In one aspect of the teachings herein, demand responsive loads are selected for involvement in a given DR event using an advantageous approach to selection that is based on using a mathematical network model to evaluate power loss in a power distribution network as a function of different combinations of demand responsive load selections and corresponding load reduction values. The mathematical network model comprises a mathematical representation of the power distribution network as a multi-phase unbalanced distribution network, including mathematical representations of the physical components in the power distribution network and the connecting relationships of those components. As overall power loss in the system is a function of different combinations of demand responsive load selections, the mathematical network model is used to evaluate system power loss under different demand response load selections, in a manner that automatically accommodates mesh networks and other complex network topologies, distri
