Kälte aus Wärme : eine wärmetechnische Analyse

The consumers' supply of power, heat and cold can be implemented into the concept of Least Cost Planning (LCP) because generating cold out of heat is technically feasable. In future both Supply Side Planning and Supply Side Management will be concerned from this aspect. Generating cold out of heat first of all follows the strategy of »Valley Filling«. Consequently, the technology of generating cold out of heat leads to further development of combined heat and power generation. In addition to heating and hot water, heat is used to provide cold. An increase of the average annual fuel utilization rate as well as the annual working hours of generating power and heat system reduce the costs of heat and cold production. Knowledge about heat engineering and applied thermodynamics make necessary the inclusion of re-cooled systems as well as transport and utilization systems of cold into present concepts of energy supply, which comprise production, transport and utilization systems. Combined generation of power, heat and cold may only find its place in the energy technology if it is realized with economically tolerable expenses. Although numerous combined power, heat and cold systems have been in successful operation for many years, the breaktrough could not yet be reached. This study is to point out how complex and difficult the heat engineering relations are and to help make planning, manufacturing and operating possible. A future intention is to expand the engineering aspects to economic aspects. Thus, the marketing of »cold out of heat« as a product may be forced with success. Integrating absorption refrigeration plants into total energy systems, their heat engineering characteristics have to be taken into consideration. This is namely the coefficient of performance from heat into cold which depends on the hot water supply temperature and the temperature of cooling water. Absorption refrigeration plants require higher hot water supply temperatures with an increasing ambient temperature, which is proportional to the temperature of cooling water. If this is the case, a higher amount of heat will be needed to achieve the same cooling rate. Concerning the dimension of the transporting system, the difference of supply and return temperature is important. Absorption refrigeration machines can be operated by central heating power stations or distributed total energy units. In case of central heating power systems the heat represents a product wich has to be rated by the amount of less produced electric power. Low demand on heat in summer in combination with simultaneous high demand on cold represents the main aspect using heat connected refrigeration machines. Therefore plant utilization rate and average annual fuel utilization rate may be increased. In case of distributed total energy units, generation of electric power is not influenced by utilization of heat. Using gasturbines, maximum fuel utilization rate can be reached by choosing supply temperatures optimized referring to the absorption refrigeration machine. The same statement is valid, using only the exhaust gas of units based on motors. Increasing fuel utilization rate requires making use of the cooling system of a motor. In this case, special coordinated supply and return temperatures are demanded. This is why the performance of combined power, heat and cold systems has to be planned by taking the heat engineering context into consideration.