PDA

View Full Version : How to provide source of make-up air?



toddreg
21-03-2009, 03:24 PM
My situation involves a printing company whereby temp and humidity are important variables due to their impact on paper. Static and curling become issues at times. Also, we are located in Georgia so the summers are pretty hot.

We have two machines exhausted to the outdoors that together move between 6000-12500 cfm depending on if both are running and which components of the machines are being utilized. I should mention that we just added the second machine and in the past struggled to keep the press room cool in summer afternoons with the one machine. Now with the second I am anticipating the task to be impossible. Obviously, this much air must make its way back into the building through every crack and crevice. Overall plant size is 45,000 sq ft in three openly connected sections.

As it is now due to the suction, we are pulling air from throughout the facility and cooling the building is very difficult. I would guess that trying to cool 12500 cfm of external make up air to be prohibitively expensive. If we dropped a duct in near the source of extraction on these machines, would this help by allowing outside air to basically circulate through the machine and right back out? Could this scenario alleviate a significant amount of the extraction of cooled air from throughout the facility?

Any other ideas for dealing with this situation? Also, what would be a ball park guestimate of the cost to provide cooled and dehumidified make up air? I would anticipate that such a conditioned make up air system to be very complicated by the fact that the amount of air exhausted varies continuously throughout the day as the machines come on and off.

chemi-cool
21-03-2009, 04:46 PM
pulling out all the cold air is no solution.

Instead you should think of adding fan coil units that will cool the specific hot area, air doe's not go where you want it to go to but where it easier for it to flow to.

your way will add double heat load and of course, cost.

Think of Small individual units that will run circulating and cooling inside air only

toddreg
21-03-2009, 11:24 PM
I think I was not clear. We are sucking out all the cold air now as it is. What I was asking was if providing a source of outside air via a duct dumping directly at the location where the suction of the machine is would avoid pulling out all the cool air from throughout the building. The source or air from this duct would in fact provide the easiest flow which is why I was thinking perhaps this would help.

dougheret0
13-04-2009, 05:18 PM
No one can give you an intelligent answer without seeing the layout of the facility. First, is it necessary to cool and dehumidify the spaces that are being exhausted? If not, then supply about 80% untempered outdoor air into that space, and then bring in the balance across a cooling coil, plus enough to pressurize the remainder of the building. The outdoor air being introduced into the cooled and dehumidified part of the building, either across the building's ac coil or pre-conditioned by a dedicated outdoor air unit, should be allowed to flow freely into the exhaust space, where it will cool that space somewhat. This is analogous to a restaurant kitchen with a large grease hood. The hood is compensating, bringing in 80% of the exhaust, and the rest of the air is delivered to the kitchen via the restaurant seving area AC unit after cooling and dehumidifying the customers.

If you are exhausting 12500 cfm, you would bring 10,000 cfm directly into the exhaust space, leaving 5000 cfm to cool and dehumidify before allowing it to flow into the exhaust space. The 5000 cfm is to allow the entire building to be pressurized - a requirement to control moisture in the building. Since 5000 cfm is probably more than the AC unit can handle, it should be pre-conditioned with an Addison, Dektron, or Desert-Aire dedicated outdoor air unit. So, if you don't need to cool and dehumidify the spaces being exhausted, you only have to pre-condition 5000 cfm, not 12500. If you must cool and dehumidify the air before it is exhausted, then you must pre-condition 15,000 cfm to keep the building pressurized.

sterl
16-04-2009, 05:45 PM
Is the Exhaust Air contaminated? As in full of dust or ink or ?

Considering its Arizona: You can go air to air recovery plus swamp cooler....Pretty low power input in total and pretty easy to manage.

That presumes hat something like 77 to 79 Deg F. is low enough for the interior temps.

sterl
16-04-2009, 05:48 PM
Sorry, that was Georgia so the swamp cooler isn't going to be as effective.