Human-body exergy balance calculation under un-steady state conditions

Abstract

We investigated the rationality and accuracy of human-body exergy balance calculation under un-steady state conditions for our immediate thermal environment changing due to a series of behaviour such as walking outdoors and coming into a mechanically air-conditioned space. We set up an experiment that the subjects stayed in two rooms, one with natural ventilation and the other with mechanical air-conditioning. According to “energy” calculation, input energy rate almost the same as the total of output energy rate, within which a portion by sweat secretion in naturally ventilated room was larger than that in mechanically air-conditioned room. On the other hand, according to “exergy” calculation, the large portion of input exergy rate consisting mainly of metabolism and liquid water by sweat secretion was found to be consumed. In naturally ventilated room, the exergy consumption rate increases by walking and then decreases gradually towards the end of staying, but in mechanically air-conditioned room it suddenly became large right after entering and dropped more sharply than in naturally ventilated room. This is because the liquid water by sweat, which has wet exergy, dispersed into the surrounding air very rapidly in mechanically air-conditioned room whose humidity is very low. The measured values of sweat evaporation rate were larger than the calculated values based on the two-node model although their patterns of variation were similar to each other. Conventional air conditioning for cooling, which necessitates a large input of exergy by electricity, was found to result in a large amount of human-body exergy consumption.