This is a Design Guide developed under ESTCP project, “Technology Transfer of Recently Completed ESTCP Project on Converting Multizone (MZ) Air Handlers from Constant Volume (MZ-CV) to Energy Efficient Variable Volume (MZ-VV) Systems.” This retrofit converts an existing constant volume multizone HVAC system (MZ–CV) to a variable volume (MZ–VV) system for increased energy efficiency. This suite of design and implementation support tools steps a potential user through technology evaluation, procurement, and performance verification.