• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.33 no.3
• /
• pp.1049-1061
• /
• 2013

In this paper, a relative heat exchange rate is numerically compared for cast-in-place concrete energy piles with different heat exchange pipe configurations, and a new design method for energy piles is proposed. An equivalent heat exchange rate was estimated for the W-type (one series loop), multiple U-type (four parallel loops), and coil-type heat exchanger installed in the same large-diameter drilled shaft. In order to simulate a cooling operation in summer by a CFD analysis, the LWT (leaving water temperature) into a energy pile was fixed at $35^{\circ}C$ and then the EWT (entering water temperature) into a heat pump was monitored. In case of continuously applying the artificial maximum cooling load for 100 hours, all of the three types of heat exchangers show the marginally similar heat exchange rate. However, in case of intermittently applying the cooling load with a cycle of 8 hours operation-16 hours off for 7 consecutive days, the coil type heat exchanger exhibits a heat exchange rate only 86 % of the multiple U-type due to measurable thermal interference between pipe loops in the energy pile. On the other hand, the W-type possesses the similar heat exchange rate to the multiple U-type. The equivalent heat exchange rates for each configuration of heat exchangers obtained from the CFD analysis were adopted for implementing the commercial design program (PILESIM2). Finally, a design method for cast-in-place concrete energy piles is proposed along with a design chart in consideration of typical design factors.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.21 no.5
• /
• pp.297-304
• /
• 2009

The aim of this study is to investigate the cooling performance of ground source multi-heat pump systems with a vertical single U-tube GLHX(U-tube system) and a vertical double tube GLHX(double tube system), which were installed in a school building located in Cheonan. All systems were operated in a part load conditions for all day, and the maximum COP of the single U-tube system and the double tube system were 6.2 and 5.2 at cooling mode, respectively. The double tube GLHX designed by the GLHEPRO, commercial program, was estimated to have the same performance as the U-tube GLHX, because the inlet temperatures of each outdoor unit heat exchanger for the former was similar to the latter. However, it is needed to prove the long tenn performance. It is suggested that the new algorithms to control the flow rate of secondary fluid for GLHX according to load variation have to be developed in order to enhance the performance of the system.

• Journal of the Korean Solar Energy Society
• /
• v.32 no.6
• /
• pp.22-28
• /
• 2012

The purpose of this study was to show how tomaintain high efficiency and to use reasonably when being applied the cold-heat storage systems to the showcase. An experimental study was performed to manufacture the showcase system in a laboratory. Comparing the result at general operation condition with that of the new condition using ice storage system, this study showed the effects of the refrigerant sub-cooling, and with using inverter. Using ice storage system, the ice making process was operated during midnight being not needed the cooling of the showcase through the continuous running of the condenser unit. And then, the refrigerant was sub-cooled using the stored cold-heat after being discharged from the air cooling condenser during the day time. Through the experiments, the load transfer rate for the showcase using inverter and ice storage was estimated about 30.0%. And showed that the total power consumption of the showcase with inverter could be reduced about 37% than that of the showcase without inverter.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.10 no.1
• /
• pp.79-87
• /
• 1998

Basic design of a 50USRT(175㎾) triple effect absorption chiller driven by hot gas has been carried out for both parallel and series flow cycles. Parallel flow cycle showed higher COP, however, the temperature in the generator was also higher than that in series flow cycle. Dynamic operation behavior of a parallel flow system at off-design conditions, such as the change in heat transfer medium temperature or the construction change of the system components, has been investigated in detail. It was found that the cooling capacity was seriously decreased by reducing hot gas flow rate and UA-value in the high temperature generator. However, the system COP was improved, because thermal load in the system components was reduced. The COP and the cooling capacity was found to be improved as cooling water temperature decreased or chilled water temperature increased. The optimum ratio of solution distribution could be suggested by considering the COP, the cooling capacity and the highest temperature in the system, which is critical for corrosion.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
• /
• v.17 no.4
• /
• pp.68-78
• /
• 2021

In order to solve the increasing deterioration of the energy shortage problem, ground-source heat pump (GSHP) systems have been widely installed. The control method is a significant component for maintaining the long-term performance and for reducing operation cost of GSHP systems. This paper presents the measurement and analysis results of the cooling performance of a GSHP system using capacity control with outdoor air temperature. For this, we installed monitoring equipments including sensors for measuring temperature, flow rate and power consumption, and then monitored operation parameters from July 9, 2021 to October 2, 2021. From measurement results, we analyze the effect of capacity control with outdoor air temperature on the cooling performance of the system. The average performace factor (PF) of the heat pump was 6.95, while the whole system was 5.54 over the measurement period. Because there was no performance data of the existing GSHP system, it was not possible to directly compare the existing control method and the outdoor air temperature method. However, it is expected that the performance of the entire system will be improved by adjusting the temperature of cold water produced by the heat pump, that is, the temperature of cold water on the load side according to the outside air temperature.

• Progress in Superconductivity and Cryogenics
• /
• v.8 no.4
• /
• pp.30-33
• /
• 2006

Several crucial issues are discussed in the design of cryogenic cooling system for high field magnets. This study is mainly motivated by our ongoing program to develop a 21 T Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FT-ICR MS). The magnets of this system will be built horizontally to accomplish the requirement of user friendliness and reliability, and the replenishment of cryogen will not be necessary by a closed-loop cooling concept. The initial cool-down and safety are basically considered in this paper. The effects of the helium II volume and the gap distance of the weight load relief valve (or safety valve) on the cool-down time and temperature rising during an off-normal state are discussed. The total amount of cryogenic cooling loads and the required helium flow rate during cool-down are also estimated by a relevant heat transfer analysis. The temperatures of cryogen-free radiation shield are finally determined from the refrigeration power of a cryocooler and the total cryogenic loads.

• Journal of Energy Engineering
• /
• v.28 no.4
• /
• pp.103-110
• /
• 2019

The domestic innovative power reactor named iPOWER will employ the passive molten corium cooling system(PMCCS) to cool down and stabilize the core melt in the severe accident. The final design concept of the PMCCS is yet to be determined, but the in-vessel retention through external reactor vessel cooling has been also considered as a viable strategy to cope with the severe accident. In this study, the two-phase natural circulation flow established between the reactor vessel and the insulation was simulated using a thermal-hydraulic system code, MARS-KS. The flow path of cooling water was modeled with one-dimensional nodes, and the boundary condition of the heat load from the molten core was defined to estimate the naturally-driven flow rate. The evolution of major thermal-hydraulic parameters were also evaluated, including the temperature and the level of cooling water, the void fraction around the lower head of the reactor vessel, and the heat transfer mode on its external surface.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.20 no.11
• /
• pp.718-726
• /
• 2008

The cooling load in winter is significant in buildings and hotels because of the usage of office equipments and the high efficiency of wall insulation. Hence, the development of a multi-heat pump that can cover heating and cooling simultaneously for each indoor unit is required. In this study, the performance of a simultaneous heating and cooling heat pump was investigated in the heat recovery mode (HR mode). The system adopted a variable speed compressor using R410A with four indoor units and one outdoor unit. In the HR mode, the capacity and COP were improved as compared with those in the cooling or heating mode because the waste heat in the outdoor unit was utilized as useful heat in the indoor units. However, energy imbalance between heating and cooling capacity of each indoor unit was observed in the 2H-1C HR mode. Therefore, the performance of the system in the 2H-1C HR mode was enhanced by controlling refrigerant flow rate through the outdoor unit.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.11 no.3
• /
• pp.301-312
• /
• 1999

Experiments were carried out to evaluate performance of the cold air distribution systems with an ice storage tank in test room. Cold air distribution systems provide primary air for comfort conditioning or process cooling at coil discharge temperatures$4^{\circ}C$ to$11^{\circ}C$. The application of a cold air distribution system allows for the downsizing of air distribution equipment and central plant equipment when ice storage tank is used. The benefit of a cold air distribution system include a decrease in the floor-to-floor height, increase floor space, reduced building capital costs, reduced energy use and demand. The use of cold air distribution can result in the most cost effective system and is currently being implemented world wise as the new standard in air conditioning systems. In this study, the cold air distribution system is compared with the general ice storage system. Under the same cooling load conditions, experimental results show that the supply air volume of cold air distribution system decrease 38%, and decrease 45% flow rate of brine for the general ice storage system.

• Journal of Korean Living Environment System
• /
• v.24 no.6
• /
• pp.810-823
• /
• 2017

The envelope is important for sustainable building. Recent commercial buildings are causing thermal degradation and cooling load due to the increase of the area of the windows. Therefore, this research studied kinetic shading system which can improve energy saving and visual environment in summer. For that, this study proposed new shading system and shape considering the orientation of the building and the location of the sun. Based on this, this study analyzed the effectiveness on energy reduction and improvement of visual environment by applying the kinetic shading system proposed in this study. As the results of this study, energy reduction rate was 35% in the east, 22.9% in the south, and 30.7% in the west depending on the application location. Also, as the result of the illuminance analysis, it was found that the effect of achieving uniformity ratio of illumination was considerable.