• 설비공학논문집
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• 제11권5호
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• pp.692-699
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• 1999

The vortex tube is a sample device for separating a compressed gaseous fluid stream into two flows of high and low temperature without any chemical reactions. The phenomena of energy separation through the vortex tube were investigated experimentally, to see the effects of the number of nozzle holes on the energy separation. The experiment was carried out with the number of nozzle holes from 1 to 10 by varying inlet pressure and cold mass fraction. The experimental results were indicated that the effective number of nozzle holes for the best cooling performance was found as 4. Also, to find effective use in a given operation conditions, the temperature difference of cold air and the cooling capacity of vortex tube was compared. The result is that cooling capacity was more important than temperature difference of cold air.

• International Journal of Air-Conditioning and Refrigeration
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• 제16권3호
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• pp.77-82
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• 2008

For heat pumps used in a cold region, it is very important to obtain appropriate heating capacity. Several studies using a variable speed compressor and an additional heater have been performed to enhance heating capacity at low ambient temperatures. However, for outdoor temperature conditions below $-15^{\circ}C$, it is still difficult to obtain enough heating capacity above the rated value. In recent studies, the application of gas injection technique into a two-stage heat pump yielded noticeable heating performance improvement at low temperature conditions. In this study, the heating performance of a two-stage gas injection heat pump with a rated capacity of 3.5 kW was measured and analyzed by varying refrigerant charge amount and EEV opening at the standard heating condition. The heating performance of the two-stage gas injection heat pump was compared with that of a two-stage non-injection heat pump. The heating capacity and COP of the two-stage gas injection heat pump were improved by 2-10% at the optimal charging condition over those of the two-stage non-injection heat pump.

• 설비공학논문집
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• 제28권7호
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• pp.293-298
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• 2016

A three-dimensional (3D) numerical model of the vertical ground-coupled heat exchanger is useful for analyzing the modern ground source heat pump system. Furthermore, a detailed description of the inner side of the exchanger allows to account for the effects of the thermal capacity. Thus, both methods are included in the proposed numerical model. For the ground portion, a FDM (Finite Difference Method) scheme has been applied using the Cartesian coordinate system. Cylindrical grids are applied for the borehole portion, and the U-tube configuration is adjusted at the grid, keeping the area and distance unchanged. Two sub-models are numerically coupled at each time-step using an iterative method for convergence. The model is validated by a reference 3D model under a continuous heat injection case. The results from a periodic heat injection input show that the proposed thermal capacity model reacts more slowly to the changes, resulting in lower borehole wall temperatures, when compared with a thermal resistance model. This implies that thermal capacity effects may be important factors for system controls.

• 설비공학논문집
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• 제16권4호
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• pp.311-317
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• 2004

In the present study, the cooling characteristics of the multi-air conditioner (A/C) using an inverter scroll compressor are experimentally investigated for the number of the indoor units and the operating conditions (2$0^{\circ}C$, 24$^{\circ}C$, 26$^{\circ}C$) under the cooling standard conditions by KS C 9306. In the case of the simultaneous operation for 3 indoor units, the cooling capacity, the mass flow rate and the input power have a decreasing trend and COP has an increasing trend, with decreasing the difference in the operating temperature of the indoor unit and the room temperature. In the case of the simultaneous operation for 2 indoor units, the COP of the indoor unit with large cooling capacity is high when the operating temperature is high, but the COP of the indoor unit with low cooling capacity is high when the operating temperature is low. In the case of the single operation for one unit, when the large cooling capacity of the indoor unit is less than 50％ the compressor operates at the minimum operation frequency region and the COP decreases.

• 설비공학논문집
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• 제25권7호
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• pp.418-426
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• 2013

With advantages of open spaces and existing HVAC facilities, subway station, if unexpected disastrous situation happens on the ground, can be used as a temporary safe place for evacuees. The main objective of this study is to establish a guideline on estimating evacuation capacity of the subway station and evaluating levels of service of evacuation for officials to control the situation. This guideline includes available spaces of the station, capacity of sanitary fixtures, and total number of passengers, etc. In this paper, we first analyzed the number of passengers of SMRT (Line 5~Line 8) during AM peak hour and then evaluated the number of passengers using toilets at that time. In addition, we calculated the seating capacity of subway stations on SMRT using the difference between the actual number of toilets and the estimated number of ones from the occupancy time of each toilet.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 동계학술발표대회 논문집
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• pp.328-333
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• 2007

The purpose of this study is modelling of system air-conditioner for TRNSYS. System air-conditioner is operated by a variable capacity compressor and accommodated by multiple evaporators. By reason of these feature, realizing performance of system air-conditioner for TRNSYS was incomplete. In this study performance data of system air-conditioner and control logics are used to make system air-conditioner module for TRNSYS. Performance data contains total capacity, power input and capacity index of system air-conditioner. The simulation was carried out in a mode of temperature level control using TRNSYS 16. The simulation shows that the system air-conditioner model operate variable capacity and can compute capacity index and power input of system.

• 설비공학논문집
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• 제20권5호
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• pp.321-326
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• 2008

This paper presents and analyzes the effects of on-grid electricity cost, fuel price and initial capital cost of a CHP system, on the optimum DG and AC capacity and NPV, by using the ORNL CHP Capacity Optimizer, which was applied to a library in a university. By considering the current domestic energy cost and initial capital cost, it is shown that the installation and operation of the CHP system is not economical. However, with the current domestic CHP installation cost and fuel price, the NPV achieved by the installation of CHP system is greater when the on-grid electricity price is a factor of ${\times}1.5$ the present value. Regarding the initial capital cost of the CHP system, the reduction of the DG cost is much more economical than that of the AC cost, with respect to NPV. Electricity cost and fuel price have opposite effects on NPV, and NPV is more sensitive to an increase of the electricity cost than an increase of the fuel price.

• 설비공학논문집
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• 제12권3호
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• pp.258-266
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• 2000

Experimental investigation and cycle simulation of a capacity modulation of a heat pump system using a hydrofluorocarbon (HFC) refrigerant mixture, R32/134a as an alternative to R22, have been done. In the cycle simulation, the refrigeration system was operated by assigning the temperatures of the external heat transfer fluids with the heat exchangers generalized by an average effective temperature difference. Heating capacity, cooling capacity, and coefficient of performance (COP) of the system were investigated at several operating conditions. Experimental apparatus which had a refrigeration part and a composition changing part was built, and the performance of the heat pump system filled with R32/134a mixture was investigated. A gas-liquid separator was used in the experiment to change the composition by collecting the vapor and the liquid Phase separately, The mass fraction of the charged refrigerant in the heat pump system was 40/60 and 70/30 by weight percentage. The composition of the refrigerant with initial composition of 40/60 varied from 29/71 to 41/59 in the refrigeration cycle. For the refrigerant with initial composition of 70/30, the composition varied from 65/35 to 75/25.

• 설비공학논문집
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• 제17권10호
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• pp.883-890
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• 2005

In this study, 2 pure hydrocarbon refrigerants of R1270 (Propylene) and R290 (Propane) and 3 binary mixtures composed of R1270, R29O and R152a were tested in a refrigerating bench tester with a scroll compressor in an attempt to substitute R502 used in most of the low temperature applications. The test bench provided 3\sim3.5$ kW capacity and water and water/glycol mixture were employed as the secondary heat transfer fluids. All tests were conducted under the same external conditions resulting in the average saturation temperatures of -28 and $45^{\circ}C$ in the evaporator and condenser, respectively. Test results showed that all refrigerants tested had $9.6\sim18.7\%$ higher capacity and $17.1\sim27.3\%$ higher COP than R502. The compressor discharge temperature of R1270 was similar to that of R502 while those of all other refrigerants were $23.7\sim27.9\%$ lower than that of R502. For all alternative refrigerants, the amount of charge was reduced up to $60\%$ as compared to R502. Overall, these alternative refrigerants offer better system performance and reliability than R502 and can be used as long term substitutes for R502 due to their excellent environmental properties.

• 설비공학논문집
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• 제5권1호
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• pp.73-83
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• 1993

Thermodynamic properties of alternatives for R12 and R22 were estimated and performances of refrigerating cycle using these refrigerants were compared. In this study, we adopt R134a, R22/R142b, R22/R152a, R22/R152a/R124 as alternatives for R12 and R32/R134a for R22. Thermodynamic properties of these refrigerants were estimated using modified CSD equation of state. Cycle simulations of the refrigerating system considering heat source were carried out in order to compare the performance of the system. R134a shows relatively lower COP than R12 but very similar VCR. R22/R142b(50/50 mass fraction), R22/R152a(10/90), R22/R152a/R124(30/25/45) are good for the substitutes of R12 and R32/R134a(30/70) is appropriate for that of R22 in view of COP and VCR.