Dynamic cooling load analysis on indoor thermal comfort state in passenger trains

Abstract

Increasing passenger density makes indoor state of train compartments not thermally comfortable. Air conditioned train compartments have been introduced to provide comfortable pleasant interior environment to the passengers. However the trains consume in a high share of electricity for thermal comfort purposes thereby reducing their fuel economy and increasing emissions. Before adopting more air conditioned train compartments to the railway system, it is necessary to understand indoor thermal comfort state expected by passengers and the energy saving potential. This study discusses the acceptable indoor thermal comfort conditions and the variation in cooling load due to fluctuation of outdoor ambient conditions in moving train compartments. It was based on the Fangers thermal comfort model and a mathematical model was built to simulate this dynamic cooling load. Indoor thermal comfort parameters were examined by surveying of passengers travelled in air conditioned trains. The survey was conducted in trains run through the Colombo-Badulla main line and the northern line in Sri Lanka by interviewing 186 numbers of passengers using standard questionnaire. As independent variables, it was considered three main indoor thermal comfort parameters: temperature, relative humidity and air velocity. Analyzing the survey data using descriptive method, a comfort zone on psychometric chart was defined and accordingly indoor temperature and relative humidity of 26˚C & 55%RH were obtained as appropriate indoor thermal comfort parameters for railway passengers in Sri Lanka. On the other hand, energy saving potential was estimated through simulating dynamic cooling load values for the selected stations in both railway lines considered. Significant differences in dynamic cooling loads of train compartment were found between different stations and between different periods of time. The steady cooling load calculated according to the usual standard method was comparatively higher than the dynamic cooling load. Application of actual maximum dynamic cooling loads of a moving train compartment has been shown 10.9 kW & 5.9 kW of power reduction in train air condition system for mainline & northern line respectively. Thus the application of dynamic cooling load with reference to the time and space can lead to a significant energy saving in passenger trains.