As part of my lease agreement with the building owner, I'm responsible for repairs. The HVAC had to be replaced July 2016 and I don't know how to depreciate it. At one point this appears to qualify for Special Depreciation, but now it's not clear how to approach it.
Click here for IRS publication 946 Figuring Depreciation Under MACRS.
If the replacing the HVAC system is a Qualified Leasehold Improvement (which according to IRS publication 946 it appears that it is), you capitalize it over 39 years. However, you can elect section 179 which allows you to write-off as an expense in the current year, subject to some limitations.