Auxiliary Heating Research Articles

Enhancing Seasonal Performance of Heat Pumps integrated into Building Ventilation Systems using a Multi-Stage Volume Enlarger: a Comparative Study across European Regions

The buildings sector is one of the largest energy consumers in the EU, accounting for approximately 40% of final energy consumption and around 36% of greenhouse gas emissions. European governments are implementing various measures to reduce these figures. One effective approach to lowering energy consumption is to enhance the energy efficiency of HVAC systems in buildings. Extending the control range of heat pumps can significantly improve their seasonal energy efficiency, thereby reducing carbon dioxide emissions and enhancing building sustainability. Modern heat pump capacity control commonly involves a variable-speed compressor and an electronic expansion valve. In this study, the authors introduce an additional control component—variable volume in the active loop of the heat pump.The paper evaluates the performance of a variable-volume heat pump integrated into a ventilation system across different European regions (Vilnius, Helsinki, and Milan). A comparison is made between the conventional control approach, which uses a compressor and expansion valve, and an enhanced control method that incorporates an additional device to regulate the heat pump circuit volume. Based on data from prior experiments—specifically, the dependencies of the heat pump heat output and efficiency on compressor speed, expansion valve position, and circuit volume—a control algorithm was developed with Matlab to simulate heat pump performance in a ventilation system over a typical meteorological year for each city.Key findings highlight that the use of additional volume control in the heat pump loop significantly extends the unit’s operational time compared to conventional control methods. Specifically, operational time increased from several percent to as much as 69.97% across the regions analysed, positively impacting seasonal performance. These results underscore the critical importance of optimizing heat pump control strategies, as they not only enhance energy efficiency but also contribute to reducing reliance on auxiliary heating and lowering overall carbon emissions. Furthermore, despite these advantages, the study notes a significant limitation: the current lack of commercially available tools for implementing dynamic volume adjustment in heat pumps, which presents challenges for practical application in the field.

Investigation on the density shoulder near the separatrix through monostatic reflectometry in EAST tokamak

Abstract The density shoulder represents a universal physical phenomenon that is closely related to the particle and energy transports occurring within the scrape-off layer (SOL) region of tokamak devices. A novel method has been developed to identify the density shoulder through the analysis of the bump structure in the time delay spectra from monostatic microwave reflectometry in EAST tokamak, obviating the need for density profile reconstruction. The density shoulder in EAST is characterized by a number of distinctive features. The density shoulder is mostly situated at a distance of 0–3 cm from the last closed flux surface, with a width of a few centimeters. No significant correlation is observed between its occurrence and the auxiliary heating or the confinement state. In the case of H-mode with quasi-coherent mode (QCM), a significant and positive correlation is observed between the density shoulder amplitude and QCM intensity. In the case of grassy-edge localized mode (ELM)-like H-mode, a density shoulder is also observed during the inter-ELM stage. Furthermore, as supersonic molecular beam injection (SMBI) deposits occur within the range of ρ = 0.9 ∼ 1, the density shoulder is also enhanced during the SMBI fueling process. Moreover, it appears that the neutral pressure has a more pronounced impact on the overall offset of the density profile than the strength of the density shoulder. These results collectively indicate that the outward particle transport from the pedestal to the SOL region plays a crucial role in the evolution of the density shoulder.

Numerical simulation of a forced circulation solar water heating system

This study presents a sophisticated numerical simulation model for a forced circulation solar water heating system (FC-SWHs), specifically designed for the unique climatic conditions of Algeria. The model aims to cater to the hot water needs of single-family houses, with a daily consumption of 246 L. Utilizing a dynamic approach based on TRNSYS modeling, the system’s performance in Ain Temouchent’s climate was scrutinized. The model’s validation was conducted against literature results for the collector outlet temperature. Key findings include a maximum monthly average outlet temperature of 38 °C in September and a peak cumulative useful energy gain of 250 W in August. The auxiliary heating system displayed seasonal energy consumption variations, with the highest rate of 500 kJ/hr in May to maintain the water temperature at 60 °C. The energy input at the storage tank’s inlet and the consistent high-level energy output at the hot water outlet were analyzed, with the former peaking at 500 W in May. The system ensured an average water tank temperature (hot, middle and bottom) and water temperature after the mixer, suitable for consumption, ranging between 55 °C and 57 °C. For applications requiring cooler water, the mixer’s exit temperature was maintained at 47 °C. The study’s key findings reveal that the TRNSYS model predicts equal inlet and outlet flow rates for the tank, a condition that is particularly significant when the system operates with high-temperature water, starting at 55 °C. The flow rate at this temperature is lower, at 7 kg/hr, while the water mass flow rate exiting the mixer is higher, at 10.5 kg/hr. In terms of thermal performance, the system’s solar fraction (SF) and thermal efficiency were evaluated. The results indicate that the lowest average SF of 54% occurs in July, while the highest average SF of over 84% is observed in September. Throughout the other months, the SF consistently stays above 60%. The thermal efficiency of the system varies, ranging from 49 to 73% in January, 43–62% in April, 48–66% in July, and 53–69% in October. The novelty of this research lies in its climate-specific design, which addresses Algeria’s solar heating needs and challenges. Major contributions include a thorough analysis of energy efficiency metrics, seasonal auxiliary heating demands, and optimal system operation for residential applications, supporting Algeria’s goal of sustainable energy independence.

Divertor Tokamak Test: Impact of NBI shine-through and beam-plasma interaction on Divertor Tokamak Test facility

IntroductionIn this work, we aim to explore numerically the behavior of beam energetic particles in the Divertor Tokamak Test (DTT), a superconductive device equipped with a Neutral Beam Injection (NBI) system capable of injecting neutrals up to 510 keV.MethodWe explore beam ionization and beam slowing down for different DTT plasma scenarios. Numerical simulations are performed using the ASCOT suite of codes, including a wide-range scan of plasma density and beam injection energy. For different plasma conditions, we estimate shine-through losses, including the heat fluxes on the first wall thanks to dedicated particle tracing simulations. Orbits of newly-born fast ions are characterized by means of the constant of motion phase space, showing how trapped energetic particles’ population and prompt losses change with plasma density and NBI energy.Results and discussionSlowing down simulations show that NBI injection at 510 keV is well coupled to DTT plasmas. DTT NBI will be one of the sources of auxiliary ion heating, with an absorbed power ratio of up to ∼50% depending on plasma and beam parameters. At low plasma densities, energetic particle confinement is less efficient, and NBI power and/or energy reduction is expected.

Techno-economic assessment of decentralized low-carbon power plants based on solid oxide fuel cell equipped with calcium looping carbon capture

Integrating solid oxide fuel cells (SOFCs) with carbon capture technologies aligns with the intention to decarbonize the electricity sector. This study explores two configurations of SOFCs combined with calcium looping (CaL) carbon capture technology (SOFC/CaL): one with auxiliary heaters and another with additional fuel to supply the energy required for the carbon capture process. Results indicate that the electrical efficiency of the SOFC/CaL system is approximately 26 % lower than that of a standalone SOFC, though the overall efficiency (considering both electricity and heat as products) remains comparable. However, CO2 emission is 314.7 kg/MWh for standalone SOFC, 125.8 kg/MWh for SOFC/CaL equipped with auxiliary heaters, and 22.4 kg/MWh for SOFC/CaL retrofitted with additional fuel. The scale of the SOFC and the fuel price significantly affect the carbon capture economy and the required CO2 tax for cost parity. For a 10 MW plant with a fuel cost of 10 USD/GJ, the levelized cost of electricity is estimated at 66.7 USD/MWh for the standalone SOFC and 82.5 USD/MWh for the SOFC/CaL. A CO2 tax of 39–53 USD/tCO2 is necessary to achieve cost parity.

Decision support tools for effective bus fleet electrification: Replacement factors and fleet size prediction

The electrification of public transit systems represents a crucial strategy for advancing sustainable urban mobility. Thus, the development of efficient charging infrastructure and the optimization of fleet size emerge as major challenges for transit agencies. Switching from diesel buses to electric buses (Ebuses) will require increasing the fleet size to accommodate the limited range of Ebuses and the significant idle time required for charging. This study develops prediction models to estimate the required Ebus fleet size to maintain same transit route services for the case of overnight depot charging, using data from Ebuses operating in the City of Toronto. The analysis reveals that Ebuses equipped with diesel auxiliary heaters are less sensitive to temperature fluctuations compared to battery-heated buses. Thus, the required replacement factor, indicating the additional fleet needed to switch from diesel to Ebuses, varies depending on the heating system. Specifically, diesel-heated buses require a lower replacement factor (1.3) compared to battery-heated buses (1.4), with winter conditions exacerbating this disparity. Furthermore, the study employs vehicular, operational, route, and external variables to develop the prediction models. Additionally, SHAP analysis is utilized to interpret the machine learning models and evaluate the influence of the inputs on the required fleet size. The results show that the total distance traveled, and the average temperature are the primary factors affecting the fleet size for Ebuses using their batteries for heating, whereas the total distance traveled, and the average bus speed are the primary factors affecting the fleet size for Ebuses with diesel auxiliary heaters.

Validation and optimization of a solar district heating system with large scale heat storage

Solar district heating systems with large-scale heat storage can contribute to a sustainable future. Currently, there are few mature systems and a lack of suitable tools, hindering large-scale applications. High-precision system models and efficient control strategies are necessary for designing optimal plants. This study developed a TRNSYS model of a large solar heating plant with components like a solar collector field, pit heat storage, heat pump, boilers, piping, pumps, and a MATLAB control system. The model is validated using a solar district heating system in Dronninglund, Denmark, showing good agreement with the measurement, with a difference in the solar thermal production of only 0.3% and an average temperature difference in the pit storage of 1 K. The model of the absorption chiller is improved for wide heat pump simulation, yielding a difference of approx. 5% compared to the measured coefficient of performance. The predicted solar fraction is 0.51, differing by 1.5% from the measurement. The study also proposed two new control strategies: adaptive low-temperature operation strategy and full-time heat pump operation strategy. These optimized strategies are compared with the original control strategy. Results show that the low-temperature and full-time optimization strategies improve the heat pump efficiency by 20%, the collector efficiency by 10%, and the solar utilization by 15%. The economic and environmental performance of the solar heating plant will also be enhanced with a maximum of 27% lower heat costs and 32 kg/MWh lower carbon emissions compared to the original system. In contrast, without the absorption heat pump, the solar heat production decreases by 10%. The system does not meet carbon neutrality if natural gas is used as the auxiliary heat source. This study aims to provide new simulation models and control strategies, which could be utilized for design of optimal large-scale solar thermal applications.

Renewable-driven hybrid refrigeration system for enhancing food preservation: Digital twin design and performance assessment

This study presents a new method for sustainable cooling systems using a hybrid refrigeration system powered by hybrid renewable energy sources. The system comprises a modular unit of vertical wind turbines integrated with bio-photovoltaic films to provide sustainable energy. The hybrid refrigeration system combines evaporative and solar thermal-driven adsorption cooling systems. In addition, a finite volume of soil is proposed for thermal energy storage. Experimental data inform the development of a digital twin for an integrated system, soil thermophysical characteristics, wind turbine performance, and technical specifications for other system components. This sustainable cooling package is cost-effective and space-efficient, particularly in remote or off-grid locations. Notably, the evaporative cooler and chilled water coil contribute to a cooling effect of 20.4 kW, and solar power generation reaches 12.38 kW at an intensity of 1053 W/m2. The annual electrical output averages 1.7 kW at a wind speed of 3.5 m/s. Under best conditions, wind power can surge to 7.99 kW at 9.88 m/s. The ratio of power generated by wind to solar energy ranges from 1.1 to 1.3. The system effectively meets a peak thermal energy demand of approximately 74 GJ/month, facilitated by solar collectors, underground thermal storage, and a renewable energy-fed auxiliary heater. This study paves the way for future techno-economic optimisation and advancements in sustainable energy solutions for remote cold storage facilities.

Integration of energy storage and determination of optimal solar system size for biomass fast-pyrolysis

This study presents a model and analysis of a heliostat field collector (HFC) system integration with fast-pyrolysis of biomass and determination of the optimal solar system size for this integrated system. Given the intermittent nature of solar energy, an auxiliary heater and a thermochemical energy storage system (TCES) are included. Four cases of HFC integration with the fast-pyrolysis process have been studied: 1) low solar radiation, 2) sufficient solar radiation, 3) high solar radiation, and 4) no solar radiation with available stored energy in TCES. The solar energy system was modeled and calculated using the Engineering Equation Solver (EES) software, while the fast-pyrolysis process and the TCES were simulated using the Aspen Plus software. A thermodynamic and economic analysis has been conducted to estimate the share of solar energy for different process configurations. Economic calculations have been conducted for three different heliostat filed areas: 4000, 8000, and 12000 m2. Solar fraction, investment and operational costs, as well as total cost were calculated for these three heliostat field areas. The results indicate that the optimum heliostat field area for the studied biomass pyrolysis plant is 8000 m2 and the average solar fraction of the required energy in summer is 0.39 and while it is 0.34 for the whole year. Simulation results considering this optimized heliostat filed area indicate that 6.27 t/h of bio-oil is produced from 10 t/h of hybrid poplar biomass. Implementing this solar-assisted system reduces CO2 emissions, increases efficiency of the system and lowers thermal energy requirement for the fast-pyrolysis process from 6 MW to 3.99 MW.

Assessment of a LPG hybrid solar dryer assisted with smart air circulation system for drying basil leaves

The fluctuation of solar radiation throughout the day presents a significant obstacle to the widespread adoption of solar dryers for the dehydration of agricultural products, particularly those that are sensitive to high temperatures, such as basil leaf drying during the winter season. Consequently, this recent study sought to address the limitations of solar-powered dryers by implementing a hybrid drying system that harnesses both solar energy and liquid petroleum gas (LPG). Furthermore, an innovative automatic electronic unit was integrated to facilitate the circulation of air between the drying chamber and the ambient environment. Considering the solar radiation status in Egypt, an LPG hybrid solar dryer has been developed to be suitable for both sunny and cloudy weather conditions. This hybrid solar dryer (HSD) uses indirect forced convection and a controlled auxiliary heating system (LPG) to regulate both temperature and relative humidity, resulting in increased drying rates, reduced energy consumption, and the production of high-quality dried products. The HSD was tested and evaluated for drying basil leaves at three different temperatures of50, 55, and 60 °C and three air changing rates of 70, 80, and 90%, during both summer and winter sessions. The obtained results showed that drying basil at a temperature of 60 °C and an air changing rate of 90% led to a decrease in the drying time by about 35.71% and 35.56% in summer and winter, respectively, where summer drying took 135–210 min and winter drying took 145–225 min to reach equilibrium moisture content (MC). Additionally, the effective moisture diffusivity ranged from 5.25 to 9.06 × 10− 9 m2/s, where higher values of effective moisture diffusivity (EMD) were increased with increasing both drying temperatures and air change rates. Furthermore, the activation energy decreased from 16.557 to 25.182 kJ/mol to 1.945–15.366 kJ/mol for the winter and summer sessions, respectively. On the other hand, the analysis of thin-layer kinetic showed that the Modified Midilli II model has a higher coefficient of determination R2, the lowest χ2, and the lowest root mean square error (RMSE) compared to the other models of both winter and summer sessions. Finally, the LPG hybrid solar dryer can be used for drying a wide range of agricultural products, and it is more efficient for drying medicinal plants. This innovative dryer utilizes a combination of LPG and solar energy, making it efficient and environmentally friendly.

Thermal performance attenuation characteristics of solar collector field in solar district heating system

In centralized solar district heating systems, the optical performance attenuation of the solar collector field significantly impacts the system’s heating efficiency and economics. However, accurate lifecycle models for the optical performance attenuation of solar collector fields are still needed. In this paper, the attenuation patterns of transmittance, absorption, and emissivity are systematically established through accelerated attenuation tests and calculation models. Based on this, a lifecycle model for optical performance attenuation was developed using TRNSYS and applied to a centralized solar heating system in Langkazi, XiZang. The results indicate that low inlet temperatures and high flow rates reduce optical performance attenuation, with ultraviolet damage of the glass cover being the main cause of performance attenuation, accounting for 74.5 % of heat loss. A 15-year lifecycle analysis shows that performance attenuation in the solar collector field results in a 16.7 % reduction in effective heat collection, a decrease in the solar fraction from 66.1 % to 55.1 %, and a 32.4 % increase in auxiliary heat supply. Increasing the heating area or thermal storage to collection area ratio helps mitigate optical attenuation. Based on this, from the perspective of mitigating the attenuation of collection efficiency, the thermal storage to collection area ratio should exceed 0.2 m3/m2, and the solar fraction is recommended to be kept below 0.7. Additionally, considering optical attenuation, the levelized cost of heat increases by over 0.03 CNY/kWh when the thermal storage to collection area ratio exceeds 0.2 m3/m2. The results provide a methodological basis for more accurate design of the solar heating system.

First integrated core-edge fluid simulation of ITER’s Limiter–Divertor transition with SolEdge-HDG

This work explores the Limiter–Divertor transition (L–D) during the current ramp-up of ITER’s Q = 10 baseline plasma scenario at various central line-integrated density nli values. The analysis, based on transport simulations performed with the latest version of SoleEdge-HDG, focuses on the time evolution of heat and ion particle fluxes, revealing regions of elevated temperature on the inner wall and plasma-facing components (PFCs) despite moderate loads. The investigation also delves into the effects of perpendicular convection flux terms on density build-up, comparing different formulations and their interplay with auxiliary heating sources. Furthermore, the paper shows the impact of taking into account the evolution of the parallel neutral momentum on plasma and neutral density at the targets in the context of an ITER steady-state scenario.

Dissipative Kerr soliton formation in dual-mode interaction Si3N4 microresonators

Dissipative Kerr soliton (DKS) microcombs based on multi-mode Si3N4 waveguides turn into an ideal tool that is compact and has precision for optical communication, precision spectroscopy, and frequency metrology. However, spatial waveguide mode interaction leads to local disturbances of dispersion, which may hinder DKS microcombs formation. In this letter, we generate the DKS microcomb in a dual-mode interaction Si3N4 microresonator without suppressing spatial waveguide mode interaction. The spatial waveguide mode interaction is investigated in the dual-mode interaction Si3N4 microresonator with a cross-sectional area of 800 × 1700 nm2. DKS microcomb is deterministically generated in the microresonator using an auxiliary light heating method. Furthermore, an integrated microcomb frequency measurement system is designed based on the DKS microcomb for frequency metrology.

Boltzmann optical thermometry for cryogenics.

We propose and implement an optical technique to access the local temperature of an erbium doped crystal by probing the electron spin population under magnetic field. We reliably extract the sample temperature in the range 2-7K. We additionally discuss the suitability of our method as a primary standard for cryogenic thermometry. By adding an auxiliary heating laser, we are able to measure the interface conductance between the dielectric crystal and the cold plate of the cryostat by exploring different cooling configurations.

The 140 GHz notch filter development for millimeter-wave diagnostics protection on the stellarator Wendelstein 7-X

The notch filter plays a crucial role as a protective component in microwave diagnostics, primarily by addressing issues related to catastrophic interference. Designed for millimeter-wave diagnostics on the stellarator Wendelstein 7-X (W7-X), a WR-6 waveguide-based notch filter has been successfully developed to effectively isolate leakage from auxiliary heating gyrotrons operating at 140 GHz. The filter incorporates cylindrical cavities resonating at 140 GHz for the TE11p mode, with coupling structures that are designed and optimized for high-efficiency coupling. This configuration simplifies fabrication, thereby ensuring high-yield production. Experimental fabrication and in-house characterization confirm the notch filter's exceptional performance, with over 60 dB rejection in the vicinity of 140 GHz and low insertion loss (< 2 dB) above and below the notch frequency across a broad frequency bandwidth (121–138 GHz, 142–163 GHz). The utilization of this high-frequency structure fabrication technology can be applied to millimeter-wave diagnostics on other machines. In addition to the design elements of the notch filter, this paper also provides a detailed discussion of the fabrication process and methodology.

Numerical investigation on the thermal performance of a molten salt tank under different electric heating method

Two-tank molten salt (MS) thermal energy storage (TES) technology is an efficient and widely used energy storage technology. This study develops a two-dimensional discrete model (2DIM) using the Modelica language to accurately and quickly represent molten salt temperature distribution and heat loss, applicable to system-level analysis in thermal power systems. It also uncovers variations in heat loss, cooling rate, and required auxiliary electric heating power across different tank volumes, liquid levels, and MS temperatures, offering guidance for optimizing design, energy management, and operational strategies. Additionally, the study examined the impact of different electric heater placements on the performance of the thermal storage system. The results show that heating the gas inside the tank is more effective than traditional direct electric heating, reducing molten salt heat loss by 25.89 % and increasing energy storage efficiency by 0.17 %.The research provide a reference for the study of efficient utilization of TES tank in different thermal systems.

Pedestal properties of negative triangularity discharges in ASDEX Upgrade

Abstract In this work, we explore the pedestal properties of negative triangularity discharges with upper triangularity of δ u ≈ − 0.35 and with both ion ∇ B drift directions. In all cases, the discharges undergo a transition to H-mode with accompanying edge-localized modes (ELMs) that are not explained by the peeling-ballooning stability analysis alone. A variation in the ion ∇ B drift direction is observed. A lower pressure gradient, shallower radial electric field well and increased temperature fluctuations are measured in the favorable case. In addition, irregular ELMs are present. This difference is more pronounced in electron cyclotron resonance heating (ECRH) plasmas compared to plasmas with combined neutral beam injection and ECRH. A comparative analysis between two discharges, featuring similar plasma parameters but varied shaping, suggests that an interplay between other parameters, such as magnetic shear, the timing of the auxiliary heating and shaping, might play a strong role in low- to high-confinement transitions. While the low shaping discharge maintained L-mode, the high shaping discharge entered H-mode with ELMs, contrary to expectations.

A new approach to evaluate the overall heat transfer coefficient of a fluidized bed biomass pyrolyzer

The heat transfer characteristics of non-pretreated rice husk pyrolysis in a fluidized bed with alumina beads (500 μm - 590 μm) as bed material are studied. Assuming instantaneous heating of biomass to the reaction temperature, the effective overall heat transfer coefficient of the system (UA) is initially calculated based on the compositions of the collected products and reaction temperature. UA ranges from 0.82 to 2.95 W/K. This heat transfer coefficient study allows ad hoc product distributions to be predicted from theoretical bases. The effects of the biomass feeding rate (F) and the bed height (H/D) on UA values are also analyzed. Highest UA and specific heat of the pyrolysis reaction of −3.35 MJ/kg are found at F = 5 g/min and H/D = 1.0, where H/D is the largest and F is the lowest in the range studied. Upon feeding of the low thermal conductivity biomass, UA typically decreases. However, if the bed materials are limited, the fed biomass and its produced char act as an auxiliary heating medium to improve the effective heat transfer coefficient. High UA improves the efficiency of the pyrolysis reaction, but it decreases the bio-oil fraction in the product due to secondary decomposition.

Hot gas bypass defrosting with auxiliary heat source in household refrigerators

Frost is inevitable in air-cooled household refrigerators. To maintain the performance of the refrigeration system and food storage quality, additional power input is required to melt the ice periodically. Hot gas bypass defrosting featured high defrosting efficiency, however, suffered insufficient defrosting power at low ambient temperatures, leading to rare application of this technology in household refrigerators. To mitigate this challenge, a novel cost-effective hot gas bypass defrosting system with an auxiliary heater wrapped along the hot gas bypass loop was proposed, and its performance was thoroughly investigated in this paper. Experimental results showed that the defrosting efficiency was 0.8 at an ambient temperature of 32 °C, which was much higher than that of baseline electric defrosting of 0.3. At 20 °C, the new defrosting system with 80 W additional power input in the auxiliary heater successfully melted all frost within 35 min, while the baseline hot gas bypass defrost system without additional heat input could not melt all frost even after 60 min. To further investigate the effects of ambient temperature, compressor speed, and auxiliary heating power, a mathematical model was established and validated by experimental data. The simulated results suggested that it was more efficient to supply more heat from the auxiliary heat source than from the compressor.

Long-term operational characteristics of subway source heat pump system under various tunnel internal heat source intensities

In recent years, subway systems have effectively alleviated urban traffic congestions. However, thermal pollution of underground spaces is a prevailing problem, which poses a serious threat to the safe and efficient operation of subways. The subway source heat pump system (SSHPS), equipped with a front-end tunnel lining heat exchanger, is an effective solution to tackle the aforementioned problem. However, the design methodology and operational strategy of the system is not yet established, which necessitates an analysis of its long-term operational characteristics. In this study, an SSHPS simulation model was developed using the TRNSYS simulation tool based on a demonstration project and the model was subsequently validated against measured data. The validated model was used to evaluate the long-term performance and operational characteristics of the subway system under various internal heat source intensities ranging from 0 W/m to 240 W/m. The simulation results showed that the tunnel air temperature steadily increased as the internal heat source intensity increased. When the internal heat source was 0 W/m, the average annual decrease in tunnel air temperature was 0.11 °C. However, the average annual tunnel air temperature did not fall below the minimum subway design specification temperature of 5 °C at any point in time. When the internal heat source was 120, 180, and 240 W/m, the tunnel air temperature exceeded the maximum temperature of 40 °C stipulated in subway design guidelines on multiple occasions. As the internal heat source intensity increased, the performance of both the heat pump unit and SSHPS progressively decreased during the cooling season and gradually increased during the heating season. The runtime of the heat pump unit gradually decreased from 92.72 % to 77.57 % during the cooling season, whereas it increased from 46.92 % to 89.41 % during the heating season. The heat pump unit exhibited an average energy efficiency ratio (EER) of 5.07, 4.95, 4.87, 4.80 and 4.76 whereas the SSHPS demonstrated an average EER of 3.04, 3.01, 3.00, 2.99 and 2.98. Throughout its operational years, the SSHPS consistently maintained stable and cyclically high performance. However, the system did not fully meet the specified cooling and heating loads under all operational conditions, indicating that there was a source–load mismatch issue within the system. Hence, it is recommended to incorporate auxiliary cold and heat sources, thereby establishing a composite heating and cooling system based on subway source heat pump technology, with the aim of enhancing the reliability of energy supply for the system. This study can serve as a valuable reference for formulating high-efficiency and energy-saving operational strategies for SSHPSs.