• International Journal of Air-Conditioning and Refrigeration
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• v.6
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• pp.27-35
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• 1998

An experimental study was performed to investigate the optimum cycle of an inverter heat pump as a function of frequency. The performance of the inverter heat pump with the rated cooling capacity of 4,141 W(3,550kcal/h) was measured with a variation of frequency, indoor and outdoor temperature, and length of capillary tube in the psychrometric test room. As a base case, the inverter heat pump with the standard capillary length of l,000mm(optimum size for the frequency of 60Hz) and ASHRAE Test condition "A" was tested by varying frequency from 30Hz to 80Hz. Then, the optimum cycles were investigated by varying the length of capillary tube at each frequency level of 30, 60 and 80Hz. Based on the experimental data, the change of system characteristics between the optimum and the base case were analyzed for each selected frequency level. Generally, for low frequency level(30Hz), the longer length of the capillary tube compared with the standard size showed the higher energy efficiency ratio(EER), while for high frequency level(80Hz) the shorter length of the capillary tube showed the higher EER.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.1
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• pp.64-72
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• 1997

An experiment study was performed to investigate the optimum cycle of an inverter heat pump as a function of frequency. The performance of the inverter heat pump with the rated cooling capacity of 4141W(3550kcal/h) was measured with a variation of frequency, indoor and outdoor temperature, and length of capillary tube in the psychrometric test room. As a base case, the inverter heat pump with the standard capillary length of 1000mm which was optimum size for the frequency of 60Hz and ARHRAE Test condition A was tested by varying frequency from 30Hz to 80Hz. Then, the optimum cycle was invesigated by varying the length of capillary tube at each frequency levels of 30, 60 and 80Hz. Based on the experimental data, the change of system characteristics between the optimum and the base case were analyzed for each selected frequency levels. Generally, for low frequency level(30Hz), the longer length of the capillary tube compared with the standard size showed the higher EER, while for high frequency level(80Hz) the shorter length of the capillary tube showed the higher EER.

• 한국신재생에너지학회:학술대회논문집
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• 2006.11a
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• pp.40-43
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• 2006

Public demand for the heat pump system as a next generation energy equipment is increasing for its eco-friendly and cost-effective advantage. Many researches have been concentrated on how to calculate and develop its own efficiency, while the possible effect of the heat pump operation on the whole subsurface temperature distribution is relatively less considered, During the current study, subsurface temperature disturbance caused by seasonal surface temperature cycle in Busan area and general W-tube heat pump operation is simulated in 3-dimensional heterogeneous medium. It shows that subsurface deeper than 10m from the surface remains nearly unchanged throughout the 4 seasons and groundwater convect ion in highly permeable layer near the surface acts like a main path of heat plume from heat pump system, This implies the significance of detail descript ion in shallow sedimentary layer or highly permeable layer which plays an important role on the regional flow advection and heat transfer. Also, the effect of groundwater convection increases when the arrangement of the 2 injection pipes and 2 extract ion well is maintained parallel to groundwater flow. Therefore, more careful and detail investigation is required before installation and operation of heat pump system that it may not cause any possible change of microbial ecosystem in the shallow subsurface environment or 'contamination of temperature' for groundwater use as well as the loss of efficiency of the equipment itself. This can also help to design the optimized grouting system for heat pump.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.4
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• pp.1125-1133
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• 1995

Experiments were performed to investigate the condensing heat transfer characteristics of non-azeotropic mixtures of R-22 and R-114 in a heat pump system with a horizontal smooth tube as a condenser. The ranges of parameters, such as heating capacity, mass flow rate of refrigerant and quality were 780-3,480W, 24-71kg/h, and 0-1, respectively. The overall compositions of R-22 in a R-22/114 mixture were 25, 50, 75 and 100 per cent by wight. The results show that the overall condensing heat transfer coefficients for the mixtures were lower than the pure R-22 values. Local heat transfer coefficient of the pure R-22 was hghest at the top of the test tube. The local heat transfer coefficient of R-22/114 (50/50 wt%) at side and bottom of the test tube was higher than that at the top. From the obtained data, a prediction for the condensing heat transfer coefficients of the mixture was done based on the method of Fujii.

• KIEAE Journal
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• v.17 no.4
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• pp.33-39
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• 2017

Purpose: The use of renewable energy system is essential for building energy independence and saving energy consumption in the building sector. Among renewable energy technologies, ground source heat pump(GSHP) system is more energy-efficient and environmental-friendly than other heat source systems due to utilize stable ground heat source. However, the GSHP system requires a high initial installation cost and installation space in limited urban area, so it is difficult to have superiority in the market of heat source system. Therefore, it is necessary to develop the installation method of low-cost and improve system performance. This paper aims to evaluate the performance of double u-tube ground heat exchanger(GHX) and verify system feasibility through real-scale experiment. Method: In this study, the real-scale experiment of vertical closed-type GSHP system was conducted using double u-tube GHX and high-efficiency grout. Through the verification experiment, heat source temperature, heat exchange rate(HER) and seasonal performance factor(SPF) were measured according to the long-term operation. In addition, the feasibility analysis was conducted comparing to the single u-tube system. Result: In the results of experiment, average HER was 136.27 W/m and average SPF was 5.41. Furthermore, compared to the single u-tube, the installation cost of the developed system could be reduced about 70% in the same heating load condition.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.5
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• pp.552-559
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• 2005

The evaporation pressure drop of $CO_2$ (R-744) in a horizontal tube was investigated experimentally. The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. The main components of the refrigerant loop are a receiver, a variable-speed pump. a mass flow meter, a pre-heater and evaporator (test section). The test section consists of a smooth. horizontal stainless steel tube of 7.75 mm inner diameter. The experiments were conducted at mass flux of 200 to $500\;kg/m^{2}s$, saturation temperature of $-5^{\circ}C\;to\;5^{\circ}C$. and heat flux of 10 to $40\;kW/m^2$. The test results showed the evaporation pressure drop of $CO_2$ are highly dependent on the vapor qualify, heat flux and saturation temperature. The evaporation pressure drop of $CO_2$ is very lower than that of R-22. In comparison with test results and existing correlations. the best fit of the present experimental data is obtained with the correlation of Choi et al. But existing correlations failed to predict the evaporation pressure drop of $CO_2$. Therefore, it is necessary to develop reliable and accurate predictions determining the evaporation pressure drop of $CO_2$ in a horizontal tube.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.12
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• pp.1134-1139
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• 2004

The evaporative heat transfer coefficient of $CO_2$ (R-744) in a horizontal tube was investigated experimentally. The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and evaporator (test section). The test section consists of a smooth, horizontal stainless steel tube of inner diameter of 7.75 mm. The experiments were conducted at mass flux of 200 to 500 kg/m$^2$s, saturation temperature of -5 to 5$^{\circ}C$, and heat flux of 10 to 40kW/m$^2$. The test results showed the heat transfer of $CO_2$ has a greater effect on nucleate boiling more than convective boiling. Mass flux of $CO_2$ does not affect nucleate boiling too much, and the effect of mass flux on evaporative heat transfer of $CO_2$ is much smaller than that of refrigerant R-22 and R-134a. In comparison with test results and existing correlations, correlations failed to predict the evaporative heat transfer coefficient of $CO_2$, therefore, it is necessary to develope reliable and accurate predictions determining the evaporative heat transfer coefficient of $CO_2$ in a horizontal tube.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.240-241
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• 2005

The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and evaporator(test section). The test section was made of a horizontal stainless steel tube with the inner diameter of 4.57 mm, and length of 4 m. The experiments were conducted at mass flux of 200 to 700 kg/$m^2s$, saturation temperature of 0$^{circ}C$ to 20$^{circ}C$, and heat flux of 10 to 30 kW/$m^2$. The test results showed the evaporation heat transfer of $CO_2$ has great effect on more nucleate boiling than convective boiling. The evaporation heat transfer coefficients of $CO_2$ are highly dependent on the vapor quality, heat flux and saturation temperature. In comparison with test results and existing correlations, correlations failed to predict the evaporation heat transfer coefficient of $CO_2$, therefore, it is necessary to develop reliable and accurate predictions determining the evaporation heat transfer coefficient of $CO_2$ in a horizontal tube.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.2
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• pp.225-233
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• 1995

Experiments were performed to investigate the heat transfer characteristics of nonazeotropic mixture R-22+R-114 in a heat pump system. The ranges of parameter, such as heat flux, mass flow rate, and quality were $8,141{\sim}32,564W/m^2$, 24~58kg/h, and 0~1, respectively. The overall compositions of the mixtures were 50 and 100 per-cent of R-22 by weight for R-22+R-114 mixture. The results indicated that there were distinct different heat transfer phenomena between the pure substance and the mixture. In case of pure refrigerant the heat transfer rates for cooling were strongly dependent upon quality of the refrigerant. Overall evaporating heat transfer coefficients for the mixture were somewhat lower than pure R-22 values in the forced convective boiling region. For a given flow rate, the heat transfer coefficient at the circumferential tube wall(top, side, and bottom of the test tube) for R-22/R-114(50/50wt%)mixture, however, was higher than for pure R-22 at side and bottom of the tube. Furthermore, a prediction for the evaporating heat transfer coefficient of the mixtures was developed based on the method of Yoshida et.al.'s. The resulting correlation yielded a good agreement with the data for the refrigerant mixtures.

• Journal of Power System Engineering
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• v.11 no.1
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• pp.63-69
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• 2007

The evaporation pressure drop of $CO_2$ (R-744) in a horizontal tube was investigated experimentally. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and an evaporator (test section). The test section consists of a smooth, horizontal stainless steel tube of 4.57 mm inner diameter. The experiments were conducted at saturation temperature of $-5^{\circ}C\;to\;5^{\circ}C$, and heat flux of 10 to $40kW/m^2$. The test results showed that the evaporation pressure drop of $CO_2$ are highly dependent on the vapor quality, heat flux and saturation temperature. The measured pressure drop during the evaporation process of $CO_2$ increases with increased mass flux, and decreased saturation temperature. The evaporation pressure drop of $CO_2$ is much lower than that of R 22. In comparison with test results and existing correlations, the best fit of the present experimental data is obtained with the previous correlation. But existing correlations failed to predict the evaporation pressure drop of $CO_2$. Therefore, it is necessary to develop reliable and accurate predictions determining the evaporation pressure drop of $CO_2$ in a horizontal tube.