CBECC Issue - HVAC - Design Occupancy Error

joesinger12 commented 8 years ago

Version = 2013_3c_760

Category = HVAC

Issue Summary:

I’m confused why I’m getting the below error message. My occupant density is above the threshold and I have an economizer. But my system type is a Single Zone Heat Pump. I do not have DDC controls. Is there something I need to check for it to recognize that I have a single zone system? Is my associated return air plenum causing the problem? Please help!

I’m also confused about the phrasing of the error message. It says things like “if is a Multizone system” and “is likely mandatory.” How strange to put it in these conditional terms, especially since I can’t respond to the error message and let it know everything is ok.

Reported by: joesinger12

Original Ticket: cbecc-com/tickets/1509

joesinger12 commented 8 years ago

11/23 DR - I believe CO2Sensor controls are required for this case. In the user's case, they have a single-zone system with an economizer serving a space with an egress occupancy >25ppl/1000ft2. If you look at Section 120.1(c)3, this meets all the requirements and does not qualify for the exceptions.

The wording for this error is not that specific since it is the same message that would be posted for both single and multizone systems, rather than checking each individual case separately.

We could split up this error checking into the different cases so the errors are more specific, and also remove the 'likely" language

Given that there are a number of exceptions in the code for DCV, and that the model may not represent them all that well, I'd suggest considering the addition of a bypass for DCV control checks which would trigger an exceptional condition for plan review checkers to confirm. This would be similar to the mandatory efficiency check bypasses we already have. This would allow the local plan reviewer to make the call on the requirement...

11/23 JA - That’s one option. Another way to deal with this is to have a code reference and terse statement for the exception, e.g.

Space Exhaust Exception – see 120.1(c)3, Exception 2

This at least forces the user to claim a specific exception. The first exception is poorly worded in the Standards, so rather than interpret the Exception, if we list the specific code reference, we leave it to the building official, while placing a little burden on the user to claim a specific exception.