Humidification of an Industrial Process Room 1

[KenRad]

I have a process room in the middle of a large manufacturing plant that has temperature/humidity requirements of 85F/50%RH. The surrounding plant is conditioned to 74F +/-2F. If I had a good vapor barrier around this room, I could maintain 50% RH year-round without much difficulty. However, there is a conveyor that passes through the wall, and the opening cannot be made any smaller than about 30" x 30". The air handler serving this room takes in no ventilation air, and the room has no exhaust, so there is very little air exchange across this conveyor opening. Unfortunately, because the migration of water vapor does not need air motion to occur, and I end up fighting a losing battle in the winter when the main plant humidity drops to 20% or so.

I've told my manufacturing people that the only thing I can do is seriously increase the amount of humidification in the room to compensate for the loss, unless they want to modify the conveyor system.

Any other ideas?

 

[fredb]

Hello Kenrad,

How about running your room with a slightly negative air pressure and then feed moisture conditioned air into your room through the tunnel when conditions are dry.

 

[ChasBean1]

KenRad, I think you're on the right track. Maybe flaps at the conveyer opening would help if not already installed. A possible idea to consider would be to cut in a duct to let a controlled volume of air from the surrounding plant (maybe 10% of the total, recirc volume) enter the AHU suction to maintain a known, positive room pressure. This way you can control the infiltration point of entry and humidify it at the source.

Without treatment of in-filtered air at the point of entry, and the possibility of a pretty good air exchange happening at the opening due to convection temperature differences or flow patterns, room humidity control can become tough.

Another thought is the air flow pattern in the room. I wouldn't want to see a downwash of air at the conveyor opening because it can tend to create a venturi effect that can draw in plant air.

And a final thought is how big and how often are slugs of air brought into the room by equipment on the conveyor? How often do people enter and leave the space? If the answer to either is "often" we might consider some sort of air lock that minimizes air exchange between the room and the plant.

Definitely continue with your thoughts of the room vapor barrier. Room should also be insulated, doors gasketed, and penetrations well-sealed. I assume none of the room's boundaries touch the outside? Any room surface 64°F and lower will condense which you and I both know will lead to destruction...

Sorry, didn't mean to get too wordy. -CB

 

[quark]

CB!

I would like to get your idea on two points in this regard.

1. Whether moisture transfers from low pressure area to high pressure area? We had a similar application (with conveyor too) where one area was to be maintained at lower humidity of 20+/-5%. Eventhough the pressure of that room was 10Pa morethan the adjacent room we found moisture penetration. (I reasoned it by saying low RH is low partial pressure of water vapor and high RH is high partial pressure of water vapor, so moisture penetrates by virtue of pressure difference)

2. Eventhough the fresh air is generally considered as 10% of volume flow rate (don't know how it was derived) we didn't require morethan 5% even the room pressure were to be maintained at 85 pascals. (a typical Injection formulation facility) Where is this 10% figure required generally?

I anticipate your response.

Regards,

Truth: Even the hardest of the problems will have atleast one simple solution. Mine may not be one.

 

[quark]

Note: I don't want anybody saying if my leakage rate is 10% I need 10% fresh air.

Regards,

Truth: Even the hardest of the problems will have atleast one simple solution. Mine may not be one.

 

[KenRad]

Appreciate the help, folks!

--KenRad

 

[mechatonics]

hello,

i am working with a humidification plants for industries to humidified the air. we take the air coming through "dampers" pass it through buffle grill to make the turbulant flow to laminar flow. then we are using showering systen to add moisture to the air and then pass it through "eliminators" to minimize or remove the water droplets. then supply fan take this air to the room through ducts.
i explain the procedure which we are using if any quetion in your mind pls ask,donot hesitate.
thanks mechanical is the mother of all technologies

 

[ChasBean1]

Quark!

1. Based on my vast wisdom (which I collected in a thimble), I would guess that your moisture increase in the high pressure area was NOT from some sort of osmosis from the low pressure area, but would likely be a sort of psychrometric phenomenon occurring within the high pressure space. We have to talk temperatures and dewpoints because you and I both know relative humidity is a sketchy... It's all relative (to temperature, that is). I believe in the mechanical supernatural under certain circumstances, but moisture penetrating from the air mass contained within a low pressure area and migrating to the air mass within a high pressure area leaves me wondering... I won't deny that humidity increase occurred in the high pressure area, but the pathway you mention is unlikely.

2. The 10% is purely whimsical. I'm not going for the ASHRAE/ACGIH/ANSI Z9.5 magical value of 100 feet per minute at the opening, because that's based on chimney effect-type factors that don't happen here. The basic assumption is net positive to prevent infiltration.

-CB

 

[quark]

CB!

Oops! I presumed you consider constant DB temperature while the RH is varying. (actually that was the case with 1 deg. variation in temperature and about 17% RH difference, at 22 to 23 deg. temp) And this was happening particularly when the other area was being mopped with wet cloth.

The humidity indicator was of Sekonic make and a very good one. The RH is controlled by a desiccant dehumidifier (Munter's) I totally rule out Osmosis because I am not talking about diffusion through walls but a clear opening.
If it may not be the problem then have you ever encountered such type of problems? Please let me know.

The second point is ok. I just wanted to have your opinion.

Note: There is always some underlying sarcasm (just like Goorah's) in your writings which I like much, for work is fun. Keep it up

Bye the way Goorah! where are you?

Regards,

 

[ChasBean1]

Quark: Never mean to be a snot. Sorry if I came across that way! :-o

 

[quark]

CB!

Did I say anything wrong? Then please consider only technical aspect of the post and reply.

Regards,

 

[ChasBean1]

Quark, cool.

Then this is a whole new can of worms you're opening.

Constant DB temperature... where?
While the RH is varying... where?
1° variation in temp and 17% RH... where?

The whole first two paragraphs of your post is in such a "by the way" format that I have no clue as to what you're talking about!

If you can clarify, maybe I can understand. (The underlying sarcasm "vast wisdom collected in a thimble" was supposed to be a bust on myself).

My main point from above was how did you know that the moisture increase in the high pressure area was from transfer of vapor from the low pressure area?

 

[gunnarhole]

This may be a little off the main topic of this thread but I remember commissioning a facility in Alaska that used ultrasonic humidifiers to raise the RH in the module. After a month or so a mineral "scale" laid down by the dissolved solids present in the water being fed to the humidifiers started shorting out circuit boards.

Regards,

Gunnar

 

[quark]

CB!

The answer to all your questions is 'in room'. In second para I emphasized that because of accuracy of the equipment the human error in minimum.

Why I came to the conclusion of moisture transfer from low pressure area to high pressure area is because it used to happen when the low pressure area was being mopped. When we totally covered the hatch provided for conveyor the problem was not repeated. (Perhaps I thought to have some explanation for this phenomenon, that is why came to this conclusion)

Perhaps my HVAC knowledge as well as using words (like 'underlying sarcasm) is very confined. I regret and end this (by saying I should not have said so)

Note: I greatly admire your posts and sorry if I offended you.

Regards,

 

[quark]

CB!

Atlast I found some printed proof for that. It is mentioned in 'The Humidification Hand Book' second edition.

You can find it in page no.14 of 5th chapter under the subheading "Moisture Infiltration against outflowing air"

It is mentioned that velocity through hatch or cutout is to be maintained at 150fpm to reduce moisture infiltration from low pressure zone to high pressure zone. However if the conditions are 15% RH and 70deg.F it is better to consider ingression in the design of dehumidifier at the rate of 50fpm airflow because it is difficult to restrict. My plant conditions were 20% RH and 20deg.C.

The phenomenon is termed as "Counter-flowing Air Infiltration"

Regards,

 

[quark]

The book was by Munter's.