Ventilation Rate

10 posts / 0 new
Last post

Hello,
For ASHRAE 90.1 Appendix G, it requires that the proposed and baseline ventilation rates be the same. I have my proposed ventilation rate. Is there a way to input a system level Ventilation rate in Trace?
Any help would be appreciated.
Thanks,

Luke Wilson, EIT, LEED AP BD+C

Wilson, Luke's picture
Offline
Joined: 2011-09-30
Reputation: 1

Are you using the templates?

Caleb B.

PRAIRIE ENGINEERING, P.C.

mr_bulow's picture
Offline
Joined: 2010-10-07
Reputation: 1

Thank you for your response Caleb.
Yes I am using templates, but since the system types are different for my proposed and my baseline, my system level ventilation rates are different as well.
Luke

Wilson, Luke's picture
Offline
Joined: 2011-09-30
Reputation: 1

Thanks for the reply.
So the minimum ventilation rates that Appendix G is referencing is on the space level and not on the system level?
Luke

Wilson, Luke's picture
Offline
Joined: 2011-09-30
Reputation: 1

An HTML attachment was scrubbed...
URL:

Craig Gann's picture
Offline
Joined: 2011-10-01
Reputation: 1

Thanks to all for the replies. So to summarize: the system level ventilation rate should be the same in both cases, but Trace doesn't have a way to specify system level ventilation.
Thanks,
Luke

Wilson, Luke's picture
Offline
Joined: 2011-09-30
Reputation: 1

Hi Luke,

Trace does have a way of specifying (forcing) the ventilation rate at the system level. I actually use this a lot since I find that using Trace to calc the ASHRAE 62 total OA quantity can sometimes get cumbersome when you have a few rooms that need a relatively high amount of outdoor air. It's sometimes faster to manipulate things at the system level than at the room or template level.

To simulate OA at the system level: go to Create Systems....Options Tab....click on the Advanced button.....in the bottom right of that screen is where you can specify the ventilation rate at the system level where it says "System Level Ventilation Overrides". This will override any OA inputs you've put in elsewhere. You can put the OA in as a % of the total SA. That may not fit your situation exactly, but, I find that I can usually create and assign a schedule/profile to that % value that will simulate the situation I'm looking for (for example if my OA constant and doesn't actually vary with my SA etc).

I recommend checking the calculation results to make sure Trace is simulating the amount of OA you actually want at the full and part load hours. I usually find this to be an iterative process: input, calc, review results, rinse and repeat. To check the OA results, use the hourly reports: go to Calc and Review...View results button....Analysis Reports tab....Graph Profiles and Energy Button. If you are not familiar with this page it can be a little tricky to get used to but its EXTREMELY useful. To view you the calc'd OA on an hourly basis: go to the View pull down menu at the top and check "Table, Settings, and Advanced". I recommend unchecking "chart" so you can get a bigger view of the table. Via the boxes and buttons on the left side of the screen, pick the system you want to view (via the Time/Selection Section at the top...not via the more intuitive list of systems at the bottom). To see the OA cfms on an hourly basis: check Table and
Demand (uncheck consumption), select HVAC Equip in the pull down menu next to "Comps", select the Airside tab just below that, scroll down and check Vent Airflow within that tab. And,voila!....you can see the OA cfm for any given system on an hourly basis among many other things if you select them.

Good luck.
Julia

Julia Beabout's picture
Offline
Joined: 2011-10-01
Reputation: 3

Julia,
Thank you for your detailed response. This is exactly what I need.
Luke

Wilson, Luke's picture
Offline
Joined: 2011-09-30
Reputation: 1

I've asked the same question to Trane CDS. Here is their response:

According to the ECB subcommittee, the total ventilation cfm (building
level) must be the same between the two alternatives. The best (and
easiest) way to model this in TRACE is as follows. First, calculate the
proposed building. Next, using the system checksums report(s), sum the
ventilation cfm for each system to determine a building level ventilation
cfm. With this done, divide this value by the building square footage to
determine a cfm/sq ft ventilation rate. Apply this rate to all rooms on the
baseline system (this can be quickly done through templates). Do not model
ASHRAE 62.1 on the baseline building or this method will not work. I hope
this helps!

Hope this helps,

-Terry

Terrence W. Budd, P.E., CPD, LEED AP

Terry Budd's picture
Offline
Joined: 2011-09-30
Reputation: 0

Luke,

The ECB subcommittee of SSPC 90.1 has ruled on an interpretation request for G3.1.2.5 stating the total outdoor air ventilation for the proposed and baseline buildings (remember that cfm is a rate) must be the same. So, if you're modeling for LEED, have TRACE run the Standard 62.1 calculations on the proposed alternative. Next, convert the resulting total OA cfm from the proposed into cfm/sqft and enter this as cooling and heating ventilation values in each room for the Appendix G baseline alternative. Do not run the 62.1 calculations on the Appendix G baseline alternative. As long as the schedules are the same between the proposed and baseline alternatives, the hourly ventilation values will also match. It is easiest to apply the new ventilation rate within the Airflows Templates.

Scott Hintz, LEED(r) AP BD+C

Hintz, Scott F's picture
Offline
Joined: 2011-10-01
Reputation: 1