Objective investigation of discomfort due to draught in a tangential air distribution system: Influence of air diffuser's offset ratio

The purpose of this paper is to investigate the influence of air diffuser's offset ratio on air velocity and turbulence intensity distribution. Air velocity, turbulence intensity and air temperature measurements were performed in a single office full-scale room in isothermal case. Then the draught rate numbers were calculated to evaluate the discomfort due to draught using Fanger's model. Different statistical tests were applied to evaluate the measured data. Results showed that the average of air velocity magnitude, turbulence intensity and draught rate was independent of the inlet offset ratio at ankle height. At the knee height and head height of seated and standing person, there was a polynomial connection between the average values and the inlet offset ratio. International standards recommend an average turbulence intensity of 40% to calculate draught rate. The results showed that 70%-80% of measured turbulence intensities were less than the standard value in the investigated range of inlet offset ratio. The draught at ankle height was within category C, while at knee height and head height of seated and standing person, the averaged draught rate numbers meet the category A and B and recommendation of CR 1752. Our results could help designers to calculate the average value of air velocity and turbulence intensity for room air distribution and indoor air comfort design.