• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1332-1336
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• 2009

If water-chillers are arranged in series-series counterflow, compressor lift of each chiller will be decreased in comparison with water-chillers in parallel. That means that compressor power of the chillers in series will be lower than that of chillers in parallel. However, the pressure drop of the water flow through the chillers in series will increase, and thus increase the power of water pumps. This disadvantage will be made good by increasing the temperature difference of water flow through evaporator and condenser, but the water flow rates will decrease. This paper explores the optimal parameters in system of series-series counterflow for central chilled water plants such as the leaving chilled water temperature, the leaving condenser water temperature, condenser water flow rate and number of chillers in series.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.910-915
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• 2009

For large reciprocating compressors in parallel operation, an analytical study has been carried out on the gas pulsation in associated discharge piping lines. Since the pressure pulsation at a valve, valve dynamics, and the gas flow rate through the valve are interrelated, affecting one another, these need to be solved simultaneously. Acoustic transfer matrix method, which relates acoustic pressure and velocity at one location to those at another location, has been adopted to calculate the effect of the gas flow at one valve location on the gas pulsation at other valve locations.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.8
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• pp.746-756
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• 2001

An experimental study was conducted to investigated the effect of refrigerant flow control on the performance of a variable-speed heat pump operating in both cooling and heating mode. For this purpose, cooling and heating capacity, EER and refrigerant mass flow rate corresponding to an electronic valve as well as a capillary tube were measured as functions of compressor speed, length of capillary tube (or valve opening of the electronic valve), refrigerant charge, and outdoor temperature. From the comparison of experimental results, it was found that the performance variation due to the electronic valve opening became significant as the operating conditions(outdoor temperature and compressor speed) deviated from the standard condition at which heating capacity and EER were rated for the indicated capillary tube.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.469-473
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• 2005

Capacities of a tandom-type air-conditioner may be modulated by turning on/off multiple compressors and adjusting positions of a electronic expansion valve. In this study. control algorithms for compressors and a electronic expansion valve were developed by using fuzzy’ logics. There algorithms were implemented in a test lab and proved to be effective for the control of indoor air temperature and superheat temperature.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.474-479
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• 2005

For the safe operation of an air conditioner, the liquid car η 'over to compressors should be minimized and compressors should be operated in the specified region of suction and discharge pressures recommended by compressor manufactures. In this study, a capillary assisted tandem-type airconditioner was considered. A variable speed outdoor fan was used to control operating points of the system. Test results showed the possibilities to move system operating points to the safe region by controlling the speed of an outdoor fan.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.9
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• pp.810-817
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• 2001

Performance of a water-to-water multi-type heat pump system using R22 which has tow indoor units has been investigated experimentally. The refrigerant flow rate of each indoor unit was regulated by an electronic expansion valve and the total refrigerant flow rate of the system was controlled by a variable speed compressor. In the system, evaporator outlet pressure of refrigerant and outlet temperatures of secondary fluid from indoor units were selected as control variables. Experiments were executed for both cooling and heating modes using PID control method with fuzzy logic, and results of the test are compared with a classical PID method. In the case of PID control with fuzzy logic, the fuzzy control rules corrects PID parameters each time. Results show that PID control with fuzzy logic has the merits of quick response and reduced overshoot.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.10
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• pp.843-851
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• 2003

The present paper studies the leakage flow model used in the performance prediction of a scroll compressor. Two leakage flow models, isentropic and Fanno flow model, are studied in detail. Their predictions are also compared with CFD solutions to check the validity as a leakage flow model. Comparison with CFD solutions shows that the isentropic flow model predicts excessive leakage flow rate, while the Fanno flow model shows acceptable agreement with CFD solutions. The excessive leakage flow rate by isentropic flow model results in under-prediction of the overall performance of a scroll compressor.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.4
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• pp.536-544
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• 1997

This study presents test results of a residential window system air-conditioner using R22 and two potential alternative refrigerants, R407C and R410B. A series of performance tests was performed for the basic and liquid-suction heat exchange cycle in a psychrometric calorimeter test facility. For R407C, the same rotary compressor was used as in the R22 system. However, compressor for the R410B system was modified to provide the similar cooling capacity. The evaporator circuit was changed to get a counter-cross flow heat exchanger to take advantage of zeotropic mixture's temperature glide, and liquid-line suction-line heat exchange cycle was also considered to improve the performance of the system. Test results were compared to those for the basic R22 system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.11
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• pp.1079-1088
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• 2001

A dynamic simulation model was developed to analyse the transient characteristics of a multi-inverter heat pump. The programs included a basic air conditioning system such as a evaporator, condenser, compressor, linear electronic expansion valve (LEV) and by-pass circuit. The theoretical model was derived from mass conservation and energy conservation equations to predict the performance of the multi-inverter heat pump at various operating conditions. Calculated results were compared with the values obtained from the experiments at different operation frequencies of compressor, area of the LEV and configuration of indoor units operation. The results of the simulation model showed a good agreement with the experimental ones, so that the model could be used as an efficient tool for thermodynamic design and control factor design of air-conditioners.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.2
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• pp.262-269
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• 1999

The application of hydrocarbon refrigerant mixtures in a hermetic reciprocating compressor for dehumidifier is investigated. The selected refrigerants are R12, R134a, HC-Blend (R290/R600a), CX(R152a/R600a) and OS-l2a. Both theoretical and experimental investigations have been performed for the selected refrigerants. The test results of hydrocarbon refrigerants have been compared to traditional refrigerant(R12) and R134a. The results show that hydrocarbon refrigerant mixtures(HC-Blend, CX and OS-l2a) are very good alternatives in the refrigeration system for R12 and R134a.