https://doi.org/10.6110/KJACR.2025.37.5.207

Seungjun Lee

In the case of the next-generation VRF system air conditioner, in order to obtain the best performance and efficiency according to site climatic factors, installation environmental conditions, and operating load, an optimal amount of R410A refrigerant according to cooling and heating operation can be continuously and intelligently varied by applying a Smart Receiver to an outdoor unit. By utilizing the amount of refrigerant charged in this receiver, sufficient target condensation pressure can be maintained to secure the outlet temperature of the indoor unit above 40 degrees Celsius during full load operation even if the outdoor temperature falls below -10 degrees Celsius during heating operation. On the other hand, during cooling operation, the refrigerant is appropriately stored in the receiver according to the indoor cooling load to prevent unnecessary increases in condensation pressure, secure the target evaporation pressure, and smartly control to reduce the amount of charged refrigerant. By improving performance according to operating conditions, a smart receiver that takes efficiency into consideration can be applied.

https://doi.org/10.6110/KJACR.2025.37.5.217

Yujin Lee ; Jaeman Song ; Hiki Hong

Ground source heat pump (GSHP) systems face long-term ground temperature decline and COP reduction due to imbalanced heating and cooling loads, which are further exacerbated in high-heating-load environments such as greenhouses. Additionally, conventional flat-plate and evacuated tube collectors utilize solar energy only as heat, limiting overall system efficiency. This study proposed a PVT-GSHP system that integrated photovoltaic thermal (PVT) technology to address these challenges and developed a solution tailored for greenhouse environments. Using TRNSYS 18, the conventional GSHP system (Case 1) was compared with two PVT-GSHP configurations (Case 2 and Case 3). Case 3 demonstrated a BTES heat emission of 47.18 MWh and a heat storage capacity of 16.63 MWh, maintaining stable ground temperatures over five years. In addition, GSHP power consumption in Case 3 was reduced by 11.5% compared to that in Case 1, with the PVT system generating 14.54 MWh of thermal energy and 7.28 MWh of electricity, offsetting 36.4% of the GSHP's energy consumption. Finally, the PVT system reduced CO2 emissions by 6444.8 kg_CO2, equivalent to the annual absorption of 658 pine trees, demonstrating its effectiveness in greenhouse gas mitigation.

https://doi.org/10.6110/KJACR.2025.37.5.228

Insoo Oh ; Jeongan Park ; Wonseok Oh ; Jinkyun Cho ; Beungyong Park

This study examined the potential of using a ductless, fixed vane air supply type ventilation system as a solution to structural and cost limitations of duct-type systems in aging buildings. The performance of such ductless, fixed vane air supply type ventilation system was evaluated based on air delivery, indoor airflow distribution, and thermal comfort. Measurements showed a turbulence intensity of 4% at the diffuser outlet, with an average velocity of 2.69 m/s and a velocity standard deviation of 0.12 m/s, indicating a stable airflow. Airflow distribution results revealed velocities between 0.05 m/s and 0.3 m/s, providing a stable and imperceptible draft sensation for seated and standing occupants. The system maintained effective air delivery up to 8 m from the diffuser, achieving uniform air distribution throughout the space. Effective Draft Temperature (EDT) analysis confirmed that airflow and temperature variations remained within the ADPI comfort zone. These findings demonstrate that ductless, fixed vane air supply systems can effectively address limitations of ducted systems while ensuring thermal comfort. This study provides a practical framework for implementing cost-effective and efficient ventilation solutions in aging buildings.

https://doi.org/10.6110/KJACR.2025.37.5.236

Minji Kwon ; Duhyun Kim ; Rin Yun

This study aimed to analyze the heating and cooling capacity and refrigerant charge variation according to the mixing ratio of R744 and R290 in a mobile heat pump system. Results showed that as the mass fraction of R290 increased, both heating and cooling capacity, as well as the coefficient of performance (COP), improved. In particular, performance differences were observed depending on the outdoor temperature. The maximum difference was 55.5% in cooling mode and 54.5% in heating mode. When applying an R-404A compressor for the present model, the COP did not exhibit a linear increase within the R290 mass fraction range of 0.4 to 0.6. Additionally, the refrigerant charge decreased linearly with an increasing R290 mass fraction, attributed to the differences in density and void fraction between R744 and R290. The maximum reduction for refrigerant charge was 52.0% in cooling mode and 56% in heating mode. This study confirms that the compressor can significantly impact the overall performance of the heat pump system, indicating that compressor selection is a critical factor in the design process of a mobile heat pump system utilizing an R290 and R744 mixture.

https://doi.org/10.6110/KJACR.2025.37.5.245

Hyun Seo Nam ; Seok Kwon Jeong

This paper aimed to design a hybrid model reference adaptive controller (H-MRAC) that would be robust to model parameter uncertainty and disturbances to achieve high precision control of variable speed refrigeration system (VSRS). The designed H-MRAC was based on the modified MIT rule with control performance that strictly followed command values by a parameter that could minimize specific error functions. The designed H-MRAC was found to have robust control performance based on simulation and experiments of disturbance application and model parameter fluctuations for VSRS. When control performance of the designed H-MRAC was compared with that of an existing PI-only controller, it was confirmed that the designed H-MRAC had a faster settling time, fewer undershoots, and fewer steady-state errors for more precise and robust control. This is due to the advantage that the parameter used in the control of H-MRAC is automatically updated without relying on characteristic parameters of the model.