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Right, so, one month in and here's what we've got on prototype 2a at this point.
1: As per the one-week update, it still reclaims a lot more heat/humidity than prototype one. Numbers are within what I'm going to call margin of error, with gains between 1.6°C and 2.1°C depending on who is doing what laundry - with 5ish points of gained humidity. As before, we never exceeded bad limits, though with one particularly long day of laundry from a housemate (which went into the dryer extra damp) I did have to turn a fan to accelerate dispersion of temperature and humidity into the rest of the house.
2: The second fabric screening material I decided to try - cut from one of my dryer bags - appears to be very effective. Weekly cleaning is optional. Biweekly cleaning is asking for reduced effectiveness. Monthly cleaning is probably out.
3: But on another(?) plus side, you don't need a vacuum to clear the lint! You can do it by hand, just like with a dryer lint trap. (I used a vacuum anyway after determining this, for neatness.)
4: As before, hinged access to the filter (lets you vacuum lint off the fabric screening material) is a necessary feature for convenience.
5: Repeat for my own notes basically: a filter this much larger needs central-axis support.
6: Annealed PLA is much more humidity/temperature stable than basic/raw printed PLA. It's staying flat even in a configuration without much reinforcement in that direction. I'm suspecting
7: MERV 13/MPR 1900 continues to be more than good enough for dust control. There's no sign of dryer lint or dust anywhere.
8: You really don't want to use scented dryer sheets with this kind of setup. I didn't expect to encounter this, but a housemate grabbed some because they were out of unscented and we all learned that was bad. (They didn't like it either and got more of the proper kind.)
But if you like scented dryer sheets, you definitely won't want to do this unless you really like that scent.
Items 7 and 1 combine to tell me that we can expect some real durability from a MPR1900/MERV 13 filter, particularly if combined (as here) with a charcoal prefilter and a lint-trapping fabric on top of that. I'm really not seeing any sign of occlusion - and I suspect the charcoal prefilter part is pretty optional, given the lack of buildup I'm seeing in the charcoal. I do think it's getting moderately saturated scent-wise, but most of that is probably that accidental two-week introduction of HEAVY HEAVY SCENT MACHINE dryer sheets.
We're heading into March, so this series of winter testing is probably about done. We'll have a couple more weekends, I imagine, before the humidity additions become counter-productive, but that's most likely all we've got.
However, from this month of testing, I do feel confident enough to move to a prototype 3, which will not be mostly made out of cardboard (lol I hope anyway) and which will need to include some sort of shutoff door. The primary filter isn't showing any signs of clogging after a month; output is being maintained pretty well, and we aren't getting leaking.
I suppose the next question is whether something like this is worth the effort. It's not lengthening the time required to dry clothing, so there's not a downside other than initial construction and operation. It does gain us measurable heat and humidity gain in winter, both as per goals. So it does work.
But does that intermittent (three days a week) additional comfort / heating cost reduction pencil out against cost of materials, including annual filter replacement?
Honestly, I don't know, and don't really have the training to know or the facilities to find out. Obviously, this is no way to heat a house, it's not close to enough and is not exactly what you'd call efficient as a primary system. But in this case, where it's a matter of recovering otherwise-lost heat and humidity resources, it's kind of infinitely efficient. It successfully retains heat that would be otherwise lost to the outside, and in our climate, it does help reduce the dryness in the building, both in amounts measurable (and not subtle) in our graphs.
Ignoring construction cost - is that worth an annual $20 or so for the filter? Is the reduction in carbon output from heating balanced by the carbon cost of making that filter? So far, I don't know.
But furnace filters aren't hard to make. These aren't high-energy-use items.
So maybe.
ETA: Of course there are extant cost of operations numbers for clothes dryers! How did I not realise that?
Based on those average numbers, the cost of heat for our dryer is around $72 for four months, give our typical number of loads. That produces dry clothing, waste heat, waste humidity. Based on surface area of exhaust tube (4" diameter) vs. filter (169" inches) about 92% of that is being recovered, let's round that down to 90%. That's $64.80.
To break even with $20, we need 30.9% of that to be heat recovery to break even on cost of one filter.
I don't know how to calculate that here, but it seems a lot to ask that hot-air-on-tumbled-clothing have a continual 69.1% drying efficiency. I have no idea what the actual number would be, but that seems high. Like, probably a lot high. Particularly given the lower-than-I-expected relative humidity of the recovered air.
And what all that means, if I'm right about drying efficiency, is that, in fact, we're coming out ahead. Maybe by... a lot.
If that efficiency is around 50/50, then we're getting $32.40 worth of de facto electric heating out of this (discounting filter cost for a moment) which translates to about 295kWh at our rates, which translates to roughly a 1500W space heater's worth of electric running a bit under 11 hours a week...
...which gets us very close to back to our number of loads of laundry.
Huh.
So... yeah.
This might actually pencil out!
1: As per the one-week update, it still reclaims a lot more heat/humidity than prototype one. Numbers are within what I'm going to call margin of error, with gains between 1.6°C and 2.1°C depending on who is doing what laundry - with 5ish points of gained humidity. As before, we never exceeded bad limits, though with one particularly long day of laundry from a housemate (which went into the dryer extra damp) I did have to turn a fan to accelerate dispersion of temperature and humidity into the rest of the house.
2: The second fabric screening material I decided to try - cut from one of my dryer bags - appears to be very effective. Weekly cleaning is optional. Biweekly cleaning is asking for reduced effectiveness. Monthly cleaning is probably out.
3: But on another(?) plus side, you don't need a vacuum to clear the lint! You can do it by hand, just like with a dryer lint trap. (I used a vacuum anyway after determining this, for neatness.)
4: As before, hinged access to the filter (lets you vacuum lint off the fabric screening material) is a necessary feature for convenience.
5: Repeat for my own notes basically: a filter this much larger needs central-axis support.
6: Annealed PLA is much more humidity/temperature stable than basic/raw printed PLA. It's staying flat even in a configuration without much reinforcement in that direction. I'm suspecting
7: MERV 13/MPR 1900 continues to be more than good enough for dust control. There's no sign of dryer lint or dust anywhere.
8: You really don't want to use scented dryer sheets with this kind of setup. I didn't expect to encounter this, but a housemate grabbed some because they were out of unscented and we all learned that was bad. (They didn't like it either and got more of the proper kind.)
But if you like scented dryer sheets, you definitely won't want to do this unless you really like that scent.
Items 7 and 1 combine to tell me that we can expect some real durability from a MPR1900/MERV 13 filter, particularly if combined (as here) with a charcoal prefilter and a lint-trapping fabric on top of that. I'm really not seeing any sign of occlusion - and I suspect the charcoal prefilter part is pretty optional, given the lack of buildup I'm seeing in the charcoal. I do think it's getting moderately saturated scent-wise, but most of that is probably that accidental two-week introduction of HEAVY HEAVY SCENT MACHINE dryer sheets.
We're heading into March, so this series of winter testing is probably about done. We'll have a couple more weekends, I imagine, before the humidity additions become counter-productive, but that's most likely all we've got.
However, from this month of testing, I do feel confident enough to move to a prototype 3, which will not be mostly made out of cardboard (lol I hope anyway) and which will need to include some sort of shutoff door. The primary filter isn't showing any signs of clogging after a month; output is being maintained pretty well, and we aren't getting leaking.
I suppose the next question is whether something like this is worth the effort. It's not lengthening the time required to dry clothing, so there's not a downside other than initial construction and operation. It does gain us measurable heat and humidity gain in winter, both as per goals. So it does work.
But does that intermittent (three days a week) additional comfort / heating cost reduction pencil out against cost of materials, including annual filter replacement?
Honestly, I don't know, and don't really have the training to know or the facilities to find out. Obviously, this is no way to heat a house, it's not close to enough and is not exactly what you'd call efficient as a primary system. But in this case, where it's a matter of recovering otherwise-lost heat and humidity resources, it's kind of infinitely efficient. It successfully retains heat that would be otherwise lost to the outside, and in our climate, it does help reduce the dryness in the building, both in amounts measurable (and not subtle) in our graphs.
Ignoring construction cost - is that worth an annual $20 or so for the filter? Is the reduction in carbon output from heating balanced by the carbon cost of making that filter? So far, I don't know.
But furnace filters aren't hard to make. These aren't high-energy-use items.
So maybe.
ETA: Of course there are extant cost of operations numbers for clothes dryers! How did I not realise that?
Based on those average numbers, the cost of heat for our dryer is around $72 for four months, give our typical number of loads. That produces dry clothing, waste heat, waste humidity. Based on surface area of exhaust tube (4" diameter) vs. filter (169" inches) about 92% of that is being recovered, let's round that down to 90%. That's $64.80.
To break even with $20, we need 30.9% of that to be heat recovery to break even on cost of one filter.
I don't know how to calculate that here, but it seems a lot to ask that hot-air-on-tumbled-clothing have a continual 69.1% drying efficiency. I have no idea what the actual number would be, but that seems high. Like, probably a lot high. Particularly given the lower-than-I-expected relative humidity of the recovered air.
And what all that means, if I'm right about drying efficiency, is that, in fact, we're coming out ahead. Maybe by... a lot.
If that efficiency is around 50/50, then we're getting $32.40 worth of de facto electric heating out of this (discounting filter cost for a moment) which translates to about 295kWh at our rates, which translates to roughly a 1500W space heater's worth of electric running a bit under 11 hours a week...
...which gets us very close to back to our number of loads of laundry.
Huh.
So... yeah.
This might actually pencil out!
