Performance analysis of a CO2 heat pump water heating system under a daily change in a standardized demand

Yokoyama, Ryohei; Wakui, Tetsuya; Kamakari, Junya; Takemura, Kazuhisa

doi:10.1016/j.energy.2009.11.008

Cited by 47 publications

(22 citation statements)

References 12 publications

(13 reference statements)

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“…For the concrete formulation of the simulation model, refer to reference (Yokoyama et al, 2010b). The validity of the simulation model has been verified through an experiment and a three-dimensional thermo-fluid numerical simulation.…”

Section: Numerical Simulationmentioning

confidence: 99%

“…The validity of the simulation model has been verified through an experiment and a three-dimensional thermo-fluid numerical simulation. For this verification, also refer to reference (Yokoyama et al, 2010b).…”

Section: Numerical Simulationmentioning

confidence: 99%

“…The remaining equations to be considered are approximate functions of the power consumption and COP, and they are expressed in relation to the air and inlet/outlet water temperatures. A detailed dynamic model is adopted for the storage tank (Yokoyama et al, 2007;Yokoyama et al, 2010b). To consider the one-dimensional vertical temperature distribution in the storage tank, it is vertically divided into many control volumes with the same volume, in each of which the water temperature is assumed to be constant.…”

Section: Numerical Simulationmentioning

confidence: 99%

“…A simplified static model is adopted for the CO 2 heat pump (Yokoyama et al, 2010b): Although the heat pump includes several components, they are not taken into account explicitly, and it is expressed by one model. The mass flow rates and temperatures of water at the inlet and outlet, COP, heat output, power consumption, and air temperature are adopted as basic variables whose values are to be determined.…”

Section: Numerical Simulationmentioning

confidence: 99%

“…On the other hand, numerical simulations have been conducted in place of the tests (Yokoyama et al, 2007;Yokoyama et al, 2008). The daily changes in system performance values have recently been investigated under a daily change in hot water demand by a numerical simulation (Yokoyama et al, 2010b;Yokoyama et al, 2010a). However, it takes long times to estimate the daily changes in system performance values by numerical simulations with complex computations, and thus it is difficult to determine the operating conPerformance Estimation and Optimal Operation of a CO 2 Heat Pump Water Heating System* ditions optimally by numerical simulations, because the optimization needs to estimate the daily changes in system performance values repeatedly under various operating conditions.…”

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Performance Estimation and Optimal Operation of a CO2 Heat Pump Water Heating System

Yokoyama¹

2013

Int. J. Thermo

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IntroductionHot water demand occupies about one-third of the energy consumption in the residential sector in Japan, and energy saving in hot water supply has been an important issue. Under this situation, water heating systems each of which is composed of a heat pump using CO 2 as a natural refrigerant and a hot water storage tank have been developed and commercialized widely (Saikawa, 2004;Hashimoto, 2006). The performance of CO 2 heat pumps has been enhanced dramatically through the technological development of their components such as compressors and gas coolers. On the other hand, importance has also been given to the performance of water heating systems in case they are operated under a daily change in hot water demand.The performance of the CO 2 heat pump only, or coefficient of performance (COP) is affected by the air temperature as well as the inlet and outlet water temperatures. Many theoretical and experimental studies have been conducted for the performance analysis on CO 2 heat pumps (Hwang and Radermacher, 1998;Nekså et al., 1998; Saikawa et al., 1999;Saikawa and Hashimoto, 2001;Nekså, 2002;White et al., 2002;Skaugen et al., 2002;Richter et al., 2003;Yokoyama et al., 2006;Laipvadit et al., 2008;Yan et al., 2010;Sarkar et al., 2010;Yamaguchi et al., 2011). On the other hand, the performance of the water heating system composed of the CO 2 heat pump and storage tank is affected by many conditions. The ambient conditions such as air and feed water temperatures, the hot water demand, and the operating conditions such as startup and shutdown, and outlet water temperature during operation of the CO 2 heat pump affect the inlet water temperature and resultantly the COP through the temperature distribution in the storage tank. In addition to the COP, the storage and system efficiencies, and the volumes of stored and unused hot water are considered as system performance values, and these are also affected by the aforementioned various conditions through the temperature distribution in the storage tank. As a result, the system performance is affected by the operational history on past several days, and changes complexly with days. Therefore, in order to attain the maximum system performance, it is necessary to estimate the daily changes in system performance values accurately in relation to those in the ambient conditions, hot water demand, and operating conditions, and determine the operating conditions optimally based on them.Some studies have been conducted for the performance analysis on water heating systems (Cecchinato et al., 2005;Stene, 2005;Minetto, 2011). However, few studies have been conducted in consideration of daily changes in the aforementioned conditions. In order to investigate the daily changes in system performance values, laboratory and field tests have been tried under simulated and practical hot water demands, respectively. However, hot water demands depend on residential houses, and it takes extremely long time to conduct the tests. Thus, it is not necessarily easy to investigate the ...

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Section: Numerical Simulationmentioning

confidence: 99%

Section: Numerical Simulationmentioning

confidence: 99%

Section: Numerical Simulationmentioning

confidence: 99%

Section: Numerical Simulationmentioning

confidence: 99%

mentioning

confidence: 99%

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Performance Estimation and Optimal Operation of a CO2 Heat Pump Water Heating System

Yokoyama¹

2013

Int. J. Thermo

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Performance Analysis and Optimization of aCO₂Heat Pump Water Heating System

Yokoyama

2021

Transcritical CO2 Heat Pump

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Preliminary investigation of a transcritical CO₂heat pump driven by a solar-powered CO₂Rankine cycle

Zhang

2012

Int. J. Energy Res.

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SUMMARY In this paper, a transcritical carbon dioxide heat pump system driven by solar‐owered CO2 Rankine cycle is proposed for simultaneous heating and cooling applications. Based on the first and second laws of thermodynamics, a theoretical analysis on the performance characteristic is carried out for this solar‐powered heat pump cycle using CO2 as working fluid. Further, the effects of the governing parameters on the performance such as coefficient of performance (COP) and the system exergy destruction rate are investigated numerically. With the simulation results, it is found that, the cooling COP for the transcritical CO2 heat pump syatem is somewhat above 0.3 and the heating COP is above 0.9. It is also concluded that, the performance of the combined transcritical CO2 heat pump system can be significantly improved based on the optimized governing parameters, such as solar radiation, solar collector efficient area, the heat transfer area and the inlet water temperature of heat exchange components, and the CO2 flow rate of two sub‐cycles. Where, the cooling capacity, heating capacity, and exergy destruction rate are found to increase with solar radiation, but the COPs of combined system are decreased with it. Furthermore, in terms of improvement in COPs and reduction in system exergy destruction at the same time, it is more effective to employ a large heat transfer area of heat exchange components in the combined heat pump system. Copyright © 2012 John Wiley & Sons, Ltd.

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Performance analysis of a CO2 heat pump water heating system under a daily change in a standardized demand

Cited by 47 publications

References 12 publications

Performance Estimation and Optimal Operation of a CO2 Heat Pump Water Heating System

Performance Estimation and Optimal Operation of a CO2 Heat Pump Water Heating System

Performance Analysis and Optimization of aCO₂Heat Pump Water Heating System

Preliminary investigation of a transcritical CO₂heat pump driven by a solar-powered CO₂Rankine cycle

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Performance analysis of a CO2 heat pump water heating system under a daily change in a standardized demand

Cited by 47 publications

References 12 publications

Performance Estimation and Optimal Operation of a CO2 Heat Pump Water Heating System

Performance Estimation and Optimal Operation of a CO2 Heat Pump Water Heating System

Performance Analysis and Optimization of aCO2Heat Pump Water Heating System

Preliminary investigation of a transcritical CO2heat pump driven by a solar-powered CO2Rankine cycle

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Product

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Performance Analysis and Optimization of aCO₂Heat Pump Water Heating System

Preliminary investigation of a transcritical CO₂heat pump driven by a solar-powered CO₂Rankine cycle