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  1. #1
    Join Date
    Apr 2009
    Location
    Mobile, AL.
    Posts
    88

    Pressurizing control room

    I have two industrial control rooms where the plant control PLCs and HMI computers are located.
    This area was built with mini-splits for heating and cooling. My problem is the dust that enters the building colgging the computer filters fairly quickly.
    The mini-splits remove the humidity fairly well and I have not measured it yet, but I plan to using my SMAN3 to get wet/dry bulb temps.
    What I am planning is installing a Williams Air Sponge as a pressurizing blower to remove the humidity from the outside air and keeping the area a net positive pressure and hopefully dry.
    The Williams is rated 400 CFM @ .6". At this time I am not planning on recirculating the dehumidifier air, but core drilling one 8" hole in the poured concrete block wall for the supply.
    We are located North of Mobile, AL> on the Alabama River and humidity IS a problem with condensing fog nearly every morning.
    We have plenty of cooling, but we need a positive pressure to keep the mill dust out. As a part of the installation we are planning on adding a plenum with filters in addition to the filter supplied with the Williams unit.
    Any observations or experineces to share?

    Thanks,

    JDB.

  2. #2
    Join Date
    Jul 2011
    Location
    East coast USA
    Posts
    1,002
    Not sure how much room you have, but in one project i had the same issues. We built a room with in the room for servers. Glass and frame simple construction.

    had a filtered supply fan pull air from one conditioned room to that one to keep it positive. as back up we also have a small Movicool for back up ac. The cost for the room was cheaper than redesigning the HVAC.

  3. #3
    Join Date
    Apr 2009
    Location
    Mobile, AL.
    Posts
    88
    We don't have that choice since the three rooms that comprise the office area are all together. The area where the computers and PLCs are is at one end of the building (within the unairconditioned big building) and the lab/operators area is on the other. We could move air from one area to the other and seal them off, but other issues that impact is the bathroom with a constantly running vent fan and there are blowout vents to vent the nitrogen deluge system for fire protection. We will have to tie everything into the fire system to cut off all vents and intakes anyway.
    My hope is that the dehumidifier will make up the exhaust air and provide a relatively dry makeup air to pressurize the rooms to reduce the dust migration into the area and help heep the air clean and dry.
    The minisplits keep it cool, but the filters leave something to be desired and of course they were installed where it is inconvenient to get to them.
    The lab needs the fresh air intake anyway so maybe we can kill two birds with one stone.
    The air from the dehumidifier will be a little warmer, but drier as well. The load on the A/C will increase due to the hotter air, but be offset to some extent by the drier incoming air.
    I guess we will see how it works.

    Thanks,

    JDB.

  4. #4
    Join Date
    Jul 2011
    Location
    East coast USA
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    1,002
    Quote Originally Posted by jbarron4 View Post
    We don't have that choice since the three rooms that comprise the office area are all together. The area where the computers and PLCs are is at one end of the building (within the unairconditioned big building) and the lab/operators area is on the other. We could move air from one area to the other and seal them off, but other issues that impact is the bathroom with a constantly running vent fan and there are blowout vents to vent the nitrogen deluge system for fire protection. We will have to tie everything into the fire system to cut off all vents and intakes anyway.
    My hope is that the dehumidifier will make up the exhaust air and provide a relatively dry makeup air to pressurize the rooms to reduce the dust migration into the area and help heep the air clean and dry.
    The minisplits keep it cool, but the filters leave something to be desired and of course they were installed where it is inconvenient to get to them.
    The lab needs the fresh air intake anyway so maybe we can kill two birds with one stone.
    The air from the dehumidifier will be a little warmer, but drier as well. The load on the A/C will increase due to the hotter air, but be offset to some extent by the drier incoming air.
    I guess we will see how it works.

    Thanks,

    JDB.
    check this out: http://www.movincool.com/ceiling-mou...ditioners/cm25

    you can mount the unit out in the unconditioned area run the supply into the server room to pressurize. add a return filter you can exhaust the condensor air outside. the only thing you need is a smoke/fire damper on the supply and tie both the damper and unit to the fire system. set the stat fan on. your other units could be used as back ups.

    anyway just a thought. let us know how it works out.

  5. #5
    Join Date
    Apr 2009
    Location
    Mobile, AL.
    Posts
    88
    I will look into the MovinCool for future applications.
    We inherited the control room setup from our client. We operate the water treatment and cooling circuits for a major new steel mill and melt shop here north of Mobile Al. and what we have to work with is what they spec'ed during design and they were trying to save as much money as they could at that time. We (of course) have to deal with whatever problems come to light as we operate and maintain the systems. Sometimes spending a little mone on the cause of problems is the least expensive approach overall.
    While HVAC is included in my responsibilities it is a small part of the overall job, but important none the less.
    The problem woud have been easier if a solution other than the mini-splits had been installed in the first place.
    Reducing the infiltration of unfiltered air will be a big aid to the cause and I hope this will work for us.

    Thanks,

    JDB.

  6. #6
    Join Date
    Jul 2011
    Location
    East coast USA
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    Quote Originally Posted by jbarron4 View Post
    The air from the dehumidifier will be a little warmer, but drier as well. The load on the A/C will increase due to the hotter air, but be offset to some extent by the drier incoming air.
    I guess we will see how it works.

    JDB.

    Ok last thing, i would double check the added load to the rooms with the extra heat you will be adding. Add make sure if 400 cfm will be enough to pressure the rooms. Has anyone checked the room with a manometer? you may want a before and after readings.

  7. #7
    Join Date
    Aug 2003
    Posts
    907
    The Williams will most likely blow too much air in your control room without being able to dry it enough. You don't need much positive pressure to make a large difference in the infiltration rate. Figure out your ACH x control room volume x 1 hour/60 min = infiltration cfm. I have setup a HEPA filter pulling air from outside, speed controlled with a variac autotransformer. The output of the HEPA filter is fed to a Thermastor dehumidifier with a "T" connection so the dehumidifier pulls the rest of the air it needs to from inside air. You just need to pull in air through the HEPA filter at a rate equal to what the infiltration cfm would be, to get rid of ~ 90% of the infiltrated dust.

  8. #8
    Join Date
    Apr 2009
    Location
    Mobile, AL.
    Posts
    88
    Thanks for the suggestions. I think that the 400 CFM @0.6" H20 is enough to pressurize the 4 rooms in the building There are two doors and no windows. One exhaust fan in the restroom seems to be on all of the time.
    There are 4 mini splits, two ate in the room dedicated the the computers and PLCs. This room has a high pressure nitrogen purge fire system that makes it not safe (according to our safety department and perhaps good sense) for people.
    Currently that sytem is locked out and we temproarially are using it for the control room. The control function will be moved into the lab area in a different area.
    The dust problem is in this "electrical"room. The hazard detected by the (in my mind overzealous) fire insurance company is a small transformer, PLC cabinet and control HMI computers (3).
    As a part of this system is a blow out louvered vent in the wall.
    Between the leaks at the doors, bathroom vents, and the vent and foot traffic in and out there is considerable dust in the control room.
    To make it more difficult the walls are cinder block reinforced with rebar and poured with concrete so making a penetration is an expensive job for the core drilling company.
    Two holes made at the same time are cheaper than having the company come out twice.
    Perhaps the williams unit working against a relatively closed box would pressurize the rooms and not have excessive flow and still dehumidify enough to not add to the load.
    We have planned to add a HEPA filter to the dehumidifier that would also reduce flow.
    I may have two 9" holes cut so that the opening would be there if we need to recirculate and draw in outside air to pressurize. I would rather err on the side of more pressurization than too little.
    As to measurements of the air operational work have been a little high to take the time to do the job right. (A poor choice perhaps, but time has it's restraints).

    Thanks again,

    JDB.

  9. #9
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,797
    Set up that Williams to recirc the air in the server room also.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  10. #10
    Join Date
    Apr 2009
    Location
    Mobile, AL.
    Posts
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    I am leaning on installing the Williams unit inside the control room and using one hole sawn through the filled block wall to draw in outside air with a damper to control the amount of outside air.
    The outside vent will have a filter for the mill dust. The internal filter for the recirculated air in the computer room.
    The unit will have an automatic shut down from the fire system which will also close the damper.
    Some of the air will be dehumidified control room air and some will be from outside to pressurize the control room.
    The drain from the dehumidifier will also be passed through the wall to the outside. So far I have not run the unit to see how noisy it is. This might make a difference was well as to where it ends up being mounted.
    Thanks for all the input.

  11. #11
    Join Date
    Jul 2011
    Location
    East coast USA
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    when you say control the outside air, what do you mean.? the only way to pressurize the room is by adding in OSA. (or some other outside source) so the damper will need to move as room pressures changes. personally I cant figure out why you would want to dump hot dry into a server room, trying to get the heat out.

  12. #12
    Join Date
    Aug 2003
    Posts
    907
    I've also used a Climate Right sitting outside to bring in outside air, cooling and dehumidifying it before it is pushed inside. Dehus aren't the only way to get the job done, especially if you have a lot of heat generated inside. The outside unit then subtracts from the needed cooling capacity, instead of adding to it like a dehu does.

    Edit: The movincool unit suggested by dlove is a similar idea, and seems a much better machine. The Climate Right is 1/10 the price and designed for outdoor use. I'm just trying to give you options.

  13. #13
    Join Date
    Apr 2009
    Location
    Mobile, AL.
    Posts
    88
    We have plenty of A/C for the control room.The air will be drawn fronm outdside of the control rooms / server rooms. The air will be considerably hotter than what is inside, but either I add a single pass airconditioner or the dehumidifier. It would not be a problem it the A/C had been a split unit with an airhandler that could have been ducted to draw outside air into the returm, but with the mini-splits there is no return to duct into.
    I suppose the units could be modified in some way, but the dehumidifer will pressurize the room and dehumidify the outside air. This will add to the cooling load, but within the capability of the four mini-splits.
    The mill dust can be filtered going into the dehumidifier and this should help limit the infiltration of dust into the more sensitive systems in the control room.

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