By Surbhi JainReviewed by Susha Cheriyedath, M.Sc.Oct 24 2022In an article recently published in the open-access journal Energies, researchers discussed the modeling and experimental testing of electrical power requirements for heated clothing.
Study: Modeling and Experimental Verification of the Required Power for Electrically Heated Clothing. Image Credit: OMfotovideocontent/Shutterstock.com
Background
A desirable solution to the issue of thermal insulation vs usability is electrically heated clothes. Even with current insulation materials, conventional clothing requires a significant amount of mass to achieve high thermal resistivity. This entails limitations on mobility and weight. Additionally, passive clothing cannot adjust to the shifting conditions of the interior or exterior environment. This is especially problematic when the person significantly modifies the activity they undertake during exposure, such as switching between standing motionless and moving quickly upwards.
The same passive clothing may be both too warm while standing stationary and too cold in such a situation when going uphill. It is essential to match the heating power when creating electrically heated clothes with the passive insulation value of the garment and the required range of external temperatures. The approach presented by ISO 11079 could be used to achieve this. It does not, however, account for a lot of potential aspects. This makes controlled-environment experimental verification crucial.
About the Study
In this study, the authors discussed the power needed for thermal comfort in electrically heated clothing, along with corresponding straightforward modeling and experimental verification. The proposed apparel was a jumpsuit with built-in heating elements that were managed by a special microprocessor system. A smartphone app was used to adjust the heating power for the user.
The team carried out the studies in a portable freezing chamber to verify the theoretical power model according to ISO 11079 to sustain thermal comfort in an environment below zero degrees Celsius. To achieve thermal comfort, three participants were instructed to modify the heating intensity. The experiment showed that the necessary power was only 40–60% of the theoretical one, which indicated that designing electrically heated garments exclusively based on theoretical models and standards would result in the heating system's wattage being oversized.
The researchers revealed that even in stationary conditions, the mean skin temperature alone was insufficient as an input to the algorithm for the automatic preservation of thermal comfort. The primary objective of the study was to determine whether the power values derived from the existing standards were suitable and appropriate for the design of protective equipment for mountain rescuers operating in actual situations.
Observations
Between the values acquired experimentally and the values calculated using the ISO 11079 standard, there was a significant discrepancy. Depending on the participant, the experimental values were only 40–60% of the theoretical ones. The participants spent only up to 60 minutes inside the chamber, which was a brief amount of time. In order to sustain thermal comfort during a long exposure, it was probable that the heater power would need to be increased. The calculations obtained from the metabolic processes that occurred in all of the body cells followed the ISO 11079 standard treatment energy. Accordingly, heat was generated within the body. On the other hand, the heat was generated outside and close to the skin when wearing electrically heated clothing.
Thermoreceptors were distributed throughout the body, although a major portion was found in the skin. Since the body was not in thermal balance and was losing heat, direct heating of the skin could give the impression that it was comfortable thermally. The power supplied to the heating insets had very little impact on the sensor data.
According to ISO 9886, the linear combination coefficients for the ISO 4-point approach were set at 0.28, 0.16, 0.28, and 0.28, respectively, while for the second approach, they were all fixed at 1/3. Since the ISO 9886 standard called for temperature measurements at eight sites in frigid environments, the methodologies used could only offer a rough approximation.
Due to the apparent wide variations, care should be taken while designing heated clothing since depending only on theoretical models and standards could result in an oversized heating system. Analysis of the experimental conditions and the participants' thermal sensations suggested that subjective responses to thermal comfort could be distorted by several factors, which led to an undersized system that was unable to provide thermal safety and thermal comfort for prolonged exposures.
The study demonstrated that the mean skin temperature alone was not an objective indicator of the amount of electrical power needed for comfort concerning the automatic computation of heating power.
Conclusions
In conclusion, this study carried out the experimental verification of the heating power estimated using the ISO 11079 standard in light of the design of the electrically heated garment. Three volunteers were used to collect data while they stood immobile in a freezing chamber wearing electrically heated jumpsuits with varying heating levels for thermal comfort. Depending on the subject, the power needed for thermal comfort during the experiment ranged from 42.85 W to 59.99 W. This power was 40 and 60 % of the power calculated in accordance with ISO 11079.
The authors believe that the only strategy that makes sense is based on the real-time controlled heating of clothing, where sensor data is combined with specific user preferences. They stated that in the first studies, artificial intelligence (AI) approaches appear to offer a potential answer. Initially, the user controls the heated clothes manually, but over time, the AI module gradually learns the user's preferences and provides autonomous, personalized control of the heating insets.
The team mentioned that to determine whether such a method can accurately predict the required power, more research is necessary.
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References
Tylman, W., Kotas, R., Kamiński, M., et al. Modeling and Experimental Verification of the Required Power for Electrically Heated Clothing. Energies, 15(20), 7713 (2022).
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