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post #1 of (permalink) Old 02-04-2019, 05:37 PM - Thread Starter
Hardware Princess
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Best coolant for -40c ?

Hey all,

I've reverse engineered an R22 dehumidifier for chiller use. Since R22 boils at -41c I am looking for a coolant that can handle that. Not sure if the whole evaporator would get down to -41c but it certainly gets below 0c, since when I run it the water just freezes into an ice block around it.

The ideal fluid would have the following properties:
1. Freezing point of -45 or so
2. Does not get too viscous or slushy at low temps (i.e. doesn't destroy pumps)
3. Decent heat transfer (specific heat of ~2.5)
4. Does not fill house with toxic fumes
5. Non-flammable

I'm looking at the following fluids, all of them in roughly a 50/50 mix with distilled water:

1. Propylene Glycol: Non-toxic and easy to dispose of. However, I've heard it turns into slush and would basically destroy pumps due to very high viscosity at low temps. Easy to buy as RV Coolant. Not sure on the mix ratio with water they sell though. Non-flammable.
2. Ethylene Glycol: Non-fuming at least, no pets or kids in house that would drink the stuff (toxic). Is this any easier to pump at low temps? Any less viscous/slushy? Very easy/cheap to buy as antifreeze concentrate and can control ratio when mixing with water. Non-flammable.
3. Methanol: Available as windshield washer fluid i.e. Rain-X de-icer. Most of these are only available as max 35% methanol which would go down to -30c or so. However, I've read that it fumes quite badly and is obviously very toxic. I don't think I could seal my reservoir well enough that I could limit the fumes so I've more or less ruled this one out. Flows nicely at low temps, but might damage rubber & plastics. Also flammable.
4. Ethanol: Not sure where to buy this, denatured alcohol looks pricey by the gallon. E85 maybe? Nowhere near as toxic as methanol, I mean, it's basically the booze we drink lol. Probably still evaporates too easily? Also flows well at low temps but could damage plastic/seals, and is flammable.

Anyone experienced with using any of these at subzero temps? Leaning towards either ethylene glycol or ethanol. Other suggestions would be welcome too.

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