AbstractPersonal cooling garments (PCGs) are designed to relieve thermal stress in occupations that require the use of personal protective clothing (e.g. fire fighter, military personnel). The cooling source in PCGs is usually delivered continuously, which over long periods requires a large battery source. Intermittent cooling has been found to be as effective as continuous cooling at maintaining thermal balance. Based on the observation that larger improvements in thermal perceptions are associated with rapid changes in skin temperature, it was hypothesised that intermittent cooling could also enhance thermal perceptions (i.e. temperature sensation and thermal comfort). The overall aim of the studies presented in this thesis was to test this hypothesis.
In order to detect differences between intermittent and continuous cooling on thermal perceptions, it was important to use a reliable measurement tool to assess perceptual responses in conditions where a PCG would be utilised. The first study described in this thesis assessed the reliability of a graphic visual analogue scale (VAS) against a Likert scale (LS) for validity and reproducibility in the measurement of thermal perceptions in non-uniform, dynamic thermal environments. The study involved three identical conditions in which thermal perceptions were measured by both the VAS and LS in response to changes in the torso microclimate. During the condition, participants walked (5km.hr-1, 2% incline) in a warm environment (35oC, 50% relative humidity [RH]) and wore clothing (1.2 clo) that covered 88% of the body. The torso microclimate was manipulated by ventilating air of different temperatures and relative humidity through an air-perfused vest (APV). These thermal conditions were similar across all the studies presented in this thesis. The VAS were found to be slightly more reproducible for local thermal perceptions than the LS, and had greater validity during both stable and non-uniform, dynamic thermal environments. Therefore the use of the graphic VAS was adopted in all subsequent studies.
To develop the intermittent cooling profiles that were assessed for their ability to enhance thermal perceptions, the second study involved ventilating different air temperatures (~15-26oC) through the APV to determine what type of fluctuations in skin temperatures are required to enhance thermal perceptions. The results suggested that the rate of change in mean skin temperature (sk) and torso skin temperatures (sktorso) had a greater influence on thermal perceptions than absolute changes in sk and sktorso. The results also confirmed the results from the first study, that increasing evaporative heat loss at the skin surface was the most effective method to manipulate the rate of change of skin temperatures, and consequently, thermal perceptions.
To compare the capability of intermittent and continuous cooling profiles to enhance thermal perceptions, whilst maintaining thermal balance, the final study involved ventilating the APV with either fluctuating or continuous air velocities during both exercise and rest. Three different intermittent cooling profiles were used; sinusoidal, sawtooth and step-change. Upon completion of the experiment, participants stated their preferred cooling profile. Based on the results it was concluded that intermittent cooling, which had 50% less air flow than continuous, maintained both thermal balance and thermal comfort when compared to continuous cooling. Out of the intermittent cooling profiles, the sinusoidal profile produced significantly cooler sensations and was 4/11 participants‟ preferred choice.
The results suggest that the presence of a significantly higher torso relative humidity (RHtorso) in the intermittent cooling profiles, compared to continuous profile, may have confounded their capability to enhance thermal perceptions over time. In addition, the cooling profile that was perceived to the „coolest‟ and/or the most „stable‟ was generally the participants‟ preferred choice. This suggests that large fluctuations in skin temperature are not always perceived favourably.
Based on the studies conducted as part of this thesis, it is concluded that in order to minimise high levels of RHtorso and provide smoother transitions in temperature sensation, an optimal cooling profile should consist of: 1) a sinusoidal pattern with a frequency greater than 0.000139 Hz, 2) have a ratio of 2:1 ON/OFF periods, 3) OFF periods no longer than 3 minutes, 4) highest flow rate not to exceed 255 L.min-1, 5) provide a rate of change in sk and sktorso of ~0.29oC.min-1 and 0.78oC.min-1, respectively, and 6) the incorporation of a drying agent into the design of an APV.
|Date of Award
|Mike Tipton (Supervisor) & Martin James Barwood (Supervisor)