Usually, the chiller and boiler efficiencies are the primary measures that are considered with respect to building HVAC systems efficiency. However, during operation, several other components consume energy as part of the HVAC system, such as pumps and fans. If a complete building HVAC system efficiency measure would like to be identified, it is necessary to combine all relevant energy uses. This paper defines such an index, called the Building Systems Load/Energy Ratio, which is the ratio of the building systems total load to the total energy input provided by all the HVAC systems components. The building systems total load is composed of the envelope load, the load from internal gains, and the ventilation air load on the secondary systems. The total energy input contains chillers, boilers, pumps and fans on both the air-side and the water-side. Hourly energy efficiency for both heating and cooling are calculated separately when there is heating or cooling load generated in a building. A building on the Texas A&M University West Campus was selected as the case study to illustrate the methodology. This structure is supplied with electricity, chilled water and heating hot water by the West Campus plants. WinAM software was used to simulate the building energy performance during the period of 9/1/2012 to 8/31/2013, in order to provide the detailed report of hourly HVAC systems operation condition. After combining equations with the WinAM report details, the hourly building load and hourly total energy input was obtained. As a result, the annual cooling efficiency is 2.09 Btu-Load/Btu-Input (1.69kW/ton), the monthly cooling efficiency varies from 1.45 to 2.68 Btu-Load/Btu-Input, and the hourly cooling efficiency ranges from 0.23 to 3.77 Btu-Load/Btu-Input. The annual heating efficiency is 0.52 Btu-Load/Btu-Input, the monthly heating efficiency varies from 0.06 to 0.6 Btu-Load/Btu-Input, and the hourly heating efficiency ranges from 0.01 to 0.69 Btu-Load/Btu-Input. Since the building is divided by lab and office areas and each area has its interior and exterior zones, there are four kinds of cooling load combinations and three kinds of heating load combinations within whole year. Under each condition of load combination, the analysis of the efficiency values mainly focuses on the chiller plant cooling energy use, plant heating energy use, heating and cooling load, plant cooling efficiency, and the outside air temperature.