• Journal of the Korean Solar Energy Society
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• v.35 no.5
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• pp.49-56
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• 2015

In this study a hybrid heating system based on geothermal source and solar heat was developed in order to save energy for greenhouse heating and its field performance was evaluated. Developed system are composed of following parts: water tank, heat exchanger, heat pump, fan coil unit and heat storage unit. The working performance test was carried out in a greenhouse cultivating oriental orchids being managed by $23^{\circ}C$. Field performance test results showed that average heating coefficient of performance ($COP_h$) was 3.4 for the period from mid-January to mid-March 2013. Heating coefficient of performance ($COP_h$) of developed hybrid heat pump system was more sensitive to water tank temperature than outside air temperature. This study showed that developed hybrid heat pump system has a potential to save the heating costs up to 91% compared to conventional agricultural oil heaters.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.198.2-198.2
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• 2010

In this study, the COP variation with the duration of Ground Source Heat Pump (GSHP) systems operation was analyzed by experiment. This experimental facility was installed in residential house as a back-up device of solar thermal heating system. The capacity of heat pump is 2.5 kW with a vertical bore hole of 150m depth. The COP of GSHP is varied, depending on the ground temperature which is used as a heat source. The ground heat source temperature influencing heating COP is the soil or rock temperature which adjoin with geo-source heat exchanger. This temperature is decreased rapidly according to the operation duration of heat pump. As a result, COP of GSHP is decreased to 3 in one hour of continuous operation time.

• Journal of the Korean Solar Energy Society
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• v.26 no.4
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• pp.9-16
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• 2006

Geothermal-energy has been getting popular as a natural energy source for green buildings these days. Public building with gross area more than $3000m^2$, planned after March, 2005, should spend about 5% of total building cost for equipment run by natural energy source (e.g. geothermal, solar heat, solar power, etc) according to renewable energy promotion law in Korea. As a result geothermal-energy using heat pump system is emerging as a effective alternative for realistic and economic plan although design guidelines and construction code for the system is in progress and technical data is far from sufficient. The quantitative analysis on the performance of geothermal-energy using heat pump system is insufficient for appropriate design of it. In this paper, cooling performance of geothermal-energy using heat pump system of residential and retail etc. mixed-use building has been analyzed on the basis of temperature comparison between inlet and outlet of heat exchangers of the operating system. Additionally, dry-bulb temperature and relative humidity have been measured and analyzed together as an index of indoor thermal environment.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.6
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• pp.509-514
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• 2012

In this research, a heat pump system with a heat source network is suggested which utilizes solar heat and ground heat as heat source for cooling and heating. This paper describes the summary of the suggested system and the results of the annual energy simulation. The heating and cooling loads, the electric consumption and the COP were calculated by TRNSYS 16 and evaluated in the cases of different local conditions and different system compositions. In the results, the superiority of the suggested system has been quantitatively evaluated comparing with the conventional heat pump system using one heat source. Furthermore, it was more significant in cold climate, in which the heating COP was 146% increased compared the air source heat pump system, than it in subtropical climate, 119% increased.

• Journal of the Korean Solar Energy Society
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• v.36 no.3
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• pp.53-61
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• 2016

Solar assisted heat pump system uses solar thermal energy as a heat source of evaporator of heat pump. So, COP can be enhanced as well as collector efficiency. For improving performance of this system, some research about hybrid solar collector that has fin-and-tube heat exchanger has been conducted. This collector can get a thermal energy from ambient air for liquid heating, so heated liquid can be used as a heat source of evaporator in heat pump even the solar radiation is not enough. In this study, numerical analysis was conducted for confirming heat gain of liquid according to fin height and pitch of fin-and-tube heat exchanger in collector. As a result, higher heat gain was obtained on lower fin height and narrow fin pitch, but the pressure drop also increased with increment of heat gain. Thus the JF factor considering both heat transfer enhancement and pressure drop was investigated and the maximum value was shown when the fin height and pitch were 40mm and 45mm. So it is considered that this installation condition has a highest heat transfer improvement when comparing with pressure drop. However heat gain of liquid at this condition was less than the other installation conditions of fin pitch on same height. Then, after establishing a proper minimum heat gain of liquid, actual production and experiment of collector will be conducted with fin height and pitch showing maximum JF factor and satisfying selected minimum heat gain of liquid on the basis of results of this study.

• Journal of the Korean Solar Energy Society
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• v.32 no.3
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• pp.114-122
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• 2012

Vertical closed-loop ground source heat pump systems(GSHP) have been installed widely in Korea since it can extract moderate temperature level of geothermal heat in a small area. As a ground heat exchanger, a vertical closed -loop type with brine circulation is mostly preferred since it is simple and less harmful to ground environment. However, it requires a secondary heat exchange loop between the refrigerant in a heat pump and the brine. By adding a geothermal heat exchanger in the secondary heat exchange loop, circulation pumps should be attached and the temperature difference between refrigerant and ground is increased, which are important parts of performance degradation. In this paper, annual and seasonal performances of direct expansion(DX) geothermal heat pump were estimated mathematically as an alternative of classical indirect geothermal heat pump based on the annual performance evaluation. As results, DX geothermal heat pump showed 43% higher annual performance than the classical U-tube geothermal heat pump.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1215-1219
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• 2009

In this study, the performance of solar assisted hybrid heat pump system with cloud cover were analyzed by using experimental method in spring season. It was consisted of concentric evacuated tube solar collector, heat medium tank, heat storage tank, heat pump, and so on. As a result, the solar radiation should be maintained over $4.1\;MJ/m^2$ in order to operate solar heating system for heating. Solar heat of collector wasn't affected by ambient temperature, but cloud cover has a big effect to collector efficiency. In addition, the collector efficiency is about 50-60%, and solar fraction is 40% for this system.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.544-549
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• 2009

The purpose of this study is to investigate the field Operation Characteristics of a sea water heat source cascade heat pump system and system applicable to Building. Cascade heat pump system is composed R410A compressor, R134a compressor, EEV, cascade heat exchanger, Plate heat exchanger etc. Building area is $890m^2$ and has five floors above ground. R410A is used for a low-stage working fluid while R134a is for a high-stage. The system could runs at dual mode. One is mode of general R410A refrigeration cycle in summer and the other is cascade cycle. In order to gain a high temperature supply water in winter season, the system is designed to perform a cascade cycle. The filed test results show that the sea water heat source heat pump system exhibits a COP of about 5.5 in cooling mode along with a heating COP of about 4.0 in 1-stage heating mode. Cascade 2-stage heat pump system is enough to supply $60^{\circ}C$ water and heating COP is about 3.0

• Journal of the Korean Solar Energy Society
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• v.27 no.2
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• pp.19-27
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• 2007

The previous study was conducted to develop an air source multi heat pump system that could be operated with the solar collector and air source heat exchangers as heat source of the system. There is a winter-sowing problems in air source multi heat pump system when the outdoor temperature goes down under freezing point. The winter-sowing problem was solved by adapting R-22 refrigerant as working fluid in the previous study. However, when the system operated at high temperature, another problems are come out such as overheating of the solar collector outlet which lead to the superheat of the compressor inlet of the heat pump system. The condition could deteriorates a compressor in some case. In this study, we installed the anti-superheating devices on the previously developed system. As results of system performance test, COP of the system with anti-superheating technique is 2.4. It is a little improved COP compare to previous study's 2.23. In the results of multi heat source heating system, during operating solar collector, COP is relatively high between $200\;W/m^2$ and $400\;W/m^2$ solar intensity. It is recommended to extend the study on performance optimization with balancing the solar collect and capacity of compressor at higher solar irradiation conditions.

• Journal of the Korean Solar Energy Society
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• v.37 no.2
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• pp.67-75
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• 2017

We have investigated the operating characteristics of $1,600m^2$ large-scale solar thermal system installed in an eco-friendly energy town in Chungbuk Innovation City. The operation criteria of the collecting pump and storage pump were different from the existing standard, and it was confirmed that each pump works well according to the changed criteria. Based on the data of the representative day, the daily collecting heat (efficiency) and the production (storing) heat (efficiency) were estimated. It was confirmed that the daily collecting heat (efficiency) of the flat plate type was higher than that of the evacuated tube type, but the useful heat production was more in evacuated tube type collector.