Performance evaluation of three attached ventilation scenarios for tiny sleeping spaces

The indoor ventilation environment has restricted the development of tiny sleeping spaces, such as capsule hotels, sleeping boxes and soft sleeper compartments, that play an increasingly important role in urban life. Thus, it is imperative to determine a ventilation method that can create comfortable sleeping environments in tiny spaces. In this study, three attached ventilation scenarios were proposed, and numerical simulations and experimental validations were conducted to investigate the airflow characteristics. The draught rate, facial-area speed ratio, predicted mean vote, CO2 concentration, ventilation effectiveness, and mean age of air were used to evaluate the performance of three ventilation scenarios. In Scenario 1, the velocity in the occupied zone was between 0.1 and 0.24 m/s, which could achieve the most comfortable facial speed distribution; the PMV also met the criteria for category B (-0.5 < PMV < +0.5), as defined in ISO 7730. Scenario 2 had a more uniform temperature distribution and minimum air age; however, the local velocity was too high (more than 0.5 m/s), and CO2 cannot be discharged from the occupied zone in time. The DR in Scenario 3 was in the range of 2.5%-5.3%, which was highly beneficial in avoiding draught. Finally, the overall performance of the three ventilation scenarios was as follows: Scenario 1 was superior to Scenario 3, which in turn, was superior to Scenario 2. The results showed that the attached ventilation could solve the problem of supply air momentum not being able to diffuse in a reasonable time in restricted spaces.