Low-Flow System

In so-called low-flow systems only about 25 litres of heat transfer fluid circulate per one square meter of Collector area, so increasing the collector's Efficiency by minimizing the volume and mass of the heat transfer fluid. This allows higher temperature differences between the collector and water tank, hence less fluid needs to be transported in order to get the same amount of energy to the water tank.

Nearly every Solar Heating System meeting today’s technological standards can be used as low-flow systems – efficient components allow a marked reduction in the amount of heat transfer fluid (cp. Müller, F.U.: Thermische Solaranlagen, 1997). However, special systems with their own optimised water tanks and heat exchangers are now on the market.

One advantage of low-flow systems is that thinner, and hence cheaper, standpipes can be used. These also minimise heat loss and, together with the reduced amount of heat-transfer fluid, they help reduce the total cost especially of bigger solar heating system.

Solar-thermal systems applying low-flow-optimised components (esp. collectors with reduced volume to square footage relation) will benefit from another advantage: Since the mass of fluid to heat in the collector is smaller, the system can react very quickly and use also small sunshine periods very efficiently. Such systems will need special positive displacement pumps to overcome the higher flow resistance in the thin standpipes and make use of elaborated concepts to optimise the Thermal Stratification in the storage tank.

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