Room Ventilation-Positive Pressure

??? is that 0.05 inches you want? of water or mercury (yuk yuk)?

What is the application?

sounds like a "critical barrier" for asbestos abatement, except the opposite. duh.

Is this a clean room? Is it all sealed up except for your (intentional) ventilation system?

If you have a blower blowing into the room and the room has only a controlled outlet for the air you will build up a slight positive pressure, controlled by the performance of the blower vs any leakage or controlled release of air.
You will need an airlock for entry.

They specified this room as:

Cleaning, inspection, lubrication and wrapping of the engine bearings will be accomplished in this clean, dust free environmentally controlled area. A controlled area for this purpose is defined as : A work space in which better than normal housekeeping is maintened . It is not to be classified as a clean room. Air hadling equipment shall be able to maintain pressure (positive) greater than the outside area.

I understand that if I bring 150cfm I will need to relief less to maintain positive pressure, but my question is if I size relief opening to be 8x6 it will release all 150cfm, if I size smaler opening it will release same amount of air but with higher velocity. I guess I am missing something.

Thank you

Once a system like this is in equilibrium, you'll always have to be releasing the same volume/unit time as is going in, otherwise the pressure would go up & up!

The smaller your outlet port is, the higher the internal pressure will be (up to the ability of your inlet fan to maintain the pressure).

Sorry it's not expressed very well, but I hope you get the idea.

It sounds fairly straightforward since you need only a slight positive pressure. Put a blower into the room (I'd make it 100 cfm per 1000 cubic foot of room to start, but what do I know). Put a small exhaust vent (use your 8 x 6 since you have it already) in the door (unless the room already leaks, which many do). Tape a couple pieces of toilet paper to the outside of the vent and see if they flutter. If they do, it's positive pressure; if they don't, close off part of the exhaust till they do. Make sure you use a filter on the blower (I'd use a standard $10 furnace filter).

Conversely, you could always ask your HVAC guy to just crank up the pressure in the room. If you have a modern system, he can do that, and he can even add some filtration in the ducts.

A simple U tube with some water in will measure/indicate the pressure difference.
One end of the U connecting to inside the room the other end to the outside, tape a rule alongside and just measure the difference.
Control it by adjusting the vent or the fan speed...
easy peasy

Del

Since Outside air need to be tempered I guess best thing will be to install hood, louver, fan, filter and heating coil to supply 150cfm of outside air.

But I still dont understand how can I control relief air, should I put control damper that will be interlocked with fan and pressure gage.

Thanks

Blimey it's not rocket science..

make a hole... put a plank half covering it....
If the pressure is too high slide the plank a bit to open the hole ...
If the pressure is too low slide the plank to close the hole a bit.
Repeat the above until it is just right ...Then write a big sign that says..

'Leave this plank alone'.
Check daily.

Slaps furry head with paw...

It's like a lot of things..once you actually start doing something it will become obvious.. Or you could hold lots of meetings instead

Del

If you want to maintain the positive pressure absolutely continuously at that fairly small CFM, you will need an "air lock" when you exit the room, which could be a simple plenum with a vinyl curtain.

a HEPA vacuum could "blow" that much air, and be a cheap but noisy route to your (semi) clean packing or assembly area.

If you want to actually measure the pressure differential, then a manometer would be required, but my "take" on your needs would be that the effect on your ears as you exit and enter the room would suffice to prove the matter.

thank you

i doubt that you will be able to build up enough pressure to even measure............

we made a nice "clean room" by simply mounting a fan in a wall and blowing air in through a hepa type filter, since this was the only source or air going it had to go somewhere.........and we just left it escaped thru the natural cracks around the door

the problem was getting inside the room... we had the door swing outward so that when opened, it pulled the air out, and then closed it slowly, once inside.......

we wore lintless smocks, hair nets, and also had a sticky matt at the entrance to clean the bottoms of our shoes.....

we never measured the actual particle count, but it seemed to work,

we were making small bearing assemblies, so the room didn't need to be that large, but i don't see why it wouldn't work with a larger area if you have more fans

good luck

NASA has portable clean rooms that are nothing more then a small; 12'x12' tubing cage with plastic wrapped around and a air handling system mounted on top. The bottom 3" around all sides of this cage has no plastic wrapped and lets the air out. This can be a class 10k or better clean room.

Hello Friend, Its really very useful and helpful post for room ventilation, To avoid obstruction of viewing he bottom of the screen should be approximately four feet (1200mm) above the floor. Thanks