[Bldg-sim] How to Model Parkade CO2 Levels forExhaust Requirements

James Hansen JHANSEN at ghtltd.com
Wed Nov 28 09:05:13 PST 2012

Be prepared to argue your case with the LEED reviewer.  On the past several projects for which I tried to take credit for CO control of garage exhaust fans, the reviewer wanted me to provide a list of newly constructed buildings in my area that had non CO-based control of parking garage ventilation systems.  They want you to prove that it is not common practice in your area.  In the DC area, almost every engineer I know is doing CO control of garage exhaust fans, so we've had to abandon this ECM for all of our LEED projects.  Would love to hear of someone arguing this point successfully, and what tactic they used! 


GHT Limited
James Hansen, P.E., LEED AP
Senior Associate
1010 N. Glebe Road, Suite 200
Arlington, VA  22201-4749
703-243-1200 (office)

703-338-5754 (cell)
703-276-1376 (fax)

www.ghtltd.com <http://www.ghtltd.com/> 


From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Fred Betz
Sent: Wednesday, November 28, 2012 10:02 AM
To: Quitadamo, Bob; Dónal O'Connor; Building SimForum
Subject: Re: [Bldg-sim] How to Model Parkade CO2 Levels forExhaust Requirements




Yes, the fans are controlled based on CO, not CO2. 


You would just create different schedules for the exhaust. The baseline is constant flow during the occupied hours plus 1 hr before and after occupancy to capture people arriving early and leaving late. ASHRAE 62.1 requires 0.75 cfm/ft2 of outside air flow. You'll have to determine what flow rate your local code requires. 


For the proposed model, create a new air flow schedule that gets you approximately 80-95% energy savings. There are several reports online that provide these ranges. Look for the ones from building owners or researchers, not manufacturers that claim 98-99% savings. The 80-95% range is based on a number of studies of these systems, as the fans spend most of their time at minimum flow, ~0.15 cfm/ft2. In general, if the building operates many hours you'll be closer to 95%, and 80% if the building operates few hours.


I like to create a profile so I capture demand charges properly rather than a flat average curve. For an office space, you'd have peaks from 7-9, a bump from 12-1 for those people going out to lunch, and another peak from 4-6 as people go home. For a hospital parking garage I just modeled, I had peaks from 11pm - 1am, 7-8am, and 4-6pm to capture shift changes. You'll have to decide what makes sense for your specific project. 


Hope that makes sense. 





P.S. CO demand control ventilation will be included in the Baseline model for ASHRAE 90.1-2010 per section Enclosed Parking Garage Ventilation. Enjoy the model savings while it lasts!



Fred Betz  PhD., LEED AP 
Sustainable Systems Analyst


5802 Research Park Blvd. | Madison, WI  53719

P: 608.236.1175 | F: 608.238.2614  
fbetz at aeieng.com <mailto:fbetz at aeieng.com>   |  www.aeieng.com <http://www.aeieng.com/>   



From: Quitadamo, Bob [mailto:bquitadamo at RDKEngineers.com] 
Sent: Tuesday, November 27, 2012 2:46 PM
To: Dónal O'Connor; Building Sim Forum
Subject: Re: [Bldg-sim] How to Model Parkade CO2 Levels for Exhaust Requirements


Hi Donal,


You'll want to control outside air off CO (not CO2) in a parking garage and be sure the controls sequence utilize the correct ppm setpoints.  Generally there is a minimum ventilation/exhaust rate to maintain even when CO levels are in check for code compliance. 


For modeling the system, a specific ventilation schedule correlating to expected usage of the car garage has worked for me in the past.  I would imagine similar schedules for this facility have been created for occupancy and lighting/plug loads.




Bob Quitadamo



From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Dónal O'Connor
Sent: Tuesday, November 27, 2012 9:55 AM
To: Building Sim Forum
Subject: [Bldg-sim] How to Model Parkade CO2 Levels for Exhaust Requirements


Dear building-sim,

I'm currently working on a LEED NC sports facility with an underground parkade for approximately 200 cars.

The parkade exhaust system (100% OA) turns on if the CO2 levels detected in the parkade exceed a particular threshold. Has anybody modeled such a system? What assumptions can be made for the CO2 profile? As it is in a northern climate, I do not want to overestimate the usage of the system which would skew the heating energy required to heat the OA to the required supply temperature.

Your help is greatly appreciated.



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