What is the proper way in HAP to get your Baseline model to use the
exact same amount of ventilation air as your proposed model when LEED
requires that HAP auto-calculate the supply CFM based on a 20 degree
rise?
Do you run the simulation once with the 20 degree rise to calculate your
supply CFM. Then switch to User-Defined Sizing mode and input the
Proposed ventilation CFM and the supply CFM that was calculated in the
first run?
Matt Scott
N.E. Fisher & Associates, Inc.
329 East Second St, 2nd Flr
Boyertown, PA 19512
e: mscott at nefisher.com
p: 610-369-3190
f: 610-369-3194
I was hoping there was a more elegant way to do it, but ok.
Just to clarify, in the "first run" of the Baseline system to size the
supply CFM, should the "ventilation sizing method" be set to ASHRAE-2007
or Sum of Spaces or does it matter? I have a feeling the calculated
supply CFM could be influenced by the ventilation calculation.
Thanks for your help. I have used the tech support extensively; just
wanted to get some feedback from other users.
Matt Scott
N.E. Fisher & Associates, Inc.
329 East Second St, 2nd Flr
Boyertown, PA 19512
e: mscott at nefisher.com
p: 610-369-3190
f: 610-369-3194
Using ASHRAE ventilation sizing will find the critical space and correct the outdoor air accordingly. The supply air affects this calculation. Sum of the spaces simply adds the outdoor air requirement for each space. I don't think the space supply air matters for this.
I use the USGBC LEED 62MZCalc excel spreadsheet and calculate the required OSA based on my proposed design. USGBC likes to see this spreadsheet, especially if I'm going for the increased ventilation credit. Then I enter the ventilation at the space level as a user defined cfm. Since the spreadsheet has already calculated the critical space, in the system I use Sum of Spaces OA airflows. When I create the Baseline system, the user-defined ventilation remains the same in the baseline space.
It's a little more work up front. The corrected OSA, as calculated by the spreadsheet, is always greater than the sum of the spaces. So the space ventilation has to be proportionally increased. But it's convenient when the baseline systems are different from the proposed system. Like when my proposed VAV air handler with 20 VAV boxes turns into 20 baseline package rooftop units.
I have one question for the Carrier techs. I understand that when calculating the space supply air, HAP will never go below the required ventilation airflow. So when a ventilation rate is entered at the system with the user-defined sizing, how does HAP make sure the space supply air is always greater than the ventilation requirement for each space?
PH MECHANICAL ENGINEERING
Reba Schaber Mechanical Engineer, P.E.
LEED Accredited Professional
1660 N. Alvernon Way Voice: (520) 731-2060
Tucson, Arizona 85712 Fax: (520) 731-2061
rschaber at phmech.com