scholarly journals Energy and Exergy Analysis of the Air Source Transcritical CO2 Heat Pump Water Heater Using CO2-Based Mixture as Working Fluid

Energies ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4470
Author(s):  
Yikai Wang ◽  
Yifan He ◽  
Yulong Song ◽  
Xiang Yin ◽  
Feng Cao ◽  
...  
Keyword(s):  
Exergy Analysis ◽  
Heat Pumps ◽  
Exergy Efficiency ◽  
Hot Water ◽  
Coefficient Of Performance ◽  
Working Fluid ◽  
Domestic Hot Water ◽  
Practical Applications ◽  
Energy And Exergy ◽  
Energy And Exergy Analysis

Given the large demand nowadays for domestic hot water, and its impact on modern building energy consumption, air source transcritical CO2 heat pumps have been extensively adopted for hot water production. Since their system efficiency is limited by significant irreversibility, a CO2-based mixture could offer a promising drop-in technology to overcome this deficiency without increasing system complexity. Although many CO2 blends have been studied in previously published literature, little has been presented about the CO2/R32 mixture. Therefore, a proposed mixture for use in transcritical CO2 heat pumps was analyzed using energy and exergy analysis. Results showed that the coefficient of performance and exergy efficiency variation displayed an “M” shape trend, and the optimal CO2/R32 mixture concentration was determined as 0.9/0.1 with regard to flammability and efficiency. The irreversibility of the throttling valve was reduced from 0.031 to 0.009 kW⋅kW−1 and the total irreversibility reduction was more notable with ambient temperature variation. A case study was also conducted to examine domestic hot water demand during the year. Pure CO2 and the proposed CO2 blend were compared with regard to annual performance factor and annual exergy efficiency, and the findings could provide guidance for practical applications in the future.

The Energy and Exergy Efficiencies of Renewable Energy Utilization in a Building Stock

2013 ◽  
Vol 361-363 ◽  
pp. 335-338
Author(s):  
Xiao Chen
Keyword(s):  
Renewable Energy ◽  
Exergy Analysis ◽  
Hot Water ◽  
Energy Utilization ◽  
Efficiency Improvement ◽  
Building Stock ◽  
Domestic Hot Water ◽  
Energy And Exergy ◽  
Energy And Exergy Analysis ◽  
Heating Mode

An surface water heat pump (SWHP) system and some solar domestic hot water (SDHW) systems were constructed in a building stock located in Xiangtan for the purpose of energy saving and environmental improvement. This study aims to evaluate the energy and exergy efficiencies of renewable energy utilization based on energy and exergy analysis. We found the energy and exergy efficiencies of the SWHP system in heating mode to be 395% and 17.78%, respectively. The energy and exergy efficiencies for the SDHW systems were found to be 34.96% and 17.5%, respectively. Some measures for the exergy efficiency improvement are discussed in this paper.

scholarly journals ENERGY AND EXERGY ANALYSIS OF A CYLINDRICAL HOT WATER STORAGE TANK: EXPERIMENTAL AND CFD ANALYSIS

2020 ◽  
Author(s):  
Tomas Kropas ◽  
Giedrė Streckienė
Keyword(s):  
Numerical Model ◽  
Storage Tank ◽  
Exergy Analysis ◽  
Water Storage ◽  
Exergy Efficiency ◽  
Hot Water ◽  
Water Storage Tank ◽  
Environment Temperature ◽  
Energy And Exergy ◽  
Energy And Exergy Analysis

Active solar water heating systems typically include hot water storage tanks. The selection of the storage system strongly affects the performance of the entire system. This article presents a detailed analysis of a hot water storage tank during charging and dynamic charging-discharging mode. A numerical model using computational fluid dynamics for the storage tank was developed to investigate the temperature distribution inside of it. Transient thermal analysis was carried using ANSYS Fluent. The numerical model was validated with the experimental results. The energy and exergy analysis as an important tool for the evaluation of the thermal systems quantitatively and qualitatively was performed. The calculation procedures were described. The energy and exergy efficiencies, heat losses were calculated for steady and dynamic processes. Effect of mass flow rate was analysed. The results from parametric analysis showed that charging dynamics reduced the thermocline and efficiency of the hot water storage tank. The dependency of the exergy efficiency of the heat storage tank on the reference environment temperature during the dynamic operation was analysed. Exergy efficiencies for two cities with different climates were compared. This indicated that the higher envi-ronmental temperature gave lower exergy efficiency of the storage tank.

scholarly journals Energy and Exergy Analysis of LiBr-aq and LiCl-aq Liquid Desiccant Dehumidification System

2020 ◽  
Vol 14 (1) ◽  
pp. 36-40
Author(s):  
Barış KavasoğullarI ◽  
Ertuğrul Cihan ◽  
Hasan Demir
Keyword(s):  
Exergy Analysis ◽  
Lithium Bromide ◽  
Exergy Efficiency ◽  
Coefficient Of Performance ◽  
Airflow Rate ◽  
Liquid Desiccant ◽  
Energy And Exergy ◽  
Liquid Desiccant Dehumidification ◽  
Energy And Exergy Analysis ◽  
Mass Flow Rates

In this study, energy and exergy analysis of experimental results obtained from a dehumidification system using LiBr-aq (lithium bromide-water) and LiCl-aq (lithium chloridewater) as desiccant was made. In dehumidifier and regenerator columns polycarbonate sheets, which have not been used before, were used as packing material to increase contact area in purposed liquid desiccant dehumidification system. In the analysis, variation of electrical coefficient of performance and exergy efficiency with airflow rate for different solution mass flow rates were investigated. Because of investigation, maximum values of electrical coefficient of performance and exergy efficiency were calculated approximately as 2.8 and 18%, respectively.

Experimental Evaluation of the Thermal Behavior of a Vertical Solar Tank Using Energy and Exergy Analysis

2005 ◽  
Author(s):  
Ali A. Dehghan ◽  
Mohammad H. Hosni ◽  
S. Hoda Shiryazdi
Keyword(s):  
Temperature Distribution ◽  
Flow Rate ◽  
Storage Tank ◽  
Thermal Stratification ◽  
Exergy Analysis ◽  
Hot Water ◽  
Second Law ◽  
Energy And Exergy ◽  
Energy And Exergy Analysis ◽  
Hot Water Supply

The thermal performance of a Thermosyphon Domestic Solar Water Heater (DSWH) with a vertical storage tank is investigated experimentally. The system is installed on a roof - top of a four person family house and its thermal characteristics is evaluated by means of carefully measuring the temperature distribution of water inside the storage tank, solar collector flow rate and its inlet and outlet temperatures as well as load/consumption outlet and inlet temperatures and the corresponding water flow rate under a realistic operating conditions. The measurements are conducted every hour starting from morning until late night on a daily basis and continued for about 120 days during August until November 2004. It is seen that thermal stratification is well established inside the tank from 11 AM until 10 PM especially during August to September enabling the tank to provide the necessary amount of hot water at an acceptable temperature. However, thermal stratification is observed to start degrading from mid-night until morning when there is no hot water supply from the collector and due to the diffusion of heat from the top hot water layers to the bottom cold region and conduction through tank’s wall. The thermal behavior of the storage tank is also assessed based on both energy and exergy analysis and its first and second law efficiencies are calculated. It is observed that the storage tank under study has an average first law efficiency of 47.8% and is able to supply the required amount of hot water at a proper temperature. The average second law efficiency of the storage tank is observed to be 28.7% and, although is less than its first low efficiency, but is high enough to ensure that the quality of the hot water supply is well preserved. The proper level of second law efficiency is due to the preservation of the thermal stratification inside the storage tank, leading to supply of hot water at highest possible temperature and hence highest possible energy potential. Experiments are also done for no-load conditions when the storage tank only interacts with the collector, without hot water withdrawal from the tank. It is seen that for no-load condition, thermal stratification continuously develops from morning until around 16 PM after which no noticeable changes in the temperature distribution inside the tank is observed.

scholarly journals Heat Pump Cycle Efficiency for Heat Supply

2020 ◽  
pp. 136-142
Author(s):  
Mykola Bosiy ◽  
◽  
Olexandr Kuzyk ◽  
Keyword(s):  
Heat Pump ◽  
Heat Supply ◽  
Exergy Analysis ◽  
Conversion Factor ◽  
Working Fluid ◽  
Heating Systems ◽  
Energy And Exergy ◽  
Energy And Exergy Analysis ◽  
Heat Supply Systems ◽  
Supply Systems

The aim of the article is to analyze the literature and scientific publications on the effectiveness of the heat pump in heat supply systems and to study the efficiency of using the steam compression cycle of a heat pump in a heat supply system. Тo conduct energy and exergy analysis of heat pump efficiency indicators, the working fluid of which is freon R134a, when using natural waters as a source of low-potential thermal energy. The article analyzes the literature sources and scientific publications on the effectiveness of the heat pump in heat supply systems. The results of research of efficiency of application of the heat pump in systems of heat supply at use of natural waters as a source of low-potential thermal energy are presented. Energy and exergy analysis of heat pump efficiency indicators, the working fluid of which is R134a freon, was performed. The energy efficiency of the heat pump cycle was determined by the conversion factor of the heat pump. The thermodynamic efficiency of the heat pump in heat supply systems was evaluated using exergetic efficiency, which is one of the main indicators of the efficiency of heat pump processes and cycles. The calculation of energy indicators of the heat pump, such as: specific heat load in the evaporator and condenser, as well as the conversion factor of the heat pump. The calculation of exergetic efficiency for ambient temperature from +10 to -10 ºC. Thus, the energy and exergy analysis of the efficiency of the heat pump, the working fluid of which is Freon R134a with a conversion factor = 4.8. This indicates that the heat pump is a reliable, highly efficient, environmentally friendly source of energy for use in heating systems. A heat pump heating system will always consume less primary energy than traditional heating systems if natural water is used as a low-temperature heat source for the heat pump. The efficiency of the steam compression cycle of the heat pump largely depends on the temperature of low-potential heat sources. The use of HV in heating systems reduces greenhouse gas emissions compared to conventional types of heat supply, which is relevant to the ecological state of the environment.

scholarly journals Energy and Exergy Analysis of Sensible Thermal Energy Storage—Hot Water Tank for a Large CHP Plant in Poland

Energies ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4842 ◽  
Author(s):  
Ryszard Zwierzchowski ◽  
Marcin Wołowicz
Keyword(s):  
Energy Storage ◽  
Ambient Temperature ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Exergy Analysis ◽  
Hot Water ◽  
Water Tank ◽  
Exergy Destruction ◽  
Energy And Exergy ◽  
Energy And Exergy Analysis

The paper contains a simplified energy and exergy analysis of pumps and pipelines system integrated with Thermal Energy Storage (TES). The analysis was performed for a combined heat and power plant (CHP) supplying heat to the District Heating System (DHS). The energy and exergy efficiency for the Block Part of the Siekierki CHP Plant in Warsaw was estimated. CHP Plant Siekierki is the largest CHP plant in Poland and the second largest in Europe. The energy and exergy analysis was executed for the three different values of ambient temperature. It is according to operation of the plant in different seasons: winter season (the lowest ambient temperature Tex = −20 °C, i.e., design point conditions), the intermediate season (average ambient temperature Tex = 1 °C), and summer (average ambient temperature Tex = 15 °C). The presented results of the analysis make it possible to identify the places of the greatest exergy destruction in the pumps and pipelines system with TES, and thus give the opportunity to take necessary improvement actions. Detailed results of the energy-exergy analysis show that both the energy consumption and the rate of exergy destruction in relation to the operation of the pumps and pipelines system of the CHP plant with TES for the tank charging and discharging processes are low.

scholarly journals Energy and Exergy Analysis of Combined Organic Rankine Cycle-Single and Dual Evaporator Vapor Compression Refrigeration Cycle

2019 ◽  
Vol 9 (23) ◽  
pp. 5028 ◽  
Author(s):  
Pektezel ◽  
Acar
Keyword(s):  
Exergy Analysis ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Working Fluid ◽  
Refrigeration Cycle ◽  
Vapor Compression ◽  
Exergy Destruction ◽  
Energy And Exergy ◽  
Energy And Exergy Analysis ◽  
Vapor Compression Refrigeration

This paper presents energy and exergy analysis of two vapor compression refrigeration cycles powered by organic Rankine cycle. Refrigeration cycle of combined system was designed with single and dual evaporators. R134a, R1234ze(E), R227ea, and R600a fluids were used as working fluids in combined systems. Influences of different parameters such as evaporator, condenser, boiler temperatures, and turbine and compressor isentropic efficiencies on COPsys and ƞex,sys were analyzed. Second law efficiency, degree of thermodynamic perfection, exergy destruction rate, and exergy destruction ratio were detected for each component in systems. R600a was determined as the most efficient working fluid for proposed systems. Both COPsys and ƞex,sys of combined ORC-single evaporator VCR cycle was detected to be higher than the system with dual evaporator.

scholarly journals Application of energy and exergy analysis to increase efficiency of a hot water gas fired boiler

2014 ◽  
Vol 20 (4) ◽  
pp. 511-521 ◽  
Author(s):  
Milena Todorovic ◽  
Dragoljub Zivkovic ◽  
Marko Mancic ◽  
Gradimir Ilic
Keyword(s):  
Exergy Analysis ◽  
Energy Analysis ◽  
Hot Water ◽  
Engineering Practice ◽  
Economic Optimization ◽  
Energy And Exergy ◽  
Energy And Exergy Analysis ◽  
Reliable Solution ◽  
Control Volumes ◽  
Functional Components

In engineering practice exergy can be used for technical and economic optimization of energy conversion processes. The problem of increasing energy consumption suggests that heating plants, i.e. hot water boilers, as energy suppliers for household heating should be subjected to exergy and energy analysis. Heating plants are typically designed to meet energy demands, without the distinguished difference between quality and quantity of the produced heat. In this paper, the energy and exergy analysis of a gas fired hot water boiler is conducted. Energy analysis gives only quantitative results, while exergy analysis provides an insight into the actually available useful energy with respect to the system environment. In this paper, a hot water boiler was decomposed into control volumes with respect to its functional components. Energy and exergy of the created physical model of the hot water boiler is performed and destruction of exergy and energy loss in each of the components is calculated. The paper describes the current state of energy and exergy efficiency of the hot water boiler. The obtained results are analyzed and used to investigate possibilities for improvement of availability and reliability of the boiler. A comparison between the actual and the proposed more reliable solution is made.

scholarly journals Energy and exergy analysis of air based photovoltaic thermal (PVT) collector: a review

2019 ◽  
Vol 9 (1) ◽  
pp. 109 ◽  
Author(s):  
Ahmad Fudholi ◽  
Mariyam Fazleena Musthafa ◽  
Abrar Ridwan ◽  
Rado Yendra ◽  
Ari Pani Desvina ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Flat Plate ◽  
Solar Collector ◽  
Exergy Analysis ◽  
Exergy Efficiency ◽  
Pv Panel ◽  
Energy And Exergy ◽  
Energy And Exergy Analysis ◽  
Flat Plate Solar Collector

<span lang="EN-US">Photovoltaic thermal (PVT) collectors convert solar radiation directly to both electrical and thermal energies. A PVT collector basiccaly combines the functions of a flat plate solar collector and those of a PV panel. This review presents thermodinamics fundamentals, descriptions, and previous works conducted on energy and exergy analysis of air based PVT collector. Studies in 2010 to 2018 of the energy and exergy analysis of air based PVT collectors are summarized. The energy and exergy efficiency of air based PVT collector ranges from 31% to 94% and 8.7% to 18%, respectively. In addition, flat plate solar collector is presented. Studies conducted on air based PVT collectors are reviewed.</span>

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