Sixty years after its opening, the National Theatre Mannheim is undergoing a comprehensive refurbishment. Air outlets from Kiefer Klimatechnik will ensure a comfortable theatre experience in the future. The Stuttgart-based specialist developed various ventilation solutions specifically for this project – including a newly engineered floor air diffuser for the auditoriums of both the opera and theatre. In the course of this, complex functional tests were carried out in the in-house room flow laboratory.

The National Theatre Mannheim (NTM) has been the city's cultural flagship for more than 60 years. However, its historical roots go back to the 18th century, when Elector Carl Theodor commissioned the conversion of an armoury into a theatre in 1775. Since only German-language plays that supported the national spirit were performed there, the venue quickly earned the name "National Theatre". Today, the NTM is considered the oldest municipal theatre in Germany. After its destruction in the Second World War, the current building, designed by architect Gerhard Weber, was inaugurated in 1957 at Goetheplatz. At the time, it was regarded as one of the most modern theatre buildings in the world and has since been officially listed as a heritage site due to its post-war modernist architecture.

Decades of use have taken their toll on the building, and without major upgrades, the operating licence would have expired in 2022. In 2016, the Mannheim-based architecture firm Schmucker & Partner was commissioned to plan and implement the general refurbishment of the theatre at a cost of over 247 million euros. Construction work began in 2022, and completion is scheduled for the 2028/29 season.

The listed building is being renovated in line with strict heritage requirements. The goal is to eliminate fire protection, structural, acoustic, and physical building deficiencies and bring the building up to modern technical and legal standards. At the same time, improvements to the internal spatial organisation will address operational and safety-related deficits. In addition to the refurbishment of the opera and drama houses and their three foyers, the theatre café will be renovated, and the orchestra rehearsal hall – located deep within the structure – will be extended under complex structural conditions. A new choir rehearsal room and production workshops will be built beneath the forecourt at Goetheplatz. Above ground, the plaza will be redesigned in accordance with heritage regulations and adapted to climate-related requirements.

In the theatre and opera house venues, an important focus is on the contemporary and energy-efficient renovation of the building and stage technology. For example, all visible surfaces such as walls, ceilings and floors are being refurbished or replaced in line with listed building requirements, as is the seating in the auditoriums. Especially in cultural venues and stage areas such as concert halls or theatres, high demands are placed on indoor air quality. In large rooms where many people come together, a consistently good indoor climate is important. Fresh, oxygen-rich air without noticeable draughts is key to ensuring comfort – and that is why the air distribution systems are also being upgraded. A new acoustic concept is being introduced in the playhouse to improve sound quality.

The new air outlets from Kiefer will contribute significantly to an undisturbed cultural experience. The supply air is fed into the auditorium by means of a pressurised floor via the seated floor steps. The existing diffusers were embedded in the concrete steps and had a trapezoidal shape. Almost every seat has its own air outlet for preconditioned outside air. The exhaust air is discharged via the ceiling. During the ventilation system upgrade, Kiefer was brought on board.

HTS Technische Gebäudesystem GmbH, based in Ludwigshafen and responsible for the complex building services engineering during the refurbishment, entrusted Kiefer with a key task: the development, evaluation and optimisation of new, project-specific air outlets for various application areas within the theatre – including integrated supply air systems embedded in the tiered seating of both auditoriums.

Martin Grüber, Managing Director of HTS GmbH, explains: “As part of the refurbishment and renewal of the ventilation system that we were carrying out, the brief for Kiefer was to design a new step outlet that would exceed the requirements of the existing air diffuser in terms of room air flow, acoustics and ease of maintenance.”

Daniel Nack, Head of Development at Kiefer Klimatechnik, adds: “The new air outlet had to match the existing design, construction and integration. This left very little room for modification, which made it a major technical challenge to meet or even exceed today’s standards.”

The first step was a detailed analysis of the existing system. At the company’s in-house airflow laboratory, part of the Kiefer Development Centre, engineers can carry out aerodynamic and acoustic measurements quickly and precisely – often in full-scale test rooms. The existing diffuser was removed by core drilling, then measured and tested in terms of air volume flow, pressure loss and acoustic performance. The results were compared with the specifications set out in the tender documents.

In the second step, the Kiefer development team set about designing and testing an initial prototype for the new air outlet. “Aspects such as airflow behaviour, acoustic performance, maintenance access and integration – in this case, a concrete-embedded outlet – were decisive in the design,” explains Nack. “The shape of the discharge flow is influenced by the geometry of the outlet neck, the grille and the internal flow contours.”

To optimise airflow, several outlet geometries were created and tested in a series of airflow measurements. These tests included analysis of throw characteristics and air distribution within the room. A three-dimensional flow visualisation using fog fluid complemented the measurements. The result: the new, optimised outlet achieved a significantly improved horizontal and vertical air distribution. The upper outlet contour directs the supply air evenly upward, while the removable lower contour acts as both an aerodynamic guide and a dust trap – making cleaning and maintenance easier.

Thanks to the modified discharge geometry, the outlet also ensures improved temperature distribution and air velocity near the floor. This leads to greater thermal comfort. At a maximum supply air volume flow of 25 m³/h per outlet, the temperature difference between supply air and room air is minimised within a short distance. The maximum local air velocity measured 5 cm above the floor was reduced from 0.52 m/s to 0.26 m/s, preventing draught-related discomfort. Local temperature deviations near the floor, previously at ±0.5 K, are now reduced to ±0.3 K with the new outlet model.

The measurements also showed a marked acoustic improvement. Venues such as theatres and concert halls place strict demands on acoustic quality. Room geometry, surface materials and the use of sound-absorbing or sound-reflecting elements all play a decisive role in achieving optimal sound distribution, speech intelligibility and low reverberation times.

This was no longer the case in the existing building. For example, rehearsals in the underground orchestra rehearsal hall could only take place with hearing protection due to the high sound pressure at full capacity. The sound pressure here reached levels that no longer complied with health and safety regulations. The new seating, including floor ventilation in the auditorium, is therefore an integral part of the acoustic room concept and is being scrutinised in detail. Poorly designed air outlets could also impair the acoustics in the room due to disruptive airflow noise. However, the A-weighted overall sound power level of the new outlet is reduced by at least 12 dB(A) in the acoustically measurable range in the echo chamber compared to the existing outlet.

The positive results from the laboratory test were evaluated and approved by Kiefer and the project partners in the third step. Based on these findings, Kiefer developed installation recommendations to ensure optimal system performance. Around 1,660 step air outlets went into series production and are expected to be installed by the end of 2024. Kiefer is also developing further displacement and floor air outlets for the foyer areas and galleries of the opera house and theatre.