The growing adoption of heat pumps presents new opportunities for flexible power system regulation. Mediumdeep ground source heat pump systems (MDGSHPS) exhibit substantial short-term power adjustment capabilities, establishing them as ideal flexible resources on the user side. However, research on MDGSHPS and their interactions with smart grids remains limited, with scarce focus on dynamic oversupply management and targeted optimization control. This study addresses these gaps by quantifying the short-term oversupply flexibility of MDGSHPS through dynamic simulation and regression analysis, which provides a quantitative basis for assessing the system's regulation potential. It further develops a tailored model predictive control (MPC) framework that synergistically optimizes renewable energy utilization and demand response, integrating load prediction models and genetic algorithm-based optimization to adapt to the system's nonlinear and time-varying characteristics. This dual approach fills the void in MDGSHPS's dynamic performance evaluation and enhances its adaptability in complex grid interaction scenarios. Results indicate that adjusting source-side water temperature and leveraging geothermal oversupply can enhance grid stability: during a 1 h pre-spike price period (15 degrees C inlet), cumulative heat intake increases by 64.4%; with thermal energy storage, heat extraction increased by 67.8% while electricity costs were reduced by 62.3%. Compared to the no-energy-storage mode, the fixed time interval control strategy cuts operating costs by 10.5%, while the MPC mode achieves an 11.5% reduction, effectively managing oversupply and supporting demand response under variable loads. This research highlights the potential of MDGSHPS to enhance grid stability and optimize renewable energy integration, thereby contributing to improved power system efficiency.

The air-conditioning loads of industrial buildings exhibit considerable nonlinearity, nonstationarity, and multi-scale variability due to the interaction between production processes and external weather conditions. This study proposes a three-stage hybrid forecasting framework that integrates Variational Mode Decomposition and Sample Entropy (VMD–SE) with a transformer–Bidirectional Long Short-Term Memory (BiLSTM) network architecture, optimized using Quantum Particle Swarm Optimization (QPSO). The VMD–SE module reconstructs the load signal by entropy-based component screening, significantly reducing high-frequency noise while maintaining essential dynamic features. The dual-path transformer–BiLSTM network concurrently captures long-term global dependencies and short-term local changes, facilitating an extensive temporal representation. By automatically adjusting its core parameters, QPSO achieves more efficient convergence, increased stability, and enhanced global search. Two real-world datasets obtained from industrial facilities in Hubei, China, reflecting distinct seasons and load levels, were utilized for validation using ablation and comparative experiments. The proposed model outperformed benchmark models such as SVR, GRU, and CNN–informer, achieving a coefficient of determination (R2) of 0.981 23 and a root mean square error of 0.181 32. The findings indicate that the proposed model is effective and versatile across various situations, offering both theoretical understanding and practical guidance for intelligent HVAC scheduling, dynamic demand response, and low-carbon energy management in industrial facilities. Our results show that the model is robust and flexible, providing a practical and theoretically grounded approach for intelligent HVAC scheduling, demand response, and industrial carbon reduction.

Deep borehole heat exchanger (DBHE) heating systems have gained increasing attention due to their high efficiency, long-term sustainability, and operational stability. However, traditional DBHE systems are primarily limited to serving as direct building heating systems through one-way heat extraction from the subsurface, lacking flexibility for integration. This study explores a novel hybrid configuration that incorporates thermal energy storage (TES) and solar collectors (SC) into a DBHE-based heating system. A detailed TRNSYS simulation model was developed for an office building in Xi'an, China, incorporating the full configurations of the DBHE, TES, and SC subsystems. Key design parameters, including the solar collector area and tilt angle, TES tank volume, and the heat pump's storage temperature setpoint, were systematically optimized to minimize the system's levelized cost of heating (LCOH). The results indicate that the DBHE-TES-SC system achieved improved heating performance with a more dynamic temperature profile during the heating season. The system also benefits from short-term thermal storage and peak-shaving strategies, offering increased operational flexibility. Over a 10-year operation period, although the coefficient of performance (COP) of the heat pump decreases from 5.63 to 5.14, the outlet temperature decay rate is only 6.5%, demonstrating superior longterm operational sustainability. From an economic perspective, the proposed system reduced annual operating costs by over 36 %, shortened the payback period by 0.45 years, and achieved a lower LCOH than that of a conventional DBHE system. In addition, a preliminary case study is presented to explore the feasibility of deep borehole thermal energy storage (DBTES) for storing intermittent solar energy during the non-heating season. The results show that this strategy can further reduce the annual electricity consumption by an average of 2.47 MWh, underscoring the need for a comprehensive analysis of DBTES in future research. These findings highlight the strong techno-economic potential of integrating TES and SC into DBHE systems. The proposed optimization method can serve as a reference for decision-makers in the geothermal community for building heating applications.

To achieve energy savings, reduce consumption, and support the “dual-carbon” strategy in China, this study applies digital twin technology to investigate the centralized air-conditioning water system of a metro-station HVAC installation and develops a high-fidelity digital twin model to reveal the thermal delay and thermal attenuation characteristics of the pipeline network. Using the noncausal modeling approach of the Modelica language, a full digital twin representation of the centralized air-conditioning water network is constructed by covering chillers, cooling towers, pumps, terminal units, the pipeline network, etc. The model is validated against real operation data to ensure high fidelity. Validation shows the predicted chilled water flow rate of the digital twin model agrees well with the measured chilled water flow rate with an RMSE of 0.27 kg/s. Validation also shows the difference is about 0.3 °C between the digital twin prediction and the measurement in the main pipe. Based on the validation digital twin model, the thermal delay and thermal attenuation characteristics of the centralized air-conditioning water system are seriously evaluated. The results indicate that branch K3, due to its longest transport distance, exhibits a delay of 227 s. The overall thermal delay of the system reaches 7.5 min. The temperature attenuation of this water system is about 0.2 °C due to heat loss through pipe walls. The findings may offer theoretical support for the optimal regulation and control, fault detection, and anomaly identification of this centralized air-conditioning water system.

This paper addresses the critical challenge of reducing energy consumption and CO2 emissions in China's space heating sector by exploring industrial waste heat recovery in a copper smelter in Chifeng City. Traditional heating systems rely heavily on fossil fuels, contributing to 4 % of national energy consumption. The research proposes a novel T-Q-C diagram model, integrating temperature, heat, and carbon emission indices, to optimize waste heat utilization. Three innovative schemes are compared with the existing process: Scheme B (absorption heat pump-based full recovery), Scheme C (terminal large-temperature-difference recovery), and Scheme D (integrated recovery). The waste heat potential (369 MW) of copper plant is analyzed, with current recovery at 212 MW (57.46 % efficiency) and CO2 emissions of 60.6 tons/MW & sdot;a. Scheme B achieves full recovery (369 MW) but lowers supply water temperature (53.4 degrees C) and reduces emissions to 49.2 tons/MW & sdot;a. Scheme C increases supply water temperature (69.9 degrees C) but recovers 93 % waste heat (344 MW) with emissions of 50.2 tons/MW & sdot;a. Scheme D combines the advantages of B and C, achieving full recovery (369 MW), higher supply water temperature (73.5 degrees C), and the lowest emissions (49.2 tons/MW & sdot;a). Economic analysis reveals Scheme D has the highest initial cost but optimal performance in heat recovery, temperature, and CO2 emissions. The T-Q-C model proves effective in balancing technical, economic, and environmental factors, highlighting the potential of integrated technologies to advance sustainable urban heating under China's carbon neutrality goals.

This paper conducted field tests and comparative studies on the operation performance of different kinds of heat pumps integrated with mid-deep borehole heat exchangers. Results show that the mid-deep borehole heat exchangers could provide heat source with temperature higher than 25 degrees C. But the constant-speed screw heat pumps failed to match the wide-range variation of heating capacity and compression ratio, especially the small values of compression ratio. Thus the internal efficiency of constant-speed screw compressor was lower than 0.50 during the whole heating season, and the energy efficiency of heat pumps was lower than 5.0. In comparison, the variable-speed centrifugal heat pumps preferentially adjusted compressor speed to match the variation of heating capacity and compression ratio, thus the internal efficiency of compressor could reach 0.62 during the heating season and the energy efficiency of heat pumps could reach 7.0. Then the control strategies of heat pumps were compared and optimized, where the user-side supply water temperature of heat pumps should be chosen as control value, which could response in time to the adjustment of heating capacity, and had significant influence on the energy efficiency of heat pumps. Furthermore, the control strategies of water distribution systems were analyzed, so as to improve the energy performance of the whole system. With the above optimization, the operational energy cost of mid-deep geothermal heat pumps could be reduced by 61.4 %, 48.7 %, and 69.8 % respectively compared with air source heat pumps, shallow-deep geothermal heat pumps and Gas Boiler. Also the CO2 emissions could be reduced by 61.4 %, 48.7 %, and 60.5 % respectively.

This study examines space cooling characteristics and energy performance of ice-storage cooling systems in a large-scale stadium in China. As for the indoor environmental effects, significant air temperature stratification, thermal inertia and unorganized air infiltration have been discovered, leading to drastic cooling load fluctuations. Without adequate control strategies, the annual average COPs of chiller plant in year of 2024 only reached 2.53. Then the three-part optimization approaches have been conducted to improve the energy performance substantially, from equipment improvement to system control. Firstly, the hydraulic balancing of cooling towers has been conducted, thus the ice storage capacity increased from 20,800 RTh to 27,500 RTh during night valleytariff periods, with better heat release effects. Then the operation parameters for ice storage and melting systems have been optimized to improve the energy performance of chiller plant from 3.21 to 3.63, achieving 13% energy savings. Furthermore, the operation mode has been optimized to fully utilize the two-hours valley-tariff periods at noon for cooling storage, thus the energy costs decreased from 0.157 Yuan RMB to 0.127 Yuan RMB per cooling capacity. In summary, this paper discussed and highlighted the importance of fully utilizing cooling storage capabilities of stadium air volumes and chilled water systems, while implementing control strategies based on accurate cooling load prediction to enhance both energy efficiency and indoor thermal comfort.

Mid-deep geothermal heat pump systems (MD-GHPs) feature high energy efficiency and low energy consumption, yet their promotion is restricted by high initial investment. While the initial investment of air-source heat pumps (ASHPs) is obviously lower, it also has a larger energy consumption. To address the complementary strengths and weaknesses of single-source heat pump systems, this paper puts forward an integrated system combining MD-GHPs and ASHPs, and the series mode was determined as the optimal integration approach for the hybrid system through comparative analysis. Simulation analysis was conducted to explore the adaptability of series mode, and numbers of mid-deep ground heat exchangers in nine cities across various climate regions were studied. The MD-GHP system is suitable for space heating in Xining and Xi’an, while ASHPs are suitable for space heating in Nanjing and Hangzhou. For intermediate resource areas like Urumqi and Tsingdao, the series mode achieves the best economic benefits during the 24th year of operation.

Ice storage systems are commonly applied for space cooling in large-scale commercial buildings to realize cost-saving effects. However, the practical operation performance is far poorer than expected. This paper conducted field tests to study the operation performance of ice storage system in a commercial building located in hot summer and warm winter area in China. Where the mismatch between ice storage capacity of chiller plant and cooling demand of buildings was found the typical issue leading to insufficient ice storage in cooling season and over ice-storage in transition season. Thus the annual average COP of Ice-storage chillers and the annual EER of whole chiller plant only reached 3.19 and 2.53 respectively, and the cooling price reached 0.194 Yuan RMB/kWh. To address this, a control strategy based on a cooling load prediction model was implemented. The model inputs the easily obtainable parameters such as ambient meteorological conditions, working/rest days, and previous cooling load data to predict the cooling demand next day, and then to guide the daily ice storage capacity during valley electricity price period, as well as the cooperation of ice melting system and direct cooling system for space cooling. Therefore, significant energy and cost-saving effects were achieved, where the cost-saving rate reached 41.9%, and the cooling price decreased to 0.111 Yuan/kWh.

The mid-deep borehole heat exchangers (MDBHEs) integrated with heat pump systems have been applied for space heating widely in China. This paper conducted field tests, simulation analysis and comparative study to evaluate the energy and economic performance MDBHEs hybrid with heat pump storage systems. Firstly, the energy performance of hybrid system in direct heat supply mode was field tested, where the coefficient of performance of the system (COPs) reached 5.82 among the heating season, but the heat capacity was mainly generated with peak and flat tariff period, thus the energy cost per heat capacity reached 50.18 Yuan RMB/GJ. Then the operation performance of system under heat storage mode was simulated and studied. When the heat storage tank is heated from 40 degrees C to 60 degrees C, the heat storage capacity reached 8.13 MWh. And the COPs among the heating season decreased to 5.19, with constant ground-side water flow rate of 13 kg/s per MDBHE. But benefiting from the valley electric price, the energy cost significantly decreased to 31.05 Yuan RMB/GJ. Then the control strategies of ground-side water distribution system were studied, where the constant water temperature differences control methods with value of 12 degrees C showed better energy and economic performance, with COPs reaching 5.28 and energy cost reaching 30.56 Yuan RMB/GJ. Furthermore, the heat storage characteristics of building spaces, heat storage tanks and MDBHEs were compared, which should be controlled synergistically, so as to improve the energy and economic performance.

This study analyzes the configurations and control strategies of hybrid heating systems of air-source heat pumps (ASHPs) and gas boilers for space heating in different climatic regions in China, with the aim of improving the comprehensive energy efficiency. Parallel and series hybrid modes were proposed, and simulation analysis was conducted to analyze the energy performance, energy costs, and CO2 emissions of different hybrid systems. The results show that the supply water temperatures of ASHPs in series mode are lower than that of ASHPs in parallel mode; thus, the COP of ASHPs in series mode reached 2.73 and was higher than the COP of ASHPs in parallel mode with a value of 2.65. Then, the optimal intermediate temperatures of hybrid system in series mode were analyzed, so as to guide the system control. The results show that compared with series mode with a fixed 50% load distribution, the operational costs and CO2 emissions were reduced by 10.0% and 10.4% in Harbin, reduced by 6.4% and 8.3% in Beijing, and reduced by 10.0% and 15.1% in Wuhan. Additionally, the optimal intermediate temperature was affected by the building load ratio, supply water temperature, ambient air temperature, and the electricity–gas price ratio. The series-hybrid ASHP and gas boiler system achieves remarkable energy and cost savings across different climatic conditions, providing a scientific basis for promoting low-carbon heating solutions.

To refine the thermodynamic cycle of the existing vapor-compression photovoltaic-thermal (PVT) heat pump systems, a novel PVT power heat pipe/heat pump composite cycle system was proposed. The switching mechanism between the PVT power heat pipe cycle and PVT heat pump cycle was investigated to achieve optimal performance under complex and variable outdoor conditions. A simulation platform for the proposed system was established, and operating control strategies were proposed, employing system exergy efficiency and supplyreturn water temperature differentials (0.5, 1.0, and 1.5 degrees C) as the switching criteria between the PVT-PHP and PVT-HP cogeneration modes. Additionally, a comparative study was performed to evaluate the system's performance under various weather conditions and different operating control strategies. The research results demonstrate that using exergy efficiency as the switching criterion yields optimal performance under sunny conditions, with the respective values for hot water production, power generation, average exergy efficiency, and average COP reaching 5.0 tons, 42.4 kWh, 13.5 %, and 8.2; whereas a supply-return water temperature differential of 0.5 degrees C as the switching criterion is more effective under non-sunny conditions. Under cloudy conditions, the corresponding values for hot water production, power generation, average exergy efficiency, and average COP are 4.0 tons, 24.3 kWh, 13.2 %, and 5.3, respectively; under overcast conditions, the corresponding values for hot water production, power generation, average exergy efficiency, and average COP are 4.0 tons, 7.1 kWh, 14.9 %, and 3.9, respectively.

Mid-deep geothermal heat pump systems (MD-GHPs) use mid-deep borehole heat exchangers (MDBHEs) to extract heat from the geothermal energy at a depth of 2–3 km, and have been used for space heating in China over the last decade. This paper proposes a comprehensive and multilevel evaluation-index system to analyze and evaluate the energy performance of MD-GHPs. The multilevel evaluation index system consists of a target layer, a criterion layer, and an index layer, where the criterion layer is subdivided into six aspects and the index layer includes 26 specific indices, reflecting the geothermal resources, heat transfer performance of the MDBHEs, energy efficiency of the heat pump systems, building space heating demand, grid dynamic response capability, and energy-saving and economic benefits. Then, based on both expert survey results and case study data, the entropy weight method and the analytic hierarchy process are integrated to determine indicator weight coefficients among the multilevel evaluation indices, comprehensively considering both subjective and objective analyses. Furthermore, a fuzzy comprehensive evaluation model is conducted to integrate these weighted indices into a multi-criteria evaluation of MD-GHP performance. Finally, the proposed method was applied to evaluate the practical performance of four projects, returning scores of 61.56, 58.33, 72.73, and 78.41. These evaluations enable an overall assessment of the energy performance of MD-GHPs, reflecting the technical weaknesses and offering optimization guidance for system design and operation.

The electric-driven heat pump technology is commonly applied for space heating and cooling for buildings,and also becomes the key link for cooperation with power grid to consume clean electricity.This paper proposes a high-efficiency heating and cooling system by combining the electric-driven heat pump technology with the medium-depth ground heat exchanger for heating in winter and the cooling tower for cooling in summer.Then the user-side energy storage system is applied for daily heat and cool storage.With this system,the design method and control strategy are proposed to fully absorb the local photovoltaic power generation and municipal clean power.Furthermore,this paper conducts a case study on a large public building with quantitative analysis,so as to analyse the actual energy-saving and CO2 emission reduction effect.

As deep borehole heat exchangers (DBHEs) extract heat from geothermal energy with depth of 2–3 kilometers, the circulation water pressure drop is larger than that of shallow-depth borehole heat exchangers, influenced by the water flow rates. This paper conducted field tests and simulation analysis to study the heat transfer performance and water circulation resistance of DBHE in coupled, where the natural circulation characteristic has been discovered and analyzed quantitatively. Results show that the water temperature and density variation along DBHE forms the driving force of natural circulation. For mechanical flow rate of 6.0 kg/s and inlet water temperature of 20.0 °C, the natural circulation flow rate reaches about 2.2 kg/s with transient heat extraction power of 78.5 kW, without energy consumption of water pumps. And the larger inlet water temperature, smaller mechanical water flow rate, higher inner tube thermal conductivity coefficient and larger depth of DBHE all contribute to the larger natural circulation water flow rate. In addition, the natural circulation could effectively decrease the comprehensive water pressure drops of DBHE, which is about 47.3

The HVACs in super high-rise buildings commonly consists of variable air volume (VAV) systems, multistage chilled and cooling water systems, primary-secondary chilled water system in chiller plant, and the chillers combination is much more complex, leading to the significantly higher energy consumption than that of normal buildings. This paper contains field tests and comparative studies on the operation performance of HVACs in two super high-rise buildings and summarized representative issues accounting for the high energy consumption. Field test results showed that the annual energy efficiency of the whole HVAC system, before being commissioned, was only 1.79 and 2.15 in two projects. The HVACs, typically VAV systems, chilled and cooling water systems, all suffered from over-supplying and energy wasting. Besides, the chillers commonly operated with a low partial load ratio (PLR), whose energy performance was much lower than expected. Aiming to dig out the typical issues, analyses were carried out from external, internal factors, and their interconnection. Furthermore, optimization methods were put forward with corrected vital indexes. Results showed that proper control strategies should maintain the VAV system, multistage chilled and cooling water system operating with significant distribution temperature differences, tiny distribution pressure drops, and high energy efficiency, thus achieving energy saving and ensuring space cooling effects. Besides, the control strategies, especially the number control of chillers, were influential during the whole cooling season to ensure the chillers operate with optimal PLR and thus achieve better energy performance.

Deep borehole heat exchanger (DBHE) extracts heat from mid-deep geothermal energy through heat transfer process. As DBHE commonly applies coaxial borehole heat exchangers with depth of 2-3 km, the volume reaches more than 30 m3, similar to the small heat tank underground. When the heat pump system turns off, the water in DBHE still extracts heat from the high-temperature ground and stores heat. This kind of heat storage characteristic of DBHE was studied in this paper with simulation analysis. Benefiting from the heat storage characteristic, the average heat extraction rate (Qr) of DBHE under intermittent operation is 8.6%-64.7% higher than Qr under continuous operation, with run-stop ratio decreasing from 24 to 0 to 8-16 per day. Then the influence of operation modes, parameters and thermo-physical properties of DBHE on the heat storage characteristic were studied quantitatively, proving the wide-range regulation ability of Qr. Therefore, the regulation ability of DBHE matches the variation of space heating load very well, and also matches the production rules of clean electric power like photovoltaic and wind power. Hence, the DBHE could further participate in the demand response of electrical power system, and absorb clean electric power.