Is the air change efficiency sufficient to assess the removal of airborne contamination in mixing ventilation?

This investigation analyze the correlation between two common methods to assess the ventilation effectiveness: An averaged contamination removal effectiveness (CRE) value based on the residual lifetime and the air change efficiency (ACE) to better understand their relationship to then give a recommendation for the IAQ-assessment of ventilation designs. The present numerical investigation puts focus on a simple mixing ventilation scenario with different conditions: air change rate, specific heat flux, supply air diffuser and exhaust position. Statistically, the results show a significant correlation. A detailed consideration, especially for the partial load range, will be necessary to for a valide determination of removing airborne contaminationpublishedVersio

Strömungstechnische Untersuchungen an einem neuartigen Wärmespeichersystem für solarthermische Kraftwerke

Mit der Entwicklung eines neuartigen Wärmespeichers für solarthermische Kraftwerke werden im Rahmen dieser Studienarbeit ungeklärte Teilaspekte untersucht. Der Schwerpunkt der Untersuchungen ist die strömungstechnische Auslegung des Speicherbehälters. Verschieden Behälterformen werden auf Druckverlust und Ausnutzung geprüft, dabei werden Auftriebseffekte berücksichtigt. Mögliche Behälterformen für den Speicher sind ein axial oder ein radial durchströmter Zylinder oder ein liegend durchströmter Quader. Die Bewertung der Ausnutzung erfolgt mit einen Gleichförmigkeitsindex, der die Abweichung des Geschwindigkeitsprofils zur mittleren Geschwindigkeit vergleicht. Zur Optimierung der Gleichförmigkeit wird eine Lochplatte entwickelt, die für kurze Einströmwege eingesetzt werden soll. Für die Erstellung der Modelle und Berechnungen wird ANSYS-CFX verwendet

Prävention luftübertragener Infektionen: Ein Vergleich von Misch- und Quelllüftung in einem Besprechungsraum

Usually, displacement ventilation is characterized by a higher ventilation effectiveness than mixing ventilation. Is it therefore a better prevention of airborne infection? This CFD investigation shows a correlation between the ventilation effectiveness and the contribution of the exhaled air of an infectious person to other occupants in a meeting room

Numerical approach to improve UVC radiation for air disinfection and investigation of the scalability

This study simulates the inactivation of SARS-CoV-2 viruses by UVC radiation. A reference case is simulated with computational fluid dynamics, which is designed the same way as the experimental decentral air purifier test device to use valid boundary data. The UVC radiation sources are small LEDs. They are implemented on the inside faces of two penetrable baffles in the airway. The distance between the two baffles and the slots in the baffles will be altered. The number of open slots determines the flow structure in the light chamber. IF all slots are open the flow is straight through the chamber. In two other cases the flow is forming a vortex. The simulations have three goals: First, validate the CFD-model with experimental data. Second, maximizing the radiation on each simulated aerosol and reducing the pressure difference of the device. Third, is to show the scalability to larger HVAC devices. In this study a maximum UVC dose is reached with partly closed slots and short distance between the baffles. Generally, more slots reduce the pressure loss. Extending the light chamber increase the radiation dosage for straight flows, in the case of vortex flow the dosage decreases. The problem is scalable, the solution is only partly scalable

Validierung von numerisch berechneten Geschwindigkeitsverteilung in isothermen Mischlüftungsfällen mit Particle Streak Tracking

This is a validation study for the velocity distribution in mixing ventilation. Two different supply air diffusers a slot and a swirl diffuser form two different room airflows. For the swirl diffuser two different and for the slot diffuser five different exhaust positionings are tested numerically and experimentally. A comparison of the flow structure shows good agreement between simulation and experiment for six air changes per hour, but not for the lower air change rate of 1.5 per hour. The velocity deviations between experiment and simulation are higher for the swirl diffuser. These exist partly due to the experimental methodology, but also due to an overestimation of the supply air momentum. Thus further sensitivity investigations are carried out for the swirl diffuser. The overestimation of the supply air momentum depends mainly on an geometric model error in the CFD simulation. A comparison of different turbulence models confirms the advantages of the RST elliptic blending turbulence model over the k-epsilon realizable model for the swirl diffuser case

Is the air change efficiency sufficient to assess the removal of airborne contamination in mixing ventilation?

This investigation analyze the correlation between two common methods to assess the ventilation effectiveness: An averaged contamination removal effectiveness (CRE) value based on the residual lifetime and the air change efficiency (ACE) to better understand their relationship to then give a recommendation for the IAQ-assessment of ventilation designs. The present numerical investigation puts focus on a simple mixing ventilation scenario with different conditions: air change rate, specific heat flux, supply air diffuser and exhaust position. Statistically, the results show a significant correlation. A detailed consideration, especially for the partial load range, will be necessary to for a valide determination of removing airborne contaminatio