Young Il Kim

Dry rooms used in battery and semiconductor research facilities require ultra-low dew-point environments, which demand significant thermal energy for desiccant rotor regeneration. In steam-regenerated systems, condensate discharged through steam traps partially evaporates due to pressure reduction, generating flash steam that is typically released into the atmosphere, resulting in substantial energy losses. This study investigates the generation and recovery potential of flash steam in dry room HVAC systems. Field measurements were conducted for 18 steam-regenerated desiccant air handling units installed in a medium-scale research facility (total floor area: 43,000 m²) in southern Gyeonggi Province, Korea. Boiler operation data—including feedwater flow rate, pressure, and operating time—were analyzed over a six-month period from March to August 2025. The results showed that the average flash steam generation rate was approximately 1.16 ton/h, corresponding to 8.56% of the average feedwater flow rate. Two recovery methods were evaluated: a steam jet thermocompressor (SJT) and an exhaust vapor condenser (EVC). The analysis revealed that the EVC system provides a more practical solution for medium-scale dry rooms because it does not require high-pressure primary steam. By recovering flash steam using three EVC units, an average heat recovery of 724 kW was achieved. The recovered heat can produce 86 °C hot water, which can be utilized as a driving heat source for an absorption chiller, generating approximately 507 kW of cooling capacity. This configuration partially offsets the cooling load of existing centrifugal chillers, thereby reducing electrical energy consumption. In addition, the proposed system eliminates atmospheric discharge of flash steam, mitigating the visible white plume phenomenon commonly observed in industrial facilities. The results demonstrate the technical feasibility of integrating flash steam recovery with absorption cooling to enhance energy efficiency in medium-scale dry room HVAC systems.

Performance prediction of an air-cooled direct expansion (DX) vertical downward-supply cooling system applied to large spaces is a key element for achieving efficient control and energy savings. Recent studies have predominantly relied on complex artificial intelligence (AI)-based or high-dimensional models that require a large number of input variables to achieve high predictive accuracy. In contrast, limited research has focused on developing simple, interpretable, and practically applicable models based on field-measured data. To address this gap, the present study proposes a physically grounded multiple linear regression model with a minimal number of variables, which can be implemented in practice using only three standard sensors: indoor air temperature, outdoor air temperature, and airflow rate. Field data were refined through physical criteria derived from ASHRAE standards (steady-state operation and removal of outliers) and by identifying steady-state ranges using the Kernel Density Estimation (KDE) method. A total of 133,718 valid samples were used for analysis. The proposed model achieved a coefficient of determination (R²) of 0.93, a root mean square error (RMSE) of 2.86 kW, and mean absolute error (MAE) of 2.31 kW, corresponding to approximately ±6% deviation from measured cooling capacity. These results satisfy the typical accuracy criteria in the HVAC field (R² > 0.9, error < 10%) and confirm high predictive reliability despite the model’s simplicity. The achieved accuracy implies that the proposed model can be extended to field-level performance prediction and energy-efficient operation. Comparison with second-order polynomial and nonlinear (1/T_out) models showed only marginal improvement in accuracy. Consequently, the proposed three-variable regression model introduces a practical framework for performance prediction and control of DX-type cooling systems that integrates simplicity, physical interpretability, and field applicability.

This study proposes sustainable natural ventilation strategies using the periodic opening and closing of windows and doors to maintain acceptable indoor air quality in a small office space during the winter season. Field experiments were conducted in a 26.8 m² university office room in Seoul, Korea, measuring the indoor and outdoor temperature, humidity, wind speed, carbon dioxide concentration, and fine dust levels. A simulation model based on a first-order differential equation was developed using EES software (version 9) to predict indoor CO₂ concentrations at one-minute intervals. The simulation results showed good agreement with the experimental data, validating the accuracy of the modeling approach. Based on the validated model, practical ventilation durations and intervals were derived according to the occupant number and room volume, ensuring that indoor CO₂ concentrations remained below the recommended 1000 ppm threshold. The results demonstrate that simple, periodic natural ventilation is effective in maintaining acceptable indoor air quality. As a passive strategy requiring no electrical energy, it offers a sustainable and low-cost solution for creating a healthy indoor environment.

This study focuses on improving the performance of desiccant dehumidifiers using desiccant rotors, which are widely utilized in various industries, such as manufacturing, food, and construction, to enhance product quality and production efficiency. The combined desiccant dehumidifier can reduce energy consumption compared to traditional standard or purge dehumidifiers. The system operates in normal mode during seasons with high outdoor humidity and in purge mode during seasons with low outdoor humidity. By utilizing dampers, the air passing through the dry desiccant rotor can either be directly discharged indoors or supplied to the regeneration section, allowing the system to operate in two modes within a single unit. The first part of the study involved comparing the performance of the equipment through experiments. The second part compared the results from the dehumidifier rotor performance simulation program to check for deviations and validate its effectiveness. In the first experiment, the energy consumption of the standard desiccant dehumidifier in normal mode was compared with that of the combined desiccant dehumidifier in normal mode. In the second experiment, the energy consumption of the standard desiccant dehumidifier in normal mode was compared with that of the combined desiccant dehumidifier in purge mode. The airflow, temperature, and humidity values used in each experiment were analyzed using a dehumidification performance simulation program, and the deviation was found to be within 10%. Therefore, the performance analysis via simulation was considered valid. The dehumidification performance of the combined desiccant dehumidifier was found to be 5% more efficient than the traditional standard desiccant dehumidifier and 9.5% more efficient than the purge dehumidifier. Furthermore, energy consumption simulations were conducted for representative regions in Korea. The results showed energy reductions of 65% in Seoul, 65% in Daejeon, and 67% in Busan. The findings of this study suggest that energy savings can be achieved by appropriately adjusting the operation mode between normal and purge modes based on outdoor conditions.

This study examined energy performance improvement factors by analyzing both energy performance and the economic impacts to reduce energy costs for senior centers. A fact-finding survey was conducted on 20 senior centers in a metropolitan area, identifying key energy improvement factors. Energy simulations of the buildings were performed using ECO2, an officially certified energy assessment program in Korea, comparing the energy requirements before and after the improvements. The energy demand, energy consumption, and floor area were analyzed, with the J, K, and S standard models selected based on the median values of these factors. To assess the impact of the improvements, blower door tests were conducted on two senior centers before and after window upgrades. Based on the ECO2 simulations and the blower door test results, improvement priorities were identified in the following order: windows, exterior walls, boilers, roofs, and doors. Finally, an economic feasibility analysis applied the construction and heating costs to the standard models. Over a 40-year period, only boiler improvements generated a net profit. Without government support, this study recommends prioritizing boiler upgrades when selecting energy performance improvements.

This study summarizes the technology level and economic feasibility of two small 500 m² public office buildings that achieved a first-class Zero Energy Buildings (ZEB) certification for the first time in Korea. In addition, a Life Cycle Assessment (LCA) reflecting the ZEB performance in the operation stage was analyzed, and the LCA factors considering the characteristics of small buildings were reviewed. Moreover, an economic analysis was performed through a Net Present Value (NPV) by reflecting the ZEB and LCA, and the results showed little economic feasibility. However, adding the environmental costs calculated through the LCA to the existing energy-saving costs could offset an additional 11.6–11.7%. Therefore, including the environmental impact and cost through these LCA evaluation techniques could be a positive step toward increasing the effectiveness of ZEB applications. This study is significant in that it conducted a comprehensive analysis through ZEB and LCA in terms of carbon reduction for small buildings that achieved a first-class ZEB certification, but it is limited to only two cases.