The MEP Analysis Extension contains 25 simple "green" HVAC (heating, ventilation, and air-conditioning) utilities for tasks like sizing duct work or piping or calculating cooling and heating loads. This application is a companion to AutoCAD MEP or Revit MEP.
Though the MEP Analysis Extension comes in 32-bit and 64-bit flavors, looking at the download numbers, 32-bit is still more popular, but 64-bit usage is significant:
32-bit downloads outnumber 64-bit almost 3 to 1 but not for long
Taking a peek at 64-bit popularity for the mechanical, electrical, and plumbing industry is alive in the lab.