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.

• From: Department of Energy & Climate Change
• Published: 14 May 2013

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