Thermal Storage Sizing for Heat Pumps

Dimension a sensible-heat storage tank for a heat pump or electrified thermal system. Provide the load you want to cover, how long it should run, the usable temperature swing, and efficiency to see the required mass and volume of the storage medium.

Heating or cooling power the storage must deliver.
How long the storage should supply the load.
Difference between charge and discharge temperatures.
Percentage of stored energy recoverable after losses.
Optional. Defaults to 4.186 for water.
Optional. Defaults to 1,000 kg/m³ for water.

Engineering estimate; confirm with detailed thermodynamic modelling before procurement.

Examples

  • 25 kW load, 6 hours, 25 °C span, 85% efficiency, water defaults ⇒ Storage mass: 6,070.66 kg | Volume: 6.07 m³ (6,070.66 L)
  • 18 kW load, 4 hours, 12 °C span, 80% efficiency, 2.4 kJ/kg·°C, 1,800 kg/m³ ⇒ Storage mass: 11,250.00 kg | Volume: 6.25 m³ (6,250.00 L)

FAQ

Can this handle phase change materials?

Yes, use the effective specific heat over the melting range and the material density to approximate volume.

How do I include standby losses?

Reduce the round-trip efficiency to reflect heat lost over the storage duration, or add extra hours to the load requirement.

Does the output consider pressure ratings?

No. Validate the resulting volume against vessel codes and structural requirements before final design.

Additional Information

  • Energy required equals peak load × storage hours; dividing by efficiency accounts for charging and discharge losses.
  • Specific heat dictates how much energy each kilogram can store per degree; water's high value keeps tank sizes manageable.
  • Density converts thermal mass into a geometric volume so you can plan tank dimensions or PCM module layouts.

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