The Effects of Warm Air Heater on the Dispersion and Deposition of Particles in an Enclosed Environment

Warm air heaters are now widely used in enclosed environments, either as primary or auxiliary heating facilities. However, the influence of these heaters on the indoor air quality has received scant attention, and the currently available data is insufficient. Therefore, this study experimentally investigated the particle concentrations, air velocity, temperature, and relative humidity in a storeroom equipped with a warm air heater. To assess the effects of the heater on the dispersion and deposition of 0.3, 0.5, 1.0, 3.0, and 5.0 μm particles, we analyzed 18 scenarios with various settings for the output power and outlet orientation. The results indicated higher particle deposition rates when the heater was operating. Furthermore, the particles’ decay rate loss coefficients increased with the heater’s output power and the particles’ proximity to the heater’s air outlet but were also influenced by the direction of the warm air flow.

). It appears that many cities in China have 50 been suffering serious haze pollutions during wintertime. Therefore, due to the higher level of 51 particulate matter concentration in winter, it is essential to pay close attention to the indoor 52 particles during the heating season, besides the thermal comfort.

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3 The influence of indoor heating systems on the airborne particle dispersion and deposition 54 has been extensively studied over the last few years. The contribution of different heating 55 systems such as electric baseboard heaters, natural gas furnace, hot water heaters, and wood 56 stoves to indoor particle exposures were discussed (Silberstein, 1979; Moriske et al., 1996;57 Weichenthal et al., 2007;Spolnik et al., 2007;Ozgen et al., 2012). For instance, Golkarfard 58 and Talebizadeh (2014) analyzed the deposition and dispersion of airborne particles in two 59 radiator and floor heating systems. Results showed that the deposition ratio of particles was 60 higher in the radiator heating system than in the floor heating system. The effect of radiators 61 on particle size distributions and concentrations was evaluated by Chen and Li (2015). It was 62 found that the environmental parameters (particle concentrations in the adjacent indoor air, 63 temperatures, relative humidity, and air velocities) were related to the particle concentrations for exposure to closed fireplaces and pellet stoves. Also, Dehghan and Abdolzadeh (2018)

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4 compared the air flow and particle dispersion in a room with three heating systems: floor 78 heating, skirt boarding heating, and radiator heating systems, indicating that the skirt boarding 79 heating system had the lowest particle concentration in the breathing zone of the manikin. To analyze the effect of warm air heaters on indoor particle dispersion and deposition,   Table 1.

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The temperature and relative humidity are monitored along with the particle concentrations  Table 1. In this paper, the particle decay rate loss coefficient, which is most commonly studied to 182 judge the particle loss in an enclosure, is used to compare the particle deposition in different 183 cases. Since the room is well sealed and the particle concentration is relatively low, the Where () Ct describes the indoor particle concentration (part/m 3 ), 0 C represents the initial 189 concentration (part/m 3 ),  is the particle decay rate loss coefficient (s -1 ) and t is the 190 elapsed time (s).

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In this study,  is calculated by fitting the decay curve of the dimensionless 192 concentrations ( 0 ( ) / C t C ). As an illustration, Fig.1(b) illustrates the exponential decay of In order to assess the influence of the temperature and the relative humidity on indoor 196 particle concentrations, the temperature rise and relative humidity drop are introduced in this 197 study.

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The temperature rise and relative humidity drop, which are expected to reduce the effect The temperature rise and relative humidity drop in different cases are summarized in Table   208 2. The temperature rise and relative humidity drop at the sampling point in this experiment

Comparison of the suspended particles in the enclosed environment with idle and working
218 warm air heater and humidifier 219 The particle dimensionless concentrations at Sampling Point I against time in Cases 1-2 are 220 presented for comparison (Fig. 2). With a similar trend to those in the case with the idle warm 221 air heater (Case 1), the particle dimensionless concentrations decrease as the elapsed time 222 increases in Case 2. The loss of indoor particles is mainly due to the particle deposition in the 223 absence of indoor and outdoor particle sources. In addition, it can be seen in Fig. 2 that the 224

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10 particle dimensionless concentrations in Cases 1 and 2 decline faster initially and then tend to result may prove that the use of a humidifier with tap water leads to a growth of particle 246 concentrations, consistent with some conclusions presented previously (Zhao, 2018). The 247 portable ultrasonic humidifier generates the vapor, water droplets, and particles due to the 248

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11 mineral composition dissolved in tap water, which may be resulting in the rise of the relative 249 humidity and particle concentrations. Comparing the patterns in Fig. 2 (a) Otherwise, as gravitational settling velocity increases to the square of the particle diameter, 260 the gravitational settling is the dominant force on particle deposition when the particle sizes orientations. According to the results, the larger the output power of warm air heater, the 296

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13 greater of the particle decay rate loss coefficient. It is also seen that the particle decay rate loss 297 coefficients in cases with the upward airflow are lowest for most particle sizes while keeping 298 the output power of the warm air heater constant. This relative relationship is similar to the 299 velocity, temperature rise, and relative humidity drop patterns. The reductions of the 300 thermophoretic force and the air velocities may lead to lower particle decay rate loss 301 coefficients in cases with the upward airflow. As shown in Fig. 5, the decay rate loss  Table 2, the data imply that the warm air heater influences the particle, air velocity, 330 temperature and relative humidity near the air outlet with various degrees.

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In this paper, the effect of the heating power, air blowing direction, distance from the air 332 outlet, humidifier, average air velocity, temperature rise, and relative humidity on particles in In the present study, the particle concentrations, air velocities, temperatures, and relative 347 humidity in a storeroom with a warm air heater are measured. The influences of the warm air 348 heater on dispersion and deposition of particles (ranging from 0.3 to 5.0 μm) in eighteen cases 349 are explored. Based upon the data generated from the experiment and according to the above 350 analysis, the main conclusions are as follows:

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(1) The particles in the case with a working warm air heater have larger deposition rates 352 than that in the case with an idle warm air heater.

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(2) The use of a humidifier with tap water in the indoor environment with the working 354 warm air heater leads to a growth of particle concentrations.

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(3) The larger particles are deposited faster than smaller particles near the air outlet of the 356 working warm air heater.

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(4) The dropping rate of particle dimensionless concentrations increases with the rising 358 output powers of the warm air heater, especially for smaller particles.

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(5) The particle decay rate loss coefficients in cases with the upward airflow are lowest for 360 most particle sizes. The decay rate loss coefficients in cases with downward airflow are higher 361 than that in cases with sideward airflow for 0.3, 0.5, and 1.0 μm, whereas the decay rate loss