From characterisation to evaluation: A review of dynamic and non-uniform airflows in thermal comfort studies

The transitioning from overall steady-state thermal conditions indoors to non-steady and non-uniform conditions encompasses the airflow field generated by means of air conditioning and ventilation systems, devices for increased air movement and even cross-ventilation in naturally ventilated buildings. The indoor airflow field is susceptible to large variations with respect to time and space, which makes its characterisation and evaluation in real occupancy buildings a complex task. A literature review focusing on dynamic and non-uniform airflows applied for human thermal comfort in buildings was conducted with the aim of documenting recent findings on three main topics: airflow characterisation, thermal comfort evaluation and thermal comfort prediction. Over 150 articles from the past two decades of research carried out in climate chambers, experimental rooms, laboratories and real occupancy buildings were reviewed. The main findings indicate that the more dynamic and unpredictable airflows tested in studies with subjects had better preference, sensation and comfort ratings when compared to constant and sinusoidal patterns. Field validation is required to (1) verify the applicability of simulated natural airflows in real occupancy buildings and (2) optimize delivered mean air speeds - up to 0.9 m/ s - and their respective time spans - from 10 seconds to 3 minutes - in intermittent airflow patterns, to avoid the risk of draughts and lack of air motion. Temporal variations in air velocity, whose standard deviation was up to 0.5 m/s in studies with sources of increased airflow, should be addressed in detail with respect to the corresponding subjective feedback. Furthermore, there is a gap to be filled regarding the incorporation of temporal variations into the prediction models to be proposed and validated.