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Testing of the stratification efficiency

At the institute for solar technology SPF a special test method was developed that allows for the determination of the stratification efficiency of solar combi-storages. The method uses the entropy produced within the tested system as a measure for the mixing processes.

  • Importance of stratification efficiency
    The stratification efficiency of a combi-storage has a decisive influence on the efficiency of the entire heating system. This is in particular true for the combination of a combi-storage with a heat pump where the electricity consumption is directly related to the stratification efficiency of the tank.
  • Test-setup
    The installation on SPF`s indoor test rig includes the combi-storage and the hydraulics for charging and discharging of the tank. The heat loads of a single family house (space heating and domestic hot water) and the heat sources (a heat pump and solar thermal collectors) are simulated and emulated in real-time through the test rig.
  • Test cycle
    Basis of the test is a 24-hour cycle. This includes weather data that is based on measurements and the thermal load of a single family house. This cycle is repeated non-stop until the results are identical for three consecutive days.
  • General conditions
    The test rig emulates a non-modulating heat pump. The thermal power, and with it also the corresponding flow rate, can be selected. The settings for the controller are set by the manufacturer and can be varied.
  • Results
    The stratification efficiency of the combi-storage is calculated from the entropy produced within the tested system. A stratification efficiency of 100 % represents an ideal (isentropic) process that exists only in theory. A fully mixed tank means a stratification efficiency of 0 %.


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