Exergoeconomic analysis of a combined heat and power (CHP) system

229

104

SUMMARYHeating and cooling energy requirements for buildings are usually supplied by separated systems such as furnaces or boilers for heating, and vapor compression systems for cooling. For these types of buildings, the use of combined cooling, heating, and power (CCHP) systems or combined heating and power (CHP) systems are an alternative for energy savings. Different researchers have claimed that the use of CCHP and CHP systems reduces the energy consumption related to transmission and distribution of energy. However, most of these analyses are based on reduction of operating cost without measuring the actual energy use and emissions reduction. The objective of this study is to analyze the performance of CCHP and CHP systems operating following the electric load (FEL) and operating following the thermal load (FTL), based on primary energy consumption (PEC), operation cost, and carbon dioxide emissions (CDE) for different climate conditions. Results show that CCHP and CHP systems operated FTL reduce the PEC for all the evaluated cities. On the other hand, CHP systems operated FEL always increases the PEC. The only operation mode that reduces PEC and CDE while reducing the cost is CHP-FTL.

Section: Introductionmentioning

confidence: 99%

Performance analysis of CCHP and CHP systems operating following the thermal and electric load

Mago

Fumo

Chamra

2009

229

104

“…The most important aspect of second-law analysis insofar as the practical design of thermal systems is concerned is thermoeconomics [20][21][22]. An important consequence of the second-law analysis is the principle of entropy generation minimization (EGM) introduced by Bejan [23][24][25].…”

Section: Introductionmentioning

confidence: 99%

An examination of exergy destruction in organic Rankine cycles

Mago

Srinivasan

Chamra

et al. 2008

101

SUMMARYThe exergy topological method is used to present a quantitative estimation of the exergy destroyed in an organic Rankine cycle (ORC) operating on R113. A detailed roadmap of exergy flow is presented using an exergy wheel, and this visual representation clearly depicts the exergy accounting associated with each thermodynamic process. The analysis indicates that the evaporator accounts for maximum exergy destroyed in the ORC and the process responsible for this is the heat transfer across a finite temperature difference. In addition, the results confirm the thermodynamic superiority of the regenerative ORC over the basic ORC since regenerative heating helps offset a significant amount of exergy destroyed in the evaporator, thereby resulting in a thermodynamically more efficient process. Parameters such as thermodynamic influence coefficient and degree of thermodynamic perfection are identified as useful design metrics to assist exergy-based design of devices. This paper also examines the impact of operating parameters such as evaporator pressure and inlet temperature of the hot gases entering the evaporator on ORC performance. It is shown that exergy destruction decreases with increasing evaporator pressure and decreasing turbine inlet temperatures. Finally, the analysis reveals the potential of the exergy topological methodology as a robust technique to identify the magnitude of irreversibilities associated with real thermodynamic processes in practical thermal systems.

“…Applications to which the concept of exergy has been applied include optimization of thermal systems [17,18], power plants [19,20], industrial processes [21] such as metal production [22], desalination [23] and paper production [24]. The concept has also been extended for resource accounting [25][26][27] and-of most relevance in the present work-for extended accounting of resource consumption across the life cycle of systems [28][29][30] and sustainability assessments [31][32][33]. The principle notion is that the presence of irreversible processes in a system's life cycle reduces its sustainability.…”

Section: Lifetime Exergy Modelsmentioning

confidence: 99%

Designing environmentally sustainable electronic cooling systems using exergo-thermo-volumes

Shah

Patel

2009

SUMMARYThermo-volumes allow the design engineer to expediently understand the thermal resistance of a given cooling solution (an indicator of performance) along with its flow resistance (an indicator of the pumping power, or energy consumption, which will be required by the fluid handler). In the present work, we expand upon thermo-volumes by including the lifetime exergy cost (in units of Joules of availability destroyed) as a means to enable the consideration of resource consumption (and thus the environmental sustainability) of the cooling solution.To achieve these exergo-thermo-volumes, we reinterpret previous definitions of thermo-volumes in terms of the entropy generated during heat transfer and fluid flow. The Guoy-Stodola theorem is used to convert this entropy generation into an 'operational' exergy loss. Next, based on the material choice and assembly processes used in creating the product, an embedded exergy consumption that accounts for the amount of exergy destroyed during extraction, transportation and disposal of the material is attached to the operational exergy loss. Thus, the total 'cradle-to-cradle' exergy loss of the solution is devised. In this framework, the optimal solution will be that which destroys the minimal amount of exergy. Correspondingly, instead of relying upon the coefficient of performance (which is focused on operational consumption), we propose evaluation of cooling solutions in terms of the heat removal capacity per unit lifetime exergy consumption.The paper concludes by illustrating applicability of the method to the design of an enterprise server. It should be noted that although the paper is focused on electronics cooling solutions, the methodology is designed to be sufficiently general for use in any thermal management application.