A definite requirement of the building envelope is to separate the natural environment from the indoor environment. Energy is one component of the environment that we sometimes wish to capture, harness, or reject. How can these actions be best performed to yield passive benefits such as solar heating or shading? This research focuses on control of solar radiation, and the role windows play as transfer medium between indoor and outdoor environments. A timely control of solar thermal energy input, and building thermal energy output with the use of operable window insulation is investigated during the heating season in the local Toronto climate. This is done through a combination of 3D finite element mathematical model and field performance tests. Model results and field tests reveal an energy imbalance attributed to unpredictable solar gains and spectrally-dependent emissivity of materials. Simulation results of the daily control show little improvement over use of a static system for a western building facade. The negligible difference versus a static system is attributed largely to human-error deficiencies associated with timely controls. (C) 2015 Elsevier B.V. All rights reserved.