Exhausting a DC Outside - A Request for Clarification

[Glen Blanchard]

In another thread I mentioned that I'd like to wall off my DC/compressor closet to decrease noise level in the shop and we got to discussing the need for return air. I have a related question to which I think I know the answer, but would like to confirm.

If I were to pull the exhaust filter (3 hp Oneida cyclone) from the system and exhausted outside, there would be no reason for return air, correct? A list of concerns exhausting to the outside would raise would include the following.....

loss of conditioned air from the shop
noise outside near the exhaust
some dust tossed into the air outside

Anything else? I don't have gas heat or gas water heater in the shop which eliminates that safety concern. This configuration would not decrease the effectiveness of the DC system, would it?

[Paul Cahill]

I exhaust directly outside. I am on the southern border of Tennessee, so I have relatively short heating and cooling seasons compared to some. However, there is a lot of thermal mass in the contents of a shop, so you don't loose as much heat/cooling as you might first expect. Another factor to take into account is how long the DC is running. I spend about 15 hours per week in my workshop, but the DC is only running a tiny fraction of that.
Noise is transmitted outside. My system is significantly less noisy than when I just circulated inside, but I still wear hearing protection. I have a muffler on the discharge and outside it sounds like a loud clothes dryer.
The only time I even see dust outside is if I overfill my cyclone drum (not that that ever happens!).
Another observation I had was that when I used a filter and circulated I sometimes got a nauseating odor in the shop from the filter. That has been eliminated entirely.

Hope this helps.
Paul

[David Hawxhurst]

you will have to have some make-up air if you exhaust outside. if your shop is not super tight then it maybe pulled in thru all the loose fitting. mine gets pulled in from mostly around the garage doors.

[Michael W. Clark]

If you remove the filter, it will actually increase your airflow at the hoods because of the reduced pressure drop from eliminating the filter. Assuming you don't add this pressure drop back in trying to get the duct outside. If you can spin the fan housing to blow directly outside throuhg the wall, this would be best. Unless your shop is super-tight, you'll get infiltration. If doors are hard to open/close, you may want to add some way for make-up air to get in. If you have to do make-up air, consider locating your vents or ducting it to an area near a hood where it can get sucked in. This would minimize any conditioned air pulled in by the DC from the shop.

Mike

[Ron Natalie]

My DC is in the next room from the shop. The biggest issue is that if the room is tightly sealed, the DC won't work as well. I've not noticed it is a problem. Since I've not got an airtight door between the shop and the rest of the place it's not apparently an issue.

[Eduard Nemirovsky]

From my own experience - venting outside will DRAMATICALLY change temperature and humidity in air conditioning shop. In my area is not acceptable with high humidity and temp during summer time.

[Van Huskey]

On the conditioned air issue there are two things to think about, not only the temperature of the air but humidity which may or may not be an issue where you are. What I have found is the temperature change is not nearly as bad if you keep the shop climate controlled all the time and not just when it is in use. If this is the case the air within the shop holds very little of the heat in the room, most of it is held in the solid matter of and in the shop, so in that case the fluctuations are low IF you don't run the DC constantly for long periods of time. If you just heat/cool the shop for use then a outside vented DC strips the conditioned are fairly quickly and since the solid matter in the room is not pre-heated or cooled the room gets uncomfortable quick (assuming the outside air is to one of the extremes).

[John Little]

If you have a gas hot water heater or furnace in the same area as your shop the negative pressure created by the DC can pull exhaust gases from these appliances back into the shop (or house) causing a high risk of carbon monoxide poisoning.

[Michael W. Clark]

If you have a gas hot water heater or furnace in the same area as your shop the negative pressure created by the DC can pull exhaust gases from these appliances back into the shop (or house) causing a high risk of carbon monoxide poisoning.

The OP said he does not have this safety concern.

[David Giles]

You got it! #1 is some concern, more so for AC than for heat. #2 depends on neighbors, normally. #3 is a low priority because the cyclones are very efficient. And you already live in dusty Texas!