The Effect of Ramps in Temperature and Electric Light Level on Office Occupants: A Literature Review and a Laboratory Experiment

When electricity demand has the potential to exceed supply, brownouts or blackouts may occur. Utilities may take steps to deliver additional power, or to reduce demand. The latter case may involve commercial buildings shedding load when prompted by the electrical utility. For example, lighting may be dimmed, and (in the cooling season) setpoint temperatures increased. However, this may degrade the indoor environment relative to prevailing operational guidelines. Although this may be a reasonable alternative to a blackout, it is still desirable to minimize negative effects on occupants. We reviewed the literature on the effect of steady changes (ramps) in temperature and illuminance from electric light on occupants. Results related to temperature suggest that changes typically associated with load shedding (around 1.5 o C over 2-3 hours) are unlikely to be detected by occupants, and if detected, would likely be acceptable in the circumstances. Studies of rapid changes in illuminance (of the order of 10-100 lx/s) suggest that illuminance can decline by up to 20% without being detected. With slower rates of change (1 lx/s or less), greater reductions in illuminance may remain undetected, and acceptable. However, studies to date have focused on detectability and acceptability of ramps, little is known about the wider effects on occupants. Further, existing studies have examined ramps in temperature and lighting independently, rather than in combination. We conducted a controlled laboratory study to address these shortcomings. Sixty-two Participants spent a day in a full-scale office laboratory, completing questionnaires and standard office tasks. One group of participants was exposed to a simulated load shed in the afternoon: workstation illuminance was reduced by 2 %/min, and temperature increased by ~1.5 o C over a 2.5 hour period; another group experienced no load shed. Analyses suggest that the group experiencing the simulated load shed experienced both positive and negative effects on satisfaction or performance. On balance, our findings suggest that load shedding typical of current suggested practice is a reasonable response to peak power emergencies. Indoor environment conditions may drift from recommended practice, but this is unlikely to create substantial hardships for occupants.