I have a situation where a mechanical room (4 actually) has two SCU units and one OA inlet. The room acts as a mixing chamber for the return air and outside air but I'm being told I have to have be able to measure the OA going to each SCU individually.
Anyone run into similar situation?
Thanks
Dylan Connelly
Mechanical EngineerIntegral Group
LEEDuser Expert
472 thumbs up
September 4, 2012 - 11:32 am
Wayne,
Your situation isn't entirely uncommon on older existing systems. We've run into similar cases with mixing chambers associate with large existing units.
Unfortunately, you do need to be able to measure each SCU's outside air intake individually. If you have a common return and OA mixing chamber that both units share you're unlikely to achieve this credit without a system retrofit.
You could submit an "alternative compliance" narrative stating you are meeting the intent of the credit but have an existing system that only allows you to measure the sum of both SCU's OA quantities. I wouldn't hold out on this credit, not all projects are suitable.
Wayne Mason
Chief EngineerLincoln Property Company
September 4, 2012 - 12:31 pm
Dylan
Thanks for the reply.
I had actually meant to post this under IEQp1. Here is what we have come up with to determine quantities to meet IEQp1 so hopefully the same methodology will apply.
Outside air fraction per unit equation:
Determine the fraction at AHU-1: (AHU-1 CFM) / ((AHU-1 CFM) + (AHU-2 CFM))
For AHU-2 the fraction is the remaining percentage [1 - (Solved Fraction above)]
Once you know that, take the fraction and multiply it by the known measured Outside airflow of the mech room.
Seems pretty straight forward.