Research on natural cooling of buildings has produced an extensive scientific bibliography since 1980s. Nevertheless, few examples of complete experimental systems are registered, and rigorous procedures for their dimensioning are currently not available. This work analyses the performance of an air-based low energy radiative cooling system in Chile. The system is composed of a series of specialized radiative air collectors, a mechanical ventilation system, and a thermal storage wall, which is part of the indoor environment. The design has been tested in an experimental prototype where external and internal environmental conditions have been monitored during a full week in midsummer conditions. The data obtained is used to validate an analytical model designed to study the behavior of each component and the system’s performance. This work studies the relationship between the radiator surface, the air volume flow rate, and the thermal storage wall volume that serves to neutralize the thermal loads, maintaining comfortable temperature conditions throughout the day. Comparison of the simulations with and without thermal conditioning has been conducted. In term of the system sizing, a thermal wall of 2.55 m³ and a total air flow rate of 48 m³/h is required to reach the optimal operating point of the first floor of the house. A sensibility analysis indicated that increasing the number of collectors slightly reduces the wall’s size. Based on these conditions, the work concludes with the proposal of a simple procedure for the sizing of passive cooling systems installed in social housing developments.