In Parts 1, 2, and 3 of this Passive Solar Design Overview series, we looked at the three main architectural styles of passive solar design (Direct Gain, Indirect Gain, and Isolated Gain), as well as the first three of the five design aspects, Aperture, Absorber, and Thermal Mass. This article will address the design aspect Controls at an overview level. All of these aspects are important regardless of whether a new building is being designed or renovation of a current building is being considered.