This paper investigates the possibility of reducing the energy use for cooling as well as improving the thermal comfort in lightweight buildings by associating new heat thermal energy storage (HTES) to the building HVAC system. The numerical model of the so-called "phase-shifter" HTES has been implemented on the SimSpark platform and validated against the analytical solution for the constant airflow and harmonic temperature profile. The experimental data has been used to assess its predictive capability with non-constant airflow. Using reduced ventilation periods has been numerically studied regarding the environmental air resource and thermal storage efficiency of the system. The size and electricity consumption were optimized by this way. Particularly, a comfort analysis based on the adaptive model was carried out on several combined building thermal inertia and HVAC configuration. The building energy simulation results demonstrate that the low-inertia building equipped with a phase-shifter presents the similar internal thermal conditions to those of a more massive night-ventilated structure. The proposed optimization can reduce significantly the size of the system (by 30%) and the electricity consumption (by at least 38%) while the temperature is out of the comfort range for an extra 5% of the total estimation period. (C) 2013 Elsevier Ltd. All rights reserved.