Capillary Heat Research Articles

Seawater source heat pump system based on capillary heat exchanger for seepage in submarine tunnel: a case study

Abstract The discharge of seepage water from undersea tunnel structures, often treated as wastewater, inherently carries a substantial reservoir of untapped low-grade thermal energy. Unfortunately, comprehensive investigations into harnessing this latent potential remain notably limited. This study introduced an innovative strategy through the design of an undersea tunnel seepage seawater source heat pump system. Distinguished by the integration of a capillary front-end heat exchanger, this system aimed to effectively exploit the frequently disregarded low-grade thermal energy present in the seepage water of undersea tunnel structures. The seawater seepage from the tunnel is transported to the car park at the tunnel entrance, and a seawater energy pool is constructed by storing seawater in its underground space. The use of capillary network placed in the energy pool in the front heat exchanger, water source heat pump units, circulating water pumps and fan coil end device composed of underground undersea tunnel seepage seawater source heat pump system for the building heating and cooling. Furthermore, a comparative assessment was conducted, contrasting this novel system with the traditional air-conditioning setup that utilizes chillers and gas boilers as cooling and heating sources. The aim was to evaluate its capacity for energy conservation and emission reduction. The findings from the study strongly affirmed the viability of the proposed seepage seawater source heat pump system within undersea tunnels. It boasted the potential to achieve annual savings of 53.55 tce, highlighting a noteworthy energy-saving rate of 21.2%. Concurrently, reductions in CO2, SO2, and particulate emissions amounted to 132.28 t/a, 1.07 t/a, and 0.54 t/a, respectively. This study not only stands as a reference for the strategic utilization of seepage seawater from undersea tunnel structures, prioritizing energy conservation and emission reduction, but also pioneers innovative approaches toward resource optimization and environmental sustainability, meeting the inherent needs of carbon peaking and carbon neutrality goals.

Impact of groundwater seepage on thermal performance of capillary heat exchangers in subway tunnel lining

The metro tunnels are currently facing challenges associated with thermal pollution, which significantly affects their operational safety and energy consumption. The subway source heat pump system (SSHPS) with front-end tunnel lining capillary heat exchangers (CHEs) is an effective technology to address this problem. The heat transfer characteristics of SSHPS have been previously investigated; however, there is a lack of research on the thermal performance of tunnel lining CHEs under groundwater seepage. This study established a numerical simulation model of tunnel lining CHEs based on a demonstration project of SSHPS. Subsequently, the influence of groundwater seepage on the heat transfer characteristics of tunnel lining CHEs was comprehensively analyzed. The findings suggest that an increase in groundwater seepage velocity leads to the initial expansion and subsequent contraction of the thermal influence range caused by CHEs. Simultaneously, the performance of CHEs is enhanced with increasing flow velocity. When the seepage velocity increases from 0 to 1 × 10−4 m/s, the heat exchange capacity per meter and efficiency of the CHEs during the cooling season increase by 450 % and 446 %, respectively. During the heating season, they experience a growth of 320 % and 310 %, respectively. In addition, the heat exchange performance of CHEs is also influenced by the relative flow direction between the fluid within CHEs and the groundwater. The counter flow arrangement exhibits a 7.7 % higher efficiency of heat exchange during the cooling season compared to the parallel flow arrangement, and a 3.9 % higher efficiency of heat exchange during the heating season. Therefore, it is highly recommended to evaluate groundwater seepage conditions during the design phase of SSHPS in order to enhance the performance of tunnel lining CHEs. This study serves as a valuable theoretical reference for the design of tunnel lining CHEs.

Analysis of the heat collection performance of a capillary solar heat collection wall structure

Solar thermal utilization in high-rise buildings is often constrained by the limited surface area of the rooftop. A novel façade-integrated capillary solar heat collection wall structure was proposed in this study, which involves embedding capillary tubes that circulate water within the cement mortar material, facilitating the integration of solar thermal collector and the exterior walls. To validate the feasibility of this new type of heat collection structure, experiments were conducted to investigate the impact of water flow rates on the heat collection performance of the proposed capillary solar heat collection wall structure under indoor solar simulator conditions, and outdoor field testing were conducted to assess its heat collection performance during winter, spring, and summer in Nanjing city. The experimental results revealed that, at water flow velocities of 0.05 m/s, 0.10 m/s, 0.15 m/s, and 0.20 m/s, the system's heat collection reached 4721 kJ, 4833 kJ, 4872 kJ, and 5326 kJ, respectively, showing a consistent increase with higher flow velocities in the capillary tube. The heat collection efficiency also increased gradually with flow velocity, but the rate of increase was relatively slow. The instantaneous heat collection efficiency decreased gradually as the experiment progressed, with a relatively small value of 47 % at a flow rate of 0.05 m/s. Data fitting revealed a linear relationship between the instantaneous collector efficiency and the normalized temperature difference at water flow velocities of 0.05 m/s and 0.1 m/s, and a quadratic exponential relationship at water flow velocities of 0.15 m/s and 0.2 m/s. During winter, spring, and summer in Nanjing city, the effective heat collection efficiency reached 45.8 %, 40.4 %, and 39.5 %, respectively, demonstrating that the capillary solar heat collection wall structure has significant potential in subtropical regions like Nanjing.

Capillary Tube Length and Heat Transfer Dynamics in Air Conditioners: A Comparative Analysis of R-12 and Its Alternatives

Capillary Tube Length and Heat Transfer Dynamics in Air Conditioners: A Comparative Analysis of R-12 and Its Alternatives

Effect of laying length on dynamic heat transfer characteristics of capillary heat exchangers in urban subway tunnel lining

The subway tunnel is a typical semi-enclosed underground space, which poses challenges in dissipating the waste heat generated by subway operations and may result in thermal environment deterioration of urban underground spaces. However, by incorporating heat exchangers into the tunnel lining, the subway can be transformed into an “energy tunnel” that effectively addresses this issue. Capillary heat exchanger (CHE) is a common type of tunnel lining heat exchanger. Recent studies have investigated its heat transfer properties and influencing factors under the assumption of homogeneity, neglecting the variability of heat transfer properties along the CHE tube. The present study developed a numerical model of tunnel-lined CHE utilizing water as the circulating medium, based on a demonstration project in Qingdao. Subsequently, an analysis was conducted to investigate the evolution of heat transfer properties for different laying lengths. The simulation results indicate that as the laying length increases from 2 to 10 m, the fluctuation range of outlet temperature decreases significantly from 10.6 °C to a mere 0.4 °C. Moreover, there is a noticeable decrease in average heat transfer per unit length from 1.9 W/m to only 0.4 W/m; however, this is accompanied by an impressive increase in average heat transfer efficiency from 28 % up to an impressive level of around 61 %. Based on the aforementioned results, it is recommended that the optimal length range for a tunnel-lined CHE should fall within 4 to 6 m. The findings of this study can serve as a valuable theoretical reference for the practical engineering applications of CHEs in urban tunnel lining.

Development of Transpiration-Type Thermoelectric-Power-Generating Material Using Carbon Nanotube Composite Papers with Capillary Action and Heat of Vaporization

A transpiration-type thermoelectric-power-generating paper based on previously developed carbon nanotube (CNT) composite paper, which is a composite material of CNTs and pulp that can generate thermoelectric power, was developed. The newly developed thermoelectric-power-generating material does not require an external high-temperature heat source due to the ability of paper to absorb liquid through capillary action and heat of vaporization generated when the liquid evaporates. The aim of this study is to investigate the feasibility of realizing the transpiration-type thermoelectric-power-generating paper. To begin with, the type of paper used as raw material for the composite paper was examined, and the fabrication process was modified in order to obtain more efficient liquid absorption based on capillary action. Then, the absorbing ability of the liquid was evaluated. Next, the feasibility of thermoelectric power generation using the heat of vaporization was confirmed. Moreover, for more efficient thermoelectric conversion, multisheet structures were also studied. Through several experiments, the material’s feasibility was verified, and it was confirmed that more power can be easily obtained through the use of multiple sheets. Specifically, a single sample spontaneously generated a temperature difference of up to 1.7 °C due to the heat of vaporization, generating an electromotive force of 36 μV. From the sample with a five-sheet structure, an electromotive force of 356 μV was obtained at a temperature difference of 2 °C. This material can be used in watery environments, such as rivers, lakes, and hot springs, and is expected to become a new energy-harvesting device.

Simulation of micropolar fluid flow with ternary nanoparticles over a permeable stretching surface involving nonlinear thermal radiation

ABSTRACT The primary goal of this research is to look into the rheological aspects of blood flow that contains ternary nanoparticles ( C u O + T i O 2 + A l 2 O 3 ). For this, the micropolar fluid model is adopted to simulate blood flow transport. Inclined magnetization and porosity characteristics are used to reveal the momentum attributes of flowing fluid, and nonlinearized radiating thermal flux is used to predict the thermal characteristics of the concerned flow. Further, the aspects of suction and injection of fluid over a permeable stretching sheet are also acknowledged. Governing system of partial differential equations are transformed into nonlinear ordinary differential equations by using similarity transformation. An effective built-in routine known as bvp4c, which is based on finite differencing, is used to acquire the solution. The results showed that the trihybrid nanofluid significantly boost fluid motion and temperature profiles more in the mass injection effect in comparison to suction phenomena. The increase in heat transfer rate is also noticed for augmented values of non-linear radiation parameter and micropolar parameter. There is a detailed discussion of the effects of the contributing parameters on the resulting dimensionless profiles. This research has significant implications for the delivery of magnetized blood, hyperthermia therapy, understanding of the bloodstream, transfer of complex bio-waste liquids, and capillary heat exchange.

The Use of Renewable Energy and Capillary Heat Exchangers for Energy Savings in the Existing Apartment

Abstract The use of capillary heat exchangers with a large area means the lowest heat carrier temperature – typically less than 30 °C for heating. This determines the very efficient use of the installed heat pump due to an increase in the coefficient of performance (COP) with a decrease in the provided water temperature. The aim of the study was to find out whether renewable energy sources and radiant capillary heat exchangers increase energy efficiency. In order to achieve the maximum energy efficiency during the renovation of the existing apartment, a combination of two green approaches was used. One of them is the replacement of the existing high-temperature radiator heating system with radiant capillary mats. The same system is also used for cooling, which was not possible with the existing system. The necessary energy is provided from renewable aerothermal energy by installing a heat pump together with PV panels to ensure electricity consumption. The measurements were made in the apartment to determine the thermal transmission properties of all boundary structures and an air exchange rate using long-term monitoring. Experimental data were used to create the heat balance, to estimate the heating and cooling powers, as well as the seasonal energy needs. The amount of capillary heat exchangers and the size of the heat pump were chosen accordingly. The very first energy consumption data allow concluding that the planned improvement of the energy efficiency has been successfully achieved by using technology combination described without improvement of the thermal properties.

Modeling of contact thermal resistance in lateral capillary tube-suction line heat exchangers with experimental validation and investigation

This paper studied the lateral capillary tube-suction line heat exchanger (CTSLHX) with different contact types and different geometries. An improved one-dimensional model of the CTSLHX was established, using the CFD model to derive the contact thermal resistance between the capillary tube and the suction tube. An experimental bench was built to test the steady-state heat transfer and flow performance. It was found that the model predicted 87.6 % and 98.9 % of the measured mass flow rate within the error band of ± 10 % and ± 15 %. The prediction error of the CTSLHX heat transfer effectiveness was within ± 10 %. Parametric effects of different operating conditions and structural parameters on the performance of CTSLHX were investigated. Furthermore, experiments were carried out to study the temperature distribution along the transition section between the exit of the capillary tube and the evaporator. The unique temperature increase reveals that it is beneficial for reducing noise by wrapping a layer of rubber around the second increaser fitting.

Energy and exergy efficiency of a daily heat storage unit for buildings heating

This paper deals with a daily solar storage system conceived and built in Laboratoire de Maîtrise des Technologies de l’Energie (LMTE, Borj Cedria). This system consists mainly of (i) a heat storage unit which consists of a wooden case with dimension of 5 m3 (5 m x 1 m x 1 m) filed with fin sand, (ii) a heat collection unit which consists of 5 m2 of south-facing solar collector mounted at a 37° tilt angle and (iii) a network of a polypropylene capillary heat exchanger with an aperture area equal to 5 m² buried inside the heat storage unit and connected to the heat collection unit. The circulation of the heated water between the heat collection unit and the polypropylene capillary heat exchanger allows heating the sand inside the heat storage unit. In order to evaluate the system efficiency during the charging period (during the day) and discharging period (during the night) an energy and exergy investigation were applied. Results showed that during the charging period, the average daily rates of thermal energy and exergy stored in the heat storage unit were 400 and 2.8 kW, respectively. It was found that the net energy and exergy efficiencies in the charging period were 32 % and 22 %, respectively. During the discharging period, the average daily rates of the thermal energy and exergy recovered from the heat storage unit were 2 kW and 2.5 kW, respectively. The recovered heat was compared to the total heat requirements of a tested room (4 m x 3 m x 3 m). The results showed that 30 % of the total heating requirement of the tested room can be achieved from the heat storage system during the whole night until in cold seasons.

Implementation and validation of effective thermal conductivity model of coal‐rock mass with rough capillary pore structure under CT three‐dimensional reconstruction

AbstractOn the strength of the capillary physical equivalent model and heat transfer law of series‐parallel combined structural unit, the calculation model of effective thermal conductivity of coal‐rock mass is obtained. The model considers the effect of roughness, porosity factor and other factors on effective thermal conductivity. CT digital core technology is applied to reconstruct the 3D model of coal‐rock mass, and one‐way heat transfer numerical simulation is carried out according to the model. It indicates that the internal temperature of coal‐rock mass is non‐uniformly distributed under the influence of pore structure, and the isothermal surface of pore region bulges towards the boundary of heat flux. Comparing the calculated and simulated values under the same conditions, the average error percentage of the theoretical calculation model is 6.95%, and the model has outstanding prediction performance in porous media with medium porosity and regular pore distribution, which provides a reference for predicting the effective thermal conductivity of coal‐rock mass.

Experimental and numerical investigation on thermal characteristics of the heat sink integrating 3D vapor chamber heat spreader and liquid cooling fins

The traditional vapor chamber/ heat pipe heat sink in high-power chip heat dissipation structures consists of two separate parts. The contact thermal resistance between these parts leads to an increase in thermal resistance during the heat transfer process. To mitigate the contact thermal resistance and improve the heat dissipation performance of vapor chamber heat sinks, this paper proposes a heat sink integrating a 3D vapor chamber heat spreader and liquid cooling fins. Experiments and simulations were carried out to analyze the heat transfer characteristics under different heating powers. The pressure drop and thermal resistance were calculated to analyze the internal phase-change heat transfer process and capillary heat transfer limit. The simulation results were in close agreement with the experimental data for heating powers ranging from 397 to 795 W, with the thermal resistance of the proposed heat sink of about 0.04℃/W. Compared to three traditional vapor chamber heat sinks operating under the same heat flux, the proposed type exhibited a noteworthy enhancement in the heat transfer performance, leading to a reduction in thermal resistance by approximately 44% to 67%.

Design and fabrication of heat pipes using additive manufacturing for thermal management

With the increase in the integration level of chips, capillary heat pipes are becoming increasingly valuable for the thermal management of high-heat-flux electronic devices. Here, we employ a thermal circuit model and 3D printing for heat pipe design and fabrication. The model was developed to predict the heat transfer performance of the heat pipe, and a heat pipe structure suitable for dissipating 20 W of heat load was designed. The aluminum heat pipes were fabricated by metal 3D printing, with acetone as the working fluid. Heat transfer experiments were conducted on the heat pipes with acetone filling ratios of 60%, 100%, and 150% (heat load: 5–40 W). The lowest thermal resistance was achieved with the 150% filling ratio at 20 W. The thermal resistance achieved with the 100% filling ratio was similar to the model’s prediction. The effective thermal conductivity was determined to increase by 5.81-fold by comparing the thermal performances of the heat pipe and a solid aluminum plate of the same volume. The results confirmed that heat pipes with desired heat transfer performances can be obtained as designed by employing a thermal circuit model and 3D printing technology.

Evaporative wicking in thin porous media

Evaporation cooling as an environment-friendly and energy-saving cooling option is usually realized by using porous medium to enhance the transport process, where the evaporation and wicking emerge simultaneously. Thin porous media are commonly applied in the evaporative wicking process. However, the evaporation on thin porous medium imposes significant impact on flow and heat transfer performance of evaporative wicking, which makes the prediction of evaporative wicking behavior more difficult. In this work, experimental studies of evaporative wicking of ethanol in Dutch Twill Weave (DTW) screens are carried out, where the evolution of wicking front and temperature distribution are captured by infrared thermography. Moreover, the numerical model that describes capillary rise, evaporation and heat transfer during evaporative wicking is built, which agrees well with the experimental results. Further investigation suggests that considering the evaporative cooling effect is indispensable for accurately predicting the evaporative wicking behavior in DTW screens. In addition, it is found that there is a rapid increase in temperature difference between the liquid and metal wires around the wicking front based on the local non-thermal equilibrium model.

Heat transfer characteristics in nanochannels with rough walls based on capillary flow: A molecular dynamics study

Passive micro/nanoscale cooling based on capillary flow has become a promising and widely used thermal management technology for electronic devices. In this study, nanochannels with different surface roughness are established based on the chord function, and the capillary flow and heat transfer in different nanochannels are investigated by molecular dynamics simulation. Compared with smooth walls, rough walls retard capillary flow, and the heat transfer process also affects capillary flow to some extent. The region of low potential energy is much larger near rougher walls in nanochannels. When fluid flows through a depression on a wall, the velocity decreases, resulting in an uneven flow velocity. An analysis of the temperature field, Nusselt number and heat transfer amount shows that although rougher structure causes more atoms to gather, thus improving the heat transfer rate, it reduces the total heat transfer amount due to reduced capillary flux. The microscopic mechanism of the impact of surface roughness on capillary flow and heat transfer is revealed at the atomic scale by potential energy analysis. Furthermore, increasing solid-liquid interaction hinders capillary flow, but it increases the heat transfer rate at the solid-liquid interface.

Experimental study on 3D printed heat pipes with hybrid screen–groove combined capillary wick structure

The integration of heat pipes as a passive thermal management system for nuclear reactors has been proposed as it provides the advantages of compact design, reliability, efficient heat transfer performance, and enhanced safety. Applying the heat pipe to a nuclear reactor without collision between systems and achieving efficient long-distance heat transfer requires the manufacturing of heat pipes with a high degree of freedom. Using three-dimensional (3D)-printing technology can be a solution for fabricating complex or bent capillary wick heat pipes into an integrated geometry. The study involves the production of a heat pipe using metal 3D-printing technology and an experimental study conducted for thermal performance evaluation. The heat pipe includes a combination of a screen-groove wick in the evaporator section, a groove wick in the adiabatic and condenser sections, and a bent wick structure in the middle. By using 3D printing technology, it is possible to create a heat pipe that has a complex wick design, a consistent porous structure and remains undistorted during the manufacturing process. The surface roughness of the 3D-printed heat pipe was 17 to 1700 times higher than the commercial stainless-steel pipe, which has the benefit for enhance capillary performance. The experimental results showed that the 3D-printed heat pipe can achieve high effective thermal conductivity up to 25.7 kW/m-K and showed 24.2% lower thermal resistance compared to the conventionally manufactured heat pipe. Furthermore, it can be successfully operated at various inclination angles.

Rapid performance prediction model for capillary heat exchangers in subway tunnel linings

Subways are typical underground spaces that help alleviate urban traffic problems; however, they also face challenges such as high energy consumption and deterioration of the thermal environment, which can seriously impact their safe and efficient operation. A subway source heat pump system (SSHPS) with tunnel-lining capillary heat exchangers (CHEs) is effective for addressing these issues. Current research has primarily focused on the heat transfer performance of tunnel lining CHEs, yet there remains a dearth of rapid prediction models for their heat flux that are suitable for efficient engineering design. In this study, numerical simulation systems for tunnel lining CHEs in rectangular and circular subway tunnels were established to analyse their heat transfer performance under different design conditions. The results show that the heat flux of flat and circular CHEs installed in tunnel lining ranges from 47.03 to 117.65 W/m2, and from 36.06 to 115.09 W/m2 in the cooling season, respectively. In contrast, in the heating season, the heat flux of flat and circular CHEs ranges from 27.03 to 89.90 W/m2, and from 19.35 to 87.77 W/m2, respectively. Based on the analysis of these results, rapid prediction models for the CHE heat flux were established using multivariate linear fitting. The established models passed a series of statistical tests, indicating high statistical significance. This study provides a theoretical basis for the engineering design and applications of tunnel lining CHEs.

Capillary limit of a sodium screen-wick heat pipe

High-temperature alkali-metal heat pipes are passive heat transfer devices, where the capillary pressure created by the menisci in the wick pumps the condensed fluid back to the evaporator. Thus, the heat pipe heat transfer capacity is limited by the maximum capillary pressure at high heat fluxes. This work presents a two-dimensional heat and mass transfer model for alkali metal heat pipes. In addition to the traditional wall heat conduction model, the model also incorporates gas–liquid flow heat transfer and capillary structure models, enabling the model to simulate both steady-state operation and transient capillary limit processes. The predictions of the model agreed well with experimental data. The predicted critical heat flux temperature has an error of less than 20℃ and a relative error of 6%. The predicted transient sequences are consistent with the measurements. The model shows that capillary limit is affected by inclination angle, heat flux, and wick structure. For inclinations, the critical heat flux at the capillary limit is linearly related to the inclination angle with the predicted temperature rising 2–10℃/s during the early stage of the capillary limit critical heat flux condition. The evaporator temperature oscillates before the capillary limit with positive inclinations. For heat fluxes, increasing the heat flux by 17% increases the temperature increase rate 10 fold with a longer dryout length. The evaporator exhibits hysteresis after the capillary limit due to partial dryout of evaporator. For wick structures, reducing the mesh screen pitch from 80 μm to 15 μm reduces the critical heat flux to 10% of the CHF at 80 μm. This model can accurately predict the heat pipe temperature variations at the capillary limit and can explain the physical mechanisms for the dryout oscillations and recovery hysteresis at the capillary limit. Thus, the measurements and model provide analytical guidelines for designing heat pipe cooling systems.

Performance analysis on the liquid cooling plate with the new Tesla valve capillary channel based on the fluid solid coupling simulation

Liquid cold plates are extensively utilized for heat dissipation in new energy vehicle fuel cell stacks. However, practical applications have revealed issues such as uneven heating and significant pressure loss in the heat dissipation channel. To address these concerns, this study introduces the design of a forward Tesla valve capillary heat dissipation channel and a reverse Tesla valve capillary heat dissipation channel, aimed at mitigating the eddy current issue at bends inside the capillary bionic flow channel. Under the same working conditions, the performance indicators such as the pressure distribution of the original, forward and reverse heat dissipation channel of liquid cold plates were obtained respectively. The results show that the forward cooling channel significantly reduced the pressure loss of the liquid cooling plate whilst the reverse channel effectively improved the heat transfer. Aiming at the problem of excessive pressure difference encountered in the reverse Tesla valve capillary channel, different numbers of valves and branches were designed on the reverse Tesla valve capillary cooling channel. It was found that a higher cooling capacity can be obtained with less pumping power when the aspect ratio between the number of valves and the number of branches of the reverse Tesla valve capillary liquid cooling plate was controlled in the range from 1.13 to 1.6.

Long-term performance of a subway source heat pump system with two types of front-end heat exchangers

The rapid development of subways and resulting deterioration of the thermal environment in tunnels have led to thermal pollution of underground spaces, which is a problem that cannot be ignored. The subway source heat pump system (SSHPS) with a tunnel-lining capillary heat exchanger (CHE) is an effective technology for solving this problem. Existing researches mainly focused on the short-term performance of the SSHPS. Few studies have analyzed the long-term performance of the system under complex periodic boundary conditions. In this study, a simulation model of an SSHPS, which conforms to an actual demonstration project located in Lingshanwei Subway Station of Qingdao Metro Line 13, was built by coupling a flat CHE for the open-cut section and a circular CHE for the concealed excavation section of a subway tunnel. Field test results of the SSHPS performance were compared with those of the simulation. The maximum relative error is 13.96%, which shows that the simulation model has high accuracy and can satisfy the requirements of practical engineering applications. Based on the verified model, the system performance under complex periodic boundary conditions was simulated for 10 consecutive years. The results indicate that the average heat flux of the flat and circular CHEs has little variation during the continuous operation of the system for 10 years, and the variations during the cooling and heating seasons are less than 1.24 W/m2 and 0.36 W/m2, respectively. The annual air temperature increments in the tunnel with flat and circular CHEs are approximately 0.226 °C and 0.324 °C, respectively. The average coefficients of performance of the heat pump unit in the cooling and heating seasons are 4.43 and 5.11, respectively, indicating that the heat pump unit operates efficiently throughout the year. The main reason for the long-term high performance of SSHPS is the annual thermal balance of the subway tunnel. The thermal balance of the subway tunnel during long-term operation should be considered when designing an SSHPS system. This study can provide a reference for optimizing the design and operation of the SSHPS.