• Journal of the Korean Solar Energy Society
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• v.33 no.2
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• pp.1-10
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• 2013

Simulation study of a solar hybrid heat pump using R744 and R22 for residential applications was carried out according to heat pump operating temperature, outdoor temperature and solar radiation. As a result, when the heat pump operating temperature increases from $40^{\circ}C$ to $48^{\circ}C$, the COP of a R744 and R22 heat pump system decrease from 2.15 to 1.7 and from 3.09 to 2.69, respectively. Besides, as the outdoor temperature rises from $3^{\circ}C$ to $11^{\circ}C$, the COP of R744 and R22 heat pump system increase from 1.73 to 2.12 and from 2.73 to 3.02. When the solar radiation increases from 10 to 20 $MJ/m^2$, the collector operating time and collector efficiency of R744 heat pump increase 10.3 times and 50.7%, respectively. The performance of R744 solar hybird heat pump is more sensitive to operation condition compared to that of R22. Besides, the solar heating system is more effective to the R744 heat pump system.

• Journal of the Korean Solar Energy Society
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• v.22 no.1
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• pp.43-53
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• 2002

This study has been carried out to study the thermal performance of an all-glass type solar collector tube when a heat transfer medium is used with a heat storage unit capable of preventing pressure build-up within the tube. The heat storage unit is devised such that it performs the dual function of relieving excessive pressure and storing solar thermal energy. Different types of heat storage medium are tested under heat-up phase of a collector tube. It is found that the proposed unit could be used quite effectively if one wishes to capitalize more aggressively in harnessing the solar energy.

• Journal of the Korean Solar Energy Society
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• v.27 no.4
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• pp.167-173
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• 2007

This study analyzed by simulation using TRNSYS as well as by experiment on the solar district heating system installed for the first time for the district heating system in Bundang. Simulation analysis using TRNSYS focused on the thermal behavior and long-term thermal efficiency of solar system. Experiment carried out for the reliability of simulation system. This solar system where the circuits of two different collectors, flat plate and vacuum tube collector, are connected in series by a collector heat exchanger, and the collection characteristics of each circuit varies. Therefore, these differences must be considered for the system's control. This system uses variable flow rate control in order to obtain always setting temperature of hot water by solar system. Specifically, this is a system that heats returning district heating water (DHW) at approximately $60^{\circ}C$ using a solar collector without a storage tank, up to the setting temperature of approximately $85{\sim}95^{\circ}C$ To realize this, a flat plate collector and a vacuum tube collector are used as separate collector loops. The first heating is performed by a flat plate collector loop and the second by a vacuum tube collector loop. In a gross collector area basis, the mean system efficiency, for 4 years, of a flat plate collector is 33.4% and a vacuum tube collector is 41.2%. The yearly total collection energy is 2,342GJ and really collection energy per unit area ($m^2$) is 1.92GJ and 2.37GJ respectively for the flat plate vacuum tube collector. This result is very important on the share of each collector area in this type of solar district heating system.

• Transactions of the Korean Society of Mechanical Engineers
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• v.7 no.4
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• pp.392-397
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• 1983

In the present study, improvement of the solar collector performance by utilizing honeycomb structures is being investigated. Installation of honeycomb structures inside of the collector induces the suppression of would-be natural convection phenomena within the collector enclosure spacing. It also minimizes infrared radiation heat loss from the collector absorber plate to the surrounding. Experiments have been carried out a collector with 40*20mm rectangular honeycombs, 20*20mm square honeycombs and without honeycombs. The results are presented for the three cases for comparisons. The collector model has been installed at various tilt angle from 15.deg. to 60.deg. measured from the ground. The influence of the tilt angle to the heat performance of the collector is also presented.

• Journal of the Korean Solar Energy Society
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• v.30 no.6
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• pp.50-58
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• 2010

Experimental study on the operating characteristics of a solar hybrid heat pump system according to indoor setting temperature were carried out during spring and winter season. The system was consisted of a concentric evacuated tube solar collector, heat medium tank, heat storage tank, and heat pump. As a result, the heating load was increased by 21.1% when the indoor setting temperature rose by 2oC for the same ambient temperature. Besides, the spring season had good outdoor conditions compared to the winter season, therefore the heating load was reduced and heat gain by collector increased, relatively. In case of the winter season, the solar fraction was shown less than 10% because the heat losses of system and space increased considerably. The solar fraction decreased significantly as the indoor setting temperature increased.

• Journal of the Korean Solar Energy Society
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• v.35 no.6
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• pp.25-33
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• 2015

In this study, heating performance of the air-cooled heat pump with vapor-injection (VI) cycles, re-heater and solar heat storage tank was investigated experimentally. Devices used in the experiment were comprised of a VI compressor, re-heater, economizer, variable evaporator, flat-plate solar collector for hot water, thermal storage tank, etc. As working fluid, refrigerant R410A for heat pump and propylene glycol (PG) for solar collector were used. In this experiment, heating performance was compared by three cycles, A, B and C. In case of Cycle B, heat exchange was conducted between VI suction refrigerant and inlet refrigerant of condenser by re-heater (Re-heater in Fig. 3, No. 3) (Cycle B), and Cycle A was not use re-heater on the same operating conditions. In case of Cycle C, outlet refrigerant from evaporator go to thermal storage tank for getting a thermal energy from solar thermal storage tank while re-heater also used. As a result, Cycle C reached the target temperature of water in a shorter time than Cycle B and Cycle A. In addition, it was founded that, as for the coefficient of heating performance($COP_h$), the performance in Cycle C was improved by 13.6% higher than the performance of Cycle B shown the average $COP_h$ of 3.0 and by 18.9% higher than the performance of Cycle A shown the average $COP_h$ of 2.86. From this results, It was confirmed that the performance of heat pump system with refrigerant re-heater and VI cycle can be improved by applying solar thermal energy as an auxiliary heat source.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.316-321
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• 2000

In this study, heat collecting performance was study of flat plate solar collector by the angle. A method of study on were made turn out artificial sun by the angle of 0, 15, 30 degrees. The heat performances were measured the tube array surface temperature by thermo-couple. The winter season natural condition for 4 times on the angles of various general and emboss glass at optimum distance(0.68m) calculated of between sun and solar collector. To sum up temperature rise is appear more or less that emboss glass is all the better for general glass. The temperature variable at below of 30 degree was appear very less. The maximum performance of this system at that it is tilt angle of 30 with general glass is appear Q:11.54(kcal/min) and ${\Delta}T=18.9^{\circ}C$.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.11 no.4
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• pp.6-18
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• 1982

The performance of two typical types of solar hot water heating system was tested in Seoul. Types of systems studied are single-tank internal external heat exchanger system and single-tank internal heat exchanger system. Comparing to experimental results, a transient system simulation program was made to analyze the performance of the selected system. The climate data, Standard Weather Year for Seoul, required for the simulation was provided. Computer simulations were used to estimate the effect of significant parameters upon system performance. The followings are obtained. 1. In the domestic solar water Heating system, the value $20-40kg/m^2\;h$ for flow rate through the collector is much better than the recommended value $72kg/m^2\;h$ in the solar heating system. 2. The effectiveness of collector heat exchanger and storage tank size are found to have only a small effect upon system performance. 3. The hot water draw pattern has a significant effect on system performance. A higher system efficiency achieved when draw-off occurred around noon than when it occurred around early morning. Using the above results, the reference solar hot water system which provides $300\ell$ of hot water per day, was selected as a guide for designer. And simplified graphical method was developed based on the modified f-chart method to determine required collector area. When the system design parameters of the proposed system differs from the reference system, required collector area can be calculated from area adjustment factors.

• Journal of the Korean Solar Energy Society
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• v.39 no.6
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• pp.83-91
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• 2019

Photovoltaic thermal (PVT) collectors are devices that simultaneously produce electricity and heat. Research on conventional air-type PVT collector focuses on installing baffles to enhance the collector's thermal performance. However, the baffles have pressure drop inside the collector which degrades the thermal performance. Thus, it is necessary to design baffles to smoothen the flow inside the air-type PVT collector. Alternatively, installing perforated baffles in air-type PVT collectors can reduce the collector weight, but parameters such as the diameter of the perforated holes and the height of the perforated plates should be considered. Therefore, the main aim of this study was to analyze thermal characteristics of each variable of perforated baffles installed inside air-type PVT collector. For this purpose, the uniformity of air flow in the collector was compared through NX program, and the resultant heat gain and thermal efficiency of the air-type PVT collector were compared and analyzed. Therefore, the main aim of this study was to analyze thermal characteristics of each variable (Baffle angle, length, height, pitch, perforated ratio) of perforated baffles installed inside air-type PVT collector. For this purpose, the uniformity of air flow in the collector was compared through CFD program, and the resultant heat gain and thermal efficiency of the air-type PVT collector were compared and analyzed. As a result, the maximum outlet temperature was increased by 1.45 times and the heat gain was increased by 193.8 Wth, depending on the perforated baffle plate, compared to the collector without the baffle. The heat transfer performance showed that the maximum internal velocity was 1.61 times higher and the Reynolds number was 1.06 times higher depending on the parameters of the baffle plate.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.2
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• pp.182-191
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• 2016

In the present work, a solar assisted heat pump (SAHP) system with a hybrid collector was analyzed. For this, a simplified thermodynamic model was developed. Based on the proposed model, the heat transfer rate, COP, and the annual operating hour of the SAHP system were estimated. The effect of the variation of system design parameters on the performance of the system was also examined. From the results, the performance was improved with increasing the effectiveness of heat exchangers and decreasing the difference between the evaporation temperature and the outlet brine temperature of the hybrid collector loop. Finally, the performance of SAHP system with a hybrid collector was compared with that of conventional serial and parallel SAHP systems. The SAHP system with a hybrid collector was substantially better than a series system and slightly worse than a parallel system for both the yearly averaged heat transfer rate and COP. However, the annual operating hour of the SAHP system with a hybrid collector was much better than that of a parallel system.