Venting and degasification of solar circuits

AbstractBy experience solar thermal systems are facing a lot of problems caused by gas enclosed in the hydraulic circuits (cavities or gas cushion). Problems known so far are flow instabilities as well as significant degradation of system efficiency. Solubility coefficients for relevant gases in solar liquids, in particular, are essential for in-depth theoretical analysis and can be presented for the first time. The measurements of the solubility coefficients of nitrogen in a typical solar fluid show a significant different behavior compared to water.The concentration of atmospheric gases was investigated in seven current large scale solar thermal systems by sampling. An indoor test rig was built and investigated in terms of solubility, corrosion and gas transport. Thus, this project presents both current data for existing solar thermal installations and also detailed results of the analysis of a system with well-controlled conditions

Transformation Roadmap from High to Low Temperature District Heating Systems

The condensed Transformation Roadmap can be expressed as: 1. Eliminate temperature errors in existing distribution networks and substations in order to make existing systems more efficient. This will reduce existing temperature levels. 2. Avoid these temperature errors in new network parts and in new substations. 3. Use heat exchangers with longer thermal lengths in substations for indirect connection of customer heating systems and closed hot water preparation. This will reduce the temperature differences between the warmer distribution waters and the colder fluids to be heated. 4. Reduce existing customer temperature demands by elimination of local temperature errors, reduction of heat demands by means of energy efficiency measures, and by installation of larger heating surfaces in radiator and ventilation systems. 5. New low temperature network parts in conjunction with existing systems can be connected by concurrent operation of these parts as secondary networks. 6. The long-term vision is to deliver heat to substations with a supply temperature of 50°C, while obtaining a return temperature of 20°C as annual average. However, the technical solutions for obtaining this low return temperature have yet not been defined