POTENTIAL IMPROVEMENT IN THE DESIGN OF IMMERSED COIL HEAT EXCHANGERS

Although there is a notable move towards fresh water stations in the European markets, using the cheaper internal solutions of smooth or finned coil heat exchangers for smaller solar thermal system storage devices still dominates. Varying significantly in type and geometry, the functions used to account for heat transfer are possibly outdated and in light of the still relatively high investment costs of solar thermal systems, not cost optimizing. An overview of the current thermal storage market implementing typical immersed heat exchanger types and variations has been collated such that geometrical dependencies and specific advantages or disadvantages can be elucidated. By analysing the correlation between parameters, the relationship between trends in design and current rules of thumb is discussed. From the market research a reference solar DHW was defined and simulated in the TRNSYS simulation environment. A method for interpreting the results in dependency of the energy transferred through an immersed coil heat exchanger at any given annual condition is presented and a selection of representative immersed coil heat exchangers is discussed for future experimentation based on the knowledge gained from the simulation results. Based on commensuration of the experiments with computational modeling (computational fluid dynamics as well as TRNSYS models), future work will entail the development of an immersed coil heat exchangers optimization methodology. 1