Room to room transfer fans

[nicholsmf]

I guess this isn't a heating and A/C question, but this seems like the most appropriate place to ask, so here goes.

My shop is 30 x 46 with an 30 x 36 open shop area and two 10 x 15 room across the back. See representation below.



So, you see the shop area and room A and room B. Room A is storage for items that are sensitive to humidity and has a permanently installed dehumidifier with drain plumbed to the outside. Room B is also storage, but for items that are less sensitive to humidity. Still, I would like to reduce the humidity in room B a little bit to stay around 50% (+/- 5%).

Room A maintains a steady 45% humidity. Room B stays around 65%. I have two room to room transfer fans I am going to install in the wall between room A and room B.

Three options:

Option 1 - Two fans pulling lower humidity air from room A to room B. Lower the humidity by pushing in air with lower humidity???

Option 2 - Two fans pulling higher humidity air from room B to room A. Pull the more humid air in to room A to be dehumidified???

Option 3 - One fan pulling from room A to room B and one fan pulling from room B to room A. Constantly exchanging air between the rooms so the dehumidifier would lower humidity in the air of both rooms???

I would appreciate an opinions you guys have and any reasoning behind them.

Thanks,
Mike

 

[nadogail]

The dehumidifier serving room A will work itself to death trying to dehumidify the make up air from B

 

[nicholsmf]

The dehumidifier serving room A is rated for 2400 square feet and is currently serving 150 square feet. The dehumidifier currently runs about 1 hour per day to maintain 45% humidity in room A. Seems like it would be easily capable of handling both rooms, no?

 

[Jackfre]

Look at the Tjernlund Airshares. I sold thousands of these. They work very well. I would usually control them on a switched outlet

 

[nicholsmf]

Look at the Tjernlund Airshares. I sold thousands of these. They work very well. I would usually control them on a switched outlet

I already have two transfer fans (Broan, I think). Since I have them, I'm gonna try them first to see if they work. If they don't, nothing lost except a small amount of time. I'm just not sure what configuration to run them in, Push, Pull, or Push Pull.

 

[Yankeefarmer]

The only right way to do it is to have one fan moving from A to B and one moving from B to A. This will effectively join the two rooms together and you should see similar humidity levels in the two rooms. If you move air from A to B, you’ll be creating a suction in A and pressurizing B. That’ll push dehumidified air from B into the shop and **** “humid” air from the shop into “A,” causing the dehumidifier to work harder. Similarly, if you just move air from B to A, B will **** air from the shop, and the higher pressure in A will push dehumidifier air into the shop.

 

[nicholsmf]

The only right way to do it is to have one fan moving from A to B and one moving from B to A. This will effectively join the two rooms together and you should see similar humidity levels in the two rooms. If you move air from A to B, you’ll be creating a suction in A and pressurizing B. That’ll push dehumidified air from B into the shop and **** “humid” air from the shop into “A,” causing the dehumidifier to work harder. Similarly, if you just move air from B to A, B will **** air from the shop, and the higher pressure in A will push dehumidifier air into the shop.

That makes sense. Thank you!

 

[Jackfre]

It is not the ”only” way to do it. We used one and either short cut the door or cut a thru passive register through to the space. You aren’t talking big cfm here and what is pushed into the room will equalize through the door or register. Again, thousands of them without a problem where engineers were looking over our shoulders.

 

[Yankeefarmer]

@Jackfre you are correct. When I wrote “the only correct way” I was referring to the three options the OP presented. A single fan (like the Aireshares you referenced) could also do the job. Like you mentioned, the key is provided a second passage for air flow to pass between A and B without using the unconditioned shop as that passage.

 

[nicholsmf]

Thanks for the replies! I'll start with push / pull with the fans I already have and monitor to see what happens.

 

[TractorJeff]

Push into B up high, Pull into A down low. Humid air is denser so it will be lower to the floor. (I think?)

 

[Yankeefarmer]

Push into B up high, Pull into A down low. Humid air is denser so it will be lower to the floor. (I think?)

No, just the opposite. Water vapor is less dense than dry air, that’s why clouds “float.” Within the height of typical rooms, it doesn’t matter. The air will very quickly reach a uniform humidity level. Now, if the OP’s shop was the Vertical Assembly Building at Cape Canaveral, it’d be a different story.