Cyclone venting - inside vs. outside

[Jim Mackell]

Been reading lots of information over at Bills site. One of the points that he seems to emphasize, that I don't see much discussion about, is venting the cyclone outside. From what I think I understand, instead of the final filters returning somewhat clean air to the shop, the "contaminated air" which has lost most of its dust load to the cyclone bin, is exhausted to the outside. Seems very simple and more efficient overall. Am I missing something here? I am aware there will be some heat loss due to the outsie exhaust. For the moment, let's ignore that, OK?

[John Lanciani]

I am aware there will be some heat loss due to the outsie exhaust. For the moment, let's ignore that, OK?

That's the 800 lb. gorilla. You live in Maine, do you want to heat the outdoors or maintain filters. I put a bypass in my system and exhaust outside when I'm running my 25" double drum sander, the rest of the time my heated (or cooled and dried) air is returned to the shop through a HEPA filter.

[James Baker SD]

One thing I do not hear mentioned often is what is the quality of your outside air? My outside air is terrible, due to dusty garden, neighbors who use those gas powered blowers, pollens from the plants, who knows, but I do know my Dylos detects about 3000 small particles when I put it in the driveway. Venting my air through a filter back into the shop with all doors closed (not hermetically sealed though), my Dylos will read around 150 after 30 minutes or so of running the cyclone. If I vented outside and used that 3000 particle air as my replacement air, I think my shop would be much poorer air quality. Not sure where I could get "clean" replacement air.

[Jim Mackell]

That's the 800 lb. gorilla. You live in Maine, do you want to heat the outdoors or maintain filters. I put a bypass in my system and exhaust outside when I'm running my 25" double drum sander, the rest of the time my heated (or cooled and dried) air is returned to the shop through a HEPA filter.

Could you describe how your bypass functions? Maybe a photo or two? That might be a good compromise solution.

[Rick Potter]

I vent my 3HP Onieda outside. Love it. Except for a trace of dust right at the exhaust, I see no dust residue, even on the adjacent planter, and the block wall 9' away. Of course, I live in SoCal, not Maine. The final straw for me was my drum sander. It clogs the filter much faster than sawdust.

I can't speak to James' situation, as I have no way to measure outside air, but my intake air is on the other side of the building, for what it's worth.

John's setup sounds like a good compromise.

Rick Potter

[Leo Graywacz]

I run my 2 1/2 HP Oneida outside and there are two great benefits from doing this. No filter mean max vacuum at all times. 2nd is a substantial noise reduction.

Heat loss for me isn't that big of a concern because my space is large. I have a smaller footprint of 1350 sq ft, but have 24 foot ceilings, so I have a large cubic footprint. If it's 20 degrees outside I have to run the DC for about 20 minutes before I notice the heat loss. I run AC in the summer and I notice that too. But the benefits are much more enticing than the small amount of money I will be loosing with heat and cooling.

[Lornie McCullough]

...... Seems very simple and more efficient overall. Am I missing something here? I am aware there will be some heat loss due to the outsie exhaust. For the moment, let's ignore that, OK?

I agree with you that it is simple and more efficient. It eliminates having to overcome the resistance of the filters, giving you more suction in the ductwork. It eliminates the cost of fine filters, and the need to clean them. And if you use a 10" or 12" flexible insulated duct to vent outside, it acts as a silencer helping to quiet your system.

FOIL FLEX DUCT.jpg

Lornie

[Leo Graywacz]

I just hard piped mine. I don't think that I'm getting to much sound transmission through the pipe. You can be right next to the machine and talk with someone without the need to raise your voice.

[glenn bradley]

If I could vent outside, I would do nothing else.

[Jim Neeley]

I think just about all of us would prefer to vent outside if it is viable for us.

I've read enough posts here about our heating or cooling systems being unable to heep up to go back and do a few calculations to validate or invalidate that assertion. Rather than voicing an opinion, let me share what I found and each of you can determine if or how that affects you.

I think we can all agree that if we dump DC air outside, that air must be made up from somewhere. It either comes directly from outside (open window, door, building leakage) or (for an attached shop) from another part of the house. If it comes from another part of the house, *that* air must be made up so we're not changing the overall effect, just the part of the shop/house that may need heating or cooling.

Further, if the temperature of outside air is acceptable for the inside of the shop, we can just turn off the AC/Heating and let it flow.

My calculation is simplified in that I'm assuming "dry air". As a result of this, the exactness of my calculation depends upon the amount of moisture in the air, with ym calculation tending to "under-predict" the amount of heating/cooling required. Still, it gives a starting point; a ballpark number if you will. It's greatest source of error will occur if you are cooling and this results in you condensing moisture (dehumidifying), as this is ignored. In this case your cooling numbers may be significantly higher than my calculation.

The next thing I did was to calculate the amount of energy necessary to heat a small flow of air (100cfm based on shop air at 68*F) by 10 degrees Fehrenheit. This came out to 1,076 BTU/hr. This may then be multiplied by how many hundreds of CFM you have and how many tens of degrees you are heating or cooling to get a blaapark number.

Thus if you were talking 600 CFM (six hundreds) and 38*F outside (68*F - 38*F = 30*F) thirty degrees (three tens) [or 98*F and dry air if cooling] you are talking

6 [hundreds of cfms] * 3 [tens of degrees F] * 1,076 BTU/hr = 19,368 BTU/hr. If AC you need a bit over 1-1/2 ton unit to keep up with continuous flow.

If you are talking 1,200 CFM and that 38*F it becomes 38,736 BTU/hr of heating or cooling [a bit over 3 ton].

If it were 8*F (60 degrees heating) and 1,200 cfm it goes to 77,500 BTU/hr and at -22*F (90*F heating) and 1,200 cfm its 116,200 BTU/hr heating.

Please keep in mind that these are ballpark numbers that do not account for the moisture in the air. This moisture would tend to *increase* the heating or cooling numbers from those calculated here.

FWIW, it's now clear to me why dumping outside is feasible in very temperate climates but quickly becomes infeasible or expensive chere extensive conditioning of the air is required unless you exhaust for very short periods and / or are willing to let the shop temperature approach the outside conditions while you're exhausting.

This is my best attempt at sharing information and not intended to start any verbal battle.. YMMV..

Jim in Alaska

[Tony Rodoracio]

I too am in S. California so the air temp is not a concern. My concern has been the noise that would be directed right at my neighbor. Does any one know the decibel level when venting outside? I have a 5hp Clearvue. Thanks

[Dan Friedrichs]

If you're going to vent outside, you really don't need a cyclone, either. A simple Thien baffle would work to separate the big chunks from the stuff that will just blow away. Or some people just exhaust into a large box, letting the big stuff settle to the bottom. The high separation efficiency of a cyclone is only needed to help keep the filters clean.

[Chris Parks]

I too am in S. California so the air temp is not a concern. My concern has been the noise that would be directed right at my neighbor. Does any one know the decibel level when venting outside? I have a 5hp Clearvue. Thanks

It is near enough to 92 db, damned loud! The most popular method of dampening the sound and the simpilist is to get some HVAC insulated flexible ducting and use that. Some have used two layers, an inner one about 8" and an outer over that. On BP's site there is a design for a muffler which from all accounts is very effective.

[Lornie McCullough]

I too am in S. California so the air temp is not a concern. My concern has been the noise that would be directed right at my neighbor. Does any one know the decibel level when venting outside? I have a 5hp Clearvue. Thanks

Hi Tony... My first attempt to duct outside was a 6 inch metal duct straight from the output of the blower atop the cyclone through a wall and pointed at my neighbor's house. It howled!!!!! My neighbor is a sweet little old lady, and she never complained, but I was very embarressed.

I took the 6 inch metal duct down, and installed the 10 inch internal diameter flexible insulated heating duct as per the picture in my earlier post. It is about 12 feet long and vents between the rafters where the bird-blocking would be. The noise now is only barely louder than a clothes-dryer vent.

Lornie

[Tony Rodoracio]

Thanks for the insight Chris. Lonnie, I know exactly how you must have felt. My neighbors are elderly and I would not want to subject them to that kind of noise. I think I will consider your approach and build some sort of muffler. It seems like a must do for the neighbors sake.