a b s t r a c tThis paper investigated the transmission of respiratory droplets between two seated occupants equipped with one type of personalized ventilation (PV) device using round movable panel (RMP) in an office room. The office was ventilated by three different total volume (TV) ventilation strategies, i.e. mixing ventilation (MV), displacement ventilation (DV), and under-floor air distribution (UFAD) system respectively as background ventilation methods. Concentrations of particles with aerodynamic diameters of 0.8 mm, 5 mm, and 16 mm as well as tracer gas were numerically studied in the Eulerian frame. Two indexes, i.e. intake fraction (IF) and concentration uniformity index R C were introduced to evaluate the performance of ventilation systems. It was found that without PV, DV performed best concern protecting the exposed manikin from the pollutants exhaled by the polluting manikin. In MV when the exposed manikin opened RMP the inhaled air quality could always be improved. In DV and UFAD application of RMP might sometimes, depending on the personalized airflow rate, increase the exposure of the others to the exhaled droplets of tracer gas, 0.8 mm particles, and 5 mm particles from the infected occupants. Application of PV could reduce R C for all the three TV systems of 0.8 mm and 5 mm particles. PV enhanced mixing degree of particles under DV and UFAD based conditions much stronger than under MV based ones. PV could increase the average concentration in the occupied zone of the exposed manikin as well as provide clean personalized airflow. Whether inhaled air quality could be improved depended on the balance of pros and cons of PV.

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a b s t r a c tThe inter-flat dispersion of hazardous air pollutants in residential built environment has become a growing concern, especially in crowed urban areas. The purpose of present study is to investigate the wind induced air pollutant transmission and cross contamination routes in typical buildings. In this paper, a series of experiments was carried out in a boundary layer wind tunnel using a 1:30 scaled model that represented the typical configuration of rectangular multi-storey residential buildings in Shanghai. Sulfur hexafluoride (SF 6 ) was employed as tracer gas in the wind tunnel tests. The conditions under two ventilation modes, i.e. single-sided natural ventilation and cross natural ventilation, were compared. The tracer gas concentration distributions under four approaching wind angles were monitored and analyzed. Computational Fluid Dynamics (CFD) method was adopted to assist in analyzing airflow patterns. The experiment results elucidated that in the two ventilation scenarios, both of the vertical and horizontal inter-flat airborne transmission could proceed. The wind direction played a key role on the pollutant concentration distribution. Compared with the single-sided ventilation mode, cross ventilation could weaken the air pollutant dispersion along the vertical direction when the contamination source was on the windward or on the leeward unit. When the wind blowing parallelly to the source unit window, namely the source room was on the sideward, cross ventilation would not suppress the vertical transport on one hand, but reinforce the horizontal transmission on the other hand. The study is helpful for the analysis of infection risk of respiratory diseases in the residential buildings.

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DC and DC/AC hybrid distribution and energy storage for shipboard power systems (SPS) are becoming a major trend due to efficiency improvement, space saving, and maneuverability enhancement. This paper has taken a real hybrid-electric-ferry as a case-study to integrate battery units (BUs) to a DC bus for supplying the propulsion motors. Further, two diesel generators (DGs) are connected to the AC bus to supply the hotel loads and a bidirectional DC/AC converter with an LCL filter is responsible for the power flow between AC and DC buses. This power topology is flexible for this ferry operation in pure electric, range extended and shore power modes. DC bus voltage is stabilized and its voltage ripple is limited by BUs' interleaved three-phase bidirectional DC/DC converter with its controller considering the operation states of propulsion motors. A coordinated power flow control between DGs and BUs is presented that the system frequency is fixed for the optimal operational efficiency of the diesel engines and a Q-V droop control plus a virtual impedance loop is used to make different AC bus voltage. Synchronization with shore power and DC/AC converter is facilitated by P-f droop control. Simulation results are presented to validate the proposed control approach in different missions.

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