Help on electromagnetic door holder

[Wsyzxxn]

Hi everybody,

I am a junior engineer seeking the advice of more experienced professionals on this forum. We have a fire door that will be kept open using an electromagnetic door holder during normal times and it will let go of the door when the fire alarm is activated.

Would a floor mounted or wall surface mounted door be better for this application? I read that the electronagnetic door holder should be fitted in the same horizontal plane or as close as practicable to the door closer to avoid inflicting twisting forces on the door leaf. In this case, would a wall mounted door holder be better?

Secondly, would a door holding force of 280N be sufficient for a 0.9m x 2.2m fire door? I imagine the calculation for door opening force would be different from calculating door holding force? I also thought of torque, but the holding force is in N instead of Nm.

Hope someone can give me some insight!

Thank you!

 

[BrianPetersen]

Go take a look at an existing installation.
Measure how much force it takes to hold the door. Or calculate it. Is wind a consideration? And of course, look at applicable building and fire codes that may dictate your course of action.

 

[Wsyzxxn]

Thanks for your response! Is there a way to calculate the force? I can only think of the torque. But door holders give holding force in N instead of Nm, which is why I'm a little confused

 

[IRstuff]

Secondly, would a door holding force of 280N be sufficient for a 0.9m x 2.2m fire door?

Again, visit some existing installations, such as large hotels. Fire doors are required to be automatically closing when released, which means there is some sort of return mechanism that the magnets are resisting. Your torque question is meaningless without knowing how the door is installed with its return mechanism. Only then can you determine whether you have sufficient holding force.

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[onatirec]

Torque is force x distance. It takes a certain amount of torque (at the hinges) to open a given door in given conditions. It takes a different amount of force if pushing at the handle vs pushing near the hinges - but the torque is the same.

 

[MacGyverS2000]

I highly doubt the (very slight) twisting force applied by a floor-/ceiling-mounted holding latch would have any measurable effect on a fire-rated door. You're holding the door open with the latches, not pulling it open.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[IRstuff]

see below; magnetic holder and hydraulic door return mechanism on the jamb side of the door; that's what the magnetic holder is resisting, the hydraulic return mechanism.

TTFN (ta ta for now)
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[SwinnyGG]

Even if you were pulling the door open- 280N FAR exceeds the opening force limit required by code for a manually operated fire door.

Don't overthink it- 280N is fine. As long as all of your hardware has been approved by your AHJ (which if you've already received your permit for the fire alarm system, it has been; door hold opens are a fire alarm device, which means they are listed on the fire alarm drawings). If you don't have your fire alarm permit yet, call your AHJ and ask them if the hold open model you are using is an approved device.

Door hold opens for fire doors are single purpose devices, it is reasonable to expect that they AHJ will approve whatever you've chosen without issue- it is difficult to find a hold open for purchase in the US that ISN'T approved.

You hold open should be at the same AFF elevation as whatever door closer is in place; if it's a standard header-mounted hydraulic closer, then the hold open goes at the top of the door. If it's a spring hinge (which would typically be installed in the center of the door leaf roughly 42" AFF) then the hold open should go at the elevation of the center line of that hinge. Ultimately what you want is that if you draw a line between the points on the door where the hold open and door closer apply force to the door leaf, that line needs to be parallel to the floor.

I highly doubt the (very slight) twisting force applied by a floor-/ceiling-mounted holding latch would have any measurable effect on a fire-rated door. You're holding the door open with the latches, not pulling it open.

It depends. If it's a fire rated hollow metal door, it would probably be fine- if it's a fire rated wood door, the 10 or 15 lbs of force continuously applied to the door over the long term (doors like this are almost always held open continuously, 24-7-365, until the fire alarm goes off) can twist the leaf. Fire rated wood doors are typically just veneer and blocking with fire rated fill; they are not super robust mechanically. It can also cause problems with the hinges; door hinges are not precision devices.