As we move towards power systems with less inertia, frequency excursions from under-frequency contingencies become more extreme and require scheduling more spinning reserves. This paper proposes an algorithm to include inertia and Primary Frequency Control (PFC) requirements in the day ahead Unit Commitment (UC) problem. A simplified dynamic model is proposed to get the frequency nadirs for every hour of the UC horizon. When the frequency drops too much, the algorithm increases the spinning reserve requirement and re optimizes the UC, repeating the process until all the nadirs are above a threshold. The algorithm is tested for three renewable generation scenarios in the Chilean Northern Interconnected System (SING). Simulation results show that the algorithm offers a feasible unit commitment that makes possible integrating higher levels of renewables. The UC solution ensures PFC adequacy, as there will be more inertia and dynamically-allocated PFC resources available to avoid load shedding after a contingency.Regular 2015FONDECYTFONDECYT