ECOFAN: Augmented aero-acoustic liners for the design of cooling and air-conditioning fans

Energy efficiency has been identified as one of the key pillars of decarbonisation in the Net Zero Emissions by 2050 roadmap. It should be specially considered for the development of sustainable cities, as almost 80 % of the population lives in towns and consumes 78% of the primary energy. It is estimated that buildings account for 20% to 40% of the total energy consumption in developed countries. From that, the operation of air-conditioning and mechanical ventilation systems accounts for nearly half of the total building electricity consumption and this can be as high as 70% for buildings in the tropics or even higher during episodes of haze. The European Commission has identified three environmental parameters for best performing fans, namely the electricity consumption during use, the leakage of refrigerants over the product life and the radiated noise during use. Unfortunately, energy efficiency and noise are often competing entities and the EU directive has established that impact of the maximum sound power level requirements on the efficiency requirements is not fully understood. Therefore, further work and experimental tests in a sufficient number of appliances are necessary for a better eco-design. In this project, we intend to address jointly both requirements to go to the least life cycle cost level.

To reduce the radiated noise, liners placed inside ducted systems are widely used. However, these methods are responsible of a pressure drop along the duct, implying that the system has to compress the circulating gases to a higher pressure, requiring extra mechanical work and less energy available. It has been shown recently that the use of perforated metamaterials with physical characteristics properly optimised can provide wideband absorption with minimal flow pressure drop. Indeed, a micrometric size of the perforations and the increase of the perforation ratio can generate boundary slip flow conditions with a very low friction factor, so that the fan generating system does not have to compensate for eventual pressure drop of the wall-treatment to keep a nominal flow rate. The main objective of this proposal is to design augmented aeroacoustic liners to reduce at source both the noise pollution and the aerodynamic drag associated to ducted fans. The augmented treatment will be integrated in the fan casing of HVAC (Heat, Ventilation and Air-Conditioning) duct systems. It will involve several strategies including the use of architectured acoustic materials shielded from the flow by innovative low drag microperforated surfaces. It addresses two timely challenges inherent to the acoustics and fluid dynamics disciplines, namely the design of subwavelength wall-treatments able to dissipate low-frequency broadband HVAC noise components and the proposal for ultra-low drag and acoustically neutral surfaces shielding the liner from the flow. The outcomes are the eco-design of ventilating systems retrofitted with augmented liners leading to low fan-noise emissions, reduced aerodynamic drag and a higher energy efficiency. These performances translate directly into noise pollution reduction and energy consumption cutting, thereby contributing towards more sustainable and environmentally-friendly buildings targeted by environmental research/regulating councils, industrials and end users.