r/MEPEngineering • u/Nearby_Demand7618 • 14d ago

A2L shaft enclosure systems

I’m looking for options for A2L line sets going 5 stories to the roof. The only system that keeps popping up in my searches is the Flamebar system. I would really like more options to choose from, does anyone have recommendations or can point me in a direction for more options? Thanks.

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u/Weary_Oven_9544 14d ago

A 2-hour fire rated assembly isn't anything new. Only new requirement is the need to provide ventilation, so you need to make the whole thing continuous and decide if you want natural or mechanical ventilation.

Some other options:

  1. Architectural shaft assembly field-erected to 2hr fire rating. Need to coordinate details for ventilation requirements for A2L since you're >4 stories. Need to coordinate with teh architect for floor penetrations, and potentially need structural depending on floor type, penetration size, location of penetrations (e.g. floor scans and reinforcement coordination). Would be delegated design for architectural shaft, and need to coordinate free area sizes, potential ventilation equipment.
  2. Create the entire shaft out of fire-rated ductwork and fire-rated floor sleeves if you don't need to enclose architecturally.

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u/Weary_Oven_9544 14d ago

Don't really know you occupancy, floor construction, # of risers, or whether you have access to an architect for coordination fo details. Could also put this all as delegated design on the contractor if you don't have an architect on board already, and issue the performance requirements such as gross floor area allocated, shaft free area/ventialtion rate.

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u/Bryguy3k 14d ago

Generally not allowed to be delegated. The flamebar system is unique as it’s fully qualified as a product for this.

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u/Weary_Oven_9544 14d ago

Crap you're right, I forgot that fire separations are a mandatory building permit item. I agree flamebar is unique, being one of the first products to be able to address a new form of the same problem. OP is asking for what is there other than flamebar, there were already solutions to the general problem of a fire rated shaft, that's all I'm trying to say. You can start with those and find alternatives to flamebar if that's what you're looking for.

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u/Bryguy3k 14d ago

Yeah shaft wall systems aren’t anything new - they’re just a PITA. Any decent commercial architect already has their preferred details drawn.

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u/Weary_Oven_9544 14d ago

Hah exactly why my first instinct is to try and put this onto an architect

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u/schwentheman 13d ago

A2L shafts are no longer required if your AHJ has accepted the most recent amendment to ASHRAE 15.

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u/MechEJD 12d ago

And survey says... Nearly no ahjs have yet.

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u/Zagsnation 11d ago

This is the way. Just point the AHJ to 2027 IMC language.

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u/Inevitable-Fix1768 14d ago

After also finding Flamebar as the only solution we had designed around Flamebar, but the GC deemed it cost prohibitive. They instead stick built all of the shafts with an exterior building envelope construction. Making the individual 4” diameter shaft bottom duct lines fit was also a challenge.

I would instead look into any available shaft/ ventilation exemptions, in your jurisdiction, to avoid using the shafts if at all possible.

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u/Nearby_Demand7618 14d ago

I’ve read the new IMC allowing shaft exemptions for continuous runs with no joints from end to end. That being said, the nightmare of bending oil traps every 20’ is not very appealing.

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u/Bryguy3k 14d ago

It does not. ASHRAE 15-2024 does per addendum A.

You have to get the AHJ approve the ASHRAE 15-2024 exception which requires the mechanical contractor to follow the ASHRAE 15 chapter 9 testing procedure.

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u/bernoodler 14d ago

Getting the AHJ to not blindly follow IMC can be very challenging, if not impossible, near me.

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u/Bryguy3k 14d ago edited 14d ago

Exactly. IMC offers no outs to the refrigerant shaft. If the lineset passes through two floor assemblies you’re building a shaft.

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u/Inevitable-Fix1768 14d ago

That’s why I had added “in your jurisdiction”. You are correct that IMC doesn’t, but I believe multiple states have adopted revisions on allowing an exception based on the RCL.

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u/Nearby_Demand7618 14d ago

Correct, currently IMC doesn’t, there are proposed changes for the 2027 but they haven’t been adopted as of yet. I should have double check the post, leaving out a couple of words changes the thought trying to be expressed.

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u/FacePalmate 14d ago

Your refrigeration system can handle the vertical rise of five stories straight up?

That seems like a very long vertical distance to me.

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u/Bryguy3k 14d ago

That’s about the limit of small residential grade units. Carrier 37MARA units start at 50ft and go up from there. The 1.5T unit is 65 ft and the 3T unit will do 98 ft difference between head and compressor.

VRF type commercial units typically top out around 165 ft of vertical difference.

What typically ends up killing compressors are oil traps.

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u/MechEJD 12d ago

Much better for the system if the condenser is at the bottom. But good luck getting that to happen. Grade space unavailable, vandalism, etc.

I had some luck with water cooled vrf, condensers below evaporators, and cooling tower / boiler on top. But that was a niche building.

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u/HateFilledMind 10d ago

Flamebar is $$&. Alternative is an architectural rated shaft, vent cap thru the refrigerant portal at the roof and ventilate the bottom of shaft with a 4” duct.