Abstract This paper presents a new control strategy for improving the performance of one interior and/or exterior planar shade(s). The control strategy is based on performing an energy balance on the fenestration system and calculating the total heat flow (i.e. solar gains + overall heat losses). The heat flow can be maximized or minimized depending on the needs of the space. A solarium model was developed in order to assess the performance of the proposed shading strategy. The solarium model can simulate passive and active thermal storage using sensible and phase change materials. A prototype solarium with motorized interior and exterior shadings has been instrumented and subjected to controlled conditions. The numerical simulations are in good agreement with experimental results. The simulation model has then been used to perform annual simulations of an attached solarium for the location of Montreal, Canada. The year was divided in a heating mode and a mixed mode. During the heating mode (i.e. October through April), heating is provided to keep a minimum temperature of 10 °C and surplus heat is considered when the temperature reaches 28 °C. By using the proposed algorithm for the control of one interior and/or exterior shade(s) in the heating mode, heating requirements of the simulated solarium have been reduced by 3–9% and an additional 9–14% of surplus heat have been collected when compared to a control based on near optimum global horizontal solar radiation levels. During the mixed mode, thermal comfort can be improved significantly (+1822 h) when the interior shade is controlled with the proposed algorithm.