제주도 지하공기의 특성과 이용성에 관한 연구

Abstract

The data used in this study were from two sources. One was GIS data developed by Korea Rural Community and Agriculture Corporation for the development of agricultural water. The other was the geologic columnar section from over 5,000 tube wells. The districts of underground geologic structure in Jeju island where underground air is distributed are lava cave, pyroclastic, open joint, and crushing zone. Such districts are identified to be a possible area to utilize underground air (85% in Jeju island). Boring depth was identified to secure an enough airflow when air ventilation layer is to secure 25-35m in depth. The district of underground air being distributed is irregular by district. Considering the frequency of securing air ventilation layer and the economic cost of boring, about more and less 50m of boring depth would be profitable. Considering the size of electronic power and airflow to secure, the borehole diameter of 250-300mm was tested. The result of this test showed that the wider the borehole diameter is, the more the airflow increase. Borehole protection pipe was established according to ground water tube well which was recommended by Water Resources Headquarter, Jeju Special Self-Governing Province. It was identified that there is no environmental geological problems such as the breaking of ground. Even though the wind flux test through underground borehole was applied in a variety of way this study, it was proved that the kind of blower fan, fan electric power, boring depth, borehole diameter, whether to establish the protection pipe were significant factors to determine difference in the inhalation of underground air. The significant differences were as follows. Blower fan (turbo engine) was more beneficial than axial fan in noise and persistence when turbo fan whose static pressure efficiency was used. The fan electric power of blower fan was stable between 5.5kw and 7.5kw, considering its establishment place and the possible quantity of air inhalation. A cold and heating equipment was established 32m in underground, using the underground air from phalaenopsis plastic film greenhouse in Sanyae Dong, Seogipo City. The temperature of air being erupted from basalt layer was 19℃ in summer and 14 in winter. This temperature provides an enough effectiveness of cold and heating efficiency in plastic film greenhouse. Even though there is a difference by district in Jeju island, it is known that about 3,000～5,000ppm of the natural CO₂ is contained. In this study a test was done on the possibility to use such a natural resource for flowering plant in plastic film greenhouse. The test was conducted on the condition that the area of low temperature treatment was 660㎡, keeping a temperature of 19～22℃ in night. The following were found to be significant. When the temperature of cold and heating system using underground air was below 23℃, flower bud differentiation on the phalaenopsis cultivation was promoted, and the growth such as leaf number and leaf thickness was good remarkably. This is judged to be caused by the fertilization of natural CO₂ contained in underground air. Based on this result, it is estimated that the economic benefit gained from the supply of natural CO₂ in plastic film greenhouse is 18,200,000Won per 1,000㎡. Using underground air instead of the existing heat pump being used as cold and heating system, the economic benefit was estimated to be 31,600 thousand Won per 1,000㎡. Applying this estimation to phalaenopsis cultivation, the suitable area was 500㎡ per underground hole for cooling in summer, and 1,000㎡ in winter. On the other hand, when two experimental treatment were treated - use of underground air and two-year old CO₂ generator contained 1,000ppm, it was identified that the latter decreased 81% and 87% of phalaenopsis in terms of leaf number and leaf thickness, respectively. This is judged to be caused by the noxious gas such as incombustible CO₂ erupted from the dilapidated facility. In addition, an experiment was conducted, boring 80m in basalt layer in paprika (Capsicum annuum) cultivation glass greenhouse of Korea Airport Service located in Gasiri, Seogipo City. The experiment proved that the natural CO₂ erupted from basalt layer was effective in the growth of plant, was stable in supply, was effective in cold and heating system, and effective as an additional fertilizer supply. When underground air was used for cultivating paprika (Capsicum annuum), the temperature in glass greenhouse was lower 5℃ on average in root zone temperature compared with 27℃ in control. Comparing with the condition keeping 800～1,000ppm being contained in CO₂ generator which is corresponded to heavy burning, the natural CO₂ erupted from underground air containing 1,000～2,000ppm increased 32% in yield potential. This would be resulted from two times higher of natural CO₂ as a fertilizer and the relative low temperature in root zone. For the latter, the number of fruiting was 1.0 more than control, showing 8.4. In addition, it was found from the latter that the sweetness degree of fruit and fruit hardness were also higher. In a comparative analysis of business management between the existing professional paprika (Capsicum annuum) cultivation and the glass greenhouse using underground air, it was found that the latter had an effectiveness to save production cost of 18,934,000Won per 1,000㎡/boring hole a year. Those findings draw a conclusion that the suitable area of Paprika is estimated to 1,000㎡ in terms of the possible utilization of CO₂ and temperature decrease in root zone (5℃). 85% of Jeju island are possible areas to use underground air. This means that underground air in Jeju island can be used almost unlimited for cold and heating natural source without the investment of material. Thus, further researches on the possibility to use underground air for a wide range of purposes should be conducted even though there is a regulation on the limited area per boring hole.