The Canada Centre Building was designed to accommodate 1,900 workers on 12 floors in a 30,000 m2 office structure in Scarborough, Canada. Its unique energy conserving features include 700 m2 of roof mounted solar energy collectors, chillers modified to operate as heat pumps, and an aquifer thermal energy storage (ATES) system operating on four 60 m deep wells producing flows of 10 to 30 L/s from a 10 m thick fine to medium sand aquifer. The ATES and solar domestic hot water heating systems have been used since 1985.Instrumentation for ATES performance monitoring was installed during construction of the building, for research and verification of geothermal models. Energy monitoring, however, was implemented in 1991, to evaluate the energy consumed in operating various energy conserving systems. Initial data show coefficients of performance (COP) of about 4 to 5 for the ATES and heat pump systems respectively.