Indoor Air Pollutant (PM 10, CO₂) Reduction Using a Vortex Exhaust Ventilation System in a Mock-Up Room

Abstract

In this study, a performance comparison experiment with a vortex exhaust installed at the end of a ventilation device to enhance the effect induced by reducing indoor pollutants was conducted. The experiment was carried out by constructing a mock-up room with a limited indoor environment, and performances were compared based on the following two tests. First, to confirm the effect of pollutant reduction, the wind speed was measured based on the distance from each exhaust system to verify the depth and speed at which wind can flow. Pollutants were induced to the vortex exhaust, general exhaust gasses were generated, and their performances were compared. Second, Arizona dust was used to confirm the performance with regard to the removal of pollutants which existed in particulate form (PM 10), and for CO₂ gas, a representative gaseous pollutant was used as a reference. Based on the results, it was confirmed that installing a vortex exhaust system can allow for the generation of wind speeds that allow propagation at greater depths (>110 mm) compared to cases in which general exhaust is used; accordingly, exhaust performance can be achieved at increased depths. In addition, the experiment confirmed that vortex exhaust can improve the efficiency of simultaneous removal of PM 10 and CO₂ compared with general exhaust. Further, it was shown that installing a vortex exhaust system can remove PM 10 and CO₂ farther from the exhaust port in a shorter period than a general exhaust port. In addition, it was inferred that vortex exhaust can be utilized to prevent indoor pollutants and diseases in combination with the latest technology.

1. Introduction

Recently, high concentrations of particulate matter (PM) have begun to be recognized as a national problem in Republic of Korea and the government has strived to reduce them. PM is divided into PM 10 and PM 2.5, depending on the aerodynamic diameter. PM 10 is a term that typically refers to fine particles, indicating that the particles’ aerodynamic diameter is smaller than 10.0 µm. PM 2.5 is a term that typically refers to ultrafine particles, and represents particles with aerodynamic diameters smaller than 2.5 µm [1].

The most effective way to reduce the concentration of fine dust and other indoor pollutants is to allow the inflow of clean air indoors to lower the concentration [2,3,4,5].

According to the World Health Organization, the annual average concentration of fine dust in Seoul in 2016 was 46 µg/m³, which is approximately 1.2 to 3.5 times higher than that of major Organization for Economic Cooperation and Development countries such as Tokyo (28 µg/m³), Paris (28 µg/m³), and Washington, D.C. (16 µg/m³) [6]. PM can be introduced into indoor spaces when it is ventilated from outdoor air which contains a high concentration of PM; its inhalation can cause bronchial diseases [7,8] and cerebrovascular diseases when it infiltrates blood vessels [9]. Furthermore, when PM enters through ventilation spaces and remains indoors, it can adversely affect the health of the occupants [10]. When the air environment outside a building is poor, naturally ventilating the indoor environment with outdoor air is nearly impossible. Mechanical ventilation, however, can realize continuous air supply and ventilation and, due to filters, can be more effective in decreasing the concentration of pollutants, such as PM, even in cases where the air environment is poor [11].

In mechanical ventilation, the suction speed decreases abruptly as the distance from the exhaust port increases in the indoor air suction process [12,13,14,15], thereby reducing the pollutant capture efficiency. To address this problem, studies have been conducted to improve the suction speed and pollutant capture efficiency by generating a jet stream in front of local exhaust ventilation systems (e.g., hoods) [16,17] or by generating a vortex using swirlers [18,19].

Lim et al. [20] mentioned that ventilation depth could be increased by five times using a vortex system, compared with conventional exhaust ports. Lee and Lee [21] reported that the use of a vortex system could increase the suction speed nine times and the capture efficiency by 70%. Therefore, a combination of a vortex system and a mechanical ventilation system is expected to improve indoor PM removal efficiency.

Furthermore, when combined with a ventilation system, the Vortex device can also reduce energy loss through ventilation. Therefore, it is expected to be more effective than existing ventilation systems when applied together with passive ventilation in the context of outdoor environments in climate and energy crises.

However, most previous studies on the use of a vortex were focused on the analysis of its effects using computer simulations or scale models [22,23,24]. Therefore, the number of experimental studies that have generated a vortex is limited.

In this study, two experiments were conducted to investigate the indoor air pollutant (PM 10 and CO₂) removal efficiency of a vortex exhaust system. First, the pollutant capture velocities with respect to the distance from the exhaust port of the general and the vortex exhaust systems were compared. Second, a mock-up room was constructed, and pollutants (PM 10 and CO₂) were added inside. Subsequently, the pollutant removal efficiencies of the general and vortex exhaust systems were compared.

The substances used in the experiment were generated and appeared indoors and outdoors. Additionally, it is believed that the performance of the vortex exhaust system can be confirmed based on its performance with regard to the removal of various substances which are representative indicators of indoor air pollution.

These experimental results will be used as basic data for removing pollutants, including indoor PM 10 and CO₂, based on the application of the vortex method.

2. Type of Exhaust System

The most-used exhaust system currently has a low-ventilation efficiency disadvantage because its size and the distance from the source of pollutants are not considered in its usage [25]. As such, an increase in the air volume of the exhaust device is required, which may also generate noise.

In contrast, the vortex exhaust device used in this study is a device that has a swirler attached to the exhaust port to generate a swirling phenomenon, to increase the capture depth and capture area. This can increase the exhaust effect.

The characteristics of each exhaust port type are shown in

Table 1. Characteristics of exhaust systems.

Exhaust Type	Ventilation Efficiency	Velocity	Swirler Attached	Increase Capture Depth
normal	low	low	none	change in wind speed
vortex	excellent	high	attached	no need to change the wind speed

.

In the case of a Vortex exhaust port equipped with a swirler, as shown in Figure 1, the surrounding air is strongly pushed out in the radial direction, and the air that is pushed out owing to the intake of the exhaust port is drawn back toward the exhaust port.

Therefore, the installation of the swirlers generates a vortex under the exhaust port and causes a gradual increase in its intensity that expands into the surrounding space, thereby increasing the capture area of the exhaust port. When the rotation speed of the vortex generated by the swirlers is increased, a stable vortex ring is formed outside the swirlers, thereby blocking the flow drawn from the side of the swirlers toward the exhaust port. Therefore, intensive airflow toward the exhaust port is formed under it, and the airflow velocity increases as the cross-sectional area of the flow decreases.

In the case of a general exhaust system, however, the ventilation efficiency is lower than that of the vortex ventilation system because the size of the outlet and its distance from the source are not considered. Therefore, when the ventilation efficiency is increased, excessive energy is consumed in conjunction with an increase in the air volume and noise of the exhaust system. When noise and energy consumption are reduced, the ventilation efficiency decreases, thereby reducing the efficiency of removal of PM generated indoors and that introduced from outside.

3. Methodology

3.1. Mock-Up Room

To minimize the influences of furniture and other internal components for the experiment using fine dust materials, a mock-up room was constructed for a comparative experiment on the pollutant reduction performances of a general and a vortex exhaust device.

The mock-up can verify the changes inside from the outside, and it was constructed airtightly using a non-interruptible transparent panel and profile to minimize the influence of static electricity and infiltration on the experimental results. The mock-up is described in

Table 2. Mock-up summary.

Classification		Description
Mock-up room size		4000 mm (D) × 3000 mm (W) × 2400 mm (H) = 28.8 m3
Components of mock-up room	Supply diffuser	high-efficiency particulate air filter mounting
	Exhaust diffuser	normal diffuser and vortex diffuser
	Distance between air supply and exhaust diffuser	1500 mm
	Mixing fan	used to mix particulate matter (PM) and CO2

and Figure 2 and Figure 3.

As shown in Table 1, the components of the mock-up room include a general air supply, exhaust, vortex exhaust, and a mixing fan. The air supply system was equipped with a high-efficiency particulate air filter so that the experimental results would not be affected by PM 10 entering the mock-up room from outside. The distance between the air supply and the exhaust diffusers was set to 1500 mm in accordance with the “Regulations for Facilities in Buildings” in Republic of Korea.

The mixing fan in the mock-up room was installed on the ceiling at its center so that PM 10 and CO₂ could be mixed well. The PM 10 and CO₂ inlet was installed at a height of 500 mm from the floor, and the measuring devices for PM 10 and CO₂ were installed 1200 mm from the position of the respiratory tract of an average-sized adult and the inhalation floor.

3.2. Experimental Method

Two experiments were conducted to obtain the exhaust efficiency of the general and vortex exhaust systems. First, the pollutant capture depth was obtained by measuring the suction flow velocity with respect to the distance from the exhaust port. Based on this, the effectiveness of the exhaust was confirmed by obtaining the capture depth and the capture velocity through the exhaust port.

The second experiment, which involved examining the ventilation efficiency of the general and vortex exhaust systems, was conducted based on the following three steps.

• Stabilization is required for preheating the measuring equipment and zero-point adjustment of the measured values. To this end, the measuring equipment was operated for 5 min followed by the injection of fine dust (Arizona Dust A2 Fine Dust) and CO₂.
• To distribute PM 10 and CO₂ evenly in the mock-up room, a mixing fan was operated.
• The general and vortex exhaust systems were operated for 30 min, and the effect of each system was examined.

In this instance, the PM 10 and CO₂ reduction efficiency of the vortex exhaust system was calculated as the ratio of the amount reduced during the experiment to the initial amount.

The particle size distribution of Arizona Test Dust ISO 12103-1 [26] A2, which was used in the experiment, is listed in

Table 3. Particle size distribution by volume.

Particle Size (μm)	Distribution by Volume (%)
0.97	4.5–5.5
1.38	8.0–9.5
2.75	21.3–23.3
5.50	39.5–42.5
11.00	57.0–59.5
22.00	73.5–76.0
44.00	89.5–91.5
88.00	97.9–98.9
124.50	99.0–100.0
176.00	100.0

. For this material, particle sizes that correspond to PM 10 account for approximately 50%.

A DustTrak II Aerosol Monitor was used to measure the PM 10 concentration, and a TSI 7525 IAQ-CLAC was used for CO₂. One-minute average measurements of each device were used.

Table 4. Experimental methods and measurement equipment.

Exhaust System Type	General Exhaust System		Airflow	140 m3/h(CMH)
	Vortex Exhaust System
Experiment method and measurement time	1. particulate matter (A2 Fine Test Dust) injection 2. mixing for 5 min using a mixing fan 3. measurement of particulate matter after 30 min of operation 4. shutdown of exhaust system, mixing of residual particulate matter
Number of experiments	Three times for each
Measuring instrument specification	measured parameter		wind speed
		name	KIMO AM I310, SOM 900
		measurement range	wind speed (m/s)	0.00–5.00
		measurement accuracy	wind speed (m/s)	±3% of the leading value ±0.05
	measured parameter		CO2 concentrations
		name	TSI 7525 IAQ-CALC Indoor Air Quality Meter
		measurement range	0–5000 parts per million (ppm)
		resolution	1 ppm
	measured parameter		concentrations of PM 10
		name	DustTrak II 8530 aerosol monitor
		concentration range	0.001–400 mg/m3
		particle size range	0.1–10 μm
		accuracy	±5%

lists the experimental methods and measuring devices.

4. Results and Discussion

4.1. Heading Airflow Velocity with Respect to the Distance from the Exhaust Vent

The outlet flow velocity of the exhaust system can be used as a comparative measure of the pollutant’s discharge efficiency. Therefore, the airflow velocity with respect to the distance from the exhaust port was measured to compare the exhaust efficiencies of the vortex and general exhaust systems, as shown in Figure 4. The measuring distance ranged from 0 mm to 600 mm at 50 mm intervals. During the measurements, the airflow was set to 140 CMH, similar to that set for testing pollutant removal efficiency. The results are shown in

Table 5. Measurements of airflow velocity at various distances.

Measuring Distance from Exhaust Vent (mm)	Airflow Velocity of General Exhaust System (m/s)	Airflow Velocity of Vortex Exhaust System (m/s)	Remark
0	0.39	1.78
50	0.22	1.18
100	0.13	0.77	airflow velocity for the general exhaust system reaches 0 m/s at a distance of 110 mm from the exhaust
150	0.00	0.58
200	0.00	0.44
250	0.00	0.36
300	0.00	0.33
350	0.00	0.27
400	0.00	0.20
450	0.00	0.17
500	0.00	0.16
550	0.00	0.15
600	0.00	0.13

.

As shown in Table 4, the airflow velocity at 110 mm from the exhaust port fell to 0 m/s for the general exhaust system. For the vortex exhaust system, however, an airflow velocity of 0.13 m/s was recorded even at 600 mm from the exhaust port.

Based on this, the equation for wind speed reduction according to the distance of the vortex and general exhaust device was calculated using the log function from the results in Figure 5, as shown in

Table 6. Wind speed reduction equation according to exhaust diffuser type.

Exhaust Diffuser Type	Equation for Wind Speed Reduction over Distance (0–150 mm)
normal exhaust diffuser	$\mathcal{y}=-0.126\mathcal{x}+0.5$
vortex exhaust diffuser	$\mathcal{y}=-0.401\mathcal{x}+2.08$

.

The wind speed reduction equation was calculated based on the distance from the exhaust port to the point at which the wind speed of the general exhaust device becomes equal to 0 m/s, which is 150 mm away. Based on this, it was determined that the vortex exhaust device can secure the induction depth and wind speed for pollutant emissions that are approximately four times greater than that of the general exhaust device, up to 150 mm.

This confirms that the vortex exhaust system can increase the capture depth for the discharge of pollutants by approximately six times compared with that of the general exhaust system.

4.2. Pollutant Removal Efficiencies of Vortex and General Exhaust Systems

The pollutant discharge efficiencies of the vortex and general exhaust systems were measured and compared. PM 10, a particulate material, and CO₂ gas, a gaseous substance, were used as pollutants.

The concentration of CO₂ was increased to the range of 2500 to 3000 ppm, and then its reduction effect was examined. For PM 10, 10 g of the International Standardization Organization (ISO) 12103-1 A2 Arizona Test Dust was added to the closed mock-up room, and the reduction effect of each exhaust system was quantified.

4.2.1. CO₂

CO₂ exists in a gaseous state, unlike PM 10. Indoor CO₂ concentration is mainly caused by human activities and is used as an important indicator of ventilation among indoor air environment factors, so the CO₂ substance removal performance among gaseous pollutants can represent the performance of the exhaust device.

Table 7. CO₂ removal rate according to exhaust type.

Measurement Time (min)	① General Exhaust System		② Vortex Exhaust System		Residual Difference (②–①) (%)
	CO2 (ppm)	Residual Rate (%)	CO2 (ppm)	Residual Rate (%)
0	2889	100.0	2575	100.0	0.0
5	2621	90.7	2212	85.7	−4.8
10	2194	75.9	1834	71.2	−4.7
15	1849	64.0	1513	58.8	−5.2
20	1601	55.4	1311	50.9	−4.5
25	1378	47.7	1096	42.6	−5.1
30	1215	42.1	949	36.9	−5.2

and Figure 6 show the results of the experiment on the performance of the vortex and general exhaust systems conducted using CO₂ gas.

The initial CO₂ concentration was set to 100% (2500 to 3000 ppm), and it was reduced by 63.1% for the vortex exhaust system and 58% for the general exhaust system after 30 min. The reduction rate of the vortex exhaust system was approximately 5% higher than that of the general exhaust system.

It is believed that the difference is due to the following characteristics: The PM 10 used in the experiment is a pollutant composed of PM, and the PM that settles to the bottom or does not float depending on the weight of the particles cannot be discharged through the exhaust system.

However, CO₂ is a gaseous pollutant, unlike PM, and is mixed in the air. Therefore, it is an object that moves easily in response to changes in pressure and airflow. It was found that there was not a large difference in the removal performance of CO₂ as a function of the type of exhaust port.

4.2.2. PM 10

PM 10 rapidly settles to the ground because it is heavy. Sinking PM 10 can be effectively removed using a ventilation system when its capture depth is long.

Table 8. PM 10 residual rate according to the exhaust type.

Measurement Time (min)	① General Exhaust System		② Vortex Exhaust System		Residual Difference (②–①) (%)
	PM 10 (mg/m3)	Residual Rate (%)	PM 10 (mg/m3)	Residual Rate (%)
0	0.870	100.0	0.657	100.0	0.0
5	0.800	91.9	0.542	82.5	−9.4
10	0.796	91.5	0.387	58.9	−32.6
15	0.623	71.6	0.275	41.9	−29.7
20	0.479	55.1	0.208	31.6	−23.5
25	0.386	44.4	0.155	23.6	−20.8
30	0.317	36.4	0.116	17.7	−18.7

and Figure 7 show the results of PM 10 removal efficiency for the vortex and general exhaust systems.

As shown in Table 8, the Vortex exhaust device yielded a decrease of 82.3% compared with the initial concentration, dropping to 17.7% after 30 min when the initial concentration was assumed to be 100%.

However, the general exhaust device yielded a decrease of 63.6% compared with the initial concentration, dropping to 36.4% after 30 min. Based on this, it was judged that the PM 10 emission of the Vortex exhaust device was approximately 18.7% more effective than the general exhaust device.

As shown in Figure 7, the reduction rate for approximately 3 min after the start of the experiment is similar for both the general exhaust and the vortex exhaust device, but the vortex exhaust device yields a rapid decrease for approximately 13 min, and the vortex exhaust device yields a reduction effect in the range of 19–24% compared with the general exhaust device until the end of the experiment. It was judged that this was due to the characteristics of the vortex system, which can achieve effects such as the resuspension of pollutants by creating deep airflow.

4.3. Discussion

In this study, two experiments were performed. First, exhaust wind speed was measured with respect to the distance from the exhaust port to identify the capture depths of the vortex and general exhaust systems. Second, pollutants (PM 10 and CO₂) were added into the mock-up room, and the pollutant concentration reduction efficiencies of the vortex and general exhaust systems were examined.

The experimental results can be summarized as follows.

• When the capture depth was investigated, it was found that the wind speed decreased as the distance from the exhaust port increased for the general exhaust system. At a distance of 110 mm, there was no exhaust effect, as the wind speed was 0 m/s. In the case of the vortex exhaust system, however, the exhaust effect was observed even at 600 mm from the exhaust port (approximately six times the distance of the general exhaust system), confirming a higher exhaust effect (by six times) compared with that of the general exhaust system. It was found that the vortex exhaust system could further reduce PM 10 by 18.7% and CO₂ by 5.1% as compared with the general exhaust system.
• Trend equations of the pollutants were derived based on the pollutant reduction rate graphs of each exhaust system. The results are shown in

  Table 9. Trend equation and equation slope ratio by pollutant and exhaust type.

  Pollution Type	General Exhaust System	R2	Vortex Exhaust System	R2	Slope Ratio
  PM 10	Y = −0.0239x + 1.0851	0.953	Y = −0.0285x + 0.9559	0.944	1.19
  CO2	Y = −0.0209x + 1.0114	0.977	Y = −0.0217x + 0.9799	0.969	1.03

  .

The results in Table 9 indicate that the vortex exhaust system can, respectively, reduce the PM 10 and CO₂ pollutants 1.19 and 1.03 times more effectively than the general exhaust system. These results were obtained owing to the effect of the capture depth of the vortex exhaust system. Therefore, it is confirmed that the vortex exhaust system is more effective in removing indoor air pollutants than the general exhaust system.

This study applied a Vortex exhaust system equipped with a swirler to increase the reduction effect of indoor pollutants and verified its effectiveness through experiments. The effectiveness was verified through mock-up experiments, and it was found that the vortex exhaust system can achieve a deeper suction effect; in particular, the exhaust effect of PM 10 substances existing in the particulate form was higher than that of general exhaust systems.

However, this study was conducted based on an experiment in a limited space and is thus associated with several limitations. First, the mock-up used in the study was configured and installed in a limited space to verify the suction effect of the exhaust system, and no changes were observed when obstacles such as actual furniture or movement of people were present. Second, as the operating variables of the ventilation fan could not be applied, additional research is needed to verify the analysis of wind speed changes. Third, additional pollutant reduction performance verification (not only for PM 10) is needed using various pollutants. Fourth, the use of electric energy in reducing pollutants in actual general exhaust systems and vortex exhaust systems should be confirmed in the future, and the application of renewable energy sources to supplement this should also be considered.

However, if the vortex exhaust system confirmed through this study is applied to an actual environment, it can achieve a high-exhaust efficiency, as was confirmed experimentally. Additionally, if this system is combined with the latest technology [26,27,28,29] for reducing indoor pollutants, it can be utilized as one of the prevention and solution measures for droplet transmission infections that may occur based on recent health and environmental crises, such as pandemics.

5. Conclusions

In this study, a vortex exhaust system was compared with a general exhaust system with a low capture depth to examine its efficiency in removing pollutants and its capture depth. To this end, PM 10 and CO₂ removal efficiencies were analyzed after constructing a mock-up room and installing the general and vortex exhaust systems in it. The results of this study can be summarized as follows:

First, when the capture depth of each exhaust system was measured, it was found that the vortex exhaust system could generate a sufficient wind speed to capture pollutants at a higher depth (≥600 mm) than that of the general exhaust system (110 mm). This confirmed that the pollutant removal effect of the vortex exhaust system is six times higher than that of the general exhaust system.

Second, when PM 10 was added to the mock-up room, it was found that the vortex exhaust system could further reduce its concentration by 18.7% compared with the reduction achieved using the general exhaust system. It is difficult to remove PM 10 using the general exhaust system, because it rapidly settles on the floor owing to its large size and weight. However, it appears that the vortex exhaust system can obtain a higher PM 10 reduction rate because of its higher capture depth.

Third, when the gaseous material removal performance was examined using CO₂, it was found that there was an approximately 5% difference in the removal efficiency between the vortex and general exhaust systems. This is because the gaseous pollutant was easier to remove than PM 10, as it moved easily even at low airflow rates and low pressures.

Fourth, when the PM 10 and CO₂ removal performance for each exhaust port type was compared using the trend equation slope, it was found that the vortex exhaust system had a higher PM 10 removal efficiency compared with that of the general exhaust system. This is because the removal effect was exhibited immediately after the operation of the vortex exhaust system, owing to its capture depth.

Therefore, when the vortex exhaust system is applied to the indoor space of the existing and new buildings, it will be able to discharge pollutants that are generated indoors or introduced from the outside efficiently and rapidly, and decrease the energy required for exhaust functions owing to the shortened exhaust system operation time.

However, in this study, there is a limit to the ability to measure the change in efficiency, owing to the actual supply of air inside the building, because the air handling unit was not installed in an actual building.

To solve this limitation, it is necessary to verify the difference between the general exhaust system and the pollutant removal effect by installing the vortex system in the actual building where the air handling unit is installed. The results of this study are expected to be used as basic data to improve the performance of the exhaust systems used in buildings.