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Understanding and Applications of Thermal Energy Storage Tanks

A thermal energy storage tank collects thermal energy, which is released to the generator when it is most needed. Here’s what it is and how it is used

To optimize a high-energy efficiency heating system, the installation of an inertial storage tank is often required, which ensures greater energy savings because it allows storing the produced energy and using it when the system is not in operation.

To discover what is meant by inertial storage and what are the principles of its operation, continue reading this article and delve into all the details and benefits of an inertial storage tank!

What does inertial storage mean?

An inertial storage – or buffer – is a tank that contains technical water, non-potable, used to temporarily store thermal energy produced by the thermal system, making it available when needed.

Generally, a storage tank is made up of a steel body that is thermally insulated. The insulation is necessary to ensure that the stored heat inside it does not dissipate to the outside.

Inertial storage tanks can be equipped with coils, i.e., immersed heat exchangers that allow receiving energy from different heat sources without mixing the various technical fluids used.

The technical water contained inside tends to stratify, in fact, the cold water is distributed in the lower part and the hot water in the upper part, ensuring the efficiency of the systems because it prevents them from unnecessarily mixing, causing energy waste.

How is an inertial storage tank used?

An inertial storage tank can be used in combination with a solar thermal system or a thermal system, such as a heat pump.

In the case of using an inertial storage tank with a solar thermal system, one can think of using a tank that aims to store sanitary water that will then be heated according to needs.
This solution is advantageous not only because it ensures the hygienic maintenance of water, avoiding the proliferation of pathogenic agents, but also because the stored water can also be used to serve the thermal system.

In the case of an inertial storage tank combined with a heat pump, its use allows to optimize its performance, as it enables it to work at full capacity and constant load, ensuring a quantity of thermal energy when needed and reducing the number of on/off cycles.

What is the purpose of an inertial storage tank?

An inertial storage tank serves to maximize the efficiency of a heating system. Using an inertial storage system allows heat pumps to:

  • reduce on/off cycles: by providing thermal inertia to the heat pump, its operation can be optimized, as in on/off cycles, the COP of the pump itself is reduced. Without the use of a tank, the heat pump would be subject to continuous variations in demand from the building, which does not happen because with the storage, the machine continues to work for sufficient time intervals, supporting the distribution system when it is not active;
  • manage defrosting: in air/water heat pumps, defrosting cycles usually take place by extracting energy from the condenser to bring it to the evaporator. If there is no inertial storage on the condenser side, but directly the building’s distribution system, thermal energy will be directly extracted from the building, thus reducing thermal comfort conditions. The presence of an inertial storage tank avoids this, as it will provide the necessary energy to defrost the evaporator;
  • separate flows between heat pump and distribution system: the use of an inertial storage system allows to divide the flows to be sent to the system or to the heat pump, optimizing the pump’s operation.

How to size an inertial storage tank?

Sizing an inertial storage tank means defining its capacity, i.e., the volume of technical water necessary for the optimal operation of the system.

Calculating the correct capacity value of an inertial storage tank allows to achieve better system efficiency, greater thermal stability, and a quicker response to load variations.

The capacity must be defined based on the heat generator and the type of system served: knowing the power and type of the system and the distribution mode, it will be possible to size the tank, identifying:

  • dimensions;
  • materials;
  • technical characteristics;
  • hydraulic connections;
  • electrical connections.
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