Room door bent by too many fans on

"Is ¹/₂psi dangerous? Yes - if it is propelling a door towards you."

Electrical interlocking between the fans is something the site electrician would be able to doodle together using a few electromechanical relays and some relatively short lengths of cable.

A manometer would be the easiest way of measuring the pressure differential. You just have to figure a way to get the tube into or connected to the room. A glycol/water tube would be just fine.

Regarding the door, I would first of all find a door(s) that can handle or be reinforced to handle the pressure differential. Once you have the appropriate doors, build a suitably enclosed vestibule with a mechanism (e.g. butterfly valve) that allows you to equalize the chamber to the degree of whether you are entering or leaving.

The other option is to install a heavily reinforced sliding door that would have both vertical rollers to support the weight and horizontal rollers to allow you to roll it with out it binding up.

What is the cubic foot volume of the overall area the fans are serving?

What is the sq. ft. area of the filtered openings?

Most designers do not want volume of air being pulled through filters to exceed 500 fpm. When all fans are running, you need 113,000 CFM of air to be replenished into the space to make up for the air that is being exhausted. That is a lot of air! Dividing 113,000 CFM by 500 fpm,determines the size of the opening required (assuming no static losses for clean or dirty filters) to be 226 sq. ft. If you add in filter losses you will probably need to increase the size of the opening by 10 - 20 % or even significantly more. Check with your filter supplier on the amount off loss you need to account for.

The better way to handle the requirements for introducing fresh air into the building is by applying dedicated make-up air units that can be staged or controlled to match your variable exhaust requirements. For large industrial areas the best way to control make-up air requirements is by applying industrial air-rotation unit(s) with variable inlet dampers controlled by closed-loop space pressure controls. Titan Aire out of Osseo, WI is an excellent manufacturer of this type of equipment. Weather-Rite out of Minneapolis, MN is another resource. Both companies likely have a manufacturers representative in your area. Where are you located?

You definitely should consider adding a mechanical means to control your make-up air requirements rather than relying on uncontrolled ventilation. Chances are you are pulling air through every crack and crevis in your building, which can result in a very dirty environment with very poor temperature control. Not to mention bent doors and other negative results.

I use to be a rep. for industrial HVAC equipment, I have experienced many sick buildings as you described. ASHRAE has guidelines that engineers follow to determine proper sizing of ventilation equipment. Go to www.ashrae.org if you're not familiar with the organization.

Good luck.

Normally the underpressure in such room should never be lower the -10 mbar, i.e. 0.15 psi. This underpressure creates already a force of about 210 kg, i.e. 463 lbf on the surface of the door.

So, first reduce the pressure difference and than take other measures.

<,but I would like to get some idea of the calculated values should be on solving this isue>

You need 1 hour professional consultancy with some University Researcher deeply into Tornados' sucking/uprooting dynamics and force quantification.

A door that will not open (with fans on) is a significant hazard. I would suggest a redesign of the entrance/exit before proceeding to size the airflows.

The door should be designed not to open when the fans are on. Most units are built this way. You really don't want to be in that room when all four fans are running. It is a safety issue. You are really walking into a wind tunnel. So I wouldn't do anything about making it easy to open the door under those conditions. You really don't need to be in that room with all of the fans running anyways. You have to shut all the fans down to replace the filters and if you have to do any maintenance on the fans the safest thing to do is shut them all down.

A Manometer would be a good thing to add it will tell you when you need to replace the filters as well as if there is any danger from the room being to negative.

It is not likely that you can get adjustable sheaves on a 35,000 cfm fan. Depending on the type of fan it could have a 40 to 50 HP motor on it. The easiest way is to add a VFD. A VFD would also allow you to bring one fan on full speed and ramp up the other as needed.

But I would only do this after you increase the size of your intake or change your filter bank. If you have a straight filter bank you might be able to change to a V-bank. This will increase your filter area while allowing you to keep the same intake opening size. The problem is that a V bank takes up a lot more room in your fan room, so if space is an issue then that may not work. Changing to a different type of filter as you will still need to not exceed 500 fpm.

Talk you your local Sheetmetal company, thats who I work for so of course thats who I would suggest. They can do what ever work you need give you recommendations as for ways to fix the problem. I would also get a Test and Balancing company to come out and take pressure and air flow readings, then you will know exactly what is happening.

Good luck,

Here is some information that might be useful.

Fan manufacturers/distributors typically can supply charts or graphs for performance of the specific fans you purchased. These relate some or all of the attributes: flow(CFM), power consumed, differential pressure across the fan, fan speed etc. This information helps you see how the fan is operating in your application. Typically as the differential pressure goes up the CFM goes down (all else being equal).

A manometer is certainly an inexpensive way to measure the differential pressure. If you are not familiar with how to use one, another option is a differential pressure gage. These are very common and inexpensive. You do need one in the right range and the above comments help you with the range. You may already have one in your plant you could temporarily borrow from a non-running dust collector. These types of gages are used to measure the differential pressure across the filter media. These gages have two tubes, one that goes to each side of whatever you want to know the pressure difference across. Such as the inside and outside of the room or before and after each fan.

This is totally not my field, but maybe figure out how to equalize the pressure so the door can be opened with the fans on. And then create an interlock that will shut off the fans when the door is opened. We use interlocks all the time at transmitter sites for the safety of personel, equipment and the building.

Sir:

Obviously your interests, as stated, are to preclude a maximum temp. in the area of the "controls".

Why not separately fan exhaust that specific control area with a separated inlet air for that cabinet/room.

Or supply some refrigerated air to off set the heat gain in control area, sized for that max load?

MR. GUY

At our paper mill we use the LOTO and try method before anyone would be allowed to enter a fan room or anywhere one might be exposed to hazardous energy or motion. Each person that is to work on the equipment has to witness the equipment lock out as written on the procedure for that pc. of equipment. Then after all locks are in place the key is placed into a lock box the remote switches are tried to prove no energy and everyone then puts their personal locks and ID tags on the box. This way no one can start the equipment with personnel in harms way. Most of these areas have locking doors that only the area owners have a key too as well. We have allot of switch gear and MC rooms and all of them has some sort of AC and/or air quality filters on it. I have never seen one with strong enough suction to collapse a door though. It sounds like a poor design as well as really dirty filters.

pipewelder

I haven't had much exp. with fans but a Lil with blowers and vacuum pumps. With vacuum .. .and it sounds like this is whats happening .... we would run the pumps at full volume to be the most effective and its easier. Then to adjust the vacuum were it was needed we would open a valve allowing air into the system. Since ambient pressure is constant and consistent (well mostly.... ok ,ok not really but close enough) it would balance the system were we wanted it. This could be applied to your fan room as well. I believe MARENG suggested a gate or valve in the door. Maybe a Lil twist on that. Try coring the door make IT a new filter bay. Put some louvers or some kind of sliding shutters to control airflow. However I would strongly caution going into this room with the fans running unless there are strong barriers between the fans themselves and you. Also opening the door while the fan is running will give the air a path of less Resistance and a rapid influx may just suck you in.... equalize first, enter second.

my personal opinion is that whoever designed this system(s) did not pay full attention to what he was doing!

Why should these fans be allowed to affect the air pressure in this room to such a degree? It sounds very dangerous to me......

Re-design asap is my tip.

1) NEVER ALLOW ANYONE INTO THAT ROOM WITH THE FANS RUNNING! ESPECIALLY IF THEY CAN GET SUCKED INTO OR REACH INTO THE MOVING FANS!!!!

2) The door being sucked in is a very bad situation. Is there any was possible for you to add a new/second inlet opening? Perhaps controlled by a damper of some kind. When both big fans come on, open the damper either by electrically controlled means, or use a gravity closed damper. If it's gravity closed, make sure the weight is small enough to allow opening before the door starts to get pulled in.

3) If both small fans and one large fan is turned on, you have already exceeded the flow rate of the current inlet. 78,000cfm vs. 75,000cfm; you might want the second inlet after all.

Its a total design failure by someone or the company that assembled it (or both!) did not have a clue on how to work correctly....

The fixes you propose, though extremely well meant, cannot fix the fundamental problems.....they are as a Band Aid on a broken leg.......sorry.

....and such a door with such problems behind it, could break more than a leg!!!

Perhaps Langert was the designer.

I would like to thank everyone for the feedback

I am studying all the comments and will be doing some redesign soon and will let you know the outcome

Again thanks for the comments as they were all very helpful in thinking this problem through for a solution

As previously noted I am not a Mechanical Engr by trade and I was not at this physical location nor involved with its design when it was designed and built 10 yeara ago

was not attempting to suggest you were. Apologies if it so seemed. Was rather attempting to make a point re: beating people up for making mistakes. Albeit this does seem quite a doozy.

cr3