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Procedía Engineering 205 (2017) 1302-1309
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10th International Symposium on Heating, Ventilation and Air Conditioning, ISHVAC2017, 1922 October 2017, Jinan, China
Improving Indoor Air Humidity in Heated Rooms based on Natural Evaporation of Water from Wetted Textile Fabric - A Pilot Study
Indoor air humidity (IAH) is one of the most important factors in the determination of in-door environmental conditions and thermal comfort. However, during the heating period in cold climates it has been reported that indoor relative humidity is often lower than 30%. This paper focused on indoor low air humidity and explored the solution to solve the issue based on a simple experiment. It was found that natural evaporation of water from the vertically wetted fiber fabric could effectively improve IAH. Both evaporation rate and evaporation quantity of water from wetted porous fiber fabric had significant influences on attainable maximum value of IAH. In addition, it was worth noting that the entire regulating process did not need to consume energy.
© 2017 The Authors. Published by Elsevier Ltd.
Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning.
Keywords: Indoor air humidity; Heating period; Natural evaporation; Moisture source
1. Introduction
Building is a place for people to work and live. In modern society, people spend most of their time inside buildings. Thus environmental conditions inside buildings have a significant impact on human's physical health, psychological wellbeing and work productivity. Indoor air humidity (IAH) is one of the most important factors in the determination of indoor environmental conditions and thermal comfort. There are numerous studies indicating that indoor humidity environment is associated with building performance and occupant's health. High levels of IAH promote the growth of mold, dust mites, and mildew on building surfaces, thereby result in poor indoor air quality,
* Corresponding author. Tel.: +86 13811342255. E-mail aMress: xiejc@bjutedu.cn
1877-7058 © 2017 The Authors. Published by Elsevier Ltd.
Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and
Air Conditioning.
10.1016/j.proeng.2017.10.384
Guangtao Fana, Jingchao Xiea *, Hong Yangb, Jiaping Liu!
2College of Architecture and Civil Engineering, Beijing University of Technology, Beijing 100124, China bCollege of Architecture and Urban Planning, Beijing University of Technology, Beijing 100124, China
Abstract
respiratory discomfort and allergies [1]. Low levels of IAH can not only bring about dryness of skin, mouth and throats [2-3], but also induce mucous membrane, sensory irritation of eyes, bronchitis, asthma, influenza [4-5], and static electricity [6-7]. Thus, controlling IAH at a correct level in buildings is a key component of indoor environmental conditions. According to ASHRAE Standard [8], relative humidity (RH) in habitable spaces should be maintained between 30% and 60%.
As is well known, in cold climates, the outdoor air temperature is usually low. In general, indoor air is heated to ensure thermal comfort. However, due to outdoor air is dry (low humidity ratio), when outdoor air is taken into indoors, the air RH becomes very low. Take Beijing of China as an example, outdoor average temperature is 0.2oC during the heating period, outdoor average RH is 43%. When outdoor air is heated to 18oC (i.e. indoor design heating temperature during the heating period according to Chinese standard), the air RH drops below 13%. Also, in numerous in situ measurements, the RH level of the indoor air during the heating period often drops below 30% [911]. Therefore, low humidity of indoor air during heating period has become an urgent problem.
Based on previous studies associated with indoor humidity regulation, building hygroscopic materials, such as straw bale, clay mineral and porous wood fiber board, have been much studied and successfully used in building constructions to moderate indoor humidity levels [12-15]. Hygroscopic interior materials can adsorb and desorb moisture from the adjacent air owing to their passive and environmental properties. When indoor air RH is high, hygroscopic materials can store moisture from the air, and return it to the space when RH is low. However, during the heating period, RH is at a low level for a long time. In this case, current hygroscopic interior materials may be powerless to regulate IAH by returning the moisture which is absorbed previously to the space. Also, Korjenic et al. [16] indicated that in some situations, it is likely to be very difficult to achieve an acceptable indoor humidity level by applying hygroscopic materials.
Life experience has taught us that porous fiber fabric is a common material for carrying moisture and it has the characteristic of moisture absorption and desorption. For instance, in the hot summer, the fabrics worn next to the skin can absorb the perspiration on the skin, then release it to exterior space, to ensure thermal comfort of the human body. This phenomenon implies that it is not whimsical to set interior decoration as a continuous moisture source (i.e. moisture absorption and desorption) to improve indoor air humidity.
In this study, we select one kind of vertical-mounted planar porous fiber fabric as moisture sources to explore its influence on indoor air humidity. The experiment is done in an unoccupied semi-basement room. The aim of these works is to present a way to improve indoor humidity conditions in heated rooms and a reference for future integrated design in the buildings.
2. Methods
This experiment chooses the common polyester fiber fabric (a hang curtain material) as the moisture carrier. The experiment was conducted in an unoccupied semi-basement room of residential buildings with ferroconcrete structure. The experimental room had only one door (the door is closed during experimentation), connected to another room (Fig. 1). The residential building was heated using the central heating system, but the experimental room had no heating radiator. In the length direction of the room, along the top corner of the room there were two heat supply pipes, which could heat indoor air.
As shown in Fig. 2, the interior space size of the room was 6300 mm*3000 mm*2700 mm. Due to limited temperature-humidity loggers, measuring points were only set up on one symmetry plane. A total of 40 measuring points were uniformly distributed, as shown in Fig. 2. The temperature-humidity data logger (Testo175-H1) was
used. Testing time was the process of natural evaporation of water from the moisture carrier and the logging interval was 20 min. Similarly, outdoor temperature and humidity was logged with the same logging period and interval as indoors. As shown in Table 1, there were a total of five experimental cases, one of which was not to set moisture source indoors. Other experiments (i.e. Cases II-V) covered different areas of fiber fabric and different water evaporation quantities. Natural evaporation water quantities consisted of initial water quantities and continuous water quantities. The initial water quantity referred to water sprayed on the fiber fabrics before the experiment, while the continuous water quantity referred to water dropped on the fiber fabrics with syringe needle during the experiment. The horizontal positions of the fiber fabrics were presented in Fig. 2. The vertical positions were shown in Table 1.
Table 1. Summary of experimental cases.
Cases_Position_Size (m2) Initial water (mL) Continuous water (mL) Total water (mL)
2.0x0.7
1.0x0.5
0.5x0.5
2.0x0.7
3. Results and discussion
3.1. Indoor air temperature and humidity for case I
Fig. 3. Indoor air temperature and humidity variation at different positions for case I : height direction (left); horizontal direction (right).
Fig. 3 shows indoor average air temperature and humidity variation for the case where there is no moisture source indoors. In height direction, air temperature in low height space is lower than that in high height space, while air RH is the opposite. This may be caused by the two heat supply pipes at the top corner of the room. Maximum difference at different heights is less than 1oC for air temperature and lower than 1.5% for air RH. In horizontal direction, air temperature at the position (i.e. A) close to the exterior wall is lower than that at the position (i.e. E) far from the exterior wall, while air RH is the opposite. Maximum difference in horizontal direction is less than 1.5oC for air temperature and lower than 2.5% for air RH.
3.2. Influence of water evaporation quantity from the wetted fiber fabric on IAH level
Table 2. Average air temperature, RH and humidity ratio at different positions in vertical direction in the cases with different water evaporation quantities.
Experimental cases
Positions Parameters H m W V
1 RH [%] 49.30±6.24 41.75±3.06 40.60±3.76 43.50±4.19
T [oC] 16.25±0.12 15.32±0.56 15.48±0.50 15.92±0.12
d[g/kg] 5.78±0.73 4.60±0.26 4.52±0.32 4.99±0.46
2 RH [%] 53.46±7.17 43.59±2.89 41.94±4.07 45.91±4.67
T [oC] 15.75±0.09 15.06±0.41 15.12±0.40 15.43±0.10
d[g/kg] 6.08±0.81 4.73±0.27 4.56±0.36 5.10±0.50
3 RH [%] 54.02±7.04 43.68±2.85 42.36±3.75 46.25±4.62
T [oC] 15.43±0.08 14.89±0.31 14.90±0.31 15.20±0.08
d[g/kg] 6.02±0.79 4.69±0.28 4.54±0.34 5.07±0.49
4 RH [%] 55.64±7.31 44.99±2.75 43.09±3.80 47.21±4.69
T [oC] 15.16±0.08 14.67±0.29 14.72±0.31 15.01±0.06
d[g/kg] 6.09±0.81 4.76±0.29 4.57±0.34 5.11±0.50
Table 3. Average air temperature, RH and humidity ratio at different positions in horizontal direction in the cases with different water evaporation quantities.
Experimental cases
Positions Parameters H m W V
A RH [%] 56.75±7.69 46.21±2.96 43.38±7.86 48.46±4.88
T [oC] 14.79±0.10 14.13±0.41 13.51±1.84 14.50±0.12
d[g/kg] 6.06±0.82 4.72±0.27 4.41±0.76 5.07±0.49
B RH [%] 53.60±6.93 44.17±3.02 41.30±7.15 46.50±4.71
T [oC] 15.45±0.09 14.71±0.43 14.27±1.76 15.09±0.09
d[g/kg] 5.98±0.78 4.69±0.27 4.39±0.71 5.06±0.49
C RH [%] 52.07±6.71 42.71±2.90 41.19±3.73 45.04±4.48
T [oC] 15.88±0.09 15.20±0.40 15.25±0.39 15.56±0.09
d[g/kg] 5.97±0.77 4.68±0.27 4.52±0.33 5.05±0.48
D RH [%] 51.23±6.63 42.19±2.85 40.92±3.69 44.62±4.49
T [oC] 16.18±0.09 15.41±0.35 15.44±0.33 15.80±0.09
d[g/kg] 5.99±0.78 4.68±0.28 4.55±0.35 5.08±0.49
E RH [%] 50.88±6.58 42.10±2.86 40.76±3.58 43.98±4.15
T [oC] 16.18±0.10 15.47±0.34 15.63±0.27 16.00±0.08
d[g/kg] 5.94±0.77 4.69±0.29 4.59±0.35 5.07±0.46
Table 2 and Table 3 show the average air temperature, RH and humidity ratio at different positions in vertical and horizontal direction in the cases with different water evaporation quantities. As can be seen from Table 2, for all cases, air average temperature in low height space is generally lower than that in high height space, while air RH is
the opposite. The difference of air average RH between layer 1 and layer 4 is 6.34%, 3.24%, 2.49% and 3.71% for CasesII-V. From Table 3, air average temperature at the position (i.e. A) close to the exterior wall is generally lower than that at the position (i.e. E) far from the exterior wall. One reason is that outdoor air temperature is low and heat transmission through the exterior wall can decrease indoor air temperature. Another reason is that moisture source is mounted close to the exterior wall and water evaporation from the moisture source also reduces the indoor air temperature. The difference of air average RH between row A and row E is 5.87%, 4.11%, 2.62% and 4.48% for Cases II -V. In addition, it is found that, other than Case V, air average RH and humidity ratio at any positions in both directions increase with the increase of the total water evaporation quantities. For CaseV, because of the relatively large initial water evaporation quantity (continuous humidification quality is 0), the indoor air RH and humidity ratio increase rapidly, so the indoor air RH and humidity ratio variation does not agree with other cases.
Table 4. Maximum variation of air RH and humidity ratio at different positions in vertical direction in the cases with different water evaporation quantities.
Positions Parameters Experimental cases
II m W V
1 RH [%] 23.5 19.8 9.3 19.0
d[g/kg] 2.8 1.5 0.8 2.1
2 RH [%] 25.4 19.8 10.0 21.4
d[g/kg] 2.9 1.7 0.9 2.3
3 RH [%] 25.3 18.2 9.7 20.7
d[g/kg] 2.8 1.7 0.9 2.2
4 RH [%] 25.6 19.4 10.0 19.2
d[g/kg] 2.8 1.8 0.9 2.0
Table 5. Maximum variation of air RH and humidity ratio at different positions in horizontal direction in the cases with different water evaporation quantities.
Positions Parameters Experimental cases
I m W V
A RH [%] 26.6 11.3 9.9 22.2
d[g/kg] 2.8 0.9 0.8 2.2
B RH [%] 25 14.8 10.2 21.2
d[g/kg] 2.8 0.9 0.9 2.2
C RH [%] 24.7 14.3 9.7 20.1
d[g/kg] 2.8 1.0 0.8 2.2
D RH [%] 24.4 13.8 10.0 20.2
d[g/kg] 2.8 1.0 0.9 2.2
E RH [%] 23.9 13.8 0.7 16.9
d[g/kg] 2.8 1.1 0.9 1.9
Table 4 and Table 5 show the maximum variation (i.e. maximum minus initial value) of air RH and humidity ratio at different positions in vertical and horizontal direction in the cases with different water evaporation quantities. It is seen that for cases II -W, the maximum variation of air RH and humidity ratio increase with the increase of total humidification quantities, in both vertical and horizontal directions. For caseV, due to the relatively large initial water evaporation quantity and no continuous water evaporation, the maximum variation is relatively large.
Fig. 4 shows the change of average indoor air temperature and relative humidity in the cases with different water evaporation quantities. It is seen that because of evaporation of the water from the wetted fiber fabric, indoor air temperature has a fall in initial evaporation stage, and then remains basically stable. Interestingly, in the initial stage, the increasing rate of indoor air RH is positively associated with the initial evaporation water quantities. For case II,
III and N, the increasing amplitude of indoor air RH is associated with total water evaporation quantity. But for case V, water evaporation quantity in initial stage is relatively big, as a result, it can make increasing amplitude of indoor air RH higher than case I and N. The above results indicate that for the actual room, both water evaporation rate and evaporation quantity have an important impact on indoor air RH. It is essential to control water evaporation rate and evaporation quantity for maintaining indoor appropriate air humidity. Optimal air RH range is about between 40 and 60%. From Fig. 4, it is seen the time of average air RH maintaining between 40% and 60% in the cases with different water evaporation quantities has a significant difference. For case I and N, the total water evaporation quantities are obviously insufficient, and indoor average air RH cannot reach 50%. With regard to case V, although air RH can increase to comfort level rapidly, because there is no continuous water, the air RH can fall off. For this experiment, case II can maintain indoor air RH level in the comfortable range for a relatively long time. In fact, the ideal case for air low air humidity is just to increase the air humidity to comfortable level from low level
Time [h]
Fig. 4. The change of average indoor air temperature and RH in the cases with different humidification quantities
4. Conclusion
To find a practical solution to solve the problem of the indoor low air humidity in heated rooms, this paper describe a simple experiment on natural evaporation of water from wetted fiber fabric to indoor air. Results showed that natural evaporation of water from the vertically hanging wetted fiber fabric could effectively improve indoor air humidity. Both evaporation rate and evaporation quantity of water had significant influences on attainable maximum value of indoor air humidity. Actually, for a heated room, outdoor weather, room ventilation rate and indoor occupancy can affect indoor air humidity, thereby influence the con-trolling of evaporation rate and evaporation quantity of water for a proper air RH. These is-sues would be investigated in further studies.
Acknowledgements
This research project was funded by the National Natural Science Foundation of China (No. 51578026 & 51590912).
References
[1] W.J. Fisk, Q. Lei-Gomez, M.J. Mendell. Meta-analyses of the associations of respiratory health effects with dampness and mold in homes. Indoor Air 17 (4) (2007) 284-296.
[2] L.M. Reinikainen, J.J.K. Jaakkola. Significance of humidity and temperature on skin and upper airway symptoms. Indoor Air 13 (4) (2003) 344-352.
[3] N. Hashiguchi, M. Hirakawa, Y. Tochihara, et al. Thermal environment and subjective responses of patients and staff in a hospital during winter. J Phys. Anthr. Appl. Human Sci. 24 (1) (2005) 111-115.
[4] M. Sato, S. Fukayo, E. Yano. Adverse environmental health effects of ultra-low relative humidity indoor air. J. Occup. Health 45 (2) (2003) 133-136.
[5] K. Jaakkola, A. Saukkoriipi, J. Jokelainen, et al. Decline in temperature and humidity increases the occurrence of influenza in cold climate. Environ. Health 13 (1) (2014) 1-8.
[6] J. Paasi, S. Nurmi, R. Vuorinen, et al. Performance of ESD protective materials at low relative humidity. J. Electr. 51-52 (1-4) (2001) 429434.
[7] M. Egawa, M. Oguri, T. Kuwahara, et al. Effect of exposure of human skin to a dry environment. Skin Res. Techn. 8 (4) (2002) 212-218.
[8] ASHRAE 62.1-2013. Ventilation for acceptable indoor air quality. American Society for Heating, Refrigerating and Air Conditioning Engineers. Atlanta.
[9] H. Zhang, H. Yoshino. Analysis of indoor humidity environment in Chinese residential buildings. Build. Environ. 45(10) (2010) 21322140.
[10] Z. Wang, A. Li, R. Jing, et al. Thermal adaptation and thermal environment in university classrooms and offices in Harbin. Energy Build. 77(7) (2014) 192-196.
[11] H. Yoshino, S. Guan, Y.F. Lun, et al. Indoor thermal environment of urban residential buildings in China: Winter investigation in five major cities. Energy Build. 36(12) (2004) 1227-1233.
[12] S. Hameury. Moisture buffering capacity of heavy timber structures directly exposed to an indoor climate: a numerical study. Build. Environ. 40 (2005) 1400-1412.
[13] Osanyintola, C.J. Simonson. Moisture buffering capacity of hygroscopic building materials: Experimental facilities and energy impact. Energy Build. 38(10) (2006) 1270-1282.
[14] Gómez, S. Guths, R. Souza, et al. Moisture buffering performance of a new pozolanic ceramic material: Influence of the film layer resistance. Energy Build. 43(4) (2011) 873-878.
[15] T. Ashour, H. Georg, W. Wu. Performance of straw bale wall: A case of study. Energy Build. 43(8) (2011) 1960-1967.
[16] A. Korjenic. T. Helene, T. Bednar. Increasing the indoor humidity levels in buildings with ventilation systems: Simulation aided design in case of passive houses. Build. Simul. 3(4) (2010) 295-310.
