Theoretically estimation of heat ingress/egress in a building is simple, but practically a bit complex & always challenging to the design engineer. Overlooking or fail to notice at designing stage, equipment/component selection, sizing air & hydronic distribution the system is doomed to be at poor performance. The optimal designing of HVAC systems is decided to minimize the energy consumption, determination of operation pattern, selection of plant & equipment's and primary energy consumption are the key factors to optimize HVAC performance.