Bessere chancen für Kälte aus Fernwärme - Erste Betriebserfahrungen mit einem neuartigen Absorptions-Kaltwassersatz

The product »Cooling from District Heat« broadens the range of offerings of the energy suppliers. It promises a multitude of utilities the expansion of their service offerings for the increase of the heating sales and for the protection of their market position, above all in competition with the decentralized co-generation of electrical power, heat and also cold. On the whole, a greater and more levelled utilization of the generation and distribution plants can be achieved during the entire year. At the same time, the generation of refrigeration from district heat with absorption chillers offers an environmentally compatible alternative to the generation of cold with compression refrigeration machines using refrigerants that interfere with the environment. Absorption or adsorption chillers or evaporating-cooling processes, such as the so-called Desiccant Evaporating-Cooling System (DEC System), are a possibility as cooling generation driven by district heat. Corresponding plants are already in trials in isolated cases. The energy efficiency of the overall system of electrical power - heat - cold - generation, the capabilities for adaptation to the existing operating characteristics of the system and the expenditure for equipment, i.e. above all the size and weight of the plant and the operational safety and operating costs, are decisive criteria for the competitiveness of the various plant concepts. Furthermore, the customary interfaces to the building equipment, i.e. connection to the existing district heating system and connection to the existing cold and cooling-water circulation systems (supply/return typically 6/12 °C and 27/35 °C), are to be observed for the use in building air conditioning. The objective of the further development was to improve the internal process of absorption chillers to such an extent that the existing district heating substations, above all, can be optimally utilized for the generation of cold with district heat and that the demand for cooling in air-conditioning systems driven by district heat can be satisfied with the available transport capacities of the system. For the better utilization of the existing transport capacities with a simultaneous minimization of the energy requirements for heat generation (low electrical power losses, low extra fuel for heat), chillers are called for that operate with a lower district-heating supply temperature and simultaneously with a lower return temperature of the district-heating water. Two pilot plants with a new type of absorption chiller working with water/lithium bromide, which is specially tailored to the operating conditions of district-heating systems with a Single-Effect/Double-Lift process (SE/DL), were designed within the framework of a project sponsored by the Federal Ministry for Education. Science, Research and Technology (BMBF) and by a consortium consisting of 15 district heat suppliers and two plant manufacturers. The first operating experiences of the plant, used by Bewag in Berlin since August of 1996 (manufacturer: Entropie GmbH), confirm the theoretical investigation. A cooling capacity of 400 kW with a coefficient of performance (COP) of 0.62 was achieved with a district heating supply/return of 95/65 °C in accordance with the design.