• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.9
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• pp.641-647
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• 2010

Ground-source(Geothermal) heat pump(GSHP) systems can achieve a higher coefficient of performance than conventional air-source heat pump(ASHP) systems. However, GSHP systems are not widespread because of their expensive installation costs. The authors have developed a GSHP system that employs the cast-in-place concrete pile foundations of a building as heat exchangers in order to reduce the initial cost. In this system, eight U-tubes are arranged around the surface of a cast-in-place concrete pile foundation. The heat exchange capability of this system, subterranean temperature changes and heat pump performance were investigated in a full-scale experiment. As a result, the average values for heat rejection were 186~201 W/m(per pile, 25 W/m per pair of tubes) while cooling. The average COP of this system was 4.6 while cooling; rendering this system more effective in energy saving terms than the typical ASHP systems.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.688-692
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• 2005

Importance of substitute energy has been increasing due to environmental issues and lack of fossil fuels. In addition, heating cost that occupies from 30 to $40\%$ of the total production cost in Korean protected cultivation needs to be reduced for profitability and global competition. But, studying on substitute energy to solve these problems has not been activated for Korean protected cultivation. Therefore, this study was conducted to develop a geothermal heat pump system for cool ing and heat ing of greenhouses at a lower cost than conventional hot air heater and air conditioner. Fundamental test of heat transfer characteristics in soil was conducted by computer simulation and controlled tests for its verification. Based on the results of the theoretical and empirical investigations, an optimum heat pump system was developed and the performance was evaluated for practical use in a greenhouse at the Pusan Horticultural Experiment Station. The system was compared with a conventional hot air heating system through a cucumber growing test and economic feasibility analysis. Results of the application test of the geothermal heat pump showed that with an initial setting of $15^{\circ}C$ the inside temperature of the greenhouse could be maintained between 15 and $17^{\circ}C$. Results of the cucumber growing test showed that there were no significant differences in average height, leaf length, leaf width, number of nods, leaf area, dry weight and yield between the plots wi th the geothermal heat pump system and a conventional hot air heater. Economic feasibility analysis indicated that the variable cost of the hot air heater could be saved $81.2\%$ using the geothermal heat pump system. It was concluded that the geothermal heat pump system might be a pertinent heating and cooling system for greenhouses because of the low operating cost and the use of environment-friendly geothermal energy.

• Journal of the Korean Solar Energy Society
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• v.32 no.5
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• pp.59-67
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• 2012

In this study,the compact type solar thermal and ground coupled heat pump hybrid system for space heating/cooling and hot water supply has been developed. This hybrid system was installed in Zero Energy Solar House(ZeSH) in KIER for the demonstration. The thermal performance and operational characteristics of this hybrid system were analysed especially. The results are as follows. (1) This hybrid system was designed in order to address the existing disadvantages of solar thermal/ground coupled heat pump system. For this design, all parts except solar collector and ground coupled heat pump were integrated into a single product in a factory. The compact type unit includes two buffer tanks, an expansion tank, pumps, valves, a controller, etc. This system has an advantage of easy installation with simple plumbing work even in narrow space. (2) The thermal charging and discharging time of the buffer tanks and its characteristics by ground coupled heat pump, and heat pump COP according to geo-source temperature and buffer storage temperature have been studied. This system was found to meet well to the heat load without any other auxiliary heating equipment. (3) The operating hours of the ground coupled heat pump as a backup device of solar thermal can be reduced significantly by using solar heat. It was also found that the minimum heating water supply setting temperature and maximum cooling water supply setting temperature make an influence on the heat pump COP. The lower heating water and the higher cooling water temperature, the higher COP. In this respect, the hybrid system's performance can be improved in ZeSH than conventional house.

• Journal of Energy Engineering
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• v.26 no.3
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• pp.90-96
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• 2017

When the hot water is supplied through the district heating (DH) pipeline, a pressure differential control valve (PDCV) protects the DH user equipment from the high pressure DH water and helps to supply DH water to long distance. It also controls the temperature and adjust the pressure in the main district heating pipeline. However, cavitation occurs in PDCV due to the use of high pressure DH water. It causes frequent failures and many problems. It also causes energy loss and complaints to both operators and users. In order to solve these problems, we will introduce the energy saving technology to replace the primary side PDCV with hydraulic turbine, convert the differential pressure into electricity, and utilize electricity as the power of the secondary side pump.

• Journal of the Korean Solar Energy Society
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• v.25 no.4
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• pp.37-44
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• 2005

An experimental study was conducted to analyze performance of a heating system with variation of control logic of the system. The system uses a solar as heat source and composed with heat pump that uses R-22 as working fluid. The difference between the developed system and the commercially available heating system is working fluid. The solar assisted heating system which was widely distributed in the market uses water as a working fluid. It could be freezing in case of the temperature drops down under freezing point. The anti-freezing fluids such as methyl-alcohol or ethylene-glycol are mixed with the water to protect the freezing phenomena. However, the system developed in this study uses a refrigerant as a working fluid. It makes the system to run under zero degree temperature conditions. Another difference of the developed system compare with commercial available one is auxiliary heating method. The developed system has removed an auxiliary electric heater that has been used in conventional solar assisted heating system. Instead of the auxiliary electric heater, an air source heat exchanger which generally used as an evaporator of a heat pump was adapted as a backup heating device of the developed system. As results, an efficiency of the developed system is higher than a solar assisted heat pump with auxiliary electric heater. The merit of the developed system is on the performance increment when the system operates at a lower solar energy climate conditions. In case of the developed system operates at a normal condition, COP of the solar collector driven heat pump is higher than the air source heat exchanger driven heat pump's.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.1
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• pp.28-35
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• 2016

The in-situ thermal response test for the design of a ground heat exchanger of geothermal heat pumps have difficulty in predicting the outlet temperature according to the variation of conditions due to the expense and time. This paper suggests a 3-D CFD analysis method to predict the heat transfer performance of vertical type ground heat exchanger, which is mostly used in national, and the outlet temperature and the slope of two in-situ thermal response tests were compared to test the proposed CFD reliability. The results of CFD analysis showed that the outlet temperature was predicted to within $0.5^{\circ}C$ of the actual value and the slope was predicted to within 1.6%. The reliability of the CFD analysis method was confirmed using this process, and the outlet temperature prediction of the two in-situ thermal response tests was obtained by changing ${\pm}20%$ of the flow rate and the effective thermal conductivity conditions, respectively. The results of CFD analysis showed that the outlet temperature of Case 1 was 28.0 (-20%) and $29.6^{\circ}C$ (+20%) for the flow rate variation and $29.6^{\circ}C$ (-20%) and $28.0^{\circ}C$ (+20%) for the effective thermal conductivity variation, and the outlet temperature of Case 2 was 28.4 (-20%) and $29.8^{\circ}C$ (+20%) for the flow rate variation and $29.7^{\circ}C$(-20%) and $28.4^{\circ}C$(+20%) for the effective thermal conductivity variation.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.288-293
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• 2008

The cooling load in winter is significant in many commercial buildings and hotels because of the usage of office equipments and the high efficiency of wall insulation. The development of a multi-heat pump that can cover heating and cooling simultaneously for each indoor unit is required. In this study, the performance of a multi-heat pump with 3-piping system was investigated as a function of refrigerant charge and its performance was analyzed in cooling mode, heating mode, and heat recovery mode. COP in the heating or cooling mode showed little dependence on refrigerant charge at overcharge conditions, while those were strongly dependent on refrigerant charge at undercharge conditions and outdoor inlet temperature. In the heat recovery mode, the performance of the system was very sensitive to charge amount at all conditions. Optimum charge amount in the heat recovery mode was 14% lower than that in the cooling mode at the standard condition because the refrigerant only passed the indoor units. It is required to store the excessive refrigerant charge in a storage tank to optimize the system performance at operating modes.

• Journal of the Korean Society of Mechanical Technology
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• v.20 no.6
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• pp.917-923
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• 2018

The drinking water supply system applicable to the laying hen consists of air-water heat pumps, drinking water tanks, heat stroage tank, circulation pumps, PE pipes, nipples, and control panels. When the heat pump system has power of 7.7 to 8.7 kW per hour, the performance coefficient is between 3.1 and 3.5. The supply temperature from the heat pump to the heat stroage tank was stabilized at about $12{\pm}1^{\circ}C$, but the return temperature showed a variation of from 8 to $14^{\circ}C$. Stratified temperature in the storage tank appeared at $12.^{\circ}C$, $13.5^{\circ}C$ and $14.4^{\circ}C$, respectively. The drinking water supply temperature remained set at $15^{\circ}C$ and $25^{\circ}C$, and the conventional tap water showed a variation for $23^{\circ}C$ to $30^{\circ}C$. As chickens grow older, the amount of food intake and drinking water increased. $y=-0.0563x^2+4.7383x+8.743$, $R^2=0.98$ and the feed intake showed $y=-0.1013x^2+8.5611x$. In the future, further studies will need to figure out the cooling effect on heat stress of livestock.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.1
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• pp.597-604
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• 2016

The aim of this study was to prevent the decrease in crop output by disease and insect pests and excessive spraying of agricultural pesticides by application uniformity. A 3m height and 15km/h speed is difficult to maintain with an unmanned helicopter for aerial application, which has been affected by the controlling habits and methods or environmental factors, such as changes in the wind. Therefore, in this study, an aerial application system was design to be attached to an unmanned helicopter, which can allow a controlled application width and spray rate automatically and verified experimentally using Rmax of MS-AVIATION. The size of agricultural land was 50 m2 and nine water sensitive cards were arranged at 1.25m intervals in 5 rows with each row having a 10m interval from the position of 5m. The unmanned helicopter was flying at speeds ranging from 7.2km/h to 17.6km/h and heights ranging from 2.32m to 3.47m. The proposed aerial application system allowed application uniformity by making a valid spraying area of 7.5 m2 with 46423 particles distributed on average.

• Magazine of the Korea Concrete Institute
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• v.20 no.6
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• pp.28-35
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• 2008

The Burj Dubai Project will be the tallest structure ever built by man; when completed the tower will be more than 700 meter tall and more than 160 floors. While the early integration of aerodynamic shaping and wind engineering considerations played a major role in the architectural massing and design of this multi-use/residential tower, where mitigating and taming the dynamic wind effects was one of the most important design criteria, the material selection for the structural systems of the tower was also a major consideration and required detailed evaluation of the material technologies and skilled labor available in the market at the time Concrete was selected for its strength, stiffness, damping, redundancy, moldability, free fireproofing, speed of construction, and cost effectiveness. In addition, the design challenges of using concrete for the design of the structural system components will be addressed. The focus on this paper will also be on the early planning of the concrete works of the Burj Dubai Project.