Earlier studies conducted in climate chambers have examined a large range of temperature ramps from 0.5 K/h to 5 K/h (0.9°F/h to 9°F/h), but their focus was mostly on establishing temperature limits for acceptable thermal comfort with non-steady-state temperatures. Thus, when this ASHRAE funded research was initiated in 2005 knowledge was lacking on how the intensity of building related symptoms, the perception of air quality and the performance of office work were affected by exposure to non-steady-state temperatures. ASHRAE Standard 55 (2004) provides recommendations for maximum rates of temperature change to avoid discomfort, but these recommendations are based mostly on engineering judgment and to some extent on results of earlier thermal comfort research. New approaches to reducing the consumption of energy for climate conditioning in buildings are often associated with indoor temperatures that drift somewhat during the day, and there was a need to extend the scope of the recommendations to cover not only thermal comfort, but also health and productivity.
The aim of the proposed research was to carry out human subject experiments and field observations to validate the scientific basis of the recommendations on non-steady-state temperatures as stated in Standard 55 and to evaluate how Sick Building Syndrome symptoms, perceived air quality and performance are affected by such changing temperatures. In addition, the feasibility of non-steady-state temperatures as a means of energy savings and reduction of installed HVAC system capacity was evaluated by dynamic simulation of building energy consumption and indoor environment, taking into account potential effects on occupants of such non-steady thermal environments. Several building HVAC configurations and locations with different outdoor climate conditions were simulated.
Two different approaches were used in the human subject experiments; a) exposure of human subjects to temperature ramps with fixed clothing insulation and b) with subjects being allowed to adjust their clothing insulation as desired. In the former experiments, subjects’ thermal sensation was expected to vary along with the drifting temperature, as a basis for the most conservative limits to design temperatures and their maximum permitted rate of change, while in the latter experiments, thermal sensations were expected to remain more stable, justifying wider temperature limits. Experiments covered short-term exposures (1 and 2 hrs) at high rates of temperature change as well as moderate to long-term exposures (4 and 8 hrs) at modest and low rates of temperature change. Temperature ramps spanned the summer and winter comfort ranges of temperature. The experiments were designed to address not only thermal comfort but also to determine whether a range of human symptoms would be affected by increasing and decreasing temperature ramps, and to quantify their effects on the performance of typical office tasks.