• Journal of Power System Engineering
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• v.20 no.6
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• pp.11-19
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• 2016

A variable speed refrigeration system(VSRS) has been received high attention for energy saving ability. This paper investigates effects of design factors such as membership function range and sampling time to control performances for systematical designing fuzzy logic controller of the VSRS. Some comparisons of control performance between the fuzzy and PI are conducted including comparative evaluation of robustness against noise by using computer simulations. The simulation results showed that the fuzzy is very useful design method for engineers in the industrial fields which have big noises system and deal with inherent nonlinear system like the VSRS.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.5
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• pp.382-388
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• 2003

Refrigerant flow rates of the multi-type air-conditioning system can be regulated by electronic expansion valves (EEV). The performance of the multi-type air-conditioning system may be improved by lowering the superheat at the compressor suction side. In this study, a superheat temperature setpoint reset algorithm was developed by using fuzzy logics, and a PI algorithm was applied to control the superheat temperature near setpoints. Experimental results showed energy savings and stable operations at a multi-type air-conditioning system. Therefore, the developed setpoint reset algorithm may be effectively used for the EEV superheat temperature control of the multi-type air-conditioning system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.6
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• pp.294-300
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• 2014

In this study, we investigated and evaluated the air conditioning operation of the driver according to the temperature difference between the inside and outside of a car parked outside during the summer. We suggest including a comfort mode to the car air conditioning system to improve the thermal comfort of the driver, in which the comfort can be maintained for a longer time. For the a result of our experiment, in the cases with temperature of above $45^{\circ}C$ inside of the car, the subjects preferred strong air blow with the face and the arms in the direction of the blow. In the cases with temperature of below $40^{\circ}C$ inside of the car, the subjects preferred lower volume of air blow. In the temperature below $28.1^{\circ}C$ inside of the car, the mean temperature on the skin of the driver reached the comfort zone.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.3
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• pp.240-246
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• 2002

Bypass air conditioning systems are divided into three types; an outdoor air bypass, a mixed air bypass and a return air bypass system. What makes the return air by pass system more effective is that it directs all of moist outdoor air through the cooling coil. The bypass air conditioning system can maintain indoor R.H (Relative Humidity) less than a conventional CAV (Constant Air Volume) air conditioning system by adjusting face and bypass dampers at part load. When a design sensible load (the ratio of sensible load to total sensible load) is 70 percent (at this time, RSHF (Room Sensible Heat Factor) . 0.7), indoor R.H was maintained 59 percent by the return air bypass system, but 65 percent by the conventional CAV air conditioning system (valve control system). The bypass air conditioning system can also improve IAQ (Indoor Air Quality) in many buildings where the number of air change is high.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.712-717
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• 2001

This paper investigates the control problem of evaporator superheat, i.e., the difference between the temperature of the refrigerant at the entrance region of an evaporator and that at the exit region, for multi-type air-conditioning/refrigeration systems. Mathematical equations describing the characteristics of compressor, condenser, evaporator, and electronic expansion valve are first derived. Then, the transfer functions from the current input of the electronic expansion valve to wall temperatures of evaporator tube at two-phase region and superheated region, respectively, are derived. The stability and performance of the closed loop system with a PI controller are analyzed by Nyquist stability criterion. Simulation results are provided.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.12
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• pp.782-790
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• 2011

Typical temperature control methods of a cooler for machine tools are hot-gas bypass and compressor variable speed control. The hot-gas bypass system has been widely used to control the cooler temperature in many general industrial fields. On the contrary, the compressor variable speed control is focused on special fields such as aerospace and high precision machine tools which need high precision control. The variable speed control system usually has two control variables such as target temperature and superheat. In other words, the variable speed control system is basically multi-input multi-output(MIMO) system. In spite of MIMO system, the proportional integral derivative(PID) feedback control methodology that based on single-input single-output (SISO) system is generally used for designing the variable speed control system. Therefore, it is inevitable to describe transfer functions for dynamic behaviors of every controlled variables and decide the PID gains with tremendous iteration process. Moreover, the designed PID gains do not provide optimum system performances. To solve these problems, high performance controller design method based on a state space model is suggested in this paper. An optimum controller is designed to minimize both control errors and energy inputs. This method was more simple to describe dynamic behaviors and easier to design the cooler controller which is MIMO system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.7
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• pp.587-595
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• 2006

A system operating algorithm was developed for the effective operation of a multi-type air-conditioning system. The system operating algorithm includes control algorithms for a safety mode, an initial operating mode, a stabilization mode, a fault diagnosis mode, an efficiency mode, and a tracking mode. Various tests were performed to show the effectiveness of these algorithms. Tests showed good results for the operation of a multi-type air-conditioning system. Therefore, these algorithms developed for this study may be used for the effective control of a multi-type air-conditioning system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.928-936
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• 1999

An experimental study was performed to investigate characteristics of an inverter driven water-to-water refrigeration system with a variation of compressor frequencies and expansion devices. The frequency of a compressor varied from 30Hz to 75Hz, and performance of the systems applying three different expansion devices such as capillary tube, thermostatic expansion valve(TXV), and electronic expansion valve(EEV) were measured. The load conditions were altered by varying the temperature of the secondary fluid entering condenser and evaporator with a constant flow rate. When the test conditions were deviated from the standard value(rated value), TXV and EEV showed better performance than capillary tube due to optimum control of mass flow rate and superheat. In the present study, it was observed that the variable area expansion device had better performance than constant area expansion device in an inverter refrigeration system due to active control of flow area with a change of compressor frequency and load conditions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.4
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• pp.187-194
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• 2015

This paper describes the PI controller design based on a practical transfer function model for centrifugal water chillers. The rotational speed of a compressor and the opening angle of an electronic expansion valve were simultaneously regulated as manipulated variables to maintain temperature reference and to ensure high efficiency of the chiller. The COP according to the change in each variable was investigated by performing some static experiments, and it was reflected in the PI controller design to accomplish the high efficiency control. Especially, the practical transfer function model of the chiller was built based on the dynamic experimental data considering the strong inherent non-linearity and complexity of the chiller system. The validity of the designed PI controller was proven by some experimental results using the test facility and the results were also compared to the conventional evaporating pressure control results.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.8
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• pp.780-786
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• 2001

For the compressor speed control of a multi-type air conditioning system, a fuzzy control algorithm was developed. The sum of zone temperature errors and its derivative were used as input variables, and the compressor speed was selected as the output variable. To test the effectiveness of the control algorithm, one outdoor environmental chamber and four indoor environmental chambers were used. In the chambers the zone temperature step change test and the indoor unit change over test were performed. Test results showed that, for the control of compressor speed, the fuzzy control algorithm was more effective than the conventional proportional control algorithm for the energy conservation.