ASHRAE 170.-ISOLATION ROOM-QUESTION. 1

[ml1367]

Hi,
I've a question about ASHRAE 170.(table 7-1 design Parameter).When it say:
"All room air exhausted directly to outdoor" and at the same time say "Minimum outdoor ach"..my doubt is, if they are establishing a "min outdoor ach". Dose it means that return air is allowed.
For example: Isolation room (aii)..ask for a min 2 ach o/a with 12 ach total. Is it allowed to return air from a AII Room to the AHU?...or all air must be exhausted to the outdoor?..

Thanks for the help.

 

[DRWeig]

All room air exhausted directly to outdoors.

No air from the isolation room may be returned to the AHU at all.


Good on ya,

Goober Dave

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[ml1367]

Thanks

DRWeig.

I'm 100 % agreed with you. But I'm still confused.
If all air must be exhausted, then that room have to be a 100 % fresh air...It dosen't make sense to mention the min 2 ach outdoor...
For example ..if I have a dedicated AHU serving just one isolated room...that unit has to be 100% outdoor...dosen't make sense to mention de 2 ach...am i right?

 

[DRWeig]

Hi ml1367,

You're correct if it is just one dedicated AHU serving just one isolation room. 12 air changes total, all outside air.

A setup like that seems odd. All I have ever dealt with are isolation rooms sharing an air handler with very large areas and multiple space types. The supply air isn't necessarily all outdoor air, it contains return from non-isolation areas. The 2 air changes OSA minimum applies in that case. We just don't have return air at all from the isolation rooms, only exhaust.

You might wait and see if anyone else pitches in, I may be missing something.



Good on ya,

Goober Dave

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[cry22]

First. I would say that you should reference the AIA healthcare guideline, NOT ASHRAE, ASHRAE is not a code, it should not be used for Isolation room design.
What I understand is that Isolation room high air changes can be achieved using HEPA filtered units for the room. i.e provide say 6 ACH for comfort (with built-in 2 OA ACH) from the main AHU, and Increase the ACH to 12 by installing room HEPA filtration units.
The room will still see 100% exhaust and have 12 ACH with HEPA filters.
you application is indeed unique as you only serve one room. I'd go with 100% OA/100% exhaust for your application.

 

[tys90]

cry22, I would say you need to reference the AIA guidelines yourself because the latest AIA guidelines (2010) adopted ASHRAE 170 for their ventilation code and actually include ASHRAE 170 as one of their chapters. Various other ASHRAE publications are also adopted as code many places, 90.1 and 62.1 are good examples.

ml1367, there are a few different scenarios you are describing here.

If you have a single AHU serving the isolation room, you must provide 2 air changes per hour of outdoor air from the AHU. Secondly, you must provide 12 ACH of air that is either:

a) In room HEPA filtered recirculating device (in room is the big key here, the air cannot leave the room to be filtered)
b) Outdoor air from the AHU
c) Return from somewhere else mixed at the AHU. This would be an odd situation to return air from another space to mix with your 2 ACH of outdoor air and supply it to just the isolation room but I suppose you could do it.

Thirdly, you have the requirement that the room must maintain a negative pressure and all air leaving the room to create the negative pressure must be exhausted.

In the case of option a, the exhaust rate could actually be less than 12 ACH to achieve your negative pressure but will always be greater than 2 ACH, which is the minimum supply air flow rate you need to the room if you are using a recirculating device.

 

[cry22]

TYS
Thank you, I did not know of this code change.
Looks like I need to get a new copy of AIA and 170.