Numerical analysis on performance enhancement of a CO2 heat pump water heating system by extracting tepid water

Ohkura, Masashi; Yokoyama, Ryohei; Nakamata, Takuya; Wakui, Tetsuya

doi:10.1016/j.energy.2015.05.013

Cited by 15 publications

(5 citation statements)

References 29 publications

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“…As for the one dimensional tank, a standard TRNSYS16 object is used (Type 60). This model was validated with experimental data taken from Ohkura et al [22]. The differences between the experimental results and the predictions obtained with Type 60 in TRNSYS16 were always lower than 3 K which is considered acceptable.…”

Section: Model Of the Systemmentioning

confidence: 67%

Seasonal performance assessment of sanitary hot water production systems using propane and CO 2 heat pumps

Tammaro

Montagud

Corberán

et al. 2017

International Journal of Refrigeration

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 CO 2 and propane heat pumps for sanitary hot water production are modelled and sized  Their COPs and heating capacities are compared in different climates  A TRNSYS model with a realistic hospital and school load profile is simulated  Propane unit's seasonal performance factor is higher in warm and average climates  Control logic of these systems has a significant impact on energy performance ABSTRACT Heat pump water heaters can increase the energy efficiency in sanitary hot water production, which is a relevant share of the final energy consumption in multiresidential and tertiary buildings. Refrigerants for

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Section: Model Of the Systemmentioning

confidence: 67%

Seasonal performance assessment of sanitary hot water production systems using propane and CO 2 heat pumps

Tammaro

Montagud

Corberán

et al. 2017

International Journal of Refrigeration

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“…The schematic of the experimental setup is shown in Figure 3. The storage tank model was made of acryl, and its specification is shown in Table 1 [36]. The 5th inlet port from the top on the side, and the outlet port on the top were used for the experiments.…”

Section: Methodsmentioning

confidence: 99%

“…In earlier years, attention has been paid to analyzing and enhancing the performance of a CO 2 HP as the main component of a WHS. Some review papers on the performance analysis of CO 2 enhance the performance by extracting tepid water from a storage tank [36]. In addition, operation and design optimizations have been tried: Yokoyama et al have estimated system performance values and have clarified the optimal operating conditions under daily change in simulated hot water demand [37]; Deng et al have analyzed and optimized the performance of a combination of a solar heater and an HP WHS [38].…”

Section: Introductionmentioning

confidence: 99%

Numerical Analysis for Performance Evaluation of a Multi-Functional CO2 Heat Pump Water Heating System

et al. 2018

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In recent years, CO2 heat pump water heating systems have been developed, and their performances have been enhanced while their functions have been expanded. In a multi-functional system, used for both hot water supply and bath heating, hot water retrieved from the top of a storage tank is returned to its bottom or side after heat exchange for bath heating, which destroys the stratified temperature distribution in the storage tank and degrades the system performance. In this paper, the performance of a multi-functional CO2 heat pump water heating system has been evaluated by numerical simulation. A system model was created by combining component models for a CO2 heat pump, mixing valves, a storage tank, a heat exchanger, and a bathtub. Partly, perfect mixing by hot water return was assumed in the component model for the storage tank, and its validity was verified through experiments. A performance analysis has been conducted under daily repeated hot water and bath heating demands, and the system performance was evaluated at a periodically steady state. As a result, the system efficiency and the volume of unused hot water in the multi-functional system decreased by 4.9% and 16.3%, respectively, as compared to those in the uni-functional system, when hot water returned to the bottom of the storage tank. When the position for hot water return is heightened, the system efficiency becomes higher than that in the uni-functional system, while the volume of unused hot water decreases furthermore.

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“…A matching rise of the water temperature will allow high COP, while low temperature rises will cause poor performance. In fact, forcing the heat pump to always heat the water side as much as possible, to cause the greatest stratification in the tank, and regulating the water supply temperature by mixing, can increase COP significantly [8]. An integrated energy system (see Figure 1) combining a heat pump, a ventilated façade and a water tank is being designed for a nearly zero-energy building (NZEB) [9].…”

Section: Introductionmentioning

confidence: 99%

Comparison of Transcritical CO2 and Conventional Refrigerant Heat Pump Water Heaters for Domestic Applications

et al. 2019

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Although CO 2 as refrigerant is well known for having the lowest global warming potential (GWP), and commercial domestic heat pump water heater systems exist, its long expected wide spread use has not fully unfolded. Indeed, CO 2 poses some technological difficulties with respect to conventional refrigerants, but currently, these difficulties have been largely overcome. Numerous studies show that CO 2 heat pump water heaters can improve the coefficient of performance (COP) of conventional ones in the given conditions. In this study, the performances of transcritical CO 2 and R410A heat pump water heaters were compared for an integrated nearly zero-energy building (NZEB) application. The thermodynamic cycle of two commercial systems were modelled integrating experimental data, and these models were then used to analyse both heat pumps receiving and producing hot water at equal temperatures, operating at the same ambient temperature. Within the range of operation of the system, it is unclear which would achieve the better COP, as it depends critically on the conditions of operation, which in turn depend on the ambient conditions and especially on the actual use of the water. Technology changes on each side of the line of equal performance conditions of operation (EPOC), a useful design tool developed in the study. The transcritical CO 2 is more sensitive to operating conditions, and thus offers greater flexibility to the designer, as it allows improving performance by optimising the global system design.

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Numerical analysis on performance enhancement of a CO2 heat pump water heating system by extracting tepid water

Cited by 15 publications

References 29 publications

Seasonal performance assessment of sanitary hot water production systems using propane and CO 2 heat pumps

Seasonal performance assessment of sanitary hot water production systems using propane and CO 2 heat pumps

Numerical Analysis for Performance Evaluation of a Multi-Functional CO2 Heat Pump Water Heating System

Comparison of Transcritical CO2 and Conventional Refrigerant Heat Pump Water Heaters for Domestic Applications

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