地下停车场凝水减少方法

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ABSTRACT

In this study, condensation reduction methods with high field applicability to various types of underground parking lots in apartment buildings were selected and tested. The selected methods included floor-insulating drainage plates, induction fans with heating wires, and an automatic control ventilation system based on indoor and outdoor temperatures and humidity. The effectiveness of these methods was evaluated via real-world field experiments. The results indicated that while the insulating drainage plates initially blocked the cold, their long-term effectiveness matched that of normal drainage plates (difference 0.1°C). The induction fan with a heating wire showed average increases of 0.8°C and 2.7°C in wall surface temperature after one and three months,compared to normal induction fans. The absolute humidity of the automatic control ventilation decreased by 1.8 g/kg after 10 h of operation during rainy weather, whereas the manual control ventilation system increased by 0.6 g/kg under the same conditions. This study offers insights into the most effective application of these methods for various parking lot configurations.

1. Introduction

Owing to its high urban population density, South Korea is increasingly developing building complexes with underground parking lots. These underground parking lots enhance the proportion of landscapes and green spaces in urban areas and ensure pedestrian safety by separating the movement of pedestrians and vehicles.Primary buildings with underground parking lots include apartment complexes, office facilities, and shopping malls, with apartment complexes constituting a significant proportion. In Korea, 63.2% of all buildings are residential, with apartments representing 63.5%(Statistics Korea 2021).

Underground parking lots in apartment buildings in Korea can be broadly classified into two types based on the building structure and size of the complex: large-scale and mixed-use complexes. Large-scale complexes, situated on extensive ground with multiple buildings forming

a single complex, typically have underground parking lots with wide floor areas for each level, usually spanning to 1–2 basement floors, as shown in Figure 1a.

Mixed-use complexes, which combine high-rise apartments with commercial buildings on smaller sites, tend to have narrower floor areas for each level of underground parking,usually extending to 3 to 4 basement floors, as depicted inFigure 1b. In cases where the site is small, but the need for parking spaces is high, some mixed-use buildings use up to seven basement levels for parking.’

The floors and walls of underground parking lots are directly exposed to soil and are significantly affected by underground temperatures. According to Cheong(Cheong 2012) and Jung (Jung et al. 2002), the underground temperature in Seoul is maintained at approximately13℃ all year round at a depth of more than 10 m above the ground. Considering the characteristics of the indoor environment according to the type of underground parking lot, air circulation is stagnant in large spaces, and natural outdoor air is hardly affected by deep floors (Lee et al. 2015). Initially, as the concrete dries, the temperature, humidity, and dew point inside the parking lot increase. However, the surface temperature of the soil-exposed areas, which is influenced by the underground temperature, increases more slowly. At this point, the surface temperature is lower than the dew point temperature, and condensation is recorded. Korea has a hot and humid climate in summer; therefore, when hot and humid outside air flows into underground parking lots, the condensation phenomenon intensifies.

When condensation occurs in underground parking lots, it leads to hygiene and aesthetic concerns such as mold growth, pipe corrosion, and paint peeling due to the condensation water. Additionally, it poses safety hazards,such as vehicle and pedestrian slips, owing to water pooling on the floor. Therefore, a method to reduce condensation is necessary.

Several studies have been conducted examining condensation in underground parking lots. Previous studies on condensation reduction can be classified based on architectural and equipment elements. The architectural elements include insulation (M. Hwang, Cho, and Kim 2013; Kim and Kim 2004), drainage plates (Cheong and Ryu 2015), finishing materials (Hong, Sung, and Kim 2010), and double walls/floors (Cheong 2012; Son and Nagai 2004). The equipment elements include induction fans (Ahn et al. 2004), supply and exhaust fans (M.Hwang, Kim, and Kim 2007), dehumidifiers (J. Park et al. 2014), and heaters (K. Park, Nagai, and Iwata 2006). These studies selected and analyzed methods that were expected to be effective in reducing condensation among these elements. However, many of the selected methods require additional space, altered appearance, or additional equipment. Without considering field applicability, these methods encounter constraints when implemented at actual construction sites.

Previous studies have not considered the various forms of underground parking lots, rendering the determination of the most suitable solutions for each type of parking lot when applied in practice challenging.Previous studies on underground parking lot condensation have employed methods such as on-site environmental measurements (H. Hwang et al. 2016;C. Lee 2017), simulations of condensation reduction techniques (Ahn et al. 2004; C. Lee et al. 2017), effect prediction through unit mockup experiments (K. Park,Nagai, and Iwata 2006), and derivation of prediction formulas for optimization (Kim and Kim 2004; K. Park and Nagai 2007; Yu, Kang, and Zhai 2020). However,the actual measurement studies do not fully reflect the morphological characteristics of underground parking lots. The simulation and predictive formula studies were limited in reflecting the complex variables that cause condensation. The mock-up experiments study conducted within a 3.5 m × 2.0 m × 2.0 m unit was limited in representing actual underground parking lots.

Therefore, in this study, we aimed to confirm the effectiveness of a condensation reduction method with high field applicability based on the morphological characteristics of underground parking lots through actualscale field experiments. The structure of this paper is as follows: Chapter 2 analyzes the current state of condensation in underground parking lots by type and provides the selection of condensation reduction methods based on morphological characteristics and field applicability.Chapter 3 presents the simulations to determine the variables for the field experiments among the selected methods. Section 4 presents the verification of the effectiveness of the selected methods for reducing condensation through field experiments. Finally, Section 5 presents our conclusions.

2. Selection of condensation reduction methods

To reduce condensation, it is necessary to maintain the surface temperatures above the dew point or reduce the absolute humidity in the air. To understand the indoor environment of actual underground parking lots where condensation occurs, measurements were conducted in apartment building underground parking lots where condensation occurred. The target sites were measured only during the first summer after completion, and measurements of the surface temperature and absolute humidity were taken in areas with and without condensation. The measurement equipment used was an infrared thermometer (Testo 835-H1), and the measurement method involved aiming the laser of the device at the target area from a distance of 1 m and taking measurements.Measurements were taken at the same location, with readings recorded after at least five measurements were taken over a 10-min period to ensure that the error range remained within the device’s accuracy of approximately 2%. The measurement locations were as follows: wall surface temperature was measured at a point 0.5 m away from the floor, while floor surface temperature was measured at a point 0.5 m away from the corner of the wall. Figure 2 shows the results of measurement of the surface temperature and absolute humidity for 38 sites with various types of underground parking lots over 17 years. In Figure 2a, the average surface temperature of the area where condensation occurred was 21.0℃, and the average surface temperature of the area where condensation did not occur was 23.4℃, showing a difference of 2.4 ℃.As shown in Figure 2b, the average absolute humidity in the area where condensation occurred was 18.2 g/kg,and the average absolute humidity in the area where condensation did not occur was 15.0 g/kg, a difference of 3.2 g/kg. The minor differences in the average surface temperature and absolute humidity between the areas with and without condensation indicate the need to control these factors to mitigate condensation in underground parking lots.

To analyze the condensation situation based on the type of underground parking lot, the evaluated sites were classified into large- and mixed-use complex types. The large complexes most commonly had only one underground floor, whereas the mixed-use complexes most frequently extended to three underground floors. Surface temperature measurements of a large complex with one underground floor and a mixed-use complex with three underground floors,both located in the same area, were analyzed.

In large complex type underground parking lots with only one floor, the surface temperatures of the walls facing the soil were measured at various locations. The results showed an average difference of 3.7℃ depending on the location, as depicted in Figure 3a. In the three-floor mixed-use complex-type underground parking, the temperature difference was an average of 2.2℃ across different locations within the third basement. Large complex type underground parking lots have multiple cores located in large spaces with complex internal structures. The area around the entrance was significantly influenced by the external environment, but the airflow stagnated in the corner far from the entrance; thus, the surface tem perature was maintained at a relatively low level. Therefore, these require humidity and temperature control considering the indoor and outdoor environments, especially in areas with stagnant air. In contrast, mixed- use complexes, which exhibit less temperature variation, have a higher proportion of walls facing soil in the same floor space, necessitating methods for increasing the face temperature of these walls.

The surface temperatures of the corner areas of each floor were measured in a three-floor mixed-use complex underground parking lot. The results, as illustrated in Figure 3b, showed average temperatures of 20.7℃ on the third (lowest) basement floor, 22.2℃ on the second basement, and 22.6℃ on the first basement. The temperature decreased with depth because the lower floors were less affected by external environmental factors. In particular, the lowermost floor, with most of its area facing the soil, was greatly influenced by the underground perature, leading to lower temperatures. Therefore, it is necessary to increase the surface temperatures of the lowermost floors in complex mixed-use underground parking lots.

To select the condensation reduction methods with high field applicability, the methods used in previous studies were reviewed. In this study, methods considered to have high “field applicability” were defined as those that do not require additional space, external appearance changes, or extra equipment, beyond existing architectural/equipment elements. According to this criterion, drainage plates, induction fans, and supply and exhaust fans are deemed to have high field applicability. These three methods have been used for poses other than condensation reduction, such as discharging inflow water and maintaining legal indoor air quality standards. The “existing methods” primarily selected based on field applicability criteria were combined and improved for condensation reduction, resulting in the final selection of “improved methods.” The selection process is summarized in Table 1.

In this study, the effectiveness of condensation reduction was assessed based on the difference in surface temperature when applying “existing methods” and the final “improved methods,” which are based on existing architectural/equipment elements. Conceptual diagrams of the existing and improved methods are presented in Figure 4. Among the selected methods, simulations were conducted to insulate the drainage plates and ventilation fans with heating wires to limit the variables for field experiments. The simulations determined the material composition of the insulating drainage plates, heat output, and installation angle for the ventilation fans with heating wires. In contrast, the indoor and outdoor temperature- and humidity-based automatic control ventilation system used the same equipment and operation schedule as the existing manual control ventilation system. Environmental changes in indoor and outdoor temperature and humidity are limited with respect to implementation via simulation, and only the operation logic of the ventilation system is changed. Therefore, the condensation reduction effect was predicted only through field experiments. Detailed explanations and research methods for existing and improved methods are provided below.

(1) Floor-insulating drainage plate: The original method used PVC drainage plates to discharge incoming water; however, materials with enhanced insulation were developed to prevent cold water. Two types of insulating drainage plates were evaluated via simulations. The first was a composite material combining a PVC drainage plate with a PS insulator of the same shape, and the second was made from highly absorbent XPS insulation shaped into a drainage plate. Among these, the one with the best condensation reduction was applied in field experiments to compare the difference in surface temperature rise with that of the original method. This method was hypothesized to be necessary for mixed-use complex types where an increase in the surface temperature of the lowest floor in deeper underground parking lots is required. Accordingly, a field experiment was conducted on the lowest floor of a four-story underground parking lot.

(2) Induction fan with heating wire: The original method used normal induction fans for air circulation.However, the new method involved equipment designed to circulate warm air by integrating heating wires into the exhaust. The effectiveness of the heat output and installation angle were analyzed through simulations. The best case for reducing condensation, determined in terms of heat output and installation angle, was then applied in the field experiments. The difference in the surface temperature rise when compared with that observed in the original method was evaluated.This method was expected to be necessary for mixed-use complex types where improving air circulation and increasing the surface temperature in the corner areas of underground parking lots are required.Field experiments were conducted on the walls and corner walls facing the soil on the second and third floors of a four-story underground parking lot.

(3) Automatic control ventilation system based on indoor and outdoor humidity (Automatic control ventilation system): The original method activates the supply and exhaust fans when CO concentrations exceed 50 ppm, as per the Ministry of Land, Infrastructure, and Transport(2021) standards. In summer, condensation reduction operates on a time-scheduled basis and is manually stopped by users if the condensation worsens. This method has the drawback of increasing the indoor humidity even on high humidity days. The new system operates the fans only under temperature and humidity conditions that are favorable for reducing condensation,based on real-time data from indoor and outdoor sensors. Field experiments were conducted to compare the change in the absolute vapor amount with the original method. For comparison with the other two methods, the differences were also analyzed in terms of surface temperature. This method was expected to be necessary for large complex types to reduce the absolute vapor amount in large underground parking lots. Field experiments were conducted in a single-floor large parking lot.

3. Simulation for selecting field experiment subjects

3.1. Heat transfer analysis for selecting materials for floor-insulating drainage plates

Heat transfer analyses were conducted to select materials for the field experiments from two types of insulating drainage plates, which included combinations of normal drainage plates with added insulation performance.Through analysis, materials that were more effective in increasing the surface temperature were selected.

3.1.1. Overview of heat transfer analysis for floor-insulating drainage plates

The target site, underground parking lot A, was a functional space with design constraints and a maximum allowable construction thickness of150 mm on a slab. The existing design included a standard 45 mm PVC product as the normal drainage plate case (ND). To interpret the surface temperature of the ND case, a PVC drainage plate with a height of 45 mm was installed, followed by pouring non-reinforced concrete to a height of 105 mm.According to Cheong and Ryu (2015), there is a minimal increase in the surface temperature with varying PS insulation thickness. Therefore, the Insulating Drainage Plate Alt 1 Case (hereafter referred to as ID 1) was configured using a 5-mmPS insulation material molded into the same shape as the existing PVC drainage plate at a height of 45mm. To interpret the surface temperature of ID 1,a 50-mm height insulating drainage plate was installed, followed by pouring non-reinforced concrete to a height of 100 mm. The Insulating Drainage Plate Alt 2 Case (hereafter referred to as ID 2) was configured to provide a drainage function by cutting a semicircular groove with a radius of 20mm longitudinally on a 50-mm EPS insulation material,which was the same height as ID 1, for comparison.To interpret surface temperature of the ID 2 case, the existing PVC drainage plate was removed,and a 50-mm height insulating drainage plate was installed, followed by pouring non-reinforced concrete to a height of 100 mm. Each case had empty internal air layers in the drainage plates (0% underground water, denoted as air) and was filled with underground water (denoted as water). The heat transfer analysis cases are listed in Figure 5.

The heat transfer analysis was conducted using THERM 7.6 software. The composition of materials,thermal performance, and boundary conditions are detailed in Table 2. The indoor temperature in the boundary condition was set based on the actual measurement data. Utilizing the average surface temperature and absolute humidity measured in the condensation areas of 38 underground parking lots over 17 years, as discussed in Chapter 2, the values were converted to air temperature and relative humidity, which yielded values of 25.6°C and 88%,respectively. Beneath the drainage plate, a concrete slab was present, but for the side facing the soil, an underground temperature of 13℃, representative of Seoul at less than 10 meters depth, was assumed.

3.1.2. Results of heat transfer analysis for floor-insulating drainage plates

The analysis was conducted for six cases involving an existing normal PVC drainage plate, two types of insulating drainage plates, and different water influx ratios. Figure 6 presents the results. The greater the increase in surface temperature compared to that of the existing material, the higher the condensation reduction effect. Condensation is possible when the surface temperature is lower than the dew point temperature (23.5℃) calculated based on the set temperature and humidity of the underground

parking lot.

Heat transfer analysis showed that using insulating drainage plates, regardless of the material type,resulted in higher surface temperatures compared to normal drainage plates, and the surface temperature increased when there was an inflow of water in the hollow layer. Comparing the details, ID 1-air showed a 0.5℃ increase, and ID 2-air a 1.5℃ increase compared to ND-air. For water-filled cases, ID 1-water increased by 2.1℃ and ID 2-water by 4.2℃ compared to ND-water. Notably, ID 2 maintained the same surface temperature on the indoor side regardless of the presence of water.

In terms of condensation risk, the analysis indicated that ND-air, ID 1-air, and ID 2-air, all without water in the hollow layers, had a low possibility of condensation under the assumed temperature and humidity conditions. However, ND-water and ID 1-water with 100% water in the hollow layers showed potential for condensation. ID 2 demonstrated a low condensation risk regardless of the presence of water. Based on these results, an XPS insulating drainage plate (ID 2) was selected for field experiments

3.2. Airflow analysis of induction fan with heating wire for selecting heat output and installation angle

CFD airflow analysis was conducted to select the heat output and installation angle for field experiments using induction fans with added heating wires. The analysis aimed to identify the heat output and installation angles that would be most effective in increasing surface temperatures.

3.2.1. Overview of airflow analysis for induction fan with heating wire

For the target site A underground parking lot, the variables for the induction fan with heating wire that could be altered compared to the existing normal induction fan were the heat output of the equipment and its installation angle. The induction fan with heating wire differs from the normal induction fan by having a heating wire at the bottom, allowing for

adjustable heat output. While induction fans are typically installed with their exhaust parallel to the wall,they can be rotated at an angle towards the wall for installation.

The heat output range was set within a maximum of 5 kW, without changing the electrical supply method,and adjusted in 2 kW increments. The equipment’s installation angle can be viewed in the 3D aspect from Figure 7a, split into the side view (X-Z plane)and top view (X-Y plane). The rotation angle of 30degrees from the ceiling slab in the X-Z plane, as shown in Figure 7b, was fixed, while the angle of rotation towards the wall in the X-Y plane, as in Figure 7c, was variable. The installation angle, adjusted between 5 to 15 degrees in 5-degree increments considering internal circulation, omitted the 10-degree midpoint due to the difficulty of making fine adjustments during actual installation.

The normal induction fan was set to Case NF with a heat output of 0 kW and an installation angle. To observe the effect of the heat output in the induction fan with a heating wire, the installation angle was fixed at 0°, and the heat output was varied to 1, 3, and 5 kW,forming Alt 1–3 cases (hereafter referred to as HF 1–3).To examine the effect of the installation angle, the heat output was fixed at 3 kW, and the installation angle was changed to 5° and 15°, forming Alt 4,5 cases (hereafter referred to as HF 4,5). The Alt 6 case (hereafter referred to as HF 6) combined the maximum values with a 5-kW heat output and 15° angle. All airflow analysis cases are listed in Table 3.

The airflow analysis focused on a section of the underground parking lot in planned experiment site A, specifically on a 50 m stretch of wall facing the soil,as indicated by the dotted line in Figure 8.

Measurement points for examining wall surface temperatures were set at a height of 0.5 m above the floor at intervals of 5 m ranging from 2.5 m to 47.5 m away from the induction fan. The modeled area was 50m x 16.8 m (excluding the core area) with a ceiling height of 3.7 m.

Airflow analysis was performed using the MIDAS NFX program. The boundary condition was set identically to that of the insulating drainage plate simulation using 17 years of cumulative underground parking lot temperature and humidity data. The air temperature at the condensation sites from this data, converted to 25.6℃, was set as the boundary condition outside the analysis target. The average surface temperature at the condensation sites, 21.0℃ from the same data,was set for the target wall. The equipment specifications are listed in Table 4.

3.2.2. Results of airflow analysis for induction fan with heating wire

The temperature distribution shapes from the seven airflow analysis cases, varying the heat output and installation angle of the induction fan, are listed in Figure 9. The Top View represents the X-Y plane at 0.5 m height from the floor, whereas the side view depicts the X-Z plane of the target wall in the 3D model. As the heat output increased (NF, HF 1–3), the

temperature of the air discharged from the fan along the airflow path increased. With larger installation angles towards the wall along the x-axis (HF 2,4,5),the range of the increased air temperature effect shortened.

A comparison of the surface temperatures at the measurement points within the analyzed wall is presented in Figure 10. Under the airflow analysis conditions of 25.6℃ and 88% humidity, walls with a surface temperature above the dew point of 23.5℃ have a low possibility of condensation. Therefore, these sections represent the range of influence in which condensation could be reduced through the use of induction fans.

When the induction fan with heating wire was set at a 0-degree installation angle and operated with varying heat outputs, the fan influenced the environment up to 5.7 meters away, regardless of the heat output.The maximum influence distance was 17.5 meters at 1W heat output and 19 m at 5 W, with a difference of approximately 1.5 meters. The highest temperature difference between 1W and 5W heat outputs was approximately 0.25℃.

When operating the induction fan with heating wire at a fixed heat output of 3 W and varying the angle from 0 to 15 degrees, the fan influenced the environment starting at less than 2.5 meters away at a 15-degree angle, 3.5 meters away at a 5-degree angle, and 5.7 meters at a 0-degree angle. However, the maximum distance of influence is approximately 18 m,regardless of the angle. The highest temperature difference observed between angles of 0 and 15 degrees was approximately 1.3℃.

To compare the combined effects of the two variables,only cases of 3 W and 5 W for heat output and angles of 0° and 15° were used for graphical comparisons.When observing the range of condensation reduction and the highest wall temperature owing to the induction fan with the heating wire, changes in the installation angle had a more significant impact on the surface temperature increase than the heat output.

Based on the results of this airflow analysis, an induction fan with a heating wire set at a 5 W heat output and a 15° installation angle towards the wall(HF 6) was selected for the field experiment.

4. Field application experiment

Floor-insulating drainage plates, induction fans with heating wires, and automatic control ventilation systems were used in the real-scale environment. The purpose of this experiment was to assess the effectiveness of these three condensation reduction methods compared with existing methods. The optimal conditions for floor-insulating drainage plates and induction fans with heating wires, as determined through simulations, were utilized.

4.1. Field application experiment setup

4.1.1.1. Floor-Insulating Drainage Plate. Target site

A for the experiment was located in South Korea and was an apartment building preparing for unreinforced concrete construction in the summer. Site A, a mixed-use complex, has a deep and narrow underground parking

lot extending to a maximum depth of four floors. The parking lot was surrounded by soil on all sides, and the nearby groundwater level was measured to be approximately the height of the second basement floor, indicating a high risk of condensation in the underground parking lot during summer.

Based on the heat transfer analysis, both the selected insulating drainage plate and the standard drainage plate were installed on the lowest floor of site A. These were placed over a 1000 mm thick concrete floor on the soil, with each material covering 50square meters in the southwest corner. Unreinforced concrete was then poured to a height of 150 mm from the floor. From June to August, immediately following construction, the surface temperatures at the center points of the unreinforced concrete above each material were measured using a laser thermometer. The details of the experimental materials are presented in Figure 11, and the construction locations and photographs are shown in Figure 12.

4.1.1.2. Induction Fan with Heating Wire.

An induction fan with a heating wire, selected through simulation based on its heat output and installation angle,was installed on the third floor of site A. A normal induction fan with the same installation angle was also installed on the second floor at the same location. One fan was placed on each of the north- and south-facing walls and one was placed in the southeast corner,where air circulation tended to stagnate, totaling three installations. A summary of the experimental equipment is presented in Figure 13.

Considering that cold air remains lower, the wall surface temperatures were measured at a height of 0.5 m from the floor were measured. The airflow analysis indicated that the range of the condensation reduction effect for HF6 was 19 m. Taking into account three months of operation, measurement points were set at 5 m intervals up to 25 m, factoring in an additional 30% for the real site. The construction locations and photographs are shown in Figure 14.

Each induction fan was operated for 9 h daily from 8 AM to 5 PM from June to August, and the surface temperature at each measurement point was recorded using a laser thermometer.

4.1.1.3. Automatic Control Ventilation System.

The ventilation system affects the overall airflow of the site throughout the site via the dry area. Because of the complexity of conducting experiments simultaneously at the same site, the original manual control system was applied at site B, whereas the improved automatic control system was used at site C. Site B, equipped with a manual control system, is located in Korea and is an apartment building with a four-floor underground parking lot near completion in the summer. Site C, where an automatic control ventilation system was applied, is located in Korea. It is an apartment complex that is nearly completed during the summer. Although the parking lot structures differed, both sites had high groundwater levels and were chosen because of their similar indoor and outdoor temperature and humidity conditions. Details of the experimental locations and construction photographs are presented in Figure 15.

A summary of the ventilation systems used in the experiments is presented in Figure 16. The basic settings for the manual-control ventilation system used for comparison activated the supply and exhaust fans when the CO concentration exceeded the legal standard of 50 ppm. In addition to the CO concentrationbased setting, it operates on a manually set schedule of 2 h of operation, followed by a 30-minute stop.

The experimental automatic control ventilation system maintained the basic settings for the CO concentration according to legal standards, similar to the manual system. However, it automatically operates the supply and exhaust fans only under specific conditions(fan operation criteria case1, 2 in Figure 16) based on real-time indoor and outdoor temperature and humidity data collected using an exterior psychrometer and four integrated air quality sensors installed indoors. These sensors measure CO, temperature,and humidity. The specific conditions involved relative comparisons of the indoor and outdoor humidity and temperature. Because there were no condensation incidents in the underground parking lots with absolute humidity below 14 g/kg, as mentioned in Chapter 2’s 17-year data, Case 2 operated the fans only when the absolute humidity was below13 g/kg, considering a 5% safety margin.

Real-time data are used to determine the operation of an automatic control ventilation system. To prevent frequent on/off cycling and potential malfunctions,the system maintains operational and rest periods similar to those of a manual control system.It determines whether to activate the supply and exhaust fans based on the average data over a 10-min period before each operation cycle. This result was sustained for 2 h, followed by a 30-min rest period. The 10-min decision period was included in the 30-min rest period. Each ventilation system was operated for up to approximately 10 h a day, with a schedule of 2 h on/30 min off from 9 AM to 9 PM from June to August. Humidity and temperature data for the manual control system were collected from data loggers installed at measurement points on all four walls, whereas the automatic system also measured the humidity and temperature at these points using integrated air quality sensors for system operation. The outdoor humidity and temperature of both systems were measured using psychrometer sensors.

4.2. Field application experiment results

4.2.1.1. Floor-Insulating Drainage Plate.

Over three months, the surface temperatures at the floor measurement points were recorded for both the insulating and normal drainage plates, as shown in Figure 17.

Immediately after construction, the surface temperature at the floor measurement points was recorded as 9.7℃ for both types of drainage plates. Initially, the surface temperature of the floor with the insulating drainage plate was approximately 1.1℃ higher than that of the normal drainage plate, indicating effectiveness in blocking cold. However, after three months, the difference reduced to only 0.1℃ higher for the insulating drainage plate. It is inferred that, while the insulating drainage plate initially impacted the surface temperature by delaying cold transfer over time, it was similarly influenced by the indoor air temperature like the normal drainage plate.

4.2.1.2. Induction Fan with Heating Wire.

The surface temperatures at six wall measurement points were recorded immediately after installing the induction fan with a heating wire and the normal induction fan at the site, and again after one month of continuous operation. The observed temperature differences are shown in Figure 18 (Normal induction fan: N-Point1 ~ 3/Average: N-Average, Induction fan with a heating wire: H-Point 1 ~ 3/Average: H-Average). No significant temperature difference was observed for the normal induction fan over the course of the month. However,the induction fan with heating wire showed an increase in wall surface temperature by up to 1.2℃,with an average elevation of 0.8℃ compared to the normal fan. The highest temperature increase was observed at 10 m from the heating wire fan. Within the measurement distance of 25 m, the heating wire fan significantly influenced the wall surface temperature.

After operating both fans for three months, the results, illustrated in Figure 19, showed an average surface

temperature increase of 2.7℃ for the heating wire fan compared to the normal fan. The data are represented as bar graphs for the monthly average surface temperatures at six points and as line graphs for the average of three fans.

4.2.1.3. Automatic Control Ventilation System.

During the summer months, the ventilation systems were operated at each site according to their control methods. The changes in humidity inside the underground parking lots before and after heavy rainfall during the rainy season are shown in Figure 20. At site C, with a single-floor parking lot, the system did not operate on two occasions when the absolute humidity exceeded 13 g/kg, despite meeting the Case 2 conditions. After 10 h of fan operation, there was a noticeable decrease in indoor humidity (1.8 g/kg reduction in vapor amount). In contrast, at site B, with a four-floor parking lot, the ventilation system operated continuously from 9 AM to 9 PM, regardless of the indoor and outdoor humidity conditions. The indoor humidity remained approximately 90%, showing an increase in moisture levels even during rainy and highhumidity conditions outside (0.6 g/kg increase in vapor amount after 10 h of fan operation). It is suggested that if the automatic control system had been applied in this scenario, it would have only operated for 2 h at11:30 AM on July 3, preventing the further intake of humid outdoor air.

After operating both ventilation systems for three months and comparing the surface temperatures, the results are displayed in Figure 21.

The monthly average surface temperatures at the four measurement points for each system are displayed as bar graphs (Manual control: Point 1 ~ 4, Automatic control: Sensor 1 ~ 4).The average values of these four points are shown in line graphs (Average of manual points: M-Average,

Average of automatic sensors: A-Average). Based on these averages, the wall surface temperatures with the automatic control system showed an increase of 0.4℃ compared to the manual control system over the three-month period.

4.3. Discussion

In a field experiment comparing floor-insulating drainage plates with normal drainage plates, while the insulating plates initially blocked cold effectively over time, the difference in floor surface temperatures between the two materials diminished owing to the influence of indoor temperatures. When used in large open spaces with extensive air exchange, insulating drainage plates showed limited long-term effectiveness in reducing condensation. However, they could be more effective in reducing condensation in specific local areas of deep underground layers, especially where underground water penetrated the hollow layers beneath the plates, bringing them under the influence of ground temperature.

A field experiment comparing induction fans with heating wires to normal induction fans showed that heating wire fans were more effective at increasing wall surface temperatures. When installed with a heat output of 5 kW at a 15-degree angle to the wall, the highest temperature increase was observed at a distance of 10 m from the equipment. Beyond this point, the concentrated effect of the surface temperature rise gradually diminished with ongoing operation owing to air movement. Heating wire fans are particularly effective in areas that require a focused temperature

increase, such as walls facing soil or corners withless airflow. Designing installation intervals between heating wire fans, considering the peak temperature point at 10 m, could maximize condensation reduction.

A field experiment comparing the automatic control ventilation system and humidity with those of a manual control system showed that the automatic system was more effective, particularly in controlling the indoor absolute vapor amount during rainy conditions.Surface temperature measurements were performed for comparison with those of the other two

methods. However, its effect on the surface temperature increase was not significant. Despite the limitations of differing site structures, the effectiveness of the automatic system in operating based on a specific logic responsive to indoor and outdoor humidity conditions was evident. This system is likely to be effective in single-floor underground parking lots with high direct moisture ingress through entrances, and in large spaces where controlling the amount of vapor can reduce condensation. A comparison of the surface temperature increases for the three condensation reduction methods is presented in Table 5.

5.Conclusion

In this study, floor-insulating drainage plates, induction fans with heating wires, and automatic control ventilation systems were selected as highly applicable densation reduction methods for apartment building underground parking lots, considering their logical characteristics. These selected methods were applied in real underground parking lot settings to evaluate their effectiveness in reducing condensation compared with existing methods. The results of this study are summarized as follows.

(1)Based on 17 years of temperature and humidity measurements in underground parking lots of 38 apartment buildings, effective condensation mitigation requires controlling both surface temperature and absolute humidity in parking lots. The study also revealed that the type of parking lot influences temperature differences, with a larger temperature disparity in large complex types than in mixed-use complexes. Humidity control and air circulation in open spaces are essential for large complexes, whereas mixed-use complexes require highface temperatures, particularly on the lowest floors.

(2)Considering the specific characteristics of apartment building underground parking lots and their practical applications, this study selected floor- insulating drainage plates, induction fans with heating wires, and an automatic controltion system as condensation reduction methods. The materials for the floor-insulating drainage plates and the specifications for the induction fans were determined through simulations.

(3)A field experiment with the floor-insulating drainage plate suggested that, although insulating materials delay the transfer of cold, their long- term effect on increasing the surfaceture is minimal, at 0.1℃. Floor-insulatingnage plates are likely to be more effective in mixed-use complex types, particularly in deep underground layers, where they are continuously affected by the ground temperature owing to water infiltration.

(4)A field experiment with an induction fan with a heating wire showed that, after one month, the average surface temperature of the walls increased by 0.8°C compared to that of normal induction fans, with the maximum surface temperature increasing by 1.2°C. After three months, the average temperature of the walls increased by 2.7°C compared to that of normal induction fans. Induction fans with a heating wire are likely to be effective in mixed-use complex types, especially in reducing condensation when applied to walls facing soil or corners with low air flow.

(5)The field experiment with the automatic control ventilation showed that during 10 h of operation in rainy weather, the indoor absolute humidity decreased and increased by 1.8 g/kg and 0.6 g/kg when using the automatic control system and the manual control system, respectively. After three months, the wall surface temperature increased by 0.4°C compared to that of the manual control system. Automatic control ventilation systems are likely to be effective in large complex types, particularly in large single-layer spaces, where the direct outdoor air influence is significant or airflow circulation effects are challenging to control, necessitating humidity regulation.

In this study, condensation reduction strategies tailored to the structural characteristics of apartment building underground parking lots were developed by improving existing architectural and facility elements. The proposed solutions are not only applicable to apartment complexes, but also to a variety of buildings with underground parking, offering high practical value in enhancing existing designs that did not initially consider condensation reduction. Furthermore, the significance of this study lies in its application of the selected strategies in real-world settings,comparing their effectiveness with traditional methods under natural indoor and outdoor temperature and humidity changes over an experimental period.

The study faced limitations in that the experiments were not conducted in identical locations and environments for both the existing and improved methods. This makes it challenging to control regional weather and site-specific conditions. Geographical locations can influence the effect of outdoor air intake owing to variations in the outdoor temperature and humidity based on the latitude and terrain. Additionally, factors such as the number of underground floors, depth, and groundwater level around a parking lot can lead to differences in concrete surface temperature, indoor temperature, and humidity, thereby affecting the effectiveness of reduction methods. Therefore, to compare the effectiveness of each condensation reduction method, further experiments in a controlled environment, like a mock-up site, are necessary to account for these variables.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes on contributors

Hye Yeon Kim, is a Ph.D. candidate at Chung-ang University and a researcher at construction company DL E&C.

Min Hee Chung, received her Ph.D. from Chung-ang University. She is an Assistant Professor at the Department of Architecture, Kyonggi University.

Jin Chul Park, received his Ph.D. from Chung-ang University. He is a professor at the School of Architecture and Building Science, Chung-Ang University.

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