Hello,
I am currently trying to calculated Ds for the cooling condition for a project I an working on. Initially, I had the Ds value for each dual fan duct duct VAV unit set to 100%, but I was told by a colleague to change the value of Ds to be Ds = the minimum cooling flowrate of VAV/ the maximum cooling flowrate (Vdzd) of VAV.
For example a room in the building has a max supply cfm of 210 and a minimum supply cfm of 63. Should Ds then be: Ds=63/210 = 30%? Or should I leave Ds as 100%?
When I switched Ds from 100% to the equation I got the critical zone needs more ventialation error message.
Omar Elrawy
Green Building Consultant | ResearcherGreenA Consultants
55 thumbs up
November 5, 2015 - 8:42 am
A direct answer to your question is: set Ds = minimum flow (30%).
I had a technical advice by the reviewer before to perform the calculations at the worst-case conditions, which was (in my case) to set most VAVs at Ds of 30%, and few VAVs that where designed with Ds of 40% (and I justified that by a narrative).
Also the worst-case case is generally during heating mode, for me, I like to check both; heating and cooling modes.