Frequency control reserves are a fundamental mechanism in the current electric power system to preserve the balance between demand and generation of active power at all times. The traditional approach is to exploit conventional power plants for frequency reserves. However, due to the increasing penetration of renewable energies, the demand side is expected to play an essential role in the near future.This paper illustrates the potential of commercial buildings as frequency reserves providers through an experimental demonstration conducted in a multi-zone university building. The proposed control methodology, that represents a first step to the full accomplishment of this task, is presented in details,including the control architecture, the controller design, model identification and hardware description. Finally, the effectiveness of the presented approach is tested by means of simulations and experiments in a very controlled environment.