District heating and cooling for efficient energy supply

Supplying customers with heating and cooling energy from district energy systems essentially contributes to the rational use of energy and to environmental protection. In the past few years, the use of district cooling has been significantly increased in some countries. The energy supply of cooling and heating for urban districts is usually separated. While a part of a district is supplied with natural gas or uses liquid fuels for heating purposes, the other part may be supplied by heat from district heating network. Cooling systems are usually based on use of electric energy and are in most cases very small units. In this case, cooling capacity of such a unit covers needs of only some small building, office or even apartment, and not cooling needs of a whole district or a group of buildings. Many times the use of particular technologies is energetically inefficient and environmentally not friendly. There may be many different energy sources in the same environment. Then such cooling and heating technologies should be used, that are environmentally, technically and economically most acceptable. In the paper concepts of energy supply systems are presented and their energy efficiencies are discussed. The possibilities of improvement of existing systems are pointed out. Development directions of energy systems in urban districts are presented. Based on analysis, solutions which enable energetically, economically and environmentally best results are presented. A method for the exergetic efficiency determination of different kinds of chillers is described and a comparison of the chillers´ exergetic efficiency in a trigeneration system, including the whole cooling loop, is shown.