Influence of Refrigerant Charge Amount and EEV Opening on the Performance of a Transcritical CO2 Heat Pump Water Heater

Zhang, Ze; Dong, Xiaojun; Ren, Zheng; Lai, Tianwei; Hou, Yu

doi:10.3390/en10101521

Cited by 15 publications

(9 citation statements)

References 21 publications

(22 reference statements)

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“…With less heat to accept (reject from the compressor) the gas cooler will be operating at a lower temperature and pressure. The simulation results correspond to the results found in the study by Zhang & Dong et al [40] who also found that gas cooler and evaporator pressure decreases with a decrease in total refrigerant mass flow rate in their investigated system. For the normal case the mass flow rate was programmed as a function of the EV orifice opening (refer to (A52) in Appendix A).…”

Section: Working Fluid Leakagesupporting

confidence: 89%

An Energy Graph-Based Approach to Fault Diagnosis of a Transcritical CO2 Heat Pump

et al. 2020

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The objective of this paper is to describe an energy-based approach to visualize, identify, and monitor faults that may occur in a water-to-water transcritical CO 2 heat pump system. A representation using energy attributes allows the abstraction of all physical phenomena present during operation into a compact and easily interpretable form. The use of a linear graph representation, with heat pump components represented as nodes and energy interactions as links, is investigated. Node signature matrices are used to present the energy information in a compact mathematical form. The resulting node signature matrix is referred to as an attributed graph and is populated in such a way as to retain the structural information, i.e., where the attribute points to in the physical system. To generate the energy and exergy information for the compilation of the attributed graphs, a descriptive thermal-fluid model of the heat pump system is developed. The thermal-fluid model is based on the specifications of and validated to the actual behavioral characteristics of a physical transcritical CO 2 heat pump test facility. As a first step to graph-matching, cost matrices are generated to represent a characteristic residual between a normal system node signature matrix and a faulty system node signature matrix. The variation in the eigenvalues and eigenvectors of the characteristic cost matrices from normal conditions to a fault condition was used for fault characterization. Three faults, namely refrigerant leakage, compressor failure and gas cooler fouling, were considered. The paper only aims to introduce an approach, with the scope limited to illustration at one operating point and considers only three relatively large faults. The results of the proposed method show promise and warrant further work to evaluate its sensitivity and robustness for small faults.Energies 2020, 13, 1783 2 of 34 Zogg also refers to a field survey [2] that indicates that the average energetic efficiencies of the heat pumps installed in Swiss buildings were about 10% lower than the efficiencies measured under standard laboratory conditions. It was also found that for some installations the performance degradation was as high as 30%. A similar study in the United States of over 55,000 air conditioning units showed that more than 90% were operating with one or more kinds of faults [3]. Yet another study surveying roof-top units indicates an operating efficiency of 80% of designed performance with 63% of these units having performance degradation due to refrigerant leakage [4]. These observations motivate the need for diagnostic techniques which ideally can monitor these energy conversion systems during transient and steady-state operating conditions.In the review papers by Zhao et al., and Shi and O'Brien [5,6] the classification of fault detection methods for energy systems are presented. Fault detection methods can be classified into two subcategories: data-based and knowledge-based. The knowledge-based methods rely on domain and prior knowledge to deri...

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Section: Working Fluid Leakagesupporting

confidence: 89%

An Energy Graph-Based Approach to Fault Diagnosis of a Transcritical CO2 Heat Pump

et al. 2020

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“…Increasing the EEV opening from its optimal value to 60% decreased the heating capacity up to 30% due to an increase in the refrigerant charge Among many types of expansion devices, the electronic expansion valve (EEV) and capillary tubes have been studied for CO 2 HPs. Zhang et al [102] experimentally studied the effect of the refrigerant charge amount and EEV opening on the performance of a CO 2 HP water heater. The EEV opening of 40% was found to be optimal for their system.…”

Section: Expansion Devicementioning

confidence: 99%

Recent Advances in Transcritical CO2 (R744) Heat Pump System: A Review

et al. 2019

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Heat pump (HP) is one of the most energy efficient tools for address heating and possibly cooling needs in buildings. Growing environmental concerns over conventional HP refrigerants, chlorofluorocarbons (CFCs), and hydrofluorocarbons (HFCs) have forced legislators and researchers to look for alternatives. As such, carbon dioxide (R744/CO2) has come to light due to its low global warming potential (GWP) and zero ozone depleting characteristics. Even though CO2 is environmentally benign, the performance of CO2 HP has been of concern since its inception. To improve the performance of CO2 HP, research has been playing a pivotal role in developing functional designs of heat exchangers, expansion devices, and compressors to suit the CO2 transcritical cycle. Different CO2 HP cycles coupled with auxiliary components, hybrid systems, and refrigerant mixtures along with advanced control strategies have been applied and tested. This paper presents a complete overview of the most recent developments of transcritical CO2 HPs, their components, and applications.

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“…Properties of the ethylene glycol solution with the mass flow rate and temperature difference of the secondary fluid across the ID HX were used to calculate the cooling capacity of the heat pump unit due to the ease in measurement and the calculation process as shown in Equation (1). COP of the heat pump unit was calculated using the cooling capacity and compressor power consumption as shown in Equation (2). Uncertainty analysis of the heat pump parameters was done according to ASHRAE Guideline 2 [14] using the Pythagorean summation of discrete uncertainties as shown in Equation (3).…”

Section: Volumetricmentioning

confidence: 99%

“…Refrigerant undercharge or overcharge conditions greatly affect the performance of heat pumps [2]. In real systems, refrigerant undercharge is caused by leakages which cause severe CO 2 emissions, while refrigerant overcharge exists due to human errors when charging the heat pump.…”

Section: Introductionmentioning

confidence: 99%

Refrigerant Charge Fault Detection and Diagnosis Algorithm for Water-to-Water Heat Pump Unit

Boahen

Choi

2019

Energies

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Refrigerant charge faults have a great adverse effect on the performance of heat pumps and must therefore be detected and diagnosed early in real time. In this study, the effect of refrigerant charge faults on a water-to-water heat pump is experimentally investigated in cooling mode and heating mode at various outdoor entering water temperature conditions. The study showed that refrigerant undercharge affects the performance of water-to-water heat pump more in heating mode than in cooling mode. Results from the study are used to develop a refrigerant charge fault detection and diagnosis (FDD) algorithm that works using correlations and rule-based refrigerant fault characteristic charts. The FDD algorithm is able to detect refrigerant charge faults in the water-to-water heat pump within an error threshold of ±4.5% and ±1.1% in cooling mode and heating mode respectively.

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Influence of Refrigerant Charge Amount and EEV Opening on the Performance of a Transcritical CO2 Heat Pump Water Heater

Cited by 15 publications

References 21 publications

An Energy Graph-Based Approach to Fault Diagnosis of a Transcritical CO2 Heat Pump

An Energy Graph-Based Approach to Fault Diagnosis of a Transcritical CO2 Heat Pump

Recent Advances in Transcritical CO2 (R744) Heat Pump System: A Review

Refrigerant Charge Fault Detection and Diagnosis Algorithm for Water-to-Water Heat Pump Unit

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