Clothes dryer heat recovery system
 

So, the attic project is winding down and I am looking for something new to do. I was reading a post here the other day about guys venting their dryers back into their houses and was thinking to myself how I wish I could do that. I don't think there is a day that goes by where my dryer isn't running in the winter. But, I have a gas dryer, so that isn't an option for me. Also, I'm not a huge fan of the amounts of water vapor is put into the air doing it. Especially when I think of the pains you go through trying to seal up your house.

So I was trying to think of a way to do this, and this is what I came up with. It really is pretty simple and eliminates the moisture problem. Start with aluminum dryer ducting and weld some aluminum fins on it. Thats it. You get yourself a relatively badly designed heat exchanger. But, its still a step up from aluminum tube, and a big step up from my current setup of wire reinforced plastic tubing. Perhaps adding a thermostatically controlled fan to blow over it when it heats up would increase efficiency.

Anyway, here are some pics.

http://ecorenovator.org/forum/attach...1&d=1233342407

Top view.
http://ecorenovator.org/forum/attach...1&d=1233342407

I like the idea. I wonder if there's a way to attach the fins that would allow for people without a welder, but still maintain the conductivity.

Out of curiosity did you use Sketchup for the model??

I used SolidWorks because I use it professionally. I have played with Sketchup, but I'm far more proficient in SW.

I inquired with a few guys at work about thermal adhesives. I'm sure you could do it with a thermal epoxy of some sort. Welding happens to be easier for me.

That looks like a lot of work. Why not just hang your clothes to dry? Wire clothes racks are very cheap. Put it beside your furnace and your laundry will dry in a few hours.

My basement is pretty small and has a real low ceiling. I'd love to hang clothes down there, but it just wouldn't be real practical. If it was just me and my wife in the house I'd try to make due with lines downstairs, but we have five others in the house right now.

Here is the current setup. As I mentioned it uses the plastic/wire ducting which I hear is really not the best stuff to use period.

http://ecorenovator.org/forum/attach...1&d=1233359089

http://ecorenovator.org/forum/attach...1&d=1233359089

http://ecorenovator.org/forum/attach...1&d=1233359089


To the right of the dryer I put a temp sensor on the table (far right end of the table). I'll monitor the temps to see how cold it stays down there.
http://ecorenovator.org/forum/attach...1&d=1233359089

How about if you instal that heat exchanger in to a larger pipe, then used forced air to boost output?

Not to sidetrack anything, but your basement looks like the inside of a Tatooine homestead from Star Wars.

...that is all.

dremd, I had thought about that, but I'd really like to keep this as simple as possible. Thats why I am considering just turning on a fan when the dryer is on. Thermostatically controlled would be great, but how hard would it be to just turn the fan on when you turn the dryer on?

I also talked to the guy who I was planning on using his TIG welder. He suggested looking for another way of putting it together as his doesn't weld aluminum very well. So, I'm looking into thermal epoxy and alternatives now. I did find this link while googling for thermal epoxy. Looks like a descent idea to me. Just have to make sure the epoxy will stick to aluminum.

Need Thermal Epoxy? - Make Your Own

I was thinking, what a neat/weird looking basement too!

Daox, I have a better idea for you - I've been planning to do it all winter, but it's been super busy and I haven't even modded my car in months.

The way I see it, the dryer really has two problems.
1. you pump lots of humid, warm air outside, leaving lots of E to be recaptured
2. removal of air from your home = lower air pressure inside, inducing drafts until pressure reaches equilibrium.

Your method addresses problem 1, but not problem 2. my idea will attack both.

Use metal dryer vent, regular style with the ridges.
In the window where your exhaust air goes out, make another hole for an inlet tube.
Using some 2 or 3 inch pvc, set up an intake to draw cold outside air from a location sufficiently distant from the humid (natural gas exhaust in your case) air exiting your vent - maybe a meter or so?
Around the outside of your 4 inch dryer vent, (I think that's the size) install a 5 inch piece of hvac duct to run the straight length of it.
Connect your inlet tube to the 5 inch duct nearest the window, and ensure that the other end of the inlet is close to the dryer's intake.

Probably want to install a dryer vent "flapper" on the inside of the intake to ensure flow only during operation, and a screen or other guard on the outside to keep critters out. Probably also wrap the hvac duct in insulation.

You could make this design as simple or complex as you wish - from the other stuff you've gone after on your car, I assume you'd be going after the complex version. ;)
For a simpler way, just use two pieces of long metal dryer vent and wrap them around one another - I don't know how well this would work though.

I got the idea from my background in biology and physics and thinking about countercurrent flow in fish gills / thermodynamic systems. Here's a wiki link.
Countercurrent exchange - Wikipedia, the free encyclopedia

I also plan on doing this with my furnace, which is a riskier proposition - need to keep the exhaust air hot enough that it still flows up the flue and out of the house, and also need to figure out what to do with condensation inside the pipe!

Oh, and I question the statement you made about water vapor - in the wintertime, water vapor in the air is scarce, and as a result, evaporation rates from your skin increase, making you feel colder. Adding water vapor to the air decreases rates of evaporation, making you feel warmer. I have a whole house humidifier on my furnace for this purpose, but I also try to line dry inside whenever I can - I just put my clothes (not the wife's) on a folding drying rack and turn on a small box fan next to them. I figure any E used to run the fan remains in the house, as does all the moisture - a good thing.
We also do cloth diapers, and we hang dry them whenever I take them out of the washer.

I also wanted to add, nice accommodation for the dryer being just a little too wide for the space - it probably makes it easier to empty, too, being higher than normal.

That is a great idea gascort. I know some of the newer gas water heaters do this, specifically the on demand ones. I'll have to take a look and see how easy it would be to make some ducting for it.

The moisture idea is interesting. I too have a whole house humidifier on my furnace, but I have turned it all the way down.

I haven't had time to work on this lately. Its been nice out so I've been working on the cars as much as possible. Later this week its supposed to drop back down though. Hopefully I'll get some time to work on it!

The humidity thing has to have a limit where it can make the cold worse... thinking on it more I think you're correct... I'm going to do some research.

I did some looking and Howstuffworks "How Humidifiers Work" explains it the best I think.
I was thinking maybe wind chill factored in humidity, plus another person posted on Metro's thread about him being cold in his apartment having to do with humidity, but I guess I was right before - more humidity = feel warmer due to decreased rates of evap. from skin.
I have my humidifier set at 40% now - probably should set it a bit lower because on really cold days we get condensation on the walls of our noninsulated plaster-walled living room. Something to fix for next year...
So.. Crank that humidifier back up! :)

gascorts idea is very similar to a direct vent fireplace. A tube within a tube acts like a heat exchanger boosting the intake air temp as it moves to the dryer and allowing a cooler setting on the dryer saving energy. Some heat needs to remain in the exhaust so condensation will not occur.

Alternatively or in addition, an automotive type intercooler (like used on turbocharging applications) with a fan could be used to draw heat out of the air, there would need to be a path for water to drain.

Has anyone thought about retrofitting a clothes dryer with a heat pump? I actually have a LG combo washer/dryer that uses a solid state heat pump to extract moisture. It has had a few problems (drain pump broke down, then a hose cracked - probably from handling while replacing the pump) and is a little expensive, but it uses only about 1/2 the energy of a regular dryer, so it has already paid off its higher initial price and repair costs by saving energy. And don't forget the convenience factor of not having to manually move the load from the washer to the dryer.

The LG dryers that used compressors are probably even more efficient, but they have not been available for years due to the upcoming R-22 phaseout. R-410A would not be a practical replacement for that application since the operating pressures (already high at 400-500PSI high side for R-22) would be too high with R-410A. Hopefully they find a HFC or alternative refrigerant that will work in that application or find a way to make the silicon heat pump work more efficiently.

Now that its getting colder out, we are starting to use the dryer more again. I tried to talk the wife into doing an indoor clothes line but she wasn't too keen on it.

So, I thought about things for a bit, then I wondered if I'd ever be able to quantify any gains by doing anything we've talked about. Thats when I did a little searching on ebay and found this:

Compact Propane or Natural Gas Meter SUBMETER 10063P1 - eBay (item 260497674459 end time Oct-28-09 14:05:36 PDT)

Its basically a kill-a-watt for gas usage. This should allow me to monitor usage for the dryer and the effects of any modifications.

I really like gascorts idea of taking my idea further with the intake ducting. So, I think I'll be looking into that.

Long tube versus short tube
 

I considered just using an extra-long uninsulated duct that weaves back and forth through a ceiling joist before exiting the house. I probably would use an extra large diameter duct too, so that the added length doesn't increase air resistance too much.

Welcome to the site fike.

If you cool the air too much you'll get condensation. Not that you can't deal with it, but you'll have to make accommodations for it.

We have a clotheshanger over the bathtub in the upstairs bathroom.

http://ecorenovator.org/forum/attach...0&d=1256891008

Each of the 6 poles has a string in it which goes through a pulley, allowing it to be lowered or raised. It doesn't impede bathing too much, especially since we usually take showers in the downstairs bathroom. The evaporating moisture helps humidify the house (and condense on the windows;) ).

Thank you for the welcom.

Yea, I guess there would be condensation, but I am not sure that it would be very harmful in the long run. I would guess in 2 years or 10 years (I have no idea how long) the duct would rust out. If it is 2 years, it probably isn't cost effective. If it is 10 years, it is probably a good idea.

I also considered putting a damper switch to direct it through a short direct route in the summer months and a long and meandering route in the winter months.

To lengthen the life of the system you could of course use aluminum ducting.

I'm not sure how bad it would be, but condensation would lead to lint build up I would think. Wet lint would hold moisture and lead to mold problems. I'm not sure how bad it would really be, but thats another thing to look out for.

I thiink if you keep the lint filter clean, it shouldn't be a problem. The exterior vent doesn't show any buildup of lint, so I would assume it is pretty lint-free.

You must have a cleaner/newer dryer than mine. Mine has lint all caked to the pipe walls. Not a ton, but its there.

Hi,

I think a large filter is the way to go, since you would recover ALL of the heat, and you would get the moisture as well. In the winter time in heated houses, the air gets very dry without some way of humidifying it.

We has a gas dryer, so maybe a carbon monoxide sensor would be a smart thing to have?

Good to see you over here Neil.

If you were to vent directly into the house, I would imagine a carbon monoxide sensor would be absolutely essential. Dryers go through quite a bit of air. I don't even know if it would be possible to vent it directly into the house without major air quality problems.

IMHO, dryers and gas hot water heaters could be a dangerous combo..

I noticed in my daughter's basement, a gas hot water heater with a PVC air input pipe.
There was a second PVC pipe for the warm exhaust gas.

I wondered if there was an air source for the dryer. Didn't see one.
When the electric dryer was running, it seems to be sucking air from the both the PVC pipes going to the hot water heater.
So, what comes in when the heater is burning gas, while the dryer is running? Exhaust gas?

I am starting to work on a system that encloses solid aluminum pipe (instaed of flex). Then surronding this with a box, and air circulating from on end to the other thus taking heat from skin of pipe .no damp air or lint problems ..I hope it works!!

This is exactly like an air to air intercooler, but will not be as efficient as a bar/plate design. Skin xfer of heat is limited to surface area, and the smaller your pipes are, the more surface area there is to xfer heat from one medium to the next. Bar and plate is one of the most efficient because there is a tradeoff between thermal xfer efficiency and pressure drop, and many of the best intercoolers on the market are borderline at 80% efficiency (of this type of design).

Also, keep in mind that the more heat you extract from your exhaust, the more you slow it down, making it more difficult for the intake fan to blow air through the dryer, and more difficult for the moisture to leave. The idea is to snake as much heat as you can right at the exhaust outlet so that there isn't a pressure increase slowing down flow.

Another way you might go about this is to minimize heat loss in all places except where you specifically want the heat to go. Insulate your exhaust and intake. If you want heat exchange from the exhaust to the intake, you don't want heat exchange anywhere else, so if you insulate the tubing, you can mitigate much of the heat loss, making the system more efficient than it would have been before, so your heat exchanger might have less of an impact on exhaust flow velocity.

Keep in mind, also, that you will need to periodically clean the heat exchange surfaces. If you don't, they will stop transferring heat. Lint is a great insulator.

???
 

thanks for the info regarind vent heat recovery. about 5-6 years ago I saw a system consising of a metal box with inlet 4" same for exhaust in the box was a fan on rear blowing the hot exhaust air forward to a foam like screen and a drip tray at the bottom this unit worked extremely well..but we are unable to find this sytem...any ideas ..thanks and have a great day.

I'm not sure I have ever seen anything like you describe, sorry.

thanks for your time anyway.I think we are going to use a solid pipe then suround that withanother enclosure and vent the warmed air into the house. thus avoiding any damp problems ..if you have any other info .we'd love to hear it as heat is a high expense here in quebec,,have a great day.w.weston(tony)

I spent a long time trying to figure out a way to cheaply retain the heat without the moisture and better yet without sucking the heat out of my house.
Well that didn't happen so I spent a small fortune and got an LG combo washer/dryer WM3988HWA Washer / Dryer Combos Home Appliances ... it solved all my issues except the cheaply part.
this uses a Ventless Condensing drying unit, uses 110 volt, This unit in drying mode warms up the kitchen real nice.

Lint is likely to collect inside dryer vent duct of any type, and regular cleaning is good practice. Smooth walled duct is better than flex in this regard. The idea to surround the dryer vent with a larger hvac duct to act as a countercurrent heat exchanger is very simple to construct and allows duct cleaning as usual.

Good practice is to provide the dryer location with an outdoor air intake to equalize pressure. This works out, as the heat exchange duct will terminate at the dryer. In a mixed climate, we don't want to temper the incoming air in the cooling seasons. An alternate, parallel air intake without heat exchange can also be fed to the dryer location. Dampers in both intake ducts dictate whether dryer heat-exchange occurs or not. These could also be electronic dampers for automatic operation.

Hey guys, if you look at a steam heating piping system, and you look at the pressure and temperature guages or instruments, you sill see what is called a steam pigtail siphon, it is just a 360 degree loop of pipe that screws into the tee in the pipe, and the other end goes to the guage or instrument, this protects the gauge from the hot steam, because the steam cannot travel around the loop, instead it condensates and runs back into the steam line. Maybe this could be incorporated into your dryer vent to remove the moisture, create a big vertical loop, and a fitting at the bottom of the loop with a hose to drain the fluid.

I like the ynot7201's idea, thinking about implementing it.

I'm thinking about putting solid aluminum pipe into a duct, rectangular or flattened 6" round one. May be adding some fins between inner and outer pipes for more efficient heat exchange.
Outer duct will draw air from outside.

I wander if anybody did this.
I'm concerned about a moisture.

In my case I have to run vent pipe 6 feet up. So if heat exchanger is efficient enough and some of the moisture condenses, it will collect in the duct.

Any experience there?

Isn't the dryer heat already transferring into the basement atmosphere, as the heated stale dryer air travels down the exhaust pipe?

I'm curious to hear if anyone actually implemented this as I've been considering it for our electric dryer. A condensing dryer sounds nice, but currently not an option on the budget side.

While I understand that other parts of the country want moisture in the winter, here in the PNW we don't, or at least the house I'm in doesn't. I've got condensation issues with the AL framed windows (to be replaced at some point) and am happy to get any and all extra moisture out of the interior envelope as possible.

Because of the ease of assembly I was also toying with this same idea for a simple HVR system for bathroom venting. I have plenty of room in a long crawl-space and a foundation drain (that now works after digging up the yard) there to dump condensation. I know efficiency would be low, but so would project costs.

One member did do this. Its a bulky system but seems to work.

http://ecorenovator.org/forum/applia...html#post21316