I’m reconfiguring my printing closet (~6’x6’) for a new printer and thought about enclosing the printer in a moderate sized cabinet (~2’x3’x6’ - one “shelf” of the closet) for thermal control. Since there will be inevitable opening and closing, as well as just normal infiltration of the ambient air (usu ~65F between 40-75% RH) it would seem like a good application for a Peltier dehumidifier to keep the RH in the chamber low and reduce my need to re-dry filament which has been on the machine during (inevitable) multi-day or -week downtime between projects.
Peltier units are solid state heat pumps with awful efficiency. Where power consumption is not an issue, It is significantly cheaper to simply get a normal resistive heating dehumidifier, as the additional heating efficiency of a Peltier operating at 0.6 COP is not worth the upfront investment.
Small heating box dehumidifiers are a bit of a misnomer too. All they do is heat the air so it’s relative humidity is lower since hot air can hold more water. The amount of water does not change. However for most environments this works OK. Only units with full refrigerant pumps inside that can cool the air to its dew point, condense the water out, then warm it back up are true dehumidifiers.
I don’t think the efficiency is a big deal; you’d only have to run the peltier intermittently (e.g. each time you open the box) as long as you can drain the condensation somehow and it’s otherwise well-sealed. I’ve idly pondered OPs idea myself and I think it’s not a terrible way to dry a box. You avoid the consumables or need to recharge your dessicant materials.
Yeah, intermittent operation based on RH% would probably be okay as far as power consumption goes. But at the same time, do you really gain anything in terms of performance and cost vs just resistance-heating the box up warm enough that the RH% drops below 30, and then cycling air in and out once in a while?
You’re right, 50%@70f (let’s say Texas indoor conditions) is 19%@100f, so you’re right that just heating is probably perfectly good.
You’d need a very sensitive filament to bother doing more. That said, if you did have a peltier with the cold side at 32f, you’d get 25%@70f or 9%@100f…which actually isn’t amazing since you still need to warm it up to 100f to get that 9%! Peltiers are inexpensive and I might still experiment with it one day, but…it doesn’t seem like a huge win.
I think it should be theoretically possible to make a Peltier based machine that will extract moisture the same as a refrigerant pump machine. Ask any overclocker who’s tried to use a Peltier directly on a CPU or motherboard; it’s perfectly possible to get the cold side of a Peltier below the dew (or frost!) point when it has little or no thermal load on it.
Now as to whether or not any commercial product exists that actually works that way is another story. I see a ton of them e.g. on Amazon, but I have not tried any out or taken one apart or anything. But with a suitably shaped heat sink you could get condensation to form on the cold side and then drip or shake or blow it off or whatever into a catch bucket, just like your basement dehumidifier does.
oh, anything is technically possible. It’s totally possible to get a peltier to drive a sufficient temperature delta to condense water at a low dew point. The issue is the exponentially worsening efficiency curve as delta-T increases that would make it’s power requirements - and waste heat generation - quickly become untenable for what you’re accomplishing.