An analysis of building energy usage and thermal load for the Solar Building during the winter heating seasons of 1974-75 and 1975-76 is reported. The one-story office building is located in Albuquerque, New Mexico. Its mechanical heating and cooling equipment is categorized as a solar-assisted heat pump system consisting of solar collectors, water thermal storage, a water-to-water heat pump and five smaller water-to-air heat pump packaged units. Building energy usage was examined with emphasis on the time of day energy was consumed and the source from which the energy was obtained; i.e., from the electricity for lighting, office equipment and mechanical equipment, and from the heat output of the thermal storage and heat pumps. The rate of electrical energy consumption was found to be very dependent on building use. High rates of electrical energy usage during occupied periods required cooling during parts of even the coldest days. Mechanical equipment heating was found to vary as a function of building usage as well as a function of the indoor-outdoor temperature differential. Energies supplied to and withdrawn from the building were examined and are presented for hourly, daily, and seasonal periods. A comparison of the two heating seasons was made. Energy losses more » and gains from the building to the surroundings were examined for both steady-state and transient load profiles. Envelope conductive heat losses and losses due to infiltration and ventilation were calculated using actual weather data through the use of the Building Environmental Analysis Program (BEAP). The effect of building thermal storage on heating and cooling loads was examined and a set of building balance-point temperatures was established. Comparisons between the building energy consumption and a calculated load were made for hourly, daily, and seasonal periods. « less