Tamás Régert, Gergely Kristóf, Tamás Lajos of Budapest University of Technology & Economics, Budapest, Hungary; and Atul Karanjkar, Fluent Europe

Budapest, the capital of Hungary, is one of the most beautiful cities in the world. One of the jewels in its architectural crown is the Budapest Opera House, built by Miklós Ybl in 1884 at the height of the Austro-Hungarian Empire. It has several ornate decorations that are stunning, and like many public buildings of its vintage, was designed with natural ventilation in mind. One ventilation feature, for example, is a central chimney above a large chandelier that hangs from the ceiling.

When a Fluent Europe staff member visited the local Fluent partner in Budapest last year, the two went to the Opera House to see Tchaikovsky’s Eugen Onegin. It was a hot day in May, and both felt that the building was quite warm during the performance. The experience inspired them to contact the technical manager of the Opera House and introduce him to Fluent’s CFD software, a tool that could help find a solution to the building’s thermal comfort control problem.

At the beginning of the last century the Opera House’s natural ventilation system relied on drafts that were governed by the temperature differential across the central chimney. This meant that higher temperatures were needed in the upper reaches of the building in comparison to the cooler temperatures outside. The natural drafts acted to draw air up and out of the auditorium. Vents underneath the seating area could be opened to permit air to flow into the auditorium, if needed. During the summer months, the incoming air passed over ice blocks to provide additional cooling. In the past decades the ventilation system was modernized several times, with the last upgrade occurring in the 1980s. During the renovations, forced ventilation and air conditioning systems were introduced, and the stage was outfitted with a separate air conditioning system, which prevents crossflow between the auditorium and stage.

Fluent’s Hungarian partner decided to offer the manager of the Opera House a free HVAC assessment of their building, with the goal of identifying hot spots during a typical performance. The CFD simulation encompassed the whole auditorium (minus the stage) with the simulated effect of an audience of 1250 heat-generating people and the lights dimmed. The realizable k-e turbulence model was used in the study and full buoyancy effects were included. The CFD results showed that the orchestra pit ventilation was poor in places, a fact that musicians all too readily confirmed from their own experiences. Thermal anomalies in the balconies were also correctly identified.

Path lines, colored by temperature, show differences of up to 5°C throughout the seating area and orchestra pit

A view from the stage of the simulated auditorium, showing temperature contours

This is not the first time that consultants have helped the Budapest Opera House. Fifty years ago, the celebrated scientist Leo Beranek, an expert in the field of acoustics, carried out a sound characterization of the building. His data is still in use today. Fluent’s CFD study will be used in an upcoming reconstruction and modernization of the Opera House, which will include an overhaul of its air conditioning system. Once the renovations are complete, opera enthusiasts in Budapest will no doubt be appreciative of Fluent’s CFD efforts for the next fifty years!

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