• Title/Summary/Keyword: Variable capacity refrigeration

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Experimental Study on Superheat Control of a Variable Speed Heat Pump (가변속 열펌프의 과열도 제어특성에 관한 실험적 연구)

  • 최종민;김용찬;하진호
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.4
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    • pp.233-241
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    • 2001
  • In the present study, various experiments were performed to investigate the capacity modulation and transient response control using a variable speed compressor and electronic expansion valve(EEV). Based on the experimental results, the operation control algorithm and real time digital control system were constructed to adjust the superheat at the inlet of the compressor. Superheat control was fulfilled using both the PI feedback controller and PI controller combined with a feedforward concept. As a result, the tracking performance of the latter was better than that of former.

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An Experimental Study on Flow Characteristics for Dual-Structured Orifice (이중구조 오리피스 팽창장치의 유동특성에 관한 실험적 연구)

  • 곽경민;김하덕;이중형;배철호;김종엽
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.14 no.12
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    • pp.1039-1046
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    • 2002
  • To investigate the characteristics of orifice as an expansion devices, the experimental apparatus was made and experiments are being peformed using R22 and R290. The main idea of this control method of refrigerant flow rate with coupled orifices is to control the ON/OFF state of T and Ball type orifice corresponding to the subdivided region of thermal load. When system requires minimum thermal load, both T and Ball type orifices are closed, but refrigerant can flow through small hole of T type orifice. In regular thermal load, when ball type orifice is closed, T type orifice is opened and mass flow rate increase more than OFF state of T type orifice, due to large diameter. In maximum thermal load, both T and Ball type orifices are open and the much refrigerant can flow. The flow characteristics on T type orifice and parallel-combined orifice are obtained in the subdivided region of thermal load.

Thermal Load Simulation Analysis on Model Building Estimating Optimum Heat Source Capacity (최적 열원용량 산정을 위한 모델건물 공조부하 시뮬레이션 분석)

  • Park, Jong-Il;Kim, Se-Hwan;Lee, Sung
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.19 no.6
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    • pp.427-433
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    • 2007
  • Generally, H.V.A.C load capacity in early planning phase can presume with maximum thermal load. Basic data can prove by air conditioning equipment system data analysis at existing building. There are poor and not reliable alternative presentation. In this paper, measured data after use H.V.A.C load calculation K-load program reply choosing standard building and variables simulation. And I founded peak load correlation graph and mode for several kinds of variable and contents of size. I wish that equipment designer is beaconed to produce optimum capacity at building as quantitative through this result.

Practical Modeling and PI Controller Design for Centrifugal Water Chillers (터보냉동기를 위한 실용적 모델링과 PI 제어기 설계)

  • Jeong, Seok-Kwon;Han, Sung-Joon;Jung, Young-Mi
    • 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.

Comparison of Performance in CO2 Cooling System with an Ejector for Various Operating Conditions (다양한 운전조건에서 이젝터를 적용한 CO2 냉동기의 성능비교)

  • Kang, Byun;Cho, Hong-Hyun
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.23 no.7
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    • pp.505-512
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    • 2011
  • Recently, many researchers have analyzed the performance of the transcritical $CO_2$ refrigeration cycle in order to identify opportunities to improve the system energy efficiency. The reduction of the expansion process losses is one of the key issues to improve the efficiency of the transcritical $CO_2$ refrigeration cycle. In this study, the analytical study on the performance characteristics of $CO_2$ cycle with an ejector carried out with a variation of outdoor temperature, gascooler inlet air velocity, evaporator inlet air velocity, and evaporator inlet air temperature. As a result, the system performance could be improved over 85% by using an ejector for various operating condition because of the reduction of compressor work. Moreover, the cooling capacity increased about 18% for variable outdoor condition. Therefore, the high performance of an ejector system could be maintained for wide operating conditions and system reliability could be improved compared to that of a basic system.

Effects of Gas Injection on the Heating Performance of a Two-Stage Heat Pump Using a Twin Rotary Compressor with Refrigerant Charge Amount

  • Heo, Jae-Hyeok;Jeong, Min-Woo;Jeon, Jong-Ug;Kim, Yong-Chan
    • International Journal of Air-Conditioning and Refrigeration
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    • v.16 no.3
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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.

Study on the Performance of a Variable Speed Cascade Heat Pump under Various Operating Conditions (운전조건에 따른 가변속 캐스케이드 열펌프의 성능 특성 연구)

  • Jeong, Kwangmoo;Choi, Jong Min
    • Journal of the Korean Society for Geothermal and Hydrothermal Energy
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    • v.9 no.2
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    • pp.1-7
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    • 2013
  • Most researches done on heat pumps have been on heat pumps for refrigeration, cooling and heating. There is therefore the need for more research on hot water heat pumps, especially for high temperature. Even though the cascade heat pump cycle has a great potential more efficient hot water generation even at low evaporating temperatures, it has been researched least for this purpose. In this study, the heating performance of a variable speed cascade heat pump was investigated by varying operating conditions. For the same heating capacity values, it was found that increasing the low stage compressor speed was more suitable for enhancing the performance of the system to get a higher temperature.

Analysis of Thermal Control Characteristics of VCHP by the Charging Mass of Non-Condensible Gas

  • Suh, Jeong-Se;Park, Young-Sik;Chung, Kyung-Taek;Kim, Byoung-Gi
    • International Journal of Air-Conditioning and Refrigeration
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    • v.14 no.4
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    • pp.125-130
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    • 2006
  • This study has been performed to investigate the thermal performance of variable conductance heat pipe (VCHP) with screen meshed wick. The active length of condenser section in a VCHP is varied by non-condensible gas, which controls the operating temperature, and the heat capacity of VCHP is controlled by the operating temperature. In this study, numerical analysis of the VCHP based on the diffusion model of non-condensible gas is done for the thermal control performance of VCHP. Water is used as a working fluid and nitrogen as a control non-condensible gas in the copper tube. As a result, the thermal conductance of VCHP has been compared with that of constant conductance heat pipe (CCHP) corresponding to the variation of operating temperature.

Analysis of Thermal Control Characteristics of VCHP by the Charging Mass of Non-Condensible Gas (불응축가스 주입량에 따른 VCHP의 열제어 특성)

  • Suh Jeong-Se;Park Young-Sik;Chung Kyung-Taek
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.12
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    • pp.1139-1144
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    • 2005
  • This study has been performed to investigate the thermal performance of variable conductance heat pipe (VCHP) with meshed wick. The length of condenser portion in a VCHP is varied by the expansion of inert gas with the operation temperature, and the heat transport capacity is thus varied with the operating temperature. In this study, numerical evaluation of the VCHP is made for the thermal performance of VCHP, based on the diffusion model of inert gas. Water is used as a working fluid and nitrogen as a control inert gas in the copper tube. As a result, the thermal performance of VCHP has been compared with that of constant conductance heat pipe (CCHP) according to the variation of operation temperature. Maximum heat transport capacity of VCHP is mainly presented for operation temperature and the variation of operation temperature is also presented for heat transfer rate of VCHP.

Experimental Study on the Performance of Heat Pump Using Refrigerant Mixture R22/R142b (R22/R142b 혼합냉매를 사용한 열펌프의 성능)

  • Kim, M.S.;Chang, S.D.;Ro, S.T.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.4 no.1
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    • pp.33-47
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    • 1992
  • Experimental investigation on the performance of a heat pump system using refrigerant mixtures is done. The condenser and the evaporator are double pipe heat exchangers of counter flow type and the compressor is driven by a variable speed motor. The refrigerant mixture used in the experiment is R22/R142b. Experiments are performed by changing the compressor speed, composition on ratio of mixture, and the average temperatures of condenser and evaporator. The compressor work, heating capacity and the coefficient of performance are calculated. Results show that the heating capacity can be changed by varying the mass flow rate of refrigerant mixtures to meet the heating load. It is shown that the capacity control by changing the composition ratio is more effective than by changing the compressor speed. Under the condition where the external conditions are fixed and the heating loads are equal, the coefficient of performance has its maximum value near 50 : 50 mass fraction of the refrigerant mixture in this study.

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