The active heating/cooling requirements to thermally sustain a human subject submerged in 10, 20, 30 and 40 °C water was measured using a system that circulated water through a zoned tubesuit garment. Water at 30 °C was circulated through the garment at a flow rate of about 0.5 L/min to each of six body regions and the outlet temperatures were measured. In addition, skin and core temperature, heat flux, and oxygen consumption was measured. The subject wore either a 6.5 mm or a 3 mm foam neoprene wetsuit. Body temperatures and heat fluxes reached steady state after 30–90 minutes and the immersions lasted 2–4 hours and core and skin temperatures remained within set thermal limits. In both wetsuits there was a linear correlation between the thermal exchange of the tubesuit and water temperature. While in the 6.5 mm wetsuit −214 to 242 W of heating (−) or cooling (+) was necessary in 10 to 40 °C water, respectively. While wearing the 3 mm wetsuit −462 to 342 W was necessary in 10 to 40 °C water, respectively. It was therefore concluded that a subject can be kept in thermal balance and comfort in 10–40 °C water with active heating/cooling.

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