Functional exergy efficiency of an air heat recovery exchanger under varying environmental temperature

Martinaitis, Vytautas; Streckienė, Giedrė; Biekša, Darius; Šiupšinskas, Giedrius; Bielskus, Juozas

doi:10.1504/ijex.2018.089548

Cited by 3 publications

(9 citation statements)

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“…It equals 0 for the evaporator as when Figure 13 shows the same temperature cases by expressing the states of heat exchangers in coenthalpies. It should be noted that in the exergy analysis of the HRE [20,45], the hot and cool working fluids of the heat exchanger are the air with the same mass flow rate, thus the results of the analysis are interpreted directly on the basis of the variation of the coenthalpies of the working fluid. When the HRE, EV and CN are assessed in an integral manner, this advantage disappears.…”

Section: Case Study -Results and Discussionmentioning

confidence: 99%

“…The authors have published papers on the impact of the varying RT on the direction of the exergy flow when the heat flow is stable [20], [44]. Here we have a stationary heat transfer process that is caused by stable temperatures Th = 20°C and Tc = -20°C.…”

Section: Exergy Efficiency Of Stationary Heat Transfer Process At Varmentioning

confidence: 99%

“…When performing the analysis of AHU components, a methodology for the thermodynamic analysis of the HRE at a varying RT when its values cross the temperatures of working fluids was prepared. Paper [44] proposes a solution using the Carnot factor while in [20], [45] coenthalpies were applied. In addition to this, the methodology for the HRE for determining universal and several functional exergy efficiencies was developed in [45].…”

Section: Features Of Exergy Analysis Of Heat Exchangers In the Ahumentioning

confidence: 99%

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From Entropy Generation to Exergy Efficiency at Varying Reference Environment Temperature: Case Study of an Air Handling Unit

Streckienė

Martinaitis

Bielskus

2019

Preprint

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The continuous energy transformation processes in heating, ventilation and air conditioning systems of buildings are responsible for 36% of global final energy consumption. Tighter thermal insulation requirements for buildings have significantly reduced heat transfer losses. Unfortunately, this has little effect on energy demand for ventilation. On the basis of the First and the Second Law of Thermodynamics, the concepts of entropy and exergy are applied to the analysis of ventilation air handling unit (AHU) with a heat pump in this paper. This study aims to develop a consistent approach for this purpose, taking into account the variations of reference temperature and temperatures of working fluids. An analytical investigation on entropy generation and exergy analysis are used, when exergy is determined by calculating coenthalpies and evaluating exergy flows and their directions. The results show that each component of the AHU has its individual character of generated entropy, destroyed exergy and exergy efficiency variation. However, the evaporator of heat pump and fans have unabated quantities of exergy destruction. The exergy efficiency of AHU decreases from 45-55% to 12-15% when outdoor air temperature is within the range of -30°C…+10°C, respectively. This helps to determine conditions and components of improving the exergy efficiency of the AHU at variable real-world local climate conditions. The presented methodological approach could be used in the dynamic modelling software and contribute to a wider application of the Second Law of Thermodynamics in practice.

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Section: Case Study -Results and Discussionmentioning

confidence: 99%

Section: Exergy Efficiency Of Stationary Heat Transfer Process At Varmentioning

confidence: 99%

Section: Features Of Exergy Analysis Of Heat Exchangers In the Ahumentioning

confidence: 99%

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From Entropy Generation to Exergy Efficiency at Varying Reference Environment Temperature: Case Study of an Air Handling Unit

Streckienė

Martinaitis

Bielskus

2019

Preprint

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“…It should especially be taken into account when the analyzed processes take place at near environmental temperatures. Processes that take place in AHUs have these exact characteristics [20]. However, when performing exergy research, different authors interpret environmental conditions differently, sparking scientific discussion [15].…”

Section: Introductionmentioning

confidence: 99%

“…However, when performing exergy research, different authors interpret environmental conditions differently, sparking scientific discussion [15]. In some cases, reference parameters are variables [20][21][22], and in others they are constant, e.g., the average reference temperature and pressure [23]. It is also noted that the use of design or mean outdoor temperatures for exergy analysis may lead to significant uncertainties [21].…”

Section: Introductionmentioning

confidence: 99%

From Entropy Generation to Exergy Efficiency at Varying Reference Environment Temperature: Case Study of an Air Handling Unit

Streckienė

Martinaitis

Bielskus

2019

Entropy

Self Cite

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The continuous energy transformation processes in heating, ventilation, and air conditioning systems of buildings are responsible for 36% of global final energy consumption. Tighter thermal insulation requirements for buildings have significantly reduced heat transfer losses. Unfortunately, this has little effect on energy demand for ventilation. On the basis of the First and the Second Law of Thermodynamics, the concepts of entropy and exergy are applied to the analysis of ventilation air handling unit (AHU) with a heat pump, in this paper. This study aims to develop a consistent approach for this purpose, taking into account the variations of reference temperature and temperatures of working fluids. An analytical investigation on entropy generation and exergy analysis are used, when exergy is determined by calculating coenthalpies and evaluating exergy flows and their directions. The results show that each component of the AHU has its individual character of generated entropy, destroyed exergy, and exergy efficiency variation. However, the evaporator of the heat pump and fans have unabated quantities of exergy destruction. The exergy efficiency of AHU decreases from 45–55% to 12–15% when outdoor air temperature is within the range of −30 to +10 °C, respectively. This helps to determine the conditions and components of improving the exergy efficiency of the AHU at variable real-world local climate conditions. The presented methodological approach could be used in the dynamic modelling software and contribute to a wider application of the Second Law of Thermodynamics in practice.

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Evaluation of the optimum pressure of the intercooler and the regenerator in the Bryton cycle based on exergy and energy analysis

Adibi

2021

Thermophys. Aeromech.

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Functional exergy efficiency of an air heat recovery exchanger under varying environmental temperature

Cited by 3 publications

References 0 publications

From Entropy Generation to Exergy Efficiency at Varying Reference Environment Temperature: Case Study of an Air Handling Unit

From Entropy Generation to Exergy Efficiency at Varying Reference Environment Temperature: Case Study of an Air Handling Unit

From Entropy Generation to Exergy Efficiency at Varying Reference Environment Temperature: Case Study of an Air Handling Unit

Evaluation of the optimum pressure of the intercooler and the regenerator in the Bryton cycle based on exergy and energy analysis

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