As most are aware by now ASHRAE Guideline 0 - 2005 states that "the Commissioning Process is a quality-oriented process for achieving, verifying, and documenting that the performance of the facilities, systems, and assemblies meets defined objectives and criteria". After 20 years of providing this service, it is appropriate to look back and identify some of the most beneficial lessons we have learned that can help building designers, owners and operators.

Over the years we have found numerous issues such as missing return air ducts, missing supply and return air duct insulation, misapplied diffusers, misapplied terminal units, and system effect issues. While these are not all that unusual, there have been issues found that have a significant impact on performance and energy consumption.

This paper will identify issues found during the commissioning process that were energy significant, comfort compromising, and most importantly re-occurring. It will also provide resolutions of the issues and the resulting benefits. Many of these issues were found on projects where the commissioning provider was not engaged until construction was almost complete or on retro-commissioning projects. Issues found in these cases are typically profound. Examples include: improper control of return air fans and building pressure; improper use of VAV plenum return air systems; improper designed or installed ducted return air systems; improper cooling coil piping connections; questionable strategies for controlling discharge air pressure in VAV systems; inadequate control of chilled water flow in primary / secondary pumping systems of large campus systems; and improper training of O&M staff.