This paper reports the design and scale-up of an active learning exercise centered around color coding of psychrometric charts. The initial version of this exercise was used with small classes of 60 students. When the class size doubled to 120 students, the previously successful exercise failed. The failure was then used as a workshop example for faculty development. Workshop participants successfully identified a number of details of planning and implementation which could be improved, and the revised exercise was once again successful in the classroom. The results are a framework for design of active learning exercises, a number of lessons learned about how to successfully implement active learning in large classes, and a highly polished 2-lecture unit on psychrometric charts, including two animated and worked examples which form part of the paper. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.