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Feng, X., Cai, Y. and Qian, L. (1998). A new performance criterion for cogeneration system. Energy Conversion and Management, 39(15), pp.1607-1609.
The summary of the journal article on ‘A new performance criterion for cogeneration systems’ presents an overview of thermal efficiency analysis of cogeneration systems. This summary advances the energy utilization as well as the costs associated with cogeneration. In order to develop a new criterion, the costs associated with heat and electricity allocation are analysed.
According to Feng et al. (1998), the formula to calculate the Energy Utilization Factor (EUF) can be stated as:
Where W is the work produced from the cogeneration plant;
is the useful heat rejected from the cogeneration plant at a temperature
, the environmental temperature; and F is the energy in fuel supplied to the cogeneration plant. EUF has the advantage of simplicity. However, EUF does not discriminate between W and
at different temperatures.’ (Feng, Cai and Qian, 1998, pp.147). The purpose of this article is to investigate this criterion to better evaluate the performance standards of Cogeneration.
The current method to determine the thermal efficiency for a cogeneration/combined heat and power plant takes into consideration the useful heat rejected, work produced and the energy supplied. Although, these parameters are not enough to define the factor of efficiency that is related to cost apportionment to heat and electricity supplied.
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Furthermore, two additional criterion to determine the performance of a cogeneration plant are by examining the thermal efficiency and exergy efficiency. However, both these efficiencies do not clearly determine energy utilization. (Feng, Cai and Qian, 1998).In order to analyse the performance, a new criterion is devised that can provide a better observation of cogeneration processes. This criterion is defined as cogeneration efficiency (Feng, Cai and Qian, 1998),
The above equation conceptualizes the exergy associated with the cogeneration cycle. Theoretically, energy is composed of exergy (useful) and anergy (no work potential) components . Hence, it is a sensible foundation for evaluating anergy in cogeneration systems as it has a significant impact on heating. In this article, performance criterion for cogeneration plant are presented in a table. According to the table, the performance criterion is marked against various categories of cogeneration plants. The table provides the Fuel Energy Saving Ratio of each plant. Reviewing the Fuel Energy Saving Ratio in contrast to cogeneration efficiency ‘
’ yields an approximately close value. (Feng, Cai and Qian, 1998)
The conclusion framed from the above article is that the analysis of anergy is of equal importance along with exergy analysis to rationally examine the thermal efficiency of cogeneration systems. Thus, a new criterion is structured to rationally identify the performance as well as the cost allotment of heat and electricity.
Rosen, M., Le, M. and Dincer, I. (2005). Efficiency analysis of a cogeneration and district energy system. Applied Thermal Engineering, 25(1), pp.147-159.
The purpose of this article on ‘Efficiency analysis of a cogeneration and district energy system’ is to provide an analysis on efficiency of a cogeneration system incorporating energy and exergy considerations. For the purpose of analysis, a district based cogeneration system at Edmonton Canada is investigated. In conclusion, the exergy efficiency and energy efficiency behaviour is compared to provide a meaningful indication.
The district based system considered for the analysis consists of a cogeneration plant as well as an electrical chiller to produce chilled liquid. In order to analyse efficiencies thermodynamically, the electrical chiller is replaced with a single-effect absorption chiller and then with a double-effect absorption chiller as a portion of cogenerated electricity is utilized for the functioning these chillers. (Rosen, Le and Dincer, 2005). For analysis purposes, seasonal periods are devised to obtain the results and subsections are created to better understand individual efficiencies of each subsection.
According to Rosen et al. (2005), the thermal efficiency for the cogeneration plant can be given as,
and for the cogeneration plant using absorption chillers as
denotes the fuel energy input rate’. (Rosen, Le and Dincer, 2005, pp.155).
In order to contrast between energy and exergy efficiency, a table with values of each subsystem efficiencies for different types of chillers are provided. (Rosen, Le and Dincer, 2005, pp.155). A prominent difference in the values of energy and exergy efficiencies can be noticed. The exergy efficiency is lower than energy efficiency due to the low exergy efficiency of the chillers. The difference in the efficiency values of energy and exergy are due to the different parameters that are taken into account during calculations. Energy based efficiency takes into consideration energy quantities while exergy based efficiency takes into consideration the performance as well as the behaviour of the system. Thus, the exergy based efficiency is more significant because it provides a deeper insight into the performance of the cogeneration system by considering electrical equivalents. (Rosen, Le and Dincer, 2005).
It can be concluded that exergy efficiency provides a more meaningful and significant analysis of the performance for a cogeneration plant than energy efficiency. This is largely due to the subsystem efficiencies taken into consideration to compute the overall exergy efficiency. Furthermore, exergy analysis provides a foundation to determine the causes of inefficiencies which are beneficial to determine actual performance.
- Feng, X., Cai, Y. and Qian, L. (1998). A new performance criterion for cogeneration system. Energy Conversion and Management, 39(15), pp.1607-1609.
- Rosen, M., Le, M. and Dincer, I. (2005). Efficiency analysis of a cogeneration and district energy system. Applied Thermal Engineering, 25(1), pp.147-159.
-  Rafique, M., Gandhidasan, P., Al-Hadhrami, L. and Rehman, S. (2015). Energy, Exergy and Anergy Analysis of a Solar Desiccant Cooling System. Journal of Clean Energy Technologies, 4(1), pp.78-83.
What are the qualifications and expertise of the expert opinions cited or quoted?
- Marc A. Rosen is a professor at University of Ontario Institute of Technology and her interests are the subjects of Heat Transfer and Thermodynamics. He was published a variety of publications in these topics and served as the President of Engineering Institute of Canada .
- Ming N.Le is affiliated with University of Ontario Institute of Technology and has a record of publishing various articles in the field of efficiency analysis .
- Ibrahim Dincer serves as a professor of Mechanical Engineering at the University Of Ontario Institute Of Technology and as a vice president for world society of Sustainable Energy Technologies .
- Xiao Feng is associated with Xi’an Jiaotong University and primarily focuses on research based on heat generation and various other thermodynamic fields .
- Y.I.Nian Cai is affiliated with the Department of Chemical Engineering at Xi’an Jiaotong University China .
- Lilun Qian is affiliated with the Department of Chemical Engineering at Xi’an Jiaotong University China .
Discuss the use of photographs, tables, figures, and other graphics. Were they used? Were they accurate? What was the source? Did they support the thesis of the article? Did they have an emotional impact – explain?
In the first article, Feng et al. (1998) propose a table for the performance criteria of various cogeneration plants. This table was used to compare the performance criterion with a clear understanding between Fuel Energy Saving Ratio and cogeneration efficiency to support the hypothesis. This table was used to develop to validate a close relationship between FESR and cogeneration efficiency that proves a more in depth performance analysis. The source is this table Noyes Data Corporation, Cogeneration Technology and economics for the Process Industries.
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In the second article, M.A Rosen et al. (2005) provide schematic diagrams of the district energy system to analyse the process entirely. This schematic consists of various subsystems clearly indicated on the diagram to examine efficiencies of each of these subsystems. Furthermore, a monthly heating and cooling load breakdown is also provided in a table. This source of this table is Engineering Report of the City of Edmonton District Energy Development Phase. Using this data, a comparison is drawn between energy and exergy efficiencies.
Could you tell the writers’ attitude towards the issue? How? Were all sides of the issue represented? What, if any sides or viewpoints, were left out? Do you think the article was biased? Why or why not?
The writers of these articles are particularly interested in developing a more effective performance measure of efficiencies for cogeneration systems. The article proposed by Feng et al. (1998) although relies on a little ambiguous analysis between FESR and cogeneration efficiency as a close approximate value does not depict a clear understanding. The viewpoint of cogeneration efficiency being more significant relies on a difference in values rather than a clear experimental evidence to back up the claim. In order to validate a new performance criteria, further justifications could have been provided. Furthermore, in order to develop a consensus on cogeneration efficiency to be better than FESR, a more neutral view could have supported the purpose of the article.
For the article proposed by M.A Rosen et al. (2005), each subsystem is studied individually to develop a concise understanding of the energy and exergy efficiencies and self-serving biases were minimised as compared to the first article.
Did the article in any way change your perception and/or interest in the subject? Discuss why or why not?
The tasks included in this essay to summarise two articles of thermal efficiency of cogeneration systems have allowed me to gain a better understanding of the efficiency calculations. I have recognised the importance of efficiency and the integral role it plays in performance analysis. My perception devised from the summary of these articles is that various factors are needed to evaluate efficiency. The more factors taken into consideration, the more realistic efficiency is provided to better evaluate the performance. Efficiencies take into account numerous factors which can always be enhanced by recognising different crucial factors that play an important role in the performance characteristics. A synthesis of exergy which is the available part of energy as well as anergy which is the unavailable part is required to carefully examine the actual efficiency.
These articles have developed a particular interest in me to explore new territories in efficiency calculation for cogeneration and other thermodynamic systems to better evaluate their performance by taking a more realistic approach. The interesting aspects of developing new criterion for performance judgement is what amuses me.
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