Barometric relief ducts

[Sifu]

Seeing a new thing that doesn't make much sense to my simple mind. Mechanical system has "barometric relief ducts" to the outside. Basically a register inside the room to convey conditioned air to the outside at the eaves. Not on the original plan, I requested a revision to the mech. plans as well as revised comcheck. I got a revision to the mech plans with no mention of how it impacts the energy efficiency. I am told by the contractor they have been added to the system because they are supplying more than they are returning to the rooms, and that they will dump the excess supply outside. Anybody seen anything like this? I don't understand how this could possibly be energy efficient. If it matters, type V, B occ., private daycare/learning facility.

 

[Msradell]

I've seen barometric relief dampers before but I've never seen them dump to the outside. Most times I've seen that they just dump back into the return side of the system. It seems like dumping outside would certainly screw up the energy efficiency of the facility

 

[tmurray]

Seeing a new thing that doesn't make much sense to my simple mind. Mechanical system has "barometric relief ducts" to the outside. Basically a register inside the room to convey conditioned air to the outside at the eaves. Not on the original plan, I requested a revision to the mech. plans as well as revised comcheck. I got a revision to the mech plans with no mention of how it impacts the energy efficiency. I am told by the contractor they have been added to the system because they are supplying more than they are returning to the rooms, and that they will dump the excess supply outside. Anybody seen anything like this? I don't understand how this could possibly be energy efficient. If it matters, type V, B occ., private daycare/learning facility.

Is the return air piped or are they using the corridor as a return plenum? The only reason I can think of that this might make sense is if they are using the corridor as a return plenum and having the barometric relief ducts dump into the corridor reduces the negative pressure and they don't get the proper air changes in the classrooms. Either way it is incredibly inefficient.

 

[Sifu]

No, the return is ducted. I see transfer air all the time to return air to another space like you describe, but this is a 12" duct from the ceiling directly to the eaves and outside. Multiple locations, one or more in every room. A real head scratcher.

 

[Msradell]

Just wondering what state is this in? It certainly going to hurt energy efficiency in any place in a nation but some places could be much worse than others. The facility also has fresh air intake from the exterior to any significant degree?

 

[Sifu]

CO which can have extreme temperatures in any season but not much humidity. And yes, several make-up ducts. Each room has its own direct vent furnace and a/c unit.

 

[north star]

$ ~ $ ~ $



Sifu,

Were the Original or the Revised Plans stamped & signed by an RDP ?

It sounds like it is time to bring in an independent RDP to render an

opinion........Something different from what the Contractor is telling

you........The install doesn't sound kosher.........Nevermind the energy

efficiency, ...it is costing the owner money to be supplying conditioned

air to the exterior.

I do not know what codes or Standards you are using.



From the `12 IMC, Section 104.3: - Inspections:

The code official shall make all of the required inspections, or

shall accept reports of inspection by approved agencies or individuals.

All reports of such inspections shall be in writing and be certified

by a responsible officer of such approved agency or by the

responsible individual............The code official is authorized to

engage such expert opinion as deemed necessary to report upon

unusual technical issues that arise, subject to the approval of

the appointing authority."



$ ~ $ ~ $

 

[cda]

Some one asked which state?

type V, B occ., private daycare/learning facility

Not an E?

"""several make-up ducts.""" Each room has its own direct vent furnace and a/c unit???

 

[north star]

% ~ %

" Some one asked which state? "

" CO which can have extreme temperatures in any season but not much humidity. And yes, severalmake-up ducts. Each room has its own direct vent furnace and a/c unit. "

CO = Colorado % ~ %

 

[cda]

That place

Maybe they are installing the exhaust certain smoking by products, that are particular to that State??

 

[north star]

& : & : &

" That placeMaybe they are installing the exhaust certain smoking by products, that are particular to that State?? "

That too would be a waste of consumption by-product, ...the THC laden smoke.Even the pot smokers need to get their full money's worth, instead of having

it discharge to the Great Colorado outdoors. ! :mrgreen:

& : &

 

[Sifu]

Correction, thanks CDA, E occupancy, 10,000sf. still no resolution..................

 

[steveray]

Which energy code?

 

[Paul Sweet]

I think these used to be fairly common in schools. A certain amount of fresh air needs to be provided, and an equal amount exhausted. The main problem is that it is uncontrolled, and negative pressure from the wind can draw a lot more air out than should be exhausted. A strong enough wind can overcome the balancing weight in the damper and blow unconditioned air in.

 

[Sifu]

2009 energy code would be where I have the question. How could these be accounted for within that context? Feels a bit silly to air seal, insulate and condition a space with giant 12" ducts dedicated to dumping all the conditioned air outside.

 

[steveray]

502.4.5 Outdoor air intakes and exhaust openings. Stair and elevator shaft vents and other outdoor air intakes and exhaust openings integral to the building envelope shall be equipped with not less than a Class I motorized, leakage-rated damper with a maximum leakage rate of 4 cfm per square foot (6.8 L/s · C m2) at 1.0 inch water gauge (w.g.) (1250 Pa) when tested in accordance with AMCA 500D.

Exception: Gravity (nonmotorized) dampers are permitted to be used in buildings less than three stories in height above grade.

503.3.1 Economizers. Supply air economizers shall be provided on each cooling system as shown in Table 503.3.1(1).

Economizers shall be capable of providing 100-percent outdoor air, even if additional mechanical cooling is required to meet the cooling load of the building. Systems shall provide a means to relieve excess outdoor air during economizer operation to prevent overpressurizing the building. The relief air outlet shall be located to avoid recirculation into the building. Where a single room or space is supplied by multiple air systems, the aggregate capacity of those systems shall be used in applying this requirement.

 

[north star]

@ ~ @



Sifu,

Section 503.2.2, `09 IECC, requires the HVAC system to be balanced

and to provide calculations to show that balance.......There should

be no "excess", or if there is, ...it should be very minimal.

From Section 502.4.5 - Outdoor air intakes and exhaust openings:

"Stair and elevator shaft vents and other outdoor air intakes and exhaust

openings integral to the building envelope shall be equipped with not less

than a Class I motorized, leakage-rated damper with a maximum leakage

rate of 4 cfm per square foot (6.8 L/s · C m2) at 1.0 inch water gauge

(w.g.) (1250 Pa) when tested in accordance with AMCA 500D."



Also, IMO, the barometric damper is not integral to the building envelope.

Without more in-depth information and a clearer explanation from seeing

the designed plans, ...it sounds like a shortcut has been installed.

**steveray** was quicker with his code reference ! :grin:

@ ~ @

 

[jeffc]

I think Steveray has the answer. He mentioned, "Economizers shall be capable of providing 100-percent outdoor air, even if additional mechanical cooling is required to meet the cooling load of the building. Systems shall provide a means to relieve excess outdoor air during economizer operation to prevent over pressurizing the building." If you are getting "free cooling" with an economizer (bringing in outside air for cooling), you are pressurizing the building and all that excess air needs to go somewhere. Without the barometric damper, you could potentially be pushing this air into the exterior stud cavities causing condensation.

 

[Sifu]

Ok, a little help. What economizer? The rooms are each conditioned with their own furnace and split a/c with air handler in attic and condenser outside. The furnaces receive all combustion air from outside. Make up air is provided. I guess I still don't understand the need to dump all that air back outside. The again I also have trouble with making a house so tight you have to cut holes in it. Seems an awful wasteful way to balance a system. BTW, contractor told me today the total btu for building is 1,500,000.

 

[cda]

How many rooms are there?

 

[north star]

& & &



Sifu,

Are there designed plans for this project ?.......If

so, ...were they stamped & signed by an RDP ?

The Mechanical Plans should show all equipment,

ducting, all systems "designed" for this project,

heating & cooling loads, BTU's, etc.



& & &

 

[Sifu]

A quick look at the approved plans show 10 classrooms, each fed by 1 of the 12 +/- 100,000 btu furnaces and 13 seer split system ac. I checked a few of the rooms, the supply is 25 to 40% greater than the return, and each unit has a makeup air duct which I assume is to make up the difference between the supply and return. The original plan did not have the relief ducts but I found them on my rough inspection and requested a revision. The revision only mentions them in a note and by a line within the room indicating approximate location. The loads indicated in the table for the rooms do not appear to have any correlation to the relief ducts. Still at a loss, maybe I'll get answers from the architect........maybe not.

 

[Paul Sweet]

A 30 student classroom would require at least 400 CFM of fresh air (IMC Table 403.3). An equal amount needs to be exhausted (dumped back outside). Most buildings with central systems use an exhaust fan in the central air handler to dump the air back outside. The barometric relief is a simpler way to do that. I just hope the fresh air intake has a motorized damper to close it when the building is unoccupied.

 

[Sifu]

Thanks Paul. After much reading I think I now understand the mechanical side of this. And yes, it does appear this is a simpler way to accomplish the goal. Still don't understand the energy efficiency side of it but all I can find in the IECC is the requirement you mention for controlling when the building is not occupied. I do believe these are incorporated, gravity dampers per the exception. Think I will turn the page on this one.