• Journal of the Korean Solar Energy Society
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• v.21 no.3
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• pp.51-60
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• 2001

A greenhouse equipped with latent heat storage system was built to obtain various thermal properties, such as greenhouse air temperature, soil surface temperature, energy flow in latent heat storage, etc., which could be used in validation of greenhouse numerical model to be developed in this study. This numerical model expressed with Newton-Raphson method was programed by C-language and utilized to simulate greenhouse thermal behavior. Greenhouse air temperature and soil surface temperature predicted by the greenhouse model developed in this study were very close to the measured data obtained through almost 3 years of experiment. Therefore, it is concluded that the greenhouse model developed and verified by measured data could be utilized for simulating various thermal behaviors of greenhouses equipped with latent heat storage system to be used for energy saving purposes.

• Journal of Biosystems Engineering
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• v.25 no.5
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• pp.379-384
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• 2000

In order to use the natural thermal energy as much as possible for greenhouse heating, the air-air heat pump system involved PCM(phase change material) latent heat storage system was composed, and three types of greenhouse heating system(greenhouse system, greenhouse-PCM latent heat storage system, greenhouse-PCM latent heat storage-heat pump system) were recomposed from the greenhouse heating units to analyze the heating characteristics. The results could be concluded as follows; 1) In the greenhouse heated by the heat pump under the solar radiation of 406.39W/$m^2$, the maximum PCM temperature in the latent heat storage system was 24$^{\circ}C$ and the accumulated thermal energy stored in PCM mass of 816kg during the daytime was 100,320kJ. In the greenhouse without heat pump under the maximum solar radiation of 452.83W/$m^2$, the maximum PCM temperature in the latent heat storage system was 22$^{\circ}C$ and the accumulated thermal energy stored during the daytime was 52.250kJ. 2) In the greenhouse-PCM system without heat pump the heat stored in soil layers from the surface to 30cm of the soil depth was 450㎉/$m^2$. 3) In all of the greenhouse heating systems, the difference between the air temperature in greenhouse and the ambient temperature was about 20~23$^{\circ}C$ in the daytime. In the greenhouse without heat pump and PCM latent heat storage system the difference between the ambient temperature and the air temperature in the greenhouse was about 6~7$^{\circ}C$ in the nighttime, in the greenhouse with only PCM latent heat storage system the temperature difference about 7~13$^{\circ}C$ in the nighttime and in the greenhouse with the heat pump and PCM latent heat storage system about 9~14$^{\circ}C$ in the nighttime.

• KIEAE Journal
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• v.12 no.4
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• pp.97-104
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• 2012

A phase-change material is a substance with a high heat of fusion which, melting and freezing at a certain temperature, is capable of storing and releasing large amounts of energy. Heat is absorbed or released when the material changes from solid to liquid. Therefore, PCMs are classified as latent heat storage (LHS) units. The purpose of this study is to analyze PCM wallboard design parameters using dynamic energy simulation. Among the factors of PCM, melting temperature, latent heat, phase change range, thermal conductivity are very important element to maximize thermal energy storage. In order to analyze these factors, EnergyPlus which is building energy simulation provided by department of energy from the U.S is used. heat balance algorithm of energy simulation is conduction finite difference and enthalpy-temperature function is used for analyzing latent heat of PCM. The results show that in the case of melting temperature, the thermal energy storage could be improved when the melting temperature is equal to indoor surface temperature. It seems that when the phase change range is wide, PCM can store heat at a wide temperature, but the performance of heat storage is languished.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.2
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• pp.189-199
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• 2000

This paper investigates the thermodynamic performance of latent heat thermal energy storage system using two phase change materials(2-PCM system). The thermodynamic merit of using 2-PCM is clear in terms of exergetic efficiency, which is substantially higher than that of 1-PCM system. Optimum phase change temperature to maximize the exergetic efficiency exists for each case. The heat transfer area ratio of high temperature storage unit, X, becomes another important parameter for 2-PCM system if the phase change temperatures of given materials are different from those of optimum conditions. It is a good approximation for X$_{opt}$ to be 0.5 when optimum phase change temperatures are used. Otherwise X$_{opt}$ is determined differently as a function of given phase change temperatures.res.

• Journal of Biosystems Engineering
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• v.16 no.4
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• pp.399-407
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• 1991

In Korea, the cultivation area under the plastic greenhouse was 1,746 ha in 1975, and 36,656 ha in 1989, it shows that the greenhouse cultivation area was increased by 21 times during last 14 years. The greenhouse cultivation area of 90~93% has been kept warm with double layers of plastic film and thermal curtain knitted with rice straw, and the rest area of 7~10% has been heated by fossil fuel energy. The use of rice straw thermal curtain is inconvenient to put it on and off, on the other hand the use of fossil fuel heating system results in the increase of production cost. To solve these problems, at first the heating load and the storable solar energy in greenhouse during the winter season were predicted to design solar utilization system, secondly a solar thermal storage system filled with latent heat storage materials was developed in this study. And then finally the thermal performance of greenhouse-solar energy storage system was analyzed theoretically and experimentally.

• Journal of Biosystems Engineering
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• v.19 no.3
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• pp.211-221
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• 1994

In this study, to maximize the solar energy utilization for greenhouse heating during the winter season, solar energy-underground latent heat storage system was constructed, and the thermal performance of the system has been analyzed to obtain the basic data for realization of greenhouse solar heating system. The results are summarized as follows. 1. $Na_2SO_4{\cdot}10H_20$ was selected as a latent heat storage material, its physical properties were stabilized and the phase change temperature was controlled at $13{\sim}15^{\circ}C$. 2. Solar radiation of winter season was the lowest value in December, and Jinju area was the highest and the lowest value was shown in Jeju area. 3. The minimum inner air temperature of greenhouse with latent heat storage system(LHSS) was $7.0{\sim}7.5^{\circ}C$ higher than that of greenhouse without LHSS and was $7.0{\sim}11.2^{\circ}C$ higher than the minimum ambient air temperature. 4. Greenhouse heating effect of latent heat storage system was getting higher according to the increase of solar radiation and was not concerned with the variation of minimum ambient air temperature. 5. The relative humidity of greenhouse with latent heat storage system was varied from 50 to 85%, but that of greenhouse without LHSS was varied from 30 to 93%. 6. The heating cost of greenhouse with solar energy-latent heat storage system was about 24% of that with the kerosene heating system.

• Journal of Biosystems Engineering
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• v.27 no.1
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• pp.39-44
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• 2002

In order to obtain the information of bio-environment control, the thermal characteristics of soil in the greenhouse heated by the heat pump and latent heat storage system were experimentally analyzed. The experimental systems were composed of the greenhouse with a heat pump and a latent heat storage system (system I), the greenhouse with a heat pump (system II), the greenhouse with a latent heat storage system (system III), and the greenhouse without auxiliary heating system (system IV). The thermal characteristics experimentally analyzed in each system were temperature of soil layers, soil heat storage and release, soil heat capacity and soil heat storage ratio. The results could be summarized as follows. 1. Time to reach the highest temperature at 20cm deep in soil layers of the crop routs in case of system I was shown to be delayed by 6 hours in comparison to the time of the highest temperature at the soil surface. 2. In the clear winter days, the stored heat capacity values fur the system I and the system II were shown to be 22.3% and 11.0% higher than the released heat capacity respectively, and the stored heat capacity values for the system III and the system IV were shown to be 6.2% and 29.6% lower than the released heat capacity respectively This confirms that the system I provided the best heat storage effect. j. The heat quantity values stored or released were shown to be highest at 5 cm depth of soil layers. And it was reduced with increasing of depth of soil layers until 20 cm and was not changed under the soil layer of 20 cm depth. 4. The heat absorption rates of soil, the ratio between supplied and stored heat energy, fur both the system I and system II were lower than 23%.

• Journal of Biosystems Engineering
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• v.21 no.1
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• pp.84-93
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• 1996

Several paraffins(CnH2n +2) can be used as the thermal energy storage medium because of their large amount of latent heat and their flexibility of phase change temperature. But they have not been used in the thermal energy storage system because their long term stability have not been verified. Paraffins(CnH2n+2) which the values of n are 23, 24, 26 and 28 were selected for this experimental research. And this research was peformed to apply them to the practical systems. The results were summarized as follows. (1) The increase of phase change cycles had no effect on their phase change temperatures. (2) According as the values of n increased from 23 to 28, the specific heats of paraffins(CnH2n+2) increased, and were in the range of 0.47 0.75 ㎉/$kg^circ C$. (3) Thermal conductivities of them were in the range of 0.14 0.17 W/$m^circ C$. and specific gravities of them were in the range of 765800 kg/m3. (4) The density of paraffins was in the range of 765 800 kg/$m^circ C$ , and the density of solid phase was larger than that of liquid phase. (5) When the number of phase change cycles was 1, 500 cycles, the latent heat of paraffins was 90% of the initial value.

• Journal of Biosystems Engineering
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• v.16 no.3
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• pp.290-297
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• 1991

For the efficient utilization of the solar thermal energy to overcome the time gap between to supply and demand, an efficient heat storage technique, especially high density-latent-heat storage system, is necessary. In this study, the performance of a panel type latent heat storage equipment during heat discharging process was analyzed theoretically and experimentally. In order to find out the performance of the system, computer simulation programs were developed by finite difference method. The governing equations were constructed by two dimensional heat conduction model with moving boundary. The results of the experimental and the theoretical analysis were reasonably well agreed. The efficiencies of the double pipe type and the panel type latent heat storage equipment were compared.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1993.10a
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• pp.453-472
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• 1993

Two types of solar energy-latent heat storage system have been developed to minimize the fossil fuel consumption and maximize the solar energy utilization in greenhouse heating during the winter season. The one was installed on the greenhouse floor, and the other in the underground of the greenhouse . Sodium suphate decahydrate was selected as a highly concentrative solar energy storage medium and its unstable thermophysicla properties were adjusted by some additives. Thermal efficiency of them was analyzed by numerical and experimental method.