Flywheel Storage: How It Works and Why Thermal Batteries Are More Efficient

Flywheel storage is a technology used to store thermal energy and gradually distribute it in heating and cooling systems. Among its main applications is the chilled water thermal flywheel, used to optimize air conditioning systems.

However, compared to more advanced solutions such as PCM thermal batteries, flywheel accumulators have some limitations in terms of efficiency and energy management. In this article, we will analyze how the thermal flywheel works, its advantages and disadvantages, and whether it is truly worthwhile compared to thermal battery solutions.

What is a Flywheel Storage System and How Does It Work?

The thermal flywheel is a heat storage system that uses a large-capacity water tank to store thermal energy and release it gradually in a heating or cooling system. This mechanism helps improve system stability and reduce temperature fluctuations.

Thermal Flywheel: What Is It Used For?

The thermal flywheel is especially useful for:

• Stabilizing temperature in heating and cooling systems.
• Reducing the number of starts and stops of heat generators, increasing system efficiency.

Chilled Water Thermal Flywheel

A specific application of flywheel accumulators is the chilled water thermal flywheel, used in air conditioning systems to:

1. Improve cooling stability in large buildings.
2. Reduce energy consumption peaks by distributing energy over time.

This technology is widely used but has some limitations, especially in terms of heat loss and space requirements.

Limitations of Flywheel Accumulators

Despite the advantages, the thermal flywheel has some drawbacks that limit its effectiveness compared to other, more modern thermal storage technologies.

High Thermal Dispersion

• Stored energy is lost over time, reducing the overall efficiency of the system.
• It requires good insulation to limit heat loss.

Bulkiness and Installation Complexity

• Flywheel accumulators require large tanks, which are often difficult to integrate into residential settings, small spaces, or historic buildings.
• They require anti-legionella systems, as the bacterium can grow in stagnant hot water.

Limited Thermal Regulation

• The ability to deliver heat or cooling depends on the mass of water contained, making regulation more complex compared to other thermal storage solutions.
• In heating systems, it is necessary to maintain proper stratification of the water inside the tank, from the bottom layer, where colder water should be, to the top layer, where the water should be hotter. Lack of stratification can lead to issues in heat distribution.

To explore other thermal storage technologies and compare them with the thermal flywheel, read our article: Sand Thermal Storage: Operation, Limitations, and Advantages

Why Is a Thermal Battery More Efficient Than a Thermal Flywheel?

PCM thermal batteries represent a more advanced alternative to the thermal flywheel, thanks to the use of Phase Change Materials (PCM) to store and release thermal energy more efficiently.

Difference Between Latent Heat and Sensible Heat

• The thermal flywheel stores sensible heat, i.e., energy that heats or cools a fluid without changing its state.
• Thermal batteries store latent heat, exploiting the phase transition of PCMs, which allows more energy to be stored in less space.

Example: A hot water tank must reach very high temperatures to store enough energy, while a PCM thermal battery can store the same amount of heat at a lower temperature and with a smaller volume.

Advantages of Thermal Batteries Compared to Thermal Flywheels

• Better heat management
  • They allow heat to be stored at specific temperatures without loss and without the need for stratification.
• Less bulk and more flexibility
  • Thermal batteries take up to 50% less space than thermal flywheels.
  • They can be installed in modular systems, adapting to the needs of each plant.
• Higher energy efficiency
  • Thermal batteries allow heat to be delivered at a constant temperature, without the need for regulation systems typical of thermal flywheels.
  • Energy waste reduction, thanks to the ability of PCMs to retain thermal energy throughout the day.
• More versatile applications
  • They can be used for both heating and cooling.
• High discharge power
  • They reach discharge power up to 8 times that of a residential heat pump.

In conclusion, flywheel storage is a useful technology to stabilize heating and cooling systems, but it has limitations in terms of bulkiness, thermal dispersion, and hot water flow management.

PCM thermal batteries offer a more compact and high-performance alternative, allowing more energy to be stored in less space and with simpler operations.

For those looking for an advanced thermal storage solution, thermal batteries are a more versatile choice compared to thermal flywheels.

Contact us to learn more about thermal storage technologies and which solution best fits your needs!