VAV system ventilation - IMC or ASHRAE 62? 2

[dub112]

I have been given the task to create a company standard for how we deal with ventilation for multi-zone spaces. From what i understand acceptance of ASHRAE 62.1-2004 differs with each local municipality, so i'm not sure i want to base it on that. IMC 2006 is the more stringent of the two, correct? Would the method described in IMC 2006 - 403.3.2 be acceptable as a baseline for all VAV systems, or does that apply only to constant volume systems? Any suggestions as to how you all handle minimum OA and minimum VAV position would be appreciated. Btw i have fairly little experience as an engineer (graduated 2006) so if this seems obvious i apologize.

 

[AbbyNormal]

2009 IMC defers to ASHRAE 62.1

The way we build has a far greater impact on our comfort, energy consumption and IAQ, than any HVAC system we install

 

[CptHk]

dub 112,

We also have the same issue in our state, technically IMC 2003 is the current mechanical code, which has the ventilation portion based on the old ASHRAE 62-1989. However, we can ask for a variance to go to 62-2004 at the beginning of each job.

IMC 403.3.2 does not address minimum VAV positions but it has higher cfm/person requirements. One of the big differences with ASHRAE 62-2004 is that it does address VAV min position when determining minimum OA, but has lower cfm/person requirements. So in the end, for VAV systems, you'll find that the OA required is not as different as the tables would suggest for any given space.

For constant volume dedicated outdoor air systems the difference between the two procedures can be very large.

Since you're new, I'd suggest asking a senior engineer if they are aware of the differences and the implications before you set your company standard.

 

[mauricestoker]

I would also recommend looking at ASHRAE 90.1-2004 if addressing standard details for VAV systems.

 

[tys90]

We developed a spreadsheet for 62.1-2004 but we use TRACE700 62.1 calcs a lot now since they have fully incorporated 62.1-2004 and have some nice outputs for verifying information.

In my opinion, looking ahead, I would base all calcs on 62.1-2004 or 2007 since IMC 2009 refers to 62.1 and a lot of states have amended IMC 2003 and 2006 to include 62.1 in lieu of the mechanical code ventilation tables. In the case that someone questions the use of 62.1 it would be very hard to argue that you should not be using it.

 

[mauricestoker]

Definitely agree, tsy90. I've run into a lot of dual duct systems and OA calculation is not addressed under IMC or the 2004.