Influence of Sensible Heat Release on the Performance of Displacement Ventilation in a Train Compartment

Abstract

The influence of sensible heat release on the performance of displacement ventilation is studied and analysed in a generic laboratory, representing the lower cabin of the DLR’s next generation train (NGT). In a first step, tests at variable mean cabin temperatures were conducted with human subjects. These tests were analysed in terms of sensible and latent heat release of real humans. In a second step, the cabin was fully equipped with thermal manikins. For different amounts of sensible heat released by the manikins, the large-scale flow fields and the temperatures at selected positions were evaluated. We found that the amounts of sensible and latent heat released by the human subjects complies with the standard EN13129 within the errors, using the temperature on chest level as mean cabin temperature. Astonishingly, the mean local velocities are not influenced significantly, which we ascribe to the limited rate of fresh air available through the fresh air lake. However, the mean velocity fields show significant differences regarding the boundary layer thickness and the observed velocity distribution. Hence, the importance of field measurements to determine comfort-relevant quantities is underlined. The performance of the displacement ventilation system, quantified by the heat removal efficiency as a figure of merit decreased with increasing mean cabin temperature during the human subject test, while it stayed stable during the test with thermal manikins.