[Equest-users] VRV with Variable Exhaust

[Tim Johnson]

Paul,

The BSUG VRV methodology seemed to work fairly smoothly.  I never did figure how to make the VRV cassette fans cycle.  What I ended up doing was running the cassettes at constant volume during scheduled periods with variable volume outside air and exhaust on a separate schedules.  I put all VRV fan energy into the heating or cooling efficiency, and setting my VRV fan power to 0 kw/cfm.  I scheduled all of my exhaust air as ventilation air from the makeup air unit so I could use the heat recovery.  The scheduling became fairly complicated as some hoods are two position with some having a minimum and others not and still others being variable volume. 

I realize this solution isn't exactly right in some spaces as my airflows are incorrect when no heating or cooling is required from the VRV system, but it was the closest approximation I could come up with.  I would love to hear from anyone else who has attempted this type of system or anyone who might see additional issues with my workaround.  

Paul, be sure to let me know how your model turns out.  I am interested to see how you deal with the systems.
 
Thanks,
Tim

Tim Johnson
Mechanical EIT, LEED-AP  
DIRECT: 208.577.5645 
FAX: 208.343-3531





CTA, INC  |  WWW.CTAGROUP.COM
AN INTEGRATED DESIGN FIRM
1185 W GROVE ST – BOISE, ID 83702
 


>>> Paul Diglio <paul.diglio at sbcglobal.net> 7/29/2010 12:59 PM >>>

Tim:

I am working on a identical renovation project, with the exception that I also have hot water baseboards in the Lab areas.  How did you make out with the BSUG VRV modeling methodology?  I looked it over, but have not dived into it yet.

Did you ever work out how to cycle the VRV cassette fans separately from the MAU fan?  I am using discharge temperature reset on my MAU, it has a steam preheat, reheat and a DX coil.

Thank you,

Paul Diglio, CEM

--- On Tue, 7/20/10, Tim Johnson <timj at ctagroup.com> wrote:


From: Tim Johnson <timj at ctagroup.com>
Subject: [Equest-users] VRV with Variable Exhaust
To: equest-users at lists.onebuilding.org
Date: Tuesday, July 20, 2010, 3:15 PM


I am attempting to model a university laboratory building that has a VRV system being used in combination with a variable volume exhaust and makeup air systems controlled by pressure independent valves.  We are doing heat recovery on the exhaust air, so from the archives, I see that the only way to account for that is to specify the exhaust flow as supply air from the makeup air unit that is 100% outside air.  Equest will then balance the supply and exhaust.  This way I can set my schedules to reflect the usage of the spaces and will account for the variable volume exhaust and makeup air.  
The issue becomes the VRV system.  Ideally, the makeup air unit would run separately providing tempered outside air for ventilation and exhaust hoods and the VRV fan coils would cycle on to meet the heating or cooling load.  I am using the VRV modeling methodology discussed at the Oregon BSUG.  Is there a way to get my VRV fans to cycle separately from the exhaust and ventilation systems?
Thanks for the help,
Tim

Tim Johnson
Mechanical EIT, LEED-AP  
DIRECT: 208.577.5645 
FAX: 208.343-3531





CTA, INC  |  WWW.CTAGROUP.COM
AN INTEGRATED DESIGN FIRM
1185 W GROVE ST – BOISE , ID 83702


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