Accommodation environment of a polar cruise ship: Stratified or mixing ventilation system

This study evaluates the thermal comfort, indoor air quality, and energy performance of four ventilation systems—displacement ventilation (DV), impinging jet ventilation (IJV), ceiling jet mixing ventilation (CJMV), and diffusive ceiling mixing ventilation (DCMV)—within a confined ship cabin equipped with bunk beds, under both cooling and heating modes. In cooling operation, CJMV and DCMV require lower supply air temperatures than DV and IJV to achieve a thermoneutral environment, leading to higher energy consumption; for instance, DCMV consumes 6% more energy than DV. However, only DCMV satisfies thermal comfort criteria, as the other systems produce a PMV difference exceeding 1.0 between the upper and lower beds. Although DCMV yields a slightly higher draft rate (DR), it remains below 5% in average. CO₂ concentration variations are negligible (CV ≤ 2.8%), but DCMV increases the mean air age by 49% compared to DV, due to opposing airflow and thermal buoyancy. Under heating conditions, DCMV requires the lowest supply temperature and thus the least energy, though differences among systems are minor (CV = 1.79%). All systems maintain PMV between -0.5 and 0.5 and volume ratio with acceptable DR close to 1.0, meeting comfort standards. CO₂ levels are again comparable, while DCMV provides the second youngest air following DV (502 s for DCMV, 479 s for DV). In summary, DCMV is the only system suitable for both cooling and heating in terms of thermal comfort, albeit with an energy increase in cooling mode.