Dear All,
I am using the "Offline Calculator" option to upload the 62MZCalc on LEEDOnline.
I noticed an input box requiring a narrative:
"For projects using ASHRAE 62.1-2007, provide a narrative describing how critical zones are selected and how all occupiable zones are accounted for in the determination of the critical zone. A critical zone is defined as the zone which requires the largest fraction of outdoor air in the primary air stream."
Any idea on what should be written here? My understanding is that 62MZCalc determines the critical zones automatically and accounts for it in calculating the required Outdoor Air.
Thanks,
Omar
Kathryn West
LEED AP BD+C, O+M, Green Globes ProfessionalJLL
154 thumbs up
February 5, 2014 - 8:48 am
The principles of LEED webinar for IEQ says "Project teams should choose several ventilation zones (these are DIFFERENT from thermal zones) per system in order to accurately determine which zone is the critical zone. [...] For a 10,000 square foot office 3 zones is usually enough to sufficiently determine the potentially critical zone. The calculator itself highlights the critical zone by turning the room title purple. DO NOT enter only 1 zone, this is not sufficient to determine the critical zone. " I think there is more information in the "directions" tab of the ASHRAE calculator supplied in the "credit resources" tab of IEQp1 in LEED Online.
Aaron Dahlstrom
In Posse, LLC4 thumbs up
February 5, 2014 - 9:07 am
Does your air handler have variable zone flow? Do some zones have heating coils that reduce the zone ventilation effectiveness to 0.8?
If so, you have the discretion to set these variables in the calculation, which can affect which zone the calculator chooses as the critical zone.
On our LEED submissions we are often entering every zone into the calculator and then tweaking the zone airflows to minimum heating positions to get critical zones calculated.
Once we've completed this task, we describe that process to let the reviewer understand why it was done.
It is feasible to simplify the calculation and enter less than every zone. ASHRAE 62.1-2007 Normative Appendix A has a systematic description of why this is possible and how you might go about picking which zones to enter in to the calculator. See "Selecting Zones for Calculation" section of Appendix A. That should help you understand why a zone is critical and give you a template for a potential response to the entry field you mentioned.
Maya Karkour
EcoConsulting872 thumbs up
February 18, 2014 - 10:14 am
Kathryn & Aaron, thank you!
So I understand that if I enter ALL the zones served by my AHU in the excel sheet, I can be confident that the calculator will properly determine the critical zones and consequently the required ventilation rates?
I have 4 big AHUs in my project, each assigned to ~30-40 zones. The Engineers already inputted all the project zones into the respective sheets (4 sheets, one for each AHU).
The HVAC Engineers specified the AHUs (their supply / ventilation rates) as per the output of the ASHRAE Calculator.
Am I good to go?
Thanks!
Lawrence Lile
Chief EngineerLile Engineering, LLC
76 thumbs up
April 29, 2014 - 3:16 pm
I am trying to figure out how to handle spaces that are not in ASHRAE 62 Table 6-1. Here is an example:
First is a Janitor's closet. Occupancy is zero. the closet is 49 square feet. It has 50 CFM of exhaust, but no supply. If I am filling out the 62MZCalc, and put zero in the Vdzd rom (supply air to the zone), the calculator blows up (Outdoor air required cell has an error).
Should I: 1. omit this space from the 62MZCalc spreadsheet, as it doesn't appear in Table 6-1? 2. Set the supply air equal to the exhaust air, even if the supply air is coming under the door and not out of a diffuser?
Andrew Mitchell, P.E.
PrincipalMitchell Gulledge Engineering, Inc.
LEEDuser Expert
126 thumbs up
April 30, 2014 - 5:32 pm
You should omit the space because it is not a regularly occupied space.