PASSENGERS’ ASSESSMENTS OF THERMAL COMFORT IN A RAILWAY CAR MOCK-UP WITH DISPLACEMENT VENTILATION

Abstract

Displacement ventilation (DV) is an air distribution system, which supplies cool fresh air at floor level and extracts exhausted air at the ceiling. Air draught is reduced as heat sources (e.g. the train passengers) generate the vertical air movement in the cabin. This study provides contributions to the question whether a displacement ventilation system could complement or replace ordinary ventilation systems in rail cars without decrements of passengers’ well-being in terms of thermal comfort. The benefit could be a reduction of energy consumption. In a first experiment, new air outlets were installed in a rail car mock-up. Outlets were integrated into the existing air conditioning system and fixed under the passenger seats. They were suitable to supply a sufficient amount of cool air with low speed to the cabin. A sample of 80 subjects participated in the first study. In a simulated train ride of several hours, four experimental groups of 20 subjects each were exposed to a total temperature range of 20 °C to 27 °C. Objective and subjective data were gathered to evaluate individual levels of thermal comfort under the different physical conditions. Typical for DV we found a rather steep temperature gradient of 5 °C between 0.1 m and 1.3 m inside the cabin. The highest level of thermal comfort was found for an average ambient temperature of 24 °C. The rather low temperature in the legroom area did not have any negative effects on the comfort assessments. Comfort ratings of the subjects were generally predictable by the average temperature. Air draught and humidity played a minor role in our study. In a further experiment we will examine whether passengers’ assessments of thermal comfort can be further increased by a combination of displacement ventilation with microjet outlets in the cabin ceiling. The intention of the hybrid ventilation concept is to compensate for the warm air layer over the passengers’ heads with a fresh air flow from above.