A numerical procedure is developed for solving transient, three-dimensional heat-transfer problems of space cooling by using cold water flowing during the night within regularly arranged pipes, embedded in the ceiling within a layer of phase change material (PCM). Such systems are advantageous over the usual ceiling cooling systems because (1) the PCM layer may store considerably greater amounts of heat than those stored in the concrete slab, and (2) night cooling takes place under reduced electricity prices and meets the requirement of smoothing out electricity consumption by reducing daily peak loads. To simulate the phase change process, the concept of effective thermal capacity function is used, which is determined experimentally and then generalized by using triangular functions. Tests are also made with related functions given in the literature. The predictions of this study showed that the use of night ceiling cooling systems with PCM-embedded piping may offer energy savings and more thermal comfort than systems without PCM, even in cases in which system parameters do not permit the user to take advantage of the entire PCM storage capacity. The developed numerical procedure may be used for defining, in each case, the proper values of the system parameters to completely take advantage of the PCM storage capacity. DOI: 10.1061/(ASCE)EY.1943-7897.0000048. (C) 2011 American Society of Civil Engineers.