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.

Future warship power systems may be subject to pulsed loads manifesting through emergent combat systems such as directed energy weapons, associated sensors and electronic warfare equipment.  The integration of combat system loads with the ship’s power system means that performance becomes intrinsically linked to combat effectiveness.  Hence, understanding the capability of the power system to service such loads is vital in ensuring the operator’s ability to fight the ship. This paper describes the challenge of pulse load integration from the perspective of the power system design authority.  Modelling and simulation has been employed to study the electrical response of a representative power system when subject to a range pulse load characteristics.  Subsequently, the effects of pulse loading are reviewed in terms of impact upon the prime mover. It is concluded that whilst electrical supply performance can be maintained within allowable power quality limits as defined by STANAG 1008, the mechanical effects can be to the detriment of engine life, highlighting key recommendations to understand both electrical and mechanical performance envelope in design for integration.

No abstract

Viable bioaerosols can deposit and multiply in airconditioning and mechanical ventilation (ACMV) systems. These bioaerosols can eventually enter indoor environments following the operation of the ACMV systems, contributing to indoor bioaerosol pollution. A method to identify and quantify viable bioaerosol emanation from an ACMV system and its impact on indoor bioaerosol pollution is proposed in this study. The method involves surface and air sampling of viable bioaerosols with analysis using a material-balance model. The proposed method was adopted to investigate the contribution of viable bioaerosol emanation from an ACMV system to indoor bioaerosol pollution in an air-conditioned room located in Singapore. The bioaerosol emanation rates from the ACMV system were found to be 2.4 CFU s-1 for viable bacteria and 3.9 CFU s-1 for viable fungi. Among various bioaerosol sources, bioaerosol emanation from the ACMV system was the largest source of indoor viable bacteria and the second largest source of indoor viable fungi in the air, behind the introduction of outdoor fungi through the mechanical ventilation. Potentially pathogenic bioaerosol species were also found in the ACMV system, which are in the genera of Staphylococcus, Moraxella and Aspergillus. Particularly, Moraxella osloensis, which is most likely to be emanated from occupants, was found to accumulate in the ACMV system, indicating the potential impact of the ACMV system's hygiene on indoor bioaerosol pollution. This study could contribute to the understanding of bioaerosol emanation from ACMV systems and their impact on indoor bioaerosol pollution. The proposed method could be used as a tool for analysing the potential sources of indoor bioaerosols and support the development of effective control measures against bioaerosol emanation from ACMV systems.

No abstract