Outside air requirement

[ssn61]

I am designing the HVAC system of a storage/warehouse in laredo, Tx, which is supposed to be kept at 70 degrees F year round. I have been told by the building contractor that there are no people in this place. Am I still supposed to implement outside air into the design to confirm with ASHRAE requirements? The second part of my question is that I have ran the load calculation using Trane Trace and not sure if the system size is large enough. This storage is 1800 sq.ft. 20' ceiling, no load except lighting, which is about total of 400 Watts. R value of walls is 19, and ceiling is 30. Load calculation result is 2.1 tons, 1164 cfm. This is about 860 sq.ft./ton, which seems a bit too high of sq.ft./ton I am used to seeing.

 

[cdxx139]

ASHRAE 62 (if that is your code requirement) still has an Area Outdoor Rate for wharehouses, so yes, you still need OA. See Table 6-1

Dont have experrience with wharehouses, but I think the sqft/ton Rule of Thumb you are used to seeing is probably for office space etc (closer to 400?, just a hunch). So without windows and OA, the ROT may climb to close to what your seeing.

Now dont forget to ad the OA


knowledge is power

 

[ssn61]

Thanks for the reply cdxx. I did some google search And found the following links. I am not sure if these are really legit or not since I ran across them online. If these douments are correct, then I believe there is no need for outside air in an unoccupied storage. From what I have been told by the builder, this space is just for purpose of storage.

http://www.ashrae.org/File Library/docLib/Public/20100203_ic_621200717.pdf

And

http://www.ashrae.org/File Library/docLib/Public/20100203_ic_621200716.pdf

 

[ssn61]

I searched the AHRAE website for the douments I posted in my previous post and they are on the website. So they appear to be legit.

 

[cdxx139]

Good one. The interpretations are legit. Questions is are they related?

The intent of 62 is safety. So if the material you store does not produce off gassing etc. And forklifts etc are not used in the space, then maybe. Again, I have never designed a wharehouse, (but have fought about the intent of 62 with LEED interpreters).

Builders want cheap, your job to design right. Send the builder an email, with the wording you describe and ask if that is what the building's intended use is, when he answers you by email, at least you have something to CYA.

knowledge is power

 

[ssn61]

Thanks again cdx. In the past I have seen engineers ask for O/A inlet to be a motorized damper, which closes shut when unit is not operating. Do you know if that is a code requirement or a design preference?

 

[cdxx139]

Not very definitive answer but maybe youll get a wharehouse-experienced engineer response as well.

My energy code (2009 IECC) requires low leakage dampers, but allows gravity dampers for buildigns less than 3 stories.

Good Luck

knowledge is power

 

[DrRTU]

I have completed numerous conditioned self storage faculties. You may not be off in the 800ft2/ton - trust your load calculations. The first few I did, I could not believe the results I got – over 1500ft2 per ton. Indoor lighting is on motion sensors and will run 0.25 w/ft2 or less. You will need to account for outside air based upon IMC or 62. Humidity and design temperature setpoint and minimum CFM/ft2 have a large impact on the loads. Here in the Midwest I have had issues with moisture in first year if it’s a precast building, condensate on outside walls in the winter due to packing stored materials tight to outside wall and smoke removal systems. Why 70F? Seems very low for a thin envelope.

 

[ChasBean1]

Do you have any exhaust? If so, the minimum make-up air you bring in should always be about 10% more than the exhaust volume...