• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.1
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• pp.147-155
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• 1999

In this work, the defrosting characteristics of PTC heating sheet used as a defrosting heat source of fin-tube heat exchanger in a refrigerator have been experimentally compared with those of conventional electric heater. It is found that the characteristics of water draining rate with defrosting time show smoothly oscillating pattern when PTC heating sheet is used, and the drained water is completely melted. The defrosting efficiency of the PTC heating sheet is about 75%, which represents about 25% higher than that of the electric heater. A reduction of defrosting time and an increase of defrosting efficiency may be obtained by improving the arrangement of heating elements of the heating sheet. It is shown that the defrosting time of PTC heating sheet increases linearly with the amount of frost, however the defrosting efficiency is nearly constant. In the application to the refrigerating system, one should notice the fact that the defrosting performance of PTC heating sheet may be defraded due to the repeated operations.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.3
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• pp.156-163
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• 2013

Ground Source Heat Pump (GSHP) systems utilize geothermal energy as a thermal source or sink, for heating, cooling and domestic hot water. It is well known that GSHP is environmentally friendly, and saves energy dramatically. For this reason, many investigative researches have been conducted on commercial and governmental buildings. However, studies on residential GSHP are few, because of the small capacity and cost. In this study, we experimented with the characteristic performance of heating, cooling and seasonal performance factor for a residential GSHP system, which consisted of two 180 m deep u-tube ground heat exchangers, a heat pump and measurement instruments. The installed capacity of the heat pump was 5RT, and the conditioning area was $62.23m^2$. From the experimental results, the cooling COP of the heat pump was 4.13, and the system COP was 3.51, while the CSPF was 3.32. On the other hand, the heating COP of the heat pump was 3.87, and the system COP was 3.39, while the HSPF was 3.39. Also, in-situ cooling COP and capacity were 93.7% and 96.4% compared with the EWT certification data, respectively, and that of heating were 98.3% and 95.7%, respectively.

• Journal of Biosystems Engineering
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• v.15 no.2
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• pp.123-133
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• 1990

Thermal performance of a solar heating plastic greenhouse designed for a hydroponic system was studied. The system was constructed with the air-water heat exchanger and thermal storage tank that were combined with hydroponic water beds. Experiments were carried out to investigate the daily average heat stored and released in thermal storage tank, average solar energy collection efficiency, average coefficient of performance, average oil reduction factor of thermal storage system, and the heat transfer coefficient during the nighttime in plastic greenhouse. The results obtained in the present study are summarized as follows. 1. Daily average heat stored in thermal storage tank and released from the thermal storage tank was 1,259 and $797KJ/m^2$ day, respectively. 2. The average solar energy collection efficiency of thermal storage tank was 0.125 during the experiment period. And the average coefficient of performance of thermal storage system in plastic greenhouse was 3.6. 3. The average oil reduction factor of thermal storage system and the heat transfer coefficient during the nighttime in plastic greenhouse were found to be 0.52 and $4.3W/m^2\;hr\;^{\circ}C$, respectively.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.15 no.1
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• pp.1-8
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• 2019

In this study, the effect of operating conditions of fan-coil unit with an oval tube type heat exchanger on its non-dimensional performance coefficient has been investigated. Pressure drops and heat transfer rates were measured under heating condition for various water flow rates, inlet temperatures and wind speeds. As a non-dimensional performance coefficient, Colburn j-factor was evaluated. The results show that the most sensitive parameter on heat flux is the inlet temperature, which affects the heat flux 4.7 and 7.2 times more than the wind speed and water flow rate, respectively. On the other hand, the Colburn j-factor as a non-dimensionalized index decreases with the wind speed, and has an maximum when the wind speed is about 1 m/s. the Colburn j-factor increases slowly with the water flow rate and inlet temperature but at a certain range of inlet temperature, the opposite phenomenon is found.

• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.237-238
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• 2012

Recently, an energy-saving due to the energy utilisation efficiency enhancement is important. In order to improve the heat efficiency of the general residential boiler, We performed an experiment of condensation heat transfer to air pre-heat exchanger adhered to the condensing boiler. In this research, We analyze the heat transfer performance through the hydrophilic surface treatment(plasma, etching). The results of the research, On plasma and etching treated surface, Overall heat transfer coefficient is displayed the tendency to increase.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.2 no.3
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• pp.218-225
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• 1990

Studies on the performance of a heat pump using non-azeotropic refrigerant mixtures are done. In order to estimate the thermodynamic properties for the selected non-azeotropic refrigerant mixtures including R22/R152a, R22/R142b, R22/R114 and R13B1/R152a, Peng-Robinson equation of state is adopted. The pressure-enthalpy diagram and the temperature-entropy diagram are plotted for each refrigerant mixture. Considerations on the capacity modulation for the heat pump system using refrigerant mixtures are taken into. Results show that when the heating load varies, the possibility for the capacity modulation is found in the heat pump system using a compressor with constant volume flow rate. Under a constant heating capacity condition in the heat pump system, the coefficient of performance increases when the refrigerant mixtures are used. The volume flow rate decreases as the mass fraction of lower boiler increases in this case.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.4
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• pp.462-471
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• 1997

The water-to-air heat pump system requires relatively lower energy consumption and less installation space. The heat exchangers used for this system are the finned-tube type for the indoor unit and the double-tube type for the outdoor unit. Mathematical models for this system are developed and programmed in computer. Experimental data from various conditions are obtained and compared with calculated values from the computer simulation program. Differences of cooling capacity and COP are 1.25% and 0.47%, and those of heating capacity and COP are 0.51% and 0.13%, respectively. Simulation results are in good agreement with test results. Therefore, the developed program is effectively used for the design and the performance prediction of water-to-air heat pump system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.4
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• pp.250-255
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• 1991

Performance analysis of double-effect absorption heat pump system has been done to find improved working pairs (or mixture) by computer simulation. Based on the thermodynamic analysis, the coefficient of performance and mass flow ratio are investigated to compare three aqueous solutions [LiCl-water, LiSCN-LiBr-water, LiCl-$CaCl_2$-$Zn(NO_3)_2$-water] which was developed for only cooling, with conventional LiBr-water solution. It is found that the performances of the new aqueous solutions are better than that of LiBr-water solution not only in cooling systems, but also in heating systems. Theoretical thermodynamic performance data can be used in heat recovery systems by basic design data.

• Journal of the Korean Solar Energy Society
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• v.38 no.5
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• pp.49-62
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• 2018

This study aims to analyze the performance of solar thermal system with heat pump for domestic hot water and heat supply. There are four types of system. Systems are categorized based on the existence of a heat pump and the ways of controlling the working fluid circulating from the collector. Working fluid is controlled by either temperature level (categorized as system 1 and 2) or sequential flow (system 3 and 4). Heat balance of the system, the solar fraction, hot water and heating supply rates, and performance of heat pump are analyzed using TRNSYS and TESS component programs. Technical specifications of the main facilities are as follow; the area of the collector to $25m^2$, the volumes of the main tank and the buffer tank to $0.5m^3$ and $0.8m^3$, respectively. Heating capacity of the heat pump in the heating mode is set to 30,000 kJ / hr. Hot water supply set 65 liters per person each day, total heat transfer coefficient of the building to 1,500 kJ / kg.K. Indoor temperature is kept steadily around $22^{\circ}C$. The results are as follows; 6 months average solar fraction of system 1 turns out to be 39%, which is 6.7% higher than system 2 without the heat pump, indicating a 25% increase of solar fraction compared to that of system 2. In addition, the solar fraction of system 1 is 2% higher than that of system 3. Hot water and heating supply rate of system 1 are 93% and 35%, respectively. Considering the heat balance of the system, higher heat efficiency, and solar fraction, as whole, it can be concluded that system 1 is the most suitable system for hot water and heat supply.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.310-315
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• 2008

In this study, experimental study on the heating performance of a $CO_2$ heat pump water heater with a variation of operating conditions such as refrigerant charge amount, outdoor temperature, compressor frequency, EEV opening and water mass flow rate. Based on the test results, the optimum charge amount was 1800 g. At the water mass flow rates of 75, 85, 95 kg/hr, the water heating temperature was 62, 67, $74^{\circ}C$ and COP was 2.6, 2.8, 3.0, respectively. Besides, the water mass flow rate and compressor frequency were varied to maintain above the water heating temperature of $60^{\circ}C$ with the decrease of outdoor temperature. So, The compressor frequency increased beyond 65 Hz and the water mass flow rate was 45 kg/hr at the outdoor temperature of $-13^{\circ}C$, 65 kg/hr at $-8^{\circ}C$, 75 kg/hr at $-3^{\circ}C$ and 85 kg/hr at 2, $7^{\circ}C$. As the outdoor temperature decreased, the heating COP decreased by 2.5-39.8%.