• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.8
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• pp.425-432
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• 2009

In this study, the improvement of cooling capacity by applying gas injection technique in a two-stage heat pump using R410A was experimentally investigated. A twin rotary type compressor with gas injection was applied to the heat pump system. The optimum refrigerant charge for the injection and the non-injection cycles was selected to achieve the maximum COP at the cooling standard condition. The injection cycle showed less optimum refrigerant charge than that of the non-injection cycle. The cooling performances of the injection and the non-injection cycles were measured and compared by varying compressor frequency from 40 to 90 Hz. The cooling capacity of the gas injection cycle was 1.6% -11.3% higher than that of the non-injection cycle. The COP of the gas injection cycle was 13.7% to 28.9% higher than that of the non-injection cycle at the same cooling capacity. The heat pump system showed stable operation after 30% of the injection valve opening.

• International Journal of Air-Conditioning and Refrigeration
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• v.16 no.4
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• pp.109-116
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• 2008

Ground temperature restoration characteristics are the crucial factors to evaluate whether a ground source heat pump system can keep long time steady operation. They are mainly dependent on soil thermal properties, layout of pile group, operation/shutoff ratio, cooling/heating load, thermal imbalance ratio and so on. On the one hand, several types of vertical pile foundation heat exchangers are intercompared to determine the most efficient one by performance test and numerical method. On the other hand, according to the layout of pile group of a practical engineering and running conditions of a GSHP system in Shanghai, the temperature distribution during a period of five years is numerically studied. The numerical results are analyzed and are used to provide some guidance for the design of large-scale GSHP system.

• International Journal of Air-Conditioning and Refrigeration
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• v.14 no.3
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• pp.85-93
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• 2006

The present study has been conducted to simulate dynamics of a gas engine-driven heat pump (GHP) for the design of control algorithm. The dynamic model of a GHP was based on conservation laws of mass and energy. For the control of refrigerant pressures, actuators such as an engine throttle valve, outdoor fans, coolant three-way valves and liquid injection valves were controlled by P or PI algorithm. The simulation results were found to be realistic enough to be applied for the control algorithm design. The model could be applied to build a virtual real-time GHP system so that it interfaces with a real controller for the purpose of developing control algorithm.

• Journal of Mechanical Science and Technology
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• v.20 no.2
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• pp.278-285
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• 2006

The present study has been conducted to simulate dynamics of a gas engine-driven heat pump (GHP) for design of control algorithm. The dynamics modeling of a GHP was based on conservation laws of mass and energy. For automatic control of refrigerant pressures, actuators such as engine speed, outdoor fans, coolant three-way valves and liquid injection valves were PI or P controlled. The simulation results were found to be realistic enough to apply for control algorithm design. The model can be applied to build a virtual real-time GHP system so that it interfaces with a real controller in purpose of prototyping control algorithm.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.539-543
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• 2009

When the suction pressure of compressor decreases under its limit, the compression ratio is increased causing the malfunctions of compressor. As the method to decrease the compression ratio, hot gas bypass system is usually adopted in heat pump system. In the hot gas bypass system, the discharged gas from the compressor is bypassed into the compressor suction, which causes the increase of suction pressure and the decrease of compression ratio. In this study, the characteristics and performances of the hot gas bypass system in heat pump was investigated experimentally with a variation of the bypass flow rate ratio. With the increase of the bypass rate ratio, the compressor suction pressure was increased, even though the total capacity and COP was decreased. From the analysis of the experimental results, the optimum pressure control algorithm was suggested in this study.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.10
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• pp.879-887
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• 2003

Buildings with heating and cooling systems have been increased, since the requirement of thermal comfort for residents is grown. Heating and cooling systems, have been changed from two separate systems to one multi-function system which includes both heating and cooling. Especially, heat pump heating and cooling system has been adopted for general classrooms in schools since education environment improvement project has been launched. This research suggests the best option for the heat pump heating and cooling system in educational buildings through economic assessments for four alternative systems based on electric heat pump (EHP) and gas engine driven heat pump (GHP), which are most widely used for elementary, middle and high schools. The model buildings are in the Y high school which has 24 classes of new construction building, which will be built soon. Annual energy consumption for alternative systems uses BECS 3.10, which can be used for system simulation.

• Journal of Power System Engineering
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• v.18 no.5
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• pp.42-47
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• 2014

In this paper, the cycle performance analysis for the COP of supercritical heat pump using various refrigerants is presented to offer the basic design data for the operating parameters of the system. The working fluids are R134a, R22, R32, R290, R600, R600a, R1270 and R744. The operating parameters considered in this study include superheating degree of evaporator, temperature of gas cooler inlet and outlet, compressor efficiency and evaporating temperature in the supercritical heat pump system. The main results were summarized as follows : Superheating degree, temperature of gas cooler inlet and outlet, compressor efficiency and evaporating temperature of supercritical heat pump system have an effect on the COP of this system. With a thorough grasp of these effect, it is necessary to design the supercritical heat pump using R134a. And, in comparison of COP of supercritical heat pump using various refrigerants, R32 and R600 is the highest, and R744 is the lowest among other refrigerants. From these results, it is confirmed that the COP of supercritical heat pump using R744 is higher than that using freon refrigerants such as R32 and R134a.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.639-644
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• 2006

The outlet temperature of gas cooler has a great effect on the efficiency of carbon dioxide heat pump system. In order to obtain a small approach temperature difference at gas cooler, near-counter flow type heat exchanger has been proposed, and larger heat transfer area is demanded. The optimum design of gas cooler involving the analysis of trade-offs between heat transfer performance and cost is desirable. In this study, the effects of geometric parameters, such as the circuit arrangement, tube diameter, transverse tube spacing, longitudinal tube spacing and the number of tube rows and fin spacing on the performance of heat transfer were investigated using the developed model. This study suggested various simulation results for optimum designs of gas cooler.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1993.11a
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• pp.78-81
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• 1993

AN EXTENSIVE RESEARCH AND DEVELOPMENT WORK WILL BE CARRIED OUT FOR THE COMMERCIALIZATION OF THE CHEMICAL HEAT PUMP SYSTEM WHICH BASED ON THE ELF AQUITAINE FRANCE PATENTED AND KIME LICENSED SOLID/GAS CHEMICAL REACTION TECHNOLOGY. TOWARD ON THAT GOAL, THE BASIC AND ENGINEERING DETAILS SUCH AS IMPEX BLOCK MATERIAL, PHYSICO-CHEMICAL AND THERMO-CHEMICAL CHARACTERISTICS OF REACTION MECHANISMS IN THE SOLID/GAS CHEMICAL REACTION HEAT PUMP SYSTEMS. THREE KIND OF APPLICATION SYSTEM ARE NOW INVESTIGATED; AIR CONDITIONING, REFRIGERATOR AND INDUSTRIAL PROCESS HEATING AND COOLING SYSTEM.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.1
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• pp.1-7
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• 2014

A field test of a 70 kW heat pump system with flue gas heat recovery was performed by an experiment at the Korea Institute of Energy Research. The flue gas is exhausted from a 320 RT absorption chiller-heater in the heating season. Using this flue gas, source water of the heat pump is heated by a condensed-type heat exchanger in the chimney. The operating characteristics of the heat recovery heat pump system were analyzed. Based on the results of the experiments, operating maps were obtained, and an optimum operating range is suggested, in which the return and heat source water temperature are $51^{\circ}C$ and $31^{\circ}C$, respectively. Additionally, economic analysis of this system was conducted and about 50% energy cost savings can be expected in the heating season.