Subjective human response to low-level air currents and asymmetric radiation (1987)

The responses of 50 subjects wearing winter clothing (0°86 clo) to two-hour-long exposures various kinds of winter indoor conditions were studied. The conditions included air speeds between 0.05 and 0.5 m/s (I0 and I00 fpm) and asymmetric radiation to a cold wall that produced radiant temperature asymmetries ranging from 0 to 20 K (0 to 36 F). The study was done at neutral or preferred temperatures and at conditions 3°C (5.4 F) lower. Some of the conclusions are: (i) The low mean radiant temperatures from the cold wall were compensated for by increased air temperature through the operative temperature concept. (2) The preferred operative temperature increased with air speed. (3) The level of occupant thermal acceptability at preferred temperatures was unaffected by air speeds of 0.25 m/s (50 fpm) less or radiant asymmetries of I0 K (18 F) or less. (4) At air velocities greater than m/s (50 fpm) the operative temperature determination procedure used seemed to overestimate radiation and underestimate convection. (5) Operative temperatures 3~C (5.4 F) less than preferred temperature are probably too low for sedentary occupancy as acceptability levels were only about 60% in these tests and at air speeds greater than 0.15 m/s (30 fpm) the subjects did not reach equilibrium. That is, acceptability and comfort decreased with time. INTRODUCTION nonuniformities such as drafts, radiant asymmetry and vertical temperature differences in an otherwise thermally comfortable space may cause discomfort and detract from the environment. This study was undertaken to quantify the separate and additive effects of drafts and radiant asymmetry on sedentary people in neutral and cool environments. ANSI/ASHRAE Standard 55-81, Thermal Environmental Conditions for Human Occupancy (ASHRAE, 1981) recommends some limits on air movement and radiant asymmetry in order to limit local discomfort. The guidelines of the standard are based on separate draft and radiation studies conducted at thermally neutral conditions by Fanger (1977, 1978), Mclntyre (1976), McNall Biddison (1970), Rohles et al. (1974), Olesen et al. (1973), and Ostergaard et al. (1974). Previously studies have not been done on the combined effect of radiation and draft acting together in neutral environments, and there was little information on their separate effects in cool environments. Drafts increase the local convective heat transfer on windward surfaces. Thus, skin temperature on the draft side may decrease and cause discomfort. Radiation to cold surfaces produces similar differences in skin temperature. The response of the two effects acting together could be greater than the sum of the separate effects. In a cool environment, peripheral blood vessels vasoconstrict to limit heat loss, and under this strain the responses to local cooling by radiation and draft could be more pronounced. It was therefore hypothesized that the human sensitivity to nonuniformities in cool environments is increased. That is, drafts and radiant asymmetries become more noticeable and detract more from the overall thermal acceptability of the space than in a neutral environment. The study was in response to ASHRAE work statement 353 and required two years to complete. L.G. Berglund, Associate Fellow, John B. Pierce Foundation Laboratory and AoP.R. Fobelets, Predoctoral Fellow, John B. Pierce Foundation Laboratory and graduate student, Department of MecNanical Engineering, Yale University, New Haven, CT. 497 ©ASHRAE. All rights reserved. Courtesy copy for SSPC 55 Committee to exclusively use for standards development. May not be distributed, reproduced nor placed on the internet.