The recent water crisis with severe impacts on hydroelectric generation - the main source of the national energy matrix - and the worsening economic crisis require efficient solutions to reduce public expenditures with electricity consumption. This article addresses this issue with the general objective of identifying the opportunities for increasing energy efficiency (EE) in a public building, with specific objectives: to map present energy losses; to point out the potentialities of energy improvement, taking into account the lower cost-benefits in implementing the necessary actions; and to evaluate the institutional difficulties to execute the public policies destined to this end. The case study was developed in a public institution, through an applied research that used a quanti-qualitative approach, and the instruments used were: tools for measurement of electrical parameters, documentary analysis, structured interview and direct observation. The results of the study indicate that lighting and air conditioning systems are the major energy consuming sources in the building and point out the potential possibilities for reducing energy consumption in the building case.