Only the first 5% to 10% of a designer's total effort on the design of an HVAC system is devoted to deciding what type of system to use. Yet, it is probably the most important decision on the entire project. This initial set of decisions establishes about 90% of the system cost and 90% of the users' satisfaction. The subsequent decisions are important, but they are just fine-tuning. The system type dictates most of the cost, and determines what performance can be achieved.