This thesis, developed within a professional design activity carried out in collaboration with an engineering company operating in the HVAC sector, develops and validates a thermo-hygrometric model for the energy-optimized design of a data center cooling system based on Air Handling Units (AHUs) maximizing direct free-cooling, as an alternative to conventional chiller-based configurations with indirect free-cooling. The engineering problem addressed concerns the reduction of mechanical cooling energy demand in data centers while ensuring compliance with the thermo-hygrometric constraints required for IT equipment reliability. The following design limits were adopted: supply air temperature of 20 °C, return air temperature up to 35 °C, and absolute humidity range between 0.005 and 0.011 kg/kg. A model based on mass and enthalpy balance equations for outdoor air and return air mixing was developed and implemented through an hourly decision-making algorithm in Excel. The model automatically determines the optimal operating regime among: full free-cooling, partial free-cooling with controlled mixing, and auxiliary chiller activation. The annual climatic analysis, conducted using meteorological data from the actual project site, shows that outdoor conditions allow free-cooling operation for a significant portion of the year (up to approximately six months), substantially extending the operational range compared to indirect free-cooling chillers, whose fully passive operation is typically limited to outdoor temperatures below approximately 9 °C. The energy comparison with a conventional system (average chiller EER of 3.1) demonstrates a substantial reduction in compressor operating hours and a consequent decrease in annual electrical consumption for cooling production. This reduction results in an improved local Power Usage Effectiveness (PUE) and a significant decrease in cooling-related OPEX. The results demonstrate that a full-air direct free-cooling approach represents an energetically dominant solution in temperate climates, provided that accurate thermo-hygrometric control and consistent airflow dimensioning are ensured.
La presente tesi, sviluppata nell’ambito di un’esperienza progettuale svolta in collaborazione con un’azienda operante nel settore impiantistico, sviluppa e valida un modello termo-igrometrico per la progettazione energeticamente ottimizzata di un sistema di climatizzazione per sale CED basato su Unità di Trattamento Aria (UTA) a massimo sfruttamento del free-cooling diretto, in alternativa a configurazioni tradizionali con chiller e free-cooling indiretto. Il problema ingegneristico affrontato riguarda la riduzione della quota di energia destinata alla produzione meccanica di freddo nei data center, mantenendo il rispetto dei vincoli termo-igrometrici imposti dall’affidabilità delle apparecchiature IT. Sono stati adottati i seguenti limiti di progetto: temperatura di mandata pari a 20 °C, temperatura di ripresa fino a 35 °C e umidità assoluta compresa tra 0,005 e 0,011 kg/kg. È stato sviluppato un modello basato su bilanci di massa ed entalpia per la miscelazione aria esterna/aria di ricircolo, implementato tramite algoritmo decisionale orario in ambiente Excel. Il modello determina automaticamente il regime operativo ottimale tra: free-cooling totale, free-cooling parziale con miscelazione controllata e attivazione del chiller di supporto. L’analisi climatica annuale, condotta sui dati meteorologici del sito reale oggetto di progettazione, evidenzia che le condizioni esterne consentono il funzionamento in free-cooling per una quota significativa dell’anno (fino a circa sei mesi complessivi), estendendo notevolmente il campo operativo rispetto a un chiller con free-cooling indiretto, il cui funzionamento completamente passivo è limitato a temperature esterne inferiori a circa 9 °C. Il confronto energetico con un sistema tradizionale (EER medio del chiller pari a 3,1) mostra una drastica riduzione delle ore di funzionamento dei compressori e una conseguente diminuzione del consumo elettrico annuo per la produzione di freddo. Tale riduzione si traduce in un miglioramento del Power Usage Effectiveness (PUE) locale e in una significativa contrazione dell’OPEX legato al raffrescamento. I risultati dimostrano che l’approccio a free-cooling diretto a tutt’aria rappresenta, nel contesto applicativo analizzato, una soluzione energeticamente dominante nei climi temperati, purché supportata da un controllo termo-igrometrico accurato e da un dimensionamento coerente delle portate d’aria.
Valutazione energetica e modellazione termo-igrometrica di sistemi di raffreddamento a tutt'aria per sale CED
Piciocco, Emanuele
2024/2025
Abstract
This thesis, developed within a professional design activity carried out in collaboration with an engineering company operating in the HVAC sector, develops and validates a thermo-hygrometric model for the energy-optimized design of a data center cooling system based on Air Handling Units (AHUs) maximizing direct free-cooling, as an alternative to conventional chiller-based configurations with indirect free-cooling. The engineering problem addressed concerns the reduction of mechanical cooling energy demand in data centers while ensuring compliance with the thermo-hygrometric constraints required for IT equipment reliability. The following design limits were adopted: supply air temperature of 20 °C, return air temperature up to 35 °C, and absolute humidity range between 0.005 and 0.011 kg/kg. A model based on mass and enthalpy balance equations for outdoor air and return air mixing was developed and implemented through an hourly decision-making algorithm in Excel. The model automatically determines the optimal operating regime among: full free-cooling, partial free-cooling with controlled mixing, and auxiliary chiller activation. The annual climatic analysis, conducted using meteorological data from the actual project site, shows that outdoor conditions allow free-cooling operation for a significant portion of the year (up to approximately six months), substantially extending the operational range compared to indirect free-cooling chillers, whose fully passive operation is typically limited to outdoor temperatures below approximately 9 °C. The energy comparison with a conventional system (average chiller EER of 3.1) demonstrates a substantial reduction in compressor operating hours and a consequent decrease in annual electrical consumption for cooling production. This reduction results in an improved local Power Usage Effectiveness (PUE) and a significant decrease in cooling-related OPEX. The results demonstrate that a full-air direct free-cooling approach represents an energetically dominant solution in temperate climates, provided that accurate thermo-hygrometric control and consistent airflow dimensioning are ensured.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/252095