Application of acoustic agglomeration to enhance air filtration efficiency in air-conditioning and mechanical ventilation (ACMV) systems

Abstract

The recent episodes of haze in Southeast Asia have caused some of the worst regional atmospheric pollution ever recorded in history. In order to control the levels of airborne fine particulate matters (PM) indoors, filtration systems providing high PM capturing efficiency are often sought, which inadvertently also results in high airflow resistance (or pressure drop) that increases the energy consumption for air distribution. A pre-conditioning mechanism promoting the formation of particle clusters to enhance PM capturing efficiency without adding flow resistance in the air distribution ductwork could provide an energy-efficient solution. This pre-conditioning mechanism can be fulfilled by acoustic agglomeration, which is a phenomenon that promotes the coagulation of suspended particles by acoustic waves propagating in the fluid medium. This paper discusses the basic mechanisms of acoustic agglomeration along with influencing factors that could affect the agglomeration efficiency. The feasibility to apply acoustic agglomeration to improve filtration in air-conditioning and mechanical ventilation (ACMV) systems is investigated experimentally in a small-scale wind tunnel. Experimental results indicate that this novel application of acoustic pre-conditioning improves the PM2.5 filtration efficiency of the test filters by up to 10% without introducing additional pressure drop. The fan energy savings from not having to switch to a high capturing efficiency filter largely outstrip the additional energy consumed by the acoustics system. This, as a whole, demonstrates potential energy savings from the combined acoustic-enhanced filtration system without compromising on PM capturing efficiency.

Numerical investigation of spatially nonhomogeneous acoustic agglomeration using sectional algorithm

“…Acoustic agglomeration, as a preconditioning technique, is a process in which small particles in a suspension collide with one another to form large agglomerates under the action of a sound field. As a result, particle size distribution can shift significantly to a range of larger particulates within a short period of time, and the efficiency of conventional particle removal technologies is greatly improved Sarabia et al 1986;Malherbe et al 1988;Caperan et al 1995;Gallego-Juarez et al 1999;Yuen et al 2014;Ma et al 2017;Ng et al 2017).…”

Ecologically safe system of cleaning the air from polydisperse dust

“…At the same time, constructive ways to increase the efficiency of collecting fine fractions of the most commonly used collectors are practically ex hausted and most of the work is aimed at finding a solu tion to this problem by influencing the fractional compo sition of dust. In works [9,10], it is suggested that the acoustic coagulation of fine dust be made before the col lector, and in the work [11], the high frequency sound waves bands, that provide the best results, are defined. The main drawback of the method is the need to use ad ditional equipment -an acoustic wave generator.…”

Contribution of bioaerosol emission from air-conditioning and mechanical ventilation system to indoor bioaerosol concentration

“…Specifically, increase of indoor bioaerosol concentrations due to bioaerosol emission from the ACMV system has not been observed and bioaerosol emission of the ACMV system is still not quantified and species-identified, which makes it debatable that whether the ACMV system is helping to control indoor bioaerosol level or is worsening indoor air by emitting bioaerosols to indoor space. In addition to being potential bioaerosol emission source for the indoor space, the operation of ACMV systems accounts for nearly half of the total building electricity consumption in buildings under temperate climate and this can reach 70% for buildings in the tropics, where ACMV systems usually operate for longer time in a day compared to their operation in temperate indoor environment (Ng et al, 2017). Therefore, it is necessary to develop new approaches to avoid the significant energy consumption of operation of the ACMV system while control indoor pollutants level effectively.…”

“…The operation of ACMV systems accounts for nearly half of the total building electricity consumption in buildings under temperate climate (Pérez-Lombard et al, 2008) and this can reach 70% for buildings in the tropics, where ACMV systems usually operate for longer time in a day compared to their operation in template indoor environment (Ng et al, 2017). In buildings, energy consumption of operation of the ACMV system is predominant compared with other energy use such as lighting and appliance.…”

“…In building with ACMV system, filters inside the ACMV system predominantly serves to remove indoor bioaerosols and around 15% to 30% of the system energy consumption is devoted to air distribution, most of which is consumed by fans in the ACMV system to overcome losses (pressure drop) in the distribution ducts and across filters (Ng et al, 2017). The power that a fan spends on overcoming pressure drop of a filter could be calculated by：…”