The principles of building energy simulation and its relationship with heating and cooling energy calculation help to make an integrated evaluation of building energy consumption. This is used to achieve a better and more energy efficient building. The sensitivity analysis of energy efficient HVAC design was used to create an energy efficient Peel Region Headquarters Building. An energy audit was conducted on the existing building to establish the Base Case Model "Peel Region Headquarters Building" to determine its annual energy consumption across all current usage. To reduce the total energy cost of the Base Case Model, different HVAC Systmes were investigated to analyze their energy-based performance and impact on the Greehouse Gas Emission (GHG). The sensitivity analysis was conducted using two whole building simulation programs, "Carrier HAP" and "eQUEST", with three different air systems, namely, "2-Fan Dual Duct Variable Air Volume System", "1-Fan Dual Duct Variable Air Volume System" and "1-Fan Dual Duct Variable Air Volume System with two Rooftop Packaged HVAC System'. Three different types of heat pumps, namely, Open Loop Water Source Heat Pump, Closed Loop Water Source Heat Pump, and Ground Source Heat Pump, were used to determine the efficiency and viability of the three proposed HVAC System with the existing infrastructure. RETScreen International Clean Energy Project Analysis Software (Version 4) was used to evaluate the energy production and savings, life-cycle costs, emission reductions and financial viability. MNECB/CBIP and ASHRAE 90.1 (2004) Building Compliance Program was used for determining the key elements for analyzing the building components and for providing recommendations for an energy efficient building. The improvement from the conventional HVAC System to implementation of an Open Loop Water Source Heat Pump resulted in 75% energy cost savings for the Peel Region Headquarters Building. The percentage contribution of CO₂ was reduced by 78%.