The Experts below are selected from a list of 618 Experts worldwide ranked by ideXlab platform

Y X Xu - One of the best experts on this subject based on the ideXlab platform.

  • research on the control laws of the electronic Expansion Valve for an air source heat pump water heater
    Building and Environment, 2011
    Co-Authors: Mingliu Jiang, J Y Wu, R Z Wang, Y X Xu
    Abstract:

    Compared to the conventional air conditioner, the air source heat pump water heater (ASHPWH) possesses wider operating ranges and more dramatic changes in working conditions. Conversely, traditional throttle devices, such as the Thermostatic Expansion Valve (TEV) and capillary tube, are restricted by narrow regulating ranges in refrigerant mass flow rate and lagging response to the superheat. This article incorporates a novel dual-fuzzy-controller to regulate the electronic Expansion Valve (EEV) specialized for the ASHPWH system. The study analyzes the effects of the EEV initial opening and the target superheat on the performance of the ASHPWH. Moreover, this research proposes a fuzzy control method of selecting the initial opening and the target superheat on the basis of the ambient temperature and water temperature, and employs superheat error (e) and the derivation of superheat error (ec) as the input variables of the fuzzy controller B to regulate the opening of the EEV during steady running process. To improve self-adaptability of the fuzzy controller, a rule modifier and a gain scheduler are introduced. In order to quantitatively reflect the difference in the performance between the TEV-controlled system and EEV-controlled one, experimental comparison between the EEV and the TEV is presented. Results demonstrate that both the stability and efficiency of the ASHPWH can be improved significantly by the EEV.

  • experimental performance analysis on a direct Expansion solar assisted heat pump water heater
    Applied Thermal Engineering, 2007
    Co-Authors: Yonglu Li, R Z Wang, J Y Wu, Y X Xu
    Abstract:

    Abstract A direct Expansion solar assisted heat pump water heater (DX-SAHPWH) experimental set-up is introduced and analyzed. This DX-SAHPWH system mainly consists of 4.20 m 2 direct Expansion type collector/evaporator, R-22 rotary-type hermetic compressor with rated input power 0.75 kW, 150 L water tank with immersed 60 m serpentine copper coil and external balance type Thermostatic Expansion Valve. The experimental research under typical spring climate in Shanghai showed that the COP of the DX-SAHPWH system can reach 6.61 when the average temperature of 150 L water is heated from 13.4 °C to 50.5 °C in 94 min with average ambient temperature 20.6 °C and average solar radiation intensity 955 W/m 2 . And the COP of the DX-SAHPWH system is 3.11 even if at a rainy night with average ambient temperature 17.1 °C. The seasonal average value of the COP and the collector efficiency was measured as 5.25 and 1.08, respectively. Through exergy analysis for each component of the DX-SAHPWH system, it can be calculated that the highest exergy loss occurs in the compressor, followed by collector/evaporator, condenser and Expansion Valve, respectively. Further more, some methods are suggested to improve the thermal performance of each component and the whole DX-SAHPWH system.

  • Experimental performance analysis on a direct-Expansion solar-assisted heat pump water heater
    Applied Thermal Engineering, 2007
    Co-Authors: Y.-w. Li, Ruzhu Wang, Jingyi Wu, Y X Xu
    Abstract:

    A direct Expansion solar assisted heat pump water heater (DX-SAHPWH) experimental set-up is introduced and analyzed. This DX-SAHPWH system mainly consists of 4.20 m2 direct Expansion type collector/evaporator, R-22 rotary-type hermetic compressor with rated input power 0.75 kW, 150 L water tank with immersed 60 m serpentine copper coil and external balance type Thermostatic Expansion Valve. The experimental research under typical spring climate in Shanghai showed that the COP of the DX-SAHPWH system can reach 6.61 when the average temperature of 150 L water is heated from 13.4 ??C to 50.5 ??C in 94 min with average ambient temperature 20.6 ??C and average solar radiation intensity 955 W/m2. And the COP of the DX-SAHPWH system is 3.11 even if at a rainy night with average ambient temperature 17.1 ??C. The seasonal average value of the COP and the collector efficiency was measured as 5.25 and 1.08, respectively. Through exergy analysis for each component of the DX-SAHPWH system, it can be calculated that the highest exergy loss occurs in the compressor, followed by collector/evaporator, condenser and Expansion Valve, respectively. Further more, some methods are suggested to improve the thermal performance of each component and the whole DX-SAHPWH system. ?? 2006 Elsevier Ltd. All rights reserved.

Dong Huang - One of the best experts on this subject based on the ideXlab platform.

  • comparison between fixed opening and variable opening throttling on two circuit evaporator performance under water maldistribution
    Applied Thermal Engineering, 2019
    Co-Authors: Rijing Zhao, Dong Huang, Xueyuan Peng, Hao Yang
    Abstract:

    Abstract Water maldistribution in the two-circuit evaporator was found to induce instabilities, and further deteriorate capacity of the refrigeration system. As a follow-up study, this article presents a comparison between throttling types on the two-circuit evaporator performance under water maldistribution. The evaporator had two circuits of the same specifications, and a fixed-opening Valve (FOV) and a Thermostatic Expansion Valve (TEV) were accessed alternatively. Results show that water maldistribution aroused random oscillations in overall outlet temperature/superheat under FOV throttling, and further triggered hunting under TEV throttling and prompted system parameters into periodic oscillations. With water maldistribution increased, oscillation amplitude in overall outlet superheat increased first but decreased later under FOV throttling with the transition from unstable to stable refrigerant flow. However, it kept increasing under TEV throttling due to greater fluctuation in refrigerant supply during hunting conditions. Moreover, capacity of the circuit with larger water flowrate increased monotonously under FOV throttling, but increased first and decreased later after hunting occurred under TEV throttling, which dominated the faster reduction in overall capacity of the two-circuit evaporator in the TEV loop. The comparison suggests that in off-design conditions, variable-opening throttling might perform worse in stability and energy efficiency than fixed-opening throttling.

  • effect of water maldistribution in multi circuit evaporator on superheat control dynamics of Thermostatic Expansion Valve refrigeration system
    Applied Thermal Engineering, 2017
    Co-Authors: Rijing Zhao, Dong Huang, Yongqiang Leng, Zhenya Zhang
    Abstract:

    Abstract Air/water mal-distribution widely occurs in multi-circuit evaporators, and may deteriorate the stability of Thermostatic-Expansion-Valve (TEV) controlled systems. In this article, effect of water maldistribution on superheat control dynamics of a TEV system was studied experimentally. The evaporator had two circuits, with the overall outlet superheat controlled by TEV. By regulating the smaller water percentage of Circuit 2 ( F 2 ) from 36.9% to 9.1%, the system underwent the stable period ( F 2 from 36.9% to 27.0%) and the hunting period ( F 2 from 21.2% to 9.1%) sequentially. In the latter period, temperature and pressure parameters of the evaporator oscillated over time. Moreover, the lag of evaporator outlet temperature responses behind TEV actions was found and considered to be a reason of hunting. The resultant superheat oscillation dynamics were also analyzed at both circuit outlets and the overall outlet, and we found that evaporator overall outlet superheat was highly influenced by the non-uniform water distribution and the final merging of the paralleled circuits.

  • effects of water mal distribution on Thermostatic Expansion Valve stability and its controlled two circuit evaporator performance
    International Journal of Refrigeration-revue Internationale Du Froid, 2014
    Co-Authors: Dong Huang, Rijing Zhao, Qinqin Gong, Xueqiang Tang
    Abstract:

    Effects of water mal-distribution on Thermostatic-Expansion-Valve (TEV) stability and its controlled two-circuit evaporator performance were investigated experimentally and numerically. 7 sets of water mal-distribution were obtained with Circuit 2 water percentage (F2) from 36.9% to 9.1%. Results showed that the TEV control-loop was stable with F2 from 36.9% to 27.0%, and the overall evaporator capacity decreased by 3.4%. However, hunting occurred with F2 from 27.0% to 9.1% due to the evaporator outlet superheat smaller than the TEV minimal stable signal (MSS), hence system parameters such as evaporator pressures and temperatures oscillated over time. Hunting introduced a sharp decrease in the refrigerant flowrate to the evaporator, thus the overall evaporator capacity decreased by 14.1%. With water mal-distribution rate increased, the decrease in overall evaporator capacity was mainly attributed to Circuit 2 with smaller overall heat transfer coefficient.

  • Effects of air flow maldistribution on refrigeration system dynamics of air source heat pump chiller under frosting conditions
    Energy Conversion and Management, 2008
    Co-Authors: Jianying Gong, Xiuling Yuan, Dong Huang
    Abstract:

    The effects of air flow maldistribution on the performance of an air source heat pump chiller under frosting conditions were investigated experimentally. The results indicated that air flow maldistribution was the dominant factor leading to hunting of the Thermostatic Expansion Valve for medium and/or large size finned tube evaporators. With air flow maldistribution degree (AMD) increasing, frost occurred earlier, and the frost layer grew faster. The operating characteristics became lower when AMD was increased. We found such phenomenon seemed to be related to both the difference of refrigerant outlet superheat and the frosting velocity. In the hunting stage, the frost block effect became the main factor degrading the refrigeration system performance. With AMD increasing, the heat pump system pertinent performance data (suction pressure, evaporation temperature, discharge pressure, refrigerant outlet temperature, etc.) were degraded more dramatically.

  • dynamic characteristics of an air to water heat pump under frosting defrosting conditions
    Applied Thermal Engineering, 2007
    Co-Authors: Dong Huang, Zhilong He, X.l. Yuan
    Abstract:

    The dynamic characteristics of a medium air-to-water heat pump with multi-circuit evaporator controlled by the Thermostatic Expansion Valve (TEV) under the frosting/defrosting conditions were investigated experimentally. The airflow maldistribution often occurs if the fin-and-tube heat exchangers in a medium heat pump are arranged in V-type or W-type position with the fan at the top. The experimental results show that the airflow maldistribution will result in the intermittent or unceasing hunting during the frosting period, which is not published in public yet. The airflow uniformity causes every circuit to see the different airflow rates. The liquid refrigerant was not evaporated completely in some circuits with the less airflow rate and a little liquid refrigerant flowed out at the outlet, which resulted in less superheat than the necessary MSS (minimum-stable-signal) of the TEV at the outlet of the evaporator. The TEV had the intermittent hunting during the first two-thirds of the frosting period. Afterwards, the combination of the airflow maldistribution and the airflow drop caused by the frost blocking resulted in more liquid refrigerant flowing out of the evaporator. Hence, the TEV had the unceasing hunting during the last one-third of the frosting period. Finally, the operating parameters for both the low-pressure and the high-pressure sides have the intermittent or unceasing hunting during the frosting period, which synchronized with that of the TEV.

R Z Wang - One of the best experts on this subject based on the ideXlab platform.

  • research on the control laws of the electronic Expansion Valve for an air source heat pump water heater
    Building and Environment, 2011
    Co-Authors: Mingliu Jiang, J Y Wu, R Z Wang, Y X Xu
    Abstract:

    Compared to the conventional air conditioner, the air source heat pump water heater (ASHPWH) possesses wider operating ranges and more dramatic changes in working conditions. Conversely, traditional throttle devices, such as the Thermostatic Expansion Valve (TEV) and capillary tube, are restricted by narrow regulating ranges in refrigerant mass flow rate and lagging response to the superheat. This article incorporates a novel dual-fuzzy-controller to regulate the electronic Expansion Valve (EEV) specialized for the ASHPWH system. The study analyzes the effects of the EEV initial opening and the target superheat on the performance of the ASHPWH. Moreover, this research proposes a fuzzy control method of selecting the initial opening and the target superheat on the basis of the ambient temperature and water temperature, and employs superheat error (e) and the derivation of superheat error (ec) as the input variables of the fuzzy controller B to regulate the opening of the EEV during steady running process. To improve self-adaptability of the fuzzy controller, a rule modifier and a gain scheduler are introduced. In order to quantitatively reflect the difference in the performance between the TEV-controlled system and EEV-controlled one, experimental comparison between the EEV and the TEV is presented. Results demonstrate that both the stability and efficiency of the ASHPWH can be improved significantly by the EEV.

  • transient characteristics and performance analysis of a vapor compression air conditioning system with condensing heat recovery
    Energy and Buildings, 2010
    Co-Authors: Mingliu Jiang, Jingyi Wu, Yu Xiong Xu, R Z Wang
    Abstract:

    The objective of this study is to evaluate the influence of condensing heat recovery on the dynamic behavior and performance of air conditioners. The article includes a test procedure utilized to evaluate the condensing heat recovery system, relevant experimental results, a detail analysis of the mechanisms, and improvement measure on such a system. The experimental results indicate that although the condensing heat recovery has a negative effect on the cooling capacity at the start of the heat recovery process, the average cooling coefficient of performance (COP) of the system can be improved. The study also incorporates a control scheme of the electronic Expansion Valve (EEV) of the condensing heat recovery system. The experimental comparison between the EEV and the Thermostatic Expansion Valve (TEV) demonstrates that the EEV has better performance in both stability and efficiency in the condensing heat recovery system.

  • experimental performance analysis on a direct Expansion solar assisted heat pump water heater
    Applied Thermal Engineering, 2007
    Co-Authors: Yonglu Li, R Z Wang, J Y Wu, Y X Xu
    Abstract:

    Abstract A direct Expansion solar assisted heat pump water heater (DX-SAHPWH) experimental set-up is introduced and analyzed. This DX-SAHPWH system mainly consists of 4.20 m 2 direct Expansion type collector/evaporator, R-22 rotary-type hermetic compressor with rated input power 0.75 kW, 150 L water tank with immersed 60 m serpentine copper coil and external balance type Thermostatic Expansion Valve. The experimental research under typical spring climate in Shanghai showed that the COP of the DX-SAHPWH system can reach 6.61 when the average temperature of 150 L water is heated from 13.4 °C to 50.5 °C in 94 min with average ambient temperature 20.6 °C and average solar radiation intensity 955 W/m 2 . And the COP of the DX-SAHPWH system is 3.11 even if at a rainy night with average ambient temperature 17.1 °C. The seasonal average value of the COP and the collector efficiency was measured as 5.25 and 1.08, respectively. Through exergy analysis for each component of the DX-SAHPWH system, it can be calculated that the highest exergy loss occurs in the compressor, followed by collector/evaporator, condenser and Expansion Valve, respectively. Further more, some methods are suggested to improve the thermal performance of each component and the whole DX-SAHPWH system.

Jose Fernandezseara - One of the best experts on this subject based on the ideXlab platform.

  • experimental evaluation of a geothermal heat pump for space heating and domestic hot water simultaneous production
    Renewable Energy, 2012
    Co-Authors: Jose Fernandezseara, Alejandro Pereiro, Santiago Bastos, Alberto J Dopazo
    Abstract:

    This paper deals with the experimental performance evaluation of a geothermal heat pump (GHP) intended to produce space heating (SH) and domestic hot water (DHW) simultaneously. The GHP uses R407C as refrigerant and its main components are a scroll compressor, a Thermostatic Expansion Valve, a plate heat exchanger as evaporator and a condensing section composed of two plate heat exchangers connected in series, operating as a desuperheater and a condenser. In the condensing section, water is heated at two temperature levels for the SH and DHW systems. The experimental results realize the high influence of the water temperature at the condensing section inlet on the GHP behaviour. The COP and the heating capacity decrease 48.7% and 5.6% by increasing the water temperature at the condenser inlet from 20 to 50 °C, respectively. The percentage of water flow rate diverted to the desuperheater for DHW production depends on the water temperature and flow rate at the condensing section inlet. However, the heat transfer rate at the desuperheater remains nearly constant regardless of the water flow rate at the condensing section inlet and the water flow rate driven through the desuperheater. The experimental results also show that the water temperature inlet at the condensing section determines the proportion of the heat transfer rate delivered at the desuperheater for DHW production and at the condenser for SH.

  • experimental analysis of a direct Expansion solar assisted heat pump with integral storage tank for domestic water heating under zero solar radiation conditions
    Energy Conversion and Management, 2012
    Co-Authors: Jose Fernandezseara, Carolina Pineiro, Alberto J Dopazo, F Fernandes, Paulo X B Sousa
    Abstract:

    Abstract This paper deals with the experimental evaluation of the performance of a direct Expansion solar assisted heat pump water heating (DX-SAHPWH) system working under zero solar radiation conditions at static heating operation mode of the storage tank. The DX-SAHPWH system includes two bare solar collectors as evaporator, a R134a rotary-type hermetic compressor, a Thermostatic Expansion Valve and a helical coil condenser immersed in a 300 L water storage tank. The zero solar radiation and stable ambient air temperature working conditions were established by placing the solar collectors into a climate chamber. The analysis is based on experimental data taken from the DX-SAHPWH provided by the manufacturer and equipped with an appropriate data acquisition system. In the paper, the experimental facility, the data acquisition system and the experimental methodology are described. Performance parameters to evaluate the energy efficiency, such as COP and equivalent seasonal performance factors (SPFe) for the heating period, and the water thermal stratification in the storage tank are defined and obtained from the experimental data. Results from the experimental analysis under transient operating working conditions of the DX-SAHPWH system and its main components are shown and discussed. Lastly, the Huang and Lee DX-SAHPWH performance evaluation method was applied resulting in a characteristic COP of 3.23 for the DX-SAHPWH system evaluated under zero solar radiation condition.

Alberto J Dopazo - One of the best experts on this subject based on the ideXlab platform.

  • experimental evaluation of a geothermal heat pump for space heating and domestic hot water simultaneous production
    Renewable Energy, 2012
    Co-Authors: Jose Fernandezseara, Alejandro Pereiro, Santiago Bastos, Alberto J Dopazo
    Abstract:

    This paper deals with the experimental performance evaluation of a geothermal heat pump (GHP) intended to produce space heating (SH) and domestic hot water (DHW) simultaneously. The GHP uses R407C as refrigerant and its main components are a scroll compressor, a Thermostatic Expansion Valve, a plate heat exchanger as evaporator and a condensing section composed of two plate heat exchangers connected in series, operating as a desuperheater and a condenser. In the condensing section, water is heated at two temperature levels for the SH and DHW systems. The experimental results realize the high influence of the water temperature at the condensing section inlet on the GHP behaviour. The COP and the heating capacity decrease 48.7% and 5.6% by increasing the water temperature at the condenser inlet from 20 to 50 °C, respectively. The percentage of water flow rate diverted to the desuperheater for DHW production depends on the water temperature and flow rate at the condensing section inlet. However, the heat transfer rate at the desuperheater remains nearly constant regardless of the water flow rate at the condensing section inlet and the water flow rate driven through the desuperheater. The experimental results also show that the water temperature inlet at the condensing section determines the proportion of the heat transfer rate delivered at the desuperheater for DHW production and at the condenser for SH.

  • experimental analysis of a direct Expansion solar assisted heat pump with integral storage tank for domestic water heating under zero solar radiation conditions
    Energy Conversion and Management, 2012
    Co-Authors: Jose Fernandezseara, Carolina Pineiro, Alberto J Dopazo, F Fernandes, Paulo X B Sousa
    Abstract:

    Abstract This paper deals with the experimental evaluation of the performance of a direct Expansion solar assisted heat pump water heating (DX-SAHPWH) system working under zero solar radiation conditions at static heating operation mode of the storage tank. The DX-SAHPWH system includes two bare solar collectors as evaporator, a R134a rotary-type hermetic compressor, a Thermostatic Expansion Valve and a helical coil condenser immersed in a 300 L water storage tank. The zero solar radiation and stable ambient air temperature working conditions were established by placing the solar collectors into a climate chamber. The analysis is based on experimental data taken from the DX-SAHPWH provided by the manufacturer and equipped with an appropriate data acquisition system. In the paper, the experimental facility, the data acquisition system and the experimental methodology are described. Performance parameters to evaluate the energy efficiency, such as COP and equivalent seasonal performance factors (SPFe) for the heating period, and the water thermal stratification in the storage tank are defined and obtained from the experimental data. Results from the experimental analysis under transient operating working conditions of the DX-SAHPWH system and its main components are shown and discussed. Lastly, the Huang and Lee DX-SAHPWH performance evaluation method was applied resulting in a characteristic COP of 3.23 for the DX-SAHPWH system evaluated under zero solar radiation condition.