Scientific Research—The Influence of Airflow on Human Body Temperature Measurement in A Quiet Indoor Thermal Environment

The Influence of Airflow on Human Body Temperature Measurement in A Quiet Indoor Thermal Environment

   A comfortable indoor thermal environment can improve the quality of sleep1 and work productivity. Previous studies have generated evaluation scales for indoor thermal comfort based on physical and personal factors, with representative physical factors including room temperature, humidity, and airflow velocity. An international common scale, the Predicted Mean Vote (PMV), has been established to summarise and standardize these factors, and it has been widely accepted in many countries. The PMV and other similar scales are based on results from an extensive survey of subjective evaluations.

   Comfort is a highly subjective feeling and cannot be measured in an objective manner in principle. Although PMV is widely used as a reliable scale, it has not yet been able to fully elucidate the mechanisms underlying this feeling. More specifically, the relationship between PMV and neuronal responses should be investigated in order to better understand the mechanisms underlying comfort. Airflow is one of the factors used to calculate PMV, and its sensation and underlying neuronal mechanisms have been investigated by a number of researchers. Although many investigations have shown the unpleasant effects of air velocity and draught by subjective reactions, few studies have addressed neurophysiological mechanisms underlying unpleasantness induced by airflow.

Figure 1. Examples of thermography during the cooling experiments.

   In order to examine the effects of airflow in indoor environments that mimic daily life, we conducted experiments under two different seasonal conditions (cooling in summer and heating in winter) and two different airflow conditions (an air conditioner with airflow and a radiant cooling and heating system without airflow) in an environment standardised for temperature and humidity. To standardise the mental states of the participants, we introduced a time-counting task. In each session, the participants were asked to press a button after mentally counting for 10 seconds with their eyes closed. Tis was repeated for up to 60 seconds per session. EEGs were recorded during five sessions, and frequency analysis was carried out.

   We hypothesised that changes in brain activity occur in response to different airflow conditions. Our aim was to determine neurophysiological markers of airflow sensation under conditions of both cooling and heating. Termography data used to assess skin temperature were measured five times per participant at the conclusion of each session in the cooling experiments, or twice per participant immediately before the first session and immediately after the fifth session in the heating experiments.

Figure 2. Examples of thermography during the heating (e, f) experiments.

   The subjective assessments, indicate that airflow in a cooling environment is perceived as unacceptable, as it leads to local cooling of the skin, while appropriate air movement in a warm environment creates comfortable feelings. Our results seem to contradict the above subjective perceptions of airflow.

   In order to examine the neuronal mechanism underlying airflow sensation in an indoor environment, we compared the seasonal experiments in different airflow conditions using both electrophysiological and psychological approaches. In both the cooling and heating experiments, higher gamma and beta oscillation activities were observed as neurophysiological markers related to airflow sensation. These markers led to the identification of some candidates of brain-intrinsic factors related to feelings associated with different airflow conditions. We investigated the effects of airflow on brain activity in a living environment. These results suggest that the observed neuronal responses are related to airflow in an indoor environment. To our knowledge, this is the first report describing differences in neuronal activity in indoor conditions with and without airflow.

Reference

Tsuyoshi Okamoto, Kaori Tamura, Naoyuki Miyamoto, et al. Physiological activity in calm thermal indoor environments. Scientific Reports. 7:11519, 2017.