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clothes dryer- hydronic?

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by barnartist, Feb 18, 2008.

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  1. barnartist

    barnartist Minister of Fire

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    Last season I fiddled around with the notion of building a heat exchanger and rigging it to our clothes dryer. But Im not tech enough to know just how to trick the dryer into running the cycle without its juice drawing, meter running, wallet draining on board heater. I made a long curling copper coil thingy that would fit inside an 8" pipe. It would probably need some fins on it to extract more heat from it though. Anyone know how many btu's or air temp it would need? Does any company make something like this already? My dryer has plenty of empty space inside for "alterations".
    Lets hear some ideas fellas.

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  2. Nofossil

    Nofossil Moderator Emeritus

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    Interesting idea. Need to have an idea of the air temperature that dryers use / need.

    My sense is that you'd have to use something like an automotive heater core or radiator to get enough surface area.

    They use a simple snap-action sensor for overtemp protection - not sure if there's anything to detect undertemp. Maybe they figure that you'd be able to tell if the heating element wasn't working....
  3. mtfallsmikey

    mtfallsmikey New Member

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    easy to find a dryer's operating temp...use an IR thermometer, stop the dryer while running, shoot a temp...might do that this evening myself!...While the discussion of car heater cores/radiators is still fresh, has anyone used one to construct a space/wall heater box?
  4. deerhuntrer

    deerhuntrer New Member

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    IM suprised that manufacturers have not come up with this yet. My wife, who an engineer, also wanted to do something like this but has ZERO time to plan this out and design it given her current job. Dryers suck electricty and we use ours alot. She wanted to make a heat exchanger from our OWB. Its an interesting idea and I think it could work but Im zero help as engineering baffles my wee little brain. Id rather make beer.
  5. hkobus

    hkobus Member

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    Hve been thinking about the same thing Barnartist, I was looking at using a small utility heater for in farm tractors. TCS has them in different sizes, with and without fan build in. Just not sure what the Btu req. would be. Build this in an air intake and run "airfluff"
  6. barnartist

    barnartist Minister of Fire

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    Im thinking it will take a bunch more wood to run one if its completed. Im thinking maybe for summer use along with my DHW, that way maybe I could still charge a storage tank every few days... It would be easier to cloths line them I know, but wife doesn't like air dried jeans much. She doesn't like the line much either.
    What about a long narrow exchange, much like a side arm does, except thinner material? If I need a big heater core, then Im not sure how to get air to pass through all of the core evenly, outside of building a furnace style ductwork.
  7. barnartist

    barnartist Minister of Fire

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    Good idea Hog, that then makes me think about a kickspace heater. Maybe a kickspace on roids would get it done.
  8. sled_mack

    sled_mack New Member

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    I've thought about this, too. But in a different way.

    My drier seems to suck air in from the bottom. My thought was to sit the drier on a pedistal, which would really be a plenum. Seal it to the bottom of the drier. Now, laying it horizontal, you could put something like a full car radiator in there.

    Even if it did not get hot enough to completely dry, it should reduce the electric heat required. If it wants to see 150 deg air, and you take room air at 70 deg, bring it up to 130 deg, now the drier only has to raise it the remaining 20 deg. Assuming the motor to spin the drier and run the fan take much less electricity than the heater, you could probably disable the heating elements and just let the drier run longer. How much longer would depend on how hot the drier normally makes the air compared to how hot your heat exchanger could make the air.
  9. steam man

    steam man Minister of Fire

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    Any hot air duct better be hooked directly to the dryer air intake, whatever that may be. I don't know many electrical/plastic components that like those temperatures. Kind of reminds me of Chernobyl. I had a refrigerator that caught on fire (electrical). Makes a hell of a mess. You should also consider how the UL rating of the dryer will be void. What would your insurance carrier think? I hate to be a party pooper but it would make a great youtube video. Years ago we converted to a propane dryer and cook top. Saved quite a bit on Maine's high electrical rates.

    Not saying it can't be done.........nothing time and money can't solve.
  10. Eric Johnson

    Eric Johnson Mod Emeritus

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    Seems to me if you use something like a toe-kick water-to-air hx that you'd never see temps in excess of 180 or 190. Is that enough heat to run a dryer? I don't see any fire danger with a setup like that. Our dryer is the only gas appliance we use in the winter, since the boiler is shut down. I'd like to find a way to take our gas consumption down to zero.
  11. barnartist

    barnartist Minister of Fire

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    surely 120-150 air would get it done. I get 90-100 out of my air ducts from my furnace.
    Be nice to make a friendly on off switch for the dryer's on board heater for when your boiler is down. All this sounds fairly simple. How much for a kick space heater ballpark?
  12. steam man

    steam man Minister of Fire

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    I'm am thinking that if you expose the whole dryer or even components to heat it wasn't meant for it could degrade them, especially electrical and plastic stuff. Hard to say what would happen. I suppose you could duct a heated air vent directly to the drum with some measure of control and safety shutdown like a motorized vent damper. Conversion of a gas dryer would seem to be easier.
  13. Sting

    Sting Feeling the Heat

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    Last season after installing my biomass boiler and making my DHW successfully I looked for the next goal - laundry- I posed this question to my buddy who is a life cycle tech for a large washer/dryer manufacturer. They produce industrial laundry dryers that use steam, gas and resistance heat exchangers. After consulting several design engineers that think about laundry appliance operation all day - he responded that I would be better served to hang the laundry in the basement circulating house air with a box fan. 180 degree hot water will not produce enough hot DRY air in an enclosed appliance regardless of the HX size - and the extended appliance cycle time will similar or only slightly better to setting the dryer on air only for the load of damp laundry.
  14. barnartist

    barnartist Minister of Fire

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    If that air is so damp, then would we not have moisture problems in our house? Not sure I buy it, but could be wrong.
  15. Nofossil

    Nofossil Moderator Emeritus

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    We need data. Without knowing the air temp that driers use, we can go in circles all day.

    Dry is not an issue. Makes no difference if you heat the air with an electric element or a hydronic HX - it's the same air. As long as you can get it hot enough, it's all good.

    The amount of energy required is in a reasonable range - 10,000 to 15,000 BTU/hr.

    Preheating the air might not be the answer. I suspect that driers merely add a fixed amount of heat to the air they draw from the room. If you preheat, you might just be increasing the air temp that goes into the drum - not a good idea. An extra 100 degrees could be bad.

    If the temps work out, my inclination would be to build an enclosure around a radiator or heater core and duct that to the drier's intake. I'd replace the heating coil with a 220vac relay, and run the relay contacts to 24VAC and a zone valve, so that when the dryer wants heat it will open the zone valve.

    The futziest bit would be the intake ducting.
  16. Sting

    Sting Feeling the Heat

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    let me contact my dryer engineer buddy - should have an answer later today
  17. Sting

    Sting Feeling the Heat

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    This was faster than I expected - he must have been online!

    ...............................

    At first it sounds like a waste of time! Unless you have nothing but time on your hands to run a hot water heat loop and radiation!

    Our gas dryer fires @ 22,000 BTU/Hr. I figured out the Current pricing on my gas fireplace if left on over night would cost me about $0.13 cents a night. and that's firing at about 25K Btu. Our dryer typically cycles off @ 260F. both Gas and Electric Again this temperature would be the Maximum, or worse case FIRE!

    Electric Heat is more energy efficient because its resistive heat. Gas is only about 80% efficient.

    We build Steam heat units however in testing they take longer to dry. 60 psi steam is super heated to about 325F. again you are transferring the heat thru a coil and heating the air as in your car heater core, not very efficient! Again this is STEAM and Not Hot water.

    I still like to hang things in the basement like sweatshirts and nice stuff, and usually the same day with just a oscillating fan blowing on the cool 65F basement air my stuff is dried quiet nicely.

    I would base my dryer decision on the price of LP, Natural and Electric. Leave us to build your quality appliances!

    Name and address withheld.
  18. barnartist

    barnartist Minister of Fire

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    Im certain steam would pet out more moisture than unboiled hot water. My dryer costs way more than 0.13.
    But thanks for the BTU rating.
  19. steam man

    steam man Minister of Fire

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    I know anybody heating in Maine with resistive heating has outrageous electric bills. The following is pretty much what I learned in college decades ago:

    From the Dept of Energy:

    Electric Resistance Heating
    Electric resistance heating converts nearly 100% of the energy in the electricity to heat. However, most electricity is produced from oil, gas, or coal generators that convert only about 30% of the fuel's energy into electricity. Because of electricity generation and transmission losses, electric heat is often more expensive than heat produced in the home or business using combustion appliances, such as natural gas, propane, and oil furnaces.

    If electricity is the only choice, heat pumps are preferable in most climates, as they easily cut electricity use by 50% when compared with electric resistance heating. The exception is in dry climates with either hot or mixed (hot and cold) temperatures (these climates are found in the non-coastal part of California; the southern tip of Nevada; the southwest corner of Utah; southern and western Arizona; southern and eastern New Mexico; the southeast corner of Colorado; and western Texas). For these dry climates, there are so few heating days that the high cost of heating is not economically significant.


    Looks like the clothesline is the cheapest way to go. If I could only get the wife to use it.
  20. Sting

    Sting Feeling the Heat

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    An exchanger powered by steam - hot water - Resistance - gas is simply an exchanger - there is no moisture to "give off"

    but there is various potential of BTU

    Is that not a correct analogy? Just trying to remain positive here!
  21. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    The hotter the air, the more rapidly it will evaporate water.

    If you are using conventional hot water, you are limited in terms of how hot you can get the air (since it will be cooler than the hot water), whereas the superheated steam was being run at over 300 degrees.

    Cooler (relatively speaking) air will require more airflow to achieve the same amount of drying.

    Whether the increased electrical usage for running a faster fan for a longer time will compare to the electrical usage of a resistance element is something that would need to be analyzed, probably experimentally, since there are a lot of "quality of drying" issues which would be hard to model computationally.

    Someone needs to get a decent dryer (one with an efficient drum motor, since some may have very inefficient motors turning the drum, accounting for a lot of the energy usage), and measure the air flow. Then install a wot water coil in place of the electric element, and attach a variable-speed fan and measure static pressure with the hot water coil in place and set it for airflow to produce similar btu's to the original heater.

    Then experiment with similarly-wet loads of clothing (I'd suggest using a certain set of towels, since they are very uniform) and use a killowatt-hour meter to find actual energy usage for a few different combinations of fan speed and drying time, to plot a rough curve and see if the most-efficient combination can be found.

    Joe
  22. Turner-n-Burner

    Turner-n-Burner New Member

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    I wanna know where in the world I should live so I can run a 25K bTU fireplace all night for $0.13. I mean, then my 100K BTU furnace would only cost me $.60 a night. Factoring in days too, I could heat my whole house for about $30 a month? yeah, right.

    methinks your buddy was a little liberal with his decimal places - or unit conversions, or afterwork cocktails...

    I think the question needs to be - how many cycles a week does your dryer run? And what is the cost of that cycle. I think you'll be surprised at how low that number is.

    Your time and energy could be better spent removing the water mechanically. i.e. run the spin cycle on your washer a second time, or upgrade the motor and pulleys so it'll spin faster !
  23. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    Yeah, even if it only runs half the time, and we call the night 8 hours, that's still #0.13 per therm, which would be extremely inexpensive gas!

    Joe
  24. wdc1160

    wdc1160 New Member

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    I love the idea B.A.

    I did a little testing, because I knew that I had to have the biggest piece of garbage 2nd hand dryer of us all.

    DISCLAIMER I am not responsible for a decline in WAF if you take this as optimum performance numbers.

    My dryer lived in a barn for about 3mnts, then resided in a bachelor house with three guys. It does dry well by bachelor standards. But, it probably ranks at about a 4 on a 1 -10 scale of performance. Which is fine for bachelors.


    After 20 minutes with a probe in the lint trap. the probe reached 135 F. The room that the dryer was in was 53F. Again this will dry your clothes. It just does it in typical bachelor style. The dryer is electric.

    Black and Decker "Best Practices and Regulations" copyright 01 says that:

    for safe wiring to clothes dryer you can expect demand at 240V 16.5 to 34 amps = a range of 4000 to 8200 watts.
    Mine falls at 240V @ 20 amps. Even though my dryer works to my standards. You can assume this old thing works far less efficiently now then most dryers you have ever seen. So.... In its day this dryer put out

    a very doable 17K btu.

    PS. My dryer costs about 50 cents an hour to run
  25. Sting

    Sting Feeling the Heat

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    If I had edited out the one line about the fireplace ....

    What else could you all find fault with???

    Lets reserve the cloths line for the laundry - not for the hangman!

    Eric - You scolded me for making non positive remarks! Do you school your favorites in a similar manor?
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