An energy analysis was performed for this building 5 story, 240,000 SF office building to evaluate five different HVAC systems. The owner was preparing to make cost effective upgrades to the existing 1974 HVAC systems which included energy intensive, constant volume, dual duct air handling units. The goal of the energy analysis was to determine the system with the best first cost and energy cost balance that provided the optimal return on investment. Systems analyzed included using an existing 25,000 gallon underground storage tank for heat recovery chiller hot water storage during heating months and off-peak produced chilled water storage during cooling months. The other system variations included energy recovery wheels, high efficiency gas boilers, air side economizer, eliminating usage of the heat recovery chiller, conversion to variable volume air handling systems and discharge air temperature reset control. The analysis revealed that the 25,000 gallon storage tank was much too small to be of any use for energy savings as the 25,000 gallons of chilled water would be used in approximately 11 minutes. It was surmised that this tank was originally designed to keep the building cool during the first ten minutes of a power outage while generators were bringing the chillers back on-line. First cost of upgrades, annual energy costs, and payback periods for the other four system variations were presented to the owner so they could make an informed decision based on their overall objectives.