without PCM when the feed water temperature is 5 C ∘. If the feed water temperature increases to 10 and 15 C ∘ , this factor changes to 1.88 and 0.59, respectively. Taken together, the results were intended to optimize the design and definition of the PCM-RCS configuration for various usage scenarios. • A novel active cooling wall module prototype embedded with MPCM is constructed. • A numerical model is developed in COMSOL Multiphysics and verified. • The impact of feed water temperature and PCM concentration is investigated. • The findings offer insights for optimizing design by balancing different performance criteria. • The results serve as a basis for refining the design by considering application scenarios. [ABSTRACT FROM AUTHOR]

• Novel flexible heat pump integrating heat storage with new defrosting mechanism. • Uninterrupted heating and constant capacity during the defrosting process. • Optimization of the storage temperature to maximize COP improvement. • Impact of defrosting time was investigated. • Up to 13.2% of COP improvement compared to a baseline heat pump with R1234yf. There has been growing interest in using air-source heat pumps as an alternative to potentially replace fossil-fuel-based heating technologies for heat decarbonisation. One of the technical issues that hinders the wide uptake of air source heat pumps is the decreasing energy efficiency caused by frequent defrosting operations under low ambient temperatures. Currently, the most widely used defrosting method is the reverse-cycle defrosting but this operation would have to interrupt the heating supply during the defrosting process. The authors recently proposed, developed, and demonstrated a flexible heat pump concept that recovers partial of the subcooled heat from the hot refrigerant exiting the condenser and stores it in an integrated thermal storage. The stored heat could later be used to save compressor power and defrosting applications. In this paper, we proposed an innovative method by using a multi-valve design of the flexible heat pump to achieve the defrosting function. In this new concept, defrosting is achieved by condensing the refrigerant inside the evaporator and simultaneously ensuring uninterrupted heating during the heat storage discharge process. A model has been established to study the heat pump performance during a full charge/discharge cycle of the storage. Results indicated that with R410a, R134a and R1234yf, the proposed flexible heat pump has the potential to respectively save up to 11.2%, 10.8% and 13.2% of compressor power, in comparison with a heat pump using the conventional reverse cycle defrosting method. Concurrently with the defrosting operation, the same heating capacity is ensured without interruption by the flexible heat pump. [ABSTRACT FROM AUTHOR]

[Display omitted] • A comprehensive review of GSHPs for cold climate applications is presented. • A systematic methodology to classify and evaluate various ground heat exchanger designs. • Critical analysis of GSHP performance improvement using solar thermal energy and thermal storage systems. • Review of control and optimization strategies for heat pumps in cold climates. Increasing concerns over anthropogenically-induced climate change are driving the search for alternative, renewable, clean technology to generate energy. Heat pumps are an efficient means of transitioning towards renewable energy sources for space heating, space cooling, and water heating in buildings. The common types of heat pumps are air source heat pumps, which use the ambient air as the energy source and sink, and ground source heat pumps (GSHPs), which use the more stable ground temperatures as the source and sink. In cold climates, the performance of both systems may be compromised, demanding careful design, optimization, and enhancement. GSHPs have the most excellent potential in cold climates where heating loads are significantly higher than cooling loads owing to their use of the more stable ground temperatures. Therefore, this paper provides a comprehensive review of GSHP systems for cold climates, beginning by first introducing the GSHP technology, including a summary of geothermal system classifications and a review of global GSHP systems and their applications. This is followed by an overview of closed-loop systems, including different configurations of ground heat exchangers, and a look at recent innovations in the design of GSHPs. Moreover, studies on the design and performance improvements of open-loop systems are discussed. As a means of improving system performance in cold climates, this paper presents a review of hybrid systems developed by several researchers. Additionally, insights on using GSHP systems for district heating and incorporating thermal storage systems to improve overall system performance are examined. Finally, the control and optimization strategies, as well as economic feasibility and environmental impacts, are reviewed. This study shows the potential to reduce thermal interference radius, thermal imbalance and the length of the heat exchanger when using GSHP systems with latent thermal storage systems and solar recharging. Nonetheless, a need remains for more robust and accurate dynamic prediction models for hybrid heating systems with GSHPs to assess long-term performance and cost-effectiveness. [ABSTRACT FROM AUTHOR]

[Display omitted] • The methodological and characterization foundation for climate shelters is established. • The modelling of climate shelter variables is achieved by experimentation with a public transport stop. • The impact of the shelter is quantified by energy and electrical variables and the COMFA index. • The climate shelter guarantees an average surface temperature of 22 °C along a heat wave of 7 days. • 90% of the time tested in the summer of 2023 showed that the occupant's comfort level was acceptable. Climate change intensifies urban uninhabitability due to increasingly frequent heat waves. To alleviate it, climatic shelters emerge as an initiative for the research community, which should deepen the integration of technologies that use natural resources for cooling. This work aims to evaluate a novel climatic shelter by characterizing its thermal behavior through an experimental study at a bus stop. It has the capacity to alleviate the thermal stress of its occupants thanks to cooling modules. The results allow to determine the capacity of the natural water-cooling system and the level of thermal storage, allowing to quantify the impact on the citizen by means of the COMFA comfort index. It is corroborated that the chilled water temperature reduces the surface temperature by 15 °C. The installation reduces overheating caused by solar radiation by 75 % compared to traditional shelters. It also demonstrates energy and electrical self-sufficiency even during high intensity heat waves. The shelter maintains daytime water temperature between 18 and 25 °C, even in heat waves exceeding 7 days and 45 °C air temperature. The COMFA index has been reduced to values between 70 and 120 W/m2 in 90 % of the worst weather conditions in Csa climates by Köppen Geiger, for the months of July and August 2023. [ABSTRACT FROM AUTHOR]

• Aging of the envelopes of historic building causes excessive energy consumption. • Retrofit technique which preserving the value of a historic building was presented. • Retrofit replaces interior finishing materials with thermal storage materials. • Annual heating and cooling energy consumption reduced by 31–42% after retrofit. • Application of retrofit offers not only energy efficiency but also economic benefits. To utilize historic buildings sustainably, the energy performance of the building must be improved through retrofit. To preserve the historical value of the target building, the range of the retrofit was limited to the indoor part, and the retrofit was implemented via simulation. Aged interior gypsum finishing materials were replaced with gypsum composites with high thermal storage and insulation performance. In this study, scenarios in which composite materials were applied to walls and scenarios in which composite materials were applied to walls, ceilings, and roofs were presented. Additionally, by comparing energy usage and estimated energy consumption, an error rate of 13.06% was derived, proving the reliability of the simulation program. As a result of analyzing energy consumption by applying the scenario to the building, approximately 20–30% of energy was saved compared with before retrofit. To evaluate the economic feasibility of the scenario, it was compared with cases in which other finishing materials were applied, and it was confirmed that the scenarios were economically efficient. This study proves that building energy can be reduced by replacing interior finishing materials with composites and that historic campus buildings can be used continuously. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive simulation suite for a residential heating and cooling system that combines a vapor-compression system (VCS) with a water-based thermal energy storage (TES) using a three-fluid heat exchanger (TriCoil™). The VCS configuration includes the TriCoil™ as the indoor coil, a fin-and-tube heat exchanger as the outdoor coil, a variable-speed compressor, and an isenthalpic expansion device. To minimize computational cost for annual simulations, an artificial neural network (ANN) was employed to develop a data-driven model for the TriCoil™. The suite integrates models of the VCS, TES, and control systems, factoring in utility rates, building load profiles, and weather data. Validation against experimental data demonstrated accurate predictions, with TES temperature profiles having a root mean square error of 0.3 K and VCS heating capacity predictions showing mean absolute errors of 4.3% for the R410A side, 5.0% for the water side, 4.9% for the air side, and 4.3% for the air-sensible side. Simulations for a cooling season in Stillwater, OK, demonstrated significant electricity cost reductions by shifting cooling loads from peak to off-peak hours. The proposed system minimizes expenses using time-of-use rates and optimized load scheduling, showcasing substantial benefits even with a small TES unit. [ABSTRACT FROM AUTHOR]

• Model Predictive Control (MPC) technique implemented in C++ using OR-Tools engine for the energy consumption optimization of residential buildings. • RC grey-box model developed for a 20-dwellings building which incorporates an external radiant heating wall. • Testing the MPC operation in 64 scenarios including weather conditions, occupancy behaviour and optimization criteria. • Optimization criteria comparison: energy, cost, emissions reduction; self-consumption increase. This study presents an optimization algorithm for Model Predictive Control (MPC) of the HVAC systems in multi-family residential buildings assessing the performance of four objective functions. Implemented in C++, using the free OR-Tools optimization library, the model is formulated a Mixed Integer-Linear Programming (MILP) problem. The study analyses the results of tests conducted on a 20-dwelling block in Switzerland across various weather and occupancy conditions, resulting in a parametric study of 64 cases. The models developed for the MPC are Grey-box type for the interconnected energy systems: the building, thermal storage tanks, a heat pump, the ventilation system and PV collectors, highlighting a radiant wall heating system integrated into the building facade. The tanks and the heat pump models were informed with manufacturer data, while for the building a R3C3 thermal-electrical equivalent model was developed, calibrated using TRNSYS simulations with a root mean square error of 1.7%. Findings demonstrate how the algorithm optimizes the operation according to the desired criteria, while ensuring indoor comfort with a 15-minute time resolution. The time execution of the majority of cases is under 3 min in a low-specs computer, affirming its practical viability for real-world implementation. [ABSTRACT FROM AUTHOR]

[Display omitted] • A controller-less PV heating system based on building envelope thermal storage was proposed. • The building envelope was designed to act as a heating terminal and heat storage. • The matching of supply and demand in PV heating systems was improved by 77%. • The PV system is economical and has a payback period of 6.5 years. Low-carbon heating in farmhouses can be achieved using photovoltaic (PV) heating. However, the severe mismatch between the PV energy supply and the building thermal load requires expensive energy storage devices and control systems. In this study, a controller-less PV heating system utilizing the building envelope for thermal storage was evaluated on a farmhouse in northern China. The building envelope simultaneously functions as the heating terminal and is composed of insulation boards, electric heating wires, and the thermal storage wall. PV electricity is fed to be absorbed by the electric heating wire to produce heat. The thermal storage wall absorbs the heat generated by the heating wire before releasing it into the room through convection and radiation. Long-term monitoring reveals that the black bulb temperature of the farmhouse was above 16 °C for more than 60 % of the time throughout the heating season. The building envelope acting as a thermal reserve improved system supply and demand matching by 77 % and the indoor temperature fluctuation was reduced by about 47 %. The thermal storage wall can provide 58 % of the heating energy when there is no PV power supply. The payback period of the heating system is only 6.5 years, verifying the good rate of return of the system. This study proposes a lower cost energy storage solution for PV heating than previous studies, and engages the building envelope into the building energy system. [ABSTRACT FROM AUTHOR]

• Compact latent heat storage assessment for domestic heat pump applications. • PCM-based system stores 30% more energy than an equivalent-sized water tank. • PCM-based system achieves 94% of efficiency under specific conditions. • PCM-based system demonstrated satisfactory integrity over 100 cycles. • Optimal thermal energy storage sizing, with an attractive ROI. Thermal energy storage devices are still scarce in the building sector, however with the increasing deployment of renewable energy sources a significant growth is expected in the following years. The ability of decoupling the energy supply from the demand turns thermal energy storage systems in attractive assets, since they allow to get benefit from periods of low electricity tariffs and their cost is much lower than batteries. Thermal energy storage systems based on phase change materials are the current focus of the scientific community due to their high energy storage density. Nevertheless, their performance must be still improved without penalising the cost to become a commercial interesting solution. In this paper a novel approach for the building sector is experimentally studied, consisting in a water tank filled with organic PCM encapsulated in a flash-like HDPE enclosure. The energy storage capacity of the system was multiplied by three, providing good performance at a reasonable cost. To evaluate the performance, 89 PCM modules were included in an 8.3 L water tank and subjected to thermal charging and discharging cycles, measuring their power response and stability. In addition, a system dynamic model was developed based on a real building scenario so that the design and cost analysis of a full-scale system can be assessed. [ABSTRACT FROM AUTHOR]

With the development of energy efficient technologies for glass envelopes, using thermal storage techniques to improve their thermal inertia has become a trend in research. In the present study, the heat transfer and day-lighting models of a building with PCM glazing curtain wall (PGC) were developed. Multiple parameters such as glazing internal surface temperature, PCM liquid phase rate, indoor temperature, natural illumination, and daylighting coefficient were quantitatively analyzed to evaluate their indoor thermal environment and daylighting performance. The results show that the application of PGC can significantly improve indoor temperature uniformity and indoor thermal comfort compared to silica aerogel glass curtain wall (SGC) and hollow glass curtain wall (HGC). By filling 10 mm thick PCM, the temperature fluctuation of the inner surface of the glass and the midpoint temperature of the room can be reduced by 35 %, the peak temperature of the inner surface of the glass can be delayed by 0.89 h, and the average indoor natural light value and indoor daylight factor are satisfactory at 453.26 lx and 9.63 %, respectively. However, as the thickness of the PCM increases to 15 and 20 mm, the liquid fraction of the PCM and the energy storage performance of the PGC are greatly reduced, and natural daylighting does not meet the GB/t-50033-2013 limit. [ABSTRACT FROM AUTHOR]

• A ternary CPCM with 2 phase change temperatures in building walls is proposed. • The novel ternary CPCM has stable property, high latent heat, and low price. • The ternary CPCM wall has a longer delay time and is less affected by environment. • CA/C18-TD (2:8) is demonstrated as the most suitable CPCM for building walls. • Building walls with ternary CPCM can satisfy the seasonal thermal energy storage. This paper introduces a ternary composite phase change material (CPCM) comprising three phase change materials, with a eutectic mixture as the low phase change temperature (PCT) component. The thermal performance and stability of the CPCM are rigorously evaluated through simulations and experiments including step cooling curves, differential scanning calorimetry (DSC), thermal cycling, and Fourier-transform infrared (FTIR) spectroscopy. The ternary CPCM CA/C18-TD (2.0:8.0) exhibits superior latent heat storage—224.53 J/g compared to 143.83 J/g for the binary CA-TD (3.0:7.0)—and maintains stability without supercooling after 300 thermal cycles. It also proves cost-effective compared to its components. In building applications, walls integrated with the CPCM CA/C18-TD (2.0:8.0) exhibited significantly enhanced thermal regulation properties, including longer thermal delay times and reduced attenuation factors across both winter and summer conditions. Specifically, the CPCM wall reduced temperature fluctuations by up to 31.91 % in comparison to ordinary wall and 21.63 % against single PCM wall in winter, 54.51 % and 44.22 % lower than the ordinary and single PCM walls respectively in summer. These walls also showed a remarkable reduction in heat flow density by up to 17.49 W/m2 and 5.41 W/m2 compared to ordinary wall under summer and winter conditions, respectively. This means that the CPCM has superior insulation performance and reduces susceptibility to external environmental changes. These findings confirm CA/C18-TD (2.0:8.0) as an optimal CPCM for seasonal thermal energy storage in energy-efficient PCM wall. [ABSTRACT FROM AUTHOR]

Medium-deep ground source heat pump (GSHP) systems have the advantages of low carbon, high heat exchange intensity, good thermal storage capacity, and intermittent operation characteristics, which are conducive to renewable energy consumption and grid demand response. The source-side parameters affect the configuration of underground borehole engineering, heat pump units, and other equipment. However, current research mainly focuses on the underground heat exchanger modeling, underground heat exchange, and system operation control, while there are few studies on multi-factor ground source-side parameter design and optimal configuration. In this study, the indicator analyzing the unsteady features and thermal balance state of medium-deep geothermal resources was introduced, and the source-side water temperatures were optimized based on the dynamic characteristics of the geothermal and building sides. A simulation configuration methodology for the source-side flow rate and storage capacity was developed considering the electricity prices, life-cycle cost (LCC), and grid interaction. The optimization of the ground source-side design temperature, flow rate, and capacity parameters of residential and office building heating scenarios were analyzed in northern China, respectively. The results showed that the borehole inlet and outlet temperature can be designed to 5.5 °C/17.5 °C under the annual sustainable state, and the optimal flowrate can be set to 65.77 m3/h, to achieve the lowest cost and highest heating season guarantee rate for the residential scenario. For the office building with optimal system and storage capacity, the average annual LCC is 192,000 yuan/year, with the cumulative peak shaving of 55.8 %, and an increase of 103.3MWh renewable electricity consumption. [ABSTRACT FROM AUTHOR]

[Display omitted] • Laser-engraving, make the wood with pretty patterns and sunlight absorption capacity. • Nano-silica reduces the leakage of PCM and improves the thermal conductivity. • Wood-based photothermal composite phase change materials regulate indoor temperature. • Wood-based photothermal composite phase change materials reduce energy consumption. Wood is used more and more in building. Phase change materials (PCM) with automatic temperature regulation and heat storage function have been widely concerned in the field of building energy conservation. However, phase-change materials have poor light induction and cannot absorb sunlight during the day in time, resulting in limited heat storage effect. For the purpose of achieving efficient energy collection and utilization, a laser-engraved method was employed in this study to directly generate a three-dimensional grid structure on the surface of wood. Then, the eutectic mixture of capric acid (CA) and stearic acid (SA) and nano-SiO 2 composite PCM (CPCM) was impregnated into the supporting substrate with photothermal conversion capability. The obtained laser-engraved wood (LEW) loaded with CA-SA/Nano-SiO 2 showed a latent heat of 64.706 J/g, a thermal conductivity of 0.732 W/(m⋅K) and a photothermal conversion efficiency of 64.46 %. Additionally, the three-dimensional porous structure of wood and the addition of nano-silica set up a double barrier for the leakage of PCM. Therefore, CPCM have prospective applications as indoor thermal insulation materials. In this research, a simple laser engraving method was adopted to endow the wooden substrate with photothermal conversion ability, which provides an idea to expand the application of photothermal conversion materials in the field of phase-change energy storage. In addition, the building simulation software validated the potential of CPCM in stabilizing indoor temperatures and reducing building energy consumption. [ABSTRACT FROM AUTHOR]

[Display omitted] There has been a notable surge in energy demand within the building sector of developing nations, particularly in the context of space cooling and heating, which constitute significant portions of energy consumption. The thermal performance of a building's roof slab plays a crucial role in determining these heating and cooling requirements. To address this, the utilization of Phase Change Material (PCM) to enhance the building's thermal energy storage capacity has emerged as an innovative strategy for reducing energy demand. This study assesses the thermal behavior of a building envelope integrated with macroencapsulated PCM in a real subtropical environment. Experimental setups include both a conventional slab unit (Ref–SU) devoid of PCM and a PCM (OM37) integrated slab unit (Exp–SU). Analysis entails examining variations in temperature, heat flow, thermal loadings, and maximum heat gain reduction. Economic metrics, such as electricity savings, simple payback periods, and CO 2 emissions savings, are also scrutinized. The investigation aims to elucidate the efficacy and underlying parameters governing the PCM's performance in reducing thermal loads in the Indian city of Rupnagar. Findings indicate that the Exp–SU configuration reduces indoor temperatures by 4.0 °C during sunny hours, resulting in 33.33 % more electricity savings for space cooling compared to heating, with a simple payback period of 5.7 years. Additionally, the heat flux in Exp–SU is reduced by 60.6 % compared to Ref–SU and thermal load by up to 49.8 %. Furthermore, Exp–SU achieves a 44.24 % reduction in CO 2 emissions for space cooling compared to heating with a maximum heat gain reduction of 40.3 %. [ABSTRACT FROM AUTHOR]

• Sorption Thermal Energy Storage system is firstly proposed. • Feasibility study of four types of building cooling load is conducted. • 68.2 kWh/m3 of thermal energy is stored with 55 % charging capacity in hotel. • Hotel scenario showcases the most effective feasibility by meeting 78.1% of demand. In the proposed sorption thermal energy storage (STES) system, the thermal energy storage (TES) tanks are integrated with solar assisted-absorption chiller (AC) to perform extended operation while matching the incompatibility of time gap between the renewable energy heat source and cooling demand of the building. In this study, the operating characteristics of sorption thermal battery (STB) at discharging process and storage capacity of STES charging process are studied. The feasibility study is conducted for four different types of buildings (hotel, hospital, single-family house, and office) to investigate the optimized discharging cooling capacity of STB and the optimized TES ratio. Under the condition of the 200 kWh of the building cooling load and cooling area of 181.63 m2, the most effectively meeting the demand is shown in the hotel, in which STES responds to 78.1 % of the cooling demand with 7.5 kW discharging cooling capacity of STB and 55 % charging the storage capacity of the STES system. The optimum energy storage density is 68.2 kWh/m3 and coefficient of performance is estimated of 0.41. The optimized STES can meet the cooling demand as much as 67.4 % for the hospital and 26.9 % for the single-family house. The office doesn't require to apply the STES due to the absence of the cooling load at discharging period. [ABSTRACT FROM AUTHOR]

• The price-responsive flexible behaviour of an office building is studied. • The price signals convey changes in temperature setpoints, offering flexible demand. • A step-by-step approach for utilising flexibility in a building is proposed. • The study shows flexibility availability is dependent upon HVAC operational modes. • Demand increases notably for prices ≤ 10 % of the highest value. Flexibility in buildings is a low-cost alternative to support the electricity network with high penetration of variable generation. There is a limited understanding of energy flexible behaviour of the buildings in response to electricity market signals. In this paper, the price-responsive flexible behaviour of a commercial building with a cooling system has been studied. A first-order virtual battery model of the building and flexibility function-based approach have been used to understand the flexible behaviour of the building to varying price signals. The price signals delivered changes in building electricity demand profile, altering cooling temperature set points. The building structural thermal storage capacity was found to vary depending on demand changes. Low price signals provoke positive demand changes with respect to the baseline demand, taking the system to charging mode. Similarly, high price signals lead the system to discharging mode, reducing the instantaneous charging condition of the system. HVAC operating states, e.g., free cooling/economiser cooling and mechanical cooling, have been found to have a notable impact on electricity demand flexibility. The flexibility function shows that for a very low-price value, the cooling setpoint approaches the lowest comfort bound, and demand increases significantly. A deviation between the maximum and minimum electricity demand of 207 kW for the studied building system gives an estimated maximum energy flexibility capacity of 7248.2 kWh. The response of the building to variable price signals yields flexible demand, delivering cost savings of 13 %. [ABSTRACT FROM AUTHOR]

The increasing demand for electricity stresses the existing electric grids. Buildings consume 73% of all U.S. electricity and are responsible for 30% of U.S. greenhouse gas emissions. Integrating thermal energy storage (TES) in building heating/cooling systems, which consume considerable electricity, can mitigate the challenges to electric grids. This study reports on a novel thermal energy storage device integrated heat pump system to reshape the building electricity demand profile while maintaining thermal comfort. The annual performance of the proposed system has been evaluated through a dynamic system simulation with high fidelity in the Modelica platform. The dynamic model of the novel hybrid component named 'dual purpose underground thermal battery' was developed and validated. It was then incorporated into the system model. Given a time-of-use tariff, a rule-based control strategy was designed to shift the electric demand and switch the heat pump source for a typical single-family house in different climate zones of the United States. The system performance of the new TES-integrated dual-source heat pump was compared with that of a conventional air-source heat pump system. The results indicate that the proposed system can reduce the annual HVAC electricity cost by up to 52% while saving 45.2% on electricity consumption. In the Northern areas, the annual peak load of the HVAC system can be reduced by 64.9%. However, this reduction is less in the Southern areas as the system's higher efficiency in winter dominates the overall energy-saving potential. [ABSTRACT FROM AUTHOR]

The integration of Phase Change Materials (PCMs) in building envelopes has gained significant attention in recent years as a promising solution for thermal energy storage. PCM technology utilizes the latent heat of a material to store and release large amounts of energy, making it an effective method for passive thermal regulation and stabilization of the indoor building temperatures. However, to fully exploit the potential of the PCM, it must be completely charged and discharged in each cycle. With this fact in mind, this work aims to assess the performance of the PCMs in Moroccan climate zones, as well as to find out the best combination of PCM and natural ventilation to enhance the overall cooling energy performance of buildings. To this end, a numerical investigation was conducted in a residential building located in six climate regions of Morocco. The EnergyPlus software with the integrated PCM hysteresis model was used. Firstly, the effect of the PCM phase change temperature throughout the year was evaluated considering six cities located in those climates. Subsequently, an analysis was conducted during the summer season, resulting in the identification of the optimal configuration regarding PCM phase change temperature and thickness for each city. Furthermore, various natural ventilation scenarios i.e. night and whole-day natural ventilation, were implemented to investigate their impact on the process of PCM charge–discharge cycle. The results reveal that the integration of natural ventilation in PCM-enhanced building was an effective method that solidifies the PCM every required cycle. The integration of PCM with night natural ventilation (NNV) leads to improve the PCM activation by between 22.4% and 26.1%, in the warm and temperate Mediterranean climate. However, whole-day natural ventilation controlled (NVC) further decreases cooling energy consumption by 2–9% compared to NNV in all studied climates, making it the best combination. [ABSTRACT FROM AUTHOR]