We are currently working on a LEED project whose Baseline Building will have an HVAC system 5 installed. Taking into account that section G3.1.1 of ASHRAE 91.1-2007 states that “for systems 5, 6, 7, and 8, each floor shall be modeled with separate HVAC system” we have modeled the system accordingly.
For each floor we have divisions with different ratios of outdoor air intake and to respect those ratios we need to set the system to operate for the critical division. Taking into account that there are divisions with 100% of outdoor air in almost every floor, then almost every systems are being modeled for 100% of outdoor air, which is causing a great increase in the heat consumption.
The problem is that by doing the aforementioned, the outdoor air intake of the Baseline will not be the same as the Proposed, but, if we do not proceed like above mentioned (i.e., if we set the system for the minimum outdoor air intake) we’ll not be ensuring that every division has the outdoor air intake that it’s supposed to have.
In your opinion what should we do to solve this problem?
Thank you.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5869 thumbs up
November 12, 2012 - 9:46 am
The OA must be identical in total in both models (unless there is DCV in the Proposed and not the Baseline). Hard to tell how you fix the problem without knowing more about how you are modeling it. You should be entering the amount of OA and not having the software calculate it. Also keep in mind that the Baseline systems do not actually have to function from a design perspective, just from an energy perspective.