5 ms·

The article doesn't describe exactly how these work... I could see 2 potential designs: Design 1: A high thermal mass piece of porous material, which air f

The article doesn't describe exactly how these work... I could see 2 potential designs: Design 1: A high thermal mass piece of porous material, which air flows in and out through the same holes. As air is exhaled, the material warms up. As air is inhaled, the material gives collected heat to the incoming air. Design 2: As above, but there are two sets of paths through the material. The paths are in a checkerboard pattern so there is good thermal conductivity between them. One set is for incoming fresh air and the other for used air. One way valves ensure air travels in the correct direction through each hole. Design 1 is great for keeping both heat and moisture (air will be pre humidified on the way in). However, it has the downside that all of the air in the tubes will be re-inhaled in each breath. Effectively your lung capacity will be reduced by the volume of the mask. Design 2 is more mechanically complex, gives you very dry air to breathe in, and will be prone to clogging with condensation, but has the advantage that you aren't rebreathing any CO2 laden air. And just 2% breathed back in causes "complaints of drowsiness and poor air"[1] [1]: https://www.dhs.wisconsin.gov/chemical/carbondioxide.htm https://www.dhs.wisconsin.gov/chemical/carbondioxide.htm

dgacmu 3y ago
They're all design 1. Here's a manufacturer link with an air flow diagram for one of the recommended ones: https://www.ergodyne.com/nferno-6970-extreme-balaclava-hot-rox.html https://www.ergodyne.com/nferno-6970-extreme-balaclava-hot-r... That said, the volume of air that could be retained in the foam heat exchange insert is quite small (eyeballing it, maybe 50-100ml?) compared to normal human inhalation volume, about 3-4L per breath during moderate exercise.
- londons_explore 3y ago
  100 ml / 4 liters = 2.5%. 2.5% of CO2 laden air (~50,000 ppm) + 97.5% fresh air (420 ppm) = 1640ppm. 1640 ppm of CO2 is very much into the 'feels drowsy and hard to concentrate' region.
  - _flux 3y ago
    However, per https://www.omnicalculator.com/ecology/co2-breathing-emission#do-humans-breathe-out-carbon-dioxide https://www.omnicalculator.com/ecology/co2-breathing-emissio..., the air a person breaths out has only 4% CO2, reducing that number to 65ppm, right?
    - londons_explore 3y ago
      (40,000 x 0.025) + (420 x 0.975) = 1409.5 ppm
      - _flux 3y ago
        Right you are! I guess the two valves in working masks are then quite essential, and normal breathing masks better have as little extra space for air in them as possible.
  - adhesive_wombat 3y ago
    Does that stay true when exercising? At rest, with a tidal volume of 500ml ish, lungs are least 5/6 full of stale air, round down to 3% ish CO2. When exercising, the tidal volumes are far higher (2-3L), and you breathe faster, so the lung air is at least twice as fresh as it was at rest, probably more, since fresh air is functionally 0% CO2, and you're moving maybe 6 times the gas volume in each direction. Does that massive change in volume and diffusion gradient (at least at the start of a breath) means that you might be able to tolerate a higher CO2 level in the inhaled air?
  - Moru 3y ago
    I'm using Lungplus version that works with something similar to design 1 and have no problem with drowsyness at all. The benefit of breathing warm moisturized air outweighs the very small amount of stale air. I measure it to about 25 ml by filling it with water and shaking it out again. Lungplus is just a silicon wrap around a package of corrugated metal wrapped around itself so the air pathway is straight and very open and easy to breath through. Each pipe is about a millimiter in height and 2-3 in width. It still heats up the air very well at least down to -35 C at which time the freehub starts freezing and I can't bike anyway :-)
heelix 3y ago
I use something similar to design 1, when deer hunting in really cold weather. Similar looking gadget in silicon. Moisture does become an issue - as water will accumulate over time. It is marginally better than wrapping up in frozen scarves.
mpreda 3y ago
I use an integrated device of design 1, it's called a "nose". Higher air resistance than the "mouth", but provides the heat and humidity exchange.
tim333 3y ago
I used a PSOLAR Heat Exchange Mask (https://www.amazon.com/PSOLAR-Heat-Exchange-Mask-Full/dp/B0012PQ9AW https://www.amazon.com/PSOLAR-Heat-Exchange-Mask-Full/dp/B00...) for high altitude mountaineering and it worked very well for keeping warm but it didn't work like that and wasn't really a 'Heat Exchanger'. What it actually had was a moisture absorbing substance stuck on a plastic comb like structure. When you breathed out damp air from your lungs the substance would absorb the moisture and when you breathed in dry air it would release the moisture making it more humid. This actually made a big difference to body heat as breathing in cold dry air onto hot moist lungs is very cooling from evaporation. It also stops your lungs drying out. If you read Everest books they all get dry lungs and chest infections the the psolar thing seemed pretty good at stopping that. I get the impression these are similar - really moisture exchangers and the 'heat exchanger' thing is marketing.

dgacmu 3y ago

They're all design 1. Here's a manufacturer link with an air flow diagram for one of the recommended ones: https://www.ergodyne.com/nferno-6970-extreme-balaclava-hot-rox.html https://www.ergodyne.com/nferno-6970-extreme-balaclava-hot-r... That said, the volume of air that could be retained in the foam heat exchange insert is quite small (eyeballing it, maybe 50-100ml?) compared to normal human inhalation volume, about 3-4L per breath during moderate exercise.

londons_explore 3y ago
100 ml / 4 liters = 2.5%. 2.5% of CO2 laden air (~50,000 ppm) + 97.5% fresh air (420 ppm) = 1640ppm. 1640 ppm of CO2 is very much into the 'feels drowsy and hard to concentrate' region.
- _flux 3y ago
  However, per https://www.omnicalculator.com/ecology/co2-breathing-emission#do-humans-breathe-out-carbon-dioxide https://www.omnicalculator.com/ecology/co2-breathing-emissio..., the air a person breaths out has only 4% CO2, reducing that number to 65ppm, right?
  - londons_explore 3y ago
    (40,000 x 0.025) + (420 x 0.975) = 1409.5 ppm
    - _flux 3y ago
      Right you are! I guess the two valves in working masks are then quite essential, and normal breathing masks better have as little extra space for air in them as possible.
- adhesive_wombat 3y ago
  Does that stay true when exercising? At rest, with a tidal volume of 500ml ish, lungs are least 5/6 full of stale air, round down to 3% ish CO2. When exercising, the tidal volumes are far higher (2-3L), and you breathe faster, so the lung air is at least twice as fresh as it was at rest, probably more, since fresh air is functionally 0% CO2, and you're moving maybe 6 times the gas volume in each direction. Does that massive change in volume and diffusion gradient (at least at the start of a breath) means that you might be able to tolerate a higher CO2 level in the inhaled air?
- Moru 3y ago
  I'm using Lungplus version that works with something similar to design 1 and have no problem with drowsyness at all. The benefit of breathing warm moisturized air outweighs the very small amount of stale air. I measure it to about 25 ml by filling it with water and shaking it out again. Lungplus is just a silicon wrap around a package of corrugated metal wrapped around itself so the air pathway is straight and very open and easy to breath through. Each pipe is about a millimiter in height and 2-3 in width. It still heats up the air very well at least down to -35 C at which time the freehub starts freezing and I can't bike anyway :-)

heelix 3y ago

I use something similar to design 1, when deer hunting in really cold weather. Similar looking gadget in silicon. Moisture does become an issue - as water will accumulate over time. It is marginally better than wrapping up in frozen scarves.

mpreda 3y ago

I use an integrated device of design 1, it's called a "nose". Higher air resistance than the "mouth", but provides the heat and humidity exchange.

tim333 3y ago

I used a PSOLAR Heat Exchange Mask (https://www.amazon.com/PSOLAR-Heat-Exchange-Mask-Full/dp/B0012PQ9AW https://www.amazon.com/PSOLAR-Heat-Exchange-Mask-Full/dp/B00...) for high altitude mountaineering and it worked very well for keeping warm but it didn't work like that and wasn't really a 'Heat Exchanger'. What it actually had was a moisture absorbing substance stuck on a plastic comb like structure. When you breathed out damp air from your lungs the substance would absorb the moisture and when you breathed in dry air it would release the moisture making it more humid. This actually made a big difference to body heat as breathing in cold dry air onto hot moist lungs is very cooling from evaporation. It also stops your lungs drying out. If you read Everest books they all get dry lungs and chest infections the the psolar thing seemed pretty good at stopping that. I get the impression these are similar - really moisture exchangers and the 'heat exchanger' thing is marketing.