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ScienceDirect Energy Procedia 105 (2017) 4627 – 4634

The 8th International Conference on Applied Energy – ICAE2016

Experimental study on ventilation effect on concentration distribution of R32 leaking from floor type air conditioner Wufeng Jina*, Pan Gaoa, Yafei Zhengb a

Tianjin Key Laboratory of Refrigeration Technology, Tianjin University of commerce, b TPersagy Energy Saving Technology Co., Ltd. Beijing, China

Abstract Under the two environmental problems of ozone depletion and global warming, study on safe and friendly refrigerant becomes extremely urgent. Under this condition, R32 obtains more favor in refrigerating and air conditioning industry, however, its inflammability limits its widely use. This paper uses experiment to study the diffusion and concentration distribution of R32 when leaking from floor type air conditioner, as well as ventilation effect on concentration variation. The results show that, R32 concentration has an obvious stratification on height direction after leaking from floor type air conditioner. It mainly gathers in area below leak hole and barely spreads upward. In area above 1m, R32 concentration is small and there’s no risk of Inflammability. Down-exhaust has better effect on R32’s dilution. But it should be noticed that R32 concentration in corner where’s away from exhaust outlet is high and it can be risk area. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2016 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and/or peer-review under responsibility of ICAE Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy.

Keywords: R32;diffusion;concentration distribution;floor type air conditioner;ventilation

1. Introduction Ozone depletion and global warming are two most important environmental issues people are facing in recent years. The 19th meeting of the Parties of "Montreal Protocol" adopted the adjustment of accelerating phase-out of HCFCs in September 2007 [1,2]. In 2009, Copenhagen Climate Conference made clear targets to each country to reduce greenhouse gas emissions. Under this situation, R32, CH2F2, obtains more favor in refrigerating and air conditioning industry because of its good thermal and physical properties and low GWP value. Many researches have been made to study the practicality of R32: Zhu studied the practicality of using R32 instead of R22, as well as the alternatives of R22 including R410A, R290 and R1234yf. Several properties were compared including thermo-physical properties,

* Corresponding author. Tel.: +8-6022-2666-7502; fax: +8-6022-2666-7502. E-mail address: [email protected]

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy. doi:10.1016/j.egypro.2017.03.1003

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environmental characteristics, safety, thermal performance and market availability. The results show that R32 is a promising alternative of R22 considering emission reduction, safety, energy saving and market availability [3,4]. Han tested the cycle characteristics of R32 and compared its properties with R410A. The results show that their pressure ratios are almost the same, the compressor power of R32 is slightly higher than that of R410A and their COP are very close. In a word, R32 has good thermos-physical properties and friendly environmental performance which make it a potential alternative refrigerant to R410A [5]. Wang poured R32 into a household air conditioning designed for using R410A. The test results show that the optimum charging quantity of R32 is about 30.4% of the original charging quantity of R410A, and the refrigeration capacity can increase 8.5% of the R22 system and the EER can increase by up to 7.1 % [6]. Liu did research using R32 replacing R410A in household air conditioner. The results show that R32 has the basic conditions for the replacement of R41A, and it is good to increase the capacity and EER of the refrigerant cycle. So it can reduce the size if the heat exchanger of the R410A unit. At the same time, it must be paid attention to the expense of COP and the discharge temperature increment [7]. It can be seen that R32 meets the requirements as an alternative refrigerant and in some properties it’s better than R410A. However, R32 is a kind of “A2L” refrigerant [8], its inflammability and risk of explosion during operation limit its widely use. Therefore, risk analysis is one necessary step before putting R32 into use. This paper, based on the study on the leakage and diffusion of R32 leaking from a wall-mounted air conditioner, uses experiment to study the diffusion and concentration distribution of R32 when leaking from floor type air conditioner, as well as ventilation effect on concentration variation. And the results will be great useful to the safety use and risk prevention of R32. 2. Methods 2.1. Impact factors There are many factors effecting the concentration distribution of R32, including: working condition of the air conditioner, leak hole position, leak amount and leak rate. In “Research on Leakage and Diffusion Characteristics of Flammable Refrigerant R32”, which has been finished already, it’s illustrated that air supply velocity and angle have no significant effect on concentration distribution when R32 leaks from a running air conditioner [9]. And considering ventilation, which is necessary to ensure indoor air quality, impact factors in this experiment can be determined as follows: leak hole position, leak amount and rate, and ventilation effects. 2.1.1 Leak hole position For split air conditioner, indoor leakage mainly occurs at the copper tube junction. For wall-mounted conditioner, which is of small size, leak hole is similar with its installation height. For floor type air conditioner, which has a bigger size, it has similar structure with wall-mounted air conditioner, but the relative position of each components is longer than that in wall-mounted conditioner. The junction in floor type conditioner is at low position, generally below 0.5m. In research on R32 leaking from floor type air conditioner in Japan, the leak hole is close to the ground, as shown in figure 1 [10]. In this experiment, set leak hole 0.3m high from floor. 2.1.2. Leak amount and leak rate


Figure 1 Indoor space, including floor-mounted indoor unit

In “Research on Leakage and Diffusion Characteristics of Flammable Refrigerant R32”, cooling load of the test room was calculated using TENGEN, which was 3334w. LS-B3541AT air conditioner using R410A as refrigerant was choose with rated cooling capacity of 3500w. Rated amount of R410A was 900g. Considering theoretical charge amount of R32 is 0.71 times of R410A [11ˈ12], this experiment use R32 650g, that means the leak amount is 650g. In the study when R32 leaks from a running air conditioner, leak process could be classified into two stages, fast leak rate stage and slow leak rate stage. In fast leak rate stage, 80% of R32 leaked into indoor in 6mins. In this study, most of R32 leaks into indoor in 6mins by adjusting value opening. 2.1.3. Ventilation effect This study analyzed dilution effect of two ventilation methods: Up-exhaust and Down-exhaust. The test room simulates a residential room with 3 human-beings. According to the standard of “Civil heating, ventilation and air conditioning design”, the ventilation rate is 30m3/h per person [13], thus 90m3/h rated amount fans are used in this experiment. In summary, test conditions can be listed as table 1: Table 1 Experimental conditions

Condition 1 2 3

Leak position 0.3m 0.3m 0.3m

Leak amount 650g 650g 650g

Time 6min 6min 6min

Ventilation None Up-exhaust Down-exhaust

2.2. Laboratory introduction The experiment was finished in Flammable Refrigerant Laboratory, as shown in figure 2. The laboratory is 3.9m*2.9m*2.75m ˈ constructed by steel with thickness of 50mm. For commodiously observing, the lab is sealed by transparent tempered glass with thickness of 8mm in south and north. This paper uses experiment to study ventilation effect on R32 concentration distribution. The leak system was made after several tests before the experiment to simulate leakage from the real machine. The experimental schematic diagram is shown in figure 3.

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Figure 2 Flammable Refrigerant Lab

20 QD6310 R32 concentration detectors are used in the experiment. Air outlets are set in north wall, air inlet and leak hole are in the east wall. Both air inlet and outlet are 120mm*120mm, and the diameter of leak hole is 6mm. The layout is shown in figure 4. And detailed positions’ shown in table 2.

1-electronic scales 2-R32 tank 3-pressure sensor 4-shut-off value 5-mass flowmeter 6-leak hole 7-concentration detector 8-dota logger Figure 3 Experimental schematic diagram

3. Results and analysis 3.1. R32 free diffusion Control value opening, set leak amount 650g, leak time 6mins, close air inlets and outlets, record R32 concentration for 2 hours. The concentration variation is shown as figure 5. It can be seen that R32 concentration has a stratification on height direction. Points in 0.2m height plane, their max concentration are around 14 except point 3; points in 1m height plane, their max concentration are around 4; points in 2m height plane, their R32 concentration are all close 0 during the whole record time. The reason R32 concentration has a stratification on height direction is that the density of R32 is bigger than that of air, after leaking into indoor area, the amount diffusing downwards is much larger than that of upwards. Thus when R32 leaks from the leak hole in 0.3m height plane, concentration of points in 0.2m height plane increase quickly, concentration of points in 1m height plane increase too but not obviously, and in 2m height plane, where R32 can hardly reach, the concentration is close to 0.

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Table 2 Experimental device placement Project

coordinate˄X,Y,Z ˅ Test room 1 0ˈ0ˈ0 Air inlet centre 1 0ˈ1.5ˈ2.2 Air up-outlet centre 1 3.64ˈ0ˈ2.4 Air down-outlet centre 1 3.64ˈ0ˈ0.3 Leak hole centre 1 0ˈ0.95ˈ0.3 Concentration sensors position 1 2ˈ1.1ˈ0.2 2 2ˈ1.1ˈ1 3 0.5ˈ0.1ˈ0.2 4 2ˈ0.1ˈ2 5 3.35ˈ1.1ˈ0.2 6 0.5ˈ2.1ˈ0.2 7 3.35ˈ2.1ˈ1 8 3.35ˈ2.1ˈ2 9 3.35,1.1,ˈ2 R32 concentration 10 3.35ˈ2.1ˈ0.2 sensor 11 2ˈ0.1ˈ0.2 12 0.5ˈ1.1ˈ1 13 0.5ˈ1.1ˈ0.2 14 0.5ˈ0.1ˈ1 15 2ˈ0.1ˈ1 16 2ˈ2.1ˈ2 17 2ˈ2.1ˈ1 18 2ˈ1.1ˈ2 19 3.35 ˈ1.1ˈ 1 20 2ˈ2.1ˈ0.2

Figure 4 Concentration detector layout

25

unit m m m m m m m m m m m m m m m m m m m m m m m m m

points 1 6 11 16

20

concentrationͧ vol%ͨ

No.

2 7 12 17

15

3 8 13 18

4 9 14 19

5 10 15 20

LFL 0.2m points

10 1m points

5

2m points

0 0

10 20 30 40 50 60 70 80 90 100 110 120 timeͧ minͨ

Figure 5 Concentration variation under free diffusion condition

Figure 6 Concentration contour map of 0.2m height plane

The concentration variation when R32 leaks into indoor area can be classified into two stages. In the first 7mins, the concentration increases quickly and reaches the top in the 7th min, then it decreases slowly until closes to 0. This is because R32 almost finishes leaking in the first 6mins, and after that there’s little

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leaking still with a low rate. Thus concentration of all test points gradually decrease by diffusing. Comparing the concentration variation of all test points, point 3 has the max R32 concentration value of 22.12, its increase rate is 3.16/min. That’s because point 3 is near the leak hole and it’s in the corner of the test room where’s easy to form eddy zone. Compare the concentrations of test points with R32 flammable limits, which is 14.1%-29.3% [7], it can be seen that concentration of points in 1m and 2m height planes are below the Lower Flammable Limit(LFL), which means it’s safe there. In 0.2m height plane, they are beyond LFL except point 1 and 5. Figure 6 shows R32 concentration contour map of 0.2m height plane at 7min and it can be seen that it’s easy to form eddy zone in corners and concentrations near sides is larger than that in the middle of the plane. 3.2 Ventilation effect Two kinds of ventilation are analyzed with leak amount 650g, leak time 6mins. 3.1.1. Up-exhaust Open up air outlet, which is 2.4m height, and record for 1hour. The concentration variation is shown in figure 7. It can be seen that the tendency of concentration variation is like that in diffusion, concentration increases quickly and then decreases slowly. The difference is that when using down-exhaust, time for concentration of points reaching top is different in different planes. Points in 0.2m height plane, their concentrations increase in the first 7mins. Except point 3, their max concentrations are around 14, according with diffusion. Points in 1m height plane, their concentrations begin increasing after 6mins and reach top, around 7, which is larger than that in diffusion, in the 14 th min, then decrease slowly. Points in 2m height plane, their concentrations are close to 0 in the first 26mins. In 26min to 34min, there are little increasing to about 2.5 before decreasing. Compare concentrations with the LFL, it can be seen that concentrations of points in 0.2m height plane are all above the LFL.

25

20

points

concentrationͧ vol%ͨ

20

2 7 12 17

3 8 13 18

4 9 14 19

5 10 15 20

points 1 6 11 16

15

0.2m points LFL

15

concentrationͧ volͨ

1 6 11 16

2 7 12 17

3 8 13 18

4 9 14 19

5 10 15 20

LFL

0.2m points

10

10

1m points

5

1m, 2m points

5

2m points 0 0

10

20

30

40

50

60

timeͧ minͨ

0 0

10

20

30

40

50

60

timeͧ minͨ

Figure 7 Concentration variation under Up-exhaust condition

Figure 8 Concentration variation under Down-exhaust condition

Up-supply has no effect on airflow in lower area at the beginning. But with continuous exhausting, upper area has low pressure which leads R32 to diffuse upwards. Though up-exhaust may have dilution effect to R32, it’s effecting time is too long which means it’s meaningless in real situation.


3.2.2. Down-exhaust Open down air outlet, which is 0.3m height, and record for 1hour. The concentration variation is shown in figure 8. It can be seen that points in 0.2m height plane, their concentrations increase in the first 7mins and reach around 12 in the 7thmin except point 3. Then decrease to about 0 in about 25mins. Concentration of point 3 reaches top of 19.1 with a rate of 2.46/min. Points in 1m and 2m height planes, their concentrations are close to 0 during the whole time. Down-exhaust ventilation has significant dilution effect of R32. That’s because the density of R32 is bigger than that of air, and when R32 leaks from a lower position, it will drift outside through air outlet effectively. 3.2.3. Comparison Table 3 lists the points and the time that their concentrations are in the flammable limits. It can be seen that up-exhaust ventilation has little effect on R32 dilution. Down-exhaust ventilation has an effectively dilution effect when R32 leaks from floor type air conditioner. It’s should be noticed that in each condition, point 3 has the biggest R32 concentration value, which means it’s hard to dilute corner concentration when refrigerant leaks into indoor. Table 3 Risk points and time

Text Point

Free diffusion

Up-exhaust

Down-exhaust

1

-

2min21s

-

3

53min55s

12min37s

4min55s

5

-

1min38s

-

6

33min03s

5min42s

-

10

18min36s

4min08s

12s

11

6min20s

2min54s

-

13

3min55s

3min01s

-

20

7min58s

5min17s

-

4. Conclusions (1) When R32 leaks from a floor type air conditioner and diffuses freely, the concentration increases quickly with a biggest rate of 3.16/min, and then decreases slowly. There’s an obviously concentration stratification on height direction. In area below leak hole, R32 concentration is high and it’s beyond the LFL. In high area above 1m, concentration is low and it’s safe area there. (2) Up-exhaust volition has little effect on R32’s dilution when it leaks from a floor type air conditioner because of its higher density. Considering its long effecting time, it can be seen as useless in real leak situation. (3) Down-exhaust ventilation has considerable effect on R32’s dilution. The max concentration value

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of point 3 is 19.1. Points in 0.2m except point 3, their max concentration values are around 12, which is below the LFL. (4) Under all of the conditions, concentrations of point 3 are beyond the LFL, thus it should be noticed that in corner areas where’s away from air outlet, R32 gathers easily which may be risk space with high R32 concentration. 5. Copyright Authors keep full copyright over papers published in Energy Procedia Acknowledgements This research was supported by the Innovative Research Groups of the National Natural Science Foundation Project of China (TD12-5048). About the corresponding author Jin Wufeng, male, Associate Professor, School of Mec-hanical Engineering, Tianjin University of Commerce, +86 13 8-0218-6472, E-main: [email protected]. Research fields: the technology of refrigeration and air-conditio-ning.

References [1] BS EN 378-2008 Refrigerating systems and heat pumps-Safety and environmental requiremengts-Part 1: Basic requirements, definitions, classification and selection criterias, S. [2] Decisions adopted by the nineteenth meeting of the parties to the montreal protocol on substances that deplete the ozone layer[EB/OL]. http://www.ozone.unep.org/. [3] Zhu Mingshan, Shi Lin. Exploration of using R32 to substitute for R22 in household commercial air-conditioning, J. Refrigeration and Air Conditioning. 2009, 9 (6), p. 31-34. [4] Shi Lin, Zhu Mingshan. Re-analysis on Using R32 to Substitute for R22 in Household/commercial Air-conditioning, J. Journal of Refrigeration. 2010, 31 (1). [5] Han Xiaohong, Xu Yingjie, Qiu Yu, Min Xuwei, Gao Zanjun, Chen Guangming. Experimental study on the cycle performance of refrigerant R32, J. Refrigeration and Air Conditioning. 2010, 10 (2), p. 68-70. [6] Wang Chaoxin, Zhu Xingwang, Gong Yi. Experiment Research on R32 Substituting for R410A in Household Air Conditioning. Fluid Machinery. 2011, 39 (7). [7] Liu Chang, Er Chima. Application research of low GWP refrigerant R32 for replace of R410A in room air-conditioner, J. Refrigerantion and Air Conditioning. 2015, 15 (11), 73-76. [8] ANSI/ASHRAE 34-2010, Designation and safety classification of refrigerants, 2010. [9] Yan Zhang. Research on Leakage and Diffusion Characteristics of Flammable Refrigerant R32, D. Tianjin University of Commerce. 2012. [10] The Japan Society of Refrigerating and Air Conditioning EngineersˊRisk Assessment of Mildly Flammable Refrigerants 2013 Progress Report, 2013. [11] Liang Bin, Zhang Mingjie,Fu Yu. Theoretical and Experimental Study of R22’s Alternative Refrigerants Performance of R32/R290/R410A., C. China Household Electrical Appliances Technology Conference, 2013. [12] Zhou Yingtao, Liu Zhongshang. Application experimental study of R32 refrigeration compressor for air-conditioning, J. Refrigerantion and Air Conditioning. 2011, 11 (2), p. 53-55. [13] GB 50736-2012. Code for Civil heating, ventilation and air conditioning design, S. China Building Industry Press, Beijing, 2012.