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Thread: Venting dc outside

  1. #31
    The DC stops running eventually, that motion is turned into heat by the friction of the bearings as it slows down.

    If you believe the shop is a closed system, that electricity all has to get turned into heat eventually.

  2. #32
    The door between the shop and where the DC is opens inward to the shop. It will definitely open the door (if not latched) when I kick on the the DC.
    I guess I'm lucky it doesn't swing the other way or I'd have to block it open when working in there.

  3. #33
    Quote Originally Posted by Michael W. Clark View Post
    Then what energy is used to spin the fan shaft?
    Here's my stab at anwering that question. The energy is used to spin the shaft, but all the resistance in the DC system is caused by the friction of the air rushing through the ducts and the turbulance caused by the fan....friction creates heat, not just in the air that exits the DC but in the ductwork all along the way. That's my theory anyhow :-)
    Mark R

  4. #34
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    Michael,

    I don't know that I could call that a test, but it sure was an eye opener, for sure. My shop is pretty well sealed up, and I doubt I have much air leakage.

    Rick P

  5. #35
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    Think on this. If all the electrical energy is turned to heat, how did the chips and dust get from the pickup point to the D.C. drum? I was always told anytime you moved anything, it took energy.

  6. #36
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    Quote Originally Posted by Dick Brown View Post
    Think on this. If all the electrical energy is turned to heat, how did the chips and dust get from the pickup point to the D.C. drum? I was always told anytime you moved anything, it took energy.
    That's my point exactly. If you are flowing 1,000 CFM, you are moving 75 lbs/minute of air (assuming standard density). This takes eletrical energy that is converted into kinetic energy in the air. The heat given off is an in-efficiency, energy that was not used to move the air, but was consumed electrically, should be a small percentage of the amp draw. The fan will heat the air slightly due to friction, but maybe only a few degrees.

  7. #37
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    Quote Originally Posted by Rick Potter View Post
    Michael,

    I don't know that I could call that a test, but it sure was an eye opener, for sure. My shop is pretty well sealed up, and I doubt I have much air leakage.

    Rick P
    It just depends on how well the shop is sealed. The pressures I quoted are from ACGIH and I have found them to be pretty accurate based on actual measurements. In fact, I know of several emission standards for fume enclosures that are written around the ACGIH infiltration tables. Obviously, if your shop is better sealed, it will have a greater impact. I have a friend in OK, that uses a 1.5 hp HF blower and exhaust his chips outside (no cyclone or filter). He doesn't have any problems in the winter when the shop is closed up. It may be looser construction.

  8. #38
    I vented my 2 1/2 HP Super Gorilla outside and it was one of the best things I did. Substantial increase in suction, like a brand new filter all the time. Substantially reduced noise level. I can have the DC running and be right next to it and have a conversation with someone without the need to raise my voice or listen harder.

    My shop has enough leaks where I need not worry about makeup air. I have 26' ceiling and about 36000 cu ft of air.

    And yes, it does add heat in the winter. Very noticeable at times. I've actually let the DC run longer in the winter just to help out with conserving my propane supply.
    LRG WoodCrafting (Google it )

  9. #39
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    Leo, do you think heat is actually added or are you recirculating the air 26' high back down to where you can feel it. Seems like their must be a 5 - 10 degree difference at that height. Dave

  10. #40
    It's adding it. The air coming out of the filter is moving very slow, it's nothing like a fan. The heat generated by moving the air through the piping at 4000 fpm causes some heat gain from resistance, plus the additional heat transferred from the motor to the impeller to the airstream. It's not like I am gong to heat my shop with it or anything, but it does add up. I'm doubting there is much interactivity between the lower air circulating and the upper air as the warmer upper air wants to stay up there.
    LRG WoodCrafting (Google it )

  11. #41
    Quote Originally Posted by Michael W. Clark View Post
    That's my point exactly. If you are flowing 1,000 CFM, you are moving 75 lbs/minute of air (assuming standard density). This takes eletrical energy that is converted into kinetic energy in the air. The heat given off is an in-efficiency, energy that was not used to move the air, but was consumed electrically, should be a small percentage of the amp draw. The fan will heat the air slightly due to friction, but maybe only a few degrees.
    I'm not an engineer but I'm intrigued by this. It takes relatively little energy to move 1000 CFM of air. Maybe my 120 volt, .5 amp floor fan that will do that? The reason our dust collectors need 2-5 hp is because we create tremendous resistance pulling that air into tiny ducts that twist and turn. Moving something with more friction, truck transportation versus train for example, takes more energy and that energy is released in the form of heat. So no, I don't know that all the energy turns to heat, but I bet it's a significant percentage.
    Mark R

  12. #42
    It all has to turn to heat eventually...that motion is eventually impeded by friction somewhere.

  13. #43
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    Quote Originally Posted by Ron Natalie View Post
    It all has to turn to heat eventually...that motion is eventually impeded by friction somewhere.
    If 'it all turns to heat eventually', that implies the motor does no work. If a motor has an efficiency rating of 80%, that means it should convert 80% of the input power into work performed; 20% goes up in heat created by copper resistance, rotational resistances, magnetic fields, etc.
    Bill Arnold
    Citizen of Texas residing in South Georgia.
    Food for Thought: The Ark was built by amateurs, the Titanic by professionals.

  14. #44
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    Air Power equation - BHP = CFM x SP / (Fan Efficiency) / 6356. Energy = power x time.

    The air may be somewhat heated depending on where you are pulling it from. My tablesaw cabinet is always a litte warmer inside than the surroundings. Same thing for the router table cabinet.

    The kinetic energy in the 1000 CFM is imparted to the surrounding air when it exhausts and causes the still air to move around. The air is circulating all around the room, this takes energy, and this energy is provided by the DC if nothing else is causing it to move.

    I'm going out on a limb here, but if your motor shaft is hot enough that it is heating the fan impeller through the coupling and imparting a noticeable temperature difference on the exhaust air, then something is not right. You may have a motor bearing going out or your motor cooling fan is not working. My blower is cool to the touch when running, the motor may get a little warm, but still easy to hold your hand on it.

  15. #45
    Quote Originally Posted by Bill Arnold View Post
    If 'it all turns to heat eventually', that implies the motor does no work. If a motor has an efficiency rating of 80%, that means it should convert 80% of the input power into work performed; 20% goes up in heat created by copper resistance, rotational resistances, magnetic fields, etc.
    No, it doesn't imply that. The motor does the work of moving the air, that energy is then converted to heat by the friction the air encounters.
    Mark R

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