SUMMARY In HVACR system design@ the need to address immediate issues such as economics@ performance@ and space constraints often prevents designers from fully considering the energy resources affected. Today's energy resources are less certain because of issues such as availability@ safety@ national interest@ environmental concerns@ and the world political situation. As a result@ the reliability@ economics@ and continuity of many common energy resources over the potential life of a building being designed are unclear. For this reason@ the designer of building energy systems must consider the energy resources on which the long-term operation of the building will depend. If the continued viability of those resources is reason for concern@ the design should provide for@ account for@ or address such an eventuality.