I think I've figured something out.

[solarbird]

I've been playing with ideas about how to recapture dryer exhaust heat in the wintertime, and how to do so with controllable humidity.

I realised during this event in particular that sometimes we want that humidity, or at least some of it. And that leads to a very, very simple - and trivial to engineer - solution.

Conveniently, today is laundry day, and I am running experiments.

Comments

[absynthe]

This is something I've pondered casually, off and on for a few years. I'm interested to see what you come up with.
Oh, if you ever need anything designed in cad, hit me up. I finally bought a personal license for Solidworks, and I'm happy to model things up for machining, 3D printing, sheetmetal work, whatever you might need.

[solarbird]

Well, thanks! I might even take you up on that. I don't officially know that I've been given an intro-level 3D printer for new year's, because everything is delayed due to reasons, but I'm pretty sure I did, and I was thinking I might use that as a first project.

[solarbird]

Mind you, there is nearly zero to this. It's not even a diversion box. It's a variable splitter with one 4" duct input from the dryer and two outputs, one 4" ductwork to the outside and constant, one rectangular, with a lint filter, which can be variably opened and closed.

Right now, I'm imagining a sliding door type contraption, possibly with gravity louvres to keep outside air leakage to a minimum when the dryer turns off but the output hasn't been fully closed off.

That's it. And that's all it seems to need to be, given that what I did today worked surprisingly well and was even simpler than that.

[kathmandu]

Your engineering is always so interesting and impressive. I look forward to hearing about this experiment.

[solarbird]

The numbers from today are very good, particularly given the limited nature of the experiment. I'm seeing a very durable 2-3 points of humidity gain across the upper two levels of the building without excess humidity gain in the laundry, and a free couple of degrees C across the northern side of the building outside the laundry, with a half degree or so even on the next floor thanks to the distribution network.

Given how ad-hoc this whole thing was, I'd call that a clear success.

It's obviously nothing building-changing, but I certainly wish I could feed the output from this directly into the HVAC intakes. I mean... it's zero additional energy expenditure heat and humidity when more of both is good. Why not do it?

(In a greater sense what all this is about is carbon output. If I can use this already-generated heat when it's positive to do so... obviously, I should.)

[malurette]

Ooh engineering experiments~ I hope it works!
yay science!!!

[solarbird]

Check the other comments above, particularly my response to kathmandu - it seems to do a bit of good! For a number of hours, at least. Which isn't a lot, but it's better than just wasting the heat and humidity entirely. Since it really is basically zero cost, it's very much a "why not do it since it does work some?" situation.

[armiphlage]

I recommend a multistage filter if you are venting dryer exhaust air into the house. We tried doing that, and ended up with grey dust on every surface, and coughed up grey gunk for a week afterwards.

An air-to-air heat exchanger would avoid particulate matter getting into your lungs, but you'd still want to filter the exhaust first to avoid clogging with lint.

[solarbird]

From reading, I’m aware of that problem, and I’m not planning on a simple venting like that. I’m trying to do only a partial bleedoff, with most of the air still going outside as normal. I've found a lot of people try to work with 100% internal venting, but that generally leads to both what you describe and also much too much moisture inside - not to mention what has to be reduced dryer efficiency.

With the primary exhaust still being external, you’ll have dramatically lower venting pressure at the bleed-off point, making simpler filtration dramatically more effective while still gaining meaningful benefit - and on top of that, much longer between filter cleanouts. Or so my simple testing across four loads of laundry last night appeared to demonstrate.

[armiphlage]

If you're only going partial, what about a permeable tube (cloth)? Moisture and hot air would diffuse through the fabric, while particulate matter accumulating on the inner surface would get blasted out by the main exhaust flow.

[solarbird]

Ah, but that’s not adjustable.

An adjustable filterer vent lets me turn it completely off in warm or humid temperatures, which is definitely required.

The temporary vent I added yesterday was very small and yet very effective.

[kevin_standlee]

The area in Fernley House that was fitted for a dryer vented directly under the house, which I suppose had a bit of a hypocaust effect; however, Lisa did not like it and considered it a hazard, especially after she went into the crawl space and looked at the mess down there. Thus we have a dryer that we can't use until Lisa figures out a way to run new vents outside the house, which is difficult because the utility space doesn't touch an outside wall.

The upstairs bathroom has a small combination under-and-over washer/dryer, where the dryer does vent outside. (The upstairs was clearly intended as a separate apartment or "mother-in-law" unit.) The plumbing doesn't work upstairs and it's never been urgent enough to spend the thousands of dollars it would take to fix, so we have a working washer downstairs where the plumbing is and a small working dryer upstairs where the vent is.

[solarbird]

Yeah, that could turn into a fire hazard, in the same way that a silo can be a fire hazard and for the same reasons.

If I might suggest: there's currently a vent into the crawlspace.

Go into the crawlspace and run a duct in there out to the side of the house.

[kevin_standlee]

That's the most likely solution. Because we do have a working dryer, it hasn't been a priority for Lisa to go crawling around down there to do so.