[Trace-users] Ventilation Rate

Julia Beabout juliabeabout at yahoo.com
Tue Apr 6 08:05:53 PDT 2010

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.

From: "Wilson, Luke" <LWilson at integral-group.net>
To: Craig Gann <cjg04austin at swbell.net>
Cc: "trace-users at lists.onebuilding.org" <trace-users at lists.onebuilding.org>
Sent: Tue, April 6, 2010 7:45:47 AM
Subject: Re: [Trace-users] Ventilation Rate

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.
From:Craig Gann [mailto:cjg04austin at swbell.net] 
Sent: Monday, April 05, 2010 4:48 PM
To: Wilson, Luke
Cc: Scott Parker; trace-users at lists.onebuilding.org
Subject: Re: [Trace-users] Ventilation Rate
To expand on the discussion..... minimum ventilation rates at the space (room) level are defined by ASHRAE 62, however the design quantity of ventilation air (cfm) introduced into the system must be the same for both proposed and baseline designs. How that ventilation air is controlled at off-peak conditions (such as with DCV, etc) is where the potential energy savings are for the proposed design. In other words both designs must introduce the same ventilation cfm at the design condition. The design ventilation quantity is to be calculated per the ASHRAE 62.1 version applicable to the particular LEED version you are using.


Craig J. Gann, P.E.; LEED AP

On 4/5/2010 3:27 PM, Wilson, Luke wrote: 
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?
From:Scott Parker [mailto:sparker at aeieng.com] 
Sent: Monday, April 05, 2010 4:25 PM
To: Wilson, Luke
Subject: RE: Ventilation Rate
You will have the same outside air per person or per area rate in the templates when you create a new alternate based on the Alternative 1.  If your system type changes so that you have a more efficient introduction of outside air, and thereby reduce the total outside air required, then this is a legitimate savings.  However, you must have the same outside air rates per person or per area (e.g. in a lab if you have a minimum of 6 ACH, once-thru, then you cannot show savings for going down to 4 ACH in the proposed design – I think this is what 90.1 wants to avoid).  
From:trace-users-bounces at lists.onebuilding.org [mailto:trace-users-bounces at lists.onebuilding.org] On Behalf Of Wilson, Luke
Sent: Monday, April 05, 2010 4:03 PM
To: trace-users at lists.onebuilding.org
Subject: [Trace-users] Ventilation Rate
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.
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