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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. Nofossil

    Nofossil Moderator Emeritus

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    This temp is after the air has been cooled by the clothes. I'm absolutely certain that the air coming off the heating element is hotter than that, even in a bachelor quality unit. It's interesting that the commercial folks use 300 degree steam, but I also suspect that the air coming off of that steam HX is less than 300 - that would be pretty hot.

    I got no reasonable way to stick a probe in mine. It's bolted to the top of our washer, and the WAF involved in moving it would be well into the negative numbers.

    If 170 degree air is reasonably close to what you need, then it's probably possible to get that off of an automotive radiator. They give you quite a bit of surface area. If you need 250 degree air, then it's not practical in my view.

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  2. leaddog

    leaddog Minister of Fire

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    I know that when people are on the net that sometimes things are written that are taken different ways. You can't see the person and not everyone is articulate (me ) so things don't get written the way it is intended. But that being said I see nothing here that hasn't been positive and I have enjoyed ALL the views on this subject as this is the way ideas can make things happen. Not every one is going to agree and not every ones math is right (mine usually) so we all have to take the posts with a grain of salt and get what knowledge we can.
    leaddog
  3. wdc1160

    wdc1160 New Member

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    I will retest
  4. wdc1160

    wdc1160 New Member

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    Let me reitterate. In my test. I had no clothing in the dryer to cool the air. Straight from element to the drum to the lint trap. 135F.
    Isn't the conclusion we can use 180 degree water to dry the clothes?

    I don't want to rip apart the dryer if I don't have to.
  5. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    Sounds like it's possible, then. At least, to get "bachelor-level" dryness...

    Joe
  6. wdc1160

    wdc1160 New Member

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    heheheh. Did you guys really predict that the airtemp would be above 190?
  7. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    The question is how much below that temp it will work at. If the dryer can only work when the boiler is going full-blast to give peak-temperature water, it's not much of an interest to me. If it can run on 150-degree water, that will be much more useful.

    Joe
  8. wdc1160

    wdc1160 New Member

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    I see your point.
    I figure my 135 F air going into the lint trap probably does equal 150 degree water. Any thing above that should be gravy. Anything lower than 150 degree water = negative WAF.
    Judging by prior girlfriends, my dryer is probably the equilibrium on WAF. Any lower temp air and you will see negative WAF. Higher temps are a certain plus.

    I have used worse dryers than mine. Sunday my dryer dried a large wet conforter in 1 hr. I have seen dryers that would take 2 hrs for this large of an item. Keep in mind this was in a 50F house which directly effects the relative humidity and the delta.

    And, older dryers like mine are very large fire hazzards. I think a 180F water conversion kit would make my old piece of crap safer.

    I will test at the element
  9. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    There probably is a niche market for high-efficiency water heaters that run off hydronic heat, with big building projects going for LEED certification and such.

    Joe
  10. mikeyny

    mikeyny Feeling the Heat

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    I have built a hydronic dryer and it works, but not too well or worth the effort. A standard dryer operates on much higher temps than you can produce with a wood fired boiler. The clothes do dry, but, it takes forever. I suspect that the cost of turning the drum and circulating the water costs more than the conventional way, not to mention the cost of the wood and the effort to load and maintain it. But then again, if you live off the grid, it would be well worth the effort. A wood fired cloths dryer could be ok, but ... a clothes line ... PRICELESS.
    Mike
  11. wdc1160

    wdc1160 New Member

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    Hey mike, What is "much higher temps" Have you measured temp inside a dryer before?
  12. Willman

    Willman Minister of Fire

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    Great topic to hash over. From my dryer repair book "135* low temp to 165* high temp." Temperature is controlled by thermostats which are actuated by the timer. Snap type thermostats are usually marked as to which temp range they are. Heater cores or small rads from a car would work. Fab up an enclosure and utilize the 12 volt blower for air movement.The blower motor resistor could also be used for variable fan speed. For proof just check out the airflow and temp on your vehicle. I realize engine temps are greater, but are just a guideline.
    My thought on a clothes dryer would be to capture and channel heat right from cabinet of boiler, possibly ducting off the stack with an air x air hx. My other thought was to build a cabinet near boiler to stack some wood in to make use of the latent heat from boiler. Hook up a small blower to move the air. Could do two things. Drive down MC and have preheated wood. Build the boiler room big enough for clothes and wood drying.
    My electric dryer hasn't been used in years. We have 3 fold able wooden drying racks. Homes in the winter can use a little extra humidity. Clothes dry out overnight.No static snaps. Clothes lines are the best. I use mine on nice days in the winter. Guys if you want to increase the WAF throw the sheets in the laundry yourself and line dry them. Nothing like it. And I don't only mean the sheets. ;-)
  13. Gooserider

    Gooserider Mod Emeritus

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    Interesting discussion... I'm not sure there is a "right" answer, as there are a lot of variables. It might help to try and break down some of the issues...

    First off - task analysis:

    You have a washer full of X pounds of clothes, which are soaked with Y pounds of water that is left over from the spin cycle. The drying job is to evaporate those Y pounds of water. This is going to take so many BTU's of energy per lb, doesn't matter whether we are talking about cordwood, greasy coveralls, or the wife's unmentionables... (note however that the X:Y ratio may change depending on the type of clothes) It also doesn't matter whether those BTU's come from solar / wind drying (aka clothesline) a rack in the basement, or a clothes dryer. Call this the "key task" as you MUST accomplish it, or plan to sleep on the sofa due to low WAF. :red:

    However all methods consume additional power in the form of delivering the BTU's needed for the key task - this is things like blowers, fans, dryer tumblers, the energy to drag that basket of clothes out to the line, etc. Call this the secondary power consumption. In the "perfect world" one would like to just use the amount of power needed for the key task, and keep the amount of secondary power to a minimum, but other issues such as time, type of secondary energy needed, WAF of the finished product, etc. is going to cause us to use secondary power to some degree. As a working assumption, I think it's safe to assume that saving time, or increasing convenience will increase secondary power consumption. Increasing WAF is likely to increase it as well, but this depends on the W (i.e. a preference for the feel of line dried stuff would lower it...)

    The power for both the key task and secondary power can come in many different forms, some more suitable for different drying techniques than others. In sticking with the question of a tumble dry clothes dryer, the secondary power would consist of the blower, the timer, and the drum turning motor, all of which are almost certainly going to be powered by electricity. The power for the key task can come in any number of forms, most commonly gas (LP or Natural) or electricity.

    The question is whether we can replace the key task power with hydronics, and if doing so is worth the time and effort. The secondary power is going to stay electric regardless, unless you want to hook up a belt to the wifes exercise bike (Caution, this approach is likely to have a LOW WAF!! :lol: )

    There are two or three parameters that would go into balancing out the choice of what we use for key power - availability, convenience, and cost of the different forms among other things. There is also a desire to minimize the length of time it takes to do a drying cycle, as longer cycles are hard on the clothes, and the secondary power consumption is a function of time. There is also the limitation that one can't apply excessive heat due to the risk of damaging the materials.

    Now for some numbers...

    1. I've read somewheres that the over temp cutout switch on most dryers is supposed to open around 180*F, which is consistent with Willman's comment that his manuals say desired operating temperature is 135-165*F

    2. I know that the amount of electric power drawn by a gas burner is negligible, thus measuring the electrical consumption on a gas dryer should give a very close number for the secondary power requirement. We have an older Whirlpool natural gas dryer, probably about 14 years old, fairly basic model, I would say about as typical as one is likely to find. I just put a "Kill-a-watt" meter on it, and find I am drawing about 325 watts starting out with a large load of mixed clothes. As the clothes dry, the power draw goes down (makes sense as the load gets lighter it should take less juice to tumble it) when the clothes were nearly dry I was showing about 275 watts. This is a significant difference, but not a huge one, I think it is safe to assume a constant 300 watt secondary power consumption to keep the math simpler.

    About 3-5 watts is the timer switch motor. There was no noticeable change in the power draw between the Low, Medium and High heat settings. (which tends to confirm the negligible power draw for the burner assumption)

    I forget for sure whether this dryer has a seperate motor for the fan, or if it just has one motor that both powers the fan and turns the drum, but I'm pretty sure it's the latter. Either way, I think it's reasonable to assume that secondary power consumption

    3. The amount of moisture that can be removed by a given volume of air going through the dryer is going to be a function of the relative humidity of the air, which in turn is a function of the input air humidity, and how much / if the air is heated. It doesn't really matter HOW the air is heated. (Exception - Gas dryers will add some extra moisture to the air as water vapor is one of their combustion byproducts, but I'm not sure how big a factor this is, probably not much)

    As a corrollary of this, the heaviest, drippiest item will still dry on the "Air fluff only / delicate" setting if you just let it crank long enough. Obviously this will reduce the amount of power consumed by the key task, but increase the secondary power consumption. One could draw a graph showing the relationship between power consumption on the secondary side, and power on the key task side as a function of dryer temperature. I don't know the exact curve shapes, but it is pretty obvious that as temperature goes up the secondary consumption would go down due to shorter drying times, and the key task consumption would go up due to energy spent heating the air. Assuming there isn't a time issue, the logical "best" drying solution would be to pick where the sum of the two power figures (and costs) intersect.

    4. According to some of the other threads here about doing water / air heat exchangers in HVAC systems, it was sounding like you CAN get 120-150* air from such an exchanger, which would work in terms of Willman's desired operating temp statement. However secondary consumption might go up if you are at the low end of that scale.

    Thus the key question IMHO is whether there are any savings in heat production costs (remember you have to power the boiler to make the BTU's, circulators, any extra blowers, etc.) and if that is enough to offset any increase in secondary power consumption.

    Gooserider
  14. mikeyny

    mikeyny Feeling the Heat

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    my dryer used a hot water heat exchanger made from an ac coil. It did actually work ok, but not while I was heating the house and hot water. if I ran it specifically from the wood boiler only and made sure it was loaded with good wood it could keep up with the demand for hot air. Take into consideration the cost of wood, time, circ pump electricity and other things it just doesn't seem practicle. I am sure the whole thing could be designed and built more efficient to work better. Trying to get 150 hot air continuously into the dryer takes a whole lot of energy and wood. If the boiler stack was close enough that might be a better attemp to get hot air after the boiler is doing its primary job of heating the house. But you would still have to keep a good hot fire to get that stack temp up continuosly.

    Mike
  15. leaddog

    leaddog Minister of Fire

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    goose------------- You are taking all the insentive out of this discussion and making this a practical discussion. All these inventive minds don't really want to save money, they want to have another reason to go out and cut more wood and use their boilers. Most of us don't have enough projects to keep us busy so we have to constantly think up more. But it don't make any difference I'm putting the dryer right there in the middle of my list. I just hope that when I get old I have got to that one.
    leaddog
  16. barnartist

    barnartist Minister of Fire

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    cute Dog.
  17. Telco

    Telco New Member

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    This is something I've also been interested in. Sorry if this is a Master of the Obvious post, but I wanted to get my thoughts out there. I've had the back of my electric dryer open, and found that the heating element is made up of 3-4 resistive elements inside of a thin metal casing, about 1.5 inch by 5 inch. Not sure on the exact measurements as I was more interested in cleaning it out than building a water powered dryer at the time. This metal case has a 4 inch round hole at the top and at the bottom of the dryer.

    An automotive heater core is typically 6 inches by 8 inches by 1 inch, and can throw off a lot of heat. Running 195 degree water through it is enough to raise the temperature of my truck's cabin to where it's summertime hot in just a few minutes, normally I heat the truck till it's comfortable then turn the dial over to mix in quite a bit of cool air. In the summertime I have to kill water to the core because it's strong enough to overcome the air conditioner. I don't have an automatic diverter on it. The blower motor is close to the same size as the blower motor on the dryer, physically, so I'd have to assume that both push the same amount of air. The cabin of the truck, however, is about 250 cubic feet, where the inside of a dryer is normally about 15 cubic feet, so that single heater core is heating a space about 16.6 times larger than we are interested in heating.

    Based on this, seems to me that you could stack 4-6 heater cores together, one on top of the other, with the inlets and outlets connected so that hot water goes into the top one (output to the clothes) and comes out of the bottom one (sucks the last bit of heat out). This could then be plumbed into the hot water supply. The heater cores would need to be mounted inside of a metal cabinet that forces all air to pass through the cores, with a good filter in front of them. This should produce enough airflow with more than enough exchange surface to heat the air by 150 degrees blowing into the dryer. This box could be attached to the outside of the dryer to the metal panel, with flexlines connecting the water cores to the hot water inlet. You would also need a standalone pump (and note the power needed to run this pump) to keep hot water moving through the system, kind of a closed loop type of thing.

    If someone wanted to test this they could hook it up so that it took hot water from the washing machine water line, then dumped the outlet into the drain. It would waste a lot of hot water, but if the clothes dried then it would be worth plumbing in water inlet/outlet lines to the dryer. This is not something that I will be in a position to test for a couple of years, but if anyone else wanted to take a whack at it...
  18. Sting

    Sting Feeling the Heat

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    Exactly!!! If you could dry laundry with low air temps - appliance manufactures would only heat air to that threshold.
    Appliance cycle times at low air temps will not be cost or time effective - but it will keep the kids busy for a while. Time better spent hanging the sheets out in the sun!
  19. Nofossil

    Nofossil Moderator Emeritus

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    So it appears that the temps work out OK. Now for the economics for those of us who care.

    Dryer heating coil is around 5000 watts. At $0.10 per kwh, 1 hour per load and 20 loads per month, over a six month heating season you'd spend about $60 on dryer electricity. Adjust for your situation.

    I can scrounge a radiator and sheetmetal. I think the dryer's own blower would work. I have some PEX lying around. I'd have to buy some fittings, a zone valve, a 220V relay to drive the zone valve, and a high current 12v relay to allow the electric element to be enabled when I don't have enough hot water. My cost would be about $100 plus the labor to do the install. Couple year payback - not horribly bad.

    Biggest issue is mounting the radiator and ductwork so as to not create negative WAF. Don't know how I'd do that yet.

    Anyone have any idea if there would be potential corrosion issues with an aluminum radiator in a hydronic system?

    I've attached a schematic for a possible control system.

    R1 is a SPST 220vac relay that is activated whenever the drier wants heat - it's connected in parallel with the drier's heat coil.

    R2 is a DPST 24vac relay that's energized whenever the hydronic system is hot enough as determined by the aquastat.

    R2 disables the drier's heating coil.

    If R1 and R2 are both energized, the zone valve opens, allowing hot water to flow through the radiator which is in a duct in series with the drier's heating coil.

    If you're concerned about leaving R2 energized all the time, you could make R1 a DPST and put the second set of contacts in series with teh R2 coil. Then R@ would only be energized if the drier were calling for heat AND the water was hot enough. The downside is that the R2 contacts would arc every time, since current would flow through them for a fraction of a second every time the drier was turned on.

    I think this might actually work.....

    Attached Files:

  20. Telco

    Telco New Member

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    Two things, what is WAF? And, grounding the radiator will reduce corrosion issues, may even eliminate them. When I was a youngster my dad was stationed in the Panama Canal. Had a problem with the heater core on the family car pinholing every few months due to the high concentration of sea air. One of the locals told him to ground the heater core, and this stopped the problem. The same heater core was in the car years later when we sold it. Any time I do a heater core now, I attach a ground wire to it, and ground the heater core to the body of the car.

    Ducting will be a bit of a problem in that you will have to somehow turn the air inlet to the elements so that it faces the back of the dryer instead of the front. The element rack looks like it is made of thin aluminum. Might have to just cut the bottom off of it, then use flexible duct that can go around the newly cut edge. At least, this is how it is on my dryer, you'd need to verify flow directions, ect, on your dryer.
  21. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    Wife Acceptance Factor or Wife Approval Factor.

    In other words, attaching a clunky contraption to the side of a dryer, or "upgrading" the dryer to "only" take three hours to dry a load of laundry may not be well-received by certain members of the household.

    Joe
  22. Telco

    Telco New Member

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    Heh heh... gotcha. Very important consideration, that.
  23. wdc1160

    wdc1160 New Member

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    Nofo, Isn't it copper with aluminum fins?
  24. Nofossil

    Nofossil Moderator Emeritus

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    Not for years, as far as I know. The ones I've seen recently are aluminum tubes and fins with composite plastic end caps. They work for a long time in cars, which have to be a worse environment.
  25. wdc1160

    wdc1160 New Member

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    Agreed, cars have to be a horrible environment. I don't know the implications of putting aluminum pipe in with black and galvan pipes. I know that pex al is a aluminum plastic composite matierial with properties of aluminum, which is the closest I have seen personally to aluminum piping.

    Maybe somebody can help us out here.
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