To increase energy efficiency of building it is to apply thermal storage systems. There are multiple successful examples of their use in countries of North Europe. The article reviewed method of thermal storage system installation in a building of SPbSTU campus for the purpose of heat supply renovation program. There was solved the problem of comparing different types of heat accumulators and selection of the most suitable system for climate conditions of St.-Petersburg, which would meet the set requirements of the task. A cafeteria for 50 seats working since 12 a.m. till 4 p.m. was considered as a benchmark data. For hot water flow calculation we had to calculate the number of conditional dishes consumed in cafeteria per hour and per day. Several variants of heat accumulating were calculated: Accumulator with single-phased accumulating material (SPAM): - SPAM is water; - SPAM is granite; - SPAM is brick; - SPAM is concrete. The result shows that performance of using water as the heat storage material is better than that of others. Applying of accumulator with single-phased accumulating material is unpractical for full and autonomous supply of cafeteria. Calculation of phase-changing heat accumulator is needed, if