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Venting and drying for efficient sweating under PPE

To cool the worker under a PPE I propose to combine venting and drying to enable efficient sweating.

Photo of Rainer Winkler
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Update 7 December 2014

This is an old posting. See for actual proposals. Actually I analyze options for secure filtered venting a PPE.

Original contribution:

Water has a Enthalpy of vaporization (heat of evaporation) of 2260 kJ/kg. Evaporating 1 kg of water per hour cools with an heat current of 630 W. A person at rest produces only about 100 W of heat.
It was proposed to used commercially availiable products for venting under cloth: (
But connecting the air flow used for venting directly to the outside creates problems. Infectious material may enter the system and would be directly blown to the skin.
The moist that is created by evaoporation of the sweat has therefore to be removed. This can happen by:
a) Using silica gel or zeolite to dry the air. This may create problems, if the heat that is released duing the absorption heats the PPE too much
b) Pumping the air through a bottle with ice or cold water. This will dry the air. Problems are, that liquid water may leave accidentially the bootle and may cause problems under the PPE.

For venting a radial fan could be used. A small radial fan creates more pressure than the axial fans used in most (but not all) computers. So it will be easier to vent clothing that is not optimized for venting. The model I have makes 2 mbar overpressure.

The radial fan coupled with 100g of silica gel absorbed in a first test 0.5mg Water per second at 16°C and 60% humidity, this is equivalent to 1W of cooling. It heated itself to about 30°C, about 15°C higher than the ambient temperature. A working device might therefore require about 10kg of silica gel, to have a sufficient absorption rate. I am shure it should be possible to saturate the silica gel faster, in that case less gel would be required. But I gave here only the numbers I measured.

For cooling using ice I guess that about 1.5 kg of ice is needed to absorb 160g Water vapor per hour, leading to a cooling power of 100 W.

Update 03 October 2014: Systems like this may be realizable, but in the moment I doubt whether this can really be done in a few month with low technical effort. The fans required to vent the PPE are quite strong, and to have a cooling power that is better than a PCM vest, is probably not easy. So I am sceptical whether this problems can be solved in the short time frame.

Cooling and adsorbing humidity with ice has the disadvantage, that no adsorption heat has to be transfered out of the PPE.

Adsorbing humidity with silica gel has the disatvantage, that the silica has to be cooled. Here the latent heat plus the energy of wetting has to be transported to the outside of the PPE.

Please follow also the discussion on this very related post: . Many ideas from the comments there can also here be applied.



Join the conversation:

Photo of Anthony Davis

Hi Rainer, I like your thinking on vents but was wondering how effective a ventilation fan would be in a non pressurized ppe suit that clings to the body. Would it create a 'suction effect' which prevents the outward flow of air and how can this be overcome?

Photo of Rainer Winkler

Hi Anthony,
you may be right. I made a simple test with venting but not with the required flow rate. There may be a suction effect, good that you mentioned it.