Hi there, I'm working on a project with VRF + DOAS, where outside air is injected into a common return plenum for all VRF indoor units. This means we can't measure outside air flow at each indoor unit. Would measuring outdoor air flow for each branch/plenum be enough in this case? If it isn't, then should we be pushing for major changes into OA distribution in order to guarantee the right amount of OA reaching each indoor unit? This option might not even be feasible.
Thanks
Regards,
Santiago.
Ben Stanley
Senior Sustainability ManagerWSP - Built Ecology
LEEDuser Expert
250 thumbs up
August 21, 2015 - 10:56 am
Hi Santiago,
We had a similar issue recently and it may be possible to conduct the outdoor air measurements at each branch/plenum. But I'd recommend issuing a credit interpretation request to get a project specific ruling from GBCI. They'll need to know a bit about the system configuration and your proposed solution for measuring outdoor air at the "system" level, which would be each branch/plenum in this case. Also, given your description, they'll want to know how your team plans to demonstrate that the outdoor air is distributed in the plenum in such a way that it reaches all of the VRF systems. The ASHRAE 62.1-2007 Users Manual has some information about Plenum Systems that may be helpful as well as your thinking through the right solution.
Dave Hubka
Practice Leader - SustainabilityEUA
LEEDuser Expert
530 thumbs up
August 21, 2015 - 11:25 am
We've also encountered similar type applications. We were successful in measuring the outside air at the air handling unit rather than the terminal units since the terminal units (heat pumps) were constant volume.
No guarantees, just thought I'd offer some of our team's past experience.
I'm interested in hearing the results from what GBCI requires your project to do.