To systematically investigate the issues of tunnel overheating and excessive humidity, this study integrates theoretical analysis, experimental research, and numerical simulations. It examines the coupled heat and moisture transfer behavior in the surrounding rock of metro tunnels and its impact on the tunnel’s thermal and humid environment. Based on the theory of heat and moisture transport in porous media, a coupled mathematical model is developed using relative humidity and temperature gradients as the driving potentials. Taking into account the climatic zoning of China, Beijing, Shanghai, Guangzhou, and Kunming are selected as representative cities for cold, hot summer/cold winter, hot summer/warm winter, and temperate climate regions, respectively. The interannual variation characteristics of the thermal and humidity conditions inside metro tunnels in these cities are analyzed and compared. The results indicate that across different climatic zones, higher outdoor peak air temperatures lead to higher peak air temperatures inside the tunnels. The thickness of the thermal regulation zone is primarily influenced by the initial rock temperature and the annual average atmospheric temperature. The thickness of the moisture regulation zone is affected by both the annual temperature fluctuation and the annual average relative humidity, increasing with greater annual atmospheric temperature variation.

Seasonal thermal energy storage (STES) technology addresses the summer-winter heat imbalance by storing surplus heat from warmer months for use in colder months, thereby improving the annual utilization efficiency of solar energy. To overcome the limitations of single-form storage and significant heat losses associated with conventional underground methods, this paper proposes a novel composite system that couples a water tank and boreholes in series, with water flowing from the tank to the boreholes to achieve cascade energy utilization. An unsteady numerical model, based on the finite volume method (FVM) and the finite difference method (FDM), was developed to analyze temperature variations, temperature field distributions, and charging/discharging characteristics. The results show that the composite system outperforms the tank-only system: its temperature rise difference ratio and temperature drop difference ratio reach up to 3.47 and 5.6 times those of the tank system, respectively. Owing to the thermal synergy between the water tank and the buried pipes, the composite system maintains a higher temperature zone near the tank sidewall during the insulation phase, approximately 24.90 degrees C, compared to only 16.77 degrees C in the tank system. During the recovery phase, the center temperature of the composite system rebounds by about 2 degrees C while the boundary temperature decreases by 1.36 degrees C, outperforming the tank system's rebound of 1 degrees C and decrease of 0.68 degrees C. The composite system also exhibits superior energy performance, achieving 4.37 MWh more cumulative stored heat and 18.52 MWh more discharged heat than the tank system, corresponding to increases of 2% and 8%, respectively. Furthermore, the storage efficiency of the composite system reaches 61%, which is 4 percentage points higher than that of the tank system (57%). A heat loss analysis of the composite system identifies the top boundary as the main heat loss path, accounting for 72% of the total loss, while the side boundaries contribute 76% of the heat absorbed from the surrounding soil during the discharging and subsequent recovery phases.

Semi-transparent photovoltaic (PV) windows can simultaneously generate electricity and significantly reshape building cooling and heating loads. Although their energy performance has been widely investigated, the influence of weather uncertainty on the coupled power-load behavior of PV-window-integrated buildings remains poorly understood, and dedicated quantitative indicators for characterizing such coupling are still lacking. Against the backdrop of climate warming and increasingly complex, non-stationary meteorological conditions, understanding weather-uncertainty-induced source-load interactions is essential for the robust design and operation of building energy systems. To bridge this gap, this study develops a weather-uncertainty modeling framework and proposes two novel indicators to quantitatively evaluate power-load uncertainty and balance in buildings equipped with semi-transparent PV windows. Furthermore, the proposed approach is applied to multiple representative climate zones in China to systematically analyze power-load uncertainty characteristics and matching performance under diverse climatic and solar conditions. Results show that the weather uncertainty method proposed in this study is effective. The semi-transparent PV windows can reduce cooling load uncertainty by 2.46% - 61.73% and the magnitude by 12.05%- 75.06%. However, heating load uncertainty and magnitude may increase by 3.25% - 21.09% and 9.04% - 13.72%, respectively. Additionally, the probability that semi-transparent windows have a positive impact on the power-load balance ranges from 25.0% to 62.5%, primarily by reducing total building loads and increasing PV output. These findings contribute quantitative evidence and methodological insights to the uncertainty-aware evaluation and application of semi-transparent photovoltaic windows.

This study developed a form-stable wood-based phase change material (FWPCM) via double cross-linking esterification (DCLE) to prevent PCM leakage and volume expansion. The mixture of polyethylene glycol (PEG) as a PCM and 1,2,3,4-butane tetracarboxylic acid (BTCA) as a cross-linking agent was vacuum-impregnated into delignified wood. Lignin removal was carried out using traditional alkali treatment (Na2SO3/NaOH) and deep eutectic solvent (DES) treatment, with the former removing most lignin and hemicellulose from the wood. The comparison revealed that DES-delignified wood (DW) avoids chemical hydrolysis of cellulose, effectively preserving the lignocellulosic skeleton. The exposed hydroxyl groups in cellulose promoted DCLE, which was confirmed by FTIR and XPS. A small amount of BTCA was added to create ester bonds with cellulose to stabilize PEG in the DW, resulting in the FWPCM that demonstrated excellent leakage resistance and a higher encapsulation rate of 84.75 %. The phase change exhibited a maximum enthalpy of 150.1 J & sdot;g-1 at 58.5 degrees C. FWPCM showed anisotropic heat transfer characteristic (radial 0.14 W/(m & sdot;K), longitudinal 0.19 W/ (m & sdot;K)), high thermal stability (283 degrees C), and excellent cycling durability (200 cycles). This study provides a reliable, cost-effective and eco-friendly thermal energy storage material for building energy conservation.

Skin temperature is a critical parameter for human health and comfort. Existing data-driven models typically use either mean temperatures or local-node temperatures as whole-body or regional indicators, neglecting node intercorrelations. This study proposes a 10-node model that takes into account the intercorrelations among multiple nodes. By combining the time-frequency information of the maximal overlap discrete wavelet transform (MODWT) and the spatial information of the graph attention network (GAT), the model identifies the dynamic thermal responses among multiple nodes in different environments and characterizes the intercorrelations between nodes through feature weights. To evaluate the model's performance in complex scenarios, validation was conducted on six environmental cases (air temperatures: 31 ' C, 34 ' C, and 37 ' C; pressures: 65.7 and 96.5 kPa). The results show that the model achieves an average recognition accuracy of 93.18%. This study reveals the intercorrelations of multi-nodes, providing a valuable research direction for monitoring and evaluating skin temperature.

Global warming has intensified extreme weather events, significantly impacting the design and operation of building energy systems. In China, such extreme weather presents substantial challenges to the performance of building energy systems, particularly for rapidly developing public buildings like high-speed railway stations (HSRS). The heating and cooling systems in HSRS buildings have faced increasing strain due to these extreme weather events. This study proposes a novel method for generating extreme meteorological years (XMY). It examines the impact of climate change on XMY generation using ECMWF Reanalysis v5 (ERA5) meteorological reanalysis data. The influence of XMY on the cooling and heating loads of three typical HSRS buildings in China is also assessed. The results indicate that climate change has led to a continuous increase in the average annual temperature of XMY. The XMY derived from distant historical weather data no longer accurately reflects the impacts of climate change. Specifically, compared to typical meteorological years (TMY), the effects of XMY on peak load in the three typical HSRS range from-20 % to 20 %, with extreme high weather increasing peak cooling load by approximately 10.00 %. The effect of extreme weather on the annual total load of most HSRS ranges from-13.00 % to 14.00 %, with extreme high weather causing a maximum increase of 9.00 % in the yearly total load. Therefore, the impact of XMY should be considered in the design of the HSRS energy system, and the system capacity should be appropriately increased.

Photothermal conversion phase-change materials (PCPCMs) effectively harvest and store solar thermal energy but suffer from high radiative losses due to their intrinsic infrared emissivity. Here, we report a bidirectional thermal regulation approach integrating spectrally selective low-infrared-emissivity surfaces with directional thermal transport channels to address this issue. This design achieves a mid-infrared emissivity of 0.34 on the surface and a 65% enhancement in internal heat transfer while maintaining enthalpy with negligible reduction. A photothermal physical model with a cutoff wavelength accurately quantifies the convective and radiative losses induced by the hot mirror. The results reveal that the heat dissipation pathway shifts from radiation dominated to convection dominated, leading to a 76% reduction in radiative loss and a 27% improvement in photothermal conversion efficiency. This work decouples optical absorption from thermal emission, providing an efficient and generalizable route for high-performance solar thermal energy harvesting and storage systems.

The two-phase closed thermosyphon (TPCT), an efficient heat transfer device, relies on the phase change of the working fluid. The distribution of the working fluid, which significantly affects the heat transfer mechanism, is influenced by the filling ratio (FR) along with other factors such as input power and geometry. Under certain conditions, the liquid pool height when the TPCT operates stably can typically be categorized into three scenarios: the liquid pool below the evaporator (often at low FRs), exceeding the evaporator (regular FRs), or reaching the condenser (high FRs). Previous research has shown that under low FRs, heat transfer deterioration occurs in the evaporator wall of TPCT. However, the existing literature has not fully elucidated the boiling mechanism underlying this phenomenon. In this paper, an improved CFD model of the TPCT was established to effectively simulate the flow and boiling process of liquid film in the evaporator section. The calculated data exhibited good consistency with experimental results, with a maximum relative error of 1.43 %. It was observed that the liquid film displays a wave-like pattern, which is attributed to the balance of gravity, surface tension, shear force, and buoyancy force when the TPCT is stable. As wall height decreases, there is an increase in amplitude for liquid film fluctuation above the evaporator wall height. Bubbles generated on the evaporator wall leads to an increase in the frequency of liquid film fluctuation and causes the liquid film to rupture. At low FRs, the distribution of liquid films in the evaporator generally can be distinguished into three scenarios: continuous liquid film, discontinuous liquid film, and dry-out areas. When the heating input is 232.89 W, the overall thermal resistance of methanol-TPCT with a 35 % FR decreased by 33.2 % compared to a 15 % FR, and only increased by 0.4 % compared to a 70 % FR. According to the findings in this paper, a proper FR of the TPCT can be employed for a given heating input, ensuring exceptional heat transfer performance and reducing the quantity of working fluid utilized.

The study of heat storage performance in the surrounding rock and heat transfer between it and the air within the subway tunnel was of significance to the thermal environment. However, most researches ignored the impact of humidity. In this study, a mathematical model coupled heat and moisture transfer was established considering the piston wind. The interannual variation of moisture and heat transfer was explored under the influence of periodic fluctuations. Simultaneously, the characteristics of moisture and heat reservoirs across various regions were analyzed. It has been revealed that the coupled moisture and heat transfer in surrounding rock influenced by the piston winds, which plays an important role in the subway tunnels. The moisture flux on the wall surface increased by 1.6 times when the piston effect was taken into account, and the heat flux increased by 1.15 times. The consideration of heat and moisture coupling lead to a 17% expansion of the surrounding rock's heat circle in 30 days and a 19.3% expansion in 365 days, respectively. Under the boundary condition of cyclic fluctuating temperature and relative humidity, the temperature and moisture of the rock in the interval tunnels exhibited interannual fluctuations, and then reached a state of dynamic equilibrium.

The temperature and humidity in tunnel should be controlled within standard range during operational transition time. Auxiliary galleries left by multi-face construction can provide channels for sectional natural ventilation to control temperature/humidity during operational transition period. Therefore, this paper concentrates on the feasibility of sectional natural ventilation on thermal/humidity control of a case high-geothermal tunnel during operational transition period. Firstly, the unique features of typical high-geothermal tunnels have been discussed, and an improved integrated model has been put forward to adapt to these features. According to calculation results, strong dynamic relations among temperature, heat pressure and natural ventilation velocity are discussed. In the further case studies, 4 programs are divided by the number of opening ventilation transverse tunnels, which are the specific construction auxiliary galleries of case tunnel. The results show that Program 3 (open transverse tunnel 1&2) is the best choice. Furthermore, this paper provides the feasibility of natural ventilation under various insulation thicknesses and operational transition time. The results shown that 10 conditions are feasible among the total 36 conditions with only natural ventilation.

Thermoelectric coolers (TECs) are expected to be utilized in personal thermal management applications due to their environmental friendliness, noise-free operation, lightweight design, and fast response time. However, the cooling efficiency of TECs heavily relies on the heat sinks of the hot side, which are typically rigid and bulky, causing them unsuitable for wearable devices. To address this issue, this work developed a phase change flexible heatsink utilizing copper foam as the framework and a ternary composite phase change material as the filler, exhibiting a high thermal conductivity of 4.92 W/(m & sdot;K) and latent heat of 139.64 J/g. A phase change composite-enabled TEC with excellent flexibility (bending radius of 15 mm) is thus successfully prepared. It can achieve a stable temperature drop of 17 degrees C over 6 h. An intelligent temperature-controlled headband has also been designed by integrating with a wireless communication module for precise temperature regulation via a mobile phone app interface. This headband ensures optimal comfort by maintaining forehead temperature around 32 degrees C even when ambient temperatures present large fluctuate. The temperature-controlled headband could be applied to emergency medicine settings, healthcare facilities, and outdoor sports activities.

The rapid expansion of mid-deep geothermal energy and underground thermal storage faces significant challenges due to the variability in geological conditions. The impact of fracture morphology on thermal storage and heat transfer has become a critical area of research, driven by the lack of comprehensive characterizations of the heat exchange processes within these systems. This research examines the heat transfer characteristics and effective thermal conductivity (ETC) of a 3-D water-rock fracture structure. Firstly, the convective heat transfer coefficient (h) at fracture surfaces within the 70-100 degrees C range is compared and selected for accuracy. Secondly, the coupled flow and heat transfer processes of water and rock in a 3-D rough fracture are quantified under varying amplitude factors (Amn). Finally, the ETC at different Amn ranges is quantitatively characterized. The study reveals that with Amn escalating from 0.01 to 0.035, the effective heat exchange area within the fracture increases by 22.73 %. Concurrently, the normalized velocity (UN) exhibits a non-linear rise of 67.64 %, escalating from 2.2 to 6.8. Afterwards the selection of proper calculation formulas for h in water-rock systems, the correlation between ETC and h is considered. It is found that ETC positively correlates with Amn, increasing by 83.33 % with rising Amn. Finally, An empirical model to describe ETC in fracture structures is proposed, contributing to the understanding of fluid flow and heat transfer in fractured rocks at high temperatures and enriching the theory for mid-deep geothermal energy exploitation.

Thermochemical adsorption systems can store significant amounts of energy. To study the heat storage characteristics of open thermochemical adsorption systems, a system was developed with a focus on solar energy applications. A novel cartridge reactor filled with 24 L of vermiculite/CaCl2 composite adsorbent was designed. Key parameters influencing heat storage and release performance were experimentally investigated. The results show that the optimal salt content to prevent solution leakage is 56.6 %. Under complete material regeneration, the reactor can continuously supply hot air above 30 degrees C for nine hours, delivering 6254.9 kJ of energy. The system achieves an energy utilization efficiency of 91.2 % and an energy storage density of 0.691 kWh/kg. The desorption temperature significantly impacts the adsorbent's exothermic performance. Even at a low desorption temperature of 60 degrees C, the system achieves a maximum temperature rise of 15.1 degrees C. During energy release, air relative humidity is a critical factor affecting output temperature and power. Increasing the air flow rate accelerates adsorption without reducing outlet air temperature, enabling higher output power.

Solar photovoltaic photothermal (PV/T) technology is capable of simultaneously generating electricity and providing thermal energy, which can significantly improve the comprehensive utilization of solar energy and can cool photovoltaic cells to improve electrical efficiency. This paper aims to study an innovative loop heat pipe based PV/T system for application in different solar resource conditions in China including annual operational performance and economic benefits. This specific system applied PV-bound flat copper tubes array as PV/ evaporator and a top-supply-top-return loop heat pipe configuration, which could enhance the temperature uniformity across the PV panel and the efficiencies of solar energy utilization. A verified computational dynamic model was developed to analyze the system annual operational performance in various solar resource regions represented by Garze, Beijing, Guangzhou, Chengdu. Further a life-cycle analytical model was developed to evaluate the economic and environmental benefits of this novel system compared to the traditional ones. The results show that the average annual electrical efficiencies of the system are nearly the same in different regions, which were 17 %, 17 %, 16.8 %, and 17.6 % respectively. While the average annual overall efficiencies are 59.5 %, 58.9 %, 54.1 %, and 53 %, respectively. In Garze, Beijing, and Guangzhou, the system's power generation not only meets the demand for heating hot water but also has a surplus. Compared to electric water heaters, the system's lifecycle CO2 reduction is the most significant in Beijing when operated in four regions. The system payback periods were 5.63, 7.46, 8.52, and 12 years, and the life-cycle net benefits were 7659 CNY, 5241 CNY, 4315.5 CNY, and 2423.2 CNY, respectively.

Although temperature/humidity of high-geothermal tunnels reduces with construction, high-temperature and high-humidity problem are still severe after tunnel through for partial tunnels, which cannot meet the requirement of traffic operation. The period from tunnel through to formal traffic operation (operational transition period) could be utilized to control temperature/humidity, where the fans already installed could be turned on for mechanical ventilation. The natural ventilation of sloping high-geothermal tunnels is strong, which could be applied to strengthen mechanical ventilation. Therefore, achieving temperature/humidity control by utilizing natural-mechanical ventilation during operational transition period is a valid method of safety, simpleness and low-cost. However, in most previous studies, operational transition period was not investigated for temperature/humidity control; hence natural-mechanical ventilation coupled mechanism and design method of the number of opening fans (N_open) among installed fans (N_install) were missing. To solve problems above, this paper concentrates on natural-mechanical coupled mechanism and design method of N_open during operational transition period. Numerical simulation and theoretical analysis are adopted. Results show that temperature/humidity control during operational transition period is feasible, and temperature control demand is more urgent than humidity control. In case tunnel, 19 conditions should consider mechanical ventilation among the total 36 conditions. For natural-mechanical coupled ventilation, natural ventilation mainly takes positive effects, and the maximum positive ratio reaches 63.17%. Sensitivity analysis proves that the number/position of opening jet fans, insulation thickness and operational transition time all perform obvious impact on temperature/ humidity distribution. However, insulation thickness and operational transition time could not be defined as design parameters during operational transition period. Therefore, design of N_open for case tunnel are provided under various insulation thickness and operational transition time. Based on case analysis, universal design method of N_open during operational transition period has been proposed.

Although two-phase closed thermosyphons (TPCTs) with low surface tension fluids are increasingly being applied in various fields, existing studies mainly focus on TPCTs with water as the working fluid under different wettability, and there is a lack of research on the condensation dynamics of low surface tension fluids in TPCTs under varying wettability. This paper addresses this gap by presenting a novel CFD model that integrates a dynamic condensation mass transfer time relaxation parameter into the Lee model and couples it with the contact angle model. The results indicate that the numerical model is more accurate in simulating the formation of a liquid film when the liquid phase is set for the primary phase and the density model of the vapor phase is used as an incompressible ideal gas. When low surface tension working fluids, such as methanol and ethanol, are used in TPCTs, the size of bubbles and boiling intensity in the evaporator are lower compared to when water is used as the working fluid. Surface tension and gravity induce the formation of a fluctuating condensate film on the condenser of a methanol-TPCT. The liquid film in the condenser of the ethanol-TPCT is approximately 1.5 times thicker than that of the methanol-TPCT. As the contact angle increases, the thickness of the liquid film on the wall decreases, leading to the phenomenon of temperature rise on the upper wall of the evaporator. These advancements provide a design tool for next-generation TPCTs in applications like data center cooling and hyperloop systems.

Tunnels in high geothermal and water-rich areas usually encounter thermal damage and water seepage problems during the tunnel construction period.Understanding the interaction between seepage and heat transfer in the surrounding rock of the tunnel is an important prerequisite for safe tunnel construction and environmental protection.This study established the tunnelling fractured rock models by using the discrete fracture network method and numerically explored the effects of geometric characteristics of fracture network and geological factors on the hydrothermal field of the rock.By designing orthogonal experiments and analyzing orthogonal cases,the changes of rock equivalent thermal conductivity(ETC) under the combined action of multiple factors were investigated.The priority of each influencing factor on ETC is in the following order:fracture inclination,fracture intensity,water temperature,water head,fracture roughness and fracture aperture.The weighted contribution rates of each factor to the ETC are 30.6%,24%,18.5%,15.5%,6% and 5.3%,respectively.Finally,a formula including all factors to determine the equivalent thermal conductivity was proposed.The results of this study can provide reference and guidance for quantifying surrounding rock heat transfer during the construction period of high geothermal tunnels.

The goal of this paper is to clarify the heat–moisture coupled regulation mechanism of deep-buried underground air tunnels and to address the research gaps in the heat–moisture coupled transfer between airflow and surrounding rock. This paper established a 560 m deep ventilation shaft with a diameter of 5 m focused on the heat–moisture coupled transfer of “surrounding rock—air tunnel—airflow” to investigate the airflow characteristics; analyze the heat and moisture changes of the tunnel surface and airflow, as well as the energy storage characteristics of the surrounding rock; and compare the induced airflow characteristics across four typical cities in China. The results show the following: there is an “inlet effect” in the deep-buried air tunnel; the wall temperature becomes basically stable after 200 m from the entrance, while a greater depth is required for the stable section of humidity; in summer, the airflow temperature decreases by more than 1 °C and the enthalpy decreases by 3.5 kJ/kg; in addition, the ground temperature in Guangzhou is relatively high, resulting in a limited effect on adjusting the intake airflow. This study aims to provide support for the energy-saving design of fresh air systems in deep-buried underground buildings.

The coupled heat and moisture transfer of the Energy Diaphragm Wall (EDW) has received insufficient attention, which is inevitable due to the high humidity of the underground environment. This paper aims to reveal the thermal transmittance through the inner surfaces and the impact of the thermal bridge (TB) when applying EDW. Firstly, the thermal characteristics were compared between the results of the pure thermal process and the coupled heat and moisture transfer process. Subsequently, the impact induced by the increasing inlet temperatures and the dynamic heat injection triggered by the daily cooling demands were discussed. The results indicate that the wall temperature is underestimated by approximately 0.97 %, while the sensible heat flux and total heat flux are underestimated by about 34.0 % and 39.9 %, respectively, if the moisture transfer process is ignored. Additionally, an "L" index is introduced to describe the thermal bridge (TB) affected area. The L1 (affected area on Slab 1) is greater than 6.0 m and demonstrates an increase following the daily cooling demand. Finally, the long-term impact of periodic load operation modes over three years was investigated. The results demonstrate that the L-indexes in fully compensated load mode are smaller than those in partially compensated load modes.

The Qinghai-Tibet Plateau is suitable for clean heating due to its abundant solar energy resources. However, the climate and living habits in this area are different from other areas of China. To study the impact of weather and residents' habits on heating load, residents' habits were obtained through field measurement and questionnaire survey, and eight typical buildings were summarized. The fifty years of reanalysis weather data are used to describe weather uncertainties. Finally, two levels of heating load uncertainty are studied. The first level is the heating load at the building level; the second level is the heating load at the village level considering the herding activities of residents. The results show that when the uncertainty of weather and behavior is considered, the peak heating load of the building in these areas will be 24.03 % to 106.78 % higher than the results under the design standard. When the uncertainty of the building occupancy rate caused by herding activities is considered, the peak heating load of the seven villages in these areas will be about 14.97 % to 45.23 % lower than the results of the design standard under the 95.0 % satisfaction rate. These results provide a reference for the future design of decentralized and centralized heating systems in the eastern Qinghai-Tibet Plateau area.