Analysis of exergy demand for air heating of an air handling unit

Misevičiūtė, Violeta; Valančius, Kęstutis; Motuzienė, Violeta; Rynkun, Genrika

doi:10.1007/s12053-016-9499-7

Cited by 9 publications

(7 citation statements)

References 16 publications

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“…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%

“…It is also noted that the use of design or mean outdoor temperatures for exergy analysis may lead to significant uncertainties [21]. When assessing the energy system of a building in a selected timeframe in terms of exergy, e.g., ventilation AHU, it is noted that the maximum energy consumption occurs only at a specific reference temperature [22,24] and does not necessary correspond with the design temperature for energy calculations.…”

Section: Introductionmentioning

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

Entropy

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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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Section: Introductionmentioning

confidence: 99%

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

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“…The use of environmental control systems has significantly increased in the building sector in order to reduce the energy consumption of heating, ventilation, and air-conditioning (HVAC) systems [1]. Air handling units (AHUs) are one of the most complex building service systems [2], and can include heating, cooling, humidifier, mixing element, and heat recovery units, in order to provide the required indoor air quality and thermal comfort in conditioned spaces [3].…”

Section: Introductionmentioning

confidence: 99%

Energy Performance Investigation of a Direct Expansion Ventilation Cooling System with a Heat Wheel

Kassai

2019

Energies

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Climate change is continuously bringing hotter summers and because of this fact, the use of air-conditioning systems is also extending in European countries. To reduce the energy demand and consumption of these systems, it is particularly significant to identify further technical solutions for direct cooling. In this research work, a field study is carried out on the cooling energy performance of an existing, operating ventilation system placed on the flat roof of a shopping center, located in the city of Eger in Hungary. The running system supplies cooled air to the back office and storage area of a shop and includes an air-to-air rotary heat wheel, a mixing box element, and a direct expansion cooling coil connected to a variable refrigerant volume outdoor unit. The objective of the study was to investigate the thermal behavior of each component separately, in order to make clear scientific conclusions from the point of view of energy consumption. Moreover, the carbon dioxide cross-contamination in the heat wheel was also analyzed, which is the major drawback of this type heat recovery unit. To achieve this, an electricity energy meter was installed in the outdoor unit and temperature, humidity, air velocity, and carbon dioxide sensors were placed in the inlet and outlet section of each element that has an effect on the cooling process. To provide continuous data recording and remote monitoring of air handling parameters and energy consumption of the system, a network monitor interface was developed by building management system-based software. The energy impact of the heat wheel resulted in a 624 kWh energy saving and 25.1% energy saving rate for the electric energy consumption of the outdoor unit during the whole cooling period, compared to the system without heat wheel operation. The scale of CO2 cross-contamination in the heat wheel was evaluated as an average value of 16.4%, considering the whole cooling season.

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“…Due to increased thermal insulation of building envelope the heat demand for space heating reduces [1]. Therefore, in modern low energy buildings the major energy consumers are ventilation and air conditioning systems that are designed to provide air of suitable quality [2,3].…”

Section: Introductionmentioning

confidence: 99%

“…Some researchers recommend using the reference (dead) state temperature, which is based on the daily or monthly average temperature [13] or on the average annual temperature of particular location [14]. Others perform studies based on seasonal temperatures [3,15,16]. Torío et al [17] has conducted research on the selection of the reference temperature for the exergy analysis.…”

Section: Introductionmentioning

confidence: 99%

A comparative thermodynamic analysis of air handling units at variable reference temperature

Martinaitis

Streckienė

Bagdanavičius

et al. 2018

Applied Thermal Engineering

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Ventilation and air conditioning systems are emerging as the major energy consumers in low energy buildings. The objective of this paper is to present new methodology for assessment of Air Handling Units (AHUs) taking into account the variations of reference temperature. The methodology using the concept of coenthalpy, developed for heat exchangers and published by the authors previously has been used. Four AHUs that comprise energy transfer devices, such as: Water-to-Air Heater (WAH), Heat Recovery Exchanger (HRE) and Heat Pump (HP) have been investigated. Thermodynamic parameters including Coefficient of Performance (COP), universal and functional exergy efficiencies have been used to compare AHUs and to calculate the exergy destruction in AHU components at variable environment temperature-30°C…+10°C. The results of this study show that using HRE the COP and exergy efficiencies are significantly better compared with AHU without HRE. Using the HRE of higher effectiveness, the thermodynamic indicators can be improved considerably. The study shows that AHUs equipped with HP with advanced control method and HRE are more advantageous compared with other investigated AHUs. The presented methodology could have practical application for evaluating of energy and exergy efficiency of AHUs at different reference temperatures when designing HVAC systems and implementing optimum control methods.

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Analysis of exergy demand for air heating of an air handling unit

Cited by 9 publications

References 16 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

Energy Performance Investigation of a Direct Expansion Ventilation Cooling System with a Heat Wheel

A comparative thermodynamic analysis of air handling units at variable reference temperature

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