Two fans kind of in series for equipment exhaust

[Dooz]

I am looking at a situation where I am trying to remove some equipment exhaust form the room. The piece of equipment itself draws in room air and then exhausts it out of the top of the unit for cooling of electronic equipment within the unit (so no combustion or anything of that nature). The unit itself has two small exhaust fans that provide this cooling. My thought was to build an "exhaust hood" (for lack of a better word) above the equipment and then have an inline fan exhaust the heat out of the room. The hood would be above the unit (maybe a foot) and not directly connected to the unit. My question is, do I have to worry about dragging the unit exhaust fan with the hood fan if I am drawing a little more air on the hood side in an attempt to help further cool the unit? I appreciate any help you can give.

 

[hollandhvac]

It sounds like a good idea to me, be aware that the extra air from the room you exhaust needs to come back into the room from some where.

 

[Dooz]

Thanks, there is an existing outside air louver for the room (it's a large electrical room). So I have a path for makeup air to come in.

 

[hollandhvac]

In that case I see no problem

 

[Dooz]

So you think that there should be sufficient clearance between the hood and the unit exhaust that I shouldn't have to worry about dragging the unit exhaust fan?

 

[hollandhvac]

I would only worry about that if you connect the two together. But since you have a clearing of one foot or 30cm I would not worry to much. And it the extra exhaust air is only small and can easely be added by makeup air from the outdoor air louvre, I would not worry. May be check it the speed through the outdoor louvre is low, than I would not worry.

 

[willard3]

It could buffet with the two fans in series as the pressure difference between the fan equalizes....you cant have the same spot with two different pressures.

If noise is not a problem, buffeting is not a problem.