Research and analysis

Investigation of the interaction between hot water cylinders, buffer tanks and heat pumps

Report prepared for DECC by Kiwa GASTEC at CRE.

Documents

Investigation of the interaction between hot water cylinders, buffer tanks and heat pumps

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Details

The report describes two laboratory tests carried out with two main aims:

  1. to investigate the best way to heat domestic hot water tanks with a heat pump
  2. to investigate the best way to integrate buffer tanks into a heat pump heating circuit.

The domestic hot water study concluded with some recommendations for installers:

  • Low heat pump flow temperatures and low storage temperatures combined with periodic sterilisation give the best system efficiencies.
  • The heat pump output must be higher than the cylinder thermostat set point, to minimise pump on-time and decrease heat loss.
  • Sterilisation should be carried out at night, or during periods of low draw off.
  • Reheat times can be shortened by fitting fast recovery coils, with a higher surface area.

The buffer tanks study also concluded with recommendations for installers:

In circuits with low central heating volumes, buffer tanks can be helpful to reduce cycling (and its adverse effect on efficiency). If used, a buffer tank should be inserted in a two pipe configuration in the return pipe.

Finally, the study concluded that further research is needed into energy-efficient ways of sterilising domestic hot water.

Published 14 May 2013