Venting DC Outside?

[Rod Sheridan]

Ken, nice spreadsheet, noticed the SaskTel address, are you in Regina?

Your spreadsheet does a great job of calculating the energy requirements for heating the make up air.

I thought I would indicate that with your calculation of 800CFM and a delta T of 37C, you need a 16.9Kw heater, or an 57,000 BTU furnace running constantly.

If you had 1,200CFM, you would need a 25Kw heater, or an 86,000 BTU furnace.

[Greg Pettis]

John - You are absolutely correct in your restatement, no special provision for makeup air. What I was trying to convey is that with a heater which utilizes outside air for combustion and a blower fan in the exhaust, is not permitting carbon monoxide to escape into the shop as a result of venting the DC outside. I do have a CO2 monitor in the shop, just to be sure. Also, the shop is a separate building, not integrated with the living space of the house.

Ken - When I built the shop, I was expecting 3 season use, definitely not full time in Minnesota winters. Accordingly, the shop has a vapor barrier in the walls and ceiling and just 6" of fiberglass batts for R19. As the lights are recessed, the ceiling vapor barrier is cut around the lights (air source). There are two sets of double doors, each 72" by 80" for access and cross ventilation in the summer (air source). Not drafty but definitely NOT tight, certainly some level of infiltration occurs providing makeup air. Also, a DC with an 1100 CFM fan constrained by 20' of 6" PVC then further constrained by a 90 degree sweep and 5' of flex hose to the hood of the planer, the actual air flow is no longer 1100 CFM. There are some formulas and theories to calculate the residual air flow but I certainly have not done the calculations. The point of my post was that, in practice, the performance of the DC improves, heat loss is not obvious to me and, in my particular shop, no special provision for makeup air was required.

The discussions on DC's and cyclones have been interesting with a lot of good information, some anecdotal such as mine, some conceptual and theoretical but all are a way to learn. Thanks for the questions and challenges.

Greg

[John Newell]

Glad I wasn't misunderstood (or didn't manage to type something with a tone I didn't intend, which is more likely).

To me, this is an incredibly interesting topic. Medium-term, putting this into motion in my bsement shop is a real goal. This is a very useful discussion.

One of the things I'm interested in seeing/reading/discussing is use of the roll-around DCs as the exhaust unit. I would rather not take up scarce space with a large, fixed (more powerful, more expensive) cyclone. If I could make this work with the currently top-rated Delta DC, for example, I'd be pretty happy.

[Chase Gregory]

Have any of you actually mounted the DC fan itself outside as well?

I was going to mount my fan up under the eave of my barn so that the only part of my DC system in the barn is the piping - thus saving more space and reducing noise. Mounting it up in the eave also reduces piping and elbows.

I've got a 24x36 shelter attached to the side of my project barn that will cover the fan and chip collection extremely well.

I bought a used Grizzly 1028 (1.5hp 110/240v) recently for this purpose and when I uncoupled it from the bags it's immediately apparent how much better it pulls when it's not pushing against the filters - and I'll only be running 1 tool at a time anyway. My total duct run should be about 20' to any given tool. Hanging the little grizzly fan will be pretty simple since there will be no bags or base or anything.

Just wondered if anyone has acutally put the whole setup outside? I've attached a few pics of the covered eave I'm talking about.

Chase

[Jack A Entrekin]

have you tought about having to heat that air that is moved in the shop every 4 min or so? my heater (or pocket book) can't keep up that!

[Greg Funk]

Out of interest I calclulated the cost of heating makeup air while running a dust collector and venting outdoors.

Assumptions:
DC Capacity - 800CFM
Outside Temp - -10F
Inside Temp - 65F

Cost to heat the makeup air using natural gas: $.83/hr

In our area we seldom see outside temperatures below 32F during the day so the costs here would be less than 40c/hr.

Given that most people, and particularly hobbiests, don't run their DCs continuously the cost to heat the makeup air is insignificant.

Greg

[Greg Pettis]

Greg

Thanks for taking the time - and having the smarts - to do the calculation on the cost of heating makeup air for a DC! Although I could not quantify it, it just did not seem like very much heated air was being lost. At $2.85 / gallon for propane this winter the checkbook knows right away if something significant has happened.

Greg Pettis

[Matt Meiser]

I can back up Greg's calculations with anecdotal evidence as well. The year I switched to outside venting I did more projects than the previous year, but didn't use any more gas. Since I have a separate tank for the shop, we knew how much went into the each tank.

[Mark Engel]

Greg

Thanks for taking the time - and having the smarts - to do the calculation on the cost of heating makeup air for a DC! Although I could not quantify it, it just did not seem like very much heated air was being lost. At $2.85 / gallon for propane this winter the checkbook knows right away if something significant has happened.

Greg Pettis

Wow. You must have caught a sale on propane. My last propane delivery was @ $3.9090

Gotta move south!

[Ken Ganshirt]

Hi Rod,

Yes, I'm in Regina.

It was a good friend of mine that created the spreadsheet so I take no credit for it.

The spreadsheet is a worst-case scenario. It works on the assumption that you will have to re-heat the total volume of air that gets exhausted. I don't believe that to be the case in reality but neither my engineer friend nor I understand enough about fluid dynamics to be able to express it in a spreadsheet so we kept it simple.

In reality, I believe that an airflow pattern will develop within a short time after the dust collector or cyclone starts up that will see a "home-run" flow from the source of the makeup air to the intake of the dust collector. That flow will work almost like a virtual pipe with the bulk of the cold air coming in, flowing directly to the DC intake and right back out the exhaust.

In that scenario you would affect the rest of the air in the shop only through the turbulence along the edges of that airflow. That might be lots or it might not be much. A lot would depend on the source of the makeup air and the path to the dust collector intake.

If it was a hole in the wall (say, cracking a door or window open) you would have a single, relatively direct path of flow. If the makeup air was coming in through leaks (say, around wall plugs and door and window frames) there could be many smaller odd-shaped flows, most of them less direct and involving more of the heated air in the shop.

It would be much too difficult to model anything useful even if we knew the math to do it. So rest assured that in reality you probably wouldn't need quite the amount of heating that the spreadsheet calculates. That seems to be supported by the experiences of some of the folks here.

John Newell,

I have recently abandoned the idea of exhausting. Not long after I got my Dylos particle counter (0.5/5 micron) I discovered that the cake in the 1 micron dust collector bag on my little King 1HP DC is working great as an air cleaner. It actually makes the shop air cleaner than the outside air.

Now I just need to figure out how to develop the same cake in the spanky clean 1 micron bag on my brand new Delta 1.5HP dust collector. Perhaps I'll just put my respirator on, turn on the Delta and suck all the fine stuff out of the bag on the King and see if that does the trick.

I don't have access here in Canada ... well, not affordable access ... to the Wynn Environmental upgrade kit or I would install their 0.5 micron paper filter cartridge and Phil Thien's baffle. That combo would give me a wonderful air filter. I'm going to try to find an equivalent air filter cartridge from a Canadian source. In the meantime I'll just have to wear my Airshield, cut lots and lots of wood and try to get an effective cake in my Delta DC bag. (To the studied, I know that will cut down the airflow but I don't care. I wear my Airshield until I get the dust levels down to an acceptable level anyway. I have no plan to spend the time, money and effort to try to hood every tool in my shop for truly effective capture at source.)

...ken...