Subject experiment on personal air-conditioning airflow using a vortex ring

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Introduction
Because of the improving the human comfort and easing the pre-set temperature of the room for the conservation of energy, various TAC (task and ambient airconditioning) systems were proposed. TAC system is a method for providing office workers with control of a local supply of air to control their individual thermal and air environment. TAC system can provide the conditioned air to an individual space, not to all the room, which leads to easy control of the occupied space with low energy.
The authors have also conducted investigation on various performances of the TAC for developing the new systems and effective control methods, e.g. TAC system which provide 100 % fresh and conditioned air to the individual space from the task unit on the desk in naturally ventilated room (hybrid ventilation) with low energy consumption and high productivity (Chikamoto 2001 [1], Chang et al. 2004 []), TAC system which is a desktop packaged air conditioning unit and supplies both direct air flow against human and wide covered air flow around human   [3]), TAC system which uses multi-flow ceiling cassette type packaged air-conditioner which is widely used in office and is not likely to be detached at the layout change, though it is likely detached at the layout change when applying it to furniture (Ishiguro et al. 2011 [4]) and TAC system on the ceiling which can supply directional or diffusible airflow selected by each office worker using his or her PC (Lee et al. 2016 [5]). * Corresponding author: tomoyuki@se.ritsumei.ac.jp Controlled variables are air temperature, velocity, direction of the supply air etc., however supply air flow is always jet created by fan. Therefore, vortex ring supplied from air-gun and its pulse flow control technic were paid attention as the new air flow of TAC. Vortex ring is easy to go straight and has more stability and less diffusivity than normal jet. Therefore, wind can be felt even if the TAC device is not set on the office worker's desk etc. and high rotating speed of the vortex ring also can be felt by office worker. The amount of the supplied air can be easily controlled by adjusting the suppling interval of the vortex ring (pulse airflow), which leads to the climate control corresponding to office worker's favor and effective airflow for cooling ( Fig. 1). With these control methods with air-gun TAC, personal microclimate with high thermal comfort can be created. The authors have so far performed PIV analysis and unsteady CFD (Large Eddy Simulation) analysis (Chikamoto et al. 2018 [6]) with the aim of understanding the airflow characteristics of the vortex ring using a large vortex ring transmitter. In addition, we fabricated a ceiling-mounted vortex ring transmitter that can be used in the office used in this study, and conducted experiments (Chikamoto et al. 2016 [7]) and CFD analysis (Chikamoto et al. 2018 [8]) to generate vortex rings. We considered the relationship between the airflow in the vortex ring and the airflow blowing out from around the vortex ring delivery hole, and the conditions for generating the vortex ring that can maintain its shape and velocity. However, when actually using the vortex ring as an air conditioner, it has not been clarified what kind of air current feeling and comfort the occupant gets from the vortex ring (Moriwaki et al. 2019 [9]). Therefore, in this paper, as subject experiment 1, we improved the turbulence of the surrounding airflow, which was a problem of the vortex ring sending device produced in the previous articles and set the blowing air volume of the vortex ring, and then conducted the subject experiment. The purpose of this study is to clarify the effects on airflow and comfort.
In addition, based on the above results, we made a new vortex ring delivery device with an enlarged device and an angle adjustment mechanism. Subject experiment 2 was conducted to clarify the effects of the vortex ring on the feeling of air current and comfort of the worker when the feeling of air current is further increased by increasing the air flow rate.  . 2 shows the outline of the vortex ring sending device used this time. The piston expands and contracts the bellows, pushing out the air inside and sending out a vortex ring. In addition, cold air is supplied into the apparatus from the cold air supply port, and the supplied cool air is blown out from the outlet around the vortex ring delivery hole. A vortex ring containing cool air can be sent out by sucking in the cool air blown from the peripheral outlet.

Vortex ring output air volume setting
In this study, it is assumed that vortex rings are used as task air conditioning. The necessary air volume for task air conditioning is ensured by the ambient blowing airflow. Therefore, in order to set the air volume around the vortex ring, it is necessary to set the amount of heat removed by the task air conditioning using the vortex ring among the heat loads generated in the building. Among the heat loads in the building, we consider that task air conditioning using vortex rings removes the heat loads in the task areas of "exhaust heat from equipment (PC)," "human sensible heat," and "human latent heat." At this time, the heat load generated in the task area per worker is 30 [W] (exhaust heat of equipment (PC)), 60 [W] (human sensible heat), 40 [W] (human latent heat), the total amount of heat to be removed by task air conditioning using vortex rings is 130 [W]. Based on this, we determined the air flow rate as 39 [m 3 /h], which was calculated assuming that the air temperature of the vortex ring was 18°C and the room temperature was 28°C, as the air flow rate around the vortex ring sending device.

Experimental conditions
The experiment was conducted from late December 2018 to early January 2019 in a laboratory at Ritsumeikan University (inner dimensions: width 3600 mm, depth 2600 mm, ceiling height 2200 mm). The vortex ring delivery device is installed on the ceiling of the laboratory, and cold air is supplied to the device from a cold air storage area through a duct. A thermocouple and a differential pressure gauge were used to measure the air volume in the laboratory environment and in task air conditioning using vortex rings (Fig. 3). The subjects were three healthy male university students, with a clothing amount of 0.8 clo (underwear, long-sleeved cutter shirt, long pants, no tie) and a metabolic rate of 1.0 met (sitting at rest). In addition, they were asked to ensure sufficient sleep on the previous day, and alcohol consumption was prohibited.

Experimental procedure
In order to standardize the experimental conditions, subjects were allowed to rest for 20 minutes in a room with a constant room temperature of 28°C with a thermocouple attached. After that, the experiment was started under the conditions for each case. Immediately after the start of the experiment, they filled out a questionnaire every minute, and the experiment ended 20 minutes after the start of the experiment (Fig. 4).

Measurement item
In addition to laboratory environmental measurements, the following measurements were made. 1) Questionnaire declaration Thermal sensation/comfort feeling was reported on his 7-point scale from -3 to +3. They were also asked to declare whether or not they felt an air current, and if they felt an air current, they were asked to report the strength of the air current on a 5-level scale from -2 to +2, and the comfort level of the air current on a 7-level scale from -3 to +3).
2) Human body physiological measurement Skin temperature was measured using a thermocouple. 9 points were measured on the forehead, upper arms, hands, feet, lower legs, thighs, torso, throat, and nape of the neck to confirm changes in skin temperature for each site.

Experiment case
In the experimental case, the room temperature was kept at a constant 28°C, and the state in which no vortex ring was sent was defined as the reference case 1 (none), and in case 2 (around) only the surrounding air was sent out. In case 3 (head), vortex rings are sent to the subject's parietal region, and in case 4 (neck), they are sent to the subject's neck ( Table 1). The outlet temperature at the vortex ring delivery was set at 18°C, and the air flow rate was set at 39 [m 3 /h]. In addition, the distance from the vortex ring sending device to the subject was unified to 1.0 m, and the vortex ring sending interval was at 2 seconds.

Thermal / comfort report
This result is the average value for all subjects. Regarding the relationship between the thermal sensation and the comfort sensation, in case 1 (none) and case 2 (around), where no vortex ring is sent out, the report is on the hot side from beginning to end, and at this time it is the report on the uncomfortable side. On the other hand, in case 3 (head) and case 4 (neck), where vortex rings are emitted, the hot side's complaint decreased over time, and the uncomfortable side's complaint decreased accordingly (Figs. 5 -6). Therefore, it is considered that the vortex ring can efficiently deliver the cool air sent from the surrounding air outlet to the subject, and has the effect of cooling the subject more effectively than the conventional air conditioning.

Airflow strength / comfort report
Comparing case 3 (head) and case 4 (neck) regarding the strength of the airflow, both cases are on the weak side, however there is a tendency for case 4 (neck) to feel the airflow more (Fig.7). This is thought to be because in case 3 (head), the hair acts as resistance and makes it difficult to feel the airflow. Therefore, it is concluded that the air currents of the vortex rings are felt more on the nape of the neck than on the top of the head. In addition, there was an overall tendency for both cases to be on the comfort side of the airflow (Fig. 8). In general, the feeling of air currents caused by conventional air conditioning makes people feel uncomfortable, however the feeling of air currents caused by air conditioning using vortex rings gives subjects a comfortable feeling.

Forehead / neck skin temperature
Regarding the forehead, the skin temperature in case 3 (head) is lower than in case 1 (none) and case 2 (around) (Fig. 9). Regarding the neck, the temperature in case 4 (neck) is lower than in case 1 (none) and case 2 (round) (Fig. 10). In case 3 (head) and case 4 (neck), the vortex ring hit the subject with cool air sent out from the surrounding air outlet, and the part of the body that hit the vortex ring containing cool air was cooled.

Neck / hand skin temperature
For the hands, the temperature in case 4 (neck) is lower than in the other cases (Fig. 11). This may be due to the cooling effect of the vortex ring on the skin of the neck, which causes the AVA (arteriovenous anastomosis) to contract to keep heat from escaping from the body, thereby reducing the blood flow to the hands and lowering the hand temperature.

Summary
As experiment 1, a subject experiment was conducted to determine the effect of vortex rings on the airflow and comfort feeling of the office workers. The findings obtained are shown below.
The vortex ring can efficiently deliver cool air delivered from the surrounding air outlets to the subjects, and the comfort feeling for the airflow of air conditioning with the vortex ring is improved compared to conventional air conditioning, which has a cooling effect on the subjects more than conventional air conditioning. Since the hair on the top of the head acts as resistance and makes it difficult to feel the airflow, we obtained declarations that the subjects felt the airflow intensity of the vortex ring more strongly in the neck area. In case 3 (head), the temperature of the forehead was about 1°C lower than in case 1 (none), and in case 4 (neck), the temperature of the neck muscles was about 1.5°C lower than in case 1 (none). It is thought that when the neck muscles are cooled by the vortex ring, the AVA contracts and blood flow to the hands is reduced, which may cause the hand temperature to drop as well.

Outline of vortex ring sending device
Improvements to the vortex ring delivery device identified in subject experiment 1 include increasing the airflow rate to increase the sense of airflow, downsizing the device for installation on office ceilings, and installing an angle adjustment mechanism to enable delivery to the neck. Fig. 12 shows an overview of the vortex wheel delivery device newly designed and manufactured to solve these problems. The vortex wheel delivery mechanism and cool air supply method are the same as those of the previous device, but the angle can be adjusted by having an independent driving part. In addition, the type of piston was changed so that it can be installed in the ceiling of many office buildings, making it possible to reduce the height. As in subject experiment 1, the ambient airflow was set to 39 [m 3 /h].

Experimental conditions
The experiment was conducted from late September 2022 to early October 2022 in a laboratory at Ritsumeikan University (inner dimensions: width 3400 mm, depth 2550 mm, ceiling height 2700 mm). The vortex ring delivery device is installed on the ceiling of the laboratory, and cold air is supplied to the device from a cold air storage area through a duct. Thermocouples were used to measure the laboratory environment (Figs. ). The subjects were four healthy male university students, with a clothing amount of 0.6 clo (underwear, short-sleeved shirt, long pants, no tie) and a metabolic rate of 1.0 met (sitting at rest). In addition, they were asked to ensure sufficient sleep on the previous day, and alcohol consumption was prohibited.

Experimental procedure
The experimental procedure is shown in Fig. 14. Before starting the experiment, subject rested in a room with a constant room temperature of 28°C for 30 minutes with the thermocouple attached. After that, the experiment started under the conditions for each experimental case. Take a 30 minute break after completing the case. This procedure is repeated until all cases are completed. Immediately after the start of the experiment, They would fill out a questionnaire every minute.

Measurement item
In addition to laboratory environmental measurements, the following measurements were made. 1) Questionnaire declaration Thermal sensation/comfort feeling was reported on his 7-point scale from -3 to +3. They were also asked to declare whether or not they felt an air current, and if they felt an air current, they were asked to report the strength of the air current on a 5-level scale from -3 to +3, and the comfort level of the air current on a 7-level scale from -3 to +3). 2) Human body physiological measurement Skin temperature was measured using a thermocouple. 9 points were measured on the forehead, upper arms, hands, feet, lower legs, thighs, torso, throat, and nape of the neck to confirm changes in skin temperature for each site. Table 2 shows experimental cases. For the experimental cases, the room temperature was kept constant at 28°C, and Case 0, in which the vortex ring was not sent out, and Case 1-3, in which the vortex ring sending air volume was varied, were set. The surrounding blowing temperature was set at 18°C, and the air flow rate was set at 39 [m 3 /h]. In addition, in all cases, the delivery angle was set to 30° so that the vortex ring hit the Table2. Experiment

Thermal / comfort report
This result is the average value for all subjects. Fig. 15 shows the results of thermal sensation declarations, and Fig. 16 shows the results of comfortable sensation declarations. Compared to Case 0, in which no vortex ring is delivered, Cases 1-3, in which vortex rings are delivered, show a decrease in the number of subjects reporting a hot side. The comfort level was also reported more often in Case 1-3 than in Case 0, indicating the cooling effect of the vortex wheel and its effectiveness as a personal air conditioner, as in subject experiment 1. However, Case 2 was superior to Case 3, which had the largest air volume, in terms of both cooling and comfort.

Airflow Strength, Airflow Range, Airflow
Comfort report Fig. 17 shows the results for airflow strength, and Fig.  18 shows the results for airflow range. With respect to the strength of the airflow, Case 2 is considered to give the greatest airflow sensation and influence the feeling of warmth, coolness, and comfort. In addition, since Case 3, which has the largest airflow, and Case 2 are comparable in terms of the range of airflow, it is considered that the airflow in Case 2 is sufficient for sending air to the neck, where the skin is less exposed. In addition, it is considered that the comfort feeling for airflow differs greatly depending on the individual's likes and dislikes for airflow.

Summary
In experiment 2, a subject experiment was conducted to clarify the effect of increasing the vortex wheel delivery air volume in personal air conditioning using vortex wheels on the airflow and comfort of the office worker when vortex wheels are delivered to the neck. The findings are as follows.
As in subject experiment 1, it was possible to deliver cool air to the subjects efficiently, suggesting that the air conditioner cooled the subjects more efficiently than conventional air conditioning.
In addition, since the range of airflow is similar in Case 3 and Case 2, it is considered that the airflow in Case 2 is sufficient to deliver to the neck, where there is less exposed skin. Moreover, the airflow in Case 2 is the strongest, which is thought to be superior in terms of both warming and cooling sensation and comfort. Based on the above, the airflow rate of Case 2 is considered to be optimal for this vortex wheel delivery system.
In the experiment, the humidity was calm and no perspiration was reported, so the influence of the humidity environment was not considered.

Conclusions
Subject experiments revealed the effectiveness of personal air conditioning using vortex rings and more effective delivery to the neck.
In addition, subject experiments with increased vortex wheel delivery air volume showed that the delivery air volume could be optimized.