The LEED Reference Guide only addresses the increased ventilation calculation at the zone level, not the system level. I understand that the outdoor air supplied to each zone needs to be increased by 30% to obtain this credit. I found a way to do this on the 62MZ spreadsheet. What about at the system level? Vot (the amount of air the system needs to suppy, i.e. the corrected outdoor air) cannot simply be increased by 30%. It is dependent on Ev, which is dependent on the critical zone. I am finding that when I increase the outdoor air to each zone by 30%, the system outdoor air (Vot) increases by much more, as much as 55%. I am getting some units with very high outdoor air percentages. I can increase the supply air to the critical room, which increases Ev and therefore decreases Vot. But it seems arbitrary, and I am not convinced this is the correct approach. Has anyone had any experience with this?
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Tristan Roberts
RepresentativeVermont House of Representatives
LEEDuser Expert
11474 thumbs up
March 11, 2011 - 2:14 pm
Laura, I've asked around and haven't been able to gather any thoughts on your questions here. Have you learned anything more since posting this?
Laura Long
Sr. Designer, Sustainability and Sr. AssociateNORR
27 thumbs up
March 17, 2011 - 2:30 pm
Hello Tristan, no, I did not, and in order to stay on schedule I had to make a decision and move forward with design. So what I did is increase the outdoor air to each zone by 30% (by multiplying the people and the area by 1.3), and let the system be whatever it is, even though it is higher. I felt this was the only way to make sure we meet the requirements. Thanks for asking around, anyway. If you do find any information, I would appreciate you posting so I know for future projects. Thanks!
Julia Weatherby
PresidentWeatherby Design & Co. Engineers
94 thumbs up
March 18, 2011 - 1:37 am
Hi, Laura-
I am having the same issue right now on a CI 2009 project, Increased Ventilation Credit submission. Mathematically, within the 62MZ spreadsheet, what you are saying makes sense. However, I get the impression that it is not the Intent of LEED for us to have to increase the outdoor air "requirement" in each zone by multiplying the people and areas. Rather, to me, their intent seems to be that we calculate the requirement, then increase the required amount of outdoor air by at least 30% and distribute it so that each zone gets at least 30% more "unused outdoor air" than it would have at the minimum outdoor air intake volume.
Some of the math seems to me to hinge on whether the extra 30% going to the breathing zone is now determined to be "used" and therefore is of no use to the other zones when it is recirculated. If you multiply the people and area by 1.3, then the extra air is considered used when it gets to the breathing zone of the space, and cannot be considered unvitiated when recirculated back as return air. But it doesn't seem like that is the LEED intent. For one thing, notice that the templates ask for the actual 62.1 breathing zone rates required; they don't check for the 30% factor until AFTER outdoor intake volume is calculated.
Nonetheless, I am still not sure how to calculate the outdoor intake volume provided for a specific zone, especially a non-critical zone.
I haven't submitted this yet, so I don't know what the response will be. Just letting you know my thoughts after hours of staring at spreadsheets Voz, Vot, etc.....
Julia Weatherby
PresidentWeatherby Design & Co. Engineers
94 thumbs up
May 11, 2011 - 9:58 am
Laura and Tristan-
While I'm still inclined to argue as in my March 18th reply above, I did receive comments from my LEED reviewer indicating that your approach was what he/she wants to see, Laura. Here is the reviewer's comment on my submission:
"The LEED Credit Form has been provided stating that the project has increased breathing zone outdoor air ventilation rates to all occupied spaces by at least 30% above the minimum rates required by ASHRAE Standard 62.1-2007. However, the calculation has applied the 30% increase at the system level, and not at the zone level. To correctly determine the required outdoor airflow rate (Vot), the system ventilation efficiency (Ev) must be adjusted to reflect the 30% increase in the required breathing zone outdoor airflow rate (Vbz). TECHNICAL ADVICE: Please revise the calculation to determine the value of Vot as a result of the increased Vbz. This can be determined by any of the following:
a. Increasing the people and area outdoor airflow rate
values (Rp and Ra) by 30% in the calculation.
b. Increasing the Vbz at the system level by 30% in the calculation.
c. Increasing the uncorrected outdoor
airflow rate (Vou) at the system level, and Vbz at the critical zone by 30% in the calculation."
It's not worth it to try arguing to the contrary on this project. Maybe I will try it sometime in the future. To me, one key is whether the outdoor air "requirement" actually increases 30% as opposed to the "requirement" staying the same, but just providing 30% more to each zone than it requires.