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.
PDF, 2.58MB, 79 pages
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The report describes two laboratory tests carried out with two main aims:
- to investigate the best way to heat domestic hot water tanks with a heat pump
- 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.