The global phase-down of high-GWP refrigerants necessitates a transition to sustainable alternatives like R290 (GWP = 3) and R32 (GWP = 675). However, their dynamic startup reliability in extreme polar climates remains poorly understood. This study experimentally investigates the transient startup performance and operational stability of R290 and R32 air-conditioning systems under real-world severe cold conditions in Mohe, China, where ambient temperatures organically reached a nadir of -42.69℃. Field tests were executed on four systems from two manufacturers (Brands A and B) exposed directly to the outdoor environment, assessing both cold start (24 h deep freeze) and warm start (10 min intermittent shutdown) scenarios. Quantitative analysis reveals that R290 systems significantly alleviate mechanical stress in deep freezing environments; during cold starts, Brand A's R290 unit exhibited a peak discharge pressure of only 0.84 MPa and a stable discharge temperature of 44.00℃, compared to a severe 2.16 MPa and 78.40℃ for its R32 counterpart. Conversely, R32 systems demonstrated faster dynamic equilibrium and superior electrical stability during rapid cycling; warm start power consumption Coefficient of Variation (CV) for Brand A's R32 was 0.44, substantially more stable than the 0.38 CV of the R290 system. Crucially, the empirical data exposes that manufacturer-specific control algorithms heavily dictate system behavior, evidenced by Brand B's R290 unit anomalously peaking at a 91.42℃ discharge temperature during warm start. These high-granularity empirical findings provide essential quantitative baselines and dynamic behavioral insights for optimizing low-GWP heat pump design and predictive fault diagnosis models in extreme cold regions.
Abstract The rising demand for energy and electricity has led to the exploration of innovative approaches to improve energy efficiency in cooling systems. This study experimentally investigates the performance of a split-type air-conditioning system using R-404A refrigerant and CNT/TiO₂ nanolubricants dispersed in polyol ester (POE) oil at mass concentrations of 0.05, 0.1, 0.2, and 0.3 wt%. The objective is to enhance the thermal and tribological performance of the compressor while reducing overall energy consumption. The incorporation of CNT/TiO₂ nanoparticles into POE oil is expected to improve system performance by reducing compressor power consumption and enhancing heat transfer capacity. To ensure effective utilization and uniform dispersion of the nanoparticles, a two-step preparation method was employed. System performance was evaluated in terms of cooling capacity, compressor power consumption, coefficient of performance (COP), and pull-down time. The experimental results demonstrate that a nanolubricant concentration of 0.2 wt% provides optimal performance, resulting in a 16.5% increase in COP, a 13.8% enhancement in cooling capacity, and an 11.2% reduction in compressor power consumption compared to pure POE oil. In addition, evaporator temperature variation over time, compressor energy consumption, and pressure drop across the evaporator were investigated. The pull-down time was reduced by 18%, while the nanolubricant exhibited excellent suspension stability throughout the experimental duration. Overall, the results confirm that CNT/TiO₂ nanolubricants significantly enhance both the cooling capacity and energy efficiency of air-conditioning systems. However, the long-term stability, durability, and large-scale applicability of the nanolubricant require further investigation. Future research should focus on system optimization and lifecycle performance evaluation.
Abstract Energy-recovery ventilators (ERV) exhaust polluted indoor air while supplying outdoor fresh air and recovering energy via heat and mass exchange. Their adoption is rapidly increasing because they simultaneously improve indoor air quality and reduce building energy consumption. This study quantifies the pressure-loss contribution of a sliding bypass damper’s gear-support bracket located in the ERV damper space of a 350 m³/h unit comprising a desiccant rotor and heat-pump dehumidification. We employ steady, incompressible RANS CFD(Reynolds averaged Navier-Stokes computational fluid dynamics) using the realizable $$\:k-\epsilon\:\:$$ turbulence model and an experiment-based porous-media method. Four internal flow paths are analyzed: OA(Outdoor air) to EA(Exhaust air), OA to SA(Supply air), RA(Return air) to EA, and RA to SA. To reduce computational cost, the section from the OA/RA inlets to the heat-exchanger face, rotor/fan rotation, and thermal effects are excluded from the domain. The fin-tube heat exchanger and desiccant rotor are modeled as porous media; their viscous and inertial resistances are inferred from dedicated fin-tube pressure-drop tests and manufacturer data and were used to validate the CFD model. Removing the damper gear-support yields the largest benefit in the OA to SA path: at 450 m³/h the total pressure drop decreases by 11.9%. In RA to EA, however, improving inlet-face flow uniformity is identified as a more effective strategy than bracket removal. For OA to EA and RA to SA, the effect of bracket removal is marginal. Across all paths, net pressure-drop reductions of 1.78%, 4.61%, and 4.77% are obtained at 250, 350, and 450 m³/h, respectively. Based on these findings, we suggest replacing the sliding bypass damper (or redesigning its support) and pursuing additional loss-reduction measures such as inlet-face flow conditioning and inlet/outlet alignment. The results demonstrate that CFD, coupled with experiment-informed porous-media modeling, is an effective tool for guiding low-cost internal-flow improvements that reduce ERV pressure losses.
Barocaloric materials promise eco-friendly alternatives to vapour compression in refrigeration, with (C9H19NH3)2CuBr4 being a focus of this study. It is a highly promising barocaloric refrigerant due to the 0.4 K hysteresis temperature and operational pressure as low as 500 Bar. A reversible and irreversible Brayton Barocaloric refrigeration cycle analysis is established. For the irreversible cycle, the irreversibility during the compression and expansion process is considered in the two adiabatic processes. Performance characteristics are investigated across various indoor and outdoor temperature ranges, material operational temperature points, and operating pressures to determine the Coefficient of Performance (COP) and Dimensionless Refrigeration Capacity (DRC). The guidance for optimising the irreversible Brayton Barocaloric refrigeration cycle analysis is provided by disclosing the impact of the irreversibility of work process efficiency, timing ratio, and heat reservoir temperatures. Moreover, several specific cases are examined in detail. The results demonstrate that maximising the phase transition region of (C9H19NH3)2CuBr4 results in a COP of 10.8 achieved at a temperature span of 3.5 K while maintaining a 0.9-time ratio and conservative irreversibility efficiency of 0.8. This material is capable of cooling by 5.0 K with a reasonable COP of 2.5 at the 0.75-time ratio for a heat source temperature of 309 K and heat sink temperature of 314 K. Finally, this study demonstrates the potential for constructing a simple Barocaloric refrigeration system to validate the concept, with opportunities for further improvement through modifications.
In the air conditioning and refrigeration market, air conditioners using mechanical compressors have become very common, leading to a significant increase in electricity consumption and contributing to the power crisis that many countries are facing. The emergence and development of absorption chillers in general, and absorption chillers without using liquid pumps in particular, provide effective cooling capabilities, energy savings, and environmental friendliness through the reuse of waste energy at low temperatures. However, improving the efficiency of absorption chillers without using liquid pumps remains a challenging problem. This paper delves into the study of the heat transfer characteristics of the thermosiphon desorber (in absorption chillers without using liquid pumps). The mass flow rate of the hot water supplied to the desorber device is varied, combined with different heights of the riser tubes (zV = 0.25 m and zV = 0.7 m). A model is formulated by simultaneously solving mass, energy, and momentum equations to calculate the heat transfer coefficient for single-phase and two-phase flows. Subsequently, an assessment is made of the heat flow and pressure drop in the riser tube of the thermosiphon desorber.
Abstract Low-temperature radiant temperatures below the dew point can now be used in hot and humid areas thanks to decoupled radiant cooling technology. In high-temperature, high-humidity air settings, condensation-free low-temperature radiant cooling has been made possible by the materials with high infrared transmittance. It is yet unknown how the human body transfers heat dynamically in low-temperature radiant cooling environments. Thus, a transient heat transport model of the human body in three dimensions was created and validated. In a thermal setting with low-temperature radiation, the dynamic process of the human body was examined. Under low-temperature radiant conditions, the variations in the body’s heat flux and skin temperature were examined. According to the findings, the radiant heat flux on the human body’s upper torso can reach 49 W/m² and the ratio of radiant heat flux can approach 70% once steady-state conditions are met. The human body can reach thermal equilibrium through radiant heat transfer using a low-temperature radiant panel when the initial air temperature is 32 °C and the radiant cooling panel’s temperature is 5 °C. This is possible when the human body’s surface heat flux density is 70 W/m².
Abstract In the present study, a numerical analysis of a vertical solar chimney with different shapes of absorber wall is carried out. The absorber wall is structured in four cases. The first case is a smooth wall. The other cases are rough structure cases A, B and C. Case A is a wall with roughness of a triangular profile. Case B is identical to case A but has a curvature profile connection to the base. Case C is a wall with a rectangular roughness and a curve profile at its base. The chimney gap varies from 10 cm to 50 cm, the uniform heat flux is varied from 200W/m2 to 600W/m2 and Rayleigh number changes from 3.9×1012 to 1.2×1013. These cases are tested under isothermal glazing wall boundary condition. The optimum case is tested under adiabatic and convective glazing wall boundary conditions and compared to the isothermal boundary condition. The results show that the air flow rate of case A is higher than that in cases B and C by 6.9% and 3.5%; respectively at heat flux of 600W/m2 and chimney gap of 20 cm. The optimum conditions that maximize air flow rate in a solar chimney of case A is obtained at chimney gap of 40 cm compared to the other gaps at all heat fluxes. For case A at heat flux of 600W/m2 and chimney gap of 40 cm, the mass flow rate increases by 71.9%, 52.8%, 21.9% and 2.5% than chimney gaps of 10 cm, 20 cm, 30 cm and 50 cm; respectively. The solar chimney of rough absorber wall case A shows backflow at chimney exit for a gap of 50 cm in the isothermal boundary condition compared to the other boundary conditions. A higher air flow rate is obtained in an adiabatic glazing wall condition while lower air flow rate is obtained in the condition of isothermal glazing wall.
This paper focuses on the cooling capacity analysis of aluminium tube evaporator for cooling compartments in domestic refrigerator. The study adapted a framework combining analytical and experimental analyses to investigate the influence of evaporator tube length on the cooling capacity of the freezer and refrigerator. Convective heat transfer co-efficient based on two-phase flow was calculated under four different correlations considering a domestic refrigerator of 246 L volume using R600a refrigerant. Cooling capacity was calculated based on the product of cooling capacity factor and cubic root of volume signifying the heat loss. The cooling capacity factor provides a concrete understanding of the variation in evaporator tube length as a function of different parameters such as thermal conductivity, thickness, temperature etc. An optimized evaporator tube length was considered for the freezer and refrigerator of 246 L domestic refrigerator bestowing uniform cooling capacity factor for four different correlations albeit convective heat transfer coefficient (HTC) varied significantly. To validate the optimized evaporator tube lengths, cooling capacity was examined through pull-down tests for two different commercially available samples of varying volumes and tube lengths for the freezer and refrigerator, as well as the optimized sample with the largest volume. A comparison of the cooling capacity of the two samples and the optimized sample showed that the optimized sample exhibited a higher cooling capacity and achieved temperature convergence earlier. Furthermore, the energy analysis conducted on all samples revealed that optimized sample attained the highest energy efficiency ratio (EER) and least Energy Efficiency Index (EEI).
Abstract This study presents a dynamic analysis of compact heat exchangers (CHEs) integrated within an aircraft Environmental Control System (ECS), with emphasis on their transient thermal behaviour under varying operating conditions. A dynamic model is developed using the ECS library in a 1-D system simulation platform. Characteristic maps of heat exchanger effectiveness as functions of hot and cold fluid mass flow rates are generated in MATLAB for the primary heat exchanger (PHE), secondary heat exchanger (SHE), reheater (RHX), and condenser (CND), and subsequently imported into the ECS library framework. The model employs pressure–temperature sources at the inlets and temperature–mass flow sinks at the outlets on both hot and cold sides. Dynamic performance is evaluated in terms of hot- and cold-side outlet temperatures, hot-side heat flow rate, and system response time. Parametric analysis reveals that the fluid channel volume has a dominant influence on transient response compared to heat exchanger effectiveness. For an isolated heat exchanger, the dynamic response time increases from approximately 10 s to 25 s as the fluid channel volume increases from 0.5 m³ to 1.5 m³. Stabilised hot-side outlet temperatures of about 86 °C, 162 °C, 369 °C, and 453 °C are obtained for effectiveness values of 0.98 (SHE), 0.84 (PHE), 0.43 (RHX), and 0.25 (CND), respectively, corresponding to hot-side heat flow rates of 339.40 kW, 288.17 kW, 146.84 kW, and 88.37 kW. Furthermore, an integrated ECS configuration combining the PHE and SHE is modelled, demonstrating longer response times for the SHE (≈ 20–40 s) compared to the PHE (≈ 10–25 s) over the same range of fluid channel volumes. The results clearly demonstrate the significance of transient analysis in the design and optimisation of compact heat exchangers for aerospace ECS applications.
Abstract The focus of this research is to experimentally explore the influence of elliptically configured coil (ECC) condenser dimensional parameters and working conditions on the coefficient of performance (COP) of vapour compression refrigeration systems (VCRS). Four ECC condensers with varying minor and major axes (maintaining the same ratio) were selected for testing various refrigerants utilized in the different internal tube diameters in a counterflow configuration. A total of 32 experiments were carried out using multiple minor and major axes, coil diameters, and refrigerants as parameters. The experimental results demonstrate that increasing the major and minor axes of the elliptical structure, in addition to coil diameter, improves the condenser COP the elliptical major and minor axes have a greater influence on COP than other factors. Experimental results indicated that elliptical condensers enhanced heat transfer and COP from 25% to 33% compared to circular condensers.
Japanese cedar pollen (Cryptomeria japonica) is a major cause of seasonal allergic rhinitis in Japan, and Cry j 1 has been identified as its principal allergen. Although current treatments provide symptomatic relief, they do not prevent sensitization, highlighting the need for novel preventive strategies. Nanosized electrostatically atomized water particles (NEAWPs) are nanometer-scale water droplets containing reactive oxygen species (ROS) that have demonstrated antimicrobial activity; however, their effects on airborne allergens remain unclear. Therefore, this study investigated whether NEAWPs could reduce the allergenicity of Cry j 1 in human bronchial epithelial cells (BEAS-2B) and monocytic antigen-presenting cells (THP-1). Briefly, Cry j 1 was exposed to NEAWPs for 24–48 h, and allergenicity was assessed by ELISA, calcium imaging, flow cytometry, and cytokine analyses. NEAWPs treatment markedly reduced Cry j 1 antigenicity in a time-dependent manner, achieving 98.6
The growing demand for energy-efficient and environmentally sustainable HVAC solutions in residential buildings has driven the adoption of Variable Refrigerant Flow (VRF) systems. VRF technology, typically using R410A as the working fluid, provides simultaneous heating and cooling with enhanced part-load efficiency and greater operational flexibility than conventional central air conditioning systems. This study aims to optimize the refrigeration cycle of a VRF high wall indoor unit to improve cooling capacity and dehumidification performance. A combination of experimental and analytical methods was employed to evaluate system behavior under varying ambient temperatures and load conditions. Special emphasis was placed on assessing resistance to surface condensate formation (sweating), which is prevalent in high-humidity environments. Results indicate that specific cycle enhancements can significantly increase capacity utilization and improve control over dew point conditions. These improvements suggest that optimized VRF systems can better meet thermal comfort and moisture regulation requirements, particularly in tropical and sub-tropical climates where both energy efficiency and humidity control are critical.
The increasing demand for space cooling poses a major challenge to energy systems and buildings, both residential and commercial applications. Cost-effective and easily deployable solutions are widely needed to tackle this challenge. Heat emitted to the indoor from equipment is critical, particularly cooling units such as refrigerators and freezers. The impact of heat rejected from refrigerators on the indoor climate of small shops and supermarkets have been widely overlooked. This study presents and investigates an innovative and low-tech solution to control the heat dissipation of indoor cooling units, leading to increased comfort and reduced cooling demand. The solution, designed to be installed as a retrofit measure, controls the exhaust air ducting. Thus, it does not provide cooling, but manages the waste heat from refrigerators. This study includes the monitoring of an actual kiosk in Stuttgart, Germany, to meter refrigerators’ power consumption, a lab-scale prototype testing to prove the methodology of the solution and additionally dynamic thermal simulations via TRNSYS18 for different climates to analyze the performance and impact of the novel solution. The prototype showed the effectiveness of the control strategy during the lab-testing. The simulation results for Stuttgart show that controlled heat dissipation can reduce overheating degree hours by up to 97 – Boxed ventilation system can reduce cooling degree hours and accordingly cooling demand in commercial shops – Experimental measurement using lab-scale prototype proves system design and control – Boxed ventilation system is more efficient compared to open exhaust air ventilation
The vertical smart-farm, characterized by multi-layer cultivation structures, predominantly employs a convection cooling system to establish crop growth environments. However, due to the configuration and arrangement of cultivation facilities, cultivation zones are likely to provide non-uniform temperature. Such uneven temperature distribution can lead to non-uniform crop growth and reduced productivity. To address this issue, this study proposes the application of radiant cooling panels, and experimentally verified their effectiveness in improving temperature uniformity. Specifically, a ceiling radiant cooling panel was proposed to establish the growth temperature throughout the entire vertical smart-farm space, while cultivation bed radiant cooling panels beneath each layer were also proposed to mitigate localized temperature increases caused by LED heat generation. To experimentally verify the improvement of temperature uniformity achieved by the proposed ceiling and cultivation bed radiant cooling panels, a mock-up test was conducted. A test cell was constructed by simulating the structure of a vertical smart-farm that actually grows lettuce, and horizontal and vertical temperature uniformity in LED–off and –on states was analyzed. As a result, horizontal temperature uniformity of more than 96
This study numerically investigated heat and mass transfer from a cooling coil in a mixed convection regime, which is particularly relevant to dehumidification processes in HVAC systems. The research utilized the ANSYS Fluent solver to analyze a 2D laminar flow model. The primary focus was on the dimensionless Richardson number (Ri), which quantifies the relative importance of buoyancy forces to inertial forces. The findings show that as Ri increases, the flow regime transitions from being dominated by forced convection to being dominated by natural convection, leading to a significant decrease in both the average Nusselt number (Nu) and the average Sherwood number (Sh). This confirms a strong analogy between heat and mass transfer in this system. The results reveals that while Nu for a spacing of S = 0.08 m is approximately 7.4, the corresponding Sh is approximately 10.5 at a low Richardson number (Ri), demonstrating that the mass transfer rate is quantitatively higher than the heat transfer rate under these conditions. The study also revealed that while tube spacing had a notable impact on heat and mass transfer, the effect of the outlet opening size was found to be minor. Overall, the results provide valuable insights into optimizing dehumidification performance by controlling the balance between fan-driven and buoyancy-driven flow.
Currently, increasing the efficiency of power generation cycles is not the only goal for engineers; the focus is also on how it is achieved, whether through conventional or non-conventional energy sources. In conventional systems, changing the working fluid in the bottoming cycle has attracted engineers’ interest to boost cycle efficiency. Among various working fluids, carbon dioxide and ammonia water mixtures show promising thermodynamic properties that enhance both first and second law efficiencies. This research explores the use of transcritical carbon dioxide as the working fluid in the bottoming cycle of a combined cycle power plant with reheat cycles. The results indicate that, under operating conditions such as a topping cycle pressure ratio of 20, an ambient temperature of 303 K, and a turbine inlet temperature of 2000 K, the system performs better, with first law and second law efficiencies reaching 44.8
Increases in operating temperature significantly degrade the efficiency of photovoltaic (PV) panels, leading to reduced power output and limiting the wider adoption of solar energy technologies. This paper reviews recent developments in PV cooling strategies, with particular emphasis on studies that employ Computational Fluid Dynamics (CFD) to analyze and enhance these approaches. The effectiveness of various active and passive cooling techniques—such as phase-change material (PCM) systems, water- and air-based cooling, and nanofluids—is compared. The review highlights that CFD has become a crucial tool for evaluating the influence of parameters such as coolant type, flow rate, film thickness, and environmental conditions on PV module temperature and performance. Key findings indicate that CFD-validated hybrid cooling strategies and the integration of advanced materials offer substantial potential for improving both efficiency and sustainability.
Microchannel heat sinks (MCHSs) are compact cooling devices that play a crucial role in modern thermal management systems. They offer efficient heat transfer and are widely used in electronic cooling. One of the major challenges in the practical implementation of MCHSs is maintaining consistent thermal performance under the temperature fluctuations experienced by microchips. Although numerical studies have demonstrated that incorporating pin-fin structures within microchannels can significantly improve heat transfer by disrupting thermal boundary layers and increasing surface area, experimental validation remains limited. This limitation is due to fabrication challenges, particularly in achieving precise and intricate geometries using conventional microfabrication methods. In this study, a rectangular MCHS with embedded pin-fins was fabricated using the lithography technique, with polydimethylsiloxane as the channel material. The fabrication process considered different exposure powers of 5 mW and 10 mW. The accuracy of the fabricated microchannel was analysed using scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDX). The heat transfer performance was then evaluated under different input temperatures: 30, 40, 45, 50, 55, and 60 °C while maintaining a constant flow rate of 500 µL/min. The results show that the heat transfer rate increases with higher input temperatures, which can be attributed to the greater temperature differentials that drive more intense heat flux through the channels. These findings highlight how temperature fluctuations in microchips affect the heat transfer rate and, consequently, the overall MCHS performance. The study also emphasises the need for improved fabrication methods to support further experimental validation and implementation of complex pin-fin designs.
This research article presents an experimental investigation of a two-stage scroll compressor using R32 refrigerant, focusing on the effects of vapor injection in heat pump applications. The study highlights the performance improvements achieved through vapor injection, with particular emphasis on operation at low ambient temperatures. Key performance indicators—heating capacity, coefficient of performance (COP), and discharge temperature—were selected to evaluate system efficiency. Notably, at an ambient temperature of − 20 °C, the vapor-injected system exhibited a 17.01
Double-skin façade (DSF) systems have emerged as a promising architectural strategy for improving thermal performance by reducing heating and cooling loads while enhancing occupant comfort. However, their effectiveness can vary depending on outdoor climatic conditions. In particular, insufficient air circulation within the cavity may lead to excessive heat capture, resulting in overheating, increased cooling loads, and diminished occupant comfort. To address these limitations, this study proposes an IoT-based smart double-skin façade (SDSF) system capable of dynamically regulating cavity thermal conditions. A full-scale field experiment was conducted to evaluate the performance of the SDSF system in improving the indoor thermal environment of curtain wall-based building types during summer. Indoor conditions were compared between a single-skin façade (SSF) and the SDSF system under various shading and ventilation control strategies. The results demonstrated that SDSF effectively reduced daytime indoor temperatures and stabilized nighttime conditions through real-time controls of exhaust fans and blinds. Predicted mean vote (PMV) analysis also further indicated improved occupant thermal comfort with SDSF. These findings provide empirical evidence that IoT-integrated SDSF system can significantly enhance both indoor thermal comfort and energy performance, offering a viable strategy for climate-responsive building envelope design.
