Let's say I'm doing a tenant job in an existing office building, and the tenant is served by an existing rooftop AC unit. I know that I've got to model the actual performance of that rooftop unit (along with the lights and other properties of the tenant space as it'll be built out), and get the required amount of energy savings (3% minimum, more to get points).

But I'm confused by the language in the "Bird's Eye View" above, where it says, "Ensure that any base building infrastructure that serves the project space – including envelope, HVAC, power, and lighting – meets the prescriptive requirements of ASHRAE 90.1–2010". If the existing rooftop AC unit has EER=10.5, and the min efficiency required by ASHRAE 90.1-2010 for a new unit of that size would be EER=11.0, does that mean that the client would have to replace that piece of equipment, or abandon LEED certification? My thinking is that, as long as the tenant-level energy simulation shows the required savings after accounting for the less than terrific performance of the existing equipment, the existing equipment can stay.

In fact, the language above also indicates that building envelope would have to meet Prescriptive requirements. So if the wall insulation doesn't meet those requirements, even though I'm getting the required energy savings - would the owner need to open it up and add insulation?