https://doi.org/10.6110/KJACR.2026.38.4.179

Jin Sub Kim ; Jung Chul Kim ; Kong Hoon Lee ; Dong Ho Kim

A density measurement system was developed for the low-GWP refrigerant mixture R1234yf-CF3I, measuring densities near the saturation state across three nominal mass ratios: 7:3, 5:5, and 3:7. This system included a vapor-liquid equilibrium (VLE) cell and a vibrating-tube density meter, both housed within a thermostatic chamber maintained at a temperature within ±0.1 K. Using reference fluids, we established a correlation between the resonant period and density for both the vapor and liquid phases, enabling the construction of a density measurement system specific to the mixture near saturation. The system was validated by measuring the near-saturation densities of the R32-R125 mixture, yielding small mean absolute percentage errors (MAPE) of 0.31% for the vapor phase and 0.08% for the liquid phase, compared to REFPROP10 data. We measured the densities of the R1234yf-CF3I mixtures at three near-saturation points, extrapolating the saturation densities from the trends observed in these data. The near-saturation density data obtained in this study are expected to enhance the accuracy of the equation of state (EOS) for these mixtures.

https://doi.org/10.6110/KJACR.2026.38.4.193

Yujin Lee ; Junyong Lee ; Jaeman Song ; Hiki Hong

Air source heat pumps (ASHP) experience performance degradation at low outdoor temperatures, resulting in a significant decrease in their COP. To address this limitation, this study proposes a hybrid operation that integrates a heat pump with a photovoltaic-thermal (PVT) system. A PVT-heated storage tank can offer a more stable heat source; however, under low-temperature thermal storage conditions, the operation of an auxiliary boiler may be necessary, leading to performance variations based on the chosen control strategy. Using TRNSYS 18, we compared two operation modes: Case 1, where a boiler reheats the tank before the water-to-water heat pump operates, and Case 2, where a dual-source heat pump automatically switches to air-source mode. Results showed that Case 1 achieved a higher seasonal COP (3.86) than Case 2 (3.65), indicating that boiler intervention effectively prevents performance degradation. In terms of energy consumption and CO2 emissions, Case 1 recorded lower CO2 emissions (1,572 kgCO2) than Case 2 (1,607 kgCO2). Moreover, Case 1's PVT system generated 5,488.9 kWh during the heating season, exceeding the heat pump's consumption (3,102.8 kWh) and enabling energy self-sufficiency. The annual CO2 reduction reached 4,247 kgCO2, offsetting system emissions and providing additional mitigation. These findings demonstrate that under low-temperature storage conditions, Case 1 represents the optimal strategy for both heating performance and environmental benefits when integrated with PVT.

https://doi.org/10.6110/KJACR.2026.38.4.204

Sanghwan Bae ; Jungyeon Yu ; Sunghwan Han

This study investigated the performance and safety of a ventilation filter that incorporates an organic salt-based antimicrobial material, designed to suppress microbial growth in HVAC systems. The organic salt, which provides contact-type antiviral and antibacterial activity, was incorporated at a concentration of 200 ppm into a polypropylene melt-blown HEPA medium. This configuration achieved over 99.9% removal efficiency for 0.3 ㎛ particles while maintaining the pressure drop characteristics specified in KS B 6141. The antiviral activity, evaluated by ISO 18184 using human coronavirus 229E, demonstrated a 3.5 log reduction (?99.9%) after 2 hours of contact. Antibacterial tests according to KS K 0693 against Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae showed a reduction of ≥99.9% after 18 hours of incubation. Antifungal resistance assessed by ASTM G21-15(2021)e1 yielded Grade 1 after 4 weeks, indicating only trace fungal growth. A 33-day repeated-dose study on ICR mice revealed no significant toxicological findings in clinical observations, body weight, hematology, or histopathology. In a 3-month field test conducted in a hospital ward ventilation system, the organic salt filter demonstrated significantly lower surface and internal contamination compared to a conventional melt-blown filter. These results confirm that the developed organic salt-based filter can enhance hygienic stability and infection control in ventilation applications.

https://doi.org/10.6110/KJACR.2026.38.4.214

Young-Joon Park ; Eui-Jong Kim

This study investigates the performance of a ground source heat pump (GSHP) system using variable-flow control based on the temperature difference between the source-side inlet and outlet (ΔT), which is affected by the entering water temperature (EWT) and flow rate. A laboratory-scale test facility equipped with a thermostatic bath was utilized to analyze the coefficient of performance (COP) during both cooling and heating operations. A regression-based model for predicting COP was developed from the experimental data. The findings revealed that, under the same EWT conditions, increasing the flow rate gradually improved the COP, particularly in high-efficiency operating regions. Using the developed model, a 10-year long-term simulation was conducted to assess system-level performance. The optimal ΔT values for minimizing total energy consumption were found to be ΔT = 5℃ in cooling mode and ΔT = 4℃ in heating mode. Notably, increasing ΔT during cooling significantly reduced circulation pump power consumption, leading to enhanced overall system efficiency.

https://doi.org/10.6110/KJACR.2026.38.4.225

Ja Kang Yang ; Chang Jae Lee ; Su In Chae ; Do Yong Park ; Sang Ki Jin

This study systematically assessed the alignment between the detailed action plans in the Second Basic Plan for the Development of the Mechanical Equipment Industry and environmental changes using the PEST analysis framework (Political, Economic, Social, Technological). Key environmental change factors?including carbon neutrality policies, digital transformation, demographic shifts, and the adoption of advanced technologies?were categorized and analyzed as either opportunities or threats. The findings reveal that 81.8% of the plan's sub-tasks are closely related to significant opportunity factors. Notably, there is a strong alignment between strategic policy tasks and technology trends such as IoT, AI, and digital twins, indicating enhanced policy effectiveness. Conversely, economic fluctuations and the rapid pace of technological change were identified as major threats. In response, this study offers specific implementation measures categorized by timeframe (short-, medium-, and long-term from 2025 to 2035), which include policy and industry strategies, increased R&D investment, and the establishment of new industrial clusters. The quantitative evaluation of policy-environment consistency not only contributes to academic knowledge but also provides practical strategic guidance for both industry stakeholders and policymakers.