Venting dc outside

[Lee Schierer]

Several things to consider:

1. If you pump air out of your shop you need to let air in or suffer a decrease in cfm.

2. Any conditioning you do on the air in your shop will be vented outside at the rate of cfm of your system. This may or may not be a problem depending on your location.

3. Adding a single 90 degree turn in a pipe is equivalent to adding ~10 feet of pipe. 45 degree bends get the same end result with half the air flow loss.

4. Dust and fines may migrate to your neighbors and coat their cars, etc with a layer of dust. The noise may also become a factor depending upon how close they live to your shop.

[david brum]

The noise may also become a factor depending upon how close they live to your shop.

I was initially concerned about the noise. After installation, I was surprised to find that there is very little noise involved in outside ventillation. My 3hp DC sounds about like a dryer vent, just a low hum that you wouldn't notice unless you were next to it.

[Michael W. Clark]

1. If you pump air out of your shop you need to let air in or suffer a decrease in cfm.

This is considered in good design practice, but it is not necessarily true. The negative pressure induced by the DC will draw air through the building envelope. Designing for make-up air allows you to control the location where the make-up air is drawn from or condition it. Make-up air will still get in even though it takes a little more force, but the reduction in CFM will be slight, if measurable.

2. Any conditioning you do on the air in your shop will be vented outside at the rate of cfm of your system. This may or may not be a problem depending on your location.

If your shop is connected to the house, you may rob the house HVAC system. The make-up air is going to take the path of least resistance. If you provide make-up air low or near the hoods as mentioned by others, you will be exhausting that air, instead of expensive conditioned air. As mentioned earlier, this is a typical practice with fume hoods, and is oftened done in conditioned industrial applications.

3. Adding a single 90 degree turn in a pipe is equivalent to adding ~10 feet of pipe. 45 degree bends get the same end result with half the air flow loss.

At 4,000 FPM 10 feet of 6" = 0.45"wg loss, a 1.5D 90ell is 0.25"wg loss, 1.5D 45ell is 0.12"wg loss (half of a 1.5D 90ell). At 4,000 FPM 10 feet of 4" = 0.71"wg, a 1.5D 90ell is 0.24"wg loss, 1.5D 45ell is 0.12"wg loss (half of a 1.5D 90ell). A 45ell does not rob you of half the CFM, but does result in half the SP loss than a 90ell. CFM loss is not directly calculated from system SP. The effect on CFM will depend on the fan curve and how it relates the system SP requirement. For example, a wall panel fan rated for the same CFM as a centrifugal fan (DC fan) will not perform as well on the DC system. An additional fitting will have a much greater impact on airflow for the wall fan than it does the DC centrifugal fan.

Mike

[Ron Natalie]

My DC is mounted outside the shop, but there's plenty of circulation between the hangar where it and the air compressor is located and my shop. I probably lose some of my air conditioning in the process but it's a lot quieter that way.

[Lee Schierer]

This is considered in good design practice, but it is not necessarily true. The negative pressure induced by the DC will draw air through the building envelope. Designing for make-up air allows you to control the location where the make-up air is drawn from or condition it. Make-up air will still get in even though it takes a little more force, but the reduction in CFM will be slight, if measurable.



Mike

Creating a negative pressure in the shop will decrease the air movement through you DC which is not desirable. Unless your building is really drafty the make up air inflow will be restricted. Another problem is that you may also over power the venting of combustion products from any gas appliances in the house/shop resulting in unhealthy conditions within the house.[

[Bill Arnold]

Reading through this thread has me thinking about my 3hp Super Dust Gorilla installation. I had originally thought about venting it outdoors but decided against the air loss and connected the filter system to it inside by the DC. It works great as far as picking up chips, etc., even if I have multiple ports open.

When I have the unit on, there is a noticeable heat rise in the shop after a very few minutes. During Winter months, that's a good thing, of course. Being in the South, I'm now wondering if I'd be better off exhausting the DC outside the shop so I eliminate most of the heat load. I'd be pushing some of my cooled air out, but the reduced heat contribution of the DC might improve the cooling efficiency. Venting to the outside would also reduce the fine dust particles in my shop air. I'm far enough from any neighbors for dust and noise not to be a problem. Plumbing wouldn't be too much work since the exhaust port and filter are already on an outside wall.

Just kinda thinking out loud.

[Lee Schierer]

When I have the unit on, there is a noticeable heat rise in the shop after a very few minutes.

I doubt that your DC motor is causing the heat rise, if it is you need to get it checked. Most likely you are pulling warm air from the ceiling down to your level or in from outside.

[Bill Arnold]

I doubt that your DC motor is causing the heat rise, if it is you need to get it checked. Most likely you are pulling warm air from the ceiling down to your level or in from outside.

Since the DC is recirculating shop air, I doubt it's pulling warm air from anywhere. My shop ceiling is 8.5'. There is no burning odor, just a heat rise. When I say 'noticeable', I mean it's something I can feel but it's not like it's getting hot in there.

[Michael W. Clark]

Creating a negative pressure in the shop will decrease the air movement through you DC which is not desirable. Unless your building is really drafty the make up air inflow will be restricted. Another problem is that you may also over power the venting of combustion products from any gas appliances in the house/shop resulting in unhealthy conditions within the house.[

Lee, I absolutely agree with you about impairing the natural draft and induced draft gas appliances. The gas appliances will be affected because of the high SP of the DC fan. The DC is going to get its air first and overcome the resistances of the other appliances. However, it takes a LOT of negative room pressure to affect the flow of the DC system. The DC system fan is operating at somewhere between 6-10 "wg of negative at the fan inlet. Gas appliances are affected at a negative room static pressure of .02 to .05"wg. Doors become difficult to open (slamming causing injury) at .05 to 0.1"wg of negative. Supposedly, you can measure a difference in DC fan performance when the room negativity is 0.1 to 0.25"wg. Even at 0.25"wg of extra SP, you are not going to see a significant change in airflow on a home DC system.

Basically, if you can open your doors fine and they do not slam violently, your DC performance is likely not impaired. However, your gas appliances may be affected as you say.

If in doubt, turn off the gas appliances, turn on the DC, shut all the doors/windows and measure the differential pressure between the shop (where the DC is drawing from) and the surrounding exterior spaces. This can be done with a long hose and a manometer. Let the DC run for a moment, it may take a few minutes for the pressure to stabalize.

I am not trying to advocate against make-up air, it is beneficial. However, I do not believe that the lack of make-up air is going to have a noticable affect on the DC performance.

Mike

[Van Huskey]

Just a note about heat/AC loss with venting outside. One thing I don't see discussed often is the fact much of the heat/cool (I know cool doesn't technically exist) is stored in the solid matter in a shop the air contains very little by comparison so heat/AC loss isn't as great as it looks on first blush. HOWEVER, if you start the heat or AC when you enter the shop to work (as opposed to keeping it heated/cooled) a much larger percentage of the heat/AC is then just in the air for quite a while as the solid matter all warms/cools. If this is the case for you there will be a MUCH bigger reduction/increase in the air temp with venting outside. This may account the widely varied opinions of how much venting outside effects the temp inside.

[Matt Meiser]

I have have seen a noticeable heat rise around the filter of my 3hp Grizzly cyclone. Not "hot" but definitely warmer. My old. Yclone was vented outside and I didn't have massive heat loss issues and it didn't affect my forced-vent Hot Dawg furnace. I'm considering going back to outside venting.

[Ron Natalie]

I doubt that your DC motor is causing the heat rise, if it is you need to get it checked. Most likely you are pulling warm air from the ceiling down to your level or in from outside.

No, it's quite possible if the shop is well insulated. A 2HP motor is going to generate 8000+ BTU/HR (all the electricity consumed is converted to heat somewhere). That's more than a small space heater would throw in the room.

[Michael W. Clark]

No, it's quite possible if the shop is well insulated. A 2HP motor is going to generate 8000+ BTU/HR (all the electricity consumed is converted to heat somewhere). That's more than a small space heater would throw in the room.

Then what energy is used to spin the fan shaft?

[Rick Potter]

About needing makeup air in the shop....I am not any kind of expert, but I can tell you that my 3 HP DC, is vented outside, and works great. BUT, one day when I started using it, I noticed the collection efficiency had dropped off within two or three minutes. I did not realize what it was untill I opened the exit door, and it almost slapped me in the face as it opened. Luckily it hit my foot, not my face.

This is a 1600 sq. ft. shop, and it only took a couple minutes. Normally, the shop has an open window ten months of the year, and I had no trouble with it till I used the DC with closed windows that day.

Can't speak for anyone else, but mine sure needs replacement air.

Rick Potter

[Michael W. Clark]

About needing makeup air in the shop....I am not any kind of expert, but I can tell you that my 3 HP DC, is vented outside, and works great. BUT, one day when I started using it, I noticed the collection efficiency had dropped off within two or three minutes. I did not realize what it was untill I opened the exit door, and it almost slapped me in the face as it opened. Luckily it hit my foot, not my face.

This is a 1600 sq. ft. shop, and it only took a couple minutes. Normally, the shop has an open window ten months of the year, and I had no trouble with it till I used the DC with closed windows that day.

Can't speak for anyone else, but mine sure needs replacement air.

Rick Potter

That's an excellent test Rick. I know you may not have a way to test it, but it would be interesting to know the differential pressure between the shop and CFM the collector was pulling with the doors shut compared to with it open.