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hdrider_chgo
11-27-2007, 08:38 AM
I'm planning a laundry room for my house and have wondered if there is any way to capture some of the heat that is put out by the clothes dryer. It seems like a lot of heat going to waste, and a pretty simple thing to save some of it. Maybe like a double-wall exhaust pipe, with a fan that blows air between the inner and outer pipe?

What is the theory on this, and why aren't more people doing anything like this (am I just a nutcase?) Is there a device on the market that accomplishes this?

The flip side of this is, how much heat is lost through the dryer exhaust pipe when the dryer is not in use, and is there a way to minimize this?

Martin Holladay
11-27-2007, 08:55 AM
HD Rider,
1. Why aren't more people doing it? Because the amount of lost heat is so low that it does not justify the investment in extra equipment (special vent pipe) or energy (additional fans) required to harvest it.

2. If you use a fan to cool the exhaust, you will encourage condensation of moisture in the exhaust gases. You have to provide a way to drain the liquid water without freeze-up problems in cold weather.

3. There are devices on the market to do what you suggest; for example:
www.indoorlinttrapfilter.com
The short version: bad idea. (a) No good for gas dryers -- dangerous exhaust fumes shouldn't be vented indoors. (b) A bad idea for electric dryers too, since adding extra moisture inside the house is risky.

hdrider_chgo
11-27-2007, 09:37 AM
HD Rider,
1. Why aren't more people doing it? Because the amount of lost heat is so low that it does not justify the investment in extra equipment (special vent pipe) or energy (additional fans) required to harvest it.

2. If you use a fan to cool the exhaust, you will encourage condensation of moisture in the exhaust gases. You have to provide a way to drain the liquid water without freeze-up problems in cold weather.

3. There are devices on the market to do what you suggest; for example:
www.indoorlinttrapfilter.com
The short version: bad idea. (a) No good for gas dryers -- dangerous exhaust fumes shouldn't be vented indoors. (b) A bad idea for electric dryers too, since adding extra moisture inside the house is risky.

I'm NOT suggesting venting the dryer to indoors, rather capturing just the heat. Now, if the Heat Recovery Ventilator concept is to try to save the heat from the indoor air that is vented outside (air that is roughly 70 degrees), why would it not pay to save the heat from the clothes dryer air, which is a much higher temperature? And as far as the condensation goes, as I understand it, the same issue exists in high-efficiency sealed-combustion furnaces, and that is easily dealt with by adding a drain.

Finally, when the winter wind is blowing against the dryer vent, you certainly must have a significant amount of air infiltration back through that exhaust pipe. Or not?

Martin Holladay
11-27-2007, 09:54 AM
HD Rider,
I never said you couldn't do it. I just said it probably wouldn't be worth the investment in extra equipment (special vent pipe) or electricity to run an additional fan.
Go ahead. You can build one. The simplest way would just be to extend a long zig-zag run of 6-inch galvanized pipe all around your house, within the conditioned envelope, to cool the exhaust gases. Oh, yes -- you need to catch the water and run it to the drain. But you know that. I'm sure you can rig it up. Be sure it's easy to disassemble to clean the lint twice a year. Remember, those joints have to be both watertight and easy to take apart and reassemble.
Or, you can rig up a double-wall pipe as you originally suggested. Again, make it both watertight and easy to dissassemble. Slope it to a drain; hook it up to a plumbing trap. Put in a fan, and calculate how much electricity it will take to run the fan; then calculate whether the cost of the electricity is more than or less than the value of the thermal heat recovered. Put in a control to interlock the operation of the fan with the operation of the dryer. Include several good backdraft dampers. Let's see-- are you done yet? Send me a picture when you've got it built.

hdrider_chgo
11-27-2007, 10:26 AM
Before I get into a little snit over the need to interlock the operation of the dryer with the circulating fan, I'd like to do some math.

Does anyone know a quick way to find out how much gas is consumed to dry a load of laundry, and perhaps the amount of heated air that is removed from the house in the process? That would help me decide whether to pursue the idea or drop it.

And what about cold air blowing in through the dryer? Certainly I can't be the only one who's noticed it.

Martin Holladay
11-27-2007, 10:48 AM
HD Rider,
One clothes dryer manufacturer (Siemens) lists the BTU input for one model of gas dryer at 18,500 BTUs:
www.siemens-home.com/Appliances-Laundry-Washing_Dryer_ultraSense-Gas-Dryer_WTXD5522UC_WZ20395_White_Laundry-Pedestal#NULL
Remember:
1. The gas burner is not on for the entire time that the clothes drying cycle is operational.
2. No heat-recovery device will recover 100% of the heat.

Finally, before you go into the business of building heat-recovery devices for clothes dryers, have your lawyer talk to the lawyer of this patent holder:
http://www.patentstorm.us/patents/7213349-description.html

hdrider_chgo
11-27-2007, 11:18 AM
Martin,

I'm not sure how you convert the BTU output that you gave to the amount of gas actually used to dry a load of clothes, or how much heated indoor air is exhausted to the outdoors in the process.

I have not been able to get your patent link to work. Although I am curious about what you are pointing to, I am not interested in going into business on this. I doubt whether something as simple as what I would envision would be patentable anyway.

I have no idea whether it's feasible to capture the dryer heat. I simply thought it was a logical question, to which I am still looking for answers.

Martin Holladay
11-27-2007, 11:36 AM
HD Rider,
The Forum software seems to clip long Web addresses. If you are trying to copy the Web address for the patent, some characters may be missing. On my screen, my post has been altered -- the Web address is shown with "..." in the middle. The missing characters between "72" and "scription.html" are "13349-de". Or you can just try clicking on the address to see if that works.
Hope that helps.

VTNorm
11-27-2007, 01:48 PM
And what about cold air blowing in through the dryer? Certainly I can't be the only one who's noticed it.

A customer of mine completed a major remodel 2 summers ago, the washer & dryer ended up in an interior closet. Dryer duct ran down into the basement and had a longish run of about 25ft in an enclosed joist bay (finished basement) and out. The duct shared the bay with plumbing. They had 3 seperate burst pipe incidents until I re-routed the dryer vent to a seperate joist bay and insulated it. So yeah, the duct is nice conduit for not just cold but frigid air.

The flappers on the exterior vent are worthless. I would isolate the ducting, insulate it and use foam to seal around any openings in the walls or flooring the duct passes through. In my own house, as long as the dryer door is kept closed there's almost zero draft. But if clothes are left in the dryer overnight in the winter, watch out, nothing wakes you up quicker than putting on chilled underwear.

-Norm

Dick Seibert
11-27-2007, 02:34 PM
This is slightly off topic, but relevant; dryer vents have come out of the IMC, so we won't be seeing them anymore. I posted a question about this on the ICC Forum and never got an answer to my basic question, which had to do with whether it was coming out of the UMC since California isn't going tot he IMC but remaining on the UMC. BTW, there is a mistake in my question, we ICC members receive the free Building Safety Bulletin, which is not the Building Safety Journal (I thought they were the same), the November issue of Building Safety Bulletin states that come January, the publications are being combined so we will be receiving the Building Safety Journal which is online. I can't link you to the Building Safety Bulletin article, but here is my question (http://www.iccsafe.org/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=002081#000000). If anyone is really interested I'll scan the article and upload it (if I haven't thrown it away).

Roger P
11-27-2007, 04:11 PM
Dick:
See Section 504 Clothes Dryer Exhaust. 504.6 Domestic clothes dryer ducts. Section 504.6.2 is quite specific about providing an exhaust duct if a dryer space is provided. Section 504.1 includes an exception: This section shall not apply to listed and labeled condensing (ductless) clothes dryers.

BigLou80
11-27-2007, 04:46 PM
HD rider,
not only are you sending a lot of heat out the vent pipe but you are drawing in a lot of unheated air in the winter. A dryer blower that runs at 125 CFM will take 7500 cubic feet of heated air out of your house for every hour it runs. To heat the make up air 60 degrees you need about 8100 BTU's or .06 gallons of oil on an 85% efficient unit. If you can use an HRV or something to recover 45 % of the 18500 BTU's you will recover 8325 BTU's Hope this helps

Lou

m beezo
11-27-2007, 05:38 PM
Most of the folks I know who have electric dryers run them into the inside of the house in the winter. You add some humidity but for most folks with a gas furnace you need some humidity added to the house. Solves you having a humidifier added to your furnace.

Not sure why it seems to be so difficult to consider. Martin, you seem to be in kind of a snit about the whole idea. I have seen everything from an old panty hose over the end of the outlet hose which helps catch lint and can be changed easily to systems that you buy and install with a filter already in them. About the only problem anyone ever mentioned to me was if they did all their laundry on the same day. If they did 10 loads then it was an overload of humid air in the house. But if they switched to doing one or two loads a day it was not a problem. Plus lots of the new washers really wring out the clothes so mine does not make the dryer run as long so not as much humid air.

My contraption cost something like 10 bucks, took 15 minutes to install, and I am getting free heat and humidity out of my dryer. If I need to do lots of laundry and do not want all the heat and humidity in the house I flip a little door and it shoots outside again.

greentree
11-27-2007, 06:42 PM
My contraption cost something like 10 bucks, took 15 minutes to install, and I am getting free heat and humidity out of my dryer.

I have the little plastic box with a flap for summer and winter, probably same one you have. Outlet hole to basement has a screen on it for lint, it still exhausts some air out the regular outdoor vent, just reduces hole for flow from 4" to maybe 1-2". My dehumidifier is right next to the box and it really doesnt run much, winter is so dry anyways.

I had the same thought as OP, why heat the outside? I dont know if it really does anything but for $10 and a "maybe", what the hell.

Travis

Dick Seibert
11-27-2007, 08:34 PM
Roger:

You wouldn't still have the October issue of Building Safety Bulletin would you? I've apparently thrown mine away, it made the case that builders could use the exception to leave the ducts out, I would surmise that the appliance industry pushed for that to force people to buy new dryers, but that's just speculation. Notice the paucity of response I got on the ICC Bulletin Board?

frenchie
11-27-2007, 09:57 PM
Not to interfere with the directions this thread is going, but... why not just buy a condensing ("ventless") dryer?

hdrider_chgo
11-27-2007, 10:31 PM
Not to interfere with the directions this thread is going, but... why not just buy a condensing ("ventless") dryer?

I did not know there was such a thing. So the carbon monoxide and other combustion products are vented directly into your living space? That does not sound like a good idea. And- where does the heat go in summer?

David Meiland
11-27-2007, 10:35 PM
HD... check out the Bosch dryers, there is a ventless model in the Axxis line and it's electric, not gas.

I have wondered for a long time why modern dryers are not running pipe similar to direct vent (pipe within a pipe), where outside combustion air is drawn thru the outside and exhaust is expelled thru the inside. This would have the effects of (a) stopping dryers from pulling heated indoor air and throwing it away outside, and (b) preheating the air going to the dryer, so that less energy would be required to get it up to temp. Seems like this would improve both issues.

Dick Seibert
11-27-2007, 10:37 PM
Harley:

Are you talking about combustion venting of gas dryers? 90% of our dryers are electric, I am talking about lint vents, that's what I thought you were talking about when you started the thread, and Frenchie is right, the industry is moving to vent-less dryers, that's why the exception in the new code.

hdrider_chgo
11-27-2007, 10:55 PM
Harley:

Are you talking about combustion venting of gas dryers? 90% of our dryers are electric, I am talking about lint vents, that's what I thought you were talking about when you started the thread, and Frenchie is right, the industry is moving to vent-less dryers, that's why the exception in the new code.

Dick,

Call me clueless, but I've never heard of a ventless dryer. Why does everyone out there run electric? Conventional wisdom here is that gas dryers cost way less to run, and most everyone I know here runs gas. If they are ventless (electric), where does the heat go in Summer?

When I started the thread, I was wondering about two things: 1) Why not recapture some of the dryer heat vented to the outdoors in Winter, and 2) How to stop the cold air from blowing back into the house through the dryer vent when the dryer is not running.

Dick Seibert
11-27-2007, 11:37 PM
Harley:

Everybody here uses electric, there was a time when there was talk about gas being cheaper, then the price of gas went through the roof. I did build one house where the plans called for both gas and a 220 volt 30 amp electric outlet so the owner had a choice, but they still have electric. He had to buy a new one recently and I pointed out to him that he had a choice, he said the store advised him against gas. Back in the 60s I bought a ventless dryer, it pumped the lint down the waste drain, they weren't very successful then, so supposedly this new generation has a new theory. Bosch Ventless Dryer (http://www.epinions.com/hmgd-Dryers-Bosch-Electric-Bosch_WTL54_Series_Condensation_Dryers/display_~reviews)

I actually bought a dryer 30 amp plug and had my electrician mount it to a TempPower cord. When we go into an existing house with no power pole, there is no way to get 220 to our tempower box in the house for everyone to plug into, we use twistlock cords inside of houses too by CALOSHA, so I plug into the dryer outlet and place the TempPower box in the center somewhere so all trades can plug into it and I've got 220.

Ray Moore
11-28-2007, 06:29 AM
I use this product by Seiho on all my projects. http://www.seiho.com/product/rcarcc/rcarcc.html

It is easy to clean and is gasketed and spring loaded. To clean it you just pull it out by hand, shake it out and put it back. It is held in by spring clips. When I blower door tested my house, the dryer vent contributed 20 cfm at 50 pascals. That is about 1 cfm under natural conditions. You need about 50 times that on average to ventilate your home. The test was done with no interior duct or equipment attached. It was just a 12" long pipe through the wall with the Seiho on the outside.

I have done a lot of research on the issue of recapturing waste heat from the dryer and providing make up air to the laundry room and believe it to be a bunny trail. On nice days, you may benefit from opening a window in the laundry room during operation if the dryer vent doesn't reintroduce the lint into the home.

The dryer vent simply provides a portion of the ventilation that the home needs. It exhausts some of the nastiest, most humid, and most perfumed air in the house to the exterior. If you try to provide cold outside wintertime air to the dryer to eliminate the loss of conditioned air, the dryer will not work well. All drying requires heat.

The best way to save energy when doing laundry is to hang the laundry outside. If that is impractical, then accept the heat loss when the unit is running and use a good damper to minimize standby losses through the duct.

Gas dryers are a very bad idea worthy of their own thread. It would probably generate a long argument. I only use gas for hot water and gas cooktops. These will probably fall out of favor in the next 10-20 years as well. We need to perfect the heat pump water heater. A heat pump may be a good solution to the electric dryer in some climates some day.

hdrider_chgo
11-28-2007, 07:58 AM
Ray, you probably noticed I started a "gas vs. electric thread" so feel free to post your thoughts there. I would like to know why you think gas dryers are bad.

Are you using the caps with or w/o backdraft damper? Was your blower door test done with or or w/o backdraft damper?

In regards to your research about capturing the heat from the dryer not being worth it, could you be more specific? (Again, I am not talking about venting the dryer into the house, which I feel is a bad idea, just taking some of the heat off the exhaust pipe).

Martin Holladay
11-28-2007, 08:30 AM
M Beezo,
I'm glad to hear that your method of venting an electric dryer indoors works for you. You're not the first person I have heard from who does it, and I know it can be done without problems.
However, generalizing from your experience is risky. There is a huge range in air infiltration rates from house to house. Many older houses are quite leaky; leaky houses are usually dry in the winter. If someone vents an electric dryer indoors, there may be no problems. Sure, they're introducing moist air into the house -- but the moist air leaves quickly, through air leaks in the second floor.
In a very tight house, introducing extra moisture can lead to all kinds of problems, ranging from soaking window stools to rotting studs.
This is a forum for builders. Builders should be wary of recommending the introduction of moist air from a clothes dryer into the interior of a house. The builder might end up with the liability when something goes wrong.
So, I wouldn't say I'm "in kind of a snit about the whole idea." Just wary.

David Meiland
11-28-2007, 08:41 AM
I didn't see it as a "snit" but I did think your tone was a little less polished than your usual... a little sarcasm thrown in. Practically everyone else here does it, and you can too.

greentree
11-28-2007, 08:57 AM
Shouldnt new homes we build be designed to cope with extra moisture being introduced in the building envelope with some kind of mechanicals?

Ray Moore
11-28-2007, 09:13 AM
Ray, you probably noticed I started a "gas vs. electric thread" so feel free to post your thoughts there. I would like to know why you think gas dryers are bad.

Are you using the caps with or w/o backdraft damper? Was your blower door test done with or or w/o backdraft damper?

In regards to your research about capturing the heat from the dryer not being worth it, could you be more specific? (Again, I am not talking about venting the dryer into the house, which I feel is a bad idea, just taking some of the heat off the exhaust pipe).

I did the test with the backdraft damper in place and always use them on exhaust appliances. I use gasketed motorized dampers on all make up air systems.

The research I did was a while back and was a little technical. I may find time to respond to that later. The system you propose is complex and problematic if done right, for the reasons that Martin offered. The short answer is that if it were done correctly it would cost more than the dryer itself and much more than the potential energy savings. A dryer is a very intermittent load and can be ignored for now. There is much lower hanging fruit that is still not being addressed. Sorry I don't have time to offer more on it right now.

I will address the gas dryer in the other thread when I have more time.

How many loads of laundry do you do per week? What is your climate? When you do your calculations remember that not all input heat goes out the vent much of it is introduced into the room. Capturing it will cause condensation. A condensing dryer may be a good idea. Are you trying to capture the waste heat from the hot water from the laundry also? Just a thought.

Martin Holladay
11-28-2007, 09:27 AM
Green Tree,
If indoor humidity is too high, it can be reduced:
1. In winter, by increasing the rate of mechanical ventilation.
2. In summer, by operating an air conditioner or dehumidifier.
Both options use energy. To my mind, it makes no sense to vent a dryer indoors if you know that the humidity level in the house will then rise to the point that the problem needs to be corrected with mechanical ventilation or dehumidification. I agree with Ray Moore -- exhausting air from a clothes dryer to the outdoors is appropriate. If you have a tightly built house, that's not the kind of air you want to introduce indoors.

BigLou80
11-28-2007, 10:06 AM
Martin and Ray,
well said. On a tight house the extra moisture will be problematic. You will save more energy by tightening up your home then you will by trying to recover the heat from your dryer by directly venting it inside the house.

Lou

Ray Moore
11-28-2007, 10:10 AM
That's not what he was trying to do. He was trying to develop a heat exchanger. The thread got off course on the subject of venting the moisture into the house. All good subjects though.

hdrider_chgo
11-28-2007, 10:11 AM
How many loads of laundry do you do per week? What is your climate? When you do your calculations remember that not all input heat goes out the vent much of it is introduced into the room. Capturing it will cause condensation. A condensing dryer may be a good idea. Are you trying to capture the waste heat from the hot water from the laundry also? Just a thought.

I'll take your and Martin's word for it, but I wish I was more clear on the math. If I knew how much gas (or electricity) was used to dry a load of laundry, I could probably take it from there, and prove to myself confidently that it's not worth it.

Laundry varies quite a bit, but about 4 loads/week. That could easily increase by quite a bit, given the flexibility of the living space I have here.

Climate is Chicago. Cold winters, varies from 40's in winter to below zero. Hot, humid Summers.

Is a condensing dryer the same as a ventless? I'm not big on that concept.

The laundry does not use much hot water. We mostly use cold for wash. I am looking at capturing the heat from the bathroom shower and tub water, since that space is part of this phase of remodel. That subject is planned for a future thread.

Ray Moore
11-28-2007, 10:36 AM
That's not what he was trying to do. He was trying to develop a heat exchanger. The thread got off course on the subject of venting the moisture into the house. All good subjects though.

On the issue of a heat exchanger, they require lots of surface area. In a dryer vent you want to minimize surface area and maximize velocity. That helps avoid lint buildup.

If you simply make a double walled pipe like is used in a vented sealed combustion fireplace, the surface area would be too small to gain very many btus. If you increase the surface area you will cause lint buildup.

If you chill the dryer vent pipe with the incoming air, you will cause condensation buildup that will collect lint and clog the line.

I couldn't even get the numbers to come close to working on simply supplying makeup air to prevent the loss of conditioned air and if I had it would have required a runtime sensor or manual control to open the motorized damper. In the end the complexity and maintainance issues made me glad that it wasn't justified from an energy standpoint. I tried really hard to figure it out though.

When thinking about any of these issues, remember this maxim. No drying occurs without heat and heat loss. As we try to reduce heat and energy demands, it is easy to create moisture issues from the reduced drying potential. Or as Joe L. and others say, "There's no such thing as a free thermodynamic lunch."

greentree
11-28-2007, 02:31 PM
I dont think he was trying to heat his house with his dryer, this thread seems to have gotten a little overcomplicated.

Try one of these, http://www.improvementscatalog.com/home/improvements/792912856-dryer-heat-saver.html , if the homes drywall starts to crumble and people start passing out because your house is too tight you can remove it.

As I said I hooked one up in my basement. My home is 102 years old and has a tiny bit of leakage here and there. I dont know if it works or not but it was $10.00 so I dont really care and I'm not too worried that my house is going to rot and collapse while I'm sleeping.

Travis