Natural slab cooling systems take advantage of evaporative and night-sky radiative processes to cool water for use in building comfort condition the following day. Benefits include reductions in both energy use and peak demand. This report identifies the conditions under which these systems are most cost-effective and describes specific applications of three different configurations of natural cooling systems. We also highlight opportunities for energy service providers and discuss barriers to market penetration. (ER-02-15; September 2002; 14 pp)