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

Abstract

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.

Eksperimentinio Šilumos Siurblio Ciklo Valdymo Algoritmo Paieška / Experimental Study of the Heat Pump Cycle Control Algorithm Search

“…Teorinis modelis. Vilniaus Gedimino technikos universiteto (VGTU) mokslininkai savo analitiniame tyrime (Martinaitis, Streckiene, Bagdanavicius ir Bielskus, 2018) palygino vėdinimo įrenginių, turinčių skirtingą komplektaciją ir veikimo režimus, efektyvumą. Jų rezultatai rodo, kad aukščiausius efektyvumo rodiklius turi tradicinis vėdinimo įrenginys su integruotu šilumos siurbliu.…”

“…Valdymo algoritmas. Bandymo metu gautos šilumos siurblio veikimo ciklo kitimo tendencijos yra palankios ir artimos teorinio ciklo kitimo tendencijoms, parodytoms VGTU mokslininkų darbe (Martinaitis et al, 2018). Tokios tendencijos yra būdingos didelio efektyvumo teoriniam šilumos siurblio modeliui.…”

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

“…Such methodology (calculation procedure, algorithms) improves the potential of applying exergy analysis in the practical research of building microclimate systems. Consistent analysis of processes taking place therein lays down the foundation for preparing the methodology of thermodynamic (exergy) analysis aimed at assessing momentary and seasonal efficiency of air handling units and other HVAC systems, taking into account varying reference environment temperatures [24,43].…”

Exergy Analysis and Process Optimization with Variable Environment Temperature

“…Both combine exergy fluxes, the former in differences, the latter in ratios. As a matter of fact, numerous articles investigate the influence of the dead state temperature on the exergy efficiency of processes [8][9][10][11][12][13][14][15][16][17][18][19]: they study how a given process, often air conditioning, operates in various environmental conditions, especially with various values of the ambient temperature. As a main result, they show how exergy efficiency depends on the ambient temperature, an influence found to be strong especially for building applications [9,20].…”

“…The literature is somehow confusing about this point. In most of the articles mentioned above [8][9][10][11][12][13][14][15][16][17][18][19][20], the variable ambient temperature is taken as 'dead state' or 'reference' (a variable 'reference' then), but without any argument for supporting this option. Some authors propose to take an ad-hoc time-averaged ambient temperature as reference, either the hourly average [10,22,23], or the monthly average [10,22], raising then the paradox that 'the dead state varies with operating time' [23] but is in fact kept constant within a given time interval.…”