Introduction
The night-time noise emission thresholds set by regulations leave no room for manoeuvre: a few decibels above them is enough to render a site non-compliant. Groupe Boët was called in to deal with noise emissions from six rooftop chillers at the Hôpital Saint-Louis in Paris, in an occupied site with simultaneous structural, aeraulic and operating constraints.
Acoustic compliance in urban hospitals
Hôpital Saint-Louis is located in the 10th arrondissement of Paris, less than fifty meters from local residents. In this context, night-time noise emissions from technical equipment are subject to strict emergence thresholds: the difference between ambient residual noise and ambient noise with equipment in operation may not exceed 3 dB(A) at night. A preliminary acoustic study established that, without specific treatment, the installation of six rooftop chillers would place the site outside regulatory compliance.
Noise reduction therefore had to be addressed prior to commissioning. The challenge wasn’t just acoustic: the work was to be carried out on a roof terrace twenty-five meters above ground, on a hospital in continuous operation, with structural load, ventilation performance and maintenance access constraints to be taken into account right from the design stage.
6 rooftop chillers: a layout with no margins
Chillers generate noise emissions from air radiation on all sides, as well as from the flow of hot air discharged at the top. Any noise control device must therefore attenuate these lateral emissions without disturbing the vertical thermal discharge – otherwise hot air will recirculate, degrading or even damaging the equipment’s performance.
On a site in operation, the constraint is even greater: the intervention must allow access to the equipment for routine maintenance operations, without dismantling the acoustic solution. Working height on the roof and resistance to wind loads also required rigorous structural dimensioning of the supporting framework.
Perimeter acoustic screen design
Groupe Boët designed a 3.50-metre-high, four-sided perimeter acoustic screen to enclose all the equipment. The solution is based on BSP 100 sound-absorbing panels, assembled on a galvanized steel framework designed to withstand the roof loads and wind forces applicable in urban areas at this height.
Particular attention was paid to the treatment of junctions between panels: any acoustic leakage or parasitic transmission at connection points would have compromised the overall efficiency of the system. The upper part of the screen was left open in a controlled manner, in order to preserve the air flows required to operate the chillers and avoid any thermal recirculation. An acoustic opening integrated into the structure allows maintenance access without breaking the continuity of the acoustic barrier. The entire project was carried out on an occupied site, over a period of around two weeks, with no interruption to hospital activity.
Groupe Boët relies on ISO 9001 and ISO 19443-certified manufacturing, in compliance with EN 15085, ASME, RCC-M, CODAP and CODETI construction codes.
Results: noise levels compliant, operations preserved
After installation of the acoustic screen, sound levels measured at the neighbouring facade were between 44 and 48 dB(A). Regulatory compliance is achieved both day and night, in compliance with the emergence thresholds applicable to the site. The aeraulic performance of the chillers has been fully preserved: no thermal recirculation has been observed. Maintenance access to the equipment is maintained via the integrated opening, with no need for dismantling.
This result confirms that noise control in hospital roofs requires an integrated design approach, simultaneously addressing acoustic, thermal, structural and operational constraints – and not an isolated acoustic approach.
An integrated acoustic approach for sensitive urban environments
This project at Hôpital Saint-Louis demonstrates that it is possible to achieve regulatory compliance for technical installations on urban roofs, without compromising equipment performance or site operation. Groupe Boët designs industrial acoustic solutions adapted to the most complex constraints, from preliminary study to implementation. For all noise control projects in sensitive environments, contact Groupe Boët for a customized acoustic analysis.