• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제18권1호
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• pp.66-72
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• 2006

This article presents the optimal operation of an air conditioner using thermoelectric modules. A prototype of air conditioner using four thermoelectric modules has been designed and built. The system performance with evaporative cooling for hot side of the module are studied in detail for several operating parameters, such as input power to the thermoelectric module, fans and pump. It is found that the optimal input voltage to the thermoelectric module and pump is selected for the best system performance based on the cooling capacity and the COP at a given operating condition. It is also found that both the cooling capacity and COP of a system is increased with an increase in the input power to fans. The cooling performance could be improved when the ambient temperature is increased and the relative humidity is decreased since the evaporative cooling at the hot side has been increased.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제18권8호
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• pp.641-648
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• 2006

In this study, a two-stage phase-separate cycle was investigated analytically to improve the performance of the $CO_2$ system in the cooling mode. The simulation results were verified with the measured data. The predictions using the simulation model were consistent with the measured data within ${\pm}20%$ deviations. The performance of the modified $CO_2$ system with the two-stage phase-separated cycle was analyzed with the variations of outdoor temperature and EEV opening. The cooling COP decreased with the increase of compressor frequency. The highest COP was 2.7 at compressor frequencies of 30 Hz and 30 Hz for the first and second compressors, respectively. In addition, the cooling COP increased by 9.3% with an application of optimum control of the first and second-stage EEV openings.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제16권5호
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• pp.438-443
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• 2004

The objective of this paper is to study the effects of the input gas flow rate and the ambient temperature variation on the absorption cycle performance. An air-cooled NH$_3$-$H_2O$ absorption chiller is tested in the present study. The nominal cooling capacity of the single effect maching is 17.6 ㎾ (5.0 USRT). The cooling capacity, coefficient of performance, burner efficiency, and each state point are measured with the variations of the heat input and the ambient temperature. It is found that the COP and cooling capacity increase with increasing the generator exit temperature up to a certain temperature and then decrease. It is also found that the COP and the cooling capacity decrease with increasing the ambient temperature. The maximum COP of 0.51 is obtained from the present experiment.

• The KSFM Journal of Fluid Machinery
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• 제10권2호
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• pp.16-21
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• 2007

Potential advantages of using vapor injection in a two stage rotary compressor for a $CO_2$ heat pump water heater system were addressed in this paper by numerical simulation. Vapor separated from a flash tank in the middle of the expansion process can be used for injection into the second stage suction plenum of the compressor to improve the system performance. Vapor injection increases the intermediate pressure between the two stages, thus increasing the first stage compressor work and reducing that of the second stage. As a whole, however, the compressor input power increases due to injected mass flow rate for the second stage. Computer simulation showed that increment of the cooling capacity by vapor injection exceeded that of the compressor work, thus improving the system performance. COP improvement by vapor injection was calculated to be about 5-14% for normal operating conditions. With vapor injection, a maximum COP was found when the displacement volume of the second stage becomes 90-95% of that of the first stage of the compressor.

• Transactions of the Korean hydrogen and new energy society
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• 제25권3호
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• pp.297-304
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• 2014

The purpose of this study is to evaluate the experimental performance characteristics of a water-to-water geothermal heat pump featuring a vapor refrigerant injection for the production of hot water. The performance of geothermal heat pump with a vapor injection was evaluated by comparing with that of a conventional geothermal heat pump without a vapor injection. For heating operation, the geothermal heat pump with a vapor injection is superior in COP and heating capacity. The vapor injection was more effective for supplying hot water while overloading. The vapor injection was effective for the improvement of the cooling capacity. However, the vapor injection was not effective for the increasing of COP according to the increased input of a compressor. The advantage of vapor injection in water-to-water geothermal heat pump become disappeared while cooling operation with lower part loading.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 춘계학술대회 논문집
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• pp.630-633
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• 2008

Geothermal heat pump systems use the earth as a heat source in heating mode and a heat sink in cooling mode. These systems can be used for heating or cooling systems in farm facilities such as greenhouses for protected horticulture, cattle sheds, mushroom house and etc. A horizontal type means that a geothermal heat exchanger is laid in the trench buried in 1.2 to 1.8 m depth. Because a horizontal type has advantages of low installation, operation and maintenance costs compared to a vertical type, it is easy to be adopted to agriculture. In this study, to heat and cool farm facilities and obtain basic data for practical application of horizontal geothermal heat pump system in agriculture, a horizontal geothermal heat pump system of 10 RT was installed in greenhouse. Heating and cooling performance of this system was estimated. The horizontal geothermal heat pump used in this study had heating COP of 4.57 at soil temperature of $14^{\circ}C$ with depth of 1.75m and heating COP of 3.75 at soil temperature of $7^{\circ}C$ with the same depth. The cooling COP was 2.7 at ground temperature at 1.75m depth of $25.5^{\circ}C$ and 2.0 at the temperature of $33.5^{\circ}C$.

• Journal of Power System Engineering
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• 제21권3호
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• pp.45-50
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• 2017

This paper presents the Coefficient of performance(COP) and mass flow ratio of cascade refrigeration system with respect to refrigerants appling to high temperature cycle. The operating parameters considered in this study include degree of superheating and subcooling, compressor efficiency, evaporating temperature, condensing temperature and internal heat exchanger effectiveness in high temperature cycle. The result of this study is as follows : The COP of cascade system increases with increasing degree of superheating and subcooling, compressor efficiency and internal heat exchanger effectiveness except increasing condensing temperature. The mass flow ratio of low and high temperature cycle increases with increasing evaporating temperature and condensing temperature, but decreases with increasing internal heat exchanger effectiveness, degree of superheating and subcooling. Also, the mass flow ratio has no correlation with compressor efficiency at high temperature cycle.

• New & Renewable Energy
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• 제3권4호
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• pp.47-53
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• 2007

Effluent ground water overflow in deep and broad ground space building. Temperature of effluent ground water is in $12{\sim}20^{\circ}C$ annually and the quality of that water is as good as living water. Therefore if the flow rate of effluent ground water is sufficient as source of heat pump, that is good heat source and heat sink of heat pump. Effluent ground water contain the thermal energy of surrounding ground. So this is a new application of ground source heat pump. In this study open type and close type heat pump system using effluent ground water was installed and tested for a church building with large and deep ground space. The effluent flow rate of this building is $800{\sim}1000ton/day$. The heat pump capacity is 5RT each. The heat pump cooling COP is $4.9{\sim}5.2$ for the open type and $4.9{\sim}5.7$ for close type system. The system cooling COP is $3.2{\sim}4.5$ for open type and $3.8{\sim}4.2$ for close type system. This performance is up to that of BHE type ground source heat pump.

• Journal of Power System Engineering
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• 제16권1호
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• pp.38-43
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• 2012

This paper describes an analysis on performance of R744-R404A cascade refrigeration system with internal heat exchanger to optimize the design for the operating parameters of the system. The operating parameters considered in this study include subcooling and superheating degree, internal heat exchanger and compression efficiency, evaporating and condensing temperature in the R744 low- and R404A high-temperature cycle and temperature difference of cascade heat exchanger. The main results are summarized as follows : COP of cascade refrigeration system increases with the increasing of compression efficiency, but decreases with the increasing temperature difference of cascade heat exchanger. Also, the COP increases with the increasing of internal heat exchanger efficiency in high-temperature cycle, but decreases with that in low-temperature cycle. Therefore, internal heat exchanger efficiency, compressor efficiency and temperature difference of cascade heat exchanger on R744-R404A cascade refrigeration system have an effect on the COP of this system.

• Journal of Advanced Marine Engineering and Technology
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• 제35권4호
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• pp.429-435
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• 2011

In this study the operational characteristics of the temperature control system between an on-offemployed cooler and a bypass type cooler is analyzed. Currently an on-off controller employed coolerwhich is the industry's leading type on the market for industrial coolers is used. The new type cooler isused a bypass controller at discharge gas. The COP of the bypass controlled cooler with discharge gas is at least 8% higher than the on-off controlled cooler. The maximum COP difference is about 20%. Based on the results, the bypass control with discharge gas shows the possible temperature control with high precision.