Infiltration value for cooling load calculation

[PacificSteve]

I am looking for a simple answer to a non-simple question.

My cooling load program requires an entry for CFM/SF for infiltration. Building in question is a corrugated steel siding, and visual inspection shows it to be not so tight.

0.1 CFM/SF, maybe higher?

Thanks

PacificSteve

 

[quark]

Better is to go for 50 fpm velocity multiplied by seal area between sheet to sheet.

Regards,

 

[lilliput1]

For cooling, consider eliminating infiltration by pressurizing the space. The OA for pressurization is brought in & conditioned in the AHU. Typical pressurization for office type buildings is 0.05 CFM/SF. For your building, its your call. CFM Pressurization = OA CFM brought in AHU - Total Exhaust CFM.
For heating, infiltration is considered because the air system providing the pressurization may be off. For office type building I typically use 1 cfm per linear feet of wall except I allow much more at doorways, entrances.

 

[ChasBean1]

Do you have mechanical system data, i.e., could you use total building supply minus total exhaust? I would go with that value. Of course it carries the assumption of still wind and your true answer would be some percentage higher. Corrugated steel siding? What is the composite wall? I don't know if you'd find a standard for that construction...

 

[ChrisConley]

PacificSteve,

I use the chart below for a good starting point on infiltration:

COMMERCIAL BUILDINGS
RANGE 0-1.0 CFM/FT2
TIGHT BUILDING: 0.1 CFM/ FT2
AVERAGE BULDING: 0.3 CFM/ FT2
LEAKY BUILDING: 0.6 CFM/ FT2

RANGE 0-10 ACH
1.0 ACH – 1 EXTERIOR WALL
1.5 ACH – 2 EXTERIOR WALLS
2.0 ACH – 3, 4 EXTERIOR WALLS
3.0 ACH - VESTIBULE

You can use either cfm/ft2 or air changes per hour (ACH) which ever you prefer.