One of the possibilities of increase of energy and economic efficiency of a small combined heat and power plant is its operation in trigeneration system, in which the conventional system of cogeneration heat and electric power production is widened by a cooling production system. Technical description and characteristics of the set of gas engine plus absorption unit as well as its technological diagram is presented. Performances and limitations of the gas engine are given. Needs for heat, cooling and electric power of a user are described. Total capital and operating costs are estimated and technical and economic conditions for the positive economic efficiency of the trigeneration system are evaluated.