Here we develop new vascular designs for the volumetric bathing of smart structures under time-varying conditions. The three flow configurations described in this paper are the first, second, and third constructal structures with optimized hydraulic diameters (D-1 and D-2) and non-optimized hydraulic diameter (D) for one system size, 20 x 20. The main objective was to determine the longest permissible time delay so that the maximum temperatures do not exceed the maximum allowable limit. It is the best to cool with the first construct in the optimized constructal configurations when pressure drop number (Be) is lower than 1 x 10(11) and the best structure is the second constructal structure when pressure drop number (Be) is greater than 2 x 10(11), whereas the best structure in the non-optimized constructal configurations is the third construct. It is also shown that the most attractive configurations have larger allowable delay times: in both the optimized and non-optimized constructal structures, the best configuration is the second construct where the pressure drop is fixed at about 1 kPa. (C) 2012 Elsevier Ltd. All rights reserved.