Non-Predominant Spaces

First you enter Table G3.1.1A based on the square footage of the predominant condition (largest sf). You then apply any of the exceptions under G3.1.1. G3.1.1 exception A only applies for the examples cited unless you can provide some similar justification. You can apply the other exceptions if you can demonstrate that the requirements within them apply.

Exception B lists differences in thermal loads and schedules. Exception C is related to air flow issues. Sounds like either one might apply to at least part of your situation. We do have considerable experience with this situation. The reason for the exceptions is to allow secondary systems for significantly difference space types within the same building. Sounds like the office area is predominant so the baseline is a system 5 or 6. The warehouse and manufacturing area also come in at a system 5 or 6 but exception b or c would likely apply allowing a system 3 or 4 as the baseline. Another option would be to apply a system 9 or 10 from 90.1-2010 to the heated only spaces.

Hi Marcus, Would like to take this opportunity to clarify the baseline HVAC system type selection from Table G3.1.1A. A footnote from Table G3.1.1A, states "where attributes make a building eligible for more than one baseline system type, use the predominant condition to determine the system type for the entire building". I understand that nonpredominant condition applied to differential of residential/nonresidential or heating source. This mean the use of predominant condition to determine the system type for the entire building is allowed when nonpredominnant condition exists. In this case, reference to ASHRAE 90.1 2007, IF nonpredominant condition does not exist (nonresidential building and same heating source for all three space), system 7 or system 8 shall be applied for entire building, IF nonpredominant condition does exist (ie. storage warehouse and manufacturing area), office area here is predominant condition, thus apply system 5 or 6 to entire building and apply exception in G3.1.1 for storage warehouse and manutacturing area if applicable. Any suggestion?

I had been interpreting the use of exceptions under G3.1.1 like you are suggesting - "use of predominant condition to determine the system type for the entire building is allowed" even if you have spaces that qualify under one of the exceptions under G3.1.1. If you read G3.1.1 it basically says follow Table G3.1.1A except where any of the exceptions apply. So the exceptions must be applied where applicable is the correct interpretation in my opinion. Exceptions b, c, and d to G3.1.1 can also trigger nonpredominant condition in addition to exception a. So it it not just residential vs non and heating fuel type, it it also schedule, thermal loads, air flows, etc. that triggers an exception.

Marcus, My project is very similar to this one. Our predominant space is actually the manufacturing area (73,000 sqft). The office is 60,000 and the warehouse is 50,000 sqft. This would make the office and warehouse both system 3 baseline. Can you tell me if there is an official document I can refer to when submitting our project for review that backs up this interpretation of 90.1?

The Advanced Energy Modeling Guide for LEED contains a summary of this approach.