In northern China, public buildings commonly use direct-expansion air-conditioning systems for cooling and district heating networks for heating, necessitating separate terminals for each function. This study proposes a multi-connected air conditioning system capable of utilizing refrigerants and water for direct heating with hot water from district heating systems. The system integrates three-fluid heat exchangers within indoor units, enabling seamless switching between direct-expansion air-conditioning and district heating systems. Using an office building in Beijing as a case study, the system was evaluated under summer cooling design conditions, and its heating performance during winter and transitional seasons was analyzed. Results reveal that during winter, the system requires user-side water temperatures below 54 ℃, while in transitional seasons, the direct-expansion mode delivers unit capacities exceeding peak heating demands with energy efficiency surpassing 3.5 over 49% of operating hours. This system simplifies existing configurations by providing a single terminal for year-round heating and cooling, enhancing efficiency and thermal comfort.

To reduce energy consumption in temperature- and humidity-independent air-conditioning systems and enhance solar energy utilization, this study developed a solar-assisted desiccant wheel and adsorption cooling system (SDCS-A) using TRNSYS 18. System performance under Guangzhou's climatic conditions was analyzed by varying collector areas and tank volumes together with evaluating metrics such as system coefficient of performance (COP_sys), solar fraction (F_s), and primary energy consumption (E_p). These results were compared with those of a solar-assisted desiccant wheel and vapor compression cooling system (SDCS-C). Findings indicate that changes in collector area significantly influence F_s and E_p, with F_s increasing by an average of 12.18%, while variations in tank volume predominantly affect COP_sys, with a maximum difference of 0.1. Compared to SDCS-C, SDCS-A achieved 6.51% higher monthly average COP_sys, a 21.05% increase in F_s, and a 21.45% reduction in E_p during the cooling season. Furthermore, the system's performance across different climates was evaluated, demonstrating that Guangzhou offers more stable and higher monthly COP_sys values than Beijing, Shanghai, and Lhasa.

Helium throttling refrigeration technology is a key cooling method used in liquid helium temperature zones in space. Research on the rapid cooling of chillers coupled with large heat capacity loads is important for the efficient operation of large heat capacity loads. To clarify the cooling characteristics of helium throttling chillers under different rapid cooling schemes, cooling experiments with no additional measures scheme, room-temperature valve bypass scheme, and thermal switch scheme were conducted based on GM pre-cooled helium Joule-Thomson chillers under different heat capacity loads. The experimental results show that the load-free pull-down times of the three schemes were 39.8 h, 20.5 h, and 19 h, respectively. Based on thermodynamics and heat transfer theories, the changes in the radiation, convection, heat conduction, and throttling source terms during no-load cooling were quantitatively analyzed, and the reasons for the difference in cooling time of helium throttling chillers under different schemes were explained. With a simulated load of 0.136 kg of copper, schemes of the room-temperature valve bypass and hot switch were adopted, and the corresponding cooling times were 25.5 h and 20 h, respectively. The experimental results show that the cooling effects of the thermal switch and room-temperature valve bypass scheme are essentially the same for the cooling of a small heat capacity load. Therefore, thermal switch cooling has significant advantages for large-heat-capacity load cooling.

Displacer-type pulse-tube cryocoolers use a displacer for phase adjustment and recovery of acoustic power, leading to high refrigeration efficiency. Despite their potential, there is limited research on highly efficient displacer-type pulse-tube cryocoolers with large cooling capacities near -100 ℃. This paper presents the design of a 100-watt displacer-type pulse-tube cryocooler for low-temperature freezers and evaluates its performance, focusing on displacement motion and compressor efficiency. A validated numerical model was employed to analyze the coupling between the pulse tube and compressor and the internal phase relationship of the cold finger. Results show that under operating conditions of a 3.0 MPa charging pressure, 64.9 Hz frequency, 20 ℃ cooling water temperature, and 500 W input power, the cryocooler achieved a cooling capacity of 160.3 W at -100 ℃ with a relative Carnot efficiency of 22.2%. The displacer led the compressor piston by 59°, the internal phase distribution of the pulse tube was optimal, and the compressor exhibited a high efficiency of 78%. This cryocooler is the most efficient displacer-type pulse-tube cryocooler in its temperature range.

The refrigeration industry is advancing towards environmentally friendly, efficient, and safe alternative refrigerants. To analyze compressor performance with various refrigerants, this study proposes a modified semi-empirical model with 13 characteristic parameters. Experiments were conducted with R22, R507, and R744 under variable operating conditions to identify parameters and validate the model. The experimental and simulated results showed strong agreement, with average relative errors of 2.07% for input power and 1.17% for mass flow rate. Using a typical operating condition, the losses and efficiencies of different refrigerants were compared at various frequencies. Results indicate that R744, with the lowest pressure, leakage, and power losses, demonstrated superior performance. While R507 and R22 showed similar efficiencies, the efficiency of R507 declined significantly at frequencies above 50 Hz due to increased pressure losses. This study provides a theoretical basis for optimizing compressor designs for various refrigerants.

Because the piston volume of a scroll compressor with variable base circle involute can be reduced under the premise of obtaining the same cooling capacity, it can satisfy the compact and lightweight requirements of vehicle air conditioning compressors. To improve the isentropic and volumetric efficiencies of the scroll compressor, a mathematical and geometric model of the scroll disc with a variable base circle involute was established. With the variable index k and the modified increment δ₀ as variables, the internal flow field of the scroll compressor is numerically simulated, and fluid dynamic analysis is conducted. The numerical results show that when the parameters of the variable base circle line are k=1 and δ₀=-0.03 mm, the specific dissipation rate of the fluid in the compressor working chamber is 180.28 s^-1, which is 103.11 s^-1 lower than the 283.39 s^-1 of the flow field in the fixed base circle compressor. The isentropic efficiency of the scroll compressor can be improved by reducing energy loss due to the turbulent kinetic energy dissipation. The performance of the scroll compressor for electric vehicle air-conditioning was tested. Compared with the fixed base circle scroll compressor, the input power of the variable base circle scroll compressor with k=1 and δ₀=-0.03 mm decreases by 1.392%, and the performance coefficient COP_el increases by 4.204%.

This study investigates the magnetocaloric properties and refrigeration performance of batch-prepared (La, Ce)(Fe, Mn, Si)₁₃H_y alloys. After heat treatment and hydrogenation, the Curie temperatures of M1, M2, and M3 were 292.9 K, 287.8 K, and 283.9 K, respectively, decreasing with higher Mn content. Arrott plots indicated an itinerant-electron metamagnetic transition. M2 exhibited the highest isothermal magnetic entropy change of 12.0 J/(kg·K) under a 2 T magnetic field, with a full width at half maximum of 11 K. Relative cooling capacities (RCP) were 110.2 J/kg, 132.0 J/kg, and 110.0 J/kg for M1, M2, and M3, respectively. Adiabatic temperature changes measured under a 1.5 T magnetic field were 3.48 K, 3.14 K, and 2.96 K for M1, M2, and M3, respectively. A maximum refrigeration temperature span of 16.9 K was achieved by cascading the alloys at an ambient temperature of 295 K.

A composite cold storage phase change material (PCM) based on Na₂SO₄·10H₂O and Na₂HPO₄·12H₂O was developed to meet the temperature requirements of cold storage air conditioning. The phase change temperature was 8.3 ℃, with a latent heat of 151.3 kJ/kg, representing a 14.24% increase in latent heat compared to previous works. Additionally, a novel thermal energy storage device utilizing spherical encapsulated PCM within a packed bed was proposed. A three-dimensional physical model of the packed bed was constructed using EDEM software to study the effects of sphere capsule size, inlet temperature, and heat transfer fluid (HTF) flow rate on the system's thermal performance. Results show that reducing the sphere capsule size, lowering the HTF inlet temperature, and increasing the HTF flow rate accelerate the thermal energy storage process and reduce charging time. For instance, when the HTF inlet temperature increases from 2 ℃ to 4 ℃, the packed bed's cold storage capacity and density decrease by 5%, the average cold storage rate drops by 41.93%, and the pressure drop remains relatively constant. However, the effect of sphere capsule size on thermal energy storage capacity and density lacks a clear trend and depends on specific engineering applications. These findings offer theoretical guidance for the practical application and broader use of packed-bed thermal energy storage systems for air conditioning.

As a core heat exchange component in forced-draft cooling towers, the performance of packing material significantly impacts the power consumption of the equipment. In this study, an experimental platform for crossflow cooling tower packing was developed to examine the effects of wind speed, water spray density, and packing height on the heat and mass transfer performance and resistance characteristics of herringbone corrugated packing. Empirical formulas were derived to analyze fan power consumption in crossflow cooling towers. Results reveal that heat and mass transfer performance improves with increased wind speed and water spray density and decreased packing height. Wind speed was found to be the most influential factor; increasing wind speed from 0.96 m/s to 2.05 m/s raised the mass-transfer coefficient by 70%. At low water spray densities, increasing the density significantly enhanced heat and mass transfer. Air resistance in the packing zone increased with air velocity, approximately proportional to the 1.68-1.91 power of wind speed. When the cooling water volume flow rate was 70 m³/h, sacrificing 20% of heat exchange capacity and reducing the inlet-outlet temperature difference from 5 ℃ to 4 ℃ reduced power consumption by approximately 71%. To maintain a power consumption ratio of 0.035 kW·h/m³, lowering the approach temperature from 4 ℃ to 3 ℃ required a 31% reduction in cooling water volume flow rate.

To address the issue of unreasonable buried pipe length design in ground-source heat pump projects, a three-dimensional dynamic simulation platform was developed. The reasonableness of the buried pipe length was evaluated by comparing the simulated outlet temperature with the designed outlet temperature based on specifications. Using a building in Beijing as a case study, the effects of soil thermal properties and borehole-related parameters on the design error in buried pipe length were analyzed. A sensitivity analysis further examined the impact of these factors. Results indicate that the relative error in buried pipe design length increases with rising soil thermal conductivity, soil volumetric heat capacity, borehole depth, and borehole spacing. Relative error ranges were 10.7%-27.3%, 8.0%-23.8%, 7.3%-12.5%, and 12.5%-17.4% for the respective factors. Sensitivity analysis revealed soil thermal conductivity as the most significant factor influencing pipe length, with a quantitative index of 0.909. Other influential factors, in descending order, were soil volumetric heat capacity, borehole spacing, number of borehole columns, and borehole depth.