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Thread: Heat energy loss from exhaust system

  1. #1
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    Heat energy loss from exhaust system

    Hello forum!!
    I'm from Canada and am getting ready to get my laser hooked up and running, a Zing 16. I looked at in-line fans, and dust collectors as options. Has anyone ever figured out what the energy loss would be when I kick on a 400 CFM exhaust fan? Our winters here are bone chilling cold (-30c and colder some days) and this has me greatly concerned. Have any of you fellow Canucks and/or close neighbours to the south seen a huge jump in your electricity bill? Has any one found a working online calculator that will figure out what I could expect for costs? My room is approx. 10' x 10' so I could expect the room temp. air to all be exhausted out in 2 1/2 minutes. If the heat loss is that great it may be cheaper in the long run to go with an internal filtration system...Any thoughts, or suggestions?? Thanks in advance...

  2. #2
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    Ron,

    Welcome to the Creek! Glad to have a Zing user on board.....everyone always asks how good they are, but almost no one on here has one. Please post a review of how you like it once you've got it going.

    I'm in NY and it gets a little chilly around here somedays.....and I never noticed any significant heat loss or noticeable jump in my electric costs since I've had my laser.
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  3. #3
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    With outside temperatures that low it would certainly be worth looking into a heat exchanger to warm up the replacement air a bit.

    My workshop - a wooden structure about 16 x 16 ft and around 7.5 feet average height - goes from not-very-warm to really cold* in around 15 minutes when I turn my blower on. At the moment the blower hose goes out through an open window which does not help, but I'm not expecting to see much improvement when I put the proper ducting in.

    * +5c, but this is England and we're softies.

  4. #4
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    If you plan on using the laser for more than a handful of minutes, you may as well not even both turning the heat on in the first place. The blower will exchange the entire room's air within several minutes, so you'll be heating air that is immediately going out of the window. Either work in an area (or during a time) when inside and outside temps are comparable and acceptable, or go for an indoor unit.
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  5. #5
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    I recently made an insulated box to put in my window to help solve the problem of losing all the heat to the outside. Before I had the hose going through a piece of acrylic that fit in the window that I had to put in the window everyday, but it let a lot of outside air in and was a pain to put in. I also plugged the blower into a power strip so I could turn it on only when needed. The box is made of 2"x4" and plywood, used a drier exhaust cover for the outside and the metal pipe to go through the center and then a dust collection shut off on the inside. Our winters are not as bad as yours but I thought I would share the idea.
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  6. #6
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    Good timing, we're at 32 already and supposed to get down to the low 20s tonight. In summer I leave the window cracked to get fresh air in but this time of year I merely keep the shop door open. There's plenty of air moving in from the rest of the house so it stays warm. The exhaust is blowing out the warm air so the furnace will have to work a little more. Time to raise the prices a little since you have higher overhead.



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  7. #7
    I have a photo of the Zing but I can't see where the intake air enters.

    A lot of lasers have an air intake at the front. If you can supply cool (unheated) air to the intake area you will not be drawing as much warm air. It would require a duct from the outside to the fresh air intake area of the laser. This will mean cold air is drawn into the chamber, over the workpiece, and up the exhaust.

    However some lasers use the intake air to cool the laser tube. I don't know how the Zing is configured. You probably don't want to flow minus 40C air over the laser tube or any electronics. So if you use this method you need to be reasonable so you don't cause any damage to internal components by over-cooling. But you could throttle the cool air with a gate to get the mix you need, and it would at least reduce your heating demand.

  8. You can calculate the energy loss like this:

    400*0.0283/60=0,1887 m3/s
    0,1887 * 1,2 = 0,2264 kg/s (1,2 is the density of air)

    dT * time * 1 * 0,2264 = kWh (1 is Cp (specific heat constant (?)))

    Where dT = room temperature - outside temperature (in celcius or kelvin)
    and time = number of hours you run the blower

  9. #9
    I thought about this myself, perhaps something like a kitchen range hood over or near the laser, with a duct leading to the exterior. That way the cooling air to the laser will be mixed with warm room air and not super cold. Plus the duct is out of the way and not interfering with my walking space. Obviously, the duct would need an insulated cover or valve that closed over the inlet on the exterior side, to prevent cold air intake, or warm air loss, when the blower was not in operation. Also I wonder if such an "unclosed" system won't just draw cold air in and blow warm air out, and make the situation worse. I think it would depend on air flow and that might be a bit unpredictable without testing it. Might be worth a try

    Dave




    Quote Originally Posted by Richard Rumancik View Post
    I have a photo of the Zing but I can't see where the intake air enters.

    A lot of lasers have an air intake at the front. If you can supply cool (unheated) air to the intake area you will not be drawing as much warm air. It would require a duct from the outside to the fresh air intake area of the laser. This will mean cold air is drawn into the chamber, over the workpiece, and up the exhaust.

    However some lasers use the intake air to cool the laser tube. I don't know how the Zing is configured. You probably don't want to flow minus 40C air over the laser tube or any electronics. So if you use this method you need to be reasonable so you don't cause any damage to internal components by over-cooling. But you could throttle the cool air with a gate to get the mix you need, and it would at least reduce your heating demand.
    Last edited by David Fairfield; 12-02-2009 at 11:15 AM.
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  10. #10
    Quote Originally Posted by David Fairfield View Post
    . . . Obviously, the duct would need an insulated cover or valve that closed over the inlet on the exterior side, to prevent cold air intake, when the blower was not in operation. Also I wonder if such a system won't just draw cold air in and blow warm air out, and make the situation worse. I think it would depend on air flow and that might be a bit unpredictable without testing it. . . .
    Dave, I agree with insulating the intake and also with having a gate in-line that can be closed completely when not in use.

    You need to position the cool intake so that it is guaranteed to be drawn into the laser in preference to the room air. I was actually thinking of cutting an opening in my box to provide a positive connection but haven't done so yet. But there are probably ways to arrange a duct (at least for an experiment) that don't require sheet metal changes as not everyone wants to modify their enclosure. I am not sure that an overhead duct would be optimum, as most intakes seem to be on the front, bottom, or sides. I suggest getting as close to the current intake. (When you said kitchen vent, I assume you meant the sheet metal assembly without the fan installed, as you just want passive makeup air, not forced.)

    On my Mercury the vents are on the front . . . when I turn on my exhaust blower, it draws air from the room and through any cracks in the room/door it can find. It gets cold standing in front of the laser as you get a draft of cool air from behind.

    The advantages of a defined cold-air intake is that it will draw in much less of the heated room air. If the cold-air makeup duct can satisfy the blower, minimal room air will be needed. As well, having a defined cold air intake reduces the risk of creating negative pressure (vacuum) in the room. (If heating with fuel, negative pressure can be hazardous as your heating appliance may not exhaust properly.)

    As I said before, the laser system must be evaluated to ensure that the use of cold intake air doesn't cause any machine issues. e.g. you want to avoid condensation problems, thermal problems with electronics etc. It really depends on the configuration of the air system.

    The other thing I would recommend to Ron is a gate in the exhaust duct if not already installed. Then the user can adjust the exhaust air as needed for the job. Running the exhaust at 100% can be wasteful. Some jobs don't create much smoke and fumes, so exhaust air can be throttled back. This will reduce heating costs.

  11. #11
    Quote Originally Posted by Ron Chapellaz View Post
    Hello forum!!
    I'm from Canada and am getting ready to get my laser hooked up and running, a Zing 16. I looked at in-line fans, and dust collectors as options. Has anyone ever figured out what the energy loss would be when I kick on a 400 CFM exhaust fan? Our winters here are bone chilling cold (-30c and colder some days) and this has me greatly concerned. Have any of you fellow Canucks and/or close neighbours to the south seen a huge jump in your electricity bill? Has any one found a working online calculator that will figure out what I could expect for costs? My room is approx. 10' x 10' so I could expect the room temp. air to all be exhausted out in 2 1/2 minutes. If the heat loss is that great it may be cheaper in the long run to go with an internal filtration system...Any thoughts, or suggestions?? Thanks in advance...
    Hi Ron,

    I live in Northern NY, on the Canadian border - we get the same frigid weather. I have not noticed any change in my heat bill, but I only run the fan when my laser is running, not all day. I also installed blast gates to close off the hole so there is no heated air loss when it's off. My laser is exhausted through the wall, with the blower outdoors for quieter running. I think any heat loss might be made up by the heat created by my air compressor.

    Hope this helps, dee
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  12. #12
    Quote Originally Posted by Ron Chapellaz View Post
    . . . If the heat loss is that great it may be cheaper in the long run to go with an internal filtration system...
    Ron, I did not notice this before - but I would definitely look at Michael's suggestion of a heat recovery system as opposed to a filter, if you are concerned about heating costs. Maybe I am too conservative but I really don't want to breathe the air that comes off burning plastics. I realize it is filtered to remove contaminants but how would you know, without having sophisticated measuring equipment, that it is taking out the chemicals to a low enough level? What level is safe? Which chemicals? How do you know it is working properly, and when to change the filters?

    In a small room I would tend to be cautious about recirculating the exhaust air through a filter. BTW the filters are not inexpensive.

    Did you try Niklas' formula?
    (For YOUR blower of 400 cfm)

    if dT = 50degrees C (20C room desired minus -30C outside = 50 degree rise needed)
    then 50C x .2264 x 1 hour = 11kW-hours
    Energy cost using electricity say $.08 per kWh (change it for your area)
    Energy Cost per hour operation = .08 x 11= $0.88

    That would be with a 100% exhaust setting, on a -30C day.

    For electric you would need about 50C x .2264 = 11 KW of electric heating to keep up to continuous 100% exhaust. But as I said elsewhere you probably do not need 100% exhaust for every job, and probably won't run the blower all day. So you might be in the area of $4-7 per day depending on what you are doing. At -5C the cost drops to half (half the temp rise).

    If gas heat you may need to convert via BTUs. Let me know if you need help. But the cost per hour will likely end up within +/- 20% of electric.

    This should give you at least a rough feel for the anticipated cost and also whether buying more equipment makes sense.
    Last edited by Richard Rumancik; 12-02-2009 at 10:24 PM. Reason: typo

  13. #13
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    Firstly I want to thank the quick responses to my question.

    I was told from Epilog that the intake vents on my zing are located on the sides. I can't confirm this as I have not hooked it up yet. (I'm biting at the bit to get it going! They also told me that some users have connected fresh air intakes to their machines to help offset precious room air from being vented out. I was told this was an ok practice as long as high humidity was not an issue. I'm not sure if I want to take the risk as these machines are worth a few bucks.

    I am likely going to buy a dust collector from Princess Auto here in Canada. The link to this model is http://www.princessauto.com/tools/corded-power-tools/stationary/8155905-dust-collector?keyword=dust+collector
    I think I will try venting it out and seeing for myself what the energy bills will be like for this winter. Has anyone tried this particular model of dust collector?

    I had planned on doing the calculation tonight, so thank you Richard for taking the time to do it. When it's broken down the cost is relatively small.

    I agree about the filtration system and not really knowing if it is working, especially in a small room.

    If by chance the energy consumption is high, then I guess I'll look at the filtration system as a last resort or make my room airtight, put on my winter jacket, crack the window open, and sip a cup of hot chocolate to keep warm. Everyone's invited for a cup!


    It's great to see the responses that came in!

  14. #14
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    Quote Originally Posted by Ron Chapellaz View Post
    I am likely going to buy a dust collector from Princess Auto here in Canada. The link to this model is http://www.princessauto.com/tools/corded-power-tools/stationary/8155905-dust-collector?keyword=dust+collector
    I think I will try venting it out and seeing for myself what the energy bills will be like for this winter. Has anyone tried this particular model of dust collector?
    The picture looks identical (except for color) to the one I got at Lowes in 2005, been working fine ever since.

    (And remove that cross-shaped grid over the intake...we had a whole thread on the subject awhile back.)

    What is this "winter" thing you people keep babbling about?
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  15. #15
    Quote Originally Posted by Ron Chapellaz View Post
    . . . I was told from Epilog that the intake vents on my zing are located on the sides. I can't confirm this as I have not hooked it up yet. . . . They also told me that some users have connected fresh air intakes to their machines to help offset precious room air from being vented out. I was told this was an ok practice as long as high humidity was not an issue. I'm not sure if I want to take the risk as these machines are worth a few bucks. . . .
    If Epilog says it's okay then I would not be too worried. Even 50% cold makeup air will help. Your -30C air will NOT have much moisture so don't worry about humidity in the winter. It will be DRY. Having the intakes on the side is an advantage as the makeup duct stays out of your way. Your heat losses would be reduced to a few dollars a day - in which case, you'd probably have a hard time investing a few thousand in a filter or heat recovery unit. You could probably find a way to hook an insulated duct to the side of the machine.

    Just wanted to emphasize that the calculation covers the cost of heat loss out the exhaust duct, not the total heating bill. You still have to heat the room during the hours when no one is there. But if you have reasonable insulation and all the ducts are closed for the night, it should not be that great.

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